Nitrogen in Runoff from Residential Roads in a Coastal Area

Non-point sources of nitrogen (N) contribute to pollution of many coastal waters. Road runoff of N has been estimated for busy highways, but residential roads could also be important non-point sources. Here we estimate N in runoff from two small residential roads (average annual daily traffic [AADT] < 1,000) and a state highway (AADT = 8,800) in a coastal watershed of Massachusetts, USA. The antecedent dry-day traffic was correlated with total dissolved nitrogen (TDN) concentrations at the beginning of each rain event for the highway, but not for the residential roads. The TDN concentrations declined exponentially with cumulative precipitation during storms. Estimated annual road runoff is about 10 kg TDN-N ha(-1) of road surface for all three roads, which is about twice the bulk precipitation input. Because much of this road runoff enters sensitive coast water bodies directly, these inputs could be important for local water quality concerns.