Quality and Quantity of Suspended Particles in Rivers: Continent-Scale Patterns in the United States

Abstract

Suspended solids or sediments can be pollutants in rivers, but they are also an important component of lotic food webs. Suspended sediment data for rivers were obtained from a United States-wide water quality database for 622 stations. Data for particulate nitrogen, suspended carbon, discharge, watershed area, land use, and population were also used. Stations were classified by United States Environmental Protection Agency ecoregions to assess relationships between terrestrial habitats and the quality and quantity of total suspended solids (TSS). Results indicate that nephelometric determinations of mean turbidity can be used to estimate mean suspended sediment values to within an order of magnitude (r(2) = 0.89). Water quality is often considered impaired above 80 mg TSS L(-1), and 35% of the stations examined during this study had mean values exceeding this level. Forested systems had substantially lower TSS and somewhat higher carbon-to-nitrogen ratios of suspended materials. The correlation between TSS and discharge was moderately well described by an exponential relationship, with the power of the exponent indicating potential acute sediment events in rivers. Mean sediment values and power of the exponent varied significantly with ecoregion, but TSS values were also influenced by land use practices and geomorphological characteristics. Results confirm that, based on current water quality standards, excessive suspended solids impair numerous rivers in the United States.