Total nitrogen loads in the basin were approximately 10 times greater than the total phosphorus loads and about 1000 times greater than the caffeine, DEET, and triclosan loads. Cholesterol plus coprostanol loads were approximately 10 times greater than the caffeine, DEET, and triclosan loads. Loads in the effluent-dominated reaches were, on average, about 20 times greater than loads from reaches dominated by combined sewer overflows. Biogeochemical processes in bottom sediments reduced some constituent concentrations by approximately two-thirds during a 6 to 8-month period.
In effluent-dominated reaches, increased caffeine and cholesterol plus coprostanol contributions to streams occurred during the winter when colder temperatures may have reduced wastewater removal rates; constituent contribution declines coincided with increased summer temperatures. For stream reaches that received only combined sewer overflows, seasonal load patterns more closely followed seasonal precipitation patterns because overflows were controlled by rainfall events. One exception was DEET, for which June to August accounted for the largest percentage of seasonal contributions at all sites.
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