Lake Thermal Regimes Research Articles

Past and future climate change effects on the thermal regime and oxygen solubility of four peri-alpine lakes

Abstract. Long-term effects of climate change on lakes globally will include a substantial modification in the thermal regime and the oxygen solubility of lakes, resulting in the alteration of ecosystem processes, habitats, and concentrations of critical substances. Recent efforts have led to the development of long-term model projections of climate change effects on lake thermal regimes and oxygen solubility. However, such projections are hardly ever confronted with observations extending over multiple decades. Furthermore, global-scale forcing parameters in lake models present several limitations, such as the need of significant downscaling. In this study, the effects of climate change on thermal regime and oxygen solubility were analyzed in the four largest French peri-alpine lakes over 1850–2100. We tested several one-dimensional (1D) lake models' robustness for long-term variations based on up to 63 years of limnological data collected by the French Observatory of LAkes (OLA). Here, we evaluate the possibility of forcing mechanistic models by following the long-term evolution of shortwave radiation and air temperature while providing realistic seasonal trends for the other variables for which local-scale downscaling often lacks accuracy. Based on this approach, MyLake, forced by air temperatures and shortwave radiations, predicted accurately the variations in the lake thermal regime over the last 4 to 6 decades, with RMSE < 1.95 ∘C. Over the previous 3 decades, water temperatures have increased by 0.46 ∘C per decade (±0.02 ∘C) in the epilimnion and 0.33 ∘C per decade (±0.06 ∘C) in the hypolimnion. Concomitantly and due to thermal change, O2 solubility has decreased by −0.104 mg L−1 per decade (±0.005 mg L−1) and −0.096 mg L−1 per decade (±0.011 mg L−1) in the epilimnion and hypolimnion, respectively. Based on the shared socio-economic pathway SSP370 of the Intergovernmental Panel on Climate Change (IPCC), peri-alpine lakes could face an increase of 3.80 ∘C (±0.20 ∘C) in the next 70 years, accompanied by a decline of 1.0 mg L−1 (±0.1 mg L−1) of O2 solubility. Together, these results highlight a critical alteration in lake thermal and oxygen conditions in the coming decades, and a need for a better integration of long-term lake observatories data and lake models to anticipate climate effects on lake thermal regimes and habitats.

Mechanisms and effects of under-ice warming water in Ngoring Lake of Qinghai–Tibet Plateau

Abstract. The seasonal ice cover in lakes of the Qinghai–Tibet Plateau is a transient and vulnerable part of the cryosphere, whose characteristics depend on the regional climate: strong solar radiation in the context of the dry and cold environment because of the high altitude and relatively low latitude. We use the first under-ice temperature observations from the largest Tibetan freshwater lake, Ngoring Lake, and a one-dimensional lake model to quantify the mechanism of solar thermal accumulation under ice, which relies on the ice optical properties and weather conditions, as well as the effect of the accumulated heat on the land–atmosphere heat exchange after the ice breakup. The model was able to realistically simulate the feature of the Ngoring Lake thermal regime: the “summer-like” temperature stratification with temperatures exceeding the maximum density point of 3.98 ∘C across the bulk of the freshwater column. A series of sensitivity experiments revealed solar radiation was the major source of under-ice warming and demonstrated that the warming phenomenon was highly sensitive to the optical properties of ice. The heat accumulated under ice contributed to the heat release from the lake to the atmosphere for 1–2 months after ice-off, increasing the upward sensible and latent surface heat fluxes on average by ∼ 50 and ∼ 80 W m−2, respectively. Therefore, the delayed effect of heat release on the land–atmosphere interaction requires an adequate representation in regional climate modeling of the Qinghai–Tibet Plateau and other lake-rich alpine areas.

Assessing the thermal regime of poorly monitored reservoirs with a combined satellite and three-dimensional modeling approach

ABSTRACT The thermal regime of lakes and reservoirs is a major driver of their functioning, yet water temperature measurements are scarce and time-series are frequently interrupted by missing data in many lakes and reservoirs. Our aim was to assess whether satellite imagery combined with 3-dimensional (3D) modeling can overcome this limitation. We assessed the performance of a 3D model (Delft3D-Flow) and compared simulated temperature to satellite data on Karaoun Reservoir in a semiarid region of Lebanon. Surface water temperatures were retrieved from Landsat 8, atmospherically corrected using a single channel algorithm and adjusted with in situ measurements as a proxy of bulk temperatures. With limited calibration, the model reproduced water level fluctuations, water temperature, stratification, and mixing, with low discrepancies from measurements. Satellite temperatures agreed well with observations and simulations. Satellite temperature distribution across the reservoir exhibited low spatial heterogeneity. The 3D model partly reproduced this spatial distribution of surface temperature and generally was able to simulate the thermal regime of the reservoir with limited datasets for initial conditions and for hydrological and meteorological forcing, and with limited calibration. For validating 3D hydrodynamic models, satellite temperatures constitute a valuable source of data complementary to point measurements. Coupling satellite imagery and modeling can improve operational surveys of poorly monitored lakes and reservoirs and enhance knowledge of their thermal functioning.

Intercomparison of Thermal Regime Algorithms in 1‐D Lake Models

AbstractLakes are an important component of the global weather and climate system, but the modeling of their thermal regimes has shown large uncertainties due to the highly diverse lake properties and model configurations. Here, we evaluate the algorithms of four key lake thermal processes including turbulent heat fluxes, wind‐driven mixing, light extinction, and snow density, using a highly diverse lake data set provided by the Inter‐Sectoral Impact Model Intercomparison Project (ISIMIP) 2a lake sector. Algorithm codes are configured and run separately within the same parent model to rule out any interference from factors apart from the algorithms examined. Evaluations are based on both simulation accuracy and recalibration complexity for application to global lakes. For turbulent heat fluxes, the non‐Monin–Obukhov similarity (MOS) based, more simplified algorithms perform better in predicting lake epilimnion temperatures and achieve high convergence in the values of the calibrated parameters. For wind‐driven mixing, a two‐algorithm strategy considering lake shape and season is suggested with the regular mixing algorithm used for spring and earlier summer and the mixing‐enhanced algorithm for summer steady stratification and fall overturn periods. There are no evident differences in the simulated thermocline depths using different light extinction algorithms or the observation. Finally, for lake ice phenology, an optimal algorithm is decided for most northern lakes while the Arctic lakes require separate consideration. Our study provides highly practical guides for improving 1‐D lake models and feasible parameterization strategies to better simulate global lake thermal regimes.

Comparing models using air and water temperature to forecast an aquatic invasive species response to climate change

AbstractUnderstanding invasive species spread and projecting how distributions will respond to climate change is a central task for ecologists. Typically, current and projected air temperatures are used to forecast future distributions of invasive species based on climate matching in an ecological niche modeling approach. While this approach was originally developed for terrestrial species, it has also been widely applied to aquatic species even though aquatic species do not experience air temperatures directly. In the case of lakes, species respond to lake thermal regimes, which reflect the interaction of climate and lake attributes such as depth, size, and clarity. The result is that adjacent waterbodies can differ notably in thermal regime. Given these obvious limitations of modeling aquatic species distributions using climate data, we take advantage of recent advances in simulating lake thermal regimes to model the distributions of invasive spiny water flea (Bythotrephes cederströmii) for current and projected future climates in the upper Midwest of the USA. We compared predictions and future projections from models based on modeled air temperatures with models based on modeled water temperature. All models predicted that the number of suitable lakes in the region will decrease with climate change. Models based on air and water temperature differed dramatically in the extent of this decrease. The air temperature model predicted 89% of study lakes to be suitable, with suitability declining dramatically in the late century with climate warming to just a single suitable lake. Lake suitability predictions from the water temperature model declined to a much lesser degree with warming (42% of lakes were predicted to be suitable, declining to 19% in the late century) and were more spatially independent. Our results expose the limitations of using air temperatures to model habitat suitability for aquatic species, and our study further highlights the importance of understanding lake‐specific responses to climate when assessing aquatic species responses to climate change. While we project a contraction in the potential range of Bythotrephes with warming in the study region, we anticipate that Bythotrephes will likely continue to expand into new lakes that will remain suitable in the following decades.

Mass Loss From Calving in Himalayan Proglacial Lakes

The formation and expansion of Himalayan glacial lakes has implications for glacier dynamics, mass balance and glacial lake outburst floods (GLOFs). Subaerial and subaqueous calving is an important component of glacier mass loss but they have been difficult to track due to spatiotemporal resolution limitations in remote sensing data and few field observations. In this study, we used near-daily 3 m resolution PlanetScope imagery in conjunction with an uncrewed aerial vehicle (UAV) survey to quantify calving events and derive an empirical area–volume relationship to estimate calved glacier volume from planimetric iceberg areas. A calving event at Thulagi Glacier in 2017 was observed by satellite from before and during the event to nearly complete melting of the icebergs, and was observed in situ midway through the melting period, thus giving insights into the melting processes. In situ measurements of Thulagi Lake’s surface and water column indicate that daytime sunlight absorption heats mainly just the top metre of water, but this heat is efficiently mixed downwards through the top tens of metres due to forced convection by wind-blown icebergs; this heat then is retained by the lake and is available to melt the icebergs. Using satellite data, we assess seasonal glacier velocities, lake thermal regime and glacier surface elevation change for Thulagi, Lower Barun and Lhotse Shar glaciers and their associated lakes. The data reveal widely varying trends, likely signifying divergent future evolution. Glacier velocities derived from 1960/70s declassified Corona satellite imagery revealed evidence of glacier deceleration for Thulagi and Lhotse Shar glaciers, but acceleration at Lower Barun Glacier following lake development. We used published modelled ice thickness data to show that upon reaching their maximum extents, Imja, Lower Barun and Thulagi lakes will contain, respectively, about 90 × 106 , 62 × 106 and 5 × 106 m3 of additional water compared to their 2018 volumes. Understanding lake–glacier interactions is essential to predict future glacier mass loss, lake formation and associated hazards.

Compound effects of water clarity, inflow, wind and climate warming on mountain lake thermal regimes

Many studies have examined the effects of climate warming on lake stability, but few have addressed environmental changes concomitant with climate change, such as alterations in water clarity and lake inflow. Although air temperature rise is a predominant factor linked to lake thermal characteristics, climate-driven changes at watershed scales can substantially alter lake clarity and inflow, exacerbating the effects of future air warming on lake thermal conditions. Without accounting for potential changes in clarity and inflow, future thermal predictions could be inaccurate. We employed the General Lake Model to simulate future thermal conditions (relative thermal resistance to mixing; RTRM) of small (< 12 ha) mountain lakes of the western United States by calibrating the model to a set of lakes in the Southern Rocky Mountains, USA. We found that after air temperature, alterations in inflow had the largest effect on lake thermal conditions, changes in wind had the least effect, and larger lakes experienced more than double the increase in lake stability than smaller lakes. Generally, clear, high inflow lakes had the lowest stability now, and in the future, while the largest overall increase in thermal stability occurred in larger lakes with low inflows and high turbidity. Assuming air temperature rise alone, summer stability of mountain lakes of the western United States was predicted to increase by 15–23% at + 2 °C air temperatures, and by 39–62% at + 5 °C air temperatures. When accounting for associated changes in clarity and inflow, lake stability was predicted to increase by 208% with + 2 °C air warming and 318% with at 5 °C air warming. Thus, ignoring the multivariate effects of climate change can substantially underestimate changes to mountain lake thermal and stratification regimes. Dimictic lakes may become more strongly stratified and polymictic lakes will experience more prolonged stratification. While predicted changes to lake temperatures may not be harmful to trout species that currently inhabit mountain lakes, longer and more intense stratification could cause indirect effects, such as hypoxia, that could reduce growth and survival of these organisms.

Snowmelt Timing as a Determinant of Lake Inflow Mixing

AbstractSnowmelt is a significant source of carbon, nutrient, and sediment loads to many mountain lakes. The mixing conditions of snowmelt inflows, which are heavily dependent on the interplay between snowmelt and lake thermal regime, dictate the fate of these loads within lakes and their ultimate impact on lake ecosystems. We use five decades of data from Lake Tahoe, a 600 year residence‐time lake where snowmelt has little influence on lake temperature, to characterize the snowmelt mixing response to a range of climate conditions. Using stream discharge and lake profile data (1968–2017), we find that the proportion of annual snowmelt entering the lake prior to the onset of stratification increases as annual snowpack decreases, ranging from about 50% in heavy‐snow years to close to 90% in warm, dry years. Accordingly, in 8 recent years (2010–2017) where hourly inflow buoyancy and discharge could be quantified, we find that decreased snowpack similarly increases the proportion of annual snowmelt entering the lake at weak to positive buoyancy. These responses are due to the stronger effect of winter precipitation conditions on streamflow timing and temperature than on lake stratification, and point toward increased nearshore and near‐surface mixing of inflows in low‐snowpack years. The response of inflow mixing conditions to snowpack is apparent when isolating temperature effects on snowpack. Snowpack levels are decreasing due to warming temperatures during winter precipitation. Thus, our findings suggest that climate change may lead to increased deposition of inflow loads in the ecologically dynamic littoral zone of high‐residence time, snowmelt‐fed lakes.

Paleolimnology of the Lake of the Woods southern basin: continued water quality degradation despite lower nutrient influx

ABSTRACTReavie ED, Edlund MB, Andresen NA, Engstrom DR, Leavitt PR, Schottler S, Cai M. 2017. Paleolimnology of the Lake of the Woods southern basin: continued water quality degradation despite lower nutrient influx. Lake Reserv Manage. 33:369–385.Despite decades of reduced nutrient inputs, Lake of the Woods, a large, shallow boreal lake on the US-Canadian border, shows little evidence of water quality improvements in the pelagic system. Here we analyzed sediments from 6 sites in the southern basin for diverse biogeochemical (loss-on-ignition, biogenic silica, pigments) and microfossil (diatoms, chrysophytes) remains to reconstruct the environmental history of the lake. Our objectives were to quantify the magnitude and direction of historical trophic change and evaluate reasons for an apparent lack of basin recovery following documented nutrient diversion. Evidence came from fossil indicator profiles and comparisons of these long-term trends with historical land use and monitoring data. Results indicate major changes in algal communities during and following peak nutrient loading in the mid-20th century as well as more recent increases in colonial cyanobacteria and high-nutrient diatom taxa. Combined, fossil indicators reflect an anthropogenically enriched system that has undergone substantial ecological change, particularly since ∼1980, due to multiple drivers. Physical changes in lake thermal regime resulting from climate warming may be exacerbating internal phosphorus release from sediments, thereby lowering nitrogen:phosphorus ratios and enhancing cyanobacterial abundance. These drivers of lake condition in the lake may apply to other large shallow lakes that exhibit only limited biological recovery from reduced external nutrient loading.

Trends and abrupt changes in 104 years of ice cover and water temperature in a dimictic lake in response to air temperature, wind speed, and water clarity drivers

Abstract. The one-dimensional hydrodynamic ice model, DYRESM-WQ-I, was modified to simulate ice cover and thermal structure of dimictic Lake Mendota, Wisconsin, USA, over a continuous 104-year period (1911–2014). The model results were then used to examine the drivers of changes in ice cover and water temperature, focusing on the responses to shifts in air temperature, wind speed, and water clarity at multiyear timescales. Observations of the drivers include a change in the trend of warming air temperatures from 0.081 °C per decade before 1981 to 0.334 °C per decade thereafter, as well as a shift in mean wind speed from 4.44 m s−1 before 1994 to 3.74 m s−1 thereafter. Observations show that Lake Mendota has experienced significant changes in ice cover: later ice-on date(9.0 days later per century), earlier ice-off date (12.3 days per century), decreasing ice cover duration (21.3 days per century), while model simulations indicate a change in maximum ice thickness (12.7 cm decrease per century). Model simulations also show changes in the lake thermal regime of earlier stratification onset (12.3 days per century), later fall turnover (14.6 days per century), longer stratification duration (26.8 days per century), and decreasing summer hypolimnetic temperatures (−1.4 °C per century). Correlation analysis of lake variables and driving variables revealed ice cover variables, stratification onset, epilimnetic temperature, and hypolimnetic temperature were most closely correlated with air temperature, whereas freeze-over water temperature, hypolimnetic heating, and fall turnover date were more closely correlated with wind speed. Each lake variable (i.e., ice-on and ice-off dates, ice cover duration, maximum ice thickness, freeze-over water temperature, stratification onset, fall turnover date, stratification duration, epilimnion temperature, hypolimnion temperature, and hypolimnetic heating) was averaged for the three periods (1911–1980, 1981–1993, and 1994–2014) delineated by abrupt changes in air temperature and wind speed. Average summer hypolimnetic temperature and fall turnover date exhibit significant differences between the third period and the first two periods. Changes in ice cover (ice-on and ice-off dates, ice cover duration, and maximum ice thickness) exhibit an abrupt change after 1994, which was related in part to the warm El Niño winter of 1997–1998. Under-ice water temperature, freeze-over water temperature, hypolimnetic temperature, fall turnover date, and stratification duration demonstrate a significant difference in the third period (1994–2014), when air temperature was warmest and wind speeds decreased rather abruptly. The trends in ice cover and water temperature demonstrate responses to both long-term and abrupt changes in meteorological conditions that can be complemented with numerical modeling to better understand how these variables will respond in a future climate.

Thermal processes of thermokarst lakes in the continuous permafrost zone of northern Siberia – observations and modeling (Lena River Delta, Siberia)

Abstract. Thermokarst lakes are typical features of the northern permafrost ecosystems, and play an important role in the thermal exchange between atmosphere and subsurface. The objective of this study is to describe the main thermal processes of the lakes and to quantify the heat exchange with the underlying sediments. The thermal regimes of five lakes located within the continuous permafrost zone of northern Siberia (Lena River Delta) were investigated using hourly water temperature and water level records covering a 3-year period (2009–2012), together with bathymetric survey data. The lakes included thermokarst lakes located on Holocene river terraces that may be connected to Lena River water during spring flooding, and a thermokarst lake located on deposits of the Pleistocene Ice Complex. Lakes were covered by ice up to 2 m thick that persisted for more than 7 months of the year, from October until about mid-June. Lake-bottom temperatures increased at the start of the ice-covered period due to upward-directed heat flux from the underlying thawed sediment. Prior to ice break-up, solar radiation effectively warmed the water beneath the ice cover and induced convective mixing. Ice break-up started at the beginning of June and lasted until the middle or end of June. Mixing occurred within the entire water column from the start of ice break-up and continued during the ice-free periods, as confirmed by the Wedderburn numbers, a quantitative measure of the balance between wind mixing and stratification that is important for describing the biogeochemical cycles of lakes. The lake thermal regime was modeled numerically using the FLake model. The model demonstrated good agreement with observations with regard to the mean lake temperature, with a good reproduction of the summer stratification during the ice-free period, but poor agreement during the ice-covered period. Modeled sensitivity to lake depth demonstrated that lakes in this climatic zone with mean depths &gt; 5 m develop continuous stratification in summer for at least 1 month. The modeled vertical heat flux across the bottom sediment tends towards an annual mean of zero, with maximum downward fluxes of about 5 W m−2 in summer and with heat released back into the water column at a rate of less than 1 W m−2 during the ice-covered period. The lakes are shown to be efficient heat absorbers and effectively distribute the heat through mixing. Monthly bottom water temperatures during the ice-free period range up to 15 °C and are therefore higher than the associated monthly air or ground temperatures in the surrounding frozen permafrost landscape. The investigated lakes remain unfrozen at depth, with mean annual lake-bottom temperatures of between 2.7 and 4 °C.

Evidence for water temperature increase in Lake George, NY: impact on growing season duration and degree days

Lake George (NY) water temperature increased significantly between 1980 and 2009, leading to a longer aquatic growing season and increased degree-days. Surface water (0–10 m) temperatures increased by 0.063 and 0.051 C/yr, and degree-days increased by 229 and 195 degree-days in the North and South basins, respectively. The aquatic growing season increased by ∼2 weeks, with extensions in both the spring and fall. The rate of warming, degree-days, and the duration of the growing season were consistently greater in the North Basin, due in part to a greater input of groundwater in the South Basin. Weather variables over the same time period changed significantly with wind speed and cloud cover decreasing, humidity and precipitation increasing, and no significant change identified for air temperature. Wind and cloud cover were correlated to the onset of the growing season and degree-days in both the North and South basins, suggesting they are influencing the lake thermal regime through reduced evaporative cooling in the fall, diminished spring mixing and increased solar radiation absorption. Warmer water temperatures have a myriad of consequences for aquatic ecosystems from increased primary production and shifting species composition to uncoupling of trophic dynamics and increased mineralization of organic carbon. While management practices are available for some of these issues, others have no management protocols, creating a foreseeable problem for lake managers in the future.

The ecology of the planktonic diatom Cyclotella and its implications for global environmental change studies.

The fossil record of diatoms in lake sediments can be used to assess the effects of climate variability on lake ecosystems if ecological relationships between diatom community structure and environmental parameters are well understood. Cyclotella sensu lato taxa are a key group of diatoms that are frequently dominant members of phytoplankton communities in low- to moderate-productivity lakes. Their relative abundances have fluctuated significantly in palaeolimnological records spanning over a century in arctic, alpine, boreal and temperate lakes. This suggests that these species are sensitive to environmental change and may serve as early indicators of ecosystem effects of global change. Yet patterns of change in Cyclotella species are not synchronous or unidirectional across, or even within, regions, raising the question of how to interpret these widespread changes in diatom community structure. We suggest that the path forward in resolving seemingly disparate records is to identify clearly the autecology of Cyclotella species, notably the role of nutrients, dissolved organic carbon and light, coupled with better consideration of both the mechanisms controlling lake thermal stratification processes and the resulting effects of changing lake thermal regimes on light and nutrients. Here we begin by reviewing the literature on the resource requirements of common Cyclotella taxa, illustrating that many studies reveal the importance of light, nitrogen, phosphorus, and interactions among these resources in controlling relative abundances. We then discuss how these resource requirements can be linked to shifts in limnological processes driven by environmental change, including climate-driven change in lakewater temperature, thermal stratification and nutrient loading, as well as acidification-driven shifts in nutrients and water clarity. We examine three case studies, each involving two lakes from the same region that have disparate trends in the relative abundances of the same species, and illustrate how the mechanisms by which these species abundances are changing can be deciphered. Ultimately, changes in resource availability and water clarity are key factors leading to shifts in Cyclotella abundances. Tighter integration of the autecology of this important group of diatoms with environmental change and subsequent alterations in limnological processes will improve interpretations of palaeolimnological records, and clarify the drivers of seemingly disparate patterns in fossil records showing widespread and rapid changes across the northern hemisphere.

Effects Of Lake Warming On Behavioural Thermoregulatory Tactics In A Cold-Water Stenothermic Fish

Despite some evidence of within-population phenotypic variation in fish thermal behaviour, the occurrence of alternative tactics of this behaviour is rarely explicitly considered when studying natural populations. Brook charr provide an example of within-population variability in behavioural thermoregulation as revealed by a recent study on a lacustrine population of this species. The objectives of the present study were (i) to determine the influence of natural variability in the lake's thermal profiles on the expression of thermoregulatory tactics, and (ii) to determine the vertical and horizontal movements of individuals at different periods of the day to better understand the spatio-temporal behaviour associated with each thermoregulatory tactic. During summer 2010, 30 adult brook charr were equipped with thermo-sensitive radio transmitters to monitor their selected temperatures and daily movements. These individuals exhibited the same four behavioural thermoregulatory tactics observed in 2003 and 2005, but the expression of two of these was weaker in 2010. This result was associated with lake warming, which constrained the expression of two thermoregulatory tactics: brook charr significantly decreased their selected temperatures and daily movements when the mean daily epilimnion temperature was above 22.4°C. This study shows for the first time that the expression of behavioural thermoregulatory tactics is related to the lake's thermal regime and that the tactics are plastic through time.

Long-term temperature evolution in a deep sub-alpine lake, Lake Bourget, France: how a one-dimensional model improves its trend assessment

Water temperature and the alternation of stratification and mixing count amongst key drivers of lake ecology. Reliable long time-series of water temperature are rare. Here, we investigated how a numerical model can fill the gaps in heterogeneous time-series and make it possible to identify a significant trend in the lake thermal regime. We computed the mean water temperature and the Schmidt stability, an indicator of the stratification strength, in a deep and well-stratified lake (Lake Bourget, France), between 1976 and 2008. We first used temperature measurements and then a one-dimensional vertical model, which we describe here. The model performs as well as the best existing models. During the 1976–2008 periods, whereas no statistically significant trend came out of the measurements, we found in the simulation results an increase of 0.12 °C per decade in the water temperature and of 5.9 days per decade in the stratification duration. This shows that the temperature history of a lake can be reconstructed and a reliable long-term trend computed when weather data and a calibrated temperature model are available. Our results also suggest that different local climatic influences cause a slower warming in this lake of the south-western Alps than in other sub-alpine lakes.

Climate change drives coherent trends in physics and oxygen content in North American lakes

Using a 25-year record of monitoring data, we show that recent climate change has affected the thermal properties and oxygen content of seven lakes in south-central Ontario, Canada, and five lakes in north-central Wisconsin, USA. Coherent patterns in autumnal lake warming were driven by increased autumn air temperature in both lake districts. Temperature increases were restricted to the epilimnion and metalimnion of the lakes, resulting in increased thermal stability of the water column. Mixing depths also decreased over the study period. Shallower mixing depths in the Ontario lakes were due to climate-driven increases in lake-water dissolved organic carbon concentrations. Collectively, changes in the thermal regime of the lakes suggest autumn mixing of the water column may be delayed. Metalimnetic oxygen also increased in the Wisconsin lakes, perhaps in response to increased algal production as lake thermal regimes changed. The response of individual lakes to climate change was modified by lake chemistry in the Ontario lake district and by lake chemistry and morphometry in the Wisconsin lake district. Our results demonstrate coherent lake response to climate change and highlight the importance of both regional and local factors in regulating individual lake response to global climate change.

Summertime fluxes of N2O, CH4and CO2from the littoral zone of Lake Daming, East Antarctica: effects of environmental conditions

AbstractNitrous oxide (N2O), methane (CH4) and carbon dioxide (CO2) fluxes were investigated from the algal-rich littoral zone of Lake Daming, East Antarctica during the summers of 2008/09 and 2009/10, using a static chamber technique. High N2O emissions occurred in the littoral zone with the mean flux range of 0.19–7.11 μmol N2O m-2h-1. The mean CH4fluxes ranged from 2.51–5.32 μmol CH4m-2h-1, and they were significantly affected by the lake thermal regime. There were significant differences (P&lt; 0.05) in CH4and N2O fluxes under the light and dark conditions, and sunlight greatly increased N2O emissions by stimulating the algal photosynthesis, but decreased CH4emissions. Overall the littoral zone represented a weak CO2sink with the mean flux range of -0.37–0.13 mmol CO2m-2h-1. The mean ecosystem respiration and photosynthesis rates varied from 0.47–2.90 mmol CO2m-2h-1and from -0.33 to -2.63 mmol CO2m-2h-1. The combined global warming potential (GWP) of N2O and CH4fluxes completely counteracted and surpassed CO2uptake by the algal photosynthesis, and high GWP-positive of N2O and CH4emissions might convert an algal-rich lake site with a net CO2uptake into a net radiative forcing source during the ice-free period.

Decadal‐scale regional changes in Canadian freshwater zooplankton: the likely consequence of complex interactions among multiple anthropogenic stressors

Summary Ecological integrity is increasingly threatened by multiple anthropogenic stressors, but the cumulative impact of stressors is poorly understood because they can interact in unexpected ways. Knowledge of these interactions and their associated impacts is needed to support the conservation of valued ecosystems. We used a large‐scale, replicated field survey and multiple regression analysis to investigate the cumulative impacts of multiple physical, chemical and biological stressors on the crustacean zooplankton assemblages of 34 Canadian Shield lakes between 1980s and 2004–2005. Zooplankton total abundance, species richness, diversity and community structure, as well as the relative abundances of prominent taxonomic orders of zooplankton, changed at a regional scale. These changes occurred in response to changes in water quality and lake thermal regime, and invasion by an exotic predator. Interactions between stressors were common and represented an important determinant of zooplankton assemblage changes over time. We provide the first evidence that the individual and combined impacts of multiple stressors cause regional ecological change over decades. Our results demonstrate the prevalence of stressor interactions in natural environments and highlight the complexity of ecosystem responses to multiple stressors. Zooplankton changes recorded here may be widespread because climate change, acidification, development and the spread of invasive species are globally pervasive. These changes could have cascading impacts because zooplankton is an essential link in aquatic food webs. Our findings highlight the need to consider the interactive effect of stressors when assessing anthropogenic impacts and will inform management and conservation of ecosystems threatened by multiple stressors.

Consequences of changing climate and geomorphology for bioenergetics of juvenile sockeye salmon in a shallow Alaskan lake

Abstract – In high northern latitudes, a wide range of geomorphic processes associated with fluvial, glacial and permafrost activity may interact with climate change to produce unexpected changes in lake thermal regimes with attendant effects on ecological processes. We coupled output from a hydrodynamics model of lake thermal structure to a bioenergetics model to assess how alternative scenarios of climate change, geomorphic evolution and habitat restoration in a shallow Alaskan lake may affect juvenile sockeye salmon bioenergetics and growth. In particular, we evaluated the metabolic costs of different thermal regimes and the potential for changes in consumption to offset those costs. Increased water temperatures associated with future climate increased metabolic costs which were partially offset if fish were able to maintain feeding rates, expressed as a constant proportion of maximum consumption. In this lake, water levels have declined substantially in the last 50 years. Simulated restored lake level had negligible effects on lake temperature and thus on sockeye salmon growth when compared to current conditions. Maintaining lake connectivity to inlet tributaries (cooling lake temperature) was crucial in reducing sockeye salmon metabolic costs particularly with further drops in lake level and climate warming. While considerable research is focused on predicting future thermal and geomorphic conditions in aquatic ecosystems, these processes are rarely considered together, especially for lakes. Understanding the biological responses to geomorphic–climate interactions will be required for developing scenarios for coping with ecosystem responses to global change and evaluating restoration alternatives, especially in high‐latitude systems that support economically and culturally important fisheries.

The distribution of littoral chironomids along an altitudinal gradient in High Tatra Mountain lakes: Could they be used as indicators of climate change?

We studied assemblages of littoral chironomids from three alpine lakes in the High Tatra Mountains (Slovakia) along an altitude range of 1725-2157 m. The study sites were selected in order to em- phasize differences in their thermal regimes. Littoral samples were taken quantitatively in the ice-free seasons of 2000 and 2001. In total, 3468 chironomid larvae and pupae were collected and 29 taxa were identified. Some parameters of the littoral chironomid assemblages showed clear patterns along the altitude gradient. The number of taxa and Shannon diversity increased markedly with decreasing altitude. Density, however, did not show any correlation with altitude. Even though gatherers highly dominated in all sites, their relative abundance decreased with decreasing altitude. The ratio of scrapers and predators correlated negatively with altitude. According to the results of a Detrended Correspondence Analysis, Pseudodiamesa arctica and Micropsectra radialis were chosen as indicator species for alpine lakes > 2000 m a.s.l. Typical subalpine lake inhabitants are Zavrelimyia sp., Prodiamesa olivacea, Corynoneura scutellata group, Cricotopus polaris, Micropsectra bavarica and Paratanytarsus austriacus. A single species, Micropsectra junci, seemed to be char- acteristic of alpine lakes < 2000 m a.s.l. This gradient lake concept could be used to predict changes in mountain lake fauna under expected climate change scenarios. Generally, an upward shift of subalpine species would be expected. The thermal regime of lakes, however, also depends on several local factors. Consequently, the schemes outlined here would not be valid for the entire Tatra lake district.