Using a sediment balance for the assessment of stream quality in the midwestern US

Abstract:

Sediment is considered a source of water quality impairment in many streams but is also an essential component of lotic ecosystems. Assessment of water quality impairment related to sediment, in contrast to synthetic chemicals, requires a framework to account for the influence of natural physiographic factors before any impairment can be attributed to anthropogenic factors. A conceptual sediment balance was applied to account for the size and stability fo bed material in a synoptic investigation of 100 streams in the midwestern US conducted collaboratively through the USGS National Water Quality Assessment and US EPA National Aquatic Resource Surveys. Basin slope and water surface gradient serve as indicators of sediment supply and transport capacity, respectively, that are associated with variation in the size of bed material across sites in the investigation. Given this general model, urban development, reservoirs, and agricultural land use emerge as other significant factors influencing the particle size-distribution of stream bed material. Sediment loading, which presumes a monotonic relation between impairment and sediment supply, is an incomplete and potentially misleading description of how anthropogenic factors influence the quality of small streams. A sediment balance provides a better conceptual model for assessing stream quality impairment because it can identify both excess and lack of sediment. A sediment balance provides additional information about whether transport capacity or sediment supply may be causal factors and how management of these factor is likely to influence stream quality.