Citation:

Fergus, C., J. Renee Brooks, Phil Kaufmann, A. Pollard, A. Herlihy, Steve Paulsen, AND M. Weber. National framework for ranking lakes by potential for anthropogenic hydro-alteration. ECOLOGICAL INDICATORS. Elsevier Science Ltd, New York, NY, 122:107241, (2021). https://doi.org/10.1016/j.ecolind.2020.107241

Impact/Purpose:

Both natural and constructed lakes and reservoirs provide valuable water-related ecosystem services such as drinking water, irrigation, cooling, flood control, recreation, and hydropower. Dams and landscape modifications such as ditches and canals facilitate and enhance these ecosystem services, but in turn can alter lake hydrology. These anthropogenic structures and activities can dampen or increase natural lake water-level fluctuations, impairing recreation, nearshore physical habitat, and water quality. Regional and national lake monitoring and assessment programs need to account for how these structures may alter lake hydrology. A clear system to integrate landscape metrics that indicate the potential for human hydrologic alteration would help to separate the geoclimatic and anthropogenic influences on lake level fluctuation. The authors developed a practical framework to rank lakes on a gradient of potential human hydrologic alteration (HydrAP) based on the presence of anthropogenic structures and activities that can alter lake hydrology: dams and land use. The premise of the HydrAP framework is that dam height and proportions of land use activities such as irrigated agriculture are indicators of the potential for human water management to alter lake water levels. The HydrAP framework uses readily accessible, national-scale geospatial information from NLA (US EPA), LakeCat (US EPA), and the National Inventory of Dams (US Army Corp of Engineers), so that lakes distributed across the conterminous US can be ranked using common data sources. The authors applied the HydrAP framework to lakes in the 2007 and 2012 NLA surveys to characterize the abundances and distributions of anthropogenic structures and activities with potential to affect water levels on CONUS lakes. The HydrAP framework is structured as a decision tree with modular components that can be adapted to different landscape contexts. This robust tool can support lake monitoring and assessment across the nation by providing critical insights on the relative influence of natural and anthropogenic influences on lake hydrologic condition and water quality and habitat attributes affected by lake level fluctuations.

Description:

Lake ecosystems face multiple disturbances and environmental change that can significantly impact lake hydrology. Human activities in the watershed (e.g., irrigated agriculture) and managed dams can alter lake inflows and outflows beyond natural ranges and changing climate conditions may exacerbate human disturbances to lake hydrology. However, we lack cost-effective indicators to quantify the range in the potential for humans to alter lake hydrology at regional and national extents. We developed a framework to rank lakes by the potential for anthropogenic alteration of lake hydrology (HydrAP) caused by dams and land use activities that can result in altered lake water balance using widely-available national-scale datasets. The principles behind the HydrAP framework are that 1) dams are primary drivers of lake hydro-alteration, 2) land use activities are secondary drivers that alter watershed hydrology, and 3) topographic relief limits where land use activities and dams are located on the landscape. We used the HydrAP framework to rank lakes in the US EPA National Lakes Assessment (NLA) on a scale from zero to seven, where a zero-rank indicates lakes that have no potential for human alteration of lake water balance, and a seven-rank indicates lakes with large dams and/or intensive land use activities with high potential to rapidly and dramatically alter lake water balance. We inferred HydrAP distributions from the sampled lakes to the population of lakes in the conterminous US (CONUS) using the NLA probabilistic weights. About half of CONUS lakes were estimated to have moderate to high hydro-alteration potential (HydrAP ranks 3-7) and the other half had no to minimal hydro-alteration potential (HydrAP ranks 0-2). HydrAP ranks largely separated out along natural and man-made lake origin classes, but each lake type exhibited variation spanning the full HydrAP gradient. Over 15% of natural lakes had moderate to high HydrAP ranks, and around 10% of man-made lakes had low HydrAP ranks. Distributions of lake HydrAP ranks varied by ecoregion, with the Great Plains, Appalachians, and Coastal Plains having the largest percentages (>50%) of lakes with high HydrAP ranks, and the West and Midwest having lower percentages (~30%). High HydrAP ranks tended to be large, deep lakes with large watershed-to-lake area ratios (WA:LA), and low HydrAP ranks tended to be small, shallow lakes with small WA:LA. Water residence time and lake water-level change were associated with HydrAP ranks and support the framework’s ability to differentiate human stressors that can alter lake hydrology. Across ecoregions, water residence times were shorter in lakes with high HydrAP ranks. But HydrAP rank relationships with lake water-level change varied by ecoregion and likely reflects different regional water management strategies. In the West and Appalachians, high HydrAP ranks were associated with greater than expected water-level decline based on least-disturbed conditions. In contrast, high HydrAP ranks in the Great Plains and Midwest were associated with less water-level change implying that water management may promote water level stabilization. The HydrAP framework is an approach to estimate human hydrologic disturbances across broad spatial extents when detailed records are not available or impractical to use. This approach offers promise to support large-scale lake hydrologic assessments.

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