Evaluation of Seasonality in Shallow Groundwater Dynamics and Storage in an Urban Prairie Nature Preserve Using a High-Frequency Sensing Network

Changing regional climate applies stresses to urban areas in the form of altered weather patterns, requiring new strategies for stormwater runoff management and flood mitigation. At the same time, the proportion of people residing in urban areas is increasing and cities are turning to greenspace as a tool for managing runoff. Gensburg Markham Prairie (GMP), located in Markham, Illinois south of Chicago, is an urban prairie nature preserve and a U.S. National Natural Landmark. Owned by Northeastern Illinois University and managed by the Nature Conservancy, GMP receives runoff from surrounding urban areas and provides valuable stormwater storage, while also hosting high biodiversity and providing critical habitat for sensitive and endemic. A successful management strategy for GMP should preserve both of these valuable ecosystem services. To understand GMP's role within the urban environment, we installed a suite of instruments in 2016 and 2017 to measure surface and groundwater levels, rainfall, soil moisture, and electrical conductivity throughout the prairie. This monitoring network includes 40 sensors collecting high frequency data (every 30 minutes). We are also collecting monthly distributed surface and groundwater samples to quantify a range of anions and cations that signal potentially detrimental anthropogenic impacts on the prairie. In addition, we are using historical and ongoing plant distribution surveys to explore the interactions between spatial patterns in vegetation and water dynamics in the prairie. The high measurement frequency and large diversity of sensor types supports holistic investigation of the response of the prairie to diverse events, including summer thunderstorms, winter road salt runoff, and spring snowmelt. The 18 months of data collected to date reveals clear patterns in response to weather events with influence from soil type and spatial variables. We are using time-series analysis with MODFLOW modelling to explore surface-groundwater interactions within the site and the effects of seasonality on the prairie's capacity for storage of stormwater runoff. This analysis supports development of management strategies to preserve the prairie's ecological diversity and provide a basis for regional-scale design of green infrastructure for flood control.