A GIS Model of Subsurface Water Potential for Aquatic Resource Inventory, Assessment, and Environmental Management

Abstract

/ Biological, chemical, and physical attributes of aquatic ecosystems are often strongly influenced by groundwater sources. Nonetheless, widespread access to predictions of subsurface contributions to rivers, lakes, and wetlands at a scale useful to environmental managers is generally lackRiver, lake, and wetland ecosystems are strongly influenced by routing of source waters because relative conmbutions of precipitation, runoff, through-flow, and groundwater shape seasonal hydrography, chemical prop erties, thermal characteristics, and ultimately, the character of aquatic biota (Dunne and Leopold 1978, Wiley and others 1997, Winter 2001. Subsurface water inputs in particular can have strong influences on local biology due to their relatively cold summer temperatures, high dis ing. In this paper, we describe a "neighborhood analysis" approach for estimating topographic constraints on spatial pattems of recharge and discharge and discuss how this index has proven useful in research, management, and conservation contexts. The Michigan Rivers Inventory subsurface flux model (MRI-DARCY) used digital elevation and hydraulic conductivity inferred from mapped surficial geology to estimate spatial patterns of hydraulic potential. Model predictions were calculated in units of specific discharge (meters per 4ay) for a 30-m-cell raster map and interpreted as an index of potential subsurface water flux (shallow groundwater and event through-flow). The model was evaluated by comparison with measurements of groundwater-related attributes at watershed, stream segment, and local spatial scales throughout Lower Michigan (USA). Map-based predictions using MRI-DARCY accounted for 85% of the observed variation in base flow from 128 USGS gauges, 69% of the observed variation in discharge accrual from 48 river segments, and 29% of the residual variation in local groundwater flux from 33 locations as measured by hyporheic temperature profiles after factoring out the effects of climate. ARhough it does not incorporate any information about the actual water table surface, by quantifying spatial variation of key constraints on groundwater-related attributes, the model provides strata for more intensive study, as well as a useful spatial tool for regional and local conservation planning, fisheries management, wetland characterization, and stream assessment.

Effects of riparian buffers on nitrate concentrations in watershed discharges: new models and management implications

“…Riparian buffers that seem well positioned according to surface topography can be ineffective when subsurface flow goes around the buffer or deep beneath the biologically active soils of the buffer zone (Denver 1991, Altman and Parizek 1995, Speiran 2010. Methods for quantifying key constraints on subsurface flow (e.g., Gerla 1999, Baker et al 2003, Kellogg et al 2008) could be incorporated to improve model results. Even without such improvements, we did observe strong and statistically significant buffer effects in the Coastal Plain and Piedmont study watersheds, which confirms that our simplifying assumptions are useful.…”

Improved methods for quantifying potential nutrient interception by riparian buffers

“…In the meantime, flow paths based on surface topography should give better results than fixed-distance approaches, which include no flow path information at all. Future improvements might include more realistic algorithms for predicting surface water flow (e.g., Tarboton 1997) or including constraints on subsurface flux (e.g., Baker et al 2003).…”

Environmental analysis of groundwater in Mecosta County, Michigan

“…Indeed, 76.4 billion gallons of groundwater are being withdrawn daily, with agricultural irrigation accounting for almost 75% of that total (Maupin and Barber 2005). Even in the Great Lakes basin, where almost 90% of the United States' surface fresh water is located, groundwater is critical for the basin's hydrology and ecological health (Baker et al 2003;Hoaglund et al 2002). Although quantity is critical to maintain flows and water levels, groundwater quality also is threatened due to changing land uses.…”