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An anoxic event and other biogeochemical effects of the Pantanal wetland on the Paraguay River
Author(s) -
Hamilton Stephen K.,
Sippel Suzanne J.,
Calheiros DÓbora F.,
Melack John M.
Publication year - 1997
Publication title -
limnology and oceanography
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.7
H-Index - 197
eISSN - 1939-5590
pISSN - 0024-3590
DOI - 10.4319/lo.1997.42.2.0257
Subject(s) - biogeochemical cycle , floodplain , tributary , anoxic waters , environmental science , environmental chemistry , wetland , hydrology (agriculture) , total organic carbon , nutrient , dissolved organic carbon , sediment , weathering , chemistry , ecology , geology , geochemistry , biology , paleontology , cartography , geotechnical engineering , geography
The Paraguay River was sampled throughout the annual cycle at two sites located downriver from most of the Pantanal, and major tributaries were occasionally sampled close to their entry into the Pantanal. The floodplains strongly modulate the discharge regime and substantially reduce runoff by enhancing evapotranspirative losses. Contact of the river water with the floodplain results in depletion of dissolved O 2 , oversaturation of CO 2 and CH 4 loss of suspended sediments, and reduced export of N and P. Oxygen depletion and associated chemical changes are most marked when river water first contacts the floodplain; in 1995, the water remained anoxic throughout the river channel for 6 weeks, causing massive fish mortality. Bottle incubations showed that the rate of O 2 consumption by the river water during the anoxic event was high at first (7.2 µM h −1 ) but declined exponentially over several hours and was not stimulated by organic carbon and nutrient additions. The O 2 demand may be due largely to bacterial CH 4 oxidation; the concentration of CH 4 in the river was particularly high (∼31 µ M) at the time of the incubations. The O 2 depletion corresponded with higher concentrations of most major ions, Si, and dissolved organic carbon but was not accompanied by elevated concentrations of inorganic N and P, H 2 S, or most of the 46 dissolved trace elements that were measured. In contrast to O 2 depletion and associated chemical changes, sediment retention by the floodplains was greatest at maximum river stages. Most chemical weathering of minerals seems to take place in the upland drainage basins rather than on the floodplains, and most major solutes display conservative mixing in the river‐floodplain system.