Lake Morphometry Research Articles

Do gravel highways affect water quality and invertebrate communities in Arctic lakes?

ABSTRACT Gravel roads are a common feature in developed areas of Canada’s Arctic. These roads can be a source of calcareous dust that drifts to roadside lakes, causing significant changes in conductivity, calcium, and pH levels. In this study, we examined if road proximity was associated with differences in water quality and invertebrate communities in lakes along the Dempster and Inuvik-Tuktoyaktuk Highways in the Northwest Territories, Canada. We collected biological and water quality data from 18 lakes selected using a stratified random sampling design, with distance from the road (0–300 m, 300–600 m, and >600 m) and region of study (boreal forest, tundra) as the two factors. We hypothesized that lakes closer to the road would exhibit differences in water quality and invertebrate communities associated with road dust pollution and other stressors caused by roads. We found no clear differences in water quality or invertebrate communities among lakes based on distance from the highways. In addition, while there were differences between regions, these did not appear to be related to the effects of the roadways. Our results suggest that variability in lake morphometry and water quality in this region might be more important than the influence of roads.

Organic carbon sink dynamics and carbon sink-source balance in global lakes during the Anthropocene

The carbon burial and greenhouse gas emissions of lakes are pivotal in the global carbon cycle to offset or accelerate global warming. However, their balance or the magnitude of anthropogenic increase of carbon burial remains uncertain in global lakes. Here, we quantified the carbon sink dynamics and the sink-source balance in global lakes with effect-size metrics, that is, the log-response ratio of organic carbon burial between post-1950 and pre-1900 periods and the carbon balance ratio between carbon burial and greenhouse gas emissions, respectively. The organic carbon burial ratios revealed an average increase of 2.45 times in carbon burial rates during the Anthropocene, while the carbon balance ratios were negative in 82.68% of lakes, indicating that most lakes had lower burial rates than emission rates and acted as carbon sources rather than carbon sinks. The organic carbon burial ratios exhibited a significantly decreasing latitudinal trend and were mainly influenced by lake’s trophic state with the explained variation of 44.79%. They were also indirectly influenced by climate, lake morphometry, and catchment properties through their interactions with the lake’s trophic state. The carbon balance ratios, however, showed a nonsignificant latitudinal trend. They were primarily affected by lake catchment properties with the explained variation of 26.21% and were also indirectly affected by climate variables via the interactions with catchment properties. Overall, our study highlights that human activities such as lake eutrophication and catchment changes have altered the carbon sink and source in global lakes during the Anthropocene, and are essential drivers for future evaluations of lake carbon budgets.

Testing and refinement of elemental proxies in tropical lakes from the Indian subcontinent

AbstractThe conventional approach of using modern values of lake hydrochemistry and sediment composition as key parameters for identifying proxies for environmental reconstruction is complicated by regional climate, catchment geology, lake morphometry and anthropogenic input. In contrast to modern studies from lakes in the north‐temperate regions, reliable proxy indicators for past environmental change from tropical lake systems are still lacking. In this study, we compare new surface geochemical and mineralogical data from the Manasbal Lake, Kashmir (India), with other lakes situated in climatically and geomorphologically distinct regimes with varying degrees of pollution (Tso Moriri in north‐western Himalaya and Lonar in central India). We characterise external (e.g., geology and weathering), internal (e.g., lake water mixing and evaporation) factors and human activities influencing sediment composition and spatial distribution of proxies in each of these lakes to evaluate the usefulness of some of the commonly used proxies, as well as ascertain conditions where they might be applicable. Our results show that (i) morphometric parameters (such as lake size, water depth and catchment vs. lake area) variably influence the spatial distribution of sediments and proxies on the lake bottom highlighting the limitations of using single cores for long‐term palaeoclimate reconstruction; (ii) hydrochemical proxies (such as Na+/Na++Ca2+and Mg/Ca) can delineate endogenic (Lonar and Tso Moriri lakes) versus allogenic (Manasbal Lake) influence on modern sediment characteristics; (iii) the compilation of heavy metal data (e.g., Fe, Zn, Mn, Cr and Ni) from all three lake basins with varying degrees of pollution highlights the limitations of using them to characterise weathering conditions in these basins; and (iv) human impact must be precluded before using the most promising endogenic minerals (calcite, aragonite, gypsum and pyrite) as palaeoenvironmental/palaeoclimate indicators.

Watershed, lake, and food web factors influence diazotrophic cyanobacteria in mountain lakes

AbstractCyanobacterial blooms can occur in freshwater ecosystems largely isolated from development and not experiencing extensive cultural eutrophication. For example, remote mountain lakes can experience intense blooms of diazotrophic (nitrogen‐fixing) cyanobacteria caused by factors acting at different spatial and temporal scales. In this study, we examined how cross‐scale interactions among watershed, lake, and food web characteristics influence diazotrophic cyanobacteria biovolume in mountain lakes. We quantified diazotrophic cyanobacteria biovolume, zooplankton abundance, and physico‐chemical variables for 29 lakes in the Cascade Mountains of Oregon, USA, in summer 2019. Watershed characteristics were compiled from historical datasets available for the region. Diazotrophic cyanobacteria biovolume ranged across the lakes from 0 to 1,930,000 μm3 mL−1; Dolichospermum was the most common genus. Random forest models showed that 11 watershed, lake, and food web characteristics explained 76% of the variance in diazotrophic cyanobacteria biovolume among the sampled lakes. Structural equation models suggested that the drainage ratio (i.e., the relative area of the lake to the watershed) was positively related to phosphorus concentrations and, in turn, to diazotroph biovolume. Among lakes, hypolimnetic dissolved oxygen was negatively correlated with diazotroph biovolume, possibly due to the release of nutrients, like phosphate and iron, bound to sediments. In addition, zooplankton grazers were negatively related to diazotrophic cyanobacteria biovolume, potentially reflecting the influence of stocked fish. Thus, lake management must account for bottom‐up factors, such as nutrient loading, which is influenced by lake morphometry and watershed size, as well as top‐down factors, such as fish stocking, to effectively mitigate diazotrophic cyanobacterial blooms.

Minor effect of wind exposure and littoral slope on macrophyte characteristics in non-impacted lowland lakes of Poland.

Aquatic vegetation is a reliable indicator of the ecological condition of surface waters. Abundance, composition and spatial structure of aquatic communities are shaped by an array of factors, which include both natural abiotic features of an ecosystem and external influences. We investigated whether the physical features, i.e., wind exposure and slope of the lake basin, have a significant impact on the taxonomic composition and spatial structure of macrophyte communities from non-impacted, highly alkaline, lowland lakes of the European plains (Poland). We further examined whether these features can affect the classification of the ecological status of lakes assessed in accordance with the Water Framework Directive requirements. Morphological, botanical and physicochemical data from 260 transects in 16 non-disturbed lakes of Polish lowlands surveyed in the years 2011-2016 were analysed. For each transect, littoral slope and wind exposure were calculated. Additionally, the total phosphorus concentration was used as a proxy of water trophy. The relationships between environmental variables and macrophyte indices as well as the syntaxonomic composition of aquatic and rush vegetation (dependent variables) were analysed using multidimensional ordination techniques (redundancy analysis, variation partitioning and indicator values), correlation and regression analysis. Among the three analysed environmental factors (littoral slope, wind exposure and water trophy), in almost all cases the latter explained the highest variance in the macrophyte community, while the contribution of the first two was at most moderate, weak or usually statistically insignificant. However, lakes with steeper slopes were more frequently inhabited by stoneworts and had better ecological status than those with a gentle littoral shape. This may be attributed to the links between lake morphometry and rate of eutrophication, with deep lakes supporting more effective dilution of substances. Furthermore, lower light requirements of charophytes than of higher plants and the capacity to growth in unstable sediments facilitate charophyte establishment in deeper and steeper parts of the littoral over higher plants. Our findings suggest that in lowland lakes with relatively small areas, moderate depths and low wind exposure typical of European plains, slopes and weaving do not hamper vegetation development and do not negatively affect the macrophyte assessment of ecological status. In such ecosystems, eutrophication seems to be a more important factor determining aquatic vegetation than physical features.

Persisting in extreme environments: What are the drivers of body conditions of introduced fish in high mountain lakes?

Abstract Salmonids are introduced in various ecosystems, including mountain lakes characterised by extreme environmental constraints. Although these constraints can affect salmonid body condition through direct and indirect pathways, they remain seldom explored despite their importance for understanding salmonid fitness and long‐term establishment. In order to fill this gap, we firstly fitted species‐specific weight–length relationships for three salmonid species in nine mountain lakes, and compared their allometric coefficients with those of 362 salmonid populations worldwide to identify potential differences in growth trajectory of salmonids in the studied lakes. We then investigated how thermal characteristics and lake morphometry could influence salmonid body conditions, both directly and indirectly through salmonid density, the presence of forage fish and resource densities. We calculated salmonid relative body condition Kn and used a structural equation model (SEM) to disentangle these direct and indirect effects. The values of allometric coefficients for the three species did not differ from those of most salmonids worldwide although ontogenetic changes in Salvelinus alpinus weight gain was observed. Kn differed significantly among the populations studied. The strongest effects were related to direct and indirect effects of lake morphometry, while thermal characteristics had mostly indirect effects on Kn. The strength and the sign of the indirect effects of morphometry and temperature were mediated by the direct effects of resource and salmonid densities on Kn. Kn estimates were greater in lakes with shallow basin slopes than those with steep slopes. Shallow basin slopes probably provide habitats that support high prey availability and require lower energy expenditure by salmonids compared to lakes with steep slopes dominated by pelagic habitats. Complementarily, higher winter and summer temperatures favour Kn by supporting higher prey densities and longer periods of feeding activity. Our results may help managers to select lakes that optimise sustainability of salmonid populations based on the joint effects of basin morphometry and the expected thermal modifications induced by global change.

Fire Characteristics and Hydrologic Connectivity Influence Short‐Term Responses of North Temperate Lakes to Wildfire

AbstractDespite increasing wildfires, few studies have investigated seasonal water quality responses to wildfire characteristics (e.g., burn severity) across a large number of lakes. We monitored 30 total lakes (15 burned, 15 control) monthly following the Greenwood Fire in Minnesota, USA, a lake‐rich region with historically prevalent wildfire. We found increases in median concentrations of total nitrogen (68%), total phosphorus (70%), dissolved organic carbon (127%), total suspended solids (71%), and reduced water clarity (48%) and pH (0.45) in burned lakes. Post‐wildfire responses in drainage lakes were often persistent or cumulative throughout the open‐water season, compared to isolated lakes. Total phosphorus (TP) increased linearly with watershed high‐severity burns, and shoreline high‐severity burns explained more variation in TP than lake morphometry and watershed variables. Post‐wildfire chlorophyll‐a responses were nonsignificant and inconsistent, possibly due to light limitation. Our results suggest that increasing wildfires have significant potential to affect water quality of inland lakes.

Prolonged Record of Hydroclimatic Changes at Antoniadi Crater, Mars

AbstractThe first billion years of Martian geologic history consisted of surface environments and landscapes dramatically different from those seen today, with flowing liquid water sculpting river channels and ponding to form bodies of water. However, the hydro‐climatic context, the frequency, and the duration under which these systems existed remain uncertain. Addressing these fundamental questions may improve our understanding of early Mars climate. Here, we reconstruct a long‐lived archive consisting of an array of fluvial systems inside the Antoniadi crater––one of the largest lake basins on Mars (9.58 × 104 km2). We found that the fluvial activity occurred throughout four major intermittent active intervals during the Late Noachian to Early Amazonian (∼3.7 to >2.4 Ga). This resulted in at least two major lakes, which formed during periods of markedly increased surface runoff production. The record of these four riverine phases is preserved in fluvial ridges, valley networks, back‐stepping or down‐stepping fan‐shaped landforms, and terrace‐like formations within an outlet canyon. These morphologies point to lake‐controlled base‐level fluctuations suggestive of episodic precipitation‐fed surface runoff punctuated by intermittent catastrophic floods that were capable of breaching crater‐lake rims and incising outlet canyons. Fluvial‐deposit thickness, junction angles of channels, and lake morphometry suggest that riverine systems lasted at least 103–106 years and episodically occurred under primarily arid and semi‐arid climates. These findings place new regional constraints on the fluvial frequency, longevity, and climatic regime of one of the largest Martian lakes, thereby bolstering the hypothesis that episodic warming likely punctuated the planet's early history.

The Importance of Habitat and Lake Morphometry for the Summer Diet Choice of Landlocked Arctic Char in Two West Greenland Lakes

Arctic char (Salvelinus alpinus) is a top predator and the most widespread fish in Arctic lakes. The presence of Arctic char affects the predator–prey dynamics of the key species in the food webs in these lakes. This study sought to elucidate the effects of habitat (littoral, pelagic, or profundal) and lake morphometry on the trophic position of this char in the food web. Using stomach content and stable isotope analyses, we investigated the effect of fish length, habitat, and time (individual survey years: 2008, 2013, 2018, and 2019) on the dietary niches of landlocked Arctic char populations during summer in two west Greenland lakes: Badesø (area 0.8 km2, mean depth 9.2 m) and Langesø (area 0.3 km2, mean depth 5.0 m). The small char (<20 cm fork length) in Badesø generally foraged less littoral macroinvertebrates than those from Langesø. The large chars were mainly piscivorous in both lakes. In Badesø, there was a shift from relying on littoral to pelagic invertebrates by the small char from 2008–2013 to 2018–2019. The proportionally larger size of the littoral habitat in the smaller Langesø led to an increased reliance on littoral-derived macroinvertebrates in the diet of the small char, more so than in the larger Badesø, where the predominant reliance was on pelagic sources.

Simple model of morphometric constraint on carbon burial in boreal lakes

A geometric theory was developed to explain the empirical relationship between carbon burial and lake shape in boreal lakes. The key feature of this model is an attenuation length scale, analogous to models of marine organic carbon fluxes. This length scale is the ratio of how fast carbon is displaced vertically versus how fast it is respired and engenders a simple model with a single easily constrained free parameter. Lake depths are modeled based on fractal area–volume relationships that reflect the approximate scale invariance of Earth’s topography on idealized lake geometries. Carbon burial is estimated by applying the attenuation length scale to these depths. Using this model, we demonstrate the relationship between the dynamic ratio—a metric of lake morphometry calculated by dividing the square root of surface area by the mean depth—and carbon burial. We use scaling relationships to predict how dynamic ratio, and by extension carbon burial, varies across the lake size spectrum. Our model also provides a basis for generalizing empirical studies to the biome scale. By applying our model to a boreal lake census, we estimate boreal lake carbon burial to be 1.8 ± 0.5 g C/m2/yr or 1.1 ± 0.3 Tg C/yr among all boreal lakes.

Primary production modeling identifies restoration targets for shifting shallow, eutrophic lakes to clear-water regimes

Benthic primary production (BPP) plays an important functional role in lakes, improving water quality by stabilizing clear-water regimes. Shallow, eutrophic lakes lacking BPP communities can be difficult to restore because self-stabilizing feedbacks of phytoplankton dominance can impede the establishment of BPP. BPP in lakes is light limited, and ecosystem models can provide guidance for determining the water clarity necessary to re-establish BPP dominance. We developed a multi-tiered framework for the restoration of shallow, eutrophic lakes that incorporates multiple turbidity sources, lake morphometry, and water-level fluctuations to determine water-clarity thresholds above which BPP dominance may be established. We present a case study applying this restoration target framework to a large, shallow lake (Utah Lake, Utah, USA), where water clarity was greatly impeded by sediment resuspension and high algal biomass. Our analysis, which used commonly available lake-monitoring data, indicated that a return to BPP dominance is possible in Utah Lake, particularly if external nutrient loading to its shallow, wind-protected bays is reduced. Our novel framework incorporates regime shift theory to improve shallow, eutrophic lake restoration efforts. By incorporating ecological feedbacks when identifying the restoration targets necessary for returning a lake to a self-stabilizing, clear-water regime, this restoration target framework offers economical and logistical advantages over strategies that focus solely on phytoplankton management or fish biomanipulation.

Drainage Ratio Controls Phytoplankton Abundance in Urban Lakes

Urban lakes located in densely populated regions are highly vulnerable freshwater ecosystems compared to lakes in rural areas due to intense anthropogenic activities. However, the impacts of intrinsic lake morphometry on the water quality of urban lakes remain unclear. In the present study, the water quality of 14 lakes and the underlying factors associated with such quality were explored in Wuhan City, China. Of these surveyed urban lakes, 92.9% were eutrophic or hypereutrophic; phytoplankton biomass ranged between 3.2 and 62.0 mg/L and was positively correlated with drainage ratio values (catchment area/lake area) during the phytoplankton bloom season. These results are consistent with the fact that small lakes associated with a large watershed area generally exhibit high levels of areal nutrient accumulation that rise with the drainage ratio, supporting phytoplankton growth. There were no significant differences in phytoplankton diversity among lakes (p > 0.05), remaining stable at the low Shannon index of 1.9–2.9, which is possibly due to high eutrophication pressure and similar local climatic conditions across the relatively limited study area. Overall, the results of this study will provide a valuable foundation for future efforts to improve water quality management efforts for urban lakes.

Concentrations of dissolved organic matter and methane in lakes in Southwest China: Different roles of external factors and in-lake biota

Many factors have been reported to affect material cycling in lakes, but the combined and cascading impacts of external environmental factors and in-lake biota on lake carbon cycling are poorly understood. We elucidated the influencing pathways of geoclimatic factors, lake morphometry, land-use type, chemical and physical factors, and biological taxa (phytoplankton and macroinvertebrates) on the concentrations of two important components of carbon cycling, i.e., dissolved organic matter (DOM) and methane (CH4) based on datasets from 64 plateau lakes in Southwest China. Partial least squares path modelling (PLS-PM) indicated that (1) geoclimatic factors influenced DOM and CH4 by affecting land use and lake physical factors (e.g., water temperature), (2) lake morphometry (water depth and lake area) had a direct and great negative effect on the CH4 concentration related to the production and oxidation of CH4 and affected phytoplankton and macroinvertebrates by influencing chemical and physical factors, (3) land-use type affected DOM and CH4 concentrations in both direct and indirect ways, (4) terrestrial humic-like DOM was mainly discharged from forestland and also affected by macroinvertebrates, while the impacts of agricultural and construction land on autochthonous DOM and CH4 concentrations mainly occurred by changing nutrients and then the aquatic biota. Moreover, changes in aquatic biota, primarily affected by water quality, influenced DOM spectral properties, and the two biotas affected DOM and CH4 concentrations differently. Phytoplankton, especially cyanobacteria contributed to (protein-like and humic-like) DOM in both direct and indirect ways related to eutrophication, whereas macroinvertebrates influenced DOM possibly by utilization, bioturbation, and microbial decomposition of feces according to their different relationships with DOM spectral indices. Additionally, CH4 production can be enhanced by DOM accumulation, and the significant positive correlations of CH4 concentrations with protein-like DOM and biological index indicate that autochthonous DOM may play an important role for the CH4 production. Our findings contribute to the understanding of lake carbon cycling under natural conditions and anthropogenic disturbances.

Patterns of thermocline structure and the deep chlorophyll maximum feature in multiple stratified lakes related to environmental drivers

Thermal stratification and the deep chlorophyll maximum (DCM), two commonly related phenomena in stratified lakes, play fundamental roles in eco-environmental processes. However, the progressive linkages among multi-dimensional environmental factors, thermal stratification and DCM were poorly explored, which greatly constrains our understanding of cross-level governance in deep lakes. In this study, the thermocline structure (i.e., thermocline depth, thickness and strength) and DCM feature (depth and thickness) and their driving factors were investigated at regional scale using data from 18 stratified lakes differing in limnological characteristics, Southwest China. Our study showed that (1) DCM occurred close to the thermocline in most lakes (represented by their depth and thickness), (2) the depths of the thermocline and DCM were both shallower than the euphotic depth, and (3) spatial heterogeneity occurred the thermocline structure and the DCM feature, reflecting different environmental factors. Specifically, water depth and light penetration depths were both positively correlated with thermocline depth and thickness and the DCM feature, and ultraviolet radiation (UVR) was more important than photosynthetically active radiation (PAR) for thermocline depth, but PAR was more important for thermocline thickness; moreover, PAR played a more prominent role than UVR for the DCM feature. As there were interactions between some environmental factors, we built a cascading path using a partial least squares path modelling for the DCM feature: lake morphometry directly impacted the thermocline structure and surface water quality; the water quality further affected light penetration depths as well as the thermocline structure; light penetration depth and thermocline structure combined directly determined the DCM feature, where the importance of light was larger. Our findings provide information on the cascading drivers of the thermocline structure and DCM feature in deep lakes and also constitute a valuable reference for deep lake management under the dual pressure of climate change and eutrophication.

Thermal Sensitivity of High Mountain Lakes: The Role of Morphometry and Topography (The Tatra Mts., Poland)

This study presents the results of a 5-year monitoring program of ice cover, water temperature, and local meteorological conditions carried out in three reference lakes in the periglacial zone of the Polish Tatra Mountains. On the basis of this information, the relationships between the weighted mean water temperature of each of these lakes and the air temperature, wind speed, precipitation, and ice–snow cover in the summer, spring, and autumn seasons, as well as year-round, were described, and the roles of the morphometry of lakes and the topography of their catchments were determined. It was found that the sensitivity of the lakes to climate warming increased with a decrease in their area/depth and shade, and with an increase in altitude and the share of wind-blown snow in the formation of the ice–snow cover. An increase in the mean annual air temperature does not necessarily translate into the warming of lakes, but, paradoxically, may result in their cooling. The current climate may not be best reflected by the most sensitive lakes, but rather by the largest ones located in the subalpine zone.

Interactive Effects of Lake Morphometry and Sticklebacks on the Trophic Position of Arctic charr, Salvelinus alpinus (L.), across Lakes in Western Greenland

The structure and functioning of Arctic ecosystems have been drastically modified by global warming, with fish species potentially performing habitat shifts such as the northern expansion of generalist and warm-adapted species. The freshwater fish species Arctic charr (Salvelinus alpinus, hereafter charr) plays a key role in Arctic lake food webs, but sticklebacks (Gasterosteus aculeatus) may impact the trophic position (TP) of charr by affecting their habitat choice and food resources. In the present study, we used multiple regression analyses to examine the role of lake morphology (i.e., depth and area) and the influence of sticklebacks on the TP of charr (estimated from δ15N and δ13C) sampled in nine Arctic lakes in Western Greenland between 2011 and 2013. Results showed that charr populations exhibited larger TP values when co-occurring with sticklebacks. Specifically, for larger and deeper lakes, a significant positive effect on TP values was observed for medium-sized (25 to 35 cm) charr. Moreover, the TP of sticklebacks had a null effect on the TP values of the largest charr (> 40 cm), suggesting that the largest-sized charr individuals did not prey on sticklebacks. We conclude that charr undergoes flexible ontogenetic trophic trajectories depending on the species composition of the Arctic fish community structure (here presence or absence of sticklebacks) and abiotic lake features.

A review of anthropogenic stressors on Lake Sevan, Armenia

The resilience of natural systems may be severely compromised by anthropogenic influences. In this paper, the principal anthropogenic influences on the ecosystem of the Armenian highland lake Sevan during the past century are identified. The diversity and severity of the pressures were influenced by national priorities and the catchment's growth. Changes in the lake's morphometry and the littoral's morphology, as well as unsustainable usage of the lake's fish resources, were among the repercussions. They are discussed depending on how each sort of disturbance affects the ecosystem. Although the timing and degree of each stressor were specified, identifying the direct effects of each stressor was often challenging. The current management decisions and future threats to the lake's ecosystem are discussed. This article describes the history of the anthropogenic change of Lake Sevan and, using it as an example, assesses the ecological footprint of people on natural resources and their repercussions.

Quantifying the resilience of coldwater lake habitat to climate and land use change to prioritize watershed conservation

AbstractManaging ecological systems for resilience can increase their capacity to maintain key functions even under global change. Oxygenated coldwater (oxythermal) habitat in lakes is an important ecological resource that is threatened by both climate change and eutrophication. Here, we quantify the resilience of oxythermal habitat in over 10,000 glacial lakes in the upper Midwestern United States to climate change and watershed disturbance and classify lakes for conservation prioritization based on their current conditions and resilience. Oxythermal habitat was predicted by lake morphometry, July air temperatures, and watershed land use. Temperatures are projected to increase by mid‐century, and the magnitude of warming, its effect on oxythermal habitat, and the uncertainty surrounding that effect varied among lakes. Under mid‐century climate conditions, the number of lakes containing suitable coldwater habitat was predicted to decline by 67%, while the number of lakes with unsuitable habitat was predicted to increase by over 200%. Lakes varied in the amount of temperature increase that they could sustain without a resultant change in habitat tier (i.e., their climate resilience). Median climate resilience was 4.3°C, with some lakes capable of remaining in their habitat tier even with temperature increases up to 14°C. Changing watershed land use was predicted to influence oxythermal habitat in 24% of lakes (n = 2391). We used the magnitude of increase in watershed development that a lake could sustain while remaining in its current habitat class as a measure of its resilience to watershed disturbance. Conversely, decreased watershed development may improve oxythermal habitat conditions and push a lake into an improved condition, and this value represented a lake's restoration potential. We classified lakes into seven management classes based on their current oxythermal habitat conditions and the resilience of oxythermal habitat to climate and watershed disturbance. To facilitate management on individual lakes, we also assessed the vulnerability and resilience of individual lakes and the uncertainty surrounding these estimates. By quantifying the resilience of lakes and how it is influenced by local action across a multistate region, we can prioritize conservation action across multiple scales to maintain the critical habitat and ecosystem function of glacial lakes.

Population niche width is driven by within-individual niche expansion and individual specialization in introduced brook trout in mountain lakes

The width of a population's resource-use niche is determined by individual diet breadth (“within-individual component”) and the degree of niche partitioning between individuals (“between-individual component”). The balance between these two factors affects ecological stability and evolutionary trajectories, and may shift as ecological opportunity permits broader population niches. Lakes in California’s Sierra Nevada Mountains vary in resource diversity for introduced brook trout (Salvelinus fontinalis) due to elevation, lake morphometry, and watershed features. We compared the relative contributions of within- and between-individual niche components to two measures of the dietary niches of thirteen populations of brook trout: prey taxonomic composition and prey size distribution. For both taxonomic and size diversity of fish diets, population niche width was positively related to both the within- and between-individual components. For taxonomic diversity, the two components increased in parallel, while for size diversity, the between-individual component became more important relative to the within-individual component in populations with the greatest niche widths. Our results support the Niche Variation Hypothesis that populations with broader niches are more heterogeneous among individuals and show that individual niche width and individual specialization can operate in parallel to expand the population niche.

Natural and anthropogenic controls on lake water-level decline and evaporation-to-inflow ratio in the conterminous United States.

Lake water levels are integral to lake function, but hydrologic changes from land and water management may alter lake fluctuations beyond natural ranges. We constructed a conceptual model of multifaceted drivers of lake water-levels and evaporation-to-inflow ratio (Evap:Inflow). Using a structural equation modeling framework, we tested our model on 1) a national subset of lakes in the conterminous United States with minimal water management to describe natural drivers of lake hydrology and 2) five ecoregional subsets of lakes to explore regional variation in water management effects. Our model fit the national and ecoregional datasets and explained up to 47% of variation in Evap:Inflow, 38% of vertical water-level decline, and 79% of horizontal water-level decline (littoral exposure). For lakes with minimal water management, Evap:Inflow was related to lake depth (β = -0.31) and surface inflow (β = -0.44); vertical decline was related to annual climate (e.g., precipitation β = -0.18) and water management (β = -0.21); and horizontal decline was largely related to vertical decline (β = 0.73) and lake morphometry (e.g., depth β = -0.18). Anthropogenic effects varied by ecoregion and likely reflect differences in regional water management and climate. In the West, water management indicators were related to greater vertical decline (β = 0.38), whereas in the Midwest, these indicators were related to more stable and full lake levels (β = -0.22) even during drought conditions. National analyses show how human water use interacts with regional climate resulting in contrasting impacts to lake hydrologic variation in the US.