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Long-term change in the trophic status and mixing regime of a deep volcanic lake (Lake Bolsena, Central Italy)
Abstract
Lake Bolsena, the fourth Italian lake for volume (9.2 × 10⁹ m³), must be considered as highly sensitive to eutrophication for its extremely long water renewal time. In this paper, temperature and chemical characteristics of the lake measured in the period 2003–2017 are used to discuss the mixing pattern and the variation in the oxygen and algal nutrient concentrations, as indicators of the trophic level. In the analysed period the lake showed oligomictic characteristics, reaching the full overturn, with homogenization of the chemical profile over the whole water column, only in 4 out of the 15 considered years. A regular decrease of oxygen and increase of phosphorus concentrations in the deepest layers has been observed in the non-circulating multi-year periods. The mean total phosphorus concentration showed a regular increase, reaching values close to 16 μg P L⁻¹ in early spring 2017, mostly because of the urban discharge from the watershed, not adequately collected from an existing sewage pipe. Chemical and mixing patterns are discussed in relation with a previous study, carried out in 1966–1971, confirming the recent increase of phosphorus concentrations and the lower frequency of full circulation. The progressive deterioration of lake water quality indicates the need of prompt actions to reduce the external nutrient load and of further studies on the physical and biological characteristics of the lake, still strongly missing.
... Regarding the cooling-induced penetrative convective mixing in the surface layer during nighttime hours, observations were examined in a small lake with the analyses using turbulent kinetic energy (Jonas et al. 2003). In contrast, complete mixing to the bottom of hypolimnion happened in significantly cold winters in sub-tropical/ temperate deep lakes [oligomictic lakes, e.g., Lake Ikeda (Ito and Momii 2015;Ushigaki et al. 2018), Lake Bolsena (Mosello et al. 2018)]. However, the overturn of lake water once several or decades of years was rarely described in tropical deep lakes. ...
... Lake Bolsena is a temperate oligomictic lake with 151 m of maximum depth and 114 km 2 of surface area in central Italy. Mosello et al. (2018) reported full overturns, with homogenization of the chemical profile over the whole water column, only in 4 out of the 15 considered years (2003)(2004)(2005)(2006)(2007)(2008)(2009)(2010)(2011)(2012)(2013)(2014)(2015)(2016)(2017). They indicated that both conditions, i.e., low AT (a few degrees lower than the average for more than a dozen days) and strong wind, had to be present to foster the mixing of the lake. ...
The ecology of a lake is mainly controlled by mixing processes; particularly, in tropical oligomictic lakes, the occurrence frequency and magnitude of convection govern the vertical mixing of chemicals and organisms. In this study, vertical profiles of water temperature, dissolved oxygen, electric conductivity, turbidity, and chlorophyll a were measured in 2014, 2015, 2017, and 2018 in two Sumatran deep lakes, Lakes Maninjau and Singkarak. In Lake Maninjau, intensive surveys on the profiles were also conducted in three different seasons in 2018. The comparison of the profiles between 2015 and 2017 indicated the events of large convection down to the lake bottoms happened in both of the lakes. Similarly, small convection down to around 30 m depth was found in the period between May and Jul, 2018. Air temperature drops up to five degrees centigrade were observed in these periods, confirmed by the changes in lake surface temperature estimated by MODIS imagery for the lakes. The magnitudes of the convective events were discussed with the observed amounts of heat loss and the estimated heat transfer through lake surface. Furthermore, the influences of such events on anoxic hypolimnetic waters were evaluated and considered from the view of climate change.
... As a tropical country, Indonesia has tiny annual temperature variations and differences in surface and bottom water temperatures (Tonolla et al., 2017). As is known, the variation of temperature cause the change in density gradient in the Phytoplankton Dynamics and Its Relation to Physicochemical Parameters in the Dry Season of Maninjau Lake, West Sumatra, Indonesia water column and will change the intensity and duration of mixing, stability of temperature, and thermocline afterward (Mosello et al., 2018). ...
... Urban lakes are vulnerable ecosystems, sensitive to eutrophication, which can impact public health . Closed lakes may accumulate large quantities of pollutants due to high water retention and slow vertical mixing (Gale et al., 2006;Mosello et al., 2018;Popa et al., 2020b). Open lakes can act both as sinks and transformation media for pollutants and organic matter, which enter open lakes by discharges, leaching or runoff. ...
... The burial, mineralization, and release of nutrients are influenced by many physical parameters in water column, such as WT, pH, and DO (Mosello et al. 2018;Lin et al. 2021). Warmer WT and higher DO in shallow-lake often contribute to increased carbon mineralization and CO 2 production (Marotta et al. 2014;Beaulieu et al. 2019). ...
The long-term accumulation, burial and release of nutrients, such as carbon (C), nitrogen (N), and phosphorus (P) in lacustrine sediments are responsible for the global lake eutrophication. Interpretation of the spatiotemporal sedimentary record of nutrients (C, N, and P) in contrasting trophic level of lakes is helpful for understanding the evolutionary process of water eutrophication. Based on the radiochronology of 210Pbex and 137Cs, a comparative study of spatial and temporal concentrations, burial of total organic carbon (TOC), total nitrogen (TN), and total phosphorus (TP), the sources of organic matter were conducted using sediment cores from two plateau lakes Dianchi (DC) and Fuxian (FX) of SW China. Results showed that concentrations and burial of C, N, and P in sediments of DC, a shallow hypertrophic lake with the maximum depth of 5.8 m, were both higher than those in FX, an oligotrophic deep lake with the maximum depth of 155.0 m. For both lakes the molar ratio of TOC/TN increased in the sediments moving from north to south. The values of TOC/TN molar ratios increased over time in DC and were higher than in FX. The extremely high values of TOC/TN appeared in the central and southern parts of FX, indicating the impacts of accumulation effect and sediment focusing in the deeper region and indirect supplement from the Lake Xingyun (XY), an adjoining lake connected with FX via the Gehe River. Time-integrated sources identification in DC indicated the contribution of allochthonous sources was dominant over the past few decades, which contributed to the increased trophic level of the lake. The comparison of relationships of carbon accumulation rates (CAR), nitrogen accumulation rates (NAR), and phosphorous accumulation rates (PAR), the ratios of N/P and the utilizations of N and P fertilizer between DC and FX implied that both of N and P inputs should be limited for reducing the trophic level, but N control was predominant in comparison with P for both lakes. The results indicated that caution is required in plateau lakes to limit transition from oligotrophic to eutrophic in these lakes.
... Even though the nutrient status of the lake was determined to be mesotrophic in terms of TP concentration, unless the necessary precautions are taken the lake might rapidly transform into a eutrophic state. In another deep lake, Lake Bolsena, it was stated that remediation of the lake will take a very long time due to the increase in the external phosphorus loading and the fact that the increase also raised algae production and mineralization in the hypolimnion, the lower thermal layer of the lake (Mosello et al., 2018). ...
... Closed lakes, in particular, are prone to increased water pollution and eutrophication due to high water retention and slow vertical mixing in the water column. [19] Vertical mixing, in closed lakes, is mostly ensured by strong winds, [20] while biological processes and photodegradation contribute to pollution reduction. Closed lakes, in Bucharest, Romania, are periodically drained and dredged at the end of autumn, through winter, and are refilled in spring to prevent eutrophication and accumulation of pollutants. ...
Closed lakes located in urban parks act as sinks of organochlorine pesticides (OCPs), which have been used, for decades, as insecticides, herbicides and fungicides. The closed lakes from Bucharest, Romania, are periodically managed to prevent eutrophication and accumulation of pollutants. However, it is not known if these practices reduce or enhance the legacy pollution with OCPs. The aim of this study was to explore the spatial variation of OCPs in closed lakes. The total concentration of OCPs in water and sediments ranged between 0.0176 and 37.1 µg/L, and between 122 to 1,890 ng/g, respectively. The concentrations of OCPs were compared with the consensus-based sediment quality guidelines (SQGs) in order to evaluate the ecological risks of sediments. The highest potential adverse effects were associated with γ-HCH exposure. Periodical draining and dredging of lakes lead to the resuspension of contaminants, increasing pesticide bioavailability and accumulation in sediments. In addition, we observed that fluorescent dissolved organic matter (DOM) might influence the OCPs cycle. The quantity and character of fluorescent DOM can provide further insight into OCPs degradation. Also, this study may help urban planners to determine the state of urban waters and to find the best solution for water management.
... Stratifikasi temperatur danau yang tidak terlalu berbeda ini juga mengakibatkan stratifikasi perbedaan dekomposisi senyawa organik yang tidak terlalu siginifikan. Perubahan heterogen secara vertikal suhu air mempengaruhi gradien densitas dalam kolom air dan selanjutnya terhadap intensitas dan durasi pencampuran serta stratifikasi vertikal, stabilitas termal, dan termoklin (Mosello, Bruni, Rogora, Tartari, & Dresti, 2018). Konsentrasi nutrien dan oksigen pada gilirannya juga dipengaruhi oleh perubahan struktur termal danau. ...
p>Danau Maninjau dalam beberapa tahun terakhir ini telah mengalami pencemaran akibat senyawa organik akibat dari aktivitas manusia maupun budi daya ikan yang semaikn meningkat di sekeliling danau. Tujuan dari penelitian ini adalah untuk menganalisis pengaruh lingkungan pH, DO dan suhu terhadap senyawa organik di Danau Maninjau berdasarkan stratifikasi kedalaman. Pengambilan sampel dilakukan pada lima titik sampling yang mewakili lokasi pemanfaatan danau yaitu pada bagian tengah, domestik, PLTA, endemik dan keramba jaring apung (KJA) sesuai dengan SNI 6989.57:2008. Parameter organik yang diukur adalah BOD5 dan COD. Korelasi parameter BOD5 dan COD terhadap parameter lingkungan berdasarkan kedalaman ditentukan dengan uji regresi. Kualitas danau Maninjau berdasarkan kadar senyawa organik berada dalam kondisi tercemar yang ditandai dengan nilai BOD5 dan COD yang diperoleh tidak memenuhi baku mutu PP 82 tahun 2001 kelas 2 yang berkisar antara 21,87-47 mg/L untuk BOD5, dan 35,2-74 mg/L untuk COD. Nilai konsentrasi BOD5 dan COD semakin meningkat seiring dengan bertambahnya kedalaman, sedangkan pada kedalaman yang dangkal danau cenderung tercampur akibat turbulensi. Parameter lingkungan lingkungan pH, DO dan suhu memiliki korelasi sangat kuat dan berbanding terbalik dengan BOD5 dan COD dengan nilai r > 0,9. Suhu tropis danau dan kecepatan angin yang cukup tinggi, mengakibatkan stratifikasi senyawa organik tidak jauh berbeda pada kedalaman sekaligus memungkinan terjadinya dekomposisi senyawa organik.
Kata kunci: Danau Maninjau, BOD5, COD, parameter lingkungan, stratifikasi kedalaman</p
The long-term accumulation, burial and release of nutrients, such as carbon (C), nitrogen (N) and phosphorus (P) in lacustrine sediments are responsible for the global lake eutrophication. Interpretation of the spatiotemporal sedimentary record of nutrients (C, N and P) in contrasting trophic level of lakes is helpful for understanding the evolutionary process of water eutrophication. Based on the radiochronology of ²¹⁰ Pb ex and ¹³⁷ Cs, a comparative study of spatial and temporal concentrations, burial of total organic carbon (TOC), total nitrogen (TN) and total phosphorus (TP), the sources of organic matter were conducted using sediment cores from two plateau lakes Dianchi (DC) and Fuxian (FX) of SW China. Results showed that concentrations and burial of C, N and P in sediments of DC, a shallow hypertrophic lake with the maximum depth of 5.8 m, were both higher than those in FX, an oligotrophic deep lake with the maximum depth of 155.0 m. For both lakes the molar ratio of TOC/TN increased in the sediments moving from north to south. The values of TOC/TN molar ratios increased over time in DC and was higher than in FX. The extremely high values of TOC/TN appeared in the central and southern parts of FX, indicating the impacts of accumulation effect and sediment focusing in the deeper region and indirect supplement from the Lake Xingyun (XY), an adjoining lake connected with FX via the Gehe River. Time-integrated sources identification in DC indicated the contribution of allochthonous sources was dominant over the past few decades, which contributed to the increased trophic level of the lake. The comparison of relationships of carbon accumulation rates (CAR), nitrogen accumulation rates (NAR) and phosphorous accumulation rates (PAR), the ratios of N/P and the utilizations of N and P fertilizer between DC and FX implied that both of N and P inputs should be limited for reducing the trophic level, but N control was predominant in comparison with P for both lakes. The results indicated that caution is required in plateau lakes to limit transition from oligotrophic to eutrophic in these lakes.
Eutrophication is a global concern that has severely deteriorated the aquatic ecosystems. This phenomenon has impacted the freshwater bodies (such as lakes and rivers) across the world due to the nutrients (mainly N and P) arising from point and non-point pollution sources. Nutrient enrichment induces cyanobacteria formation, hypoxia, and release of bloom toxins, causing their accumulation in aquatic organisms and humans. Preventing the use of chemicals (such as fertilizers) at the source can avoid nutrient release in the run off streams, thus controlling non-point pollution. While point source pollutants can be effectively controlled at the sewage treatment plants. Although freshwater eutrophication managements have been widely discussed, a systematic eutrophication characterization of lakes and rivers worldwide, with their effective, economically feasible, eco-friendly, and beneficial bio-treatments is still scarce. Hence, in this review a complete eutrophication-based characterization of lakes and rivers all over the world is provided. Different cost-effective and efficient bio-remediations to control point and non-point pollution are discussed, additionally with a comparative account for the selection of a suitable microbe and remediation approach. A combined point and non-point pollution management can eradicate eutrophication.
Deep lakes south of the Alps (DSL: Maggiore, Lugano, Como, Iseo and Garda) are characterised by varying trophic states and dissolved oxygen (DO) concentrations. Some of these lakes experience anoxic conditions in deep waters. We hypothesised that the increase in temperature and water-column stability observed in these lakes during recent decades influenced the deep-water DO concentration. In particular, we tested whether the thermal regime of the lakes and the depth of mixing affect oxygen replenishment during winter–spring turnover. To this aim, we analysed long-term trends and seasonal variability of oxygen levels in the DSL during 1992–2016. We included in our analysis the effects of environmental variables, such as winter air temperature and atmospheric modes of variability. Our results showed a recent decrease in the deep-water oxygen content in lakes Maggiore, Como and Garda and an increase of the extent of anoxic conditions in lakes Lugano and Iseo. Our results suggest that, beside cultural eutrophication, rising environmental pressures, such as global warming, can influence the future trends of the oxygen levels and ecological states of deep lakes.
The long-term research carried out since the 1970s in the deep perialpine Lake Garda documented more than a threefold increase of total phosphorus (TP) in the whole water column until mid-2000s and a continuous warming. We evaluated the impact of these changes on phytoplankton, assessing similarities and peculiarities compared with other lakes. The increase of TP favoured cyanobacteria (microcystins producer Planktothrix rubescens (De Candolle ex Gomont) Anagnostidis & Komárek) and large diatoms. The warming of the lake caused a decrease in the frequency of full mixing episodes, which stopped completely after 2006, and a lower supply of nutrients to the upper layers. This “climate warming-induced oligotrophication” was mediated by the physiographic characteristics typical of deep lakes. The decrease of nutrients in the upper layers induced by the long period of incomplete mixing caused a decline of the mesotrophic P. rubescens, which was partially replaced by anatoxins producer Tychonema bourrellyi (J.W.G. Lund) Anagnostidis & Komárek. Lake warming favoured a higher development of mixotrophic dinoflagellates and cryptophytes. Many dinoflagellates are adapted to grow in warm and low nutrient lakes, therefore it is likely that the development of selected species will increase in large (meso-)oligotrophic lakes because of climate change.
Human impacts on the few ancient lakes of the world must be assessed, as any change can lead to an irreversible loss of endemic communities. In such an assessment, the sensitivity of Lake Ohrid (Macedonia/Albania; surface area A = 358 km(2), volume V = 55 km(3), > 200 endemic species) to three major human impacts-water abstraction, eutrophication, and global warming-is evaluated. It is shown that ongoing eutrophication presents the major threat to this unique lake system, even under the conservative assumption of an increase in phosphorus (P) concentration from the current 4.5 to a potential future 9 mg P m(-3). Eutrophication would lead to a significant reduction in light penetration, which is a prerequisite for endemic, deep living plankton communities. Moreover, a P increase to 9 mg P m(-3) would create deep water anoxia through elevated oxygen consumption and increase in the water column stability due to more mineralization of organic material. Such anoxic conditions would severely threaten the endemic bottom fauna. The trend toward anoxia is further amplified by the predicted global warming of 0.04 degrees C yr(-1), which significantly reduces the frequency of complete seasonal deep convective mixing compared to the current warming of 0.006 degrees C yr(-1). This reduction in deep water exchange is triggered by the warming process rather than by overall higher temperatures in the lake. In contrast, deep convective mixing would be even more frequent than today under a higher temperature equilibrium, as a result of the temperature dependence of the thermal expansivity of water. Although water abstraction may change local habitats, e.g., karst spring areas, its effects on overall lake properties was shown to be of minor importance.
Lake Ohrid in southeastern Europe is one of the few ancient, long-lived lakes of the world, and contains more than 200 endemic species. On the basis of integrated monitoring of internal and external nutrient fluxes, a progressing eutrophication was detected (~∼3.5-fold increase in phosphorus (P) concentration in the lake over the past century). The lake is fortunately still oligotrophic, with high concentrations of dissolved oxygen (DO) in the deep water that are requisite for the unique endemic bottom fauna. Hypolimnetic DO is not only very sensitive to changes in anthropogenic P load - via mineralization of organic material - but also to global warming via decrease of vertical mixing and less frequent complete deep convection. Moreover, these two human effects amplify each other. To keep DO from falling below currently observed minimal levels - given the predicted atmospheric warming of 0.04°C yr -1 - the P load must be decreased by 50% in coming decades. However, even with such a reduction in P load, anoxia is still expected toward the end of the century if the rate of warming follows predictions. © 2007, by the American Society of Limnology and Oceanography, Inc.
Volcanic lakes carry fluids that range from ultra acid, high TDS brines to largely meteoric fluids. Their water compositions are governed by volcanic fluid inputs, which range from almost raw, cooled volcanic gases (largely S-Cl-F-CO2 rich fluid) to more mature solutions that result from interaction of these acid fluids with volcanic rocks. Volcanic inputs can have reacted with mature protoliths (low degrees of neutralization) or with freshly intruded magma (high degrees of water rock interaction), the latter often resulting in the precipitation of secondary minerals such as alunite. The detailed chemical lake water composition is a reflection of mineral precipitation, fractionation of trace elements in the precipitated phases (such as the rare earThelements and metals in sulfides) and element vapor phase transport by the volcanic gases. Variations in lake composition result from a changing volcanic input composition or magnitude and thus are important in volcano monitoring. The lake water dynamics also impact the lake water composition over time, and variations in evaporation rate, meteoric water input and dramatic changes in input may cause changes in element concentrations and ratios related to non steady state effects. The recovery time to steady state differs strongly between open and closed lake systems. The stable isotope compositions of volcanic lake waters reflect W/R interaction (higher δ18O), degree of volcanic gas input (higher δ18O and δD), and evaporation at elevated temperatures (flat evaporation lines). Isotope ratios of other elements usually reflect the nature of the volcanic inputs or dissolved rock. Volcanic lakes can be charged with toxic elements that upon release may impact local ecosystems and agricultural land or drinking water downstream. Volcanic lakes charged with poorly soluble gases such as CO2 and methane may represent hazards of limnic eruptions. Failure of retaining walls or dams of acid lakes may cause acid floods with damage to land and livestock downstream.
The influence of morphometry on maximum and minimum heat content and on pluriannual heat budgets of 31 Italian lakes is analysed. The energy parameters are highly correlated with the morphometric parameters through power regressions. The lakes which markedly deviate from the regression curves are examined on the basis of their environmental conditions or their internal hydrodynamics. In deep lakes (i.e. depth >50 m) there is a high correlation between depth and maximum and minimum heat content, while the heat budget is correlated only with fetch and depths of 50 and 90% annual heat exchange. In shallow lakes there is no relationship between fetch and heat budget, while it is high with all the considered depths. This is due to the different thickness of the water layer, in relation to the maximum depth, which is involved in the annual heat exchanges. We evaluated the water thicknesses within which 40 to 90% of the total heat exchanges take place; the results showed that in deep lakes 90% of the energy exchange is confined to a layer comprising 14-16% of the maximum depth, while in shallow lakes it can reach 82% of the maximum depth. In Lago Maggiore the 90% heat exchange depth increased by 0.34 m per year from 1963 to 1999, thus contributing to heating the whole water mass of the lake.
Climate change-derived higher air temperatures and the resulting increase in lake surface temperatures are known to influence the physical, biological and chemical processes of water bodies. By using hydrodynamic lake models coupled with regional climate models the potential future impact of a changing climate can be investigated. The present study hence elucidates limno-physical changes at the peri-Alpine, 83-m deep, currently dimictic Ammersee in southeastern Germany, both to underline the role of lakes as sentinels of climate change and provide a sound basis for further limnological investigations. This was realised by using water temperatures simulated with the hydrodynamic model DYRESM for the period 2041-2050, based on the results of the regional climate model REMO (IPCC A1B emission scenario). Modelling of future heat content resulted in a projected increase in the upper 3 m of the epilimnion from end of March to mid-November, whereas a decrease in future total heat content (January-December) of the entire water column was simulated compared to that observed in 1997-2007. Lake thermal stability is projected to be higher in the period 2041-2050 than in 1985-2007. Stratification is expected to occur earlier and to last longer in the future than the pattern observed in 1985-2007. The future mean May-June depth of the thermocline is simulated to be situated above its past average vertical position, whereas an increase of mean thermocline depth is projected for the beginning of August to October. Furthermore, the mean May-October thickness of the metalimnion is simulated to increase. Additionally, we investigated the sensitivity of these limno-physical results to changes in the model parameter light extinction coefficient which determines how the solar radiation is absorbed by the lake water. The elucidation of physical changes at Ammersee by means of a regional climate model provides a sound basis on which to face the new challenges of lake modelling.
Lake littoral ecosystems help to preserve a significant degree of local and regional species richness. However, lakes are subjected to a range of human impacts that dramatically affect the local biota structurally and functionally. Unfortunately, the data available for numerous taxonomic groups in many river and lake systems are still somewhat scanty, especially in the Mediterranean area. We conducted a floristic study in 2010 and compared our data with historical data recorded over the last century (1908–2006) in six Italian volcanic lakes (central-southern Italy). Floristic data about charophytes and vascular plants were collected according to standardized sampling procedures along randomly selected transects and were partitioned into four functional groups (emergent species, floating-leaved, submerged and free-floating macrophytes).
A total of 49 aquatic taxa was recorded, including 11 taxa of charophytes, emphasizing the contribution of local stoneworts to regional and European species richness. Temporal trends in macrophyte species richness and distribution over the last century mirrored trends in lakeshore development and catchment land use, and water quality. In the long term, a clear reduction in emergent species and submerged macrophytes richness was recorded in some lakes; on the other hand, in recent decades a progressive improvement of water quality supports the partial recovery of aquatic plant richness in others. As a result, the loss of native aquatic plants is concentrated along the lakeshores and in the first meters of depth.
We investigate changes in the probability density functions and the probability of moderate extremes for maximum and minimum daily temperature anomalies in Italy from 1951 up to 2008. Evaluation of trends in time-varying percentiles and higher-moment analysis of empirical density functions give no evidence of long-term changes in scale or shape of daily anomaly distributions, their temporal evolution being essentially driven by a forward, nonuniform shift in the mean. In this context, on the basis of an appropriate theoretical model for daily anomalies, we provide a realistic representation of the temporal evolution of moderate warm and cold extremes by explicitly considering the inherent nonlinearity between changes in the mean and those in exceedance probabilities. Consistency between expected and observed exceedance probabilities suggests that changes in moderate extremes can be well understood with a simple, rigid shift of the density functions alone, without invoking any change in shape.
The residence time of a lake is highly dependent on internal physical processes in the water mass conditioning its hydrodnamics; early attempts to evaluate this physical parameter emphasize the complexity of the problem, which depends on very different natural phenomena with widespread synergies. The aim of this study is to analyse the agents involved in these processes and arrive at a more realistic definition of water residence time which takes account of these agents, and how they influence internal hydrodynamics. With particular reference to temperate lakes, the following characteristics are analysed: 1) the set of the lake's caloric components which, along with summer heating, determine the stabilizing effect of the surface layers, and the consequent thermal stratification, as well as the winter destabilizing effect; 2) the wind force, which transfers part of its momentum to the water mass, generating a complex of movements (turbulence, waves, currents) with the production of active kinetic energy: 3) the water flowing into the lake from the tributaries, and flowing out through the outflow, from the standpoint of hydrology and of the kinetic effect generated by the introduction of these water masses into the lake. These factors were studied in the context of the general geographical properties of the lake basin and the watershed (latitude, longitude, morphology), also taking account of the local and regional climatic situation. Also analysed is the impact of ongoing climatic change on the renewal of the lake water, which is currently changing the equilibrium between lake and atmosphere, river and lake, and relationships.
Anthropogenic-induced changes in nutrient ratios have increased the susceptibility of large temperate lakes to several effects of rising air temperatures and the resulting heating of water bodies. First, warming leads to stronger thermal stratification, thus impeding natural complete water turnover (holomixis), which compensates for oxygen deficits in the deep zones. Second, increased water temperatures and nutrient concentrations can directly favour the growth of harmful algae. Thus, lake-restoration programmes have focused on reducing nutrients to limit toxic algal blooms. Here we present evidence that the ubiquitous harmful cyanobacterium Planktothrix rubescens has become the dominant species in a large lake during the past four decades, although the phosphorus content of the ecosystem decreased fivefold. However, the nitrogen input was not diminished concomitantly, favouring this non-N2-fixing cyanobacterium owing to increased N:P ratios. P. rubescens contains gas vesicles that allow for buoyancy to accumulate within the depth of optimal irradiance. As the toxic cyanobacterium has low consumption by predators, water turnover represents the main mechanism of seasonal population control. Thus, unidirectional lake-restoration measures in parallel with recurrent absence of holomixis owing to lake warming may lead to similar undesired effects that have formerly emerged from fertilization.
A synthesis is made of biological data collected in the last three decades on five volcanic lakes in Central Italy with the aim of evaluating their environmental status by means of biological parameters related to zooplankton, littoral and profundal zoobenthos frequently used to detect water quality changes in lakes. A number of bioindicators and bioindices were selected for this purpose, as far as possible following an integrated approach using information drawn from physical and chemical variables. Our results allowed the lakes to be classified according to their biological quality level, which proved to be in good agreement with physical and chemical diagnoses. Lake Bracciano exhibited the best environmental quality, due to the presence of a ring waste water collecting system, to its large size and depth, and to its strong hydrodynamism. Lake Martignano followed, with some symptoms of stress in the hypolimnion due to a marked summer deoxygenation. Oxygen depletion in the profundal characterized also Lake Vico, which showed a mesotrophic condition in the sixties, and 20 years later now shows clear signs of increased trophy (meso-eutrophy). Lake Albano seemed meso-eutrophic with total absence of fauna below a depth of 120 m due to a meromictic status. Finally Lake Nemi, exposed to domestic wastes in the 70s, suffered a heavy eutrophication with dramatic algal blooms and fish kills. Following the diversion of discharges that occurred in the early 90s, today this lake is characterized by the partial improvement of many ecological features. The need for integration between physical and chemical analyses and biological data in order to obtain a reliable evaluation of lake environmental quality is stressed, especially as far as routine implementation in managing and recovery procedures is concerned.
Human impacts on the few ancient lakes of the world must be assessed, as any change can lead to an irreversible loss of endemic communities. In such an assessment, the sensitivity of Lake Ohrid (Macedonia/Albania; surface area A = 358 km2, volume V = 55 km3, > 200 endemic species) to three major human impacts—water abstraction, eutrophication, and global warming—is evaluated. It is shown that ongoing eutrophication presents the major threat to this unique lake system, even under the conservative assumption of an increase in phosphorus (P) concentration from the current 4.5 to a potential future 9 mg P m−3. Eutrophication would lead to a significant reduction in light penetration, which is a prerequisite for endemic, deep living plankton communities. Moreover, a P increase to 9 mg P m−3 would create deep water anoxia through elevated oxygen consumption and increase in the water column stability due to more mineralization of organic material. Such anoxic conditions would severely threaten the endemic bottom fauna. The trend toward anoxia is further amplified by the predicted global warming of 0.04°C yr−1, which significantly reduces the frequency of complete seasonal deep convective mixing compared to the current warming of 0.006°C yr−1. This reduction in deep water exchange is triggered by the warming process rather than by overall higher temperatures in the lake. In contrast, deep convective mixing would be even more frequent than today under a higher temperature equilibrium, as a result of the temperature dependence of the thermal expansivity of water. Although water abstraction may change local habitats, e.g., karst spring areas, its effects on overall lake properties was shown to be of minor importance.
In spite of its importance as regards size (volume 9.2 10 6 m 3 , max depth 151 m) and as a source of drinking water, Lake Bolsena has not been studied from a hydrochemical point of view since the second half of the 60s, when a group of researchers from the Isti-tuto Italiano di Idrobiologia co-ordinated a complete study of the limnology of the Latium lakes Bolsena, Albano, Vico, and Brac-ciano. In the following years analyses were performed sporadically; since the 90s, temperature and oxygen profiles and other studies were made by the Associazione Lago di Bolsena. Based on chemical profiles made in 2001-2003, this paper discusses the present chemical composition of Lake Bolsena waters, and compares them with those of other volcanic lakes in Latium (Bracciano, Albano, Nemi and Vico). The paper briefly considers the main factors influencing the water chemistry of Lake Bolsena, the variations ob-served from the analyses of the 60s, and the main sources of risk to water quality.
The relations of morphometric parameters with maximum stability (S) and maximum Birgean work (B) are analysed for 31 Italian lakes. Results show that in deep lakes the depths are more correlated with S, while fetch is more correlated with B. In con-trast, in shallow lakes the depths are correlated both with S and B, while the correlation with fetch is insignificant. Power regres-sions are used to define the relation between maximum depth, S and B, and an analysis is made of lakes showing a marked deviation from the curves, whether on account of their environmental features or their internal hydrodynamic state. In meromictic lakes total stability is subdivided into chemical and thermal stability; major inferences are made as to the depth of their winter mixing. The re-lationship between B and maximum depth is less significant than that between z max and S, as lakes with depth >100 metres and therefore with a very thick hypolimnion do not fully satisfy the regression function. Lastly, heating efficiency (E) is evaluated and related to depth and surface area of the lakes; the conclusion is that shallow lakes are more efficiently heated than deep ones.
The Italian monthly temperature (mean, maximum and minimum) and precipitation secular data set was updated and completely revised. Station density and metadata availability were greatly improved and the series were subjected to a detailed quality control and homogenisation procedure. The data homogenisation is described in detail. The bias affecting original data is quantified by studying the temporal evolution of the mean adjustments applied to the series and examined in the light of the stations history. The results stress the importance of homogenisation in climate change studies.
The final data set was clustered into climatically homogeneous regions by means of a Principal Component Analysis. Yearly and seasonal trend analyses were performed both on regional average series and on the mean Italian series. The results highlight a positive trend for mean temperature of about 1 K per century all over Italy; it is generally higher for minimum temperature than for the maximum temperature. The progressive application of trend analysis shows that, in the last 50 years, behaviour is the opposite; the maximum temperature trend being stronger than that of the minimum temperature. This has led to a negative trend in the daily temperature range that for the last 50 years has become positive. Precipitation shows a decreasing tendency, even if low and rarely significant, the negative trend being only 5% per century on a yearly basis. Copyright
Pilot studies have investigated the sedimentological records of Lakes Bolsena, Bracciano and Albano (Latium, central Italy)
for their climatic and tectonic histories. Literature has also been reviewed to assess the chronology of lake formation during
the Pleistocene (for the above lakes ca. 150 ka, 100 ka, 50 ka BP, respectively) and for evidence that the large Lakes Bolsena
and Bracciano were affected by young regional tectonic activity and are not typical caldera lakes. Our field studies, using
a high resolution seismic reflection method (3.5 kHz system), focus on the sedimentary evolution of the above lakes. Seismic
stratigraphy shows three units with similar characteristics in all three lakes: unit I, interpreted as Holocene deposits,
overlies latest Glacial and last Glacial maximum sediments (unit II), over middle- and early-Würm deposits (unit III). Truncation
of up to 50m-thick sediment packages on one side of both Lakes Bolsena and Bracciano is observed. The truncation was caused
by faults which were probably active toward the end of the last Glacial. A shallowing-upward deepening-upward lacustrine sequence
subsequently developed in places. Lake level changes appear to have been controlled by tectonic- and/or climatic boundary
conditions for Lakes Bolsena and Bracciano. There is no evidence for synsedimentary faulting in the maar Lake Albano.
Recent winter warming over Central Europe associated with a positive phase of the North Atlantic Oscillation (NAO) strongly influenced the thermal and water column stability properties of deep Lake Constance (zmean = 101 m).Volumet- rically weighted average water temperatures have increased since the 1960s by an average of 0.017 degree C yr-1, and its interannual variability was strongly related to the variability in winter air temperature and the NAO winter index (NAOW). The influence of NAOw on water temperature was more persistent than its influence on air temperature. The seasonal persistence of the NAOw signal increased with water depth. Deep-water temperatures were related to the NAOw from one spring mixing period to the next. This caused a time lag of 1 yr in the response of deep-water winter temperatures to the NAOw. Reduced winter cooling during high-NAOw years resulted in the persistence of small temperature gradients that possibly resisted complete mixing. This, in turn, resulted in less upward mixing of nutrients (total phosphorus and total silica), which accumulated in the hypolimnion during the previous stratification period. A second effect of incomplete mixing was the lack of the replenishment of deepwater oxygen during high-NAOw years. Hence, besides its strong impact on the thermal regime, climate variability influenced both the causes (nutrient supply for phytoplankton growth) and symptoms (the degree of hypolimnetic oxygen deficiency) of trophic changes in Lake Constance.
The paper presents an overview of the information contained in the literature - mainly produced by the limnology group of the Dipartimento di Biologia Animale e dell'Uomo of the "La Sapienza' University of Rome - on the limnological and biological situation in Latium, with particular reference to the volcanic lakes. The data demonstrate the level of trophic evolution reached in these lakes and the need in some cases for recovery or protective action. -Author
Using water column temperature records collected since 1968, we analyzed the impacts of climate change on thermal properties, stability intensity, length of stratification, and deep mixing dynamics of Lake Tahoe using a modified stability index (SI). This new SI is easier to produce and is a more informative measure of deep lake stability than commonly used stability indices. The annual average SI increased at 16.62 kg/m2/decade although the summer (May-October) average SI increased at a higher rate (25.42 kg/m2/decade) during the period 1968-2014. This resulted in the lengthening of the stratification season by approximately 24 d. We simulated the lake thermal structure over a future 100 yr period using a lake hydrodynamic model driven by statistically downscaled outputs of the Geophysical Fluid Dynamics Laboratory Model (GFDL) for two different green house gas emission scenarios (the A2 in which greenhouse-gas emissions increase rapidly throughout the 21st Century, and the B1 in which emissions slow and then level off by the late 21st Century). The results suggest a continuation and intensification of the already observed trends. The length of stratification duration and the annual average lake stability are projected to increase by 38 d and 12 d and 30.25 kg/m2/decade and 8.66 kg/m2/decade, respectively for GFDLA2 and GFDLB1, respectively during 2014-2098. The consequences of this change bear the hallmarks of climate change induced lake warming and possible exacerbation of existing water quality, quantity and ecosystem changes. The developed methodology could be extended and applied to other lakes as a tool to predict changes in stratification and mixing dynamics. © 2015 Association for the Sciences of Limnology and Oceanography.
Large-scale climatic fluctuations, such as the El Nino Southern Oscillation and the North Atlantic Oscillation (NAO), are known to influence variability in abiotic site conditions and organism population dynamics in both terrestrial and aquatic ecosystems. Here we demonstrate that the influence of the NAO on lake water temperatures-one of the major factors controlling ecological processes in lakes-differs substantially among lake types of different thermal structures and mixing regimes, even under identical climatic forcing. A frequently circulating polymictic lake was found to be least influenced by the winter effects of the NAO, with an effect lasting only into early spring. In contrast, in a deep dimictic lake with stable summer stratification, the NAO signal persisted in the hypolimnion until the following winter. A shallow dimictic lake revealed an intermediate response, as weather conditions both in April and midsummer probably modified the strength and persistency of the NAO signal in the hypolimnion of that lake. Based on these results, it is to be expected that NAO effects on ecological processes vary significantly among lakes. Because the study period (1979-1998) includes a series of uncommonly warm winter and spring seasons, our findings also suggest that the influence of anticipated climate warming will vary substantially among lake types.
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The least squares estimator of a regression coefficient β is vulnerable to gross errors and the associated confidence interval is, in addition, sensitive to non-normality of the parent distribution. In this paper, a simple and robust (point as well as interval) estimator of β based on Kendall's [6] rank correlation tau is studied. The point estimator is the median of the set of slopes (Yj - Yi)/(tj-ti) joining pairs of points with ti ≠ ti, and is unbiased. The confidence interval is also determined by two order statistics of this set of slopes. Various properties of these estimators are studied and compared with those of the least squares and some other nonparametric estimators.
Physically, lakes have traditionally been viewed as individual systems forced by statistically stationary local weather. This view implies that the physical response of a lake to external physical forcing is unique and stationary. Recent recognition of the importance of large-scale climatic forcing in driving physical lake processes, combined with the realisation that this forcing is undergoing a long-term trend as a result of climate change, has led to a shift in this paradigm. The new physical paradigm views lakes more in terms of a local response to large-scale climatic forcing modulated by the addition of local noise. A strong climate signal leads to large-scale spatial coherence in the physical lake response, while the existence of trends in large-scale climatic forcing associated with climate change means that both the forcing and the physical lake response are statistically non-stationary. Thus increasing realisation of the importance of climate and climate change is invalidating the tacit assumptions of individuality and stationarity that underlie the old conceptual framework, resulting in its gradual abandonment in favour of a new paradigm based on the concepts of spatial coherence and temporal non-stationarity. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
Dissolved inorganic carbon (DIC) and dissolved oxygen (DO) are commonly measured to compute metabolism of aquatic ecosystems. However, concentrations of DIC and DO depend on many factors in addition to ecosystem metabolism, such as water temperature, gas exchange with the atmosphere, abiotic chemical reactions, and inputs in precipitation, groundwater, and surface water. We used 20-year time series from seven lakes to understand how DIC and DO concentrations are controlled as a function of time scale. Diel cycles of both solutes are controlled primarily by metabolism, exchange with the atmosphere, and temperature. At seasonal and annual scales, metabolism is important, but physical processes associated with spring and autumn mixing, as well as solute loading from the watershed, have comparably large effects. At decadal scales, effects of metabolism are negligible. Controls of the two solutes diverge, with variance in DIC explained largely by solute inputs and variance in DO explained largely by water temperature. Like other indicators in many ecosystems, variability of DIC and DO is strongly scale dependent and associated with different drivers depending on the time scale of the analysis. Key words: aquatic ecosystem metabolism; dissolved inorganic carbon (DIC); dissolved oxygen (DO); drivers of DIC and DO; ecosystem drivers; lake concentrations of DIC and DO; long-term ecological research; temporal scale.
The pioneer works of Einsele, Mortimer, and Ohle on the linking between phosphorus (P) and iron (Fe) cycles seven decades ago created the theoretical basis for a long‐standing paradigm among limnologists i.e. , ‘oxygen controls the P release from sediments’. While many empirical studies as well as strong correlations between oxygen depletion and P release seem to support this paradigm, various field observations, laboratory experiments, and repeated failures of hypolimnetic oxygenation measures cast doubt on its universal validity. The temporal existence of a thin oxidized sediment surface‐layer could affect only fluctuations of the temporary P pool at the sediment surface but not the long‐term P retention. On longer time scales P release is the imbalance between P sedimentation and P binding capacity of anoxic sediment layers. The P retention of lake sediments strongly depends on sediment characteristics and land use of the catchment. The presence of redox‐insensitive P‐binding systems such as Al(OH) 3 and unreducible Fe(III) minerals can enhance the P retention and completely prevent P release even in case of anoxic conditions. Alternative release mechanisms such as a dissolution of calcium‐bound P and decomposition of organic P under both, aerobic and anaerobic conditions, are often more important than the redox driven Fe‐coupled P cycle. Additionally, bacteria affect P cycling not only by altering the redox conditions but also by releasing P during mineralization of organic matter and by accumulation and release of bacterial P. Since microbial processes consume oxygen and liberate P it is difficult to distinguish whether oxygen depletion is the result or the cause of P release. Nowadays, the old paradigm is discarded and a paradigm shift takes place. Sedimentary P exchange ought to be considered as a complex process which is mainly determined by the amount and species of settled P as well as their subsequent diagenetic transformation in the sediment. The classical paradigm is only valid in special cases since reality is much more complex than suggested by that paradigm.
Everything should be made simple as possible, but not simpler!
Albert Einstein (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Different tests have been made to determine some characteristics of the persulphate oxidation method for the simultaneous determination of total nitrogen and total phosphorus in water. A description of the method is outlined. Results of tests for calibration and capabilities, comparison with a former method using separate determinations, stability of stored samples and the oxidation reagent, as well as the influence of the time elapsed between sampling and cooking, are given. The new method has been used with good results for two years.
Lago Di Bolsena 2017-Lake Bolsena
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Structure and dynamics of pelagic zooplankton in Lake Bolsena, Bracciano and Vico (Central Italy)
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Lago di Bolsena: caratteristiche chimiche delle acque pelagiche
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Ground water budget of the Vulsini basin
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Observaciones paleolimnológicas en un lago italiano de origen volcánico (Lago Bolsena. Italia central)
- Massaferro