INFLUENCE OF URBANIZATION ON A PREDOMINANTLY AGRICULTURAL WATER SHED: WHITE RIVER, INDIANA

This study qualifies and quantifies the impact of industrial cities of increasing size on the water and sediment geochemistry in a mid-western, agriculturally impacted watershed. The study area is located in east-central Indiana, along the west fork of the White River. The headwater region of the White River is entirely dominated by agriculture. As the river increases in size, it flows through several cities of increasing population size from small towns to metropolitan areas: Winchester, Muncie and Anderson, and Indianapolis (population ~5,000; ~65,000; ~2,000,000 respectively). To quantify the cities’ influence on the river geochemistry, water and sediment samples were collected in 2008, 2010 and 2012, up- and down-stream of the cities. Temperature and pH were measured in-situ; water samples were analyzed for major cation and anion concentrations, trace metals, as well as total suspended solids; trace metals were measured in the sediment samples. Tributaries, unaffected by urbanization but affected by agriculture, were sampled for comparison. Trace metals in water increase after the river passes through the first town but then stay fairly constant, as a combined result of the high pH of the river that favors the metals being adsorbed to particle surfaces and the dilution by non-contaminated tributaries. Metals in sediments, on the other hand, increase several-fold every time the river flows through a city. Even though the trace metal concentrations in the sediment decrease somewhat downstream of each city, probably by dilution of less-affected sediments, they never decrease to the original level. Cities effectively and permanently increase the trace metal load in the sediments. Similar behavior is observed for major anions and cations, especially K, Na and Cl, in water. Nitrate is the only anion that is influenced as much as by agriculture as it is by urbanization –fertilizer application increases nitrate concentrations in headwaters relatively more than the cities affect the concentrations downstream. The results will be discussed with respect to increasing discharge and drainage area, population density, and potential influences of the summer 2012 drought.