Dynamics, chemical properties and bioavailability of DOC in an early successional catchment

[摘要] The dynamics of dissolved organic carbon (DOC) have been intensively studiedin mature ecosystems, but little is known about DOC dynamics and thesignificance of DOC as a substrate for microbial activity inearly-successional catchments. We determined the concentration, chemicalcomposition, source, radiocarbon age, and bioavailability of DOC along thehydrological flow path from soil solution to a downstream pond in a recentlyconstructed catchment (Chicken Creek Catchment, Germany). Soil solution,upwelling ground water, stream water, subsurface water in an alluvial fan,and pond water all had high DOC concentrations (averages: 6.0–11.6 mgDOC L^–1), despite small carbon stocks in both vegetation and soil ofthe catchment. Solid-state CPMAS ¹³C NMR of DOC in upwelling groundwater revealed a higher proportion of aromatic compounds (32%) and alower proportion of carbohydrates (33%) than in pond water (18% and45%, respectively). The average ¹⁴C age of DOC in upwelling groundwater was 2600 to 2900 yr, while organic matter of the Quaternarysubstrate of the catchment had a ¹⁴C age of 3000 to 16 000 yr. Boththe ¹⁴C age data and ¹³C NMR spectra suggest that DOC partlyderived from organic matter of the Quaternary substrate (about 40 to 90%of the C in the DOC), indicating that both recent and old C of the DOC cansupport microbial activity during early ecosystem succession. However, in a70 day incubation experiment, only about 11% of the total DOC was found tobe bioavailable. This proportion was irrespective of the water type.Origin of the microbial communities within the catchment (enriched from soil,stream sediment or pond water) also had only a marginal effect on overall DOCutilization.

[学科分类] 地球化学与岩石