TRANSFORMATION AND RETENTION OF NITROGEN IN A COASTAL FOREST ECOSYSTEM

Transformations and fluxes of N were examined in three forested sites located along a gradient of soil texture in the coastal forests of the Waquoit Bay watershed on Cape God. Total N leaching losses to ground water were 0.5 kg ha(-1) yr(-1) in the loamy sand site and 1.5 kg ha(- 1) yr(-1) in the fine sand site. Leaching loss to groundwater was not measured in the coarse sand site due to the prohibitive depth of the w ater table but total N leaching loss to Im depth in the mineral soil w as 3.9 kg ha(-1) yr(-1). DON accounted for most of the leaching losses below the rooting zone (77-89%) and through the soil profile to groun d water (60%-80%). Differences in DON retention capacity of the minera l soil in the sites along the soil texture gradient were most likely r elated to changes in mineral soil particle surface area and percolatio n rates associated with soil texture. Forests of the watershed functio ned as a sink for inorganic N deposited on the surface of the watershe d in wet and dry deposition but a source of dissolved organic N to gro und water and adjoining coastal ecosystems.