Monitoring the water balance of seepage lakes to track regional responses to an evolving climate

Understanding the causes of large fluctuations in lake water levels is important for adaptive resource management. The relatively simple water budgets of small seepage lakes make them potentially useful model systems, provided that key water balance components can be well constrained. Here, spatial variability in measured rates of evaporation (E) and precipitation (P) at the whole lake scale was investigated, and the effect on daily and seasonal water balance estimates was quantified. To estimate spatial variability, triplicate sensor platforms were deployed on and near an 18 ha seepage lake. Lake stage (S) was monitored at a single node in the lake. The water balance was closed by estimating net groundwater seepage (Gnet) analytically as Gnet = ∆S – (P – E). Instrumentation on a second seepage lake was maintained by citizen scientists to assess the potential for more widespread sensor deployments. Data were collected every 30-minutes for six months. The results indicate that low-cost sensor networks with single nodes to measure E, P and ∆S provide well-constrained water budgets at daily and seasonal time scales.

Characterizing Groundwater Interaction with Lakes and Wetlands Using GIS Modeling and Natural Water Quality Measurements

Wetlands provide many benefits, including flood attenuation, groundwater recharge, water-quality improvement, and habitat for wildlife. As their structure and functions are sensitive to changes in hydrology, characterizing the water budgets of wetlands is crucial to effective management and conservation. The groundwater component of a budget, which often controls resiliency and water quality, is difficult to estimate and can be costly, time-consuming, and invasive. This study used a GIS approach using a digital elevation model (DEM) and the elevations of lakes, wetlands, streams, and hydric soils to produce a water-table surface raster for a portion of the Itasca Moraine, Minnesota, U.S. The water-table surface was used to delineate groundwatersheds and groundwater flow paths for lakes and wetlands, and map recharge and discharge rates across the landscape. Specific conductance and pH, which depend on the hydrological processes that dominate a wetlands water budget, were measured in the field to verify this modeling technique. While the pH of surface waters varied in the study area, specific conductance increased from 16.7 to 357.5 μS/cm downgradient along groundwater flow paths, suggesting increased groundwater interaction. Our results indicate that basic GIS tools and often freely available public-domain elevation datasets can be used to map and characterize the interaction of groundwater in the water budgets of lakes and wetlands, as exemplified by the Itasca Moraine region. Combining this with grid cell-by-cell water balance provides a means to estimate recharge and discharge, thereby affording a way to quantify groundwater contribution to and from lakes and wetlands. Applied elsewhere, this cost-efficient technique can be used to assess the vulnerability of lakes and wetlands to changes in land use, groundwater development, and climate change.

Boundary condition and oceanic impacts on the atmospheric water balance in limited area climate model ensembles

Regional climate models (RCMs) are indispensable in climate research, albeit often characterized by biased terrestrial precipitation and water budgets. This study identifies excess oceanic evaporation, in conjunction with the RCMs’ boundary conditions, as drivers contributing to these biases in RCMs with forced sea surface temperatures in a CORDEX RCM ensemble over Europe. The RCMs are relaxed to the prescribed lateral boundary conditions originating from a global model, effectively matching the driving model's overall atmospheric moisture flux divergence. As a consequence, excess oceanic evaporation results in positive precipitation biases over land due to forced internal recycling of moisture to maintain the overall flux divergence prescribed by the boundary conditions. This systematic behaviour is shown through an analysis of long-term atmospheric water budgets and atmospheric moisture exchange between oceanic and continental areas in a multi-model ensemble.