Composition of the suspended load as a measure of stream health

Objectives of this exploratory research were: 1) to characterize the contribution of size-specific and total concentrations of organic and inorganic components to the suspended load during high and low flow periods in 4 streams in coastal northern California; and 2) to evaluate relationships between composition and nutritive quality of the suspended loa d with feeding efficiency and condition of salmonid fishes and the abundance of their invertebrate prey. In addition, we conducted laboratory feeding trials to evaluate the effects of suspended sediment concentration, organic: inorganic particle ratios, and their interaction on feeding rates of juvenile steelhead trout. Two levels of suspended sed iment concentration (producing turbidities of approximately 25 and 50 NTU’s), and three levels of organic: inorganic particle ratios (25,50, and 75% organic su spended sed iments) were tested.

Suspended sediments, macroinvertebrates, and salmonids were sampled from 200-m reaches in North Fork Caspar and South Fork Caspar creeks (Caspar Creek basin in Mendocino County), and Little Lost Man and Upper Prairie creeks (Redwood Creek basin in Humboldt County) in three high flow and three low flow periods from October 2002 through December 2003. Stream sites differed in size and in riparian vegetation and land use history, and were chosen to represent a range of discharge and suspended load conditions.