Dissolved organic nitrogen concentrations

Generally, N03 dominates over NH4+ at sites close to emission sources (8,12). Dissolved organic nitrogen (DON) concentrations are highly variable in precipitation but often amount to 25-50% of inorganic N deposition (8, 12-14). In some areas, DON can occur in greater concentrations than the inorganic species (15). 

The major objective of this chapter is to examine and synthesize the published literature with respect to sources and production of terrestrially derived DOC, its relationship with dissolved organic nitrogen (DON), and the mechanistic controls on their export from terrestrial ecosystems to surface waters. With the exception of wet precipitation (which is ranked by continental landmass), we have classified data for throughfall and soil solution under biome type. Where possible, we have shown mean and standard deviations of some biomes to illustrate the amount of variance within and between biomes. Relationships between DOC and DON are illustrated using only those studies that report both DOC and DON concentration. Because most research on DOC and DON has been accomplished in relatively undisturbed areas, particularly forests, this chapter concentrates on the aspect of diffuse-source allochthonous inputs to surface waters and not point-source inputs from urban and agricultural areas. Recent work by Westerhoff and Anning (2000), however, indicates that more research on effluent or point-source DOC as a contributor to riverine allochthonous inputs may be... 

Dissolved organic nitrogen also shows some reduction in mineral soil solution relative to the organic soil horizon. Although few data are currently available for mineral soil solution DON concentration and flux, DON reduction in mineral soil is comparable to that of DOC (Fig. 5). 

Table 8.9 Rates of dissolved organic nitrogen (DON) release published and ratios of DON release to gross nitrogen (N) uptake, expressed as a percent, in the field. Rates were determined using N tracer techniques ( N) or changes in concentrations (CC)... 

During the last twenty years, water column concentrations of dissolved N were probably the most intensively measured feature of N in estuarine environments. For example, about 8000 measurements of each of the common dissolved N species (i.e., NO2, NO3, NF44 and dissolved organic nitrogen) were made per year for the... 

Table i8.i Concentrations of Total Dissolved Nitrogen (TDN) and Dissolved Organic Nitrogen (DON) from Surface Waters of a Variety of Estuarine Systems... 

Concentrations of dissolved organic material expressed as dissolved organic carbon (DOC), dissolved organic nitrogen (DON) and dissolved organic phosphorus (DOP) in mg m (ppb) for surface microlayer (M) and subsurface water (Sub) samples... 

Dissolved organic nitrogen DON concentrations are significant in the open ocean, typically >4pM in surface waters, decreasing to 2 pM in deep water. Fluxes associated with the DON pool are among... 

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