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Nutrient Transformations in Sediments as Influenced by Oxygen Supply
Author(s) -
Moore P. A.,
Reddy K. R.,
Graetz D. A.
Publication year - 1992
Publication title -
journal of environmental quality
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.888
H-Index - 171
eISSN - 1537-2537
pISSN - 0047-2425
DOI - 10.2134/jeq1992.00472425002100030014x
Subject(s) - mineralization (soil science) , biogeochemical cycle , chemistry , nutrient , oxidizing agent , environmental chemistry , organic matter , ammonium , sediment , microcosm , decomposition , redox , nitrogen , oxygen , mineralogy , inorganic chemistry , geology , paleontology , organic chemistry
The oxidation status of sediments greatly affects biogeochemical processes. The objective of this study was to determine the influence of various levels of O 2 on nutrient transformations in lake sediments. Decomposition of sediment organic matter was evaluated under varying levels of O 2 . Bulk sediment samples obtained from a hypereutrophic lake in central Florida were incubated in stirred microcosms at 25°C for 100 d at four O 2 levels. The O 2 levels were accomplished by bubbling N 2 containing 0, 0.2, 2.0, and 20.0% O 2 through the stirred suspensions. Redox potential (Eh) measurements indicated that the two highest O 2 levels (i.e., 2.0 and 20.0% O 2 ) resulted in oxidizing conditions (Eh > 400 mV), whereas the lowest O 2 levels (0 and 0.2% O 2 ) resulted in reduced conditions (Eh < −300 mV). First‐order rate constants calculated based on CO 2 evolution were 0.00010, 0.00027, 0.00062, and 0.00068 d −1 for the 0, 0.20, 2.0, and 20.0% O 2 levels, respectively. Methane was detected in the sediments incubated under 0 and 0.2% O 2 level, with CO 2 /CH 4 ratios of 3.5 and 160, respectively. Accumulation of soluble organic C (SOC) was greater under reduced conditions than oxidized conditions. Ammonium concentrations decreased rapidly in the oxidized treatments, with concurrent increases in NO 3 ‐N concentrations, whereas under reducing conditions NH 4 ‐N concentrations slowly increased. Rates of N mineralization were slightly higher under oxidized conditions. Although the ratio of N mineralized to CO 2 evolved was higher at low O 2 levels, the amount of N mineralized vs. the sum of C metabolites (CO 2 + CH 4 + SOC) was relatively constant under all O 2 levels (6.7:1). Reducing conditions resulted in a depletion of SO 2− 4 , whereas under oxidizing conditions SO 2− 4 concentrations increased, probably due to sulfide oxidation. Soluble reactive P concentrations were lower under oxidizing conditions.