Nonpoint source (NPS) pollution in the United States causes nearly $10 billion in damage yearly. Though it is often believed agricultural areas are the primary source of NPS pollution, urban areas have also been identified as a significant source of NPS pollution, and it is becoming increasingly essential to understand how hydrologic impacts of land use changes affect the surface/subsurface water, since urban/non-urban areas primarily depend on these as a drinking water source. In urbanizing watersheds, conversion from non-urban to urban land uses leads to increased imperviousness and consequently increased runoff. The result is often flooding, stream degradation, erosion, loss of wildlife habitat, and depletion of groundwater supply. The present study forms part of a broad investigation into the long-term effects of major land use change on the hydrology and water quality of watersheds in north Texas. In this paper we examine runoff, sediment, and nutrient dynamics in two headwater basins of the Trinity River Watershed. We present results on the spatial and temporal patterns of surface runoff and pollutant flux, determine the effect of land use on these fluxes, and quantify pollutant export in order to determine whether levels are potentially serious.