Gross Solids Collected from Urban Catch Basins in North Carolina: A Potential Pollutant Accounting and Capture Opportunity

Gross solids are particles at least 5 mm in diameter and characterized as organic debris, litter, or coarse sediments. These large particles are conveyed to water bodies via storm drainage networks and contribute to nonpoint source pollution. Previous research in North Carolina, US, has characterized gross solids pollution along highways, but there are a lack of data quantifying the nutrient concentrations and loads of organic debris passing through urban catch basins. Sixteen catch basins located across the state were monitored for approximately 1 year to measure gross solid nutrient loads. Within four municipalities, four land uses were examined: (1) high-density residential, (2) low-density residential built before 1990 or (3) after 2000, and (4) downtown ultra-urban districts. Catch basins were retrofitted with custom-made traps to collect gross solids. Monthly total nitrogen (TN) loads ranged from 3.36×10−4 kg/ha to 7.32 kg/ha, while monthly total phosphorus (TP) loads varied between 1.68×10−5 kg/ha and 7.28×10−2 kg/ha. Statistical analyses determined nutrient loads were affected by location, land use, and season. Significant differences (p-value<0.05) were attributed to variations in rainfall, tree abundance, and pollination. Because TN and TP accounted for 0.40% to 3.43% and 0.03% to 0.25% of the dry leaf litter, respectively, this study illustrates that jurisdictions can reduce nonpoint source pollution through typical municipal activities (cleaning collected debris from catch basins).