“TURBID” WATERS OF THE KAYADEROSSERAS: HUMAN CAUSED OR GLACIALLY INFLUENCED?

The turbidity of streams can be caused by land use change, such as residential or commercial development and agricultural practices, or by natural erosion of stream banks. In order to determine the cause of turbidity in the Kayaderosseras Creek Watershed, we choose four sets of paired watersheds that ranged in size from approximately 5 km² to 14 km². Each pair had comparable basin wide slopes, surficial sediments, soil hydrology distributions, basin areas, and land use patterns. We measured stream discharge and turbidity in each watershed at several different discharges during the fall of 2005. Preliminary results show that discharge per unit area (Q/A) was controlled mostly by soil infiltration capacity and surficial geology, while residential and commercial development seemed to have little effect on the magnitude of Q/A. Although the change in Q/A was minimal for the pair of basins that were dominated by well-drained soils, development was significant, 6 and 23 percent of total basin areas, and Q/A increased 60 percent faster for the more developed basin. Turbidity showed consistent trends with Q/A. Generally, turbidity increased consistently as a function of Q/A, with higher turbidity measurements in basins with higher percentages of farming. Again, the exceptions are the basins with the well-drained soils with high percentages of development. Here, small changes in Q/A are associated with up to a six-fold increase in turbidity. Our preliminary results suggest that farming practices increase stream turbidity, but the relationship between development and increased stream turbidity is less certain.