Nitrogen Mineralization and Nitrification in Suburban and Undeveloped Atlantic White Cedar Wetlands

Abstract

AbstractThe presence of urban and suburban lands adjacent to wetlands may cause changes in nutrient‐cycling processes, due to changes in the quality of the ground‐ and surface waters that drain from the developed uplands into the wetland. We studied N‐cycling processes in Atlantic white cedar [Chamaecyparis thyoides (L.)] swamps in the New Jersey Pinelands to determine their sensitivity to the development of adjoining uplands. We conducted a 19‐wk aerobic incubation to measure N mineralization and nitrification potentials in wetland soils from both developed and undeveloped watersheds. The cumulative inorganic N mineralized during the incubation was two to three times higher in soils from developed sites than from the undeveloped sites. There was virtually no nitrification in undeveloped wetlands, while in developed wetlands, most N mineralized was further nitrified. In developed sites, there was also more nitrification in hollow soils than in hummock soils. Both nitrification and the fraction of soil organic matter mineralized were highly correlated with pH and with soil ash content. These results suggest that increases in ash content of peats attributable to sediment transported and deposited in urban runoff, causes increases in pH, which in turn allows large populations of nitrifiers to develop. Excess mineral N generated within the wetlands through changes in microbial function thus may be as important as N inputs in drainage water in affecting plant community composition, and may cause wetlands to become sources of N to downstream ecosystems rather than serving as regional sinks.