The Role of Geologic Heterogeneity to Constrain Root Water Uptake
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Under a future climate, shifting hydrologic conditions may impact the distribution of wetland plant communities, threatening ecological functions such as biogeochemical cycling, flood protection, heat island effects, and habitat diversity for hundreds of species of birds, mammals, insects, and amphibians. In humid climate wetlands, such as those found in the Great Lakes basin, predictive ecohydrology models focus on plant responses to increasing soil moisture conditions and a fluctuating water table. However, these models have ignored the geologic heterogeneity that constrains water availability in the shallow subsurface. The focus of this research is to use numerical modeling to assess the statistical significance of geologic heterogeneity to constrain the hydrologic conditions that maintain plant diversity in a representative humid climate wetland under both current and forecasted climates. Like many wetlands in northeastern United States, the geology underlying the project site, a 300m 2 plot at Iroquois National Wildlife Refuge in western New York, is comprised of glacially derived soil. Distinct patterns of heterogeneous soil texture and layer thickness found beneath the six plant communities found at the project site supports the development of vegetation specific, field based variably saturated flow models using Richard’s equation. In the development of these field based models, measurements from groundwater wells and soil moisture probes established initial and boundary hydrologic conditions, while lab analysis of soil cores collected beneath each plant community provide parameters for root water uptake and heterogeneous geologic profiles. To analyze the role of geologic heterogeneity to constrain hydrologic conditions under variable climate scenarios, soil moisture profiles (model outputs) from the heterogeneous models were statistically compared to several homogeneous models. Significant differences between the homogeneous and heterogeneous variably saturated flow model results indicate the importance of incorporating geologic heterogeneity into ecohydrology models, particularly under future, wetter climate conditions. Further, results indicate an important role of geologic heterogeneity under future climates in the preservation of hydrologic niche diversity; with implications for improved restoration efforts that rely on forecasts of shifting habitats.