SEASONAL INFLUENCE ON LAND USE BIOGEOCHEMICAL FINGERPRINTS IN SURFACE WATER BODIES

Five synoptic sample events targeting seasonal and hydrologic variation within the Saginaw Bay Watershed, Michigan, were collected to evaluate the associations between land use and major chemical species. The watershed as a whole did not exhibit strong temporal fluctuation of sodium and bromide concentrations despite considerable application of salt applied as a road-deicer in the winter months. However, strong local fluctuations of solutes were documented, attributed to proximity of urban centers and agricultural land use. The lowest concentrations of solutes were observed in association with forested land use. Factor analysis revealed the relative strength of a biogeochemical fingerprint for a particular land use type to be dependant upon season. Agricultural land use exhibited its most significant fingerprint during a summer low flow and a spring high flow which possibly coincided with agricultural practices. Urban land use exhibited its strongest fingerprint during winter high flow, likely due to road deicing salt application.