Nutrient and Sediment Runoff and Nitrous Oxide Losses From Urban Landscapes.

Residential lawn management practices (mowing, fertilizer, irrigation, reseeding, and aeration) result in aesthetically appealing landscapes, but can result in nutrient losses via overland flow or gaseous losses to the atmosphere (e.g. nitrous oxide - N₂O).  The overall objective of this study was to determine the effect of lawn management on nutrient losses from residential lawns. The specific objectives were: modify a passive sampling system to determine nutrient loads due to overland flow from lawns; evaluate differences in overland flow frequency, volumes, and nutrient losses during rainfall events (≥ 2.54 cm); and compare N₂O losses following rainfall events. Three lawn schemes were studied: a high maintenance fescue (Festuca arundinacea) lawn (HMFL), a low maintenance fescue lawn (LMFL), and a mixed forested residential landscape (RFL). The modified passive sampling system allowed 100% recovery of overland flow and demonstrated that differences in maintenance influenced the overland flow frequency, volumes, and nutrient losses. The LMFL had the greatest overland flow volumes and nutrient unit area loads, although N and P concentrations in overland flow exceeded USEPA recommendations from all three lawns. Nutrient losses (g ha^-1 yr^-1) from all three residential landscapes were 1000 times less than fertilizer (kg ha^-1 yr^-1) and throughfall (kg ha^-1 yr^-1) inputs, due in part to the presence of well-structured soils (low bulk densities and high infiltration rates).  Irrigation practices between the HMFL and LMFL explained the differences in overland flow volumes and nutrient loads, especially during the first half of the study when drought conditions existed at the study site (Cary, North Carolina). Lack of irrigation in the LMFL resulted in early dormancy, a minimal thatch layer and lower plant density, resulting in higher volumes of overland flow. Trends in the N₂O losses from the HMFL and LMFL were associated with timing of fertilizer applications, presence or absence of irrigation, and seasonal growth patterns of the fescue.  For the RFL, the presence of a decomposing litter layer limited N₂O production. Well-maintained residential lawns, receiving recommended fertilizer N applications and frequent irrigation, reduce nutrient losses via overland flow but may provide optimum conditions for greater N₂O fluxes.