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

Estimates of epipelic algal primary production using C-14 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 C-14 uptake among intact sediment cores exposed to different C-14 ratios between interstitial and overlying water. In addition, we evaluated the effect of varying time between addition of C-14 and light incubation (preincubation time) and the effect of photosynthetic uptake on final distribution of C-14. Both preincubation time and photosynthetic uptake affected final C-14 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 C-14 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 (R-2 = 0.84). Similar assessments should be applied in other systems for accurate C-14 estimates of epipelic algal production.