| Summary |
Litterfall, stemflow, throughfall, and precipitation were collected from a young alluvial swamp forest on the Tar River in Eastern North Carolina to determine nitrogen input to the forest floor and canopy leaching. Surface water, soil, and interstitial water were sampled to determine nitrogen concentrations in each compartment. Nitrate and ammonium were added to surface water isolated from the soil and to surface water overlying the soil to determine removal rates and relative effects of soil and surface water. The major input of nitrogen to the forest floor was by litterfall with a flux of 66 kg N/ha and 11 kg N/ha during the presence and absence of foliage, respectively. Corresponding aqueous fluxes were 2.1 and 2.4 kg N/ha by canopy leaching and 3.0 and 2.8 kg N/ha by precipitation. Annual input to the forest floor by litterfall (77 kg N/ha) and aqueous forms (throughfall + stemflow = 10.3 kg N/ha) was 87 kg N/ha. Levels of total nitrogen in interstitial water averaged 5.2, 5.0, and 4.8 mg N/ liter in June, October, and February, respectively. Total nitrogen in the soil was 1.4%, 1.4%, and 1.1% of dry weight in June, October, and February, respectively. Corresponding levels of exchangeable ammonium in the soil were 73, 121, and 38 mg NHâ‚„-N/kg of dry soil. Of the nitrate added to the surface water, losses were 94%, 93%, and 86% at the end of 10 days in July, November, and February, respectively. Corresponding losses of ammonium were 46%, 41%, and 40%. Losses of both ammonium and nitrate were greater from surface water in contact with soil than from isolated surface water. The return of nitrogen to the forest floor in the swamp forest is higher than that of other forested ecosystems in temperate latitudes. This is a result of high litterfall nitrogen, not canopy leaching which falls within the range of that measured for other forested ecosystems. The amount of nitrogen stored in the soil, primarily as organic nitrogen, is larger than upland soils, but about equal to that of peat soils, indicating that the system accumulates nitrogen. Removal rates of nitrate from the surface water suggest that the system has a large capacity for denitrification and is a nitrogen sink. The implications of this attribute for nitrate removal from floodwaters and wastewater should be examined more closely. |
