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Responses of trophic structure and zooplankton community to salinity and temperature in Tibetan lakes: Implication for the effect of climate warming
Abstract
Warming has pronounced effects on lake ecosystems, either directly by increased temperatures or indirectly by a change in salinity. We investigated the current status of zooplankton communities and trophic structure in 45 Tibetan lakes along a 2300 m altitude and a 76 g/l salinity gradient. Freshwater to hyposaline lakes mainly had three trophic levels: phytoplankton, small zooplankton and fish/Gammarus, while mesosaline to hypersaline lakes only had two: phytoplankton and large zooplankton. Zooplankton species richness declined significantly with salinity, but did not relate with temperature. Furthermore, the decline in species richness with salinity in lakes with two trophic levels was much less abrupt than in lakes with three trophic levels. The structural variation of the zooplankton community depended on the length of the food chain, and was significantly explained by salinity as the critical environmental variable. The zooplankton community shifted from dominance of copepods and small cladoceran species in the lakes with low salinity and three trophic levels to large saline filter-feeding phyllopod species in those lakes with high salinity and two trophic levels. The zooplankton to phytoplankton biomass ratio was positively related with temperature in two-trophic-level systems and vice versa in three-trophic-level systems. As the Tibetan Plateau is warming about three times faster than the global average, our results imply that warming could have a considerable impact on the structure and function of Tibetan lake ecosystems, either via indirect effects of salinization/desalinization on species richness, composition and trophic structure or through direct effects of water temperature on trophic interactions.
... Previous studies reported that algal communities in many remote glacial lakes of the Northern Hemisphere have shifted in response to warming (He et al. 2022;Liang et al. 2021;Ouyang et al. 2023). In fact, rising temperatures could not only promote algal growth and community succession directly but also indirectly affect alpine lake ecosystems by altering a series of lake physicochemical environments, including nutrients, salinity, thermal stratification, ice cover, and so on (Lin et al. 2017;Xu et al. 2024). For example, lake expansion and the dilution effect due to meltwater input are widely observed on the TP, especially in the northern parts, where salinity has been decreasing for 20 years (Liu et al. 2023;Song et al. 2022). ...
... Alpine lakes are usually characterised by low biomass and a simple food web (Lin et al. 2017). Phytoplankton communities are sensitive to environmental changes, and their morphological remains in lake sediment provide reliable information over long time scales (Li et al. 2022(Li et al. , 2023. ...
... The sustained lake expansion in TP lakes reflects broader environmental shifts under climate change, presenting profound ecological consequences (Sills et al. 2018;Stibal et al. 2020). Our study investigates the interaction between global warming, meltwater input and salinity decline from a long-term temporal perspective, providing a valuable supplement to understanding the dynamics of ecosystems along various salinity gradients at a regional scale (Li et al. 2021;Lin et al. 2017;Zhang et al. 2022;Zhong et al. 2016). ...
Global warming has caused widespread shifts in lake hydrological conditions due to the increasing glacial meltwater input on the Tibetan Plateau. It is anticipated that favourable conditions for algal growth will be developed as a result of a rise in temperature, nutrient supply and salinity decline. However, the long‐term ecological process is rarely explored, and the underlying mechanism remains poorly understood.
Here, we investigated Bangdag Co., a glacier‐fed and high‐salinity lake located in the northwest of the Tibetan Plateau, which has been experiencing a rapid expansion in recent decades. We reconstructed the algal community dynamics using sedimentary subfossil pigments to explore the lake's ecological trajectory over the past century. Combining remote sensing and regional instrumental data, we analysed how the lake ecosystem responds to climate warming, hydroclimatic change, and their interactions.
Our results showed that pigment assemblages from total algae, chlorophytes, siliceous algae and cyanobacteria were well‐preserved and stable before the 2000s, followed by an accelerated abundance increase with lake expansion. Random forest and structural equation modelling analyses revealed that the rapid ecological shift was attributed to meltwater input, salinity decline and regional warming. Our analysis demonstrates that elevated salinity prior to 2000 hindered phytoplankton growth, suggesting that ongoing glacial melting and lake dilution are restructuring remote saline lake ecosystems in a warming world.
This study improves the understanding of primary producer succession inhabiting hypersaline environments with rapid hydrological shifts on the Tibetan Plateau, emphasising the significant impact of lake expansion induced by glacial meltwater on ecosystem dynamics.
... In temperate and subtropical lakes, the biomass of zooplankton tends to decrease with increasing salinity [13,14]. It is generally believed that the salinity threshold for freshwater zooplankton ranges from 2-5 g/L [13,15,16]. However, these studies have not explored the effects of salinity on benthic Ostracoda [13,15,16]. ...
... It is generally believed that the salinity threshold for freshwater zooplankton ranges from 2-5 g/L [13,15,16]. However, these studies have not explored the effects of salinity on benthic Ostracoda [13,15,16]. Additionally, the impact of salinity on zooplankton biomass in tropical lakes remains unclear. ...
... Consistently, in temperate fjords, zooplankton biomass decreased with salinity increasing from 0.3 to 3.8 g/L [13]. Besides, in temperate plateau lakes (Tibetan), most freshwater zooplankton species were restricted to salinities below 3 g/L [16]. In another tropical lagoon, the limitation of zooplankton growth is at a salinity level of ca. 2 g/L [15]. ...
Both the increasing salinity levels and the decline of submerged macrophytes represent growing concerns in global freshwater ecosystems, posing a threat to water quality and various aquatic organisms. However, there is a limited understanding of the interactive effects of salinity and submerged macrophytes on zooplankton and benthic Ostracoda in tropical zones. To address this knowledge gap, we conducted a controlled experiment spanning 6 months, comparing the biomass of zooplankton (including copepods, cladocerans, and rotifers) and benthic Ostracoda in mesocosms with three levels of salinity, at the presence or absence of submerged macrophytes. Our results showed that in tropical zones, both zooplankton and benthic Ostracoda biomass exhibited a noteworthy decrease in response to increasing salinity, but the presence of submerged macrophytes did not have a significant influence on the zooplankton biomass. However, the presence of submerged macrophytes had a positive effect on the benthic Ostracoda biomass. Interestingly, submerged macrophytes had a strong interaction with salinity on the Ostracoda biomass, which increased with macrophyte presence under intermediate salinity conditions (2 g/L). In summary, our study sheds light on the interplay between salinity, submerged macrophytes, and the biomass of zooplankton and benthic Ostracoda in tropical freshwater ecosystems.
... Worldwide climatic change has the potential to affect many fundamental properties of lakes, with the increase in temperature modifying numerous chemical and physical parameters of aquatic environments and, ultimately, their biotic communities [10,11]. Great efforts are required to understand the effects on aquatic communities, especially on population structure (e.g., biodiversity, density, biomass; [12][13][14]), ecosystem functionality (trophic relationships, redundancy, resilience; [15][16][17][18]) and on variation in the trophic position of organisms. The ecological role of an organism in an aquatic ecosystem is subject to seasonal fluctuations, depending on ecological variables such as variations of the population structure, food source availability, and chemical and physical environmental variables [19][20][21][22]. ...
... During the decadal period (2009-2020), the three filter-feeder cladocerans D longispina-galeata gr., Bosmina and Diaphanosoma brachyurum had comparable val δ 15 The smallest ranges of δ 13 C ( Figure 1b) were found for Diaptomids and Cyclopoids, both characterised by more negative values (mean of −34.2 δ 13 C‰ for Diaptomids and mean of −33.8 δ 13 C‰ for Cyclopoids) than the other zooplankton taxa. Diaphanosoma had the least negative δ 13 C signature (mean of −27.5 δ 13 C‰, median of −26.7 δ 13 C‰, significantly different from all other taxa (p ≤ 0.03), likely due to its limited presence during the year, preferring warm months, and its tendency to occupy superficial waters. ...
... Water 2023, 15, 3143 ...
The purpose of this study was to elucidate the patterns and mechanisms driving seasonal and interannual variations of carbon and nitrogen stable isotopes in the zooplankton crustacean community of Lake Maggiore (Italy), during the period 2009–2020. Different zooplankton taxa and groups showed different ranges of δ13C signatures, giving an insight into food sources and niche partition. In particular, cyclopoids had a restricted range with more negative δ13C‰ values and an increase in δ13C fractionation with the establishment of water thermal vertical stratification, highlighting the importance of vertical distribution as a key factor for taxa coexistence in a vertically heterogenous environment. The δ13C values of the zooplankton community and of Daphnia were positively related to water temperature (R2 = 0.58 p < 0.0001 and R2 = 0.68 p < 0.0001, respectively), and the δ13C Daphnia signature was positively related to chlorophyll a (R2 = 0.32, p < 0.0001). Decomposition of the time-series data for zooplankton carbon and nitrogen signatures and environmental parameters identified increasing trends in water temperature, chlorophyll a and water conductivity and a decrease in nitrate that matched changes in carbon isotopic signature trends in some zooplankton taxa (Bosmina, Daphnia and Diaptomids). Overall, the observed patterns in zooplankton isotopic signatures were interpreted as integrations of the effects of climate warming in Lake Maggiore, affecting both the availability of food sources and environmental conditions.
... The TP represents the largest and highest lake area on Earth, and most of its lakes are closed (Zhu et al. 2019). The intensive changes of lakes have caused lake salinity to become an important indicator reflecting lake physical and chemical qualities ) and influencing lake water plankton (Lin et al. 2017). A large spatial-temporal scale investigation on lake salinity on the TP is a key component of regional aquatic studies. ...
... The magnitudes of these factors varied significantly from region to region ). In addition, study showed that the zooplankton species composition was most sensitive to changes in salinity in lakes (Lin et al. 2017). ...
... Although the lake water color changes with dissolved mineral density, it also varies with dissolved mineral types. However, total lake salinity has a close relation with lake water plankton (Lin et al. 2017), which is linked to optical remote sensing retrieve parameters such as CDOM or water clarity. Therefore, the lake salinity retrieval model based on the correlation between the in-situ lake salinity data (N = 87) and the MODIS-calculated clarity data (SD value) was determined in this study. ...
Salinity is an essential factor of lake water environments and aquatic systems. It is also sensitive to climatic changes and human activities based on concentration variations of solved minerals. However, there are few consecutively temporal studies on lake salinity variations on the Tibetan Plateau because the harsh environmental conditions make it difficult to carry out in-situ observations for several lakes. In this study, we constructed a remote sensing retrieval model for lake salinity based on 87 in-situ lake investigations; moreover, interannual lake salinity and associated variations from 152 lakes larger than 50 km² were analyzed on the Tibetan Plateau. A significant decreasing trend in lake salinity was observed between 2000 and 2019 (p < 0.01). The spatial variation of lake salinity was negatively correlated with lake area changes, and the optical characteristics of salt mineral solutions were generally positively correlated with mineral concentration based on the absorption coefficients of ionic solutions. The decreasing trend of lake salinity was not directly affected by the precipitation, but was potentially dominated by the expanding lake water volume. This study improves the understanding of regional water environmental changes and management efficacy of water resources.
... Great efforts are required to understand the effects on aquatic communities, especially on population structure (e.g. biodiversity, density, biomass; [13,14], ecosystem functionality (trophic relationships, redundancy, resilience; [15][16][17][18], and on variation in the trophic position of organisms. The ecological role of an organism in an Disclaimer/Publisher's Note: The statements, opinions, and data contained in all publications are solely those of the individual author(s) and contributor(s) and not of MDPI and/or the editor(s). ...
... Changes in phytoplankton species composition may influence the use of nitrogen sources (N2 fixation vs. uptake of dissolved combined nitrogen). Under nitrogen limitation, cyanobacterial N2 fixation is stimulated, resulting in depleted δ 15 N‰ values, which may then be transferred to zooplankton through feeding, resulting in a low zooplankton δ 15 N-signature [116]. Although daphnids cannot ingest the largest forms of cyanobacteria, they are capable of feeding on the smaller, decomposing pieces [118] and on the associated bacteria, so they will still reflect δ 13 C-signature of the baseline during cyanobacterial blooms [78]. ...
... Comparison of seasonally decomposed trends of chlorophyll-a (a) and nitrate (N-NO3) (b) with carbon isotopic signatures of selected zooplankton taxa ((c): red line= Bosmina; green line= diaptomids; purple line= Daphnia), during the period 2009-2020.arbon isotopic values vs. cyclopoids' carbon fractionation (F).Our results for δ 15 N‰ Daphnia and δ 15 N‰ Bosmina time series decomposition (Figure A3) showed a common decreasing trend after 2014/2015, corresponding to the time of decrease in NO3 concentration in the epilimnion of the lake (while no decreasing or increasing trend in δ15 N‰ was detected for the other taxa and groups). ...
The purpose of this study was to elucidate patterns and mechanisms driving seasonal and inter-annual variations of carbon and nitrogen stable isotopes in the zooplankton crustacean commu-nity of Lake Maggiore (Italy), during the period 2009-2020. Different zooplankton taxa and groups revealed different ranges of d13C signatures, giving an insight into food sources and niche partition. In particular, cyclopoids had a restricted range with most negative d13C‰ values and increase in d13C fractionation with the establishment of water thermal vertical stratification, high-lighting the importance of vertical distribution as key factor for taxa coexistence in a vertically heterogenous environment. d13C of the zooplankton community and of Daphnia were positively related to water temperature (R2=0.58 p <0.0001 and R2=0.68 p <0.0001, respectively) and d13C Daphnia signature to chlorophyll-a (R2=0.32, p < 0.0001). Decomposition of time series data for zooplankton carbon and nitrogen signatures and environmental parameters identified increasing trends in water temperature, chlorophyll-a and water conductivity and decrease in nitrate, that matched changes in carbon isotopic signature trend in some zooplankton taxa (Bosmina, Daphnia and diaptomids). Overall, the observed patterns in zooplankton isotopic signatures were interpreted as integrations of climate warming effects in Lake Maggiore, affecting both food sources availability and environmental conditions.
... Отношения типа «хищник-жертва» довольно неплохо изучены в гиперсоленых водах (Por, 1980;Wurtsbaugh, Berry, 1990;Балушкина и др., 2009;Carrasco, Perissinotto, 2012;Lin et al., 2017;Голубков и др., 2018;Шадрин, Ануфриева, 2018б;Anufriieva et al., 2018a, c;Shadrin et al., 2019e, 2020cShadrin et al., 2019e, , d, 2021c. При этом в таких водоемах роль хищников выполняют всеядные беспозвоночных животные или посещающие водоем птицы и летающие насекомые (Ануфриева, Шадрин, 2015;Shadrin et al., 2019e). ...
... В настоящее время накоплено достаточно данных, чтобы сформулировать некоторые общие закономерности изменения структуры трофических сетей с ростом солености (Por, 1980;Wurtsbaugh, Berry, 1990;Балушкина и др., 2009;Carrasco, Perissinotto, 2012;Lin et al., 2017;Голубков и др., 2018;Шадрин, Ануфриева, 2018б и др.). Часть тенденций, приводимых ниже, сформулирована разными авторами ранее. ...
... 1. С увеличением солености длина трофической цепочки уменьшается (Балушкина и др., 2009;Carrasco, Perissinotto, 2012;Lin et al., 2017;Голубков и др., 2018;Шадрин, Ануфриева, 2018б). Увеличение трат на обмен и уменьшение ассимилированной энергии с ростом солености (глава 6) ведет к уменьшению К 2 , эффективности использования усвоенной энергии на рост, как следует из уравнения (Заика, 1985; Шадрин, 2011; Алимов и др., 2013): К 2 = P/A = (A-R)/A, (7.1) где К 2 -эффективность использования усвоенной энергии на рост, P -суммарная продукция, R -суммарные траты на обмен, A -ассимилированная из пищи энергия. ...
... Отношения типа «хищник-жертва» довольно неплохо изучены в гиперсоленых водах (Por, 1980;Wurtsbaugh, Berry, 1990;Балушкина и др., 2009;Carrasco, Perissinotto, 2012;Lin et al., 2017;Голубков и др., 2018;Шадрин, Ануфриева, 2018б;Anufriieva et al., 2018a, c;Shadrin et al., 2019e, 2020cShadrin et al., 2019e, , d, 2021c. При этом в таких водоемах роль хищников выполняют всеядные беспозвоночных животные или посещающие водоем птицы и летающие насекомые (Ануфриева, Шадрин, 2015;Shadrin et al., 2019e). ...
... В настоящее время накоплено достаточно данных, чтобы сформулировать некоторые общие закономерности изменения структуры трофических сетей с ростом солености (Por, 1980;Wurtsbaugh, Berry, 1990;Балушкина и др., 2009;Carrasco, Perissinotto, 2012;Lin et al., 2017;Голубков и др., 2018;Шадрин, Ануфриева, 2018б и др.). Часть тенденций, приводимых ниже, сформулирована разными авторами ранее. ...
... 1. С увеличением солености длина трофической цепочки уменьшается (Балушкина и др., 2009;Carrasco, Perissinotto, 2012;Lin et al., 2017;Голубков и др., 2018;Шадрин, Ануфриева, 2018б). Увеличение трат на обмен и уменьшение ассимилированной энергии с ростом солености (глава 6) ведет к уменьшению К 2 , эффективности использования усвоенной энергии на рост, как следует из уравнения (Заика, 1985; Шадрин, 2011; Алимов и др., 2013): К 2 = P/A = (A-R)/A, (7.1) где К 2 -эффективность использования усвоенной энергии на рост, P -суммарная продукция, R -суммарные траты на обмен, A -ассимилированная из пищи энергия. ...
... In recent years, the effects of salinity on zooplankton have received much attention. Previous studies have revealed that salinity is an important environmental filter that may control the species composition and biomass of zooplankton communities in coastal estuarine ecology [7,[13][14][15]. The direct or first-order effects of salinity result from changes in organisms' osmoregulatory ability, food digestibility, and hormonal stimulation. ...
... Many studies have reported that salinity is an important factor affecting the zooplankton community. Ecologically, salinization or a rise in salinity alters zooplankton composition and abundance [14,15,36]. Gao et al. indicated that the variation in salinity in an estuary resulted in regional and seasonal alterations in the dominant species [37]. ...
... Previous studies have found that as salinity increases, zooplankton abundance and biomass decrease [14,15,36]. Consistent with previous studies, in this study, with the increase of salinity, species abundance showed a trend of decreasing first and then increasing, and the turning point was 5.02 ppt (p < 0.05) (Figure 5a), which was similar with the study in Hau River, Vietnam [7]. ...
As the primary consumers in aquatic organisms, zooplankton play an important role in aquatic ecosystems. It is valuable for management and researchers to have an insight into the responses of zooplankton community patterns to environmental factors. In this study, RDA and variation partitioning analysis were adopted to determine the important environmental factors affecting zooplankton abundance and biomass, as well as the relative importance of different environmental factors. The findings reveal that TN (total nitrogen), WD (water depth), pH, and SAL (salinity) were all important abiotic factors shaping the zooplankton community pattern in the study area. TN affected protozoa by influencing Stentor amethystinus, while the effects of WD on copepods may have been mainly induced by the responses of Calanus sinicus and Paracyclopina nana. By inhibiting Stentor amethystinus and Vorticella lutea, pH significantly affected protozoa. In addition, Rotifera and copepods were affected by SAL mainly through the responses of Brachionus calyciflorus, Calanus sinicus, and Ectocyclops phaleratus. Importantly, fundamental alternations in the variation trends of zooplankton abundance and biomass along the salinity gradient were found when the salinity was approximately 4–5. By combining these results with the findings on phytoplankton responses to salinity in previous studies, it can be concluded that salinity may influence the river ecosystem by influencing zooplankton abundance and biomass rather than phytoplankton.
... Soil salinization is a significant global issue, particularly severe in Asia, where large areas of land are affected [7]. It is mainly caused by factors such as climate, topography, and The northeastern part of the Tibetan Plateau has three typical inland river basins, which are ecologically fragile and climate-sensitive, resulting in complex changes in soil water and salt elements, and they are often prone to soil degradation processes such as soil salinization [28]. Therefore, the regulation of soil moisture across layers on the soil salinization of the northeast Tibetan Plateau has been explored in this study to better describe the regional characteristics of soil water and salt transport. ...
... The northeastern part of the Tibetan Plateau has three typical inland river basins, which are ecologically fragile and climate-sensitive, resulting in complex changes in soil water and salt elements, and they are often prone to soil degradation processes such as soil salinization [28]. Therefore, the regulation of soil moisture across layers on the soil salinization of the northeast Tibetan Plateau has been explored in this study to better describe the regional characteristics of soil water and salt transport. ...
The evaporation of soil water drives the upward movement of salt and its accumulation on the surface, which ultimately leads to soil salinization in agroecosystems. With the rapid development of remote sensing technology, the soil water and salt transport can be monitored accurately. Based on Landsat 8 satellite imagery and ERA5-Land reanalysis datasets, this study explored the variation characteristics of soil water and salt in the northeast Tibetan Plateau from 2013 to 2023, inferred by geostatistical methods like ridge regression, windowed cross correlation, and machine learning algorithms. The results show that the negative correlation effect between deep soil moisture (100–289 cm) and soil salinization is stronger. Moreover, soil water and salt also have a time lag effect compared with instant responses, meaning that the soil salinization caused by deep soil moisture may require longer transport times. As the potential driving factors, an increase in soil organic carbon and runoff is beneficial for alleviating salinization while abundant runoff also promotes soil humidification. This study has elucidated the specific regulation of soil salinization by soil moisture within different profiles, which is beneficial for understanding the ecological balance of soil water and soil salt in agroecosystems.
... Salinity was reported as the dominant factor driving changes in the structure, species richness and productivity of algae communities in Tibetan lakes Li et al., 2021). Drastic fluctuations in salinity not only alter the physicochemical properties of lakes but also affect the stability of the structure and function of aquatic ecosystems (Lin et al., 2017;Xu et al., 2024). It is necessary to acquire high-resolution records of algae communities and salinity over longer time-scales to comprehensively examine the response mechanisms of lake physicochemical properties and aquatic ecosystems to climatic and environmental changes, for predicting the dynamics of lake ecosystems under future scenarios (Castañeda and Schouten, 2011;Smol, 2010;Song et al., 2022). ...
... From the ecological mechanism perspective, algae cells have the highest nutrient consumption rate and photosynthesis efficiency under appropriate salinity conditions that promote algae productivity (Chen et al., 2019b). Lower salinity is unfavorable to nutrient absorption and frustule production of algae cells (Diego et al., 2015), while higher salinity not only leads to algae cells being unable to maintain normal osmotic stress and depresses photosynthesis rate (Redden and Rukminasari, 2008) but also enhances topdown grazing pressure from large filter-feeding zooplankton on algae communities by altering the trophic structure of Tibetan lake ecosystems, which further reduces algae biomass (Lin et al., 2017). Thus, the response pattern of pigment concentrations across the salinity gradient was in accordance with the ecological mechanisms of the salinity control Table 4 The performance statistics of the pigment-salinity transfer function based on nine pigments (chlorophylls separated from pheophytins) and seven pigments (chlorophylls merged with pheophytins, underlined numbers) (dataset after screening). ...
Recent limnic environment on the Tibetan Plateau is fluctuating dramatically due to anthropogenic warming, significantly affecting primary producers and the stability of aquatic ecosystems. Subfossil pigments in lake sediments have been widely used to track the response process of algal communities to climatic and environmental changes, but their potential in quantitative reconstructions is rarely explored, particularly in remote mountains with monitoring data scarcity. Here, the relationship between water environmental variables and surface sediment pigment assemblages identified by high-performance liquid chromatography (HPLC) covering 95 Tibetan lake sampling sites was investigated based on multivariate statistical analysis. Salinity was considered as the most important factor determining the distribution pattern of pigment assemblages, and pigment concentrations differed significantly along the lake salinity gradient. Nine chlorophyll, xanthophyll and carotenoid pigments were comprehensively assessed to develop the pigment-salinity transfer function. Sedimentary pigment preservation and salinity range have been taken into consideration, and locally weighted weighted average (LWWA, R2 = 0.74, RMSEP = 0.99 g/L) and locally weighted weighted average partial least squares (LWWAPLS, R2 = 0.74, RMSEP = 0.95 g/L) were identified as the best performing models. The pigment-based transfer function was then applied to quantitatively reconstruct the salinity of Haidingnuoer Lake on the northeastern Tibetan Plateau over the past 150 years, and the reliability and robustness of the reconstruction were verified. Comparison with other paleoclimatic and meteorological records revealed that the lake salinity was mainly influenced by climate-mediated changes in regional precipitation and effective moisture. This study established a new algal pigment-based salinity transfer function, and provided a promising indicator and method to quantitatively reconstruct past lake environmental conditions on the Tibetan Plateau.
... Urbanization, anthropogenic water intake, resource extraction, agriculture, the long-term use of deicing road salts, climate change are factors leading to the global increase in ion concentrations in aquatic ecosystems (Brucet et al. 2010;Cunillera-Montcusí et al. 2022;Dugan et al. 2017;Kaushal et al. 2021;Valleau et al. 2020). Specifically, zooplankton diversity and population dynamics are strongly influenced by the concentration of various dissolved ions with compounds of NaCl frequently dominating the ionic content (Huang et al. 2022;Lin et al. 2017;Mungenge et al. 2023;Santangelo et al. 2014;Velasco et al. 2019). Fluctuations in the ionic content force aquatic organisms to regulate their internal ion concentrations, resulting in increased stress and/or mortalities (Mungenge et al. 2023). ...
... Fluctuations in the ionic content force aquatic organisms to regulate their internal ion concentrations, resulting in increased stress and/or mortalities (Mungenge et al. 2023). When salinity reaches critical levels for individual species, significant modifications in the structure, composition, and function of zooplankton communities are observed (Mungenge et al. 2023;Lin et al. 2017;Reid et al. 2019;Zadereev et al. 2022). ...
Worldwide freshwater salinization may significantly alter ecosystem functioning and affect biodiversity. We studied the effect of salinity on hatching success of resting eggs of different ages and life history traits of post-diapause females of cladoceran Moina macrocopa. The hatching success of resting eggs was almost unaffected by the salinity we tested (up to 5.9 g L⁻¹). We observed a distinct difference in the hatching success of resting eggs of different ages, which was lower by ca. 50% for 4-year-old resting eggs compared with 1-year-old resting eggs. We found a decrease in the values of the life-history traits of the females hatched from 4-year-old resting eggs compared with the females hatched from 1-year-old resting eggs exposed to salinity within the range of 0.08–3.5 g L⁻¹: a shorter lifespan, a lower juvenile somatic growth rate, a delay in the day of the first reproduction, and a smaller number of parthenogenetic clutches produced. Analysis showed that at a salinity of 3.5 g L⁻¹, females hatched from resting eggs are more vulnerable to the effect of salinity than directly developing females. The post-diapause females exposed to salinity showed a shorter lifespan and reduced reproduction parameters (produced fewer clutches and neonates) compared with the directly developing females. Thus, the hatching of resting eggs can be considered as a critical period of the development of a species with the diapause in its life cycle due to the vulnerability of post-diapause females to increased salinity, which can be crucially important for the ecological success of the population.
... Salinization leads to strong changes in community composition through species sorting. Communities of inland saline waters often are a nested subset of freshwater communities [14,23,24], whereas species replacement becomes more prominent at higher salinities [13,24,25]. Parallel to environmental sorting structuring metacommunities, salinity changes can also exert strong selection pressures impacting the evolution of local populations and consequently metapopulation structure [26,27]. ...
... Salinity is a major abiotic stress factor for freshwater biota, strongly impacting community composition and diversity [13,24,25]. Salinization is an important component of global change, with several drivers increasing salinity in inland waters [20,21]. ...
Understanding the spatial scales at which organisms can adapt to strong natural and human-induced environmental gradients is important. Salinization is a key threat to biodiversity, ecosystem functioning and the provision of ecosystem services of freshwater systems. Clusters of naturally saline habitats represent ideal test cases to study the extent and scale of local adaptation to salinization. We studied local adaptation of the water flea Daphnia magna, a key component of pond food webs, to salinity in two contrasting landscapes—a dense cluster of sodic bomb crater ponds and a larger-scale cluster of soda pans. We show regional differentiation in salinity tolerance reflecting the higher salinity levels of soda pans versus bomb crater ponds. We found local adaptation to differences in salinity levels at the scale of tens of metres among bomb crater pond populations but not among geographically more distant soda pan populations. More saline bomb crater ponds showed an upward shift of the minimum salt tolerance observed across clones and a consequent gradual loss of less tolerant clones in a nested pattern. Our results show evolutionary adaptation to salinity gradients at different spatial scales, including fine-tuned local adaptation in neighbouring habitat patches in a natural landscape.
... The increase in nutrient supply (i.e., nitrogen and phosphorus) could trigger ecological cascade effects, profoundly altering the whole lake ecosystem through the bottom-up effects (Matsuzaki et al., 2018). Since lakes in the QTP are typically characterized by simple food webs and oligotrophy (Lin et al., 2017), a tiny elevation in nutrient concentration may have significant impacts on lake ecosystems, particularly in the context of climate warming (Echeverría-Galindo et al., 2023). ...
... Meteorological data reveals that QTP has experienced a significant warming trend since the 1950s at a rate approximately twice as fast as the global average (Zhou and Zhang, 2021). Climate change has profoundly altered the physicochemical properties of lakes in the QTP in many aspects, including water temperature, thermal stratification, salinity level, ice phenology and transparency (Du et al., 2022;Lin et al., 2017;Wan et al., 2018). In addition, climate change has a significant influence on the nutrient cycling and organic carbon sequestration in the QTP (Chen et al., 2022a), improving nutrient transport from pedosphere and the cryosphere to lakes (Zhao et al., 2020). ...
Lakes on the Qinghai-Tibet Plateau (QTP) have been subject to multiple environmental pressures from rapid climate change and intensified human activity in recent decades. However, their ecological effects on the lake ecosystem remain largely unclear due to the lack of long-term monitoring data. This study presented the environmental and ecological changes of the lake Yamzhog Yumco (Southern QTP) over the past three decades based on multi-proxy analysis (geochemistry and sedaDNA) on a high-time resolution sediment core. The result showed that the lake exhibited a continuous eutrophication process from 2004 CE, which has accelerated since 2014 CE. The nutrient enrichment was mainly attributed to anthropogenic emissions from the catchment. The sedimentary ancient DNA (sedaDNA) metabarcoding data registered a sensitive response of aquatic communities to the additional nutrient supply. Eukaryotic algae and aquatic invertebrate communities exhibited similar temporal dynamics, characterized by the increase in eutrophic taxa and the decrease in oligotrophic taxa. Change points analysis suggested that lake ecosystems underwent a slight ecological shift in 2003 CE and an abrupt shift in 2012 CE driven by nutrient enrichment. Quantitative analysis revealed that nutrients and human activity accounted for 27.9 % and 21.7 % of the temporal variation in aquatic communities, whereas climate change only explained 6.9 % of the total variation. From a paleolimnological view, our study supported that regional human activity could distinctly alter the nutrient level and aquatic community structure of lake ecosystems in the QTP. Considering that anthropogenic disturbance will continuously increase, it is crucial to strengthen the field monitoring of the lakes on the plateau and make effective management measures to avoid irreversible ecological consequences.
... Salinisation leads to strong changes in community composition through species sorting. Communities of inland saline water bodies often are a nested subset of freshwater communities [3,12,13], whereas species replacement becomes more prominent at higher salinities [2,13,14]. Parallel to environmental sorting structuring metacommunities in the landscape, changes in salinity can also lead to strong selection pressures impacting the evolution of local populations and thereby affecting metapopulation structure [15,16]. ...
... Salinity is a major abiotic stress factor for freshwater biota strongly impacting community composition and diversity [2,13,14]. Salinisation is an important component of global change and there are several drivers of increasing salinity in inland systems [9][10][11]. ...
Freshwater salinisation is an important threat to biodiversity, ecosystem functioning, and the provision of ecosystem services. Therefore, understanding the capacity of species to adapt to salinity gradients is crucial. Clusters of naturally saline habitats represent ideal test cases to study the extent and scale of local adaptation to salinisation. We studied local genetic adaptation of the water flea Daphnia magna, a key component of pond food webs, to salinity in two contrasting landscapes - a dense cluster of sodic bomb crater ponds and a larger-scale cluster of soda pans. We show regional differentiation in salinity tolerance reflecting the higher salinity levels of soda pans versus bomb crater ponds. We found local adaptation to differences in salinity levels at the scale of tens of metres among bomb crater pond populations but not among geographically more distant soda pan populations. The population-level salinity tolerance range was reduced in more saline bomb crater ponds through an upward shift of the minimum salt tolerance observed across clones and a consequent gradual loss of less tolerant clones in a nested pattern. Our results show genetic adaptation to salinity gradients at different spatial scales and fine-tuned local adaptation in neighbouring habitat patches in a natural landscape.
... This indicates that the vulnerability of populations to emerging stressors may depend on the trophic status of their habitat. Notably, the salt concentrations used in our experiments are within the range of natural salinities reported in both lake [101,102] and stream [103] ecosystems. Our results imply that salt pollution could have a disproportionately detrimental impact on organisms in oligotrophic systems compared to eutrophic ones, suggesting a heightened vulnerability of nutrient-poor aquatic environments to rising salinity levels. ...
Understanding the evolutionary responses of organisms to multiple stressors is crucial for predicting the ecological consequences of intensified anthropogenic activities. While previous studies have documented the effects of selection history on organisms' abilities to cope with new stressors, the impact of the sequence in which stressors occur on evolutionary outcomes remains less understood. In this study, we examined the evolutionary responses of a metazoan rotifer species to two prevalent freshwater stressors: nutrient limitation and increased salinization. We subjected rotifer populations with distinct selection histories (salt-adapted, low phosphorus-adapted and ancestral clones) to a reciprocal common garden experiment and monitored their population growth rates. Our results revealed an asymmetric evolutionary response to phosphorus (P) limitation and increased salinity. Specifically, adaptation to low P conditions reduced rotifer tolerance to increased salinity, whereas adaptation to saline conditions did not show such cross-inhibitory effects. Instead, the addition of moderate concentrations of salt enhanced the growth of the salt-adapted population in low P conditions, potentially as a consequence of evolved cross-tolerance. Our findings, therefore, underscore the importance of considering historical stressor regimes to improve our understanding and predictions of organismal responses to multiple stressors and also have significant implications for ecosystem management.
... Salinity and water temperature, which are significant determinants [71], showed no direct correlation with other mesozooplankton species. Studies have revealed a major shift in zooplankton dynamics occurs when certain salinity or water temperature thresholds are reached [72,73]. Moreover, increased salinity can result in cascading trophic interactions, indicating that these factors indirectly affect zooplankton dynamics through upper or lower trophic levels [74]. ...
Mesozooplankton are critical components of marine ecosystems, acting as key intermediaries between primary producers and higher trophic levels by grazing on phytoplankton and influencing fish populations. They play pivotal roles in the pelagic food web and export production, affecting the biogeochemical cycling of carbon and nutrients. Therefore, accurately modeling and visualizing mesozooplankton community dynamics is essential for understanding marine ecosystem patterns and informing effective management strategies. However, modeling these dynamics remains challenging due to the complex interplay among physical, chemical, and biological factors, and the detailed parameterization and feedback mechanisms are not fully understood in theory-driven models. Graph neural network (GNN) models offer a promising approach to forecast multivariate features and define correlations among input variables. The high interpretive power of GNNs provides deep insights into the structural relationships among variables, serving as a connection matrix in deep learning algorithms. However, there is insufficient understanding of how interactions between input variables affect model outputs during training. Here we investigate how the graph structure of ecosystem dynamics used to train GNN models affects their forecasting accuracy for mesozooplankton species. We find that forecasting accuracy is closely related to interactions within ecosystem dynamics. Notably, increasing the number of nodes does not always enhance model performance; closely connected species tend to produce similar forecasting outputs in terms of trend and peak timing. Therefore, we demonstrate that incorporating the graph structure of ecosystem dynamics can improve the accuracy of mesozooplankton modeling by providing influential information about species of interest. These findings will provide insights into the influential factors affecting mesozooplankton species and emphasize the importance of constructing appropriate graphs for forecasting these species.
... In freshwater ecosystems, zooplankton control water purity, energy, and nutrients as vital food sources for higher trophic levels (Pace and Orcutt Jr, 1981). A decline in zooplankton species richness has been linked to increasing salinity (Jeppesen et al., 2007;Lin et al., 2017). This decline occurs when eggs are exposed to environments with increased salinity (Nielsen et al., 2008). ...
Freshwater salinisation is a growing problem worldwide, affecting surface and groundwater resources. Compared with other global environmental issues, freshwater salinisation has been studied extensively in North America, Australia, and Europe but less so in South America, Asia, and Africa. Both the natural and anthropogenic sources can contribute for freshwater salinisation, through the concentration of dissolved salts in water rising above its normal levels. This review provides a comprehensive assessment of the causes of freshwater salinisation, the impacts on freshwater communities and ecosystem functions, the adaptive mechanisms for survival in an increasingly saline environment, and the management strategies available to control freshwater salinisation. Many human activities contribute to freshwater salinisation, including road salt use, agricultural practices, resource extraction, reservoir construction, and climate change. Aquatic organisms have evolved mechanisms to survive in increasingly saline environments, but excessive salinity can lead to mortality and non-lethal effects. Such effects can have cascading impacts on the structure and function of aquatic communities and ecosystem services. Therefore, monitoring programmes and chemical fingerprinting are needed to identify highly salinised areas, determine how various human activities contribute to freshwater salinisation, and implement management strategies. Furthermore, current research on freshwater salinisation has been limited to a few regions of the world. It is essential to expand the research further into exploring the impacts of salinisation on freshwater resources in unexplored geographic areas of the world that are mainly impacted by climate change scenarios.
... Among the environmental factors analysed, zooplankton were governed mainly by the salinity gradient. Similar results were also reported by Costa et al. (2008), Lin et al. (2017), Yuan et al. (2020) and ...
Studies on the zooplankton community are essential for diagnosing the health of aquatic ecosystems, as these systems respond quickly to environmental changes. Using the multimetric TRIX index for the assessment of trophic status, we assessed the trophic state and its association with zooplankton composition, distribution, and environmental variables in a tropical estuary on the Brazilian equatorial margin. The results showed that significant seasonal and sectoral environmental differences contributed to biological heterogeneity, with the second spatial sector (SII) exhibiting the greatest impact, leading to decreased alpha diversity compared to that of the first spatial sector (SI). Salinity, pH, SiO23, and NO2− exhibited significant seasonal and sectoral variations (p < 0.05). The community consisted of 65 taxa, with copepods (81.5%), mainly from the Oithonidae and Paracalanidae families, dominating species number. Overall, the community exhibited medium diversity, low richness, and heterogeneity. Beta diversity, calculated using PERMDISP, reflected environmental heterogeneity with significant seasonal differences and biological variability between rainy and dry periods. Indicator species analysis identified 15 taxa, including copepods such as Euterpina acutifrons and Clytemnestra scutellata. Of these, nine taxa (60%) were indicators for the SI, and six (40%) were indicators for the SII. This study underscores the importance of identifying environmental filters and indicator species to understand estuarine dynamics and assess ecosystem trophic states.
... Studies of lakes in northwest China showed large reductions in biodiversity and food chain length, indicating loss of ecological functioning, with increasing salinity [73]. Although fish [74] and macrophyte abundances [33] also determine the structure of cladoceran communities, in high salinity lakes, due to the lack of fish predation of zooplankton, there are usually only two trophic levels: zooplankton and phytoplankton [75]. ...
... [15] . 湖泊的盐度会因未来水量的增加而降低, 进一步改变 湖泊生态系统的物种丰富度和营养结构 [16] . ...
50%，对区域水循环、生态环境和气 候调节具有重要意义 [1,2] 。1990s 中期以来，由于降水和冰川融水增加，青藏高原湖泊面 积急剧扩张，水位显著上升，其中大于 1 平方公里的湖泊数量增加至 1400 个(增加约 400 个) ，总面积增加至 5 万平方公里(扩张约 1 万平方公里) 。湖泊的显著扩张对青藏 高原生态环境的可持续发展带来了潜在威胁，亟需开展湖泊未来变化的模拟与评估研究。 目前，青藏高原湖泊未来变化预估研究受到以下因素的限制：存在针对特定区域的 方法，但由于空间异质性，这些方法对具体湖泊的适用性仍不确定；由于缺乏入湖径流 观测数据(仅色林错和纳木错等少数湖泊有入湖径流观测) ，陆面和水文模型的大尺度 应用受到限制；未考虑地形对湖泊未来变化的约束以及湖泊之间的水文连通性；机器或 深度学习方法缺乏可解释性。总的来说，现有研究主要侧重于青藏高原内流区或特定湖 泊，未能全面反应青藏高原湖泊的未来变化及其相应的影响 [3~6] 。 1970s~2020 年， 青藏高原内流湖的水量变化占全部湖泊变化的 95%以上 (161.9±14 Gt) ，而外流湖则保持相对稳定(7.8±5.8 Gt) [7] 。因此，预估内流湖的未来变化是关键。 考虑了影响湖泊变化的主要因素，包括降水、冰川融水、陆面蒸散发和湖面蒸发，针对 内流湖构建了一个基于数据驱动的通用模拟框架，以模拟其未来的面积、水位和水量变 化 [8] 。该框架包括两个主要步骤： (1) 对每个湖泊定义了稳定期和变化期，并基于历史 A c c e p t e d https://engine.scichina.com/
... Among the environmental factors analysed, zooplankton were governed mainly by the salinity gradient. Similar results were also reported by Costa et al. (2008), Lin et al. (2017), Yuan et al. (2020) and ...
This study emphasises the importance of environmental filters in the dynamics of the zooplankton community and the ecological relationships with phytoplankton in three zones of a tropical mesotidal estuary.
Thus, sampling was carried out in six different locations strategically positioned along the Preguiças River estuary, with the following objectives: to characterise the abundance of zooplankton and, through this, determine changes in the community's α‐ and β‐diversity indices depending on variables environmental; to define environmental filters that affect the indicator species of ecosystem zones; and to identify the interaction between phytoplankton and zooplankton along the estuarine gradient.
The zooplankton community contained 80 species, including 14 phyla, with Arthropoda being the most diverse, followed by Ciliophora and Mollusca. The class Copepoda stood out, with Paracalanus crassirostris , Pseudodiaptomus gracilis , and Oithona nana dominating the community. In total, 21 species were selected as indicators, including Temora turbinata in the coastal zone, Rhizodomus tagatzi in the mixing zone, and Moina micrura in the tidal river zone. The environmental heterogeneity showed significant spatial differences, with variations governed mainly by salinity, temperature, and suspended organic matter, which acted as the principal environmental filters. The coastal zone and mixing zone species demonstrated direct ecological relationships with the blooms of the diatoms Skeletonema costatum and Asterionellopsis glacialis , in which the abundance of zooplankton was favoured by their occurrence, denoting top‐down control of the trophic network. For the partitioning of β diversity, the turnover component was responsible for the diversity value due to environmental heterogeneity, which distinguished communities across zones.
Our findings represent the first comprehensive investigation into the relationship between environmental heterogeneity and zooplankton within this tropical ecosystem, subject to mesotides. These discoveries are pivotal in identifying environments highly susceptible to degradation (low β diversity) and those acting as dispersal centres (high β diversity), thereby facilitating targeted conservation efforts and more efficient management of estuarine systems. Therefore, our results provide a crucial basis for the sustainable management of similar coastal ecosystems in different parts of the world.
... In specific, small freshwater invertebrates such as cladocerans are highly sensitive to increased salinity (Goncalves et al. 2007;Schuler et al. 2019;Vignatti et al. 2022;Zadereev et al. 2022). Likewise, the increase in salinity is inversely related to the richness and abundance in lentic (Lin et al. 2017;Mariani et al. 2023) and lotic systems (Ginatullina et al. 2017;Gutierrez et al. 2023), wetlands (Nielsen et al. 2003b), and ponds (Anton-Pardo and Armengol 2012) and has been identified as a determinant of community structure and composition (Schallenberg et al. 2003;Echaniz and Vignatti 2017;Gutierrez et al. 2018;Yuan et al. 2020). ...
Daphnia spinulata Birabén, 1917 is an endemic cladoceran species, frequent in the zooplankton communities of the shallow lakes of the Pampean region of Argentina. These lakes have varying salinity levels and, being located in agricultural areas, are frequently subject to pesticide pollution. This study aimed to determine the effects of the herbicide glyphosate (Panzer Gold®) in combination with different salinity levels on the biological parameters of D. spinulata and its recovery ability after a short exposure. Three types of assays were performed: an acute toxicity test, a chronic assessment to determine survival, growth and reproduction, and recovery assays under optimal salinity conditions (1 g L⁻¹). The LC50-48 h of glyphosate was 7.5 mg L⁻¹ (CL 3.15 to 11.72). Longevity and the number of offspring and clutches were significantly reduced due to the combined exposure of glyphosate and increased salinity. The timing of the first offspring did not recover after glyphosate exposure. Our results reveal that D. spinulata is sensitive to the herbicide Panzer Gold® at concentrations well below those indicated in the safety data sheet of this commercial formulation, which causes stronger negative effects in conditions of higher salinity. Further research is needed to shed light on the sensitivity of this cladoceran to glyphosate and its variability under other interactive stress factors.
... For example, salinity, particulate organic carbon and WT, etc., (Shan et al., 2019;Navas-Parejoa et al., 2020). Salinization of freshwater environment can indirectly affect the abundance of planktonic algae by changing water quality or increasing the intake rate of planktonic algae by zooplankton (Lin et al., 2017;Kaushal et al., 2019). Meanwhile, phytoplankton communities are also sensitive to environmental changes and can reflect changes in aquatic ecosystems in a short time (Suikkanen et al., 2007). ...
The Qinghai-Tibet Plateau is an ecologically fragile region. The changes in physicochemical parameters of water quality [PPOWQ] and land use types [LUT] in different regions will affect the phytoplankton community in rivers, thus threatening the ecosystem. Taking the phytoplankton community as an indicator variable, it is of great significance to study the relative influence of symbiotic factors on regulating human activities and river ecological protection. The results showed that the proportions of Bacillariophyta, Cyanophyta, and Chlorophyta were >84% in the phytoplankton community of taxa composition. The abundance of the phytoplankton community varied from 1.47 × 105 to 7.58 × 105 cells/L. Bacillariophyta had the highest average abundance (>82%). The results of the variance partitioning analysis showed that PPOWQ was the main variable affecting the changes in the phytoplankton community. Redundancy analysis showed that local factors (total nitrogen, salinity, water temperature) and regional factors (forestland, grassland, unused land) (p < 0.05) were the main factors causing the changes in community structure and abundance of dominant algae. The analysis of structural equation models showed that LUT had the least direct impact on the abundance of the phytoplankton community, mainly through changing nutrients and physical parameters. Water temperature and nutrients are still the main factors affecting phytoplankton community abundance. Farmland and forestland are the main sources of total nitrogen in rivers. In general, in the ecologically vulnerable area, it is of guiding significance for the ecological monitoring and management of plateau rivers. In addition to considering water quality, it is also necessary to reasonably plan the LUT around rivers.
... The impact of rising temperature is notably significant in the lakes of the Tibetan Plateau, and precipitation tends to increase in the east and north. As a result, the lakes in the Tibetan Plateau experience a warm and wet climate (Zong-Xue et al., 2006;Yao et al., 2007;Liao et al., 2013;Lin et al., 2017). This leads to increases in lake water temperature and nutrients, but a decrease in salinity, potentially facilitating the growth of nuisance algae such as cyanobacteria (Jeppesen et al., 2010). ...
Owning to their extreme environmental conditions, lakes on the Qinghai-Tibet Plateau have typically displayed a simplistic food web structure, rendering them more vulnerable to climate change compared to lakes in plains. Phytoplankton, undergoing a changing aquatic environment, play a crucial role in the material cycle and energy flow of the food chain, particularly important for the unique fish species of the Tibetan Plateau. To identify the changing environment indexes and determine the response of phytoplankton composition to the environment change in alpine lakes, three lakes—Lake Qinghai, Lake Keluke and Lake Tuosu—were selected as study areas. Seasonal sampling surveys were conducted in spring and summer annually from 2018 to 2020. Our findings revealed there were significant changes in physicochemical parameters and phytoplankton in the three lakes. Bacillariophyta was the predominant phytoplankton in Lake Qinghai from 2018 to 2020, with the genera Synedra sp., Navicula sp., Cymbella sp. and Achnanthidium sp. predominated alternately. Lake Keluke alternated between being dominated by Bacillariophyta and cyanobacteria during the same period. Dolichospermum sp., a cyanobacteria, was prevalent in the summer of 2018 and 2019 and in the spring of 2020. In Lake Tuosu, Bacillariophyta was the predominant phytoplankton from 2018 to 2020, except in the summer of 2019, which was dominated by cyanobacteria. Synedra sp., Oscillatoria sp., Pseudoanabaena sp., Chromulina sp. and Achnanthidium sp. appeared successively as the dominant genera. Analysis revealed that all three lakes exhibited higher phytoplankton abundance in 2018 that in 2019 and 2020. Concurrently, they experienced higher average temperatures in 2018 than in the subsequent years. The cyanobacteria, Bacillariophyta, Chlorophyta and overall phytoplankton increased with temperature and decreased with salinity and NH4-N. Besides, the ratios of cyanobacteria, and the ratios of Bacillariophyta accounted in total phytoplankton increased with temperature. These findings suggest that cyanobacteria and phytoplankton abundance, especially Bacillariophyta, may have an increase tendency in the three alpine lakes under warm and wet climate.
... The relatively lower virus-mediated bacterial mortality in Tibetan lakes may be due to the high proportion of lysogenic infections, suggesting viruses might have a modest impact on bacterial mortality in alpine lakes. Other factors, such as grazing by protists, abundant in Tibetan lakes (Lin et al. 2017), likely play a more significant role in bacterial loss Säwström et al. 2009). ...
Viruses are major players in the biosphere, yet little is known about their dynamics and life strategies in alpine lakes, particularly those on the Tibetan Plateau. We investigated microbial abundance, viral dynamics, and viral life strategies in 10 high-altitude Tibetan lakes and found that they harbor high levels of active viruses. Salinity was identified as a crucial factor influencing viral abundance, dynamics, as well as viral life strategies. Lytic and lysogenic viral productions in moderate-and high-salinity lakes were significantly higher than those in freshwater lakes. A trade-off between viral life strategies resulted in a switch from lysis to lysogeny in high-salinity lakes. Virus-mediated cell lysis and virus decay in sampled Tibetan lakes could release about 162.72 and 2.84 μg C L-1 d-1 , respectively. These findings revealed the crucial role of viruses in the carbon cycle of Tibetan lakes, and a switch in viral life strategies may impact their contribution to the carbon cycle. The potential impact of salinity changes triggered by climate change on the carbon cycle in alpine lakes worldwide is highlighted.
... Furthermore, whereas zooplankton communities of Arctic and Subarctic lakes outside of Western Siberia were studied in sufficient details (Rautio, 2001;O'Brien et al., 2004;Samchyshyna et al., 2008;Carter and Schindler, 2012;Paterson et al., 2014;Bégin and Vincent, 2017;Hayden et al., 2017;Novichkova and Azovsky, 2017;MacLeod et al., 2018;Beaver et al., 2019;Lau et al., 2020), the majority of works on zooplankton in Siberian inland waters concern southern, permafrost-free zone (i.e., 80 references Web of Science by 2024), and only a few works addressed zooplankton features in permafrost-affected Siberian waters, exclusively in northeastern Siberia such as the Lena River basin (Nigamatzyanova et al., 2016;Abramova et al., 2017;Frolova and Nigamatzyanova, 2019;Chertoprud and Novichkova, 2021;Chertoprud et al., 2023) and the Anadyr region (Streletskaya, 2010). Recently, limited data became available on zooplankton in permafrost peatlands of NE European Arctic (Nazarova et al., 2021;Sobko et al., 2023) and high altitude permafrost-affected lakes of Tibet (Lin et al., 2017;Ren et al., 2022;Su et al., 2018Su et al., , 2022Zhao et al., 2022). Overall, the information on zooplankton in peatlandhosted (organic-rich) thermokarst waters is highly limited. ...
Humic thermokarst lakes of permafrost peatlands in Western Siberia Lowland (WSL) are major environmental controllers of carbon and nutrient storage in inland waters and greenhouse gases emissions to the atmosphere in the subarctic. In contrast to sizable former research devoted to hydrochemical and hydrobiological (phytoplankton) composition, zooplankton communities of these thermokarst lakes and thaw ponds remain poorly understood, especially along the latitudinal gradient, which is a perfect predictor of permafrost zones. To fill this gap, 69 thermokarst lakes of the WSL were sampled using unprecedented spatial coverage, from continuous to sporadic permafrost zone, in order to assess zooplankton (Cladocera, Copepoda, Rotifera) diversity and abundance across three main open water physiological seasons (spring, summer and autumn). We aimed at assessing the relationship of environmental factors (water column hydrochemistry, nutrients, and phytoplankton parameters) with the abundance and diversity of zooplankton. A total of 74 zooplankton species and taxa were detected, with an average eight taxa per lake/pond. Species richness increased towards the north and reached the maximum in the continuous permafrost zone with 13 species found in this zone only. In contrast, the number of species per waterbody decreased towards the north, which was mainly associated with a decrease in the number of cladocerans. Abundance and diversity of specific zooplankton groups strongly varied across the seasons and permafrost zones. Among the main environmental controllers, Redundancy Analysis revealed that water temperature, lake area, depth, pH, Dissolved Inorganic and Organic Carbon and CO2 concentrations were closely related to zooplankton abundance. Cladocerans were positively related to water temperature during all seasons. Copepods were positively related to depth and lake water pH in all seasons. Rotifers were related to different factors in each season, but were most strongly associated with DOC, depth, CH4, phytoplankton and cladoceran abundance. Under climate warming scenario, considering water temperature increase and permafrost boundary shift northward, one can expect an increase in the diversity and abundance of cladocerans towards the north which can lead to partial disappearance of copepods, especially rare calanoid species.
... In this sense, several authors have shown that variations and increases in salinity strongly shape community structure and composition (Schallenberg et al. 2003; Echaniz and Vignatti 2017; Gutierrez et al. 2018; Yuan et al. 2020). In the case of zooplankton, the increase in salinity has been inversely related to the richness and abundance of zooplankton in lentic (Lin et al. 2017;Mariani et al. 2023) and lotic systems (Ginatullina et al. 2017), wetlands (Nielsen et al. 2003), and ponds (Anton-Pardo and Armengol 2012). ...
Daphnia spinulata Birabén, 1917 is an endemic cladoceran species, frequent in the zooplankton communities of the shallow lakes of the Pampean region of Argentina. These lakes have varying salinity levels and, being located in agricultural areas, are frequently subject to pesticide pollution. This study aimed to determine the effects of the herbicide glyphosate (Panzer Gold®) in combination with different salinity levels on the biological parameters of D. spinulata and its recovery ability after a short exposure. Three types of assays were performed: an acute toxicity test, a chronic assessment to determine survival, growth and reproduction, and recovery assays under optimal salinity conditions (1 g L − 1 ). The LC 50 -48h of glyphosate was 7.5 mg L − 1 (3.15–11.72). Longevity and the number of offspring and clutches were significantly reduced by glyphosate and high salinity exposure, whether in isolation or combined. The timing of the first offspring did not recover after glyphosate exposure. Our results reveal that D. spinulata is sensitive to the herbicide, which causes stronger negative effects in conditions of higher salinity. Further research is needed to shed further light on the sensitivity of this cladoceran to glyphosate and its variability under other interactive stress factors.
... They exhibit an elevated sensitivity toward natural and anthropogenic alterations in the environment, and their community structures are closely related to the water physicochemical factors (Adamczuk et al., 2015;Hamil et al., 2021;Jin et al., 2012;Stamou et al., 2021). Since the mid-1980s, numerous studies have demonstrated the relationship between zooplankton and the trophic state of lakes (Blancher, 1984;Gebrehiwot, 2020;Lin et al., 2017). Therefore, zooplankton is frequently considered as an indicator to reflect environmental change and studying the community structure of zooplankton holds significant importance in exploring the ecological security of lakes (Caroni & Irvine, 2010;Duggan et al., 2001;Xiong et al., 2019). ...
This study investigated zooplankton species, density, biomass, and water physicochemical factors in Hongze Lake between 2016 and 2020. The correlation between zooplankton community changes and physicochemical factors was explored using canonical correspondence analysis and Spearman correlation analysis. The investigation found 48 species of protozoa, 52 species of rotifers, 36 species of cladocera, and 32 species of copepoda. The yearly mean density fluctuated between 529.01 and 2234.51 individuals per liter. The yearly mean zooplankton biomass was 950.14 mg/L, ranging from 271.92 to 1365.835 mg/L. A high diversity of zooplankton was found in the Overwater Area, with a large proportion of protozoa and copepoda. Correlation analysis revealed that nitrogen content, pH, water temperature, chemical oxygen demand, biochemical oxygen demand, water transparency, and chlorophyll a were important factors influencing the distribution of zooplankton in Hongze Lake. These factors collectively contributed to the evolution of the zooplankton community structure in Hongze Lake.
... With the disappearance of fish, an increase in zooplankton biomass occurred, as well as a change in the size distribution of phytoplankton particles with an increase in the proportion of cladocerans of the zooplankton. Similar findings were identified in a study of Tibetan lakes [9], except in the control of phytoplankton. The interactive effects of salinity and eutrophication strongly depended on the size and depth of the lakes, and it was concluded that small shallow lakes will be the most vulnerable to the joint effect of increased salinity and eutrophication, with the degradation of ecosystem functioning and water quality at moderate salinities of 3-20 g L −1 . ...
Temperature and precipitation patterns are changing considerably worldwide because of global climate change [...]
... Salinity is an important indicator of the hydrological condition of inland lakes and a key parameter for interpreting hydrological changes such as precipitation, evaporation, runoff and drought in lake basins (Chen et al., 2010). Salinity not only affects the growth and metabolism of algae and the adsorption of nitrogen and phosphorus nutrients by suspended particles but also plays an important role in the structure and dynamics of lake ecosystems (Lin et al., 2017). Furthermore, related studies have found that saline lakes exhibit usually higher DOC concentrations than freshwater lakes . ...
Dissolved organic matter (DOM) plays an essential role in the global lake carbon cycle. Understanding DOM composition and monitoring its spatiotemporal dynamics are of great significance for understanding the lake carbon cycle, controlling water pollution, and protecting water resources. However, previous studies have focused mainly on eutrophic freshwater lakes, with limited attention given to saline lakes. Based on in situ data collected in ten lakes in northwestern China, this study reported the changes in DOM components in different lake types. Parallel factor analysis (PARAFAC) was used to analyze the three-dimensional excitation emission matrix (EEMs) to obtain the DOM fluorescence components. The contributions of different environmental factors to the changes in DOM components were quantified by the generalized linear model (GLM). The results showed that the eutrophication index was significantly positively related to dissolved organic carbon (DOC) (R2 = 0.95, p < 0.01) and colored DOM (CDOM) (R2 = 0.96, p < 0.01) concentrations. Terrestrial humic-like and tryptophan-like components, which are highly correlated with human activities, explained 62% and 64% of the variations in DOC and CDOM, respectively. In sum, the contributions of human activities to the DOC and CDOM variations were 61% and 57%, respectively. Salinity also showed significant positive correlations with both DOC (R2 = 0.88, p < 0.01) and CDOM (R2 = 0.87, p < 0.01). Lake salinization led to increases in DOM concentration, and salinity contributed 20% and 16% to the DOC and CDOM variations, respectively. Therefore, human activities and salinity codetermined the DOM concentration and its composition in the western arid lakes. Based on these findings, this study proposed a feasible flowchart for remotely estimating DOM in saline lakes using satellite data. This study is significant for the long-term monitoring of the carbon cycle and the effective protection of lake water resources in saline lakes.
... The effect of low and moderate salinities (up to 5 g/L) on the ability of zooplankton to control phytoplankton is of great research interest. Such salinity is still below the threshold for the presence of fish and supports many species of freshwater zooplankton, specifically various cladocerans that considered being effective filter feeders (e.g., Lin et al., 2017). At such salinity, a lake continues to provide ecosystem services typical for freshwater lakes such as support of species diversity or fish provisioning. ...
Cladocera are filter feeders abundant in freshwaters, which consume phytoplankton particles in wide size and taxonomic ranges. The ability of cladocerans to control phytoplankton abundance by grazing is determined by various factors including the characteristics of phytoplankton. Freshwater salinization may reduce the strength of top-down grazing control of phytoplankton because of the detrimental effects of salinity on the grazing intensity of zooplankters. We performed grazing experiments with two species of Cladocera of different body lengths to test their ability to graze on phytoplankton in natural waters differing in salinity and size and taxonomic composition of food particles. Grazing experiments demonstrated that the grazing rate was mostly controlled by the abundance of phytoplankton in the medium. The grazing rate was reduced at salinity ca. above 3 g/L of NaCl in the medium. The lower grazing rate was observed in the medium with larger phytoplankton particles. Both species predominantly consumed phytoplankton particles with a diameter of 6–12 µm, which may shift the size distribution of phytoplankton towards a larger average diameter of particles. The taxon-specific feeding was also observed, as both species predominantly consumed diatom algae. Thus, we found that because of grazing, the size and taxonomic characteristics of phytoplankton are shifted towards a less edible community. The detrimental effect of elevated salinity on grazing rate supports growing concern about freshwater salinization negatively affecting water quality, particularly reducing top-down grazing control of phytoplankton.
... On the other hand, the positive effect of temperature on species richness is consistent with the increase in species numbers characteristic of temperate environments. Declines in species richness with increasing salinity have been reported for various sets of lakes from different regions, such as Denmark and Spain (Brucet et al., 2009), the Tibetan Plateau (Lin et al., 2017) and northwest China (Gutierrez et al., 2018). However, none of these studies showed a positive relationship between species richness and temperature, even though its potential effect was explicitly investigated. ...
Body size is a master trait controlling biological communities and ecosystem functioning. Mean population size not
only depends on the size of individuals, but also on the size distribution of individuals within the population. Mean
community size is additionally influenced by the composition of species (larger- or smaller-sized species). Shallow
lakes within semi-arid landscapes are prone to experience large changes in temperature and salinity, which affect the
zooplankton size structure. Higher temperatures are expected to result in smaller average body size, while the effect of
salinity appears to depend on the range under study. Here we analyze zooplankton body size patterns across shallow
lakes from the semi-arid central region of Argentina. All community size descriptors point to decreasing size and a
narrow size range at higher temperatures. On the other hand, the maximum average community body size occurred at
intermediate (∼30 gL−1) salinity levels. The combined effect of both variables resulted in a bell-shaped pattern, with
maximum community body size toward lower temperatures and intermediate salinities. Based on future temperature
scenarios, one may anticipate an overall decrease in community body size. But such prediction is strongly conditioned
by regional and local trends in salinity.
This paper summarises results of a three-year research aimed at investigating the variability of chemical composition and species diversity and functional structure of planktonic communities in saline lakes of Transbaikalia (Russia). According to the ionic content, the lakes were classified either as soda (13 lakes), chloride (3 lakes), and sulphate (2 lakes) types. Water salinity ranges widely, from 0.5 to 334.5 g L−1 in soda lakes, from 8.2 to 257.8 g L−1 in chloride ones, and from 21.3 to 146.8 g L−1in sulphate lakes. In all lakes the cation Na+ dominated, with its concentration increasing as the salinity of the water rises. An increase in salinity, accompanied by a sequential change in the chemical types and subtypes of lakes, led to an excess of bioavailable forms of nitrogen and phosphorus. Diversity and density of phytoplankton and zooplankton depended on both to an increase in the total salt content and the anionic composition of water. Salinity constrains species composition and functional diversity and leads to changes in trophic structure and density of some aquatic organisms. We determined two assemblages of aquatic organisms: Anabaenopsis knipowitschii and Brachionus angularis preferring sulphate dominated habitats and Limnospira fusiformis, Ascomorpha ecaudis, and Hexarthra mira commonly associating with carbonate dominated habitats.
Zooplankton play a crucial role in estuarine ecosystems by aiding nutrient cycling through trophic chains and contributing to large-scale water filtration. The present review highlights the zooplankton research conducted over the last decade (2014–2024) in the Indian Sundarbans, with a focus on research trends, species distribution, hydrological associations, and long-term monitoring and conservation strategies. The study reveals a surge in zooplankton research after 2019, with an emphasis on both small- and large-scale studies. However, tidal creek/canals remain less explored compared to rivers. A lack of methodological standardization in zooplankton research is evident across the Indian Sundarbans. The Saptamukhi-Thakuran-Matla river stretch exhibited the highest species diversity, with 70 species recorded. Similarly, the tidal creeks and canals of Sagar Island were identified as species-rich habitats, with 63 species reported. Oithona brevicornis was found in seven riverine stretches, while Paracalanus parvus and Labidocera euchaeta were each recorded from six rivers, but Bestiolina similis was mostly reported as the numerically predominant zooplankton species. Salinity emerged as the most influential hydrological factor for zooplankton distribution, followed by dissolved oxygen and water temperature. However, increasing pollution, climate change-induced cyclones, salinization, and human activities are threatening zooplankton communities of the Indian Sundarbans. Furthermore, the review underscores the need for long-term monitoring strategies in the Sundarbans, by addressing the integration of remote sensing method, automated devices, data repositories, and ecological modeling approaches. Additionally, the present review recommends future policies for zooplankton conservation, emphasizing habitat protection, water quality assessment, stakeholder engagement, and securing funding to implement long-term monitoring initiatives.
Zooplankton plays crucial roles in the food web by transferring energy from primary producers to higher trophic
levels. The Indian Sundarbans, being a large mangrove-estuarine ecosystem, harbors rich aquatic diversity but
endures several threats from anthropogenic activities. The present review comprehensively summarizes the
status of zooplankton in the Indian Sundarbans. This review discusses the distribution of zooplankton across
rivers and tidal creeks/canals, the influences of water parameters, possible threats, and conservation proposals
through potential long-term monitoring. Calanoid copepods (~32.02 %) are predominant in the Indian Sundarbans, followed by Choreotrichida (~17.8 %), Cyclopoida (~8.67 %), Decapoda (~7.55 %), and Harpacticoida
(~5.66 %). As per previous studies, calanoid Pseudodiaptomus serricaudatus is predominant in rivers, followed by
Paracalanus parvus, Bestiolina similis, Acartia plumosa, and Acartiella tortaniformis. Salinity is the key water
parameter influencing the assemblage and distribution of zooplankton in the Indian Sundarbans. Zooplankton in
this region face several threats, such as pollution, natural disasters, and the development of river dykes, which
may raise serious concerns about their survival. This review recommends conservation and long-term monitoring
programs, including mass culture, database development, and the use of advanced techniques to support conservation policies for zooplankton communities. Special emphasis is given to habitat conservation and the
implementation of river conservation programs like “Namami Gange” initiated by the Government of India.
Additionally, this review outlines a baseline draft on zooplankton monitoring in the Indian Sundarbans,
addressing sampling frequency, sampling locations, and possible funding opportunities for the smooth running of
this program.
Rising water temperatures in rivers due to climate change are already having observable impacts on river ecosystems. Warming water has both direct and indirect impacts on aquatic life, and further aggravates pervasive issues such as eutrophication, pollution, and the spread of disease. Animals can survive higher temperatures through physiological and/or genetic acclimation, behavioral and phenological change, and range shifts to more suitable locations. As such, those animals that are adapted to cool‐water regions typically found in high altitudes and latitudes where there are fewer dispersal opportunities are most at risk of future extinction. However, sub‐lethal impacts on animal physiology and phenology, body‐size, and trophic interactions could have significant population‐level effects elsewhere. Rivers are vulnerable to warming because historic management has typically left them exposed to solar radiation through the removal of riparian shade, and hydrologically disconnected longitudinally, laterally, and vertically. The resilience of riverine ecosystems is also limited by anthropogenic simplification of habitats, with implications for the dispersal and resource use of resident organisms. Due to the complex indirect impacts of warming on ecosystems, and the species‐specific physiological and behavioral response of organisms to warming, predicting how river ecosystems will change in the future is challenging. Restoring rivers to provide connectivity and heterogeneity of conditions would provide resilience to a range of expected co‐occurring pressures, including warming, and should be considered a priority as part of global strategies for climate adaptation and mitigation.
This article is categorized under: Science of Water > Water and Environmental Change
Water and Life > Nature of Freshwater Ecosystems
Water and Life > Stresses and Pressures on Ecosystems
Human activities and climate change cause abiotic factors to fluctuate through time, sometimes passing thresholds for organismal reproduction and survival. Multiple stressors can independently or interactively impact organisms; however, few studies have examined how they interact when they overlap spatially but occur asynchronously. Fluctuations in salinity have been found in freshwater habitats worldwide. Meanwhile, heatwaves have become more frequent and extreme. High salinity pulses and heatwaves are often decoupled in time but can still collectively impact freshwater zooplankton. The time intervals between them, during which population growth and community recovery could happen, can influence combined effects, but no one has examined these effects. We conducted a mesocosm experiment to examine how different recovery times (0‐, 3‐, 6‐week) between salt treatment and heatwave exposure influence their combined effects. We hypothesized that antagonistic effects would appear when having short recovery time, because previous study found that similar species were affected by the two stressors, but effects would become additive with longer recovery time since fully recovered communities would respond to heatwave similar to undisturbed communities. Our findings showed that, when combined, the two‐stressor joint impacts changed from antagonistic to additive with increased recovery time between stressors. Surprisingly, full compositional recovery was not achieved despite a recovery period that was long enough for population growth, suggesting legacy effects from earlier treatment. The recovery was mainly driven by small organisms, such as rotifers and small cladocerans. As a result, communities recovering from previous salt exposure responded differently to heatwaves than undisturbed communities, leading to similar zooplankton communities regardless of the recovery time between stressors. Our research bolsters the understanding and management of multiple‐stressor issues by revealing that prior exposure to one stressor has long‐lasting impacts on community recovery that can lead to unexpected joint effects of multiple stressors.
Alpine lakes play pivotal roles in plateau hydrological processes but are highly sensitive to climate change, yet we lack comprehensive knowledge of their multitrophic biodiversity patterns. Here, we compared the biodiversity characteristics of diverse taxonomic groups across water depths and in surface sediments from a freshwater lake and a hypersaline lake on the northwestern Tibetan Plateau. Using multi-marker environmental DNA metabarcoding, we detected 134 cyanobacteria, 443 diatom, 1,519 invertebrate, and 28 vertebrate taxa. Each group had a substantially different community composition in the two lakes, and differences were also found between water and sediments within each lake. Cooccurrence network analysis revealed higher network complexity, lower modularity, and fewer negative cohesions in the hypersaline lake, suggesting that high salinity may destabilize ecological networks. Our results provide the first holistic view of Tibetan lake biodiversity under contrasting salinity levels and reveal structural differences in the ecological networks that may impact ecosystem resilience.
Lakes on the Tibetan Plateau are expanding rapidly in response to climate change. The potential impact on the local environment if lake expansion continues remains uncertain. Here we integrate field surveys, remote sensing observations and numerical modelling to assess future changes in lake surface area, water level and water volume. We also assess the ensuing risks to critical infrastructure, human settlements and key ecosystem components. Our results suggest that by 2100, even under a low-emissions scenario, the surface area of endorheic lakes on the Tibetan Plateau will increase by over 50% (~20,000 km²) and water levels will rise by around 10 m relative to 2020. This expansion represents approximately a fourfold increase in water storage compared with the period from the 1970s to 2020. A shift from lake shrinkage to expansion was projected in the southern plateau around 2021. The expansion is primarily fuelled by amplified lake water inputs from increased precipitation and glacier meltwater, profoundly reshaping the hydrological connectivity of the lake basins. In the absence of hazard mitigation measures, lake expansion is projected to submerge critical human infrastructure, including more than 1,000 km of roads, approximately 500 settlements and around 10,000 km² of ecological components such as grasslands, wetlands and croplands. Our study highlights the urgent need for water hazard mitigation and management across the Tibetan Plateau.
The Transbaikalia (Russia) hosts a number of shallow endorheic saline alkaline lakes. The outcome of our studies demonstrated changes in phytoplankton and zooplankton in selected lakes covering a wide salinity gradient (from 0.69 to 128.33 g/L) over a number of years. Our main goal is to assess the variability of structural and functional indicators of phytoplankton and zooplankton communities at the various salinity levels. The gradient of abiotic factors significantly determines the dynamics of planktonic community diversity, abundance, biomass, and production. High values of secondary production was ensured by nonpredators (bacteriovorous, herbivorous, and detrivorus). We found that species and functional diversity of phytoplankton and zooplankton decrease with increasing salinity, whereas their abundance, biomass, and daily secondary production did not. In phytoplankton, a shift occurred from the small-medium cell size unicellular and colonial non-flagellated forms to the large-extra large filamentous cyanobacteria and colonial algae. A shift from selective raptorial and microphagous carnivores to herbivorous copepods and cladocerans and further to more generalist filter-feeder of rotifers and anostracans was observed in zooplankton. These findings are important because they provide a meaningful view of phytoplankton-zooplankton trophic interactions and contribute to an improved understanding their functional effects on aquatic ecosystems. Our results also complement existing knowledge and provides new information about the diversity and functioning of planktonic communities in soda lakes.
The paper summarises the results of a three-year research study (Russian Science Foundation grant: 22-17-00035) aimed at investigating the variability of chemical composition and the species diversity and functional structure of planktonic communities in saline lakes of Transbaikalia (Russia). According to the ionic content, the lakes were classified either as soda (13 lakes), chloride (3 ones), and sulphate (2 ones) types. Water salinity ranges widely, from 0.5 to 334.5 g/L in soda lakes, from 8.2 to 257.8 g/L in chloride ones, and from 21.3 to 146.8 g/L in sulphate ones. In all lakes the cation Na ⁺ dominated, with its concentration increasing as the salinity of the water rises. An increase in salinity, accompanied by a sequential change in the chemical types and subtypes of lakes, led to an excess of bioavailable forms of nitrogen and phosphorus. Diversity and density of phytoplankton and zooplankton depent both to an increase in the total salt content and to the anionic composition of water. Salinity constrains species composition and functional diversity and leads to changes in trophic structure and density of some aquatic organisms. We determined two assemblages of aquatic organisms: Anabaenopsis knipowitschii and Brachionus angularis prefering sulphate dominated habitats and Limnospira fusiformis, Ascomorpha ecaudis , and Hexarthra mira commonly associating with carbonate dominated habitats.
The Qinghai-Tibet Plateau is one of the areas the richest in salt lakes and Artemia sites. As a result of climate
warming and wetting, the areas of salt lakes on the plateau have been increasing, and the salinities have
decreased considerably since 1990s. However, the impact of salinity change on the genetic diversity of Artemia is
still unknown. Kyˆebxang Co is the highest (4620 m above sea level) salt lake currently with commercial harvesting of Artemia resting eggs in the world, and harbors the largest Artemia population on the plateau. Its salinity
had dropped from ~67 ppt in 1998 to ~39 ppt in 2019. Using 13 microsatellite markers and the mitochondrial
cytochrome oxidase submit I (COI) gene, we analyzed the temporal changes of genetic diversity, effective
population size and genetic structure of this Artemia population based on samples collected in 1998, 2007 and
2019. Our results revealed a steady decline of genetic diversity and significant genetic differentiation among the
sampling years, which may be a consequence of genetic drift and the selection of decreased salinity. A decline of
effective population size was also detected, which may be relative to the fluctuation in census population size,
skewed sex ratio, and selection of the declined salinity. In 2007 and 2019, the Artemia population showed an
excess of heterozygosity and significant deviation from Hardy-Weinberg Equilibrium (p < 0.001), which may be
associated with the heterozygote advantage under low salinity. To comprehensively understand the impact of
climate warming and wetting on Artemia populations on the plateau, further investigation with broad and
intensive sampling are needed.
As an important freshwater resource in the Qinghai-Tibet Plateau, glacial lakes are being immensely affected by global warming. Due to the lack of long-term monitoring data, the processes and driving mechanisms of the water ecology of these glacial lakes in a rapidly changing climate are poorly understood. This study, for the first time, reconstructed changes in water temperature and photosynthetic microbial communities over the past 200 years in Lake Basomtso, a glacial lake on the southeastern Tibetan Plateau. Temperatures were reconstructed using a paleotemperature proxy based on branched glycerol dialkyl glycerol tetraethers (brGDGTs), the cell membrane lipids of some bacteria, and photosynthetic microbial communities were determined by high-throughput DNA sequencing. The reconstructed mean annual air temperature (MAAT) at Lake Basomtso varied between 6.9 and 8.3 °C over the past 200 years, with a rapid warming rate of 0.25 °C /10 yrs after 1950s. Carbon isotope of sediment and n-alkane analyses indicate that ≥95% of the organic matter in Lake Basomtso is derived from a mixture of terrestrial C3 plants and endogenous organic matter inputs, and the proportion of endogenous organic matter in the sediments has gradually increased since the 1960s. The sedimentary DNA analyses of the sediment core reveal that Chloracea is the most dominant prokaryotic photosynthetic microbial group (84.5%) over the past 200 years. However, the relative abundance of Cyanobacteria has increased from ≤6.8% before the 1960s to 15.5% nowadays, suggesting that warmer temperatures favor the growth of Cyanobacteria in glacial lakes. Among eukaryotic photosynthetic microorganisms, the Chlorophyceae have been gradually replaced by Dinoflagellata and Diatomacae since the 1980s, although the Chlorophyceae still had the highest average relative abundance overall (30-40%). The Pb isotopic composition, together with the total phosphorous concentration, implies that human activity exerted a minimal impact on Lake Basomtso over the past 200 yrs. However, the synchronous fluctuations of total organic carbon (TOC), total nitrogen (TN), and metal elements in sediments suggest that temperature appears to have a strong influence on nutrient input to Lake Basomtso by controlling glacial erosion. Global warming and the concurrent increase in glacial meltwater are two main factors driving changes in nutrient inputs from terrestrial sources which, in turn, increases the lake productivity, and changes microbial community composition. Our findings demonstrate the sensitive response of glacial lake ecology to global warming. It is necessary to strengthen the monitoring and research of glacial lake ecology on the Tibetan plateau, so as to more scientifically and accurately understand the response process and mechanism of the glacial lake ecosystem under global warming.
Salinity and temperature are known to be important factors driving species richness and species composition in inland waters, but their effect and interaction are still not completely clear. In this paper we examine their interaction on species richness and species composition of planktonic rotifers in Turkey, controlling for other confounding effects. Eighty-four species of Rotifera belonging to 32 genera were recorded from eight sampling sites in Develi Plain (Middle Anatolia, Kayseri, Turkey), collecting repeated samples in different seasons (April, July, October and December 2007), and measuring water parameters (electrical conductivity, pH and temperature). Generalised Linear Models and Mixed Effect Models were used to disentangle the effect of the environmental parameters on species richness and composition. Temperature positively affected species richness as expected from previous studies. Whereas this effect was clear in the freshwater habitats (less than 1000 μS cm-1), it was not observed at all at higher salinities. Surprisingly, species richness significantly increased with salinity in subsaline waters between 1000 and 6000 μS cm-1. Species composition varied among sampling sites (accounting for 36.2% of total variation), but no other factors were found to be involved
During 2009-2010, surface water samples from 34 Tibetan lakes were collected and measured for major ions. The distribution pattern of ionic concentrations and its response to regional climatic change were investigated. Results revealed a large range of major ionic concentrations as well as other water parameters for the lakes. Most lakes showed higher ionic concentrations than lakes in other regions of China and even the world. Most of the lakes' water types were found to be Na(K)-Cl with a few as Ca(Mg)-SO4. Due to the effect of evapoconcentration, water types of Tibetan lakes showed a gradient variation in the order of Ca(Na)-HCO3-Na(K)-SO4-Na(K)-Cl along the southeast-northwest transect. Compared with the pre-1990s data, the concentrations of major ions in the majority of the lakes decreased and the water type of several lakes also changed. The variation of major ions and water types of Tibetan lakes indicated an obvious response in lake water chemistry to the regional climatic changes over decades. � 2016 by Journal of Lake Sciences.
1930 Climate change may have profound eff ects on phosphorus (P) transport in streams and on lake eutrophication. Phosphorus loading from land to streams is expected to increase in northern temperate coastal regions due to higher winter rainfall and to a decline in warm temperate and arid climates. Model results suggest a 3.3 to 16.5% increase within the next 100 yr in the P loading of Danish streams depending on soil type and region. In lakes, higher eutrophication can be expected, reinforced by temperature-mediated higher P release from the sediment. Furthermore, a shift in fi sh community structure toward small and abundant plankti-benthivorous fi sh enhances predator control of zooplankton, resulting in higher phytoplankton biomass. Data from Danish lakes indicate increased chlorophyll a and phytoplankton biomass, higher dominance of dinophytes and cyanobacteria (most notably of nitrogen fi xing forms), but lower abundance of diatoms and chrysophytes, reduced size of copepods and cladocerans, and a tendency to reduced zooplankton biomass and zooplankton:phytoplankton biomass ratio when lakes warm. Higher P concentrations are also seen in warm arid lakes despite reduced external loading due to increased evapotranspiration and reduced infl ow. Th erefore, the critical loading for good ecological state in lakes has to be lowered in a future warmer climate. Th is calls for adaptation measures, which in the northern temperate zone should include improved P cycling in agriculture, reduced loading from point sources, and (re)-establishment of wetlands and riparian buff er zones. In the arid Southern Europe, restrictions on human use of water are also needed, not least on irrigation. O n average, global surface temperatures have increased by about 0.74°C over the past 100 yr (Trenberth et al., 2007), with the majority of the increase (0.55°C) occurring over the past 30 yr. We may expect marked changes to occur in the global climate during this century (IPCC, 2007). Increasingly reliable regional climate projections are available for many regions of the world, but fewer projections are available for many developing countries than for the developed world (Christensen et al., 2007). Th e warming generally increases the spatial variability of precipitation with reduced rainfall in the subtropics and increases at higher latitudes and in parts of the tropics. Th e changes in temperature and rainfall lead to changes in agricul-tural land use and management, including changes in soil cultivation and in the rates and timing of fertilization (Howden et al., 2007). Th ese changes have cascading eff ects on the P cycling, directly and indirectly, that aff ect the aquatic environment. Th e direct eff ects are related to the increased temperatures, increased rainfall intensity, and changes in winter rainfall that are expected to enhance the P loading to freshwaters in the temperate zone (IPCC, 2007) and the Arctic (Arctic Climate Impact Assessment, 2002) and to reduce the loading, but not the concentrations, in streams and freshwater lakes in the Mediterranean region. However, a few quantitative studies are avail-able (Chang, 2004; Andersen et al., 2006). Th e indirect eff ects are related to changes in the choice of crops, crop rotations, use of catch crops, and agricultural practices, including tillage and fertilization. In northern temperate areas, new heat-demanding, warm-season crops (e.g., maize and sunfl ower) will replace many of the present grain cereals and oilseed crops (Olesen and Bindi, 2002). At the same time, changes occur in planting and harvesting times (Olesen, 2005) and in fertilization rates and strategies (Olesen et al., 2007). Crop rotation must be adapted to changes in crop choices, in crop maturing, and in the need to control weeds, pests, and diseases. Th is will aff ect the amount of P released to freshwaters and its seasonal pattern. More-Abbreviation: TP, total phosphorus.
Salinity and temperature are known to be important factors driving species richness and species composition in inland waters, but their effect and interaction are still not completely clear. In this paper we examine their interaction on species richness and species composition of planktonic rotifers in Turkey, controlling for other confounding effects. Eighty-four species of Rotifera belonging to 32 genera were recorded from eight sampling sites in Develi Plain (Middle Anatolia, Kayseri, Turkey), collecting repeated samples in different seasons (April, July, October and December 2007), and measuring water parameters (electrical conductivity, pH and temperature). Generalised Linear Models and Mixed Effect Models were used to disentangle the effect of the environmental parameters on species richness and composition. Temperature positively affected species richness as expected from previous studies. Whereas this effect was clear in the freshwater habitats (less than 1000 µS cm -1), it was not observed at all at higher salinities. Surprisingly, species richness significantly increased with salinity in subsaline waters between 1000 and 6000 µS cm -1 . Species composition varied among sampling sites (accounting for 36.2% of total variation), but no other factors were found to be involved.
In Australia, many freshwater wetlands are becoming saline. Knowing which elements of a biotic community will persist as wetlands turn saline is relevant to their future management. We simulated gradual and sudden increases in salinity in outdoor mesocosms to test the hypotheses that: (1) aquatic plant and zooplankton communities exposed to a gradient of increasing salinity over time would initially resemble freshwater communities, but as the salinity increased they would resemble communities found in more saline systems; and (2) that a gradual change in salinity over 6 months influences zooplankton and plant communities in the same way as a sudden salinity change. Below 1000 mg L–1, as salinity increased gradually, communities rich in species and numbers of individuals resembled freshwater communities. However, as the salinity exceeded 1000 mg L–1, taxa were progressively lost and communities became less diverse. When salinities exceeded 3000 mg L–1 the diversity decreased rapidly and few taxa remained at 5000 mg L–1. Both sudden and gradual increases in salinity induced similar decreases in diversity. We predict that as natural wetlands become more saline, few freshwater biota will survive once the salinity exceeds 5000 mg L–1. In the long term, such salinised wetlands would need to be recolonised by salt-tolerant taxa for a functional wetland to persist.
Intermittent saline intrusions are a common feature of many coastal lakes and wetlands. These ecosystems are often important sites of biodiversity, biological productivity, and ecosystem services such as the removal of sediment, nutrients, and contaminants from inflowing rivers. Predicted effects of global climate change, including sea level rise, are likely to intensify saline intrusions into such ecosystems. Analyses of taxonomic diversity and abundance of zooplankton at different salinities in Lake Waihola, South Island, New Zealand, are supported by results of laboratory studies of salinity tolerances of 3 crustacean taxa Gladioferens pectinatus, Boeckella hamata and Daphnia carinata obtained from the lake. The field and laboratory analyses show that severe perturbations of zooplankton community structure and abundance are caused by even minor saline intrusions into Lake Waihola that raise the salinity to >1.2 psu. Our analyses of Lake Waihola, and data from brackish ecosystems around the world, show that even relatively small increases in salinity levels can drive such systems to a state of depleted biodiversity and abundance, altering ecosystem functioning.
Feeding of the different developmental stages of Calanipeda aquaedulcis on natural particles (bacterio-, phyto- and microzooplankton) was measured in a Mediterranean salt marsh (Emporda wetlands, NE Iberian Peninsula). Bottle incubations were performed in the field both in autumn and spring. The results showed differences in the diet of the different developmental stages due to both prey type and size. In general, the size of the ingested prey increased with increasing size of the C. aquaedulcis stage. While C. aquaedulcis adults had high ingestion rates and selection coefficients for large prey (micro- and nanoplankton), nauplii preferentially consumed smaller prey items (picoplankton). Copepodites showed the widest prey size range, including pico-, nano- and microplankton. Nevertheless, the lower size limit for particle capture was similar for all stages, i.e. between 1.7 and 2.1 mu m. Omnivory was observed in all stages of C. aquaedulcis. Heterotrophic prey (picoplankton, dinoflagellates and ciliates) were the most ingested items. The ability to partition the available food among the different developmental stages could represent an advantage in times of food scarcity because it may reduce intraspecific competition. This may explain how C. aquaedulcis is able to predominate in the zooplankton community for several weeks during spring and summer even in situations of low food availability.
We have surveyed 7 inland salt lakes and 14 coastal saltworks in the People's Republic of China (P. R. China) which are natural habitats for the brine shrimpArtemia. We report here on the location of the lakes, the mode of reproduction of theArtemia and the opportunities for achieving self sufficiency in cyst production for use in the local aquaculture industry. Because of frequent misunderstandings regarding the identification of a specific habitat, a new identification system for each population is proposed, using a numerical code which identifies the province, the habitat and the date of collection. Information of newArtemia populations is included as well as data on their reproduction mode.
The amphipod Gammarus lacustris is generally considered as a herbivore or a detritivorous scavenger, but we and others have observed it preying on pelagic zooplankton in fishless alpine lakes of the Canadian Rockies. We tested the hypothesis that G. lacustris predation alters the plankton community structure of alpine lakes by manipulating G. lacustris density in large (2800 L) in situ enclosure experiments. Compared with control enclosures (no Gammarus), Daphnia middendorffiana abundance was reduced 49, 85, and 100% in the low, medium, and high (40, 200, and 400 individuals·m-2) Gammarus density enclosures, respectively. Hesperodiaptomus arcticus density was not significantly related to G. lacustris density. Comparison of mesocosm results with lake data showed that G. lacustris predation on D. middendorffiana in the lake was lower, possibly because a pelagic deepwater refugium allows Daphnia to escape predation. The results show that G. lacustris predation can affect the plankton community structure in small fishless alpine lakes.
The indicator properties of zooplankton assemblages in a coastal lagoon were evaluated, by means of canonical correspondence analysis, along environmental gradients of trophic state and marine influence caused by anthropogenic impact. Changes in zooplankton species composition were significant indicators of environmental heterogeneity patterns. Species diversity was insensitive to eutrophication but decreased with increasing marine influence. The rotifer species Brachionus plicatilis and Synchaeta bicornis as well as cirriped nauplii were good indicators of mesohaline conditions. The rotifer species Asplanchna brightwelli, Brachionus angularis, Brachionus falcatus, Filinia terminalis, and Polyarthra remata were good indicators of eutrophic conditions. The other species investigated were good indicators of oligohaline and mesotrophic conditions. The rotifer genus Brachionus proved to be a better indicator organism for these environmental gradients than the entire zooplankton assemblage. Hence, this taxon can be considered a target taxon for more intensive monitoring and conservation planning. The method used here to assess the indicator properties of species assemblages and to select target taxa can be widely applied in any aquatic ecosystems to any group of organisms, spatial and temporal scales, and environmental gradients.
We know little about how ecosystems of different complexity will respond to global warming1±5. Microcosms permit experimental control over species composition and rates of environmental change. Here we show using microcosm experiments that extinc- tion risk in warming environments depends on trophic position but remains unaffected by biodiversity. Warmed communities disproportionately lose top predators and herbivores, and become increasingly dominated by autotrophs and bacterivores. Changes in the relative distribution of organisms among trophically de®ned functional groups lead to differences in ecosystem func- tion beyond those expected from temperature-dependent physio- logical rates. Diverse communities retain more species than depauperate ones, as predicted by the insurance hypothesis, which suggests that high biodiversity buffers against the effects of environmental variation because tolerant species are more likely to be found6,7. Studies of single trophic levels clearly show that warming can affect the distribution and abundance of species2,4,5, but complex responses generated in entire food webs greatly complicate inferences based on single functional groups.
This paper is a review of direct and indirect effects of elevated temperatures (≥25°C) on freshwater Zooplankton in temperate latitudes. Effects of temperature on aspects of behavior, individual growth, development and reproduction, and population dynamics are compared across Zooplankton taxa. Thermal responses vary markedly among co-occurring species and among clones within parthenogenetic species. There is strong evidence that elevated temperature can produce a reduction in body size within Zooplankton populations. Also, some Zooplankton assemblages become increasingly dominated by smaller bodied forms under warm conditions. We hypothesize that certain cold-water Zooplankton species show the greatest risk of local extinction during late summer heating events because of their dependence on thermal refugia, and their lack of diapausing or dispersal stages. Indirect effects of elevated temperature mediated by changes in the algal food supply or by altered interspecific interactions are also explored. Elevated temperature can change algal community structure and algal food quality, all of which can affect the outcome of Zooplankton interspecific competition. Size-selective predation rates of planktivorous fish are also likely to increase with increasing temperature or when Zooplankton are driven from the hypolimnion. The onset of fish feeding is also likely to begin earlier in the season thus reducing the time that large Zooplankton are present during the ice-free season. Reductions in the size structure of Zooplankton assemblages are likely to alter water clarity, nutrient regeneration and fish abundances.
Salinity is restricting habitatability for many biota in prairie lakes due to limited physiological abilities to cope with increasing osmotic stress. Yet, it remains unclear how salinity effects vary among major taxonomic groups and what role other environmental parameters play in shaping food-web composition. To answer these questions, we sampled fish, zooplankton and littoral macroinvertebrates in 20 prairie lakes (Saskatchewan, Canada) characterized by large gradients in water chemistry and lake morphometry. We showed that salinity thresholds differed among major taxonomic groups, as most fishes were absent above salinities of 2 g L-1, while littoral macroinvertebrates were ubiquitous. Zooplankton occurred over the whole salinity range, but changed taxonomic composition as salinity increased. Subsequently, the complexity of fish community (diversity) was associated with large changes in invertebrate communities. The directional changes in invertebrate communities to smaller taxa indicated that complex fish assemblages resulted in higher predation pressure. Most likely, as the complexity of fish community decreased, controls of invertebrate assemblages shifted from predation to competition and ultimately to productivity in hypersaline lakes. Surprisingly, invertebrate predators did not thrive in the absence of fishes in these systems. Furthermore, the here identified salinity threshold for fishes was too low to be a result of osmotic stress. Hence, winterkill was likely an important factor eliminating fishes in low salinity lakes that had high productivity and shallow water depth. Ultimately, while salinity was crucial, intricate combinations of chemical and biological mechanisms also played a major role in controlling the assemblages of major taxonomic groups in prairie lakes.
Synergies between large-scale environmental changes, such as climate change(1) and increased humic content (brownification)(2), will have a considerable impact on future aquatic ecosystems. On the basis of modelling, monitoring and experimental data, we demonstrate that community responses to global change are determined by food-chain length and that the top trophic level, and every second level below, will benefit from climate change, whereas the levels in between will suffer. Hence, phytoplankton, and thereby algal blooms, will benefit from climate change in three-, but not in two-trophic-level systems. Moreover, we show that both phytoplankton (resource) and zooplankton (consumer) advance their spring peak abundances similarly in response to a 3 degrees C temperature increase; that is, there is no support for a consumer/resource mismatch in a future climate scenario. However, in contrast to other taxa, cyanobacteria-known as toxin-producing nuisance phytoplankton(3)-benefit from a higher temperature and humic content irrespective of the food-chain composition. Our results are mirrored in natural ecosystems. By mechanistically merging present food-chain theory with large-scale environmental and climate changes, we provide a powerful framework for predicting and understanding future aquatic ecosystems and their provision of ecosystem services and water resources.
The effects of global and local environmental changes are transmitted through networks of interact-ing organisms to shape the structure of communities and the dynamics of ecosystems. We tested the impact of elevated temperature on the top-down and bottom-up forces structuring experimental freshwater pond food webs in western Canada over 16 months. Experimental warming was crossed with treatments manipulating the presence of planktivorous fish and eutrophication through enhanced nutrient supply. We found that higher temperatures produced top-heavy food webs with lower biomass of benthic and pelagic producers, equivalent biomass of zooplankton, zoo-benthos and pelagic bacteria, and more pelagic viruses. Eutrophication increased the biomass of all organisms studied, while fish had cascading positive effects on periphyton, phytoplankton and bacteria, and reduced biomass of invertebrates. Surprisingly, virus biomass was reduced in the pres-ence of fish, suggesting the possibility for complex mechanisms of top-down control of the lytic cycle. Warming reduced the effects of eutrophication on periphyton, and magnified the already strong effects of fish on phytoplankton and bacteria. Warming, fish and nutrients all increased whole-system rates of net production despite their distinct impacts on the distribution of biomass between producers and consumers, plankton and benthos, and microbes and macrobes. Our results indicate that warming exerts a host of indirect effects on aquatic food webs mediated through shifts in the magnitudes of top-down and bottom-up forcing.
Climate warming is occurring in concert with other anthropogenic changes to ecosystems. However, it is unknown whether and how warming alters the importance of top-down vs. bottom-up control over community productivity and variability. We performed a 16-month factorial experimental manipulation of warming, nutrient enrichment, and predator presence in replicated freshwater pond mesocosms to test their independent and interactive impacts. Warming strengthened trophic cascades from fish to primary producers, and it decreased the impact of eutrophication on the mean and temporal variation of phytoplankton biomass. These impacts varied seasonally, with higher temperatures leading to stronger trophic cascades in winter and weaker algae blooms under eutrophication in summer. Our results suggest that higher temperatures may shift the control of primary production in freshwater ponds toward stronger top-down and weaker bottom-up effects. The dampened temporal variability of algal biomass under eutrophication at higher temperatures suggests that warming may stabilize some ecosystem processes.
Dominance by cyanobacteria hampers human use of lakes and reservoirs worldwide. Previous studies indicate that excessive nutrient loading and warmer conditions promote dominance by cyanobacteria, but evidence from global scale field data has so far been scarce. Our analysis, based on a study of 143 lakes along a latitudinal transect ranging from subarctic Europe to southern South America, shows that although warmer climates do not result in higher overall phytoplankton biomass, the percentage of the total phytoplankton biovolume attributable to cyanobacteria increases steeply with temperature. Our results also reveal that the percent cyanobacteria is greater in lakes with high rates of light absorption. This points to a positive feedback because restriction of light availability is often a consequence of high phytoplankton biovolume, which in turn may be driven by nutrient loading. Our results indicate a synergistic effect of nutrients and climate. The implications are that in a future warmer climate, nutrient concentrations may have to be reduced substantially from present values in many lakes if cyanobacterial dominance is to be controlled.
The alternative stable states hypothesis for the behaviour of shallow lake communities requires switches to transform clear‐water macrophyte‐dominated communities to turbid algal‐dominated ones. Such switches have rarely been demonstrated experimentally. This study shows the role of rising salinity as such a switch while contributing a solution to the conservation problems of an important nature reserve.
Hickling Broad changed from a clear‐water, charophyte‐dominated lake to a turbid, phytoplankton‐dominated lake in the early 1970s, probably owing to guanotrophication by gulls and to increased salinity from more intensive pumping of the agricultural land that separates its main inflow from the nearby North Sea. Following a decline in nutrient loading as the gull flock moved away, the plants began to return during the 1980s and 1990s. In 1998/99, the water cleared and charophytes, including some very rare species, were abundant.
This was welcome to conservation bodies, but the vigorous growth precluded competitive sailing and there were conflicts with the local sailing club. The plants, however, began an irregular decline in 2000, though nutrient loadings and other conventional chemical drivers have remained steady.
Our hypothesis was that the unstable nature of the plant community was linked to high salinity, and that if salinity were lowered there would be vigorous and reliable growth, enabling annual cutting of plants to allow sailing races. In an experiment using mesocosms, salinities straddling the current values in the Broad led to declines in plant biomass, macrophyte species richness and macrophyte Shannon–Weaver diversity through increased release of phosphorus from the sediments, increased algal turbidity and reduction of zooplankton grazer activity.
Stabilization of the plant community of Hickling Broad would be achieved by a reduction of present salinities by about 20%. This would be possible by use of existing Environmentally Sensitive Area (High Level Environmental Stewardship) arrangements or diversion of some pumped drainage water to the sea. There remain some uncertainties about the future of the area because of rising sea levels.
Copyright © 2007 John Wiley & Sons, Ltd.
High-resolution data collected over the past 60 years by a single family of Siberian scientists on Lake Baikal reveal significant warming of surface waters and long-term changes in the basal food web of the world's largest, most ancient lake. Attaining depths over 1.6 km, Lake Baikal is the deepest and most voluminous of the world's great lakes. Increases in average water temperature (1.21 °C since 1946), chlorophyll a (300% since 1979), and an influential group of zooplankton grazers (335% increase in cladocerans since 1946) may have important implications for nutrient cycling and food web dynamics. Results from multivariate autoregressive (MAR) modeling suggest that cladocerans increased strongly in response to temperature but not to algal biomass, and cladocerans depressed some algal resources without observable fertilization effects. Changes in Lake Baikal are particularly significant as an integrated signal of long-term regional warming, because this lake is expected to be among those most resistant to climate change due to its tremendous volume. These findings highlight the importance of accessible, long-term monitoring data for understanding ecosystem response to large-scale stressors such as climate change.
Organism size is one of the key determinants of community structure, and its relationship with abundance can describe how biomass is partitioned among the biota within an ecosystem. An outdoor freshwater mesocosm experiment was used to determine how warming of∼4 °C would affect the size, biomass and taxonomic structure of planktonic communities. Warming increased the steepness of the community size spectrum by increasing the prevalence of small organisms, primarily within the phytoplankton assemblage and it also reduced the mean and maximum size of phytoplankton by approximately one order of magnitude. The observed shifts in phytoplankton size structure were reflected in changes in phytoplankton community composition, though zooplankton taxonomic composition was unaffected by warming. Furthermore, warming reduced community biomass and total phytoplankton biomass, although zooplankton biomass was unaffected. This resulted in an increase in the zooplankton to phytoplankton biomass ratio in the warmed mesocosms, which could be explained by faster turnover within the phytoplankton assemblages. Overall, warming shifted the distribution of phytoplankton size towards smaller individuals with rapid turnover and low standing biomass, resulting in a reorganization of the biomass structure of the food webs. These results indicate future environmental warming may have profound effects on the structure and functioning of aquatic communities and ecosystems.
Fish play a key role in the trophic dynamics of lakes, not least in shallow systems. With climate warming, complex changes
in fish community structure may be expected owing to the direct and indirect effects of temperature, and indirect effects
of eutrophication, water-level changes and salinisation on fish metabolism, biotic interactions and geographical distribution.
We review published and new data supporting the hypotheses that, with a warming climate, there will be changes in: fish community
structure (e.g. higher or lower richness depending on local conditions); life history traits (e.g. smaller body size, shorter
life span, earlier and less synchronised reproduction); feeding mode (i.e. increased omnivory and herbivory); behaviour (i.e.
stronger association with littoral areas and a greater proportion of benthivores); and winter survival. All these changes
imply higher predation on zooplankton and macroinvertebrates with increasing temperatures, suggesting that the changes in
the fish communities partly resemble, and may intensify, the effects triggered by eutrophication. Modulating factors identified
in cold and temperate systems, such as the presence of submerged plants and winter ice cover, seem to be weaker or non-existent
in warm(ing) lakes. Consequently, in the future lower nutrient thresholds may be needed to obtain clear-water conditions and
good ecological status in the future in currently cold or temperate lakes. Although examples are still scarce and more research
is needed, we foresee biomanipulation to be a less successful restoration tool in warm(ing) lakes without a strong reduction
of the nutrient load.
KeywordsAquatic food webs-Sub-tropical lakes-Piscivory-Planktivory-Benthivory-Eutrophication-Salinisation-Biomanipulation
Although salinity and aquatic biodiversity are inversely related in lake water, the relationship between types of salts and zooplankton communities is poorly understood. In this study, zooplankton species were related to environmental variables from 12 lakes: three saline lakes with water where the dominant anions were SO4 and CO3, four saline lakes with Cl-dominated water, and five dilute, subsaline (0.5–3 gl–1 total dissolved solids) lakes of variable anion composition. Although this study comprised only 12 lakes, distinct differences in zooplankton communities were observed among the two groups of chemically defined saline lakes. Canonical correspondence analysis identified total alkalinity, sulphate, chloride, calcium, sodium, potassium, and total phosphorus as all contributing to the first two ordination axes (1=0.97 and 2=0.62, PBrachionus plicatilis and the harpactacoid copepod Cletocamptus sp. prevailed lakes with Cl-dominated water. In contrast, the calanoid copepods Leptodiaptomus sicilis and Diaptomus nevadensis were dominant in the SO4/CO3-dominated lake water with elevated potassium (79–128mg l–1) and total phosphorus concentrations (1322-2915g l–1). The contrasting zooplankton species distribution among these two saline lake types is likely explained by variable selective pressure on zooplankton and their predators from differing physiological tolerances to salt stress and specific ions. While inland saline lakes with Cl as the dominant anion are relatively rare in Canada and SO4/CO3 are the common features, our study provided an opportunity to compare zooplankton communities across the two groups of lakes.
Diel horizontal migration (DHM), where zooplankton moves towards macrophytes during daytime to avoid planktivorous fish, has
been reported as a common migration pattern of zooplankton in shallow temperate freshwater lakes. However, in shallow eutrophic
brackish lakes, macrophytes seem not to have the same refuge effect, as these lakes may remain turbid even at relatively high
macrophyte abundances. To investigate the extent to which macrophytes serve as a refuge for zooplankton at different salinities,
we introduced artificial plants mimicking submerged macrophytes in the littoral zone of four shallow lakes, with salinities
ranging from almost freshwater (0.3) to oligohaline waters (3.8). Furthermore, we examined the effects of different salinities
on the community structure. Diel samples of zooplankton were taken from artificial plants, from areas where macrophytes had
been removed (intermediate areas) and, in two of the lakes, also in open water. Fish and macroinvertebrates were sampled amongst
the artificial plants and in intermediate areas to investigate their influence on zooplankton migration. Our results indicated
that diel vertical migration (DVM) was the most frequent migration pattern of zooplankton groups, suggesting that submerged
macrophytes were a poor refuge against predation at all salinities under study. Presumably, this pattern was the result of
the relatively high densities of small planktivorous fish and macroinvertebrate predators within the submerged plants. In
addition, we found major differences in the composition of zooplankton, fish and macroinvertebrate communities at the different
salinities and species richness and diversity of zooplankton decreased with increasing salinity. At low salinities both planktonic/free-swimming
and benthic/plant-associated cladocerans occurred, whilst only benthic ones occurred at the highest salinity. The low zooplankton
biomass and overall smaller-bodied zooplankton specimens may result in a lower grazing capacity on phytoplankton, and enhance
the turbid state in nutrient rich shallow brackish lakes.
KeywordsShallow brackish lakes-Zooplankton-Migration patterns-Community structure-Salinity
Experimental warming of a marine food web suggests that ocean warming can lead to greater consumer abundance but reduced overall biomass, providing a potentially species-independent response to environmental warming.
The effects of nutrients on the biological structure of brackish and freshwater lakes were compared. Quantitative analysis of late summer fish, zooplankton, mysid and macrophyte populations was undertaken in 20–36 shallow brackish lakes of various trophic states and the findings compared with a similar analysis of shallow freshwater lakes based on either sampling (fish) or existing data (zooplankton, mysids and macrophytes). Special emphasis was placed on differences in pelagic top-down control. Whereas the fish biomass (CPUE, multiple mesh-size gill nets) rose with increasing P-concentration in freshwater lakes, that of brackish lakes was markedly reduced at P-concentrations above ca. 0.4 mg P 1−1 and there was a concomitant shift to exclusive dominance by the small sticklebacks (Gasterosteus aculeatus and Pungitius pungitius); as a result, fish density remained relatively high. Mysids (Neomysis integer) were found at a salinity greater than 0.5‰ and increased substantially with increasing P-concentration, reaching levels as high as 13 ind. 1−1. This is in contrast to the carnivorous zooplankton of freshwater lakes, which are most abundant at intermediate P levels. The efficient algal controller, Daphnia was only found at a salinity below 2‰ and N. integer in lakes with a salinity above 0.5‰. Above 2‰ the filter-feeding zooplankton were usually dominated by the less efficient algal controllers Eurytemora and Acartia. In contrast to freshwater lakes, no shift to a clearwatex state was found in eutrophic brackish lakes when submerged macrophytes became abundant. We conclude that predation pressure on zooplankton is higher and algal grazing capacity lower in brackish eutrophic-hypertrophic lakes than in comparable freshwater lakes, and that the differences in trophic structure of brackish and freshwater lakes have major implications for the measures available to reduce the recovery period following a reduction in nutrient loading. From the point of view of top-down control, the salinity threshold dividing freshwater and brackish lakes is much lower than the conventionally defined 5‰.
1. Decades of introductions of exotic sportfish to mountain lakes around the world have impoverished them biologically, and this may be exacerbated by global warming. We assessed the current status of invasive salmonids and native zooplankton communities in 34 naturally fishless lakes along an elevational gradient, which served as an environmental proxy for the expected effects of climate change.
2. Our main goal was to explore how climate‐related variables influence the effects of stocked salmonids on the total biomass, species richness and taxonomic composition of zooplankton. We predicted that warmer conditions would dampen the negative predatory effects of exotic brook trout ( Salvelinus fontinalis ) on zooplankton communities because more temperate lakes contain a greater diversity of potentially tolerant species.
3. Instead, we discovered that the persistence of stocked brook trout in the warmer lakes significantly amplified total zooplankton biomass and species richness. In colder and deeper lakes, zooplankton were relatively unaffected by S. fontinalis , which however persisted better in alpine lakes than at lower elevations after stocking practices were halted over two decades ago. Warmer lake conditions and higher concentrations of dissolved organic carbon (DOC) were significant primary drivers of zooplankton species turnover, both favouring greater species diversity.
4. Our findings of an ecological surprise involving potential synergistic positive effects of climate warming and exotic trout on native zooplankton communities presents a conundrum for managers of certain national mountain parks. Present mandates to eradicate non‐native trout and return the mountain lakes to their naturally fishless state may conflict with efforts to conserve biodiversity under a rapidly changing climate.
The anticipated impacts of climate change on aquatic biota are difficult to evaluate because of potentially contrasting effects of temperature and hydrology on lake ecosystems, particularly those closed-basin lakes within semi-arid regions. To address this shortfall, we quantified decade-scale changes in chemical and biological properties of 20 endorheic lakes in central North America in response to a pronounced transition from a drought to a pluvial period during the early 21st century. Lakes exhibited marked temporal changes in chemical characteristics and formed two discrete clusters corresponding to periods of substantially different effective moisture (as Palmer Drought Severity Index, PDSI). Discriminant function analysis (DFA) explained 90% of variability in fish assemblage composition and showed that fish communities were predicted best by environmental conditions during the arid interval (PDSI < -2). DFA also predicted that lakes could support more fish species during pluvial periods, but their occurrences may be limited by periodic stress due to recurrent droughts and physical barriers to colonization. Zooplankton taxonomic assemblages in fishless lakes were resilient to short-term changes in meteorological conditions, and did not vary between drought and deluge periods. Conversely, zooplankton taxa in fish-populated lakes decreased substantially in biomass during the wet interval, likely due to increased zooplanktivory by fish. The powerful effects of such climatic variability on hydrology, and the strong subsequent links to water chemistry and biota indicate that future changes in global climate could result in significant restructuring of aquatic communities. Together these findings suggest that semi-arid lakes undergoing temporary climate shifts provide a useful model system for anticipating the effects of global climate change on lake food webs.This article is protected by copyright. All rights reserved.
Glacial retreat on the Tibetan Plateau and surrounding regions is characteristic since the 1960s and has intensified in the past 10 yr. The magnitude of glacial retreat is relatively small in the interior of the Tibetan Plateau and increases to the margins of the plateau, with the greatest retreat around the edges. Glacial retreat in this region is impacting the hydrological processes in the Tibetan Plateau and surrounding regions. The glacial retreat has caused an increase of more than 5.5% in river runoff from the plateau. In some areas, such as the Tarim River basin, the increase in river runoff is greater. Glacial retreat has also caused rising lake levels in the areas with large coverage of glaciers, such as the Nam Co Lake and Selin Co Lake areas. Rising lake levels are devastating grasslands and villages near the lakes.
The impacts of global warming on aquatic ecosystems are expected to be most pronounced at higher trophic levels in cold-water environments. Therefore, we hypothesized that warming of fishless alpine ponds would suppress large-bodied consumers (e.g., cladocerans, copepods) and stimulate fast-growing microorganisms (e.g., phytofla- gellates, rotifers), thereby altering the community composition and total abundance of zooplankton and phytoplank- ton. This hypothesis was tested using three blocks of four experimental mesocosms (1000-liter capacity) that were located next to alpine ponds in Banff National Park, Canada. Each block received unfiltered pond water and sediment from a pond following ice out in June 2000. A warming treatment (control vs. 3.68C warmed) was achieved by controlling the ventilation of greenhouse canopies that were suspended over each of the mesocosms. By the end of our 50-d experiment, warming significantly suppressed total zooplankton biomass because large cladocerans (Daph- nia pulex) declined while rotifer (Keratella cochlearis, Conochilus unicornis ) abundance increased during the second half of the experiment. In contrast, warming did not affect total phytoplankton biomass but significantly altered community composition by favoring phytoflagellates ( Mallomonas, Synura, Trachelomonas ) over larger filamentous green algae (Mougeotia, Phymatodocis ). Warming did not significantly increase dissolved nitrogen and phosphorus concentrations. Therefore, warmer growing conditions and reduced grazer biomass best explained the increased abundance of more edible, fast-growing phytoflagellates in the warmed mesocosms. Our findings support the hy- pothesis that moderate warming can destabilize plankton dynamics, thereby potentially reducing the reliability of water quality and food resources for higher trophic levels (e.g., planktivorous fish) in shallow cold-water ecosystems.
In this study, we report on the existence of a new bisexualArtemia species, found in the high plateaus of Tibet (P. R. China). Different disciplines have been used to characterize this new
population: biometrics of cysts and nauplii, morphometry of adults, cytogenetics, allozyme and DNA analyses and cross-breeding/fertility
tests with knownArtemia species. The results obtained justify that there is enough evidence to support the view thatArtemia from Tibet is a new species with the proposed nameArtemia tibetiana.
Freshwater lake of the Tibetan plateau has great ecological value and extreme vulnerability. The water samples have been collected in Daggyaima Co at an altitude of 5 080 m +/- 10 m. This study has investigated the sources, the major controlling factors of the major ions, and hydrochemical evolution trend according to the hydrochemical composition of water samples. The results showed that the major cations and anion of lake water were Ca(2+), Na(+) and HCO3(-), respectively, and the hydrochemical type was HCO3 -Ca, The total dissolved solid (TDS) was in the range of 71.2-199.8 mg x L(-1). The concentrations of EC, Ca(2+) and HCO3(-) in water samples from Southeast areas were relatively low resulted from the rich aluminum and poor calcium of geological background and the dilution effect of surface runoff. The Na(+)/(Na(+) + Ca(2+)) of water samples was 0.08-0.75, Cl(-) /(Cl(-) + HCO3(-)) was 0.11-0.35, Ca/Na was 0.58, Mg/Ca was 0.12, and HCO3/Na was 1.46, which suggested that the hydrochemical composition of the lake water was mainly controlled by silicate rock weathering based on Gibbs model and analysis of elemental stoichiometry. The minerals participated in weathering processes included plagioclase (anorthite, albite), potassium feldspar, biotite, calcite, dolomite, gypsum, rock salt, etc. The average value of K/Na was 0.059, indicating the weathering level of potassium feldspar was relatively low. The saturation index (SI) of calcite, dolomite, gypsum, quartz and hematite contained in the lake was higher than zero, while the SI of rock salt was lower than 0, revealing the trend that the freshwater lake is turning into salt water lake in Tibetan Plateau.
We study the correspondence between quantum spectra and classical
orbits in the equilateral triangular billiards. The eigenstates of such
systems are not separable functions of two variables even though the
problem is exactly solvable. We calculate the Fourier transform of a
quantum spectral function and find that the positions of the peaks match
well with the lengths of the classical orbits. This is another example
showing that the quantum spectral function provides a bridge between
quantum and classical mechanics.
We sought to identify environmental factors influencing crustacean zooplankton species richness in brackish lagoons and to elucidate whether crustacean zooplankton species richness and trophic structure of brackish lagoons differ among two regions with contrasting temperatures. We sampled 35 and 42 brackish lagoons (salinity ranging from 0.3 to 55‰) in Mediterranean Catalonia (NE Spain) and northern-temperate Denmark, respectively. No significant differences were found in total crustacean zooplankton species richness or cladoceran richness between the climatic regions. Calanoid richness was higher in Denmark than in Catalonia, while cyclopoid richness was higher in Catalonia. Salinity was the most important variable associated with zooplankton species richness in both regions, richness of total zooplankton species, cladocerans and cyclopoids being negatively related with salinity. In both regions, a shift occurred from dominance of large filter feeding cladoceran species at low salinities to copepods and small cladoceran species at higher salinities. Cladoceran richness increased with increasing total phosphorus, but was not influenced by total nitrogen or chlorophyll-a. Trophic structure in Mediterranean brackish lagoons showed a more pronounced seasonal variation than in north temperate brackish lagoons. Our results imply that the indirect effects of climate warming, such as changes in salinity and hydrology, will have a larger impact on brackish lagoon ecosystems than the increase in temperature per se.
The paper considers the extent to which salinity determines the structure of biological communities (composition and species
richness and diversity) in saline lakes, i.e. inland bodies of water with salinities in excess of 3 g l-1. It also considers
the extent to which oxygen, ionic composition, pH, hydrological patterns (degree of permanence and impermanence of water),
geographical position, palaeoclimatic events, chance, human intervention, and biological interactions especially predation
determine biological communities in salt lakes. It suggests that salinity is less significant as a determinant of community
structure in salt lakes than has been assumed.
Differences in the dynamics of ecological processes between Mediterranean and colder temperate aquatic systems could imply
different patterns in faunal communities in terms of composition and biodiversity (i.e. species richness and rarity). In order
to identify some of these patterns the crustacean and aquatic insect composition and biodiversity of four water body types,
classified according to their salinity and water permanence, were compared. Moreover, the relationships between species richness
and water, pond and landscape variables were analysed. A total number of 91 water bodies located throughout Catalunya (NE
Iberian Peninsula) were sampled. Three species assemblages were observed: one for permanent freshwaters, another for temporary
freshwaters, and a third one for saline waters (SW), since permanent and temporary saline water bodies had similar composition.
Differences in salinity were associated with proportion of crustaceans versus insects and with singularity. Thus, saline ponds
had a higher proportion of crustaceans, and lower values of singularity. Conductivity was significantly related to total (crustaceans
plus insects) richness, and also related to insect richness. The main difference between the models obtained for crustacean
species richness and insect species richness is the significance of landscape variables in the latter, and this fact could
be related to the different dispersion types of these two faunal groups: active for insects versus passive for crustaceans.
KeywordsMediterranean water bodies-Faunal composition-Species richness-Trophic state-Pond characteristics-Landscape variables
The effects of nutrients on the biological structure of brackish and freshwater lakes were compared. Quantitative analysis of late summer fish, zooplankton, mysid and macrophyte populations was undertaken in 20–36 shallow brackish lakes of various trophic states and the findings compared with a similar analysis of shallow freshwater lakes based on either sampling (fish) or existing data (zooplankton, mysids and macrophytes). Special emphasis was placed on differences in pelagic top-down control. Whereas the fish biomass (CPUE, multiple mesh-size gill nets) rose with increasing P-concentration in freshwater lakes, that of brackish lakes was markedly reduced at P-concentrations above ca. 0.4 mg P l-1 and there was a concomitant shift to exclusive dominance by the small sticklebacks (Gasterosteus aculeatus and Pungitius pungitius); as a result, fish density remained relatively high. Mysids (Neomysis integer) were found at a salinity greater than 0.5 and increased substantially with increasing P-concentration, reaching levels as high as 13 ind. l-1. This is in contrast to the carnivorous zooplankton of freshwater lakes, which are most abundant at intermediate P levels. The efficient algal controller, Daphnia was only found at a salinity below 2 and N. integer in lakes with a salinity above 0.5. Above 2 the filter-feeding zooplankton were usually dominated by the less efficient algal controllers Eurytemora and Acartia. In contrast to freshwater lakes, no shift to a clearwater state was found in eutrophic brackish lakes when submerged macrophytes became abundant. We conclude that predation pressure on zooplankton is higher and algal grazing capacity lower in brackish eutrophic-hypertrophic lakes than in comparable freshwater lakes, and that the differences in trophic structure of brackish and freshwater lakes have major implications for the measures available to reduce the recovery period following a reduction in nutrient loading. From the point of view of top-down control, the salinity threshold dividing freshwater and brackish lakes is much lower than the conventionally defined 5.
Climate in central Asia is dominated by the Asian monsoon. The varying impact of the summer monsoon across the Tibetan (Qinghai-Xizang) Plateau provides a strong gradient in precipitation, resulting in lakes of different salinity. Diatoms have been shown to indicate changes in salinity. Thus, transfer functions for diatoms and salinity or related environmental variables represent an excellent tool for paleoclimatic reconstructions in the Tibetan Plateau. Forty freshwater to hypersaline lakes (salinity: 0.1 to 91.7 g l–1) were investigated in the eastern Tibetan Plateau. The relationship between 120 diatom taxa and conductivity, maximum water depth and major ions were analyzed using an indicator value approach, ordination and taxon response models. Canonical correspondence analysis indicated that conductivity was the most important variable, accounting for 10.8% of the variance in the diatom assemblages. In addition water depth and weathering were influential. Weighted Averaging (WA) and Weighted Averaging Partial Least Square (WA-PLS) regression and calibration models were used to establish diatom-conductivity and water depth transfer functions. An optimal two-component WA-PLS model provided a high jack-knifed coefficient of prediction for conductivity (r2
jack = 0.92), with a moderate root mean squared error of prediction (RMSEPjack = 0.22), a very low mean bias (0.0003), and a moderate maximum bias (0.26). A WA model with tolerance downweighting resulted in a slightly lower r2
jack (0.89) for water depth, with RMSEPjack= 0.26, mean bias = –0.0103 and maximum bias = 0.26.
Based on data from 233 Danish lakes, enclosure experiments, full-scaleexperiments and published empirical models we present evidence that top-downcontrol is more important in shallow lakes than in deep lakes, excepting lakeswith a high abundance of submerged macrophytes. The evidence in support is: (1)That at a given epilimnion total phosphorus concentration (TP) the biomass offish per m2 is independent of depth, which means that biomassper m3is markedly higher in shallow lakes. (2) That the biomass of benthic invertebratesis higher in shallow lakes, which means that the benthi-planktivorous fish areless dependent on zooplankton prey than in deep lakes. By their ability to shiftto zooplankton predation their density can remain high even in periods whenzooplankton is scarce and they can thereby maintain a potentially high predationpressure on zooplankton. (3) That the possibilities of cladocerans to escapepredation by vertical migration are less. (4) That the zooplankton:phytoplanktonmass ratio per m2 is lower and presumably then also thegrazing pressure onphytoplankton. (5) That nutrient constraints appear to be weaker, as evidenced bythe fact that at a given annual mean TP, summer TP is considerably higher inshallow lakes, especially in eutrophic lakes lacking submerged macrophytes. (6)That negative feedback on cladocerans by cyanobacteria is lower as cyanobacterialdominance is less frequent in shallow lakes and more easily broken (at least inNorthern temperate lakes), and (7) That top-down control by benthi-planktivorousfish is markedly reduced in lakes rich in submerged macrophytes because theplants serve as a refuge for pelagic cladocerans and encouragepredatory fish at the expense of prey fish. We conclude that manipulation of fishand submerged macrophytes may have substantial impact on lake ecosystems, inparticular in shallow eutrophic lakes. On the contrary, if the conditions formore permanent changes in plant abundance or fish community structure are lackingthe feed-back mechanisms that endeavour a return to the original turbid state willbe particularly strong in shallow lakes.
Based on 11004 satellite images from CBERS CCD and Landsat TM/ETM, changes in the spatial characteristics of all lakes in
China were determined following pre-established interpretation rules. This dataset was supported by 6843 digital raster images
(1:100000 and 1:50000), a countrywide digital vector dataset (1:250000), and historical literature. Comparative data were
corrected for seasonal variations using precipitation data. There are presently 2693 natural lakes in China with an area greater
than 1.0 km2, excluding reservoirs. These lakes are distributed in 28 provinces, autonomous regions and municipalities and have a total
area of 81414.6 km2, accounting for ∼0.9% of China’s total land area. In the past 30 years, the number of newly formed and newly discovered lakes
with an area greater than 1.0 km2 is 60 and 131, respectively. Conversely, 243 lakes have disappeared in this time period.
KeywordsChina–lake number–lake area–spatial distribution
High and often variable salinity is an obvious feature of salt lakes. Correspondingly, salinity is usually assumed to be an important ecological determinant in such lakes. An investigation of the macroinvertebrate fauna of 79 lakes (salinities from 0.3 to 343 g 1–1) in the Western District of Victoria, Australia, examined this assumption. Over the total range of salinity, species richness and composition are highly correlated with salinity. However, these relationships become nonsignificant over intermediate ranges of salinity. Furthermore, many taxa have very broad tolerances to salinity at these intermediate ranges, implying that factors other than salinity may determine their distribution. An appreciation of scale (that is, the range of salinity over which observations are considered) resolves the paradox that, despite these broad tolerances by most taxa, species richness and composition strongly reflect salinity over the entire salinity range.
In brackish lagoons, Daphnia is replaced by calanoid copepods (Eurytemora affinis, Acartia spp.) and rotifers when a certain threshold (depending on, for instance, fish density) is reached. We hypothesize that loss of Daphnia induces a regime shift from clear to turbid at high nutrient concentrations. We conducted a factorial designed enclosure experiment with contrasting salinities (0–16‰), low fish predation (one three-spined stickleback, Gasterosteus aculeatus, m−2) and three levels of nutrient loading in a shallow brackish lagoon. A change point analysis suggests a strong regime shift from a clear to a turbid state at 6–8‰ salinity at low and high loading, but not for the control. From the low to the high salt regime, chlorophyll a (Chla), Chla:total phosphorus (TP) and Chla:total nitrogen (TN) ratios shifted highly significantly for all nutrient treatments, and the bacterioplankton production followed the changes in Chla. These changes occurred parallel with a shift from cladoceran and cyclopoid copepod to rotifer dominance. Monitoring data from 60 Danish brackish lagoons show increasing Chla with increasing TP and TN as well as interactive effects of TN and salinity, peaking at intermediate salinity. A relatively weak effect of
salinity at low nutrient concentrations and the stronger effect at intermediate high salinity are in accordance with the experimental results. However, these data suggest a lower salinity threshold than in the experiment, which may be explained by a higher fish density. Our results have implications for the management of coastal lagoons both at present and in a future (predicted) warmer climate: (1) improved water quality can be obtained by reducing the nutrient loading or enhancing the freshwater input
to a level triggering a shift to Daphnia dominance (typically <2‰), (2) fish manipulation is probably not a useful tool for brackish lagoons, unless the salinity is below the threshold for a potential shift to a clear Daphnia dominated state, and (3) more abrupt changes will expectedly occur in low-saline coastal lagoons at increasing salinity during summer in a future warmer climate.
Zooplankton in saline lakes of the Southern Interior Plateau of British Columbia were collected on three occasions: mid-May and early August, 1990, and in late July, 1991. Salinities ranged from 2.6 to 45.8 g L−1. Of the 17 lakes examined, 13 were hyposaline (∼-20g L−1), four, mesosaline (20–50 g L−1) and none, hypersaline (>50 g L−1). pH ranged from 8.7 (Three Mile) to 10.7 (Goodenough), with values <9.6 in 10, and <9.0 in only three lakes. Lakes with high pHs had high bicarbonate-carbonate alkalinities.
Thirty one species of zooplankton occurred: Protista (1), Rotifera (13), Anostraca (2), Cladocera (7), Ostracoda (1) and Copepoda (7). Sixteen species were restricted to hyposaline waters, with seven found only in salinities of ≤5 gL−1. Two species (Diaptomus connexus, Artemia franciscana) were restricted to mesosaline waters of salinity >35 g L−1. Eurysaline species includedBrachionus plicatilis, Hexarthra fennica, Limnocythere staplini, Artemia franciscana andDiaptomus connexus. Most species were abundant in 1+ lakes, but six species always had low populations.B. plicatilis, Hexarthra polyodonta, A. franciscana, Limnocythere staplini, Daphnia similis andD. connexus had densest populations in one or more of the three most saline lakes, viz. Long, Goodenough and Three Mile. Cladocerans other thanD. similis (Alona sp., Ceriodaphnia quadrangula, Daphnia pulex) were usually abundant in lakes of low salinity (<5 g L−1).Diatomus sicilis, present in all except the three most saline lakes, also occurred in abundance in ten of these lakes.Moina hutchinsoni andH. polyodonta were present in both hyposaline and mesosaline lakes, but, more importantly, tended to occur only at higher pH values (>pH 9.4) but not in all such lakes. These can be regarded as alkaline-saline species.
Sorensen’s Coefficient of Community Similarity was used to compare communities in Alberta-Saskatchewan and British Columbia. It was low (0.37). A comparison restricted to just Cladocera gave a slightly higher value, 0.44, but a comparison of Copepoda gave a value of 71 per cent similarity between the regions. Multiple regression analyses using pH, TDS and K regressed on species richness for all samples accounted for only 41 per cent of the variance. However, when the analysis was seasonally restricted (May), and thus to a limited chemical range, 47 to 77.5 per cent of the variance was accounted for by these three variables.
Saline lakes may be divided into two categories — those primarily saline because they are endorheic and those secondarily saline (brackish) because of natural or anthropomorphic inputs of sea water. Endorheic lakes have greatly varying composition and salinity, occur in arid regions and are not as abundant for that reason as exorheic lakes. The area of land surface over which they are the characteristic types, is, however, very considerable. Many endorheic lakes have communities of low diversity but the reason for this is not necessarily high salinity — the world's largest endorheic lake, the ocean, has a very high diversity — but the temporariness of many of these habitats which has led to wide and unpredictable fluctuations in salinity and to periodic drying out.
Secondarily saline lakes are rather different. They generally have an ionic composition which is that of diluted sea water, and although they do not have the high diversity of marine communities, they often have comparable, if slightly lesser, diversities with those of freshwaters. There are no firm salinity boundaries between fresh and brackish waters, only ones drawn (e.g. at 5 per mille total salts) by convention.
Brackish waters have the particular interest that estuarine organisms including mysid shrimps and essentially marine members of the algal division, the Haptophyta, may colonize and establish themselves in food webs otherwise characteristic of freshwaters. A comparison is made between the systems of brackish and freshwater lakes in the Norfolk Broadland of eastern England, most of which have undergone eutrophication. Although at first sight appearing very different, both fall into a similar pattern when processes of change are considered. Increases in salinity serve as indirect switch mechanisms which, like other but different mechanisms in freshwaters, may cause the lake community to change from submerged plant dominance to phytoplankton dominance at intermediate states of nutrient loading. The current drought in eastern England is inducing small salinity changes that support this assertion.
Cladocerans are essentially freshwater organisms, many of which have been able to penetrate slightly saline waters (up to 5 salinity), both thalassic and athalassic, some of which occur at high salinities, and a few of which, mostly non-chydorids, penetrate still higher salinities (15–30 and even higher) and may be confined to these salinities. Three previous studies from Saskatchewan, Iran, and Germany (the latter including thalassic waters) have been analyzed, and records for the athalassic saline waters of the World have been summarized; all results show a decline, at some point, in species number against increasing concentration of salinity.Examination of samples for 67 waterbodies in southern Australia and 167 in South Africa, covering the full salinity range over which cladocerans occur, reveals much the same relationships. Graphical analysis was carried out using salinity intervals defined along a logarithmically-scaled conductivity axis.The mean number of chydorid taxa per site was considerably greater in Australia than in South Africa, and this was true for both freshwater (< 5="">–1) and saline (> 5 mScm–1) sites. In both countries, the number of chydorid taxa per site showed little variation with conductivity over the freshwater range but declined rather abruptly at conductivities > mScm–1. For South Africa, there was also some indication of reduced numbers of chydorid taxa in the most dilute (< 0.2="">–1) waters.Non-chydorid taxa, which were analysed only on a generic basis, averaged much more numerous in Australian saline sites than in either South Africa saline sites or Australian freshwater ones. Mean number of non-chydorid taxa per site was about the same for Australian and South African freshwater sites.Plots of total number of taxa observed per conductivity interval had maxima in the 0.2–0.7 mScm–1 conductivity range and decreased at higher and lower conductivities. This trend to some extent only reflected the effect of the variation in number of sites per interval; a negative impact on chydorids of very low conductivities (–1) is nevertheless suggested.
Data Analysis Using Regression and Multilevel/Hierarchical Models, first published in 2007, is a comprehensive manual for the applied researcher who wants to perform data analysis using linear and nonlinear regression and multilevel models. The book introduces a wide variety of models, whilst at the same time instructing the reader in how to fit these models using available software packages. The book illustrates the concepts by working through scores of real data examples that have arisen from the authors' own applied research, with programming codes provided for each one. Topics covered include causal inference, including regression, poststratification, matching, regression discontinuity, and instrumental variables, as well as multilevel logistic regression and missing-data imputation. Practical tips regarding building, fitting, and understanding are provided throughout.