EXPLORING THE EFFECTS OF URBAN AND AGRICULTURAL LAND USE ON SURFACE WATER QUALITY

Urbanization influences the water cycle through changes in flow and water quality. The working hypothesis of this research is that the influences on water quality can be quantified. Previous work has shown that urban land use (Na-K-Cl) may be differentiated from other land uses, such as agricultural (Ca-Mg), through the use of biogeochemical fingerprints. In this study we attempt to validate the applicability of these fingerprints and more specifically, investigate the influence of urban land use on nutrient cycles. Our approach compares land use and water quality in two Great Lakes watersheds over the Michigan Basin; Muskegon River and Grand Traverse Bay. Samples were analyzed for nutrients (TN, NO_x, TP, SRP, NH₃, SiO₂, DOC) major ions (Ca, Mg, Na, K, alkalinity, Cl, SO₄, F) and trace metals (Mn, Fe, Sr, Rb, Mo, U, Ba, Cr, Cu, Cd, Pb, Ni, Sc, Al, Zn, As, Ti, V, Co). Sampling sites were selected to represent surface water source sheds with a variety of dominant (e.g., urban) and mixed (e.g., urban, agricultural, forest) land use types. Factor and cluster analysis were used to investigate the processes controlling the effects of land use on river chemistry. Biogeochemical fingerprints of land use were referenced to the natural environment aiding in the identification of the unique contributions of urban and agricultural land uses to surface water chemistry. Selected results are that 1) similar biogeochemical fingerprints are found between the two watersheds (Urb: Na, K, Cl / Ag: Ca, Mg) and 2) additional correlations were found for nutrients (Ag: N & Urb: N, P) and for selected trace metals (Urb: F, Mn, Rb, Mo, Sr and Ba / Ag: U). The higher correlations of urban than agricultural land uses with nutrients were not expected and may reflect the effects of fertilization and wastewater or the season the samples were taken. More study in different geologic and urban (suburban, city) settings is needed to help quantify these fingerprints. These studies could lead to a rapid assessment tool for the quality and sources for degradation (e.g., septic) of urban environments.