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Freshwater salinization from anthropogenic activities threatens water quality and habitat suitability for many lakes and rivers in North America. Recognizing that salinization is a stress on freshwater environments globally, research on watershed salt transport is necessary for informed management strategies. Prior to this research, there were few studies that examined salt export regimes along a river–lake continuum to investigate the drivers, temporal dynamics, and modulators of freshwater salinization. Here, we use high-frequency in situ monitoring to assess specific conductance–discharge (cQ) relationships, chloride concentrations and fluxes, and the role of lakes in downstream salt transport. The Upper Yahara River Watershed in southern Wisconsin, USA, is a mixed urban and agricultural watershed where the lakes' chloride concentrations have risen from < 5 mg L−1 in the 1940s to > 50–80 mg L−1 in 2021. Our results suggest cQ behavior depends on land use, with urban areas exhibiting more frequent mobilization events during stormflow and agricultural areas exhibiting predominantly dilution dynamics. In addition, chloride loading is driven by hydrology and watershed size whereas concentrations and yields are a function of anthropogenic drivers like urbanization. We demonstrate how an in-network lake attenuates downstream salinity, dampening the hydrologic, anthropogenic, and seasonal patterns observed in rivers upstream of the lake. Importantly, biogeochemical processes in lakes overlay a seasonal signal on salinity that must be considered when investigating temporal dynamics of anthropogenic salinization. This research contributes to understanding of temporal dynamics of salt export through watersheds and can be used to inform management strategies for habitat protection. 

This repository includes the setup and output from the analysis ran on Lake Mendota to explore the trophic cascade caused by invasion of spiny water flea in 2010. Scripts to run the model are located under /src, and the processed results for the discussion of the paper are located under /data_processed.

 

Climate change is leading to shifts in not only the average timing of phenological events, but also their variance and predictability. Increasing phenological variability creates a stochastic environment that is critically understudied, particularly in aquatic ecosystems. We provide a perspective on the possible implications for increasingly unpredictable aquatic habitats, including more frequent trophic asynchronies and altered hydrologic regimes, focusing on ice-off phenology in lakes. Increasingly frequent phenological extremes may limit the ability of organisms to optimize traits required to adapt to a warming environment. Using a unique, long-term ecological dataset on Escanaba Lake, WI, USA, as a case study, we show that the average date of ice-off is shifting earlier and becoming more variable, thus altering limnological conditions and yielding uncoupled food web responses with ramifications for fish spawn timing and recruitment success. A genes-to-ecosystems understanding of the responses of aquatic communities to increasingly variable phenology is needed. Our perspective suggests that management for diversity, at the intra- and interspecific levels, will become paramount for conserving resilient aquatic ecosystems. 

Salt pollution is a threat to freshwater ecosystems. Anthropogenic salt inputs increase lake and stream salinity, and consequently change aquatic ecosystem structure and function. Elevated salt concentrations impact species directly not only through osmoregulatory stress, but also through community‐level feedbacks that change the flow of energy and materials through food webs. Here, we discuss the implications of road salt pollution on freshwater rivers and lakes and how “one size fits all” ecotoxicity thresholds may not adequately protect aquatic organisms.

This article is categorized under:

Science of Water > Water Quality

Water and Life > Nature of Freshwater Ecosystems

Water and Life > Stresses and Pressures on Ecosystems

 

Conductivity and chloride were measured for 2 years in nine tributaries of Lake Mendota and Lake Monona in Dane County, WI. HOBO Conductivity loggers continuously measured absolute conductivity and water temperature every 30 minutes. Breaks in data collection were due to a calibration period or if the loggers were out of the water. Grab samples for chloride concentration occurred weekly or biweekly. Conductivity and water temperature were measured with a field meter at each sampling excursion. This data was needed for a master’s research thesis with the goal of characterizing the spatial distribution and loading of chloride in the Upper Yahara River Watershed. 

Widespread and increasing use of road deicing salt is a major driver of increasing lake chloride concentrations, which can negatively impact aquatic organisms and ecosystems. We used a simple model to explore the controls on road salt concentrations and predict equilibrium concentrations in lakes across the contiguous United States. The model suggests that equilibrium salt concentration depends on three quantities: salt application rate, road density, and runoff (precipitation minus evapotranspiration). High application combined with high road density leads to high equilibrium salt concentrations regardless of runoff. Yet if application can be held at current rates or reduced, concentrations in many lakes situated in lightly to moderately urbanized watersheds should equilibrate at levels below currently recommended thresholds. In particular, our model predicts that, given 2010–2015 road salt application rates, equilibrium chloride concentrations in the contiguous United States will exceed the current regulatory chronic exposure threshold of 230 mg L⁻¹in over 2000 lakes; will exceed 120 mg L⁻¹in over 9000 lakes; and will be below 120 mg L⁻¹in hundreds of thousands of lakes. Our analysis helps to contextualize current trends in road salt pollution of lakes, and suggests that stabilization of equilibrium chloride concentrations below thresholds designed to protect aquatic organisms should be an achievable goal.

 

Lakes and reservoirs, as most humans experience and use them, are dynamic bodies of water, with surface extents that increase and decrease with seasonal precipitation patterns, long-term changes in climate, and human management decisions. This paper presents a new global dataset that contains the location and surface area variations of 681,137 lakes and reservoirs larger than 0.1 square kilometers (and south of 50 degree N) from 1984 to 2015, to enable the study of the impact of human actions and climate change on freshwater availability. Within its scope for size and region covered, this dataset is far more comprehensive than existing datasets such as HydroLakes. While HydroLAKES only provides a static shape, the proposed dataset also has a timeseries of surface area and a shapefile containing monthly shapes for each lake. The paper presents the development and evaluation of this dataset and highlights the utility of novel machine learning techniques in addressing the inherent challenges in transforming satellite imagery to dynamic global surface water maps.

 

Anthropogenic freshwater salinization affects thousands of lakes worldwide, and yet little is known about how salt loading may shift timing of lake stratification and spring mixing in dimictic lakes. Here, we investigate the impact of salinization on mixing in Lakes Mendota and Monona, Wisconsin, by deploying under-ice buoys to record salinity gradients, using an analytical approach to quantify salinity thresholds that prevent spring mixing, and running an ensemble of vertical one-dimensional hydrodynamic lake models (GLM, GOTM, and Simstrat) to investigate the long-term impact of winter salt loading on mixing and stratification. We found that spring salinity gradients between surface and bottom waters persist up to a month after ice-off, and that theory predicts a salinity gradient of 1.3–1.4 g kg-1 would prevent spring mixing. Numerical models project that salt loading delays spring mixing and increases water column stability, with ramifications for oxygenation of bottom waters, biogeochemistry, and lake habitability.