|Abstract or Summary
- In undisturbed N-limited forested catchments, DON may represent over 90% of the total N lost in streams. Some ecologists have suggested that plant-derived reactive polyphenols may be responsible for DON binding and transport because polyphenol-protein complexes are known to precipitate out of solution, bind to mineral surfaces or organic matter in the soil, or be leached from the system. Sources of reactive polyphenols include tannins produced by plants, lignin degradation products, and fungal melanins. Therefore, polyphenols produced in natural ecosystems might have profound effects on the biogeochemistry and fertility of unpolluted forests. We investigated the hypothesis that reactive polyphenols are the mechanism behind the observation that pristine streams lose nitrogen primarily in the dissolved organic (DON) form compared to inorganic N (DIN).
More knowledge of natural C and N dynamics in unpolluted ecosystems is vital to improve our understanding of the real and potential effects of anthropogenic N pollution. Despite the interest in polyphenols as a mechanism of DON sequestration and transport, no study has investigated the flux of water-soluble phenols from the forest floor to the stream, or estimated the relative proportion of phenolic DOC in the ecosystem.
We examined the concentration and characteristics of phenols, DOC, and N in an unpolluted, N-limited second-order catchment in the Western Cascades of Oregon in order to estimate the relative proportions of each over sources and storm events. Samples were collected from soil lysimeters, from a physically isolated hillslope component, and from the stream.
We estimated that between 4.8 and 16.6% of the DOC was phenolic, while the aromatic DOC was between 27.5 and 65.8% phenolic. The proportion of reactive polyphenols was
approximately 74%, and highest in the organic horizon and a small tributary. Stream DON averaged 94.6% of the total N, but many of the total N and most of the inorganic N results were below detection limits.
We found positive correlations between DON and total phenols in some sources but not in others. While we found some support for the hypothesis that polyphenols are an important mechanism of DON transport and sequestration, future examination of phenols, DOC, and N, under controlled conditions with more sensitive N analysis might prove fruitful.