Oxygen and nitrate respiration in a reed swamp sediment from a eutrophic lake

Abstract

Seasonal measurements of the oxygen and nitrate uptake by a reed swamp sediment were carried out in a shallow, eutrophic Danish lake, Arreskov Sø. The oxidation of organic carbon in the sediment by aerobic and nitrate respiration was 290 and 188 g C m−2 yr−1 respectively. During winter, nitrate respiration amounted to 94% of the total carbon oxidation, whereas it was zero during summer. On an annual basis nitrate respiration constituted 39% of total respiration. Sediment nitrate uptake was correlated to nitrate concentration. In consequence of this the nitrate uptake rates varied during the year from zero in summer to 55 mg N m−2 d−1 in spring.Oxygen uptake rates varied from 30 to 250 mg O2 m−2 h−1 during the year, with a maximum uptake in August. The oxygen uptake per year was calculated to 860 g O2 m−2. The oxygen uptake rate was correlated to lake temperature and Kjeldahl nitrogen content of the sediment. The oxygen uptake rate, however, showed no correlation with loss on ignition of the sediment. A Q10‐value of 2.2 was found for lake measurements in the temperature interval of 5–15°C. The corresponding O10‐value in the laboratory was 2.6. A high microbial biomass indicated by the maximum content of Kjeldahl nitrogen and the lowest ratio of loss on ignition on Kjeldahl nitrogen appeared in late August, when the maximum oxygen uptake occurred. The oxygen uptake rate increased during the time interval from sampling to the start of the experiments.