DENITRIFICATION DISTRIBUTIONS IN 4 VALLEY AND RIDGE RIPARIAN ECOSYSTEMS

Denitrification in riparian ecosystems can reduce the amount of nitrog en transported from farm fields to streams. In this study, we examine denitrification in lour riparian ecosystems common to the Valley and R idge physiographic province in Pennsylvania, USA. The sites exhibit di fferent vegetation, are underlain by different rock types, and are dow ngradient of farm fields. Mean site denitrification rates ranging from 0.6 to 1.9 mu g N/kg soil/day were measured using intact core incubat ion techniques. The three riparian sites covered with grass each exhib ited greater denitrification rates than the wooded site. Denitrificati on rate was correlated with moisture content but not with nitrate-N or organic carbon contents. Denitrification rates were greatest near the soil surface and at positions nearest the stream. Rates decreased uni formly with distance away from the stream and also with depth in the s oil for each site. While patterns oi nitrate-N, moisture, and organic carbon content differ among the sites, their combined effects on denit rification support the observed, consistent denitrification rate patte rn.