The time scales established to address water quality issues in watershed and channel management should accommodate a range of causes and a variety of sources. A short time scale will reflect the short term variability typical of stormwater and some nonpoint sources of contamination. An intermediate time scale will accommodate the constancy of input, typical of point sources. A long time scale will reflect cumulative effects and trends, and is appropriate for determination of watershed and landuse influence on water quality.

This research area addresses a range of issues associated with time scales, and associated spatial relationships. For example, the episodic nature of nonpoint sources requires a paradigm shift to adequately perform effect analysis in any system assessment. This shift recognizes that traditional toxicity testing procedures, which assume constant flow, are inappropriate for the assessment of episodic exposures produced by, in particular, stormwater/wet weather discharges. In storm events, concentrations may vary over several orders of magnitude over very short time periods (seconds to minutes). In addition, the paradigm shift also requires a re-analysis of cumulative effects where both the frequency of exposure and the accumulation/storage of contaminants leads to system degradation.

Recently, this research focus has developed in a research project "Region Specific Time-Scale Toxicity in Aquatic Ecosystem" funded by the Water Environment Research Foundation.