Do oxic–anoxic transitions constrain organic matter mineralization in eutrophic freshwater wetlands?
- 347 Downloads
This study aims at investigating decomposition processes in wetlands that are daily or seasonally exposed to intermittent oxic and anoxic conditions. We hypothesized that in wetland ecosystems where anoxia regularly establishes, decomposition rates are not affected by oxygen shortage, especially when nitrates are available. Monitoring and experiments were performed from December 2003 to January 2005 in one of the widest (81 ha) freshwater wetlands in the Po river floodplain (Natural Reserve Paludi del Busatello, Italy). Intact sediment cores were sampled on a seasonal basis. Sediment–water fluxes of oxygen, dissolved inorganic carbon, methane, and inorganic nitrogen were determined under oxic and anoxic conditions. Oxic–anoxic transitions always resulted in enhanced ammonium, dissolved inorganic carbon, and methane effluxes. At high temperatures, the methane release from sediments was inversely related to both nitrate concentrations and uptake. Likely, nitrate can compensate for the oxygen deficiency while maintaining an oxidative metabolism, either supporting microbial decomposition as an electron acceptor or stimulating the oxidation of the byproducts of the anaerobic metabolism, e.g., methane. This is a key point as the number of temperate wetlands with concurrent nitrate pollution and oxygen shortage is increasing throughout the world.
KeywordsEutrophic wetlands Oxygen availability Nitrate Organic matter mineralization
- APHA, 1998. Standard Methods for the Examination of Water and Wastewaters, 20th ed. APHA, Washington, DC.Google Scholar
- Dalsgaard, T., L. P. Nielsen, V. Brotas, P. Viaroli, G. J. C. Underwood, D. B. Nedwell, K. Sundback, S. Rysgaard, A. Miles, M. Bartoli, L. Dong, D. C. O. Thornton, L. D. M. Ottosen, G. Castaldelli & N. Risgaard-Petersen, 2000. Protocol handbook for NICE-Nitrogen Cycling in Estuaries: a project under the EU research programme. Marine Science and Technology (MAST III).Google Scholar
- Kemp, W. M., W. R. Boynton, J. E. Adolf, D. F. Boesch, W. C. Boicourt, G. Brush, J. C. Cornwell, T. R. Fisher, P. M. Glibert, J. D. Hagy, L. W. Harding, E. D. Houde, D. G. Kimmel, W. D. Miller, R. I. E. Newell, M. R. Roman, E. M. Smith & J. C. Stevenson, 2005. Eutrophication of Chesapeake Bay: historical trends and ecological interactions. Marine Ecology Progress Series 303: 1–29.CrossRefGoogle Scholar
- Koroleff, F., 1970. Direct determination of ammonia in natural waters as indophenol blue. Information on Techniques and Methods for Seawater Analysis. ICES Journal of Marine Science 114: 799–801.Google Scholar
- Lenth R., 2015. lsmeans: least-squares means. R package version 2.20-23.Google Scholar
- Pinheiro, J., D. Bates, S. DebRoy, D. Sarkar & R Core Team, 2014. nlme: linear and nonlinear mixed effects models. R package version 3.1-118.Google Scholar
- R Core Team, 2014. R: A language and environment for statistical computing. R Foundation for Statistical Computing, Vienna.Google Scholar