Ecosystem metabolism and turnover of organic carbon along a blackwater river continuum

  • Meyer J
  • Edwards R
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the Ogeechee River (Georgia, USA) basin, a sixth-order by warm water temperatures, low stream gradient, Abstract. Variation in ecosystem metabolism and organic carbon turnover length was blackwater river, to determine if the patterns observed in other rivers are also seen along a river continuum characterized and tea-colored water. The study was in two parts: an intensive study of seasonal variation in metabolism and organic carbon turnover length at a fourth-order compared with an earlier study at a sixth-order extensive riparian swamps, site, which can be site, and a study of the variation in system metabolism at five second- through sixth-order sites along the continuum. Metabolism varied seasonally at the fourth-order site that was studied most intensively; mean gross primary production (GPP, measured as 02) was 0.8 g.m-2 d-1 and mean community respiration (CR, also measured as 02) was 4.1 gm-2d-1. The community production/ respiration ratio (P/R) ranged from 0.02 to 0.4 with an annual mean of 0.2. This is clearly a heterotrophic inputs of organic matter from extensive riparian swamps. Mean annual organic carbon turnover length at the fourth-order was much less, with a median of 1 4 km. Turnover lengths are significantly stream reach, where high rates of community respiration are supported by site was 570 km, although on most dates the length less than those at the sixth-order site, but much greater than observed in other rivers of similar size, probably because most of the organic carbon export in this river is dissolved organic carbon (DOC), which is less efficiently retained. Seasonal variation in turnover length reflected variation in transport. At five sites along the Ogeechee River continuum ranging from second to sixth order, GPP, CR, and P/R increased with stream order, as observed in other rivers; yet P/R was always < 1, and net daily metabolism was always negative and became more negative with increasing stream order. In contrast to other river continua studied, metabolism in this low-gradient blackwater river becomes more dependent on allochtho- nous organic carbon with increasing stream size despite downstream increases in GPP; floodplains and riparian swamps appear to be the source of allochthonous carbon. Riparian influences increase rather than decrease along the continuum in this river. Although first- through third-order only 4% of basin-wide GPP and 9% of basin-wide CR occurs in them. Higher order streams are less efficient streams represent 32% of the channel area in the sixth-order in organic carbon processing (longer turnover lengths), carbon spiraling; primary production; PIR; River Continuum Concept; st

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  • J. L. Meyer

  • R. T. Edwards

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