Use of spatial surrogates to assess the potential for non‐point source pollution in large watersheds

Abstract

Sediment represents a major non-point source pollutant throughout the world. In addition to reduced agricultural productivity as the result of the loss of fertile soil, soil erosion also can have significant water-quality impacts in downstream waterbodies, reducing water transparency, degrading aquatic habitats and reducing the operational life and water storage capacity of reservoirs producing hydroelectric power. Various other pollutants also can absorb to sediment particles, creating additional downstream water-quality concerns for humans and the natural environment. In view of its human and environmental significance, two indices (an erosion index and runoff index) were developed to identify areas within the US portion of the Rio Grande Basin exhibiting physical characteristics conducive to producing significant non-point source pollution loads, focusing on land erosion as a sediment source. The erosion index is an adaptation of the Universal Soil Loss Equation, being the product of rainfall erosivity (R factor), soil erodibility (K factor), and a topographic factor (LS factor). The erosion index correlated well with measurements of sediment yields from runoff plots. The Curve Number was used as the runoff index. In conjunction with identified pollutant-generating land uses, or source landscapes, these indices were used to identify sub-watersheds within the US portion of the Rio Grande Basin that merit further investigation for non-point source pollution prevention and control via the use of hydrologic modelling techniques.