Climate-driven changes in energy and mass inputs systematically alter nutrient concentration and stoichiometry in deep and shallow regions of Lake Champlain

Concentrations of nitrogen (N) and phosphorus (P) in lakes may be differentially impacted by climate-driven changes in nutrient loading and by direct impacts of temperature and wind speed on internal nutrient cycling. Such changes may result in systematic shifts in lake N:P under future climate warming. We used 21 years of monitoring data to compare long-term and intra-annual trends in total N (TN), total P (TP) and TN:TP at 15 sites in Lake Champlain to concurrent measurements of watershed nutrient inputs and meteorological drivers. TN:TP declined sharply lake-wide, particularly in the past decade, yet the drivers of this trend varied based on site depth. In deep sites, declines were driven by changes in watershed loading of dissolved P and N and (in some cases) by decreases in hypolimnetic dissolved oxygen. In shallow sites, declines in TN:TP were primarily driven by long-term increases in temperature and decreases in wind speed, and exhibited systematic seasonal variability in TN:TP due to the timing of sediment P loading, N removal processes, and external nutrient inputs. We developed a conceptual model to explain the observed trends, and suggest that while climate drivers have affected nutrient dynamics in shallow and deep sites differently, both deep and shallow sites are likely to experience further declines in N:P and increases in cyanobacteria dominance if recent climate trends continue.     

Unexpected stasis in a changing world: Lake nutrient and chlorophyll trends since 1990

The United States (U.S.) has faced major environmental changes in recent decades, including agricultural intensification and urban expansion, as well as changes in atmospheric deposition and climate—all of which may influence eutrophication of freshwaters. However, it is unclear whether or how water quality in lakes across diverse ecological settings has responded to environmental change. We quantified water quality trends in 2913 lakes using nutrient and chlorophyll (Chl) observations from the Lake Multi‐Scaled Geospatial and Temporal Database of the Northeast U.S. (LAGOS‐NE), a collection of preexisting lake data mostly from state agencies. LAGOS‐NE was used to quantify whether lake water quality has changed from 1990 to 2013, and whether lake‐specific or regional geophysical factors were related to the observed changes. We modeled change through time using hierarchical linear models for total nitrogen (TN), total phosphorus (TP), stoichiometry (TN:TP), and Chl. Both the slopes (percent change per year) and intercepts (value in 1990) were allowed to vary by lake and region. Across all lakes, TN declined at a rate of 1.1% year^?1, while TP, TN:TP, and Chl did not change. A minority (7%–16%) of individual lakes had changing nutrients, stoichiometry, or Chl. Of those lakes that changed, we found differences in the geospatial variables that were most related to the observed change in the response variables. For example, TN and TN:TP trends were related to region‐level drivers associated with atmospheric deposition of N; TP trends were related to both lake and region‐level drivers associated with climate and land use; and Chl trends were found in regions with high air temperature at the beginning of the study period. We conclude that despite large environmental change and management efforts over recent decades, water quality of lakes in the Midwest and Northeast U.S. has not overwhelmingly degraded or improved.     

Possible effects of global climate change on the ecosystem of Lake Tanganyika

Any change in the air temperature, wind speed, precipitation, and incoming solar radiation induced by increasing greenhouse gasses and climate change will directly influence lakes and other water bodies. The influence can cause changes in the physical (water temperature, stratification, transparency), chemical (nutrient loading, oxygen) and biological (structure and functioning of the ecosystem) components of the Lake. In this work an influence of the likely effects of the climate change on the above three components of Lake Tanganyika are studied by means of a simple ecological model. Simulations for the years 2002–2009 have been performed using the wind and solar radiation data from the National Centres for Environmental Protection (NCEP) reanalysis. Various possible climatic scenarios are studied by changing the surface layer depth, its temperature and the wind stress. Any change in any of the above physical forcing parameters modifies the timing and intensity of the dry season peaks of the biogeochemical parameters. It is seen that the gross production increases as temperature of the surface layer increases and its depth decreases. High temperature and low wind stress, reduces the biomass. The effects of a slight increase in lake water temperature on the Lake Tanganyika ecosystem might be mitigated by increased windiness, if the latter was sufficient to induce greater mixing.     

Predicting cyanobacterial dynamics in the face of global change: the importance of scale and environmental context

There is growing concern that harmful cyanobacterial blooms are increasing in frequency and occurrence around the world. Although nutrient enrichment is commonly identified as a key predictor of cyanobacterial abundance and dominance in freshwaters, several studies have shown that variables related to climate change can also play an important role. Based on our analysis of the literature, we hypothesized that temperature or water‐column stability will be the primary drivers of cyanobacterial abundance in stratified lakes whereas nutrients will be the stronger predictors in frequently mixing water bodies. To test this hypothesis, as well as quantify the drivers of cyanobacteria over different scales and identify interactions between nutrients and climate‐related variables, we applied linear and nonlinear mixed‐effect modeling techniques to seasonal time‐series data from multiple lakes. We first compared time series of cyanobacterial dominance to a published lake survey and found that the models were similar. Using time‐series data of cyanobacterial biomass, we identified important interactions among nutrients and climate‐related variables; dimictic basin experienced a heightened susceptibility to cyanobacterial blooms under stratified eutrophic conditions, whereas polymictic basins were less sensitive to changes in temperature or stratification. Overall, our results show that due to predictable interactions among nutrients and temperature, polymictic and dimictic lakes are expected to respond differently to future climate warming and eutrophication.     

Summer heatwaves promote blooms of harmful cyanobacteria

Dense surface blooms of toxic cyanobacteria in eutrophic lakes may lead to mass mortalities of fish and birds, and provide a serious health threat for cattle, pets, and humans. It has been argued that global warming may increase the incidence of harmful algal blooms. Here, we report on a lake experiment where intermittent artificial mixing failed to control blooms of the harmful cyanobacterium Microcystis during the summer of 2003, one of the hottest summers ever recorded in Europe. To understand this failure, we develop a coupled biological–physical model investigating how competition for light between buoyant cyanobacteria, diatoms, and green algae in eutrophic lakes is affected by the meteorological conditions of this extreme summer heatwave. The model consists of a phytoplankton competition model coupled to a one-dimensional hydrodynamic model, driven by meteorological data. The model predicts that high temperatures favour cyanobacteria directly, through increased growth rates. Moreover, high temperatures also increase the stability of the water column, thereby reducing vertical turbulent mixing, which shifts the competitive balance in favour of buoyant cyanobacteria. Through these direct and indirect temperature effects, in combination with reduced wind speed and reduced cloudiness, summer heatwaves boost the development of harmful cyanobacterial blooms. These findings warn that climate change is likely to yield an increased threat of harmful cyanobacteria in eutrophic freshwater ecosystems.     

Regional versus local drivers of water quality in the Windermere catchment,Lake District,United Kingdom: The dominant influence of wastewater pollution over the past 200 years

Freshwater ecosystems are threatened by multiple anthropogenic stressors acting over different spatial and temporal scales, resulting in toxic algal blooms, reduced water quality and hypoxia. However, while catchment characteristics act as a ‘filter’ modifying lake response to disturbance, little is known of the relative importance of different drivers and possible differentiation in the response of upland remote lakes in comparison to lowland, impacted lakes. Moreover, many studies have focussed on single lakes rather than looking at responses across a set of individual, yet connected lake basins. Here we used sedimentary algal pigments as an index of changes in primary producer assemblages over the last ~200 years in a northern temperate watershed consisting of 11 upland and lowland lakes within the Lake District, United Kingdom, to test our hypotheses about landscape drivers. Specifically, we expected that the magnitude of change in phototrophic assemblages would be greatest in lowland rather than upland lakes due to more intensive human activities in the watersheds of the former (agriculture, urbanization). Regional parameters, such as climate dynamics, would be the predominant factors regulating lake primary producers in remote upland lakes and thus, synchronize the dynamic of primary producer assemblages in these basins. We found broad support for the hypotheses pertaining to lowland sites as wastewater treatment was the main predictor of changes to primary producer assemblages in lowland lakes. In contrast, upland headwaters responded weakly to variation in atmospheric temperature, and dynamics in primary producers across upland lakes were asynchronous. Collectively, these findings show that nutrient inputs from point sources overwhelm climatic controls of algae and nuisance cyanobacteria, but highlights that large‐scale stressors do not always initiate coherent regional lake response. Furthermore, a lake's position in its landscape, its connectivity and proximity to point nutrients are important determinants of changes in production and composition of phototrophic assemblages.     

Biological responses to permafrost thaw slumping in Canadian Arctic lakes

1. Rapid environmental change occurring in high‐latitude regions has the potential to cause extensive thawing of permafrost. Retrogressive thaw slumps are a particularly spectacular form of permafrost degradation that can significantly impact lake–water chemistry; however, to date, the effects on aquatic biota have received little attention. 2. We used a diatom‐based palaeolimnological approach featuring a paired lake study design to examine the impact of thaw slumping on freshwater ecosystems in the low Arctic of western Canada. We compared biological responses in six lakes affected by permafrost degradation with six undisturbed, reference lakes. 3. Slump‐affected lakes exhibited greater biological change than the paired reference systems, although all systems have undergone ecologically significant changes over the last 200 years. Four of the six reference systems showed an increase in the relative abundance of planktonic algal taxa (diatoms and scaled chrysophytes), the earliest beginning about 1900, consistent with increased temperature trends in this region. 4. The response of sedimentary diatoms to thaw slumping was understandably variable, but primarily related to the intensity of disturbance and associated changes in aquatic habitat. Five of the slump‐affected lakes recorded increases in the abundance and diversity of periphytic diatoms at the presumed time of slump initiation, consistent with increased water clarity and subsequent development of aquatic macrophyte communities. Slump‐affected lakes generally displayed lower nutrient levels; however, in one system, thaw slumping, induced by an intense fire at the site in 1968, ostensibly led to pronounced nutrient enrichment that persists today. 5. Our results demonstrate that retrogressive thaw slumping represents an important stressor to the biological communities of lakes in the western Canadian Arctic and can result in a number of limnological changes. We also show that palaeolimnological methods are effective for inferring the timing and response of aquatic ecosystems to permafrost degradation. These findings provide the first long‐term perspective on the biological response to permafrost thaw, a stressor that will become increasingly important as northern landscapes respond to climate change.     

Climate drivers of diatom distribution in shallow subarctic lakes

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Rates of change in physical and chemical lake variables – are they comparable between large and small lakes?

Changes over time in 16 physical and chemical variables were analysed and compared between Sweden’s largest lakes, Vättern and Vänern, and 48 smaller Swedish reference lakes during spring over the period 1984–2003. The rates of changes varied substantially among lakes and among variables, and they were clearly influenced by changes in both climate and atmospheric deposition. Rates of change of variables associated with atmospheric deposition such as sulphate concentrations were dependent on lake morphometry. This also applied to the rates of change of variables associated with climate change effects in the catchment such as calcium and magnesium concentrations. However, climate change effects could also be comparable between large and small lakes. Rates of change in physical and chemical variables directly influenced by the climate via the lake water surface, e.g., surface water temperature, and variables associated with the spring phytoplankton development such as phosphate–phosphorus and nitrate–nitrogen concentrations, were similar and therefore independent of lake morphometry. This study shows that climate change effects that act via the lake surface can be of the same order of magnitude among large and small lakes, but climate change effects that act via the catchment differ substantially in large lakes. It is essential to differentiate between these two types of climate effects in order to assess the impacts of climate change and the adaptation and vulnerability of lake ecosystems.     

Modelling lake cyanobacterial blooms: Disentangling the climate‐driven impacts of changing mixed depth and water temperature

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Spatiotemporal water dynamic modelling of Ramsar-listed lakes on the Victorian Volcanic Plains using Landsat,ICESat-2 and airborne LiDAR data

Spatiotemporal dynamic information on surface water area and level is a prerequisite for effective wetland conservation and management. However, such information is either unavailable or difficult to obtain. In this study, for the first time, we leverage Landsat imagery, ICESat-2 and airborne LiDAR data to develop time series of water body dynamics over the last 35 years (1987–2021) using machine learning method on a cloud computing platform for lakes identified as international importance in the Western District Lakes Ramsar site in Victoria, Australia. Our results reveal distinct seasonal (dry and wet) variation patterns and long-term changes in trends of lake water areas and levels in response to seasonal rainfall variations and regional climate changes for the periods of before, during and after the Millennium Drought when southeast Australia experienced unprecedented dry conditions. Lake water bodies have not recovered to the status of pre-Millennium Drought, and many permanent Ramsar-listed lakes in the region have become to ephemeral lakes due to climate change. The outcome of this study provides a baseline to help understand the historical and ongoing status of the Ramsar-listed lakes in a warming and drying climate in support of the development of strategic plan to implement international obligations for wetlands protection under the Ramsar Convention.     

The Environmental Control of Near-Surface Thermoclines in Boreal Lakes

We report on the effect of lake size, water transparency, and wind on the frequency of transient near-surface thermoclines in 39 boreal lakes from the Experimental Lakes Area (ELA) and Northwest Ontario Lake Size Series (NOLSS). This study was based on more than 3000 archived temperature profiles amassed over a 25-year period for lakes ranging from 2 ha to 8 million ha in surface area. The incidence of transient thermoclines decreased with increasing lake size from 90% of all summer days in small lakes (less than 4 ha) to 40% or less in the larger NOLSS lakes (up to 34,700 ha). No transient near-surface thermoclines were detected in Lake Superior. Forest fires and climatic variability were also found to affect the frequency of near-surface thermoclines. Long-term trends indicate an increase in average annual wind velocity in the area, possibly as the result of extensive forest fires and clearcutting. The subsequent decrease in the frequency of shallow secondary thermoclines in aquatic ecosystems has possible consequences for the lake biota, as the result of changes in radiation, turbulence, and the nutrient regime. Received 8 November 2000; accepted 30 April 2001.     

Increased nutrient loading and rapid changes in phytoplankton expected with climate change in stratified South European lakes: sensitivity of lakes with different trophic state and catchment properties

We hypothesised that increasing winter affluence and summer temperatures, anticipated in southern Europe with climate change, will deteriorate the ecological status of lakes, especially in those with shorter retention time. We tested these hypotheses analysing weekly phytoplankton and chemistry data collected over 2 years of contrasting weather from two adjacent stratified lakes in North Italy, differing from each other by trophic state and water retention time. Dissolved oxygen concentrations were higher in colder hypolimnia of both lakes in the second year following the cold winter, despite the second summer was warmer and the lakes more strongly stratified. Higher loading during the rainy winter and spring increased nutrient (N, P, Si) concentrations, and a phytoplankton based trophic state index, whilst the N/P ratio decreased in both lakes. The weakened Si limitation in the second year enabled an increase of diatom biovolumes in spring in both lakes. Chlorophyll a concentration increased in the oligo-mesotrophic lake, but dropped markedly in the eutrophic lake where the series of commonly occurring cyanobacteria blooms was interrupted. The projected increase of winter precipitation in southern Europe is likely to increase the nutrient loadings to lakes and contribute to their eutrophication. The impact is proportional to the runoff/in-lake concentration ratio of nutrients rather than to the retention time, and is more pronounced in lakes with lower trophy.     

The impacts of changing nutrient load and climate on a deep,eutrophic, monomictic lake

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湖南省大通湖百余年环境演化历史及营养物基准的建立

科学有效地治理退化湖泊需要知晓湖泊的演化历史,并设立合理的参照目标(即环境基准)来及时评判治理效果.湖南省大通湖位于经济发达的长江中下游地区,发挥着重要的湖泊水生态系统服务功能.在强烈的人类活动干扰下,该湖近年来生态系统退化严重,但其水环境演变的历史缺少详细的记录.研究对大通湖沉积钻孔的年代、烧失量、化学元素、沉积物总...     

From clear lakes to murky waters – tracing the functional response of high‐latitude lake communities to concurrent ‘greening’ and ‘browning’

Climate change and the intensification of land use practices are causing widespread eutrophication of subarctic lakes. The implications of this rapid change for lake ecosystem function remain poorly understood. To assess how freshwater communities respond to such profound changes in their habitat and resource availability, we conducted a space‐for‐time analysis of food‐web structure in 30 lakes situated across a temperature‐productivity gradient equivalent to the predicted future climate of subarctic Europe (temperature +3°C, precipitation +30% and nutrient +45 μg L^?1 total phosphorus). Along this gradient, we observed an increase in the assimilation of pelagic‐derived carbon from 25 to 75% throughout primary, secondary and tertiary consumers. This shift was overwhelmingly driven by the consumption of pelagic detritus by benthic primary consumers and was not accompanied by increased pelagic foraging by higher trophic level consumers. Our data also revealed a convergence of the carbon isotope ratios of pelagic and benthic food web endmembers in the warmest, most productive lakes indicating that the incorporation of terrestrial derived carbon into aquatic food webs increases as land use intensifies. These results, reflecting changes along a gradient characteristic of the predicted future environment throughout the subarctic, indicate that climate and land use driven eutrophication and browning are radically altering the function and fuelling of aquatic food webs in this biome.     

The Landscape–Atmosphere Continuum Determines Ecological Change in Alpine Lakes of SE Tibet

Remote alpine regions were considered to be largely unimpacted by anthropogenic disturbance, but it is now clear these areas are changing rapidly. It is often difficult to identify the causal processes underpinning ecological change because the main drivers (direct and indirect climate forcing, land use change and atmospheric deposition) are acting simultaneously. In addition, alpine landscapes are morphometrically complex with strong local environmental gradients creating natural heterogeneity which acts as a variable filter to climate and anthropogenic forcing, emphasizing the need for analyzing responses at multiple sites. The eastern margin of Tibet is a hotspot of global biodiversity and is affected by both atmospheric N and dust deposition, whereas regional climate warming is comparatively recent. Here we use ²¹⁰Pb and ¹³⁷Cs dated sediment records from nine alpine lakes, and statistical measures of diatom ecological change (turnover and PCA axis 1 scores) to determine regional scale patterns in community response to global environmental change forcing over approximately the last 150 years. The study lakes showed contrasting ecological responses with increased nutrient input as the primary driver of change, mediated by lake morphology and catchment characteristics. Turnover rates of diatom composition, although low, are significantly associated with lake volume, lake area, altitude and DOC.     

Drought-induced changes in nutrient concentrations and retention in two shallow Mediterranean lakes subjected to different degrees of management

While extensive knowledge exists on the relationship between nutrient loading and nutrient concentrations in lakes in the cold temperate region, few studies have been conducted in warm lakes, not least in warm arid lakes. This is unfortunate as a larger proportion of the world’s lakes will be situated in arid climates in the future due to climate change and a larger proportion will suffer from a higher frequency of intensive drought. We conducted a comprehensive 11–13 year mass balance study in two interconnected shallow Mediterranean lakes in Turkey, covering a period with substantial changes in climate conditions. The upstream lake was only affected by natural changes in nutrient loading, while the downstream lake was additionally influenced by sewage diversion and restoration by fish removal. Contrasting to experience from north temperate lakes we found an increase in in-lake concentrations of total phosphorus and inorganic nitrogen (ammonia as well as nitrate) in dry years despite lower external nutrient loading, and submerged macrophytes did not increase the nitrogen retention capacity of the lakes. In contrast, fish removal modulated the nitrogen concentration as in north temperate lakes, but the effect was not long-lasting. Our results suggest that climate warming reduces the nutrient retention capacity of shallow lakes in the Mediterranean and exacerbates eutrophication. Lower thresholds of nutrient loading for shifting turbid shallow lakes to a clear water state are therefore to be expected in arid zones in a future warmer climate, with important management implications.     

Effects of temperature and macronutrients on phytoplankton communities across three largely different lakes identified by a time–space trade-off approach

The impacts of temperature and eutrophication on Cyanobacteria blooms were investigated thorugh a time–space trade-off approach. The limnological data of three Lakes, Taihu, Yanghe and Miyun, monitored from 2010 to 2012 were used. After categorising the three lakes by trophic state and water temperature, the study tested: (1) the response of phytoplankton to elevated temperature, by comparing Lakes Taihu and Yanghe, which are different in climate but similar in trophic state; and (2) the response of phytoplankton to higher nutrient concentrations, by comparing Lakes Yanghe and Miyun, which are different in trophic state but similar in climate. Results clearly showed that water temperature was the principle factor contributing to the higher abundance of Microcystis in Lake Taihu compared to Lake Yanghe. By contrast, higher abundance of Microcystis in Lake Yanghe compared to Lake Miyun could be clearly associated with higher nutrient levels in Lake Yanghe, supported by findings of PO₄-P limitation in Lake Miyun. The study demonstrated that time–space trade-off is a promising approach to manipulate short datasets from different lakes to discover meaningful information.     

Effects of re‐oligotrophication and climate change on lake thermal structure

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