Sensitivity of dissolved organic carbon exchange and sediment bacteria to water quality in mangrove forests
Poor water quality affects the biogeochemistry functions and the biological community structure of coastal ecosystems. In this study we investigated the effect of water quality on: (a) The exchange of dissolved organic carbon (DOC) between floodwater and mangrove forests, (b) the abundance of sediment bacteria, (c) the microbial community composition, and (d) the microbial catabolic activity. We selected six mangrove forests that were flooded by creeks with differing water qualities to test for thresholds of nutrient concentrations associated with changes in DOC dynamics and the microbial community. Our results show that in sites flooded by water high in soluble reactive phosphorus (SRP) (>20 μg l−1) and NH4 + (>30 μg l−1) the DOC concentrations in the floodwater were higher than in ebb water, suggesting DOC import by the mangroves. In contrast, in sites flooded by water low in SRP (<20 μg l−1) and NH4 + (<30 μg l−1), DOC concentrations in the floodwater were lower than in the ebb water, suggesting DOC export by the mangroves. Bacterial abundance was higher in sediments with low bulk density, high organic carbon and when flooded by water with low N:P (1–2), but the microbial composition and total catabolic activity assessed using Biolog Ecoplates™ did not differ among sites. The relationship between water quality, microbial communities and DOC exchange suggests that, at least during some periods of the year, poor water quality increases bacterial abundance and modifies DOC exchange of mangrove forests with floodwater and thus, their role in supporting near-shore productivity.
KeywordsNutrients Wetlands Eutrophication Phosphorus Moreton Bay Avicennia marina
We thank the Mexican Council for Science and Technology (CONACYT, Mexico), The School of Biological Sciences at The University of Queensland and CINVESTAV-IPN (Centro de Investigación y de Estudios Avanzados del Instituto Politécnico Nacional), Unidad Mérida for financial and logistic support. We also want to acknowledge Dr. Aldrie Amir, Dr. Alistar Grinham, Dr. Jock Mackenzie, and Dr. Esteban Marcellin for field assistance and Dr. Timothy Mercer for field and editing assistance. This work was partially supported by ARC Linkage award LP0561498. I also like to thank the Queensland Environmental Protection Agency for giving access to data from their monitoring program. We appreciate the time and comments provided by two anonymous referees.
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