The role of bacteria in the nutrient exchange between sediment and water in a flow-through system |
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Authors: | T Kairesalo L Tuominen H Hartikainen K Rankinen |
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Institution: | (1) The Environmental Unit, University of Helsinki, Niemenkatu 73, FIN-15210 Lahti, Finland;(2) Department of Limnology and Environmental Protection, University of Helsinki, P.O. Box 27, FIN-00014, Finland;(3) Department of Applied Chemistry and Microbiology, University of Helsinki, P.O. Box 27, FIN-00014, Finland |
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Abstract: | The contribution of bacteria to phosphorus (P) and nitrogen (N ) release from, or retention in, sediment was studied in a flow-through system. Live and formaldehyde-killed sediment communities were incubated in 25-liter bottles with a continuous flow of P- or P + N-enriched water. Sediment bacteria in the killed communities were inhibited by adding formaldehyde (final concentration 0.04% v/v) to the sediment before the start of the experiment. Bacterial activity in the live sediments measured with 3H]thymidine and 14C]leucine incorporation techniques did not change essentially during the experiment period (7–8 days). Chemical mechanisms were found to be of principal importance in PO4-P retention in the sediment. In the live samples, the net retention of PO4-P was lower than in the killed samples, which was likely due to the reduced O2 conditions in the sediment as a consequence of bacterial mineralization. In total P exchange, however, bacteria increased the retention rate by recycling dissolved organic P in the sediment. In the live communities the retention of N was very efficient, and all the introduced NH4 -N and NO3-N was immobilized by sediment bacteria. Nitrogen enrichment, however, did not alter the P exchange rates. The gradual emergence of bacterial activity (and grazing) in the killed communities, subsequent to the dilution of formaldehyde concentration, enhanced the release of PO4-P and NH4-N from sediment. |
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