caa a22 4500 445892447 CHVBK 20180317145620.0 cr unu---uuuuu 170323e20110701xx s 000 0 eng 10.1007/s10750-011-0683-7 doi (NATIONALLICENCE)springer-10.1007/s10750-011-0683-7 Nitrogen dynamics in Lake Okeechobee: forms, functions, and changes [Elektronische Daten] [R. James, Wayne Gardner, Mark McCarthy, Stephen Carini] Total nitrogen (TN) in Lake Okeechobee, a large, shallow, turbid lake in south Florida, has averaged between 90 and 150μM on an annual basis since 1983. No TN trends are evident, despite major storm events, droughts, and nutrient management changes in the watershed. To understand the relative stability of TN, this study evaluates nitrogen (N) dynamics at three temporal/spatial levels: (1) annual whole lake N budgets, (2) monthly in-lake water quality measurements in offshore and nearshore areas, and (3) isotope addition experiments lasting 3days and using 15N-ammonium (15NH4 +) and 15N-nitrate (15NO3 −) at two offshore locations. Budgets indicate that the lake is a net sink for N. TN concentrations were less variable than net N loads, suggesting that in-lake processes moderate these net loads. Monthly NO3 − concentrations were higher in the offshore area and higher in winter for both offshore and nearshore areas. Negative relationships between the percentage of samples classified as algal blooms (defined as chlorophyll a>40μgl−1) and inorganic N concentrations suggest N-limitation. Continuous-flow experiments over intact sediment cores measured net fluxes (μmolNm−2h−1) between 0 and 25 released from sediments for NH4 +, 0-60 removed by sediments for NO3 −, and 63-68 transformed by denitrification. Uptake rates in the water column (μmolNm−2h−1) determined by isotope dilution experiments and normalized for water depth were 1,090-1,970 for NH4 + and 59-119 for NO3 −. These fluxes are similar to previously reported results. Our work suggests that external N inputs are balanced in Lake Okeechobee by denitrification. Springer Science+Business Media B.V., 2011 Lake Okeechobee nationallicence Nitrogen nationallicence 15N isotope studies nationallicence Algal bloom nationallicence Nutrient budgets nationallicence N-fixation nationallicence Denitrification nationallicence Sediment-water interactions nationallicence James R. Water Quality Treatment Technologies Division, South Florida Water Management District, West Palm Beach, FL, USA aut Gardner Wayne Marine Science Institute, The University of Texas at Austin, Port Aransas, TX, USA aut McCarthy Mark Marine Science Institute, The University of Texas at Austin, Port Aransas, TX, USA aut Carini Stephen Marine Science Institute, The University of Texas at Austin, Port Aransas, TX, USA aut Hydrobiologia Springer Netherlands 669/1(2011-07-01), 199-212 0018-8158 669:1<199 2011 669 10750 https://doi.org/10.1007/s10750-011-0683-7 text/html Onlinezugriff via DOI 1 research-article jats NATIONALLICENCE 856 40 https://doi.org/10.1007/s10750-011-0683-7 text/html Onlinezugriff via DOI NATIONALLICENCE 700 1- James R. Water Quality Treatment Technologies Division, South Florida Water Management District, West Palm Beach, FL, USA aut NATIONALLICENCE 700 1- Gardner Wayne Marine Science Institute, The University of Texas at Austin, Port Aransas, TX, USA aut NATIONALLICENCE 700 1- McCarthy Mark Marine Science Institute, The University of Texas at Austin, Port Aransas, TX, USA aut NATIONALLICENCE 700 1- Carini Stephen Marine Science Institute, The University of Texas at Austin, Port Aransas, TX, USA aut NATIONALLICENCE 773 0- Hydrobiologia Springer Netherlands 669/1(2011-07-01), 199-212 0018-8158 669:1<199 2011 669 10750 Metadata rights reserved Springer special CC-BY-NC licence nationallicence BK010053 XK010053 XK010000 NATIONALLICENCE NATIONALLICENCE NL-springer