Dissolved inorganic carbon sources for epipelic algal production: Sensitivity of primary production estimates to spatial and temporal distribution of 14C

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Estimates of epipelic algal primary production using 14C are sensitive to whether the presumptive source of dissolved inorganic carbon (DIC) is the overlying water, the interstitial water, or both. To determine the source of DIC, we compared 14C uptake among intact sediment cores exposed to different 14C ratios between interstitial and overlying water. In addition, we evaluated the effect of varying time between addition of 14C and light incubation (preincubation time) and the effect of photosynthetic uptake on final distribution of 14C. Both preincubation time and photosynthetic uptake affected final 14C distribution, but the magnitude of the photosynthesis effect was larger. Estimates of primary production ranged between 50 and 200 mg C m−2 h−1, depending on the presumed DIC source and whether we accounted for differential photosynthetic depletion of 14C and DIC. Using nonlinear regression, our best estimate of epipelic production was 114 mg C m-2 h-1, and the fraction of DIC sequestered from overlying water was 0.5 (R2 = 0.84). Similar assessments should be applied in other systems for accurate 14C estimates of epipelic algal production.



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