Sediment oxygen consumption in an organic-rich, subtropical lagoon, Brazil

Abstract

Sediment oxygen consumption (SOC) and pelagic primary production were estimated during austral spring (1986), late summer, autumn and winter (1987) in the eutrophic, sub-tropical lagoon of Guarapina, southern Brazil. SOC measurements were conducted by in vitro incubations of intact sediment cores (diameter, 8 cm; volume 0.81) and also in situ with “Bell Jars” (diameter, 60 cm; volume, 551). Primary production in terms of oxygen was estimated from in situ light/dark bottle incubations. SOC rates (g O 2m −2day −1) were 0.98 ± 1.18 ( n = 8) in spring, 2.26 ± 0.86 ( n = 14) in late summer, 1.95 ± 0.38 ( n = 14) in autumn and 1.49 ± 0.39 ( n = 18) in winter. This corresponds to a mean of approximately 53, 42, 54 and 44%, respectively, of the daily net pelagic primary production. Results obtained from dark incubations with cores and “Bell Jars” agreed extremely well. The former method yielded SOC rates of 1.87 ± 0.60 g O 2m −2day −1 ( n = 27) and the latter 2.08 ± 0.97 gO 2m −2day −1 ( n = 11). Organic-rich muddy sediments (particulate organic carbon (POC), 8–12%), which are predominant in the lagoon, in contrast to sandy sediments, showed the highest consumption rates. On some occasions, littoral sandy sediments covered with an organic-rich flocculent layer attained similar SOC rates as muddy sediments.