UNDERSTANDING ECOSYSTEM BIOGEOCHEMICAL CONTROLS ON TIME-LAGGED WATER QUALITY RESPONSES TO LAND USE / LAND COVER

Change in land use causes biogeochemical changes in aquatic ecosystems; as land is changed from its natural state into land for various anthropogenic uses, the geochemical signal changes as well. Previous studies have demonstrated the link between land use/land cover (LULC) to response in aquatic ecosystem chemistry, but studies have often assumed that the surface water quality measured is representative of the current LULC. It has been demonstrated that groundwater contributes a significant portion of the chemistry represented by historical land use. Using combined historical LULC and groundwater travel-time models is referred to as land use legacy maps; land use legacy maps can be used to study the relationships between dynamic LULC and water chemistry. Studies of land use impacts on surface water have not accounted for the biogeochemical dynamics played by the receiving water in different ecosystems and assume that the water chemistry parameters are generalizable across aquatic ecosystems.

The aim of this study is to investigate how dynamic legacy land use is expressed differently in varying hydrologic systems; this will be done by comparing the different chemical assemblages found in streams, wetlands, and lakes. Land use in the study area, the Muskegon River Watershed, mostly consists of forest, followed by agricultural and urban. A combined total of 267 water samples were collected from streams, wetlands, and lakes. The water chemistry of each sample was analyzed and recorded. R was used to conduct multiple linear regressions analyzing the water chemistry between current and legacy LULC. We expect to find that LULC geochemical signals will be strongest in lakes, as streams tend to rapidly flush out chemical inputs and the biologic reactivity of wetlands may mute the LULC signal. The results of this study may also provide insights on the distortion of legacy land use signals. Land use has been rapidly changing near bodies of water and it is important to understand the accuracy of land use legacy maps so that they can be used for improved watershed management.