Temperate Freshwater Lakes Research Articles

Beyond Phosphorus: Salinization as a driver of eutrophication symptoms in North American lakes

The acceleration of global urbanization continues to fuel concerns surrounding water quality impairments in urban lakes, particularly eutrophication. Eutrophication of freshwater environments is generally assumed to be driven by increased anthropogenic phosphorus (P) supplies which can alleviate limitations on primary production. Salinization is also recognized as a stressor on urban freshwater quality, particularly in cold temperate climate regions where salts are applied to road surfaces as de-icing agents. While the ecological damages caused by P enrichment and salinization to freshwaters are both well established, thus far, their impacts on water quality have only been considered independently. Although improvements to the management of urban stormwater and wastewater have decreased P inputs to freshwater systems in recent decades, many lakes worldwide remain eutrophic, as indicated by declining dissolved oxygen (DO) concentrations and rising dissolved inorganic P (DIP) concentrations in the hypolimnion. Our previous study of an urban freshwater lake in Ontario, Canada, showed that persistent eutrophication symptoms are linked to salinization associated with impervious land cover expansion, rather than increased external P loading. In this research, we present a multiple decade of water chemistry data analyses for several other urban lakes in Ontario, Wisconsin, and Minnesota to determine how increased lake salinization rates intersect with water temperature and morphometry to alter water column stratification, thus, increasing eutrophication symptoms. Our trend analysis shows progressive salinization (observed through significant increases in chloride or electrical conductivity) of all the lakes investigated. Calculations of lakes mixing indices over time show that, on average, lake stratification is becoming more stable with increased salinity playing a crucial role in enhancing lake stratification. Overall, salinity is becoming a stronger regulator of water density than temperature in the cold temperate urban freshwater lakes of North America. The increasing salinity trends are accompanied by increasing hypolimnion hypoxia and increasing DIP to total P (TP) ratios in all lakes, thereby demonstrating the mechanistic link between salinization and internal P loading. Rising salinity intensifies water column stratification, in turn, reducing the oxygenation of the hypolimnion and enhancing internal P loading from the sediments. These results highlight that stricter management of de-icing salt application rates should be considered to control lake eutrophication symptoms in cold climate regions.

Methane Production in a Temperate Freshwater Lake during an Intense Cyanobacterial Bloom

Methane Production in a Temperate Freshwater Lake during an Intense Cyanobacterial Bloom

Methane Production in a Temperate Freshwater Lake during an Intense Cyanobacterial Bloom

Abstract—Seasonal cyanobacterial blooms have a negative impact on freshwater ecosystems. The role of cyanobacteria in methane production and their relationship with methanogenic archaea are not yet well understood. The goal of the present work was to identify the features of methanogenesis in the water column and sediments of a profoundal part of the freshwater Lake Senezh (Moscow oblast) during a period of cyanobacteria over-bloom. Analytical, radiotracer, microscopic, molecular biological, and incubation techniques were used. Alkalization and oxygen oversaturation of the 0–2-m water layer were caused by intensive photosynthesis. The near-bottom water (4 m) was pH-neutral and hypoxic; the sediments were reduced. Methane was detected throughout the water column; its concentration in the surface water was an order of magnitude lower than in the near-bottom water and 4 orders of magnitude lower than in the sediments. Cyanobacteria of the species Microcystis aeruginosa predominated in the photic zone (up to 30% of the total number of the 16S rRNA gene fragments). The sequences of cyanobacteria and freshwater members of the SAR11 clade, which can potentially be involved in aerobic methanogenesis via decomposition of methylphosphonates (MPn), were also detected. The sequences of hydrogenotrophic methanogens of the genus Methanoregula, which are potentially capable of methanogenesis in cooperation with cyanobacteria, were revealed in oxygen-supersaturated water. Hydrogenotrophic and aceticlastic pathways of methanogenesis predominated in reduced sediments. Sequences of methanogens of to the orders Methanomicrobiales, Methanobacteriales, Methanosarciniales, and Methanomassiliicoccales were detected there. Cyanobacterial bloom promoted methanogenesis both in the photic zone of Lake Senezh (due to MPn decomposition and anaerobic methanogenesis in association with cyanobacterial aggregates) and in the near-bottom water and sediments (due to oxygen depletion and excessive release of substrates caused by sedimentation and degradation of cyanobacterial mortmass).

Water Chestnut (Trapa natans L.): Functional characteristics, nutritional properties and applications in food industry: A review

An annual floating-leaved aquatic plant, the water chestnut (Trapa natans L.), is found in temperate and tropical freshwater wetlands, rivers, lakes, ponds, and estuaries. Hydrophytes that produce starch called water chestnut has the potential to serve as a reliable food supply, particularly in flood-prone wasteland areas. It is loaded with minerals and essential nutrients. Water chestnuts are not actually nuts, despite their name. They are aquatic tuber vegetables that may be found in shallow lakes, paddy fields, marshes, and ponds. Water chestnuts are indigenous to numerous islands in the Indian and Pacific oceans, as well as Southeast Asia, Southern China, Taiwan, Australia, and Africa. When the corm, or bulb, acquires a dark brown hue, they are picked. They are a typical ingredient in Asian recipes including stir-fries, chop suey, curries, and salads because of their crisp, white meat, which may be eaten raw or cooked. The huge, nourishing seed of the water chestnut, a native of Eurasia and Africa, has been widely collected since the Neolithic, and it is now grown for food throughout Asia. Water chestnuts have several advantages over other foods, including being particularly nutrient-dense and low in calories. A wonderful source of fibre, water chestnuts may aid in promoting bowel movements, lowering blood cholesterol, neuro-protective, controlling blood sugar levels, and maintaining the health of your gut. In addition, carbohydrates account for the majority of the calories in water chestnuts. Although they are abundant in fibre, potassium, manganese, copper, vitamin B6, and riboflavin, uncooked water chestnuts are 74% water, which means they are often low in calories. Due to its usage in the treatment of gastrointestinal illnesses, genitourinary system disorders, liver, kidney, and spleen disorders, Trapa natans is one of the most significant medicinal plants in Indian Ayurveda.

Methane Cycle in a Littoral Site of a Temperate Freshwater Lake

Methane Cycle in a Littoral Site of a Temperate Freshwater Lake

Long‐term phytoplankton community dynamics in Lake Stechlin (north‐east Germany) under sudden and heavily accelerating eutrophication

Abstract Climate warming and legacy phosphorus (P) in sediments are two main factors counteracting current efforts to prevent eutrophication of temperate freshwater lakes and reservoirs. Climate warming impacts lacustrine thermal regimes, accelerates harmful cyanobacterial growth, and increases the probability of periodic anoxic bottom conditions. Legacy P in sediments becomes influential over eutrophication because of its reactivation under anoxic conditions. Lake Stechlin is a deep glacial lake of the Baltic Lake area, Germany in which artificial external P loading has been effectively blocked for more than 3 decades. The lakes trophic status was oligotrophic, until roughly 2 decades ago when it accelerated toward higher trophic levels. Here we analyse the temporal dynamics of Lake Stechlin phytoplankton biomass and composition in relation to chemical and hydrological covariates, based on monitoring data from 1994 to 2019 at sampling frequency of c. 27 samples per year. Our results show an assemblage change toward cyanobacterial dominance that took place at several temporal scales. Intra‐annual compositional change became more pronounced over the study period, mainly because of changes during the autumn and winter seasons. Results from a structural break point analysis of the phytoplankton time series with covariates, and from a hierarchical cluster analysis show that major changes occurred in 2007–2011. An analysis of early warning indicators did not unambiguously support this period as a critical transition. The change rather occurred as a rapid succession of major events during these years. Results from convergent cross‐mapping causality tests are consistent with the hypothesis that increasing relative water column stability may drive eutrophication, and additionally, that the intra‐annual timing of the biomass change plays an important role in the lakes P loading. Although quantitative data on internal P loading are unavailable, internal P mobilisation from sediments appears to be the most plausible mechanism behind the increased phytoplankton biomass. Lake Stechlin, therefore, is an example of the challenges that legacy P poses to the management of freshwater ecosystems in the context of climate warming, even when external P sources are effectively blocked, and local protective measures are in place.

The influence of macrophyte ecological groups on food web components of temperate freshwater lakes

Aquatic macrophyte taxonomic composition, species abundance and cover determine the physical structure, complexity and heterogeneity of aquatic habitats – the structuring role of macrophytes. These traits influence richness, distribution, feeding and strength of the relationships between food web communities in lakes. The aim of this study was to determine how lakes with different dominating macrophyte ecological groups affect planktonic food web components, emphasising the influence on young of year (YOY) fish and large (≥1 +) fish community. We hypothesised that different dominating macrophyte ecological groups have different structural effects on food web components and YOY fish growth, abundance and feeding. Studied lakes categorised into three different macrophyte ecological groups – lakes dominated by emergent, floating+floating-leaved or submerged vegetation. We found that all dominating ecological groups had a strong influence on plankton communities (except heterotrophic bacterioplankton and nanoflagellates), YOY fish and large fish. Floating-leaved plant dominance was positively related to planktonic food web structure and YOY fish weight, length, abundance and the consumption of zooplankton as a prey of all major species of YOY fishes. Larger fish tended to favour the presence of emergent vegetation. This conclusion has important implications for local managers and conservationists in respect to the maintenance and protection of littoral habitats and fish resources.

Does bait type and bait container configuration influence the performance of remote underwater video systems in temperate freshwater lakes for assessing fish community structure?

Does bait type and bait container configuration influence the performance of remote underwater video systems in temperate freshwater lakes for assessing fish community structure?

Top-Down Controls of Bacterial Metabolism: A Case Study from a Temperate Freshwater Lake Ecosystem.

In freshwater environments, limited data exist on the impact of mortality forces (viruses and heterotrophic nanoflagellates) on bacterial growth efficiency (BGE, index of bacterial carbon metabolism) compared to resource availability. An investigation to determine the relative influence of viral lysis and flagellate predation (top-down forces) on BGE was conducted in a mesotrophic freshwater system (Lake Goule, France) with time and space. Viral abundance was significantly (p < 0.001) related to bacterial abundance by a power law function with an exponent less than 1, emphasizing that the increases in host population (bacteria) together with viruses were not proportionate. A lytic viral strategy was evident throughout the study period, with high lysis of the bacterial population (up to 60%) supported by viral production rates. Viral processes (lysis and production) that were influenced by bacterial production and heterotrophic nanoflagellate abundance had a positive impact on BGE. Estimates of BGE were variable (9.9–45.5%) due to uncoupling between two metabolic parameters—namely bacterial production and respiration. The existence of a synergistic relationship between viruses and flagellates with bacteria in Lake Goule highlighted the decisive impact of top-down agents in sustaining the bacterial carbon metabolism of non-infected population through the nature of vital resources released via mortality processes.

Enhancing ecological integrity while preserving ecosystem services: Constructing soft‐sediment islands in a shallow lake

Abstract Ecosystems are increasingly managed to provide multiple benefits to humans, which often degrades their ecological integrity. This strongly applies to aquatic ecosystems, in which engineering can enhance flood protection, drinking water supply, fisheries and recreation. Although these activities typically increase ecosystem functionality to humans, they often impair key aspects of biodiversity and natural functioning. Classical restoration of such degrading freshwater ecosystems can lead to societal opposition, if returning to a former ecosystem state affects previously acquired ecosystem services. Innovative nature‐based solutions are therefore needed that enhance natural values in ecosystems, without affecting existing services. We present a large‐scale project aiming to increase the ecological integrity of a human‐modified freshwater lake while maintaining its services to humans. The freshwater lake Markermeer in the Netherlands was formed by closing off an estuary for flood protection. The ecological integrity of this lake diminished over time, likely because a declining primary productivity impaired biodiversity at higher trophic levels. This decline is associated with a lack of gradual land–water transitions, strong resuspension of fine sediments, low nutrient availability and lack of dynamics typically to be expected in a natural temperate freshwater lake. Restoring the lake to its former marine state would conflict with current ecosystem services. A nature‐based solution was initiated in 2016, consisting of constructing a five‐island archipelago from the lake's own soft‐sediments called the ‘Marker Wadden’. The project aims to increase the lake's primary production by creating gradual land–water transitions, more heterogeneity in water depths and decreasing turbidity by creating shelter and deep sinks reducing fine‐sediment resuspension by the wind – thus introducing currently missing elements that are typical for natural lakes. We present the underlying ecological framework and first scientific results of this innovative ongoing project. Within 4 years, the Marker Wadden project shows how forward‐looking sustainable development of lake ecosystems using a rewilding approach can enhance natural processes and attract birds and fish, without conflicting with existing ecosystem services. This inspires new directions for halting and reversing the degradation of other vital ecosystems worldwide.

EDNA metabarcoding outperforms traditional fisheries sampling and reveals fine‐scale heterogeneity in a temperate freshwater lake

AbstractUnderstanding biodiversity in aquatic systems is critical to ecological research and conservation efforts, but accurately measuring species richness using traditional methods can be challenging. Environmental DNA (eDNA) metabarcoding, which uses high‐throughput sequencing and universal primers to amplify DNA from multiple species present in an environmental sample, has shown great promise for augmenting results from traditional sampling to characterize fish communities in aquatic systems. Few studies, however, have compared exhaustive traditional sampling with eDNA metabarcoding of corresponding water samples at a small spatial scale. We intensively sampled Boardman Lake (1.4 km2) in Michigan, USA, from May to June in 2019 using gill and fyke nets and paired each net set with lake water samples collected in triplicate. We analyzed water samples using eDNA metabarcoding with 12S and 16S fish‐specific primers and compared estimates of fish diversity among methods. In total, we set 60 nets and analyzed 180 1 L lake water samples. We captured a total of 12 fish species in our traditional gear and detected 40 taxa in the eDNA water samples, which included all the species observed in nets. The 12S and 16S assays detected a comparable number of taxa, but taxonomic resolution varied between the two genes. In our traditional gear, there was a clear difference in the species selectivity between the two net types, and there were several species commonly detected in the eDNA samples that were not captured in nets. Finally, we detected spatial heterogeneity in fish community composition across relatively small scales in Boardman Lake with eDNA metabarcoding, but not with traditional sampling. Our results demonstrated that eDNA metabarcoding was substantially more efficient than traditional gear for estimating community composition, highlighting the utility of eDNA metabarcoding for assessing species diversity and informing management and conservation.

Common Presence of Phototrophic Gemmatimonadota in Temperate Freshwater Lakes.

ABSTRACTMembers of the bacterial phylum Gemmatimonadota are ubiquitous in most natural environments and represent one of the top 10 most abundant bacterial phyla in soil. Sequences affiliated with Gemmatimonadota were also reported from diverse aquatic habitats; however, it remains unknown whether they are native organisms or represent bacteria passively transported from sediment or soil. To address this question, we analyzed metagenomes constructed from five freshwater lakes in central Europe. Based on the 16S rRNA gene frequency, Gemmatimonadota represented from 0.02 to 0.6% of all bacteria in the epilimnion and between 0.1 and 1% in the hypolimnion. These proportions were independently confirmed using catalyzed reporter deposition-fluorescence in situ hybridization (CARD-FISH). Some cells in the epilimnion were attached to diatoms (Fragilaria sp.) or cyanobacteria (Microcystis sp.), which suggests a close association with phytoplankton. In addition, we reconstructed 45 metagenome-assembled genomes (MAGs) related to Gemmatimonadota. They represent several novel lineages, which persist in the studied lakes during the seasons. Three lineages contained photosynthesis gene clusters. One of these lineages was related to Gemmatimonas phototrophica and represented the majority of Gemmatimonadota retrieved from the lakes’ epilimnion. The other two lineages came from hypolimnion and probably represented novel photoheterotrophic genera. None of these phototrophic MAGs contained genes for carbon fixation. Since most of the identified MAGs were present during the whole year and cells associated with phytoplankton were observed, we conclude that they represent truly limnic Gemmatimonadota distinct from the previously described species isolated from soils or sediments.IMPORTANCE Photoheterotrophic bacterial phyla such as Gemmatimonadota are key components of many natural environments. Its first photoheterotrophic cultured member, Gemmatimonas phototrophica, was isolated in 2014 from a shallow lake in the Gobi Desert. It contains a unique type of photosynthetic complex encoded by a set of genes which were likely received via horizontal transfer from Proteobacteria. We were intrigued to discover how widespread this group is in the natural environment. In the presented study, we analyzed 45 metagenome-assembled genomes (MAGs) that were obtained from five freshwater lakes in Switzerland and Czechia. Interestingly, it was found that phototrophic Gemmatimonadota are relatively common in euphotic zones of the studied lakes, whereas heterotrophic Gemmatimonadota prevail in deeper waters. Moreover, our analysis of the MAGs documented that these freshwater species contain almost the same set of photosynthesis genes identified before in Gemmatimonas phototrophica originating from the Gobi Desert.

Microbial community and abiotic effects on aquatic bacterial communities in north temperate lakes

The aquatic bacterial community (BC) plays a vital role in determining the nature and rate of ecosystem function. However, the biotic and abiotic factors influencing BC structure and function are largely unknown. Hence, the current study characterizes the impact of biotic and abiotic factors on aquatic bacterial biodiversity to determine whether the dominant effects are biotic or abiotic by partitioning their relative effects across temperate Canadian lakes. We collected water samples from sixty southern Ontario lakes and characterized their BC and microbial eukaryotic community (MEC) compositions using high throughput metabarcode sequencing of 16S and 18S rRNA gene fragments. The diversity and richness of aquatic BCs differed considerably among our study lakes, and those differences were explained by environmental, spatial, and biotic (MEC) factors (31%, 23%, and 23% of variance explained, respectively). The relatively large contribution from biotic and abiotic factors (54%), relative to spatial effects, shows deterministic processes prevail in shaping BC assembly in freshwater lakes. However, spatial effects also contributed significantly, highlighting the role of stochastic processes (ecological drift and coupled with limited dispersal) in shaping BC structure. Furthermore, our co-occurrence network analysis showed strong positive and negative interactions within and between the BCs and MECs, indicating mutualistic or antagonistic co-occurrence patterns relationships play important roles in driving the variation in BC composition among our sampled lakes. Considered together, our community analyses show that deterministic and stochastic processes combined contribute to determining the aquatic BC composition, and hence likely function as well, across a broad array of temperate freshwater lakes.

Environmental Risks from Pollution and Climate Change: An Updated Review

Climate change expected for the next century could occur in an ecosystem already stressed by UV-B amplification, air pollution, and rising nutrient fluxes. We investigated the relationships among these many environmental challenges by focusing on specific habitats, temperate zone forests, freshwater lakes, and estuaries. The increase in oxidant levels across the lower atmosphere and hydrosphere is a significant chemical consequence of atmospheric change. These changes may result in net nutrient transfer from land to coastal ocean, resulting in forest degradation and coastal eutrophication. Local adjustments may already be occurring, but the synergistic nature of the pressures threatens to speed up the process over the next few decades. Aside from any direct effects of climate change, the worsening of current environmental problems is a significant indirect effect.

Drivers of variability in mercury and methylmercury bioaccumulation and biomagnification in temperate freshwater lakes

The four largest freshwater lakes in southwestern France are of both ecological and economic importance. However, some of them are subjected to mercury (Hg) contamination, resulting in the ban of human consumption of piscivorous fish. Moreover, beyond predatory fish, little information exist regarding Hg levels in other species of these ecosystems. In this context, we used a food web analytical approach to investigate Hg bioaccumulation and biomagnification in relation to the trophic structure of these four lakes. More specifically, various organisms (macrophytes, epiphyton, invertebrates and fish) were collected at the four lakes and analysed for carbon and nitrogen stable isotopes as well as for total Hg (THg) and methylmercury (MeHg). A spatial variability of bioaccumulation in organisms was observed, particularly in carnivorous fish, with higher Hg levels being found in the two more northern lakes (median±SE: 3491 ± 474 and 1113 ± 209 ng THg.g−1 dw in lakes HC and L, respectively) than in the southern pair (600 ± 117 and 911 ± 117 ng THg.g−1 dw in lakes CS and PB, respectively). Methylmercury biomagnification was observed through the food webs of all four lakes, with different trophic magnification slopes (HC = 0.16; L = 0.33; CS = 0.27; PB = 0.27), even though the length of the food chains was similar between the lakes. Our results suggest that rather than the food web structure, anthropogenic inputs (sulfate in northern lakes and phosphorus inputs in southern ones) may have a strong impact, more or less directly, on Hg methylation in freshwater environments, and lead to concentrations exceeding environmental recommendations despite low Hg backgrounds in sediment and water.

Variation in phytoplankton pigment composition in relation to mixing conditions in temperate South-Central Chilean lakes

Thermal lake properties are sensitive to changes in windiness and precipitation, and affect the physical and chemical properties of the water column, which in turn control phytoplankton dynamics and primary production. We assessed the use of phytoplankton pigment profiling as a potential indicator of stratification conditions in temperate lakes in South-Central Chile. Spring and early summer phytoplankton pigment profiles and the physical and chemical limnology were analyzed in 43 lakes ranging in size, depth, altitude and catchment characteristics. Eleven lakes were sampled during both seasons. Variation in pigment composition between lakes was primarily related to stratification conditions and mixed layer light availability at the time of sampling. The dinoflagellate marker pigment peridinin was more abundant in more deeply mixed lakes with a lower mean irradiance, while chlorophyte pigments (chlorophyll b, lutein) tended to be higher in shallow (high-light) epilimnia. Diatom and chrysophyte pigments (fucoxanthin) dominated under less thermally stable and more variable light conditions. Cyanobacteria pigments (zeaxanthin), probably derived from picocyanobacteria, were relatively more abundant in very transparent, low productive lakes. Lakes in close vicinity of active volcanoes were enriched in silica and PO4-P and characterised by elevated chlorophyte marker pigments. Within strongly stratified lakes, in which the euphotic zone extended into the hypolimnion, cryptophyte pigments (alloxanthin) characterized the deep chlorophyll maxima while the epilimnion was consistently enriched with the photoprotective xanthophyll-cycle pigment violaxanthin. We conclude that major algal groups, represented by pigment biomarkers, are largely driven by changes in lake water column stratification and related mixed layer light availability as well as nutrient concentrations in temperate Chilean freshwater lakes.

Diluting a salty soup: Impact of long-lasting salt pollution on a deep Alpine lake (Traunsee, Austria) and the downside of recent recovery from salinization

Saline emissions can elevate water densities and have the potential to alter stratification and mixing dynamics in lakes. In the light of rising anthropogenic salinization of temperate freshwater lakes, it is highly relevant to understand how saline emissions, as well as the rehabilitation from salt pollution might affect lake circulation patterns. In this study, we present the impact of industrial pollution with chloride salts on the deep Alpine lake Traunsee in Austria from 1930 to 2005 and the observed limnological changes during the recovery from salinization in the following 12 years. We assembled and analysed a unique dataset of monthly sampling profiles covering chloride, conductivity, temperature and dissolved oxygen over a 87-year period. We quantified the impact of saline emissions on the lake’s total chloride content, water densities, stability indices and deepwater oxygen concentrations. Time-series of water density profiles and stability indices revealed a significant impact of salinization on seasonal stratification and mixing. Higher dilution and shallower release of saline wastes and the short water retention in Traunsee helped to prevent a long-lasting density stratification. Nevertheless, two periods of salt-induced meromixis occurred in the lake. The first was caused directly by the disposal of saline wastes into the deepwater in the 1930s and 1940s, whereas the second was induced by the recovery from salinization in recent years. The naturally faster wash-out of salts from shallower water layers reinforced the density gradient and impeded vertical water circulation after salt pollution ceased. The rehabilitation from salinization had a stronger effect on stratification intensity and deepwater oxygen concentration than the continuous salt pollution over the last century.

Pond bank access as an approach for managing toxic cyanobacteria in beef cattle pasture drinking water ponds.

Forty-one livestock drinking water ponds in Alabama beef cattle pastures during were surveyed during the late summer to generally understand water quality patterns in these important water resources. Since livestock drinking water ponds are prone to excess nutrients that typically lead to eutrophication, which can promote blooms of toxigenic phytoplankton such as cyanobacteria, we also assessed the threat of exposure to the hepatotoxin, microcystin. Eighty percent of the ponds studied contained measurable microcystin, while three of these ponds had concentrations above human drinking water thresholds set by the US Environmental Protection Agency (i.e., 0.3μg/L). Water quality patterns in the livestock drinking water ponds contrasted sharply with patterns typically observed for temperate freshwater lakes and reservoirs. Namely, we found several non-linear relationships between phytoplankton abundance (measured as chlorophyll) and nutrients or total suspended solids. Livestock had direct access to all the study ponds. Consequently, the proportion of inorganic suspended solids (e.g., sediment) increased with higher concentrations of total suspended solids, which underlies these patterns. Unimodal relationships were also observed between microcystin and phytoplankton abundance or nutrients. Euglenoids were abundant in the four ponds with chlorophyll concentrations > 250μg/L (and dominated three of these ponds), which could explain why ponds with high chlorophyll concentrations would have low microcystin concentrations. Based on observations made during sampling events and available water quality data, livestock-mediated bioturbation is causing elevated total suspended solids that lead to reduced phytoplankton abundance and microcystin despite high concentrations of nutrients, such as phosphorus and nitrogen. Thus, livestock could be used to manage algal blooms, including toxic secondary metabolites, in their drinking water ponds by allowing them to walk in the ponds to increase turbidity.

Taxonomical Resolution and Distribution of Bacterioplankton Along the Vertical Gradient Reveals Pronounced Spatiotemporal Patterns in Contrasted Temperate Freshwater Lakes.

We examined the relationship between viruses and co-occurring bacterial communities across spatiotemporal scale in two contrasting freshwater lakes, namely meromictic Lake Pavin and dimictic Lake Aydat (Central France). Next-generation sequencing of 16S rRNA genes suggested distinct patterns in bacterioplankton community composition (BCC) between the lakes over depths and seasons. BCC were generally dominated by members of Actinobacteria, Proteobacteria, and Bacteroidetes covering about 95% of all sequences. Oxygen depletion at the bottom waters in Aydat and existence of permanent anoxia in the monimolimnion of Pavin resulted in the occurrence and dominance of lesser known members of lake communities such as Methylotenera, Methylobacter, Gallionella, Sulfurimonas, and Syntrophus in Pavin and Methylotenera and Sulfuritalea in Aydat. Differences in BCC appeared strongly related to dissolved oxygen concentration, temperature, viral infection, and virus-to-bacteria ratio. UniFrac analysis indicated a clear distinction in BCC when the percentage of viral infected bacterial cells and virus-to-bacteria ratio exceeded a threshold level of 10% and 5, respectively, suggesting a link between viruses and their potential bacterial host communities. Our study revealed that in both the lakes, the prevailing environmental factors across time and space structured and influenced the adaptation of bacterial communities to specific ecological niches.

Extending Class A pan evaporation for a shallow lake to simulate the impact of littoral sediment and submerged macrophytes: a case study for Keszthely Bay (Lake Balaton, Hungary)

Class A pan evaporation rate, Ep with sediment cover (S) and submerged aquatic macrophytes (Ps) was analysed in a temperate freshwater shallow lake at Keszthely (Hungary), over three growing seasons between 2014 and 2016. The aim was to identify the importance of this water body’s natural components (S and Ps) on Ep. Measured Ep together with reference E of Shuttleworth (E0) and the FAO-56 equation ET were also derived. Pan coefficient, Ka for filled in pans with S and Ps were computed as the ratio of Ep of the planted pan (Ps/S) and Ep. Ka values determined on-site were tested in the estimation of E for an open water body, namely Keszthely Bay of Lake Balaton. Overall seasonal mean evaporation rate was lower for Ep (3.2 ± 1.05 mm day−1) than the seasonal daily average Ep of S (3.7 ± 1.16 mm day−1) and the Ep of Ps (4.0 ± 1.28 mm day−1). Interannual variation of Ep was controlled by variations in seasonal air temperature, Ta. Data of the wet 2014 season showed a significant suppression of Ep, and this was related to humid and cooler weather conditions causing late emergence and early senescence of the submerged macrophytes (Potamogeton perfoliatus L., Myriophyllum spicatum L. and Najas marina L.) at Keszthely Bay. Overall seasonal mean Ka was greater than 1.0 as determined for the three-season time period in pans with S and Ps (Kas: 1.14 ± 0.04; Kap: 1.20 ± 0.05). Except for a previous study from our group (Anda et al., 2016, J Hydrol 542: 615–626) over a two-season period, no such ratio or coefficients have been published, until now. The dominant component of the energy balance was latent heat flux, which accounted for more than 60% of net radiation in Keszthely Bay, depending on Class A pan filling (S and Ps). Diurnal variation in heat storage of the pan also changed due to the occurrence of sediment cover and macrophytes inside the evaporimeters. The most important daily meteorological variables were used to develop the Ep model and to validate S and Ps. Our results show that linear models, even with more input variables, performed better than tree-based models with respect to mean absolute errors (MAE), root mean square errors (RMSE) and determination coefficient (R2) in predicting daily Ep of S and Ps. The use of pan coefficients Kas and Kap increased seasonal E of Keszthely Bay by 4.2, 14.4 and 17.1% during the 2014–2016 seasons, respectively. Total seasonal increments for Keszthely Bay (surface area is about 39 km2) accounted for 0.97, 4.31 and 3.91 million m3 throughout 2014–2016, respectively. In the warmer seasons, an increasing trend in the growth of Keszthely Bay’s E was detected. These results indicate that Class A pan Ep rates need to be modified to take into account sediment cover and submerged macrophytes to derive open water E. This approximation may lend additional credit to the estimation of E in lakes. Given that appropriate estimation of E can effectively impact the management of an ecologically functional lake’s water, maintaining the proper water level and quality can contribute to the sustainability of lakes in the long run.