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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.
... 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. ...
... 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.
... Climate warming tends to increase or decrease Chl-a concentration in phytoplankton-rich or -deficient lakes, respectively [83]. An investigation of TP lakes found fish only in lakes with salinity less than 7 g/L in the total investigated lakes [84]. They concluded that the ratio of Chl and total phosphorus was positively related to temperature in lakes with predators, and negatively in lakes without predators. ...
... For most saline or salty lakes in TP with no predators (such as fishes or gammarid), there are only two trophic levels: phytoplankton and zooplankton. Rising temperature would benefit zooplankton development, which then restrains phytoplankton growth [84]. Therefore, only 1/3 of the 318 Figure 10. ...
... Climate warming tends to increase or decrease Chl-a concentration in phytoplanktonrich or -deficient lakes, respectively [83]. An investigation of TP lakes found fish only in lakes with salinity less than 7 g/L in the total investigated lakes [84]. They concluded that the ratio of Chl and total phosphorus was positively related to temperature in lakes with predators, and negatively in lakes without predators. ...
Lake chlorophyll-a (Chl-a) is one of the important components of the lake ecosystem. Numerous studies have analyzed Chl-a in ocean and inland water ecosystems under pressures from climate change and anthropogenic activities. However, little research has been conducted on lake Chl-a variations in the Tibet Plateau (TP) because of its harsh environment and limited opportunities for in situ data monitoring. Here, we combined 95 in situ measured lake Chl-a concentration data points and the Landsat reflection spectrum to establish an inversion model of Chl-a concentration. For this, we retrieved the mean annual Chl-a concentration in the past 35 years (1986–2021) of 318 lakes with an area of > 10 km2 in the TP using the backpropagation (BP) neural network prediction method. Meteorological and hydrological data, measured water quality parameters, and glacier change in the lake basin, along with geographic information system (GIS) technology and spatial statistical analysis, were used to elucidate the driving factors of the Chl-a concentration changes in the TP lakes. The results showed that the mean annual Chl-a in the 318 lakes displayed an overall decrease during 1986–2021 (−0.03 μg/L/y), but 63%, 32%, and 5% of the total number exhibited no significant change, significant decrease, and significant increase, respectively. After a slight increase during 1986–1995 (0.05 μg/L/y), the mean annual lake Chl-a significantly decreased during 1996–2004 (−0.18 μg/L/y). Further, it decreased slightly during 2005–2021 (−0.02 μg/L/y). The mean annual lake Chl-a concentration was significantly negatively correlated with precipitation (R2 = 0.48, p < 0.01), air temperature (R2 = 0.31, p < 0.01), lake surface water temperature (LSWT) (R2 = 0.51, p < 0.01), lake area (R2 = 0.42, p < 0.01), and lake water volume change (R2 = 0.77, p < 0.01). The Chl-a concentration of non-glacial-meltwater-fed lakes were higher than those of glacial-meltwater-fed lakes, except during higher precipitation periods. Our results shed light on the impacts of climate change on Chl-a variation in the TP lakes and lay the foundation for understanding the changes in the TP lake ecosystem.
... On the Qinghai-Tibet Plateau (QTP), 40% of the land area is covered by permafrost (Zou et al., 2017), with thermokarst lakes extensively distributed (Niu et al., 2011;Luo et al., 2020). Although zooplankton communities in some large brackish lakes of QTP have been studied (Lin et al., 2017;Zhu et al., 2019;Liang et al., 2021), the spatial patterns of zooplankton communities in thermokarst lakes and their responses to environmental variation are largely unknown. In this study, our objectives were to answer two questions: ...
... Such low richness in our studied lakes is comparable to that of thermokarst lakes in high Arctic and subarctic regions, where the median taxonomic richness of crustacean zooplankton was previously reported as 3 and 5, respectively (Schartau et al., 2021). In large brackish lakes on the QTP, zooplankton also shows in low diversity (Lin et al., 2017;Zhu et al., 2019;Liang et al., 2021). For example, only 2 species of Cladocera and 3 species of Copepoda were reported in saline lake Namuka Co in Northern Tibet (Zhao et al., 2010). ...
... For example, the richness and density of both Cladocera and Copepoda were positively correlated with DO, which has been described previously as a strong factor affecting zooplankton community structure, diversity, and abundance (Patoine et al., 2002;Beisner et al., 2006;Wen et al., 2010). Previous studies of other Tibetan lakes also suggested that salinity is a main factor limiting zooplankton species diversity (Lin et al., 2017;Zhu et al., 2019). In our studied thermokarst lakes, however, conductivity (a substitute measure of salinity) was not correlated with zooplankton species richness. ...
Global warming is accelerating permafrost thaw, forming new thermokarst lakes and substantially influencing the old ones. However, the biological communities in thermokarst lakes on the Qinghai-Tibet Plateau (QTP) are rarely studied. Here, we assessed the biogeographical patterns of zooplankton communities in 44 thermokarst lakes across the QTP. Across all lakes, 17 Cladocera and 13 Copepoda species were identified, with most of the lakes dominated by Cladocera. Chydorus sphaericus and Cyclops vicinus were the most frequently detected species. Both cladoceran and copepod communities had very low species richness and density, which lacked a clear spatial pattern but positively associated to dissolved oxygen. In general, species richness was negatively influenced by seston particle quantity while the density was positively influenced by water nutrient concentrations. Cladoceran and copepod communities had a high β-diversity (0.89 and 0.91, respectively), which was dominated by species turnover. However, Cladocera had significantly lower β-diversity and turnover component than copepod communities. β-diversity of Cladocera and Copepoda showed a significant but weak distance decay relationship and also significantly correlated with longitude, latitude, mean annual temperature, as well as concentrations of seston particle carbon and nitrogen. In addition, their β-diversities differentially correlated to other environmental variables. Overall, the results suggested that the geographical barriers, climate, and some local environmental variables are key factors in shaping the biogeography of zooplankton community. Although a general biogeographic pattern of zooplankton across the QTP cannot be drawn from this limited dataset, this study provided the first large spatial scale investigation and analyses of zooplankton biogeography in thermokarst lakes on the QTP. Given the important roles of zooplankton in aquatic ecosystems, this study could provide insights for understanding the influences of future environmental changes on thermokarst lake ecosystems.
... Our first hypothesis, consistent with many studies on saline lakes in different regions of the world [11][12][13][14], was confirmed. The number of pelagic zooplankton species decreased with the salinity increase. ...
... At the same time, the zooplankton species diversity was similar at a salinity range of 15-40 g L −1 . This observation partly coincides with the results by Lin et al. [11]. ...
... Previously, Lin et al. [11] proposed a conceptual model of salinity-related changes in the taxonomic structure of the zooplankton community. This model is very simplified and represents the change of zooplankton taxonomic structure with salinity increase as a sequence of Copepods and small cladocerans-Large cladocerans-Artemia. ...
Many continental saline lakes are under the effects of salinity increase and anthropogenic eutrophication exacerbated by global change. The response of the food web to these drivers of change is not straightforward. To understand the consequences of salinity and eutrophication interactive effects on the food web, we studied the seasonal dynamics of zooplankton and phytoplankton and water quality parameters in 20 lakes of different salinity (from freshwater to hypersaline) and nutrient status (from oligotrophic to eutrophic) located in southern Siberia. We observed a pronounced bottom-up effect of nutrients, which induced an increase in the biomass of phytoplankton and zooplankton and a decline in water quality. A significant decrease in the species abundance of zooplankton was observed at a threshold salinity of 3 g L−1 and the disappearance of fish at 10 g L−1. The top-down effect induced by salinity manifested itself in an increase in the biomass of zooplankton with the disappearance of fish, and in the change of the size distribution of phytoplankton particles with an increase in the proportion of cladocerans in the zooplankton. Even though we observed that with the salinity increase the food web in saline lakes transformed from three-trophic to two-trophic without fish, we conclude that in the salinity range from 10 to 20–30 g L−1 this transition in most cases will not increase the ability of zooplankton to control phytoplankton. Interactive effects of salinity and eutrophication strongly depend on the size and depth of the lake, as deep stratified lakes tend to have a better water quality with lower biomasses of both phyto- and zooplankton. Thus, the salinity per se is not the driver of the decline in water clarity or the uncontrolled development of phytoplankton. Moreover, for deep lakes, salinity may be a factor affecting the stability of stratification, which mitigates the consequences of eutrophication. Thus, small shallow lakes will be the most vulnerable to the joint effect of salinity increase and eutrophication with the degradation of ecosystem functioning and water quality at moderate salinities of 3–20 g L−1.
... 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.
... Furthermore, the lakes and surrounding grasslands are important settlements and natural pastures for Tibetan herders; hence, they also play a crucial role in sustaining the regional social systems. In general, the lakes have low biodiversity and simple food webs (Lin et al., 2017), and are therefore extremely responsive to climate change. The annual mean air temperature of the Tibetan Plateau has increased 2.5°C over the past 60 years (GISTEMP, 2019). ...
... Climate warming will accelerate the release of activated nutrients from thawed permafrost on the Tibetan Plateau as a result of stimulated decomposition and mineralisation of organic nutrients, which will further augment the nutrient loading of lakes in this region (Zhao et al., 2018). Investigations of freshwater lakes on the Tibetan Plateau show that temperature is a key limiting factor for the structure and functions of these lakes, and the plankton is generally more diverse in lakes in warmer regions (Lin et al., 2017). The current anthropogenic warming, which has a much higher amplitude than that of the natural warming during the MWP, will improve the nutrient absorption efficiency of algae and hence promote the development of phytoplankton (e.g., Jeff et al., 2019;Phillips et al., 2016;Scheffer et al., 1993;Smol et al., 2005). ...
The Tibetan Plateau has ∼1,200 lakes larger than 1 km ² with a total area of ~46,000 km ² . The annual mean air temperature of the Tibetan Plateau has increased 2.5°C over the past 60 years. Lakes in this region are extremely responsive to climate changes as a result of their low biodiversity and simple food webs. However, it is unclear whether the current anthropogenic warming will benefit or threaten the aquatic ecosystems in this region.
We assessed patterns of change associated with climate change in a shallow, freshwater lake (Genggahai Lake) on the NE Tibetan Plateau over the past ~1,600 years based on diverse aquatic fossils (macrophytes, molluscs, cladocerans and diatoms), total organic carbon (TOC) and total nitrogen (TN) of a sediment core.
The abundances of macrophytes, molluscs and cladocerans, and the concentrations of TOC and TN in the sediments were high during the Mediaeval Warm Period (MWP, ~940–1,410 CE) but low during the Dark Ages Cold Period (DACP, ~390–940 CE) and the Little Ice Age (LIA, ~1,410–1970 CE), suggesting that modest natural warming was associated with the biomass of macrophytes and consumers in the food web. By contrast, low abundance of macrophytes and high abundance of planktonic diatoms were recorded in the sediments during the Current Warm Period (CWP, ~1970–2020 CE). Current anthropogenic warming has resulted in significantly higher temperatures than during the MWP, associated with the development of planktonic algae rather than macrophytes.
Our findings show that the current anthropogenic warming, coupled with increased atmospheric nitrogen deposition and activated nutrients from thawed permafrost, is associated with phytoplankton dominance in lakes on the Tibetan Plateau, and may lead to significant reductions in ecosystem services provided by the lakes.
... A study comparing lakes with wide salinity gradients in north-west China showed a significant functioning loss of the lake ecosystem with increasing salinity, suggested by drastic reduction of biodiversity, food chain length, and average trophic position in the food chain (Vidal et al., 2021). A study of 45 Tibetan lakes in China, moreover, showed that pronounced shifts in the structure and functions of lake ecosystems may be expected when certain critical salinity levels are passed (Lin et al., 2017). ...
... Such changes have been widely reported in mesocosm experiments (Thompson and Shurin, 2012;Lind et al., 2018;Moffett et al., 2020;Coldsnow and Relyea, 2021;Greco et al., 2022;Hébert et al., 2022;McClymont et al., 2022) and field investigations (Brucet et al., 2009;He et al., 2020;Zadereev et al., 2022) at moderate to low conductivities. However, at higher conductivities, the food web transforms from threetrophic to two-trophic without fish, and large cladocerans such as Daphnia may become dominant until they reach a critical level at high conductivities (Lin et al., 2017). ...
Both eutrophication and salinization are growing global environmental problems in freshwater ecosystems, threatening the water quality and various aquatic organisms. However, little is known about their interactive effects on theses stressors and the role of lake depth on these interactions. We used field surveys to compared zooplankton assemblages over four seasons in eight Yunnan Plateau lakes with different trophic states, salinization levels, and water depths. The results showed that: 1) the species number (S), density (DZoop), and biomass (BZoop) of zooplankton exhibited strong seasonal dynamics, being overall higher in the warm seasons. 2) Data collected over four seasons and summer data both revealed highly significant positive relationships of S, DZoop, and BZoop with total nitrogen (TN), total phosphorus (TP), and phytoplankton chlorophyll a (Chl a). 3) S, DZoop, and BZoop displayed a unimodal relationship with salinity, peaking at 400–1000 μS/cm (conductivity, to reflect salinity). 4) The two large-sized taxa (cladocerans and copepods) generally increased at low-moderate levels of TN, TP, Chl a, and Cond and was constant or decreased at high levels. The average body mass (biomass/density) of crustaceans decreased with increasing TN, TP, Chl a, and conductivity. Our findings indicate that zooplankton may be more vulnerable in deep lakes than in shallow lakes when exposed to conductivity stress even under mesotrophic conditions, and the overall decrease in size in zooplankton assemblages under the combined stress of eutrophication and salinization may result in a lowered grazing effect on phytoplankton.
... Alternatively, some microbes can reduce nitrate to ammonium via dissimilatory nitrate reduction to ammonium (DNRA), and retain N as a more bioavailable form (Burgin and Hamilton 2007;Giblin et al., 2013). Therefore, understanding the nitrate reduction, whether it is removed (via denitrification) or retained (via DNRA), have far-reaching implications for evaluating and predicting the N fate in aquatic ecosystems (Dong et al., 2011;Jiang et al., 2020;Nizzoli et al., 2010;Scott et al., and semiarid lakes (Brucet et al., 2012;Lin et al., 2017). Lakes in arid or semiarid region are usually naturally saline, as the evaporative concentration process leads to progressive salt accumulation (Wurtsbaugh et al., 2017;Yapiyev et al., 2017). ...
... It is well known that salinity fundamentally shapes the structure and function of lake ecosystems (Brucet et al., 2012;Dugan et al., 2017;Lin et al., 2017). The change in salinity can cause decreases or increases in cytoplasmic volume through imposing considerable osmotic and matric stress on the involved microbes, resulting in the loss of metabolic activity (Neubauer et al., 2019;Zaghmouri et al., 2018;Zhao et al., 2013). ...
Salinization caused by climate change and nitrogen (N) pollution are both important environmental threats for inland lakes. However, evaluating their interactive effects continues to be challenging. Here, field observation and microcosmic experiments were conducted in six lakes of East Asia with the different salinity and climate characteristics, to explore the response of the key N cycle processes related to N fate to the climate-induced change in salinity. The results indicated that increased salinity inhibited denitrification, which was the outcome of two cumulative effects: the long-term microbial adaptation effect and the direct salinity stress. Whereas increased salinity had unsignificant or positive effects on dissimilatory nitrate reduction to ammonium. It had caused that N retention capacity is relatively stronger in saline than freshwater lakes. Inland lakes are long-term basin-wide integrators of climatic conditions that drying (salinization) and wetting (desalination) with climate change. In semi-arid regions of East Asia, lake shrinkage, salinization and increasing temperature driven by climate warming and drying may exert a negative impact on N pollution through concentrating, decreasing denitrification and increasing ammonium release from sediment. The threat of climate change on these lakes is not just the quantity of water, but its quality.
... However, current understanding of how salinity change in aquatic environments will impact zooplankton communities is mostly limited to the salinization of freshwater environments (e.g. Hintz et al., 2017;Lin et al., 2017;Moffett et al., 2020), estuaries (e.g. Gao et al., 2008) or single-species responses (e.g. ...
... Cervetto et al., 1999), while community-level changes and consequences for food web interactions in marine environments remain poorly understood. Studies on the effects of salinization of freshwater environments, have reported a range of responses including, dominance shifts and disruption of trophic interactions (Lin et al., 2017;Gutierrez et al., 2018). These results imply that a similar response to salinity change could be expected in marine environments. ...
Climate change predictions indicate global changes in salinity with negative implications for plankton food webs; an important baseline for functioning of marine ecosystems. Current understanding of how salinity change will impact plankton communities is mostly limited to the salinization of freshwater environments, with little known about the effects of changing salinity in marine systems. In this study, we investigate the effect of salinity change on zooplankton communities under different salinity change scenarios of the Baltic Sea. Projections for future salinity change derived from regional physical-biogeochemical models were used to set-up an outdoor mesocosm experiment in the coastal area of the Gulf of Finland. Each mesocosm was inoculated with natural plankton using a mixture of both marine and freshwater communities, mimicking the natural influx of freshwater species from rivers into the Baltic Sea. Zooplankton diversity and composition changed possibly due to different salinity tolerances among the species. Among zooplankton, rotifers dominated in low salinities (74%) and cladocerans and copepods (69%) in high salinities. Our results suggest that the zooplankton community will shift to a rotifer dominated community in areas with declining salinity due to the intolerance of other zooplankton groups to freshening.
... 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.
... 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.
... Involvement of plankton is crucial in the food web of aquatic animals as they transfer and cycle the nutrient in the water that is important for the sustainable production of small larvae (Du et al., 2015;García-Chicote et al., 2017). It has long been assumed that it is one of the earliest and most sensitive taxonomic groups to be influenced by environmental change, such as changes in aquatic ecosystem trophic structure (Lin et al., 2017). Environmental filtering produced by local pollution restricted zooplankton populations at the river size since different environmental variation was simple to arise as a result of frequent human disturbance at fine geographic scales Yang, et al., 2018b;Yang et al., 2018a). ...
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... Mean annual precipitation between 1960 and 2015 is 355 mm, but evaporation (925 mm) is 2-3 times higher than precipitation (Li et al., 2022). In recent years, the surface area of Qinghai Lake has continued to expand, and its water level has continued to rise (>3 m), which is due to the increase in precipitation and accelerated melting of glaciers (Lin et al., 2017). Currently, Qinghai Lake encompasses an surface area of about 4199.23 to 4494.99 km 2 , and an average water depth of 21 m (Chen et al., 2022;Li et al., 2007). ...
Microbial carbon fixation in saline lakes constitutes an important part of the global lacustrine carbon budget. However, the microbial inorganic carbon uptake rates in saline lake water and its influencing factors are still not fully understood. Here, we studied in situ microbial carbon uptake rates under light-dependent and dark conditions in the saline water of Qinghai Lake using a carbon isotopic labeling (14C-bicarbonate) technique, followed by geochemical and microbial analyses. The results showed that the light-dependent inorganic carbon uptake rates were 135.17-293.02 μg C L-1 h-1 during the summer cruise, while dark inorganic carbon uptake rates ranged from 4.27 to 14.10 μg C L-1 h-1. Photoautotrophic prokaryotes and algae (e.g. Oxyphotobacteria, Chlorophyta, Cryptophyta and Ochrophyta) may be the major contributors to light-dependent carbon fixation processes. Microbial inorganic carbon uptake rates were mainly influenced by the level of nutrients (e.g., ammonium, dissolved inorganic carbon, dissolved organic carbon, total nitrogen), with dissolved inorganic carbon content being predominant. Environmental and microbial factors jointly regulate the total, light-dependent and dark inorganic carbon uptake rates in the studied saline lake water. In summary, microbial light-dependent and dark carbon fixation processes are active and contribute significantly to carbon sequestration in saline lake water. Therefore, more attention should be given to microbial carbon fixation and its response to climate and environmental changes of the lake carbon cycle in the context of climate change.
... A decrease in the number and biomass of certain members of the food web, as well as their elimination, lead to changes in the structural and functional parameters of aquatic ecosystems and disruption of relationships between hydrobionts of different trophic levels [58][59][60][61][62]. The functioning of higher trophic levels and the transfer of substances and energy in aquatic ecosystems are determined by the development of the primary link in food webs, algae, one of the main producers of organic matter. ...
Data of monitoring studies (2014–2016) on the state of hydrobionts in watercourses during the development of a hydrocarbon deposit on the Yamal Peninsula have been analyzed. The increased content of suspended solids has the greatest effect on hydrobionts. While the background values of concentration of sus pended solids is 4–6 mg/L, in the area of the entrance of the pit effluents to the watercourses, their concen tration increases up to 440 mg/L and higher. The effect of increased turbidity on the qualitative and quanti tative indicators of planktonic organisms has not been found. An increase of suspended solids in water has a negative effect on zoobenthos (rSp = –0.426, p = 0.030 for the number of species; rSp = –0.590, p = 0.002 for the abundance; rSp = –0.480, p = 0.013 for the biomass) and fish (rSp = –0.567, p = 0.004 for ecological den sity of small fish species). Especially sensitive fish to the increased content of suspended solids are whitefishes and lake minnows. The most tolerant to turbidity are the nine-spined stickleback and Barbatula toni. Increased concentrations of suspended solids in autumn are the reason for the cessation of up-stream migra tion of whitefishes from the Gulf of Ob to the deep lakes.
... The removal of N in these ecosystems depends mainly on the self-purification capacity of the system (Valiente et al., 2018) because they are land-locked drainage networks (Yapiyev et al., 2017). Increased temperature and salinity in arid endorheic lakes due to climate change is introducing new challenges for these aquatic ecosystems that may impact how Nr is removed (Tao et al., 2015;Greaver et al., 2016;Lin et al., 2017). In a endorheic lake in Northwest China, Jiang et al. found that lake sediments had a high potential for the use of denitrification as a way to efficiently remove N from sediments. ...
... The effects of freshwater salinization (FS) on biological communities can lead to trophic cascades with implications for ecosystem functioning Hintz and Relyea, 2019;Lin et al., 2017;Vidal et al., 2021). Within this context, zooplankton is a key component of lake food webs, since it facilitates energy transfer by grazing on phytoplankton (Hébert et al., 2017;Jeppesen et al., 2010). ...
Freshwater ecosystems are becoming saltier due to human activities. The effects of increased salinity can lead to cascading trophic interactions, affecting ecosystem functioning and energy transfer, through changes in community and size structure. These effects can be modulated by other environmental factors, such as nutrients. For example, communities developed under eutrophic conditions could be less sensitive to salinization due to cross-tolerance mechanisms. In this study, we used a mesocosm approach to assess the effects of a salinization gradient on the zooplankton community composition and size structure under eutrophic conditions and the cascading effects on algal communities. Our results showed that zooplankton biomass, size diversity and mean body size decreased with increased chloride concentration induced by salt addition. This change in the zooplankton community did not have cascading effects on phytoplankton. The phytoplankton biomass decreased after the chloride concentration threshold of 500 mg L⁻¹ was reached, most likely due to direct toxic effects on the osmotic regulation and nutrient uptake processes of certain algae rather than as a response to community turnover or top-down control. Our study can help to put in place mitigation strategies for salinization and eutrophication, which often co-occur in freshwater ecosystems.
... Recent studies demonstrate that freshwater ecosystems, even in high latitude and altitude areas, face multiple stressors produced by human activities and the global climate change (Smol et al., 2005;Anderson et al., 2013Anderson et al., , 2014Zhang et al., 2017;Jeff et al., 2019;Liang et al., 2021). Lakes in high latitude and altitude areas generally have a simple ecosystem structure and low biodiversity and are, therefore, extremely sensitive to anthropogenic perturbations and climate changes (Smol et al., 2005;Lin et al., 2017). Although these areas generally are less anthropogenically impacted, the air temperature has increased substantially over the past several decades (GISTEMP-Team, 2019), which may lead to increased water temperatures, decreased ice cover and longer growing seasons for aquatic organisms (Rouse et al., 1997;Smol et al., 2005). ...
Glacier retreat in high altitude areas triggered by anthropogenic warming exerts a profound impact on the ecology of glacier-fed lakes. In this paper, we report on the results of a multi-proxy analysis of a Lateglacial (13.3–11.3 cal kyr B·P.) core obtained from the glacier-fed Kanas Lake in the Altai Mountains, China, to understand the responses of aquatic ecosystems to meltwater influxes. Core intervals with high sand fractions and enriched silicon dioxide and zirconium (~11.5, 11.7, 11.8, 12.2 and 13.0 cal kyrs B·P.) reflect intense meltwater pulses from alpine glaciers. In the core, these pulses generally coincide with low abundance of littoral cladocerans, high abundance of planktonic Pediastrum, and high phosphorus concentrations. Our results suggest that intense meltwater influxes not only brought nutrients (nitrogen and phosphorus) into the lake and promoted phytoplankton growth, they also generated cold, turbid water masses and restricted the growth of benthic algae and invertebrates. Therefore, we infer that future anthropogenic warming may lead to significant changes in the structure and function of aquatic ecosystems in glacier-fed lakes worldwide.
... Снижение численности и биомассы организмов отдельных звеньев трофической сети, а также их элиминация приводят к изменениям структурно-функциональных параметров водных экосистем и нарушениям взаимосвязей между гидробионтами различных трофических уровней [58][59][60][61][62]. Функционирование высших трофических уровней и перенос веществ и энергии в водных экосистемах определяются развитием первичного звена пищевых сетей -водорослей, одного из основных продуцентов органического вещества. ...
Проанализированы данные мониторинговых исследований (2014-2016 гг.) состояния гидробионтов в водотоках при обустройстве месторождения углеводородов на полуострове Ямал. Показано, что наибольшее влияние на гидробионтов оказывает повышенное содержание взвешенных веществ. При фоновых значениях 4-6 мг/л концентрация взвешенных веществ в зоне попадания в водотоки стоков с карьеров достигает 440 мг/л и выше. Влияние повышенной мутности на качествен-ные и количественные показатели планктонных организмов не установлено. Увеличение содержа-ния взвешенных веществ в воде оказывает негативное влияние на зообентос (для числа видов r Sp = =-0.426, p = 0.030; для численности r Sp =-0.590, p = 0.002; для биомассы r Sp =-0.480, p = 0.013) и рыб (для экологической плотности мелких видов рыб r Sp =-0.567, p = 0.004). Особо чувствительны к повышенному содержанию взвешенных веществ сиговые рыбы, из карповых-озерный гольян. Наиболее толерантны к мутности девятииглая колюшка и сибирский голец-усач. Повышенные концентрации взвешенных веществ в осенний период-причина прекращения подъемной миграции сиговых рыб из Обской губы в глубокие верховые озера.
... We also did not include sediment, which can mediate water chemistry (McGowan et al. 2020). Finally, our simplified food webs did not include planktivorous fish, which can dramatically impact zooplankton responses to increasing salinity (Lin et al. 2017). Research investigating responses to salinization under various environmental contexts is warranted (Cunillera-Montcusí et al. 2022). ...
Across the Northern hemisphere, chloride concentrations in lakes are increasing from decades of road salt use, threatening aquatic ecosystems. Zooplankton are sensitive to increasing chloride but few studies have considered how additional stressors, such as soft water or increasing lake temperatures interact with the negative effects of chloride. To determine the effects of increasing chloride and temperature on freshwater zooplankton and phytoplankton communities, we conducted a mesocosm experiment using 30 concentrations of chloride from ambient levels to 1500 mg L−1, ambient or warmed (+2.7°C) temperatures, and plankton from a softwater lake. We compared the results with current Canadian Water Quality Guidelines (CWQG) for chronic exposure to chloride. Although warming elicited little response, increasing chloride concentrations led to reduced zooplankton biomass and richness, even at concentrations below the CWQG, and an increase in cyanobacteria abundance, suggesting that policies regulating road salt application should be reevaluated to better protect aquatic ecosystems.
... TDS). These lakes are located at a distance of ~200 km (north-western direction) and ~100 km (north-eastern direction) to Shen Co and are also dominated by the chironomid morphotypes Procladius and P. sordidellus-type (Zhang et al., 2007;Lin et al., 2017). ...
Understanding climate and monsoonal dynamics on the Tibetan Plateau is crucial, as recent hydrological changes, evidenced by rising lake levels, will be accelerated by current global warming and may alter aquatic habitats and species inventories. This study combines chironomid assemblages with sedimentological, mineralogical and geochemical data of a short sediment core (37.5 cm) from the high-altitude (> 4,733 m asl), saline (9 g L-1) and shallow (~5 m water depth) Shen Co, located in the southern part of the central Tibetan Plateau. The predominantly littoral, species-poor (10 chironomid morphotypes) chironomid assemblages are dominated by salt-tolerant taxa, that are highly sensitive to lake level fluctuations and macrophyte vegetation dynamics, making them ideally suited for tracking lake level changes over time. Results indicate a period (from ca. 1830 to 1921 CE) of drier conditions with low runoff and high evaporation rates in the Shen Co catchment, as indicated by a dominance of low-Mg calcite and dolomite and increased Ca/Fe and Sr/Rb ratios. This resulted in a decline in lake levels, an increase in salinity and the periodic occurrence of desiccation events at the sampling site. The first chironomid morphotype to appear after the dry period is Acricotopus indet. morphotype incurvatus, which indicate still low (
... The Tibetan Plateau is one of the most sensitive areas to global climate change. Since 1960, precipitation has risen by 12%, and temperatures have increased by 0.4°C per decade, which is three times the global average (Lin et al., 2017). This has led to glacier retreat and degradation of permafrost (Yao et al., 2012;Cheng and Jin, 2013). ...
High-resolution multi-proxy records from two lakes on the southern Tibetan Plateau, Nam Co and Tangra Yumco, are used to infer long-term variations in the Asian monsoon system with a novel set of ostracod shell chemistry proxies. We track the moisture evolution since the Last Glacial Maximum using the trace element, rare earth element (REE) and stable isotope composition of ostracod shells. The sediment records covering the past 18.8 cal. ka BP and 17.4 cal. ka BP, respectively, demonstrate the suitability of REEs as indicators of weathering intensity and thus hydrological changes and moisture sources in the catchment. In Nam Co, high concentrations of light REEs between 14 to 13 cal. ka BP suggest an increased drainage from the glaciated Nyainqêngtanglha Mountains in the south, pointing to meltwater input. REEs in ostracod shells therefore provide additional information on water sources critical for the interpretation of stable isotope records. Mg/Ca, Sr/Ca and Ba/Ca ratios reflect salinity and thus changes in effective moisture. Asynchronous behavior of Mg/Ca, Sr/Ca and Ba/Ca ratios are controlled by changes in dominance of precipitating carbonate minerals in the lake. Synchronous behavior reflects calcite precipitation, indicating low-Mg/Ca warm-wet conditions. Constantly low Sr/Ca ratios reflect aragonite precipitation, indicating high-Mg dry conditions. Increased Sr/Ca and Ba/Ca relative to Mg/Ca ratios show monohydrocalcite precipitation, indicating high-Mg/Ca cold-dry conditions. Furthermore, Fe/Ca, Mn/Ca and U/Ca ratios in ostracods reflect changes in oxygen saturation in lake bottom waters controlled by lake level and microbial activity.
The paleoclimate histories reconstructed from Nam Co and Tangra Yumco show high similarity throughout the late Quaternary. We identified two major dry periods, corresponding to Heinrich 1 and the Younger Dryas, followed by strengthening in Indian summer monsoon precipitation. The early Holocene is characterized by a moisture maximum, reflecting abundant water supply by a strong ISM. A time-delayed shift to dry conditions occurred at 2.6 cal. ka BP at Tangra Yumco, and at 2 cal. ka BP at Nam Co, resulting in decreasing lake levels, caused by weakened monsoon intensity due to a southeastward migration of the ISM-Westerly boundary with an estimated velocity of approximately 600 m per year.
... In Northwest China, temperatures have risen markedly in recent decades and faster than in the surrounding regions (Shi et al., 2007;Yang et al., 2020). Climate change can influence lakes either through higher temperatures or by changes in salinity (Mosley, 2015;Greaver et al., 2016), the latter is particularly influential in arid and semiarid lakes (Brucet et al., 2012;Lin et al., 2017). Climate change is affecting the hydrological cycle with more frequent and intense precipitation, altered snow accumulation and melt, and changes in evaporation (Sorg et al., 2012;Zhou et al., 2015), leading to large-scale changes in lake salinity (Jeppesen et al., 2015;Rusuli et al., 2015). ...
Endorheic lakes in arid regions of Northwest China are generally vulnerable and sensitive to accelerated climate change and extensive human activities. Therefore, a better understanding of the self-purification capacity of ecosystems, such as denitrification, is necessary to effectively protect these water resources. In the present study, we measured unamended and amended denitrification rates of Lake Bosten by adding the ambient and extra nitrate isotopes in slurry incubations. Meanwhile, we investigated the abundances and community structure of nitrous oxide-reducing microorganisms using qPCR and high-throughput sequencing, respectively, in the surface sediments of Lake Bosten to study denitrification potential in endorheic lakes of arid regions as well as the response of those denitrifiers to climatically induced changes in lake environments. Amended denitrification rates increased by one order of magnitude compared to unamended rates in Lake Bosten. The great discrepancy between unamended and amended rates was attributed to low nitrate availability, indicating that Lake Bosten is not operating at maximum capacity of denitrification. Salinity shaped the spatial heterogeneity of denitrification potential through changes in the abundances and species diversity of denitrifiers. Climate change had a positive effect on the water quality of Lake Bosten so far, through increased runoff, decreased salinity, and enhanced denitrification. But the long-term trajectories of water quality are difficult to predict alongside future glacier shrinkage and decreased snow cover.
... Accordingly, in our study, high water salinity often concurred with high concentration of organic carbon/nitrogen ( Table 2 ). In these regions, salinity is a dominant force influencing the ecological status and trophic structure of the lakes Wu et al., 2009 ;Lin et al., 2017 ;Jeppesen et al., 2020 ;Vidal et al., 2021 ). ...
Anthropogenic and natural disturbance to inland aquatic ecosystems displays a notable
spatial difference, yet data to measure these differences are scarce. This study encompasses 217 lakes distributed over five lake regions of China and elucidates the environmental factors determining the spatial variability of the water quality and trophic status. A significant correlation between human modification index in surrounding terrestrial systems (HMT) and trophic status of lake ecosystems (TSI) was found, and the regression slope in each region was similar except in the Qinghai-Tibet Plateau region. It was further noted that the pattern of environmental factor network (EF network) differed among freshwater and saline lakes. The EF network was complex for freshwater lakes in less human-influenced areas, but intensive man-made influence disrupted most relationships except for those between total nitrogen, total phosphorus, chlorophyll- a , and water turbidity. As for regions including saline lakes, correlations among water salinity and organic forms of carbon and nitrogen were apparent. Our results suggest that HMT and EF network can be useful indicators of the ecological integrity of local lake ecosystems, and integrating spatial information on a large scale provides conservation planners the option for evaluating the potential risk on inland aquatic systems.
... In addition, the connectivity of both zooplanktonic and phytoplanktonic nodes was significantly associated with low salinities. This observation could be due to the salinity increase not only could significantly decreased the zooplanktonic and phytoplanktonic diversity, but short the oceanic food chain (Brucet et al., 2009;Lin et al., 2017;Mo et al., 2021). ...
Although autotrophic phytoplankton and heterotrophic zooplankton both play important roles in the food web of marine ecosystem, their comprehensive interactions and spatial patterns at continental scale remain poorly studied. Here, we collected 251 seawater samples along 13,000 km of Chinese coastline, and microscopically investigated the latitudinal gradients of planktonic diversities. In total, 307 phytoplanktonic and 311 zooplanktonic species were visually identified. Using the newly developed Inter-Domain Ecological Network (IDEN) approach, the phytoplankton-zooplankton interaction networks were constructed. We found that the phyto-zooplankton network structure was varied across three regions, more complex and numerous connections along the southern coast than in the north. In addition, some particular associations between zooplanktonic and phytoplanktonic groups were found to be localized in specific regions. For example, autotrophic Chaetoceros lorenzianus was only associated with heterotrophic Copepoda in the northern regions. Furthermore, and the seawater temperature and salinity were the major driving force for shaping planktonic interaction networks. These results provide a deeper understanding of planktonic biogeography and phytoplankton-zooplankton interaction patterns.
... The factors elaborated above are imperative to phytoplankton, especially for phytoplankton of the alpine lakes in the Tibetan Plateau. The lakes in the Tibetan Plateau experience a warm and wet climate [55,56], leading to changes in the water temperature, nutrients, and salinity and eventually facilitating the growth of phytoplankton [57]. Particularly, phytoplankton blooms may occur in those brackish lakes with enough nutrients under climate change. ...
In this paper, two trophic lakes: Lake Taihu and Lake Yanghe, and three alpine lakes: Lake Qinghai, Lake Keluke, and Lake Tuosu, were investigated to discover the connections between environmental factors and the phytoplankton community in lakes with differences in trophic levels and climatic conditions. Three seasonal data, including water quality and phytoplankton, were collected from the five lakes. The results demonstrated clear differences in water parameters and phytoplankton compositions in different lakes. The phytoplankton was dominated by Bacillariophyta, followed by Cyanobacteria and Chlorophyta in Lake Qinghai, Lake Keluke, and Lake Tuosu. It was dominated by Cyanobacteria (followed by Chlorophyta and Bacillariophyta in Lake Yanghe) and Cyanobacteria (followed by Chlorophyta and Cryptophyta in Lake Taihu). The temperature was an essential factor favoring the growth of Cyanobacteria, Chlorophyta, and Bacillariophyta, especially Cyanobacteria and Chlorophyta. The pH had significantly negative relationships with Cyanobacteria, Chlorophyta, and Bacillariophyta. Particularly, a high pH might be a strong and negative factor for phytoplankton growth in alpine lakes. A high salinity was also an adverse factor for phytoplankton. Those results could provide fundamental information about the phytoplankton community and their correlated factors in the alpine lakes of the Tibetan Plateau, contributing to the protection and management of alpine lakes.
... With salinity increased, biodiversity declined exponentially. Lin et al. (2017) invested zooplankton communities in 45 lakes of the Tibetan Plateau and found that species richness declined significantly with salinity. In addition, our unpublished data of benthic macroinvertebrates in 40 lakes of the Tibetan Plateau showed that the taxa composition in saline lakes was significantly different from that in freshwater lakes. ...
Biodiversity patterns along the elevational gradient of vertebrates have been widely focused on in previous studies, but they are still insufficient on invertebrates in lakes to a wide elevational extent. Based on field samplings and literature, we compared biodiversity patterns among different taxonomic groups of benthic macroinvertebrates in 104 lakes of China and India along an elevational gradient of 2–5,010 m a.s.l. and revealed the key driving factors, and then, we discussed the key mechanisms underlying elevational biodiversity patterns. We found that elevational biodiversity patterns of different taxonomic groups were not uniform, e.g., an exponentially decreasing pattern of Bivalvia, a first horizontal and then decreasing pattern of Gastropoda, and a linear decreasing pattern of Oligochaeta and Insecta. Elevation and elevation-controlled variables (temperature and salinity) were the key driving factors to biodiversity patterns. Their effects were strongest on Bivalvia and less on Gastropoda, whereas they were relatively weak on Oligochaeta and Insecta. Finally, we discussed three important mechanisms that shaped elevational biodiversity patterns and assemblage variations of benthic macroinvertebrates by linking our results with the classic hypotheses about biodiversity patterns, including climate/productivity, environmental heterogeneity, and dispersal/history. These results could improve our understanding of biodiversity patterns and biodiversity conservation.
... The Tibetan Plateau features the largest number of lakes in China (> 1500 lakes); most of these are salt lakes [32], and more than 97% as inland lakes [33]. Lakes play a key role in the hydrological cycle in Tibet and greatly affect the regional climate, water resources, and terrestrial/aquatic ecosystems [34]. ...
Background
Lake is a critical part of Tibet's hydrological cycle, the lake–terrestrial ecotone is the most sensitive area in the water and terrestrial ecosystem. For the ecological protection and maintenance of the lakeside zone, defining the upper boundary of the lake–terrestrial ecotone is a key issue that needs to be solved urgently. However, the ecological characteristics of lake–terrestrial ecotone made it difficult to delimit. Wetland herbs are characteristic plants of the lake–terrestrial ecotone, and their distribution width can be used to reflect the upper boundary of the lake–terrestrial ecotone. We took Baksum Lake, Yamdroktso, Namtso, Siling Co as examples, based on the spatial structure of the lake–terrestrial ecotone, used the moving split-window technology (MSWT) delimited the width of wetland herbs.
Results
The results of the MSWT showed the distribution width of wetland herbs in each lake–terrestrial ecotone with the natural-wetland type sampling line of Baksum Lake, Yamdroktso, Namtso, Siling Co was 51 m, 56 m, 33 ~ 53 m, 19 ~ 31 m. The detrended correspondence analysis (DCA) showed quantity of wetland herbs species, BK1 > YT1 = NT1 > NT2 > SC1 = SC2. The principal component analysis (PCA) and the (redundancy analysis) RDA showed soil moisture content (SMO), pH, soil moisture content (SSC), and soil nutrient content had obvious correlation with distribution width.
Conclusion
The MSWT was a feasible method to determine the width of lake – terrestrial ecotone. SMO, pH, SSC, and soil nutrient content were all important environmental factors affecting the wetland herbs distribution width of the four lakes; and the SMO was the most important factor. Besides, compared with the lakes in the Middle-Lower Yangtze Plain, the high-density population distribution, high-intensive human activity invaded the plants' growth area, resulting in a smaller distribution width. The distribution edge of wetland herbs is equivalent to the upper boundary of lake–terrestrial ecotone. It determines the management boundary of the lake–terrestrial ecotone, provides a theoretical basis for the construction of environmental protection projects, and is of great significance to the lake ecological restoration and management in watershed control planning.
... This result is consistent with studies reporting relatively high salt tolerance in rotifers (Schallenberg et al. 2003). However, in contrast to our expectation, the decrease in crustacean abundance and, therefore, competition for phytoplankton, was not accompanied by an increase in rotifer abundance, as observed elsewhere (Jeppesen et al. 2007;Van Meter and Swan 2014;Lin et al. 2017). Furthermore, the parallel study by Hintz et al. ...
Human-induced salinization increasingly threatens inland waters; yet we know little about the multifaceted response of lake communities to salt contamination. By conducting a coordinated mesocosm experiment of lake salinization across 16 sites in North America and Europe, we quantified the response of zooplankton abundance and (taxonomic and functional) community structure to a broad gradient of environmentally relevant chloride concentrations, ranging from 4 to ca. 1400 mg Cl/L. We found that crustaceans were distinctly more sensitive to elevated chloride than rotifers; yet, rotifers did not show compensatory abundance increases in response to crustacean declines. For crustaceans, our among-site comparisons indicate: (1) highly consistent decreases in abundance and taxon richness with salinity; (2) widespread chloride sensitivity across major taxonomic
groups (Cladocera, Cyclopoida, and Calanoida); and (3) weaker loss of functional than taxonomic diversity. Overall, our study demonstrates that aggregate properties of zooplankton communities can be adversely affected at chloride concentrations relevant to anthropogenic salinization in lakes.
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.
Mediterranean endorheic wetlands are
strongly affected by local meteorological events, so
they undergo frequent unpredictable disturbances,
such as episodes of high salinity or desiccation. In
this context, salinity and temperature may be crucial
for determining the structure of zooplankton communities
and regional biodiversity, since they may trigger
the hatching of egg bank in different ways. The
goal of this study is to assess the combined role of
these two variables on the zooplankton assemblage
emerging from the egg bank. We hypothesize that
temperature and salinity affect the community structure
in a non-linear way, that is, both factors interact and modify the magnitude of their effects. We performed
a laboratory factorial design where the same
sediment was incubated under different thermal and
salinity conditions, reducing the potential effects of
other possible confusion factors. Community structure
was described by measuring cumulative abundances,
species composition, richness, and diversity.
Our results showed that the community structure was
strongly determined by salinity at all experimental
temperatures. In contrast, the magnitude of the temperature
effect depended on salinity. The high variability
among replicates when salinity and temperature
increased suggests that climate change might lead to
unpredictable patterns of the community emerging
from the egg bank.
Eutrophication and salinization are serious global environmental problems in freshwater ecosystems, occasionally acting jointly to exert harmful effects on aquatic ecosystems. To elucidate the interactive effects of nutrients and salinity on phytoplankton assemblages, we conducted a four-season study during 2020–2021 of eight lakes from Yunnan Plateau (Southwest China) with a wide range of conductivities (Cond, reflecting degree of salinization), eutrophic states, and water depths and used General Additive Modeling (GAM) of the data. We found that: (1) species number (SN), density (DPhyt), and biomass (BPhyt) of phytoplankton showed stronger seasonal dynamics in shallow lakes than in deep lakes, all being, as expected, higher in the warm season; (2) annual and summer data revealed highly significant positive relationships between SN, DPhyt, and BPhyt with total nitrogen (TN) and total phosphorus (TP), which became weaker at high TP occurring when the N:P ratio was low, indicating N limitation; (3) SN, DPhyt, and BPhyt showed a unimodal relationship with salinity, peaking at 400–1000 μS/cm (Cond); (4) the two dominant taxa (cyanobacteria and chlorophyta) showed different patterns, with chlorophyta generally dominating at low TN and cyanobacteria at high TN and Cond, suggesting the synergistic effect of nitrogen and Cond on cyanobacterial dominance.
Eukaryotes exist widely in aquatic ecosystems. It is of great importance to study their species composition, diversity, and relationship with environmental factors to protect and maintain ecosystem balance. Salt lakes are essential lakes rich in biological and mineral resources and have significant research value. To understand the characteristics of eukaryotic diversity in salt lake sediments, we conducted a sampling survey of the benthos in Kyêbxang Co, Tibet, in July and August 2020. The sampling area was divided into littoral, sublittoral, and profundal zones. A total of 42 species of Metazoa, 159 species of Protozoa, 63 species of Viridiplantae, and 46 species of Fungi were identified by the high-throughput sequencing of 18S ribosomes. Alpha diversity analysis revealed significant differences in species composition among the three study zones. The littoral zone had the highest Sobs index and Chao index, indicating that the eukaryotic diversity and richness in this zone were significantly higher than those in the profundal and sublittoral zones. Redundancy analysis (RDA) showed that water depth, temperature, and sediment organic matter content significantly affected the community structure of eukaryotes zones, especially the distribution of dominant genera such as Dunaliella, Psilotricha and Brachionus. Cooccurrence network analysis showed that Dunaliella, Aphelidium, temperature, water depth, and organic matter represent essential nodes in the entire network. This study can provide baseline data and new insights for eukaryotic diversity research for salt lakes.
Despite significant climate change on the Tibetan Plateau, the historical succession trend and underlying driving mechanism of aquatic ecosystem in alpine lake remain unclear. In this study, palaeolimnological analysis and high-throughput sequencing of sedimentary DNA were used to investigate environmental changes, primary productivity, and eukaryotic algal community succession over the past millennium in Lake Yamzhog Yumco of the southern Tibetan Plateau. Lake primary productivity significantly increased after ~1850 CE and algal community succession occurred in three stages including the Medieval Warm Periods (approximately 1000–1250 CE), the Little Ice Age (1250–1850 CE), and the Current Warm Period (1850–2020 CE). Moreover, succession was synchronous with inferred climate changes. Partial least square path modeling indicated that climate factors affected primary productivity and eukaryotic algal community structure by affecting nutrient loading. The results suggest that glacier melting and permafrost degradation caused by climate warming, combined with increased precipitation, may be the major driving factors of nutrient concentration increases, phytoplankton biomass increases, and shifts in community composition. Considering the expected trends of future climate change and continuous warming, the restoration of vegetation cover and reduction of non-point source nutrient loading in the Tibetan Plateau is urgently needed to mitigate climate change impacts on alpine lake aquatic ecosystems.
In nowadays, world trade and cargo transportation mainly rely on shipping, and inland ports provide valuable and essential services to the maritime transport. With the increase of trade volume, the discharge of ballast water from ships is also increasing, which brings in ecological challenges. The International Maritime Organization stipulates that the number of organisms in discharged ballast water should be limited to prevent biological invasion to recipient waters. However, ballast water still contains many substances of source water, and may affect the plankton community in the recipient waters. In this study, the effects of ballast water on nature freshwater plankton community were evaluated at laboratory scale. It was observed that the abundance and diversity of planktons decreased with increase of water salinity. Through 10 days of continuous monitoring, it was found that ≥ 50 µm organisms were more sensitive to rising salinity than 10–50 um organisms, when water salinity was not over 3.6‰, there was no significant difference on ≥ 50 µm organisms quantity and diversity compared with the freshwater control group after 10 days, and the biota maintained certain recovery ability, while 10–50 um organisms had recovery ability when water salinity was not over 6.5‰. However, when the water salinity was over 6.5‰, both species composition and organism density showed irreversible and rapid reduction. In addition, organism species Platyias sp., Polyarthra sp., Tribonema sp., Navicula sp. were found to be very sensitive to salinity change and could be considered as indicative organisms for monitoring and evaluating ecological effect of discharge of saline ballast water. This is of great significance for the scientific management of ballast water discharge in fresh waters in the future.
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.
