Response of boreal lakes to changing wind strength: coherent physical changes across two large lakes but varying effects on primary producers over the 20th century

Near‐surface wind speeds have changed over recent decades, raising questions about the extent to which these changes are altering the vertical thermal structure of lakes and affecting lake food webs. Neo‐ and paleolimnological techniques were used to assess wind‐driven changes in lake thermal habitat and resulting effects on primary producers in two lakes in Isle Royale National Park, an island archipelago located in Lake Superior, where wind speed has increased in recent decades. Responses in Siskiwit Lake, a large (16 km2 surface area), deep (Zmax = 49 m), oligotrophic lake, were compared to those of Lake Desor, a moderately large (4.3 km2) but shallower (Zmax = 13 m), mesotrophic lake. High‐frequency sensor data suggested that changes in wind speed affected epilimnion thickness in both lakes synchronously (ρ = 0.7, p [less than] 0.001). Diatom‐inferred mixing depths suggested a coherent shift in both lakes to deeper mixing (an increase of 3 and 6 m) since 1920 (ρ = 0.8), which was correlated with an increase in regional wind speed during the 20th century at the decadal‐scale in Lake Desor and Siskiwit Lake (ρ = 0.6 and 0.4, respectively). In Lake Desor, algal biomass declined as mixing deepened from 1920 to 1980, and then cyanobacteria and cryptophyte pigments increased from 1980 to present, a period of inferred stable and deep mixing. Algal pigment concentrations in Siskiwit Lake were unchanged as mixing depth deepened. Although changes in wind speed altered lake physical structure similarly, the ecological consequences of these changes differed between lakes and were most likely influenced by lake‐specific variability in nutrient and light availability

Global data set of long-term summertime vertical temperature profiles in 153 lakes

Climate change and other anthropogenic stressors have led to long-term changes in the thermal structure, including surface temperatures, deepwater temperatures, and vertical thermal gradients, in many lakes around the world. Though many studies highlight warming of surface water temperatures in lakes worldwide, less is known about long-term trends in full vertical thermal structure and deepwater temperatures, which have been changing less consistently in both direction and magnitude. Here, we present a globally-expansive data set of summertime in-situ vertical temperature profiles from 153 lakes, with one time series beginning as early as 1894. We also compiled lake geographic, morphometric, and water quality variables that can influence vertical thermal structure through a variety of potential mechanisms in these lakes. These long-term time series of vertical temperature profiles and corresponding lake characteristics serve as valuable data to help understand changes and drivers of lake thermal structure in a time of rapid global and ecological change

Global data set of long-term summertime vertical temperature profiles in 153 lakes

Measurement(s) : temperature of water, temperature profile Technology Type(s) : digital curation Factor Type(s) : lake location, temporal interval Sample Characteristic - Environment : lake, reservoir Sample Characteristic - Location : global Machine-accessible metadata file describing the reported data: https://doi.org/10.6084/m9.figshare.14619009Climate change and other anthropogenic stressors have led to long-term changes in the thermal structure, including surface temperatures, deepwater temperatures, and vertical thermal gradients, in many lakes around the world. Though many studies highlight warming of surface water temperatures in lakes worldwide, less is known about long-term trends in full vertical thermal structure and deepwater temperatures, which have been changing less consistently in both direction and magnitude. Here, we present a globally-expansive data set of summertime in-situ vertical temperature profiles from 153 lakes, with one time series beginning as early as 1894. We also compiled lake geographic, morphometric, and water quality variables that can influence vertical thermal structure through a variety of potential mechanisms in these lakes. These long-term time series of vertical temperature profiles and corresponding lake characteristics serve as valuable data to help understand changes and drivers of lake thermal structure in a time of rapid global and ecological change

Deciphering Climate-Mediated Changes in Boreal Lake Ecosystems

Climate change is expected to have profound effects on boreal lakes; however, the nature and magnitude of these effects across broad spatial and temporal scales is poorly understood. Here, I used neo- and paleo-limnological tools to decipher the extent to which climate-mediated changes in energy (irradiance, heat, and wind) or mass (water, suspended particles, and dissolved substances) are contributing to broad changes in boreal lakes. I selected lakes in two regions of boreal forest in the United States that are experiencing changes in either energy (air temperature and wind changes in Isle Royale National Park (ISRO) in the Upper Midwest) or mass (changes in the amount and chemical characteristics of precipitation in the Northeast). To assess long-term variability in lake response to changes in heat and wind in ISRO, high frequency monitoring of lake temperature was paired with paleolimnological analyses of diatom- inferred mixing depth and fossil algal pigments in two lakes in ISRO during the 20th century. To determine the effects of extreme weather on surface water chemistry in the northeastern U.S., a 30-year database of surface water geochemistry for 84 lakes was combined with newly developed landscape data and watershed-specific weather data to model lake chemical response during an extreme wet and an extreme dry year as a function of watershed features. A separate dataset that included lakes in Acadia National Park in Maine and the Pocono Mountains in Pennsylvania was used to evaluate water clarity as a sentinel of environmental changes that modified mass influx across the region. Broad patterns in lake response to climate were consistent with expected changes in both regions; however, the magnitude of change was dependent on watershed and lake- specific characteristics. Lake mixing depth deepened as wind strength increased in ISRO. This had a greater effect on physical lake habitat in the shallower and more productive lake. Episodic changes in lake chemistry occurred in response to extreme weather in the northeastern U.S. Episodic acidification was observed during drought and episodic brownification was observed during wet years. This change may be contributing to accelerated recovery from acidification and reduced water clarity in recent decades

Key differences between lakes and reservoirs modify climate signals: A case for a new conceptual model

Lakes and reservoirs are recognized as important sentinels of climate change, integrating catchment and atmospheric climate change drivers. Climate change conceptual models generally consider lakes and reservoirs together despite the possibility that these systems respond differently to climate-related drivers. Here, we synthesize differences between lake and reservoir characteristics that are likely important for predicting waterbody response to climate change. To better articulate these differences, we revised the energy mass flux framework, a conceptual model for the effects of climate change on lentic ecosystems, to explicitly consider the differential responses of lake versus reservoir ecosystems. The model predicts that catchment and management characteristics will be more important mediators of climate effects in reservoirs than in natural lakes. Given the increased reliance on reservoirs globally, we highlight current gaps in our understanding of these systems and suggest research directions to further characterize regional and continental differences among lakes and reservoirs

Extreme weather years drive episodic changes in lake chemistry: implications for recovery from sulfate deposition and long-term trends in dissolved organic carbon

Interannual climate variability is expected to increase over the next century, but the extent to which hydroclimatic variability influences biogeochemical processes is unclear. To determine the effects of extreme weather on surface water chemistry, a 30-year record of surface water geochemistry for 84 lakes in the northeastern U.S. was combined with landscape data and watershed-specific weather data. With these data, responses in sulfate (SO42−) and dissolved organic carbon (DOC) concentrations were characterized during an extreme wet year and an extreme dry year across the region. Redundancy analysis was used to model lake chemical response to extreme weather as a function of watershed features. A response was observed in DOC and SO42− concentration in response to extreme wet and dry years in lakes across the northeastern U.S. Acidification was observed during drought and brownification was observed during wet years. Lake chemical response was related to landscape characteristics in different ways depending on the type of extreme year. A linear relationship between wetland coverage and DOC and SO42− deviations was observed during extreme wet years. The results presented here help to clarify the variability observed in long-term recovery from acidification and regional increases in DOC. Understanding the chemical response to weather variability is becoming increasingly important as temporal variation in precipitation is likely to intensify with continued atmospheric warming

Response of Cyclotella species to nutrients and incubation depth in Arctic lakes

The relative abundances of small centric diatoms have increased in many Arctic lakes over the past century, with these changes commonly attributed to warming. However, the specific mechanisms by which diatom community structure is changing in response to warming remain unclear. We investigated the responses of two common centric diatoms to nutrient enrichment and incubation depth, the latter used to manipulate light availability which is a key factor that changes with altered mixing depths in lakes. We conducted 2 × 2 factorial experiments, manipulating nutrients (none added or N + P addition) and incubation depth (shallow or deep), and measured changes in growth rates and cell densities of Discostella stelligera and Puncticulata radiosa. A second set of experiments was conducted on D. stelligera in a growth chamber to separate temperature and light effects associated with incubation depth. Puncticulata radiosa was always more abundant in the shallow depth incubations, regardless of nutrient conditions. In contrast, D. stelligera responded most strongly to nutrient additions, and cell densities of this species were affected by interactions between nutrients and incubation depth or light. Our research suggests that processes that alter light availability (such as water clarity and water column stability) and nutrient concentrations are likely to play a major role in controlling the growth of small centric diatoms in Arctic lakes

Over half a century record of limnology data from Lake Powell, desert southwest United States: From reservoir filling to present day (1964–2021)

Abstract Lake Powell is a large water storage reservoir in the arid southwestern United States. Here, we present a 58‐yr limnology dataset that captures water quality parameters from reservoir filling to present day (temperature, salinity, major ions, total suspended solids), as well as a 38‐yr record of Secchi depth, and a ~ 30‐yr record of nutrients, phytoplankton, and zooplankton assemblages. The dataset includes 5208 unique site visits spanning 258 unique sites of which 9 have been consistently visited. It also spans the establishment of an invasive bivalve (Dreissena bugensis, i.e. Quagga mussel) which was first detected in 2012. Given the general lack of long‐term data from lakes or reservoirs in arid regions, this dataset represents a unique contribution to regional, continental, and global‐scale limnology studies. As the hot drought in the desert southwest continues, we expect this dataset will inform water management decision‐making for this largest reservoir in the Upper Colorado River Basin

Nitrogen deposition to lakes in national parks of the western Great Lakes region: Isotopic signatures, watershed retention, and algal shifts

Atmospheric deposition is a primary source of reactive nitrogen (Nr) to undisturbed watersheds of the Great Lakes region of the U.S., raising concerns over whether enhanced delivery over recent decades has affected lake ecosystems. The National Atmospheric Deposition Program (NADP) has been measuring Nr deposition in this region for over 35 years. Here we explore the relationships among NADP-measured Nr deposition, nitrogen stable isotopes (δ15N) in lake sediments, and the response of algal communities in 28 lakes situated in national parks of the western Great Lakes region of the U.S. We find that 36% of the lakes preserve a sediment δ15N record that is statistically correlated with some form of Nr deposition (total dissolved inorganic N, nitrate, or ammonium). Furthermore, measured long-term (since 1982) nitrogen biogeochemistry and inferred critical nitrogen loads suggest that watershed nitrogen retention and climate strongly affect whether sediment δ15N is related to Nr deposition in lake sediment records. Measurements of algal change over the last ~ 150 years suggest that Nr deposition, in-lake nutrient cycling, and watershed inputs are important factors affecting diatom community composition, in addition to direct climatic effects on lake physical limnology. The findings suggest that bulk sediment δ15N does reflect Nr deposition in some instances. In addition, this study highlights the interactive effects of Nr deposition and climate variability

Transparency, Geomorphology and Mixing Regime Explain Variability in Trends in Lake Temperature and Stratification across Northeastern North America (1975–2014)

Lake surface water temperatures are warming worldwide, raising concerns about the future integrity of valuable lake ecosystem services. In contrast to surface water temperatures, we know far less about what is happening to water temperature beneath the surface, where most organisms live. Moreover, we know little about which characteristics make lakes more or less sensitive to climate change and other environmental stressors. We examined changes in lake thermal structure for 231 lakes across northeastern North America (NENA), a region with an exceptionally high density of lakes. We determined how lake thermal structure has changed in recent decades (1975–2012) and assessed which lake characteristics are related to changes in lake thermal structure. In general, NENA lakes had increasing near-surface temperatures and thermal stratification strength. On average, changes in deepwater temperatures for the 231 lakes were not significantly different than zero, but individually, half of the lakes experienced warming and half cooling deepwater temperature through time. More transparent lakes (Secchi transparency >5 m) tended to have higher near-surface warming and greater increases in strength of thermal stratification than less transparent lakes. Whole-lake warming was greatest in polymictic lakes, where frequent summer mixing distributed heat throughout the water column. Lakes often function as important sentinels of climate change, but lake characteristics within and across regions modify the magnitude of the signal with important implications for lake biology, ecology and chemistry