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

Estimates of epipelic algal primary production using 14 C 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 14 C uptake among intact sediment cores exposed to different 14 C ratios between interstitial and overlying water. In addition, we evaluated the effect of varying time between addition of 14 C and light incubation (preincubation time) and the effect of photosynthetic uptake on final distribution of 14 C. Both preincubation time and photosynthetic uptake affected final 14 C 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 14 C 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 14 C estimates of epipelic algal production.