Chemical composition of biodegradable dissolved organic matter in streamwater

Abstract

Plug-flow biofilm reactors colonized by microorganisms in streamwater were used to measure the concentration and composition of biodegradable dissolved organic C (BDOC) in White Clay Creek. During the 4-month study period, DOC ranged from 0.8 to 10.4 mg C liter-' and was, on average, composed of 75% humic substances, 13% carbohydrates, 2% amino acids, and 18% > 100 kDa. The carbohydrates were predominantly polysaccharides, nearly all amino acids were present in the combined form, and most carbohydrates and amino acids were humic bound. BDOC ranged from 0.2 to 2.9 mg C liter-', averaged 25% of the DOC, and was composed of 75% humic substances, 30% carbohydrates, 4% amino acids, and 39% DOC >lOO kDa. The carbohydrate portion of the BDOC was primarily polysaccharide or humic bound. Similarly, the amino acid portion of the BDOC was overwhelmingly present in the combined form and primarily humic bound. Glycine and aspartic acid were the dominant amino acids in White Clay Creek DOC and in the BDOC pool. Our data broaden the perspective on substrates important to microbial metabolism and energy flow in streams and provide the first direct evidence that humic substances, although largely refractory, are an important component of streamwater BDOC.Dissolved organic matter (DOM) comprises most of the reduced carbon in aquatic ecosystems and provides energy and carbon resources for the metabolism of heterotrophic bacteria. Not all DOM is biologically labile or even biodegradable. Although numerous investigations in both freshwater and marine environments have reported on the quantity and composition of DOM, fewer studies have addressed the biodegradable fraction. Identifying biodegradable DOM (BDOM) constituents and quantifying their contribution to heterotrophic metabolism can increase our understanding of ecosystem function and bacterial ecophysiology.From a limited number of studies we know that BDOM in streams and rivers includes both low-molecular-weight (Kaplan and Bott 1983) and high-molecular-weight (Meyer

Source, biogeochemical cycling, and fluorescence characteristics of dissolved organic matter in an agro‐urban estuary

“…These results have important implications for DOM cycling in estuaries because they provide evidence that multiple pools of DON exist in estuaries, similar to fast and slow cycling pools of DON observed in freshwater ecosystems (Brookshire et al 2005). For instance, amino acids typically account for a small but dynamic fraction of DOM in surface waters (Volk et al 1997) and bulk analyses of DOC and DON, which reflect the combined result of both production and removal processes, cannot detect many C and N transformations. Thus, a decrease in certain fractions of DOC or DON could be offset by an increase in other fractions, resulting in the apparent conservative mixing of bulk DOM.…”

Bioavailability of DON from natural and anthropogenic sources to estuarine plankton

“…1997; Volk et al 1997;Stepanauskas et al 2000). In the following calculations, we assumed that our DON bioavailability measurements were representative of both storm and nonstorm flow conditions.…”

Fluorescence characteristics and biodegradability of dissolved organic matter in forest and wetland soils from coastal temperate watersheds in southeast Alaska

“…In particular, DOM derived from wetland soils contains high concentrations of dissolved humic substances that have conventionally been considered recalcitrant and largely unavailable for bacterial degradation (Geller 1986). However, evidence suggests that this recalcitrant DOM may be more available than previously presumed and that terrestrially-derived humic substances might represent an important component of the streamwater BDOC pool (Moran and Hodson 1990;Volk et al 1997). Since DOM is an important source of C and energy for microbial heterotrophs and given its heterogeneous nature, scientists have developed a variety of simple indicators for BDOC in natural ecosystems.…”