The Experts below are selected from a list of 27408 Experts worldwide ranked by ideXlab platform
Donald A. Goolsby - One of the best experts on this subject based on the ideXlab platform.
-
Transport of nitrate in the Mississippi River in July-August 1999
2013Co-Authors: Richard H. Coupe, Donald A. Goolsby, William A. Battaglin, John Karl Böhlke, Peter B. Mcmahon, Carol KendallAbstract:Lagrangian sampling was conducted on the Mississippi River in late July through early August 1999 to test the hypothesis that nitrate (NO 3 - ) is transported conservatively in the Mississippi River. Three different approaches were pursued to test the hypothesis: (1) a mass balance for NO 3 - was evaluated for evidence of net gains and losses, (2) stable isotopes of NO 3 - were measured (δ 15 N and δ 18 O) to determine if fractionation occurred, and (3) the concentrations of dissolved gases (N 2 O, N 2 and Ar) in River water were measured and compared to theoretical equilibrium concentrations. Integrated water samples and flow measurements were obtained at 10 sites on the Mississippi River and 7 sites near the mouths of major tributaries from northern Iowa to southern Louisiana, a distance of about 2,250 River kilometers. Mass balance calculations indicate that more than 80 percent of the NO 3 - mass discharged from the Mississippi River (1,930 metric tons/day) during the study period originated in the first 500 River kilometers of the study reach. The mass balance calculations also indicate that NO 3 - was not lost from the water column upstream of Vicksburg, MS, but that there might have been some loss of NO 3 - in the lower 700 kilometers of the study reach. The stable isotope ratios of N and O (δ 15 N and δ 18 O) of NO 3 - were consistent with mixing and transport in the absence of fractionating gains or losses. The concentrations of nitrogen (N 2 ) and argon (Ar) dissolved in River water decreased in the downstream direction, approximately in equilibrium with air at increasing temperatures, giving no evidence of gains or losses of N 2 by nitrogen fixation or denitrification. Nitrous oxide (N 2 O) concentrations in the Mississippi River were approximately 26 to 200 percent of air saturation, indicating relatively low net production by combination of nitrification and denitrification. Results from this study indicate that most (>90%) of the NO 3 - that entered the Mississippi River during July-August 1999 was transported to the Gulf of Mexico. Permanent URL: http://hdl.handle.net/2047/d20003062
-
relating net nitrogen input in the Mississippi River basin to nitrate flux in the lower Mississippi River a comparison of approaches
Journal of Environmental Quality, 2002Co-Authors: Gregory F. Mcisaac, Mark B. David, George Z. Gertner, Donald A. GoolsbyAbstract:A quantitative understanding of the relationship between terrestrial N inputs and Riverine N flux can help guide conservation, policy, and adaptive management efforts aimed at preserving or restoring water quality. The objective of this study was to compare recently published approaches for relating terrestrial N inputs to the Mississippi River basin (MRB) with measured nitrate flux in the lower Mississippi River. Nitrogen inputs to and outputs from the MRB (1951 to 1996) were estimated from state-level annual agricultural production statistics and NO y (inorganic oxides of N) deposition estimates for 20 states that comprise 90% of the MRB. A model with water yield and gross N inputs accounted for 85% of the variation in observed annual nitrate flux in the lower Mississippi River, from 1960 to 1998, but tended to underestimate high nitrate flux and overestimate low nitrate flux. A model that used water yield and net anthropogenic nitrogen inputs (NANI) accounted for 95% of the variation in Riverine N flux. The NANI approach accounted for N harvested in crops and assumed that crop harvest in excess of the nutritional needs of the humans and livestock in the basin would be exported from the basin. The U.S. White House Committee on Natural Resources and Environment (CENR) developed a more comprehensive N budget that included estimates of ammonia volatilization, denitrification, and exchanges with soil organic matter. The residual N in the CENR budget was weakly and negatively correlated with observed Riverine nitrate flux. The CENR estimates of soil N mineralization and immobilization suggested that there were large (2000 kg N ha -1 ) net losses of soil organic N between 1951 and 1996. When the CENR N budget was modified by assuming that soil organic N levels have been relatively constant after 1950, and ammonia volatilization losses are redeposited within the basin, the trend of residual N closely matched temporal variation in NANI and was positively correlated with Riverine nitrate flux in the lower Mississippi River. Based on results from applying these three modeling approaches, we conclude that although the NANI approach does not address several processes that influence the N cycle, it appears to focus on the terms that can be estimated with reasonable certainty and that are correlated with Riverine N flux.
-
Evaluating the influence of source basins on downstream water quality in the Mississippi River
Journal of the American Water Resources Association, 2002Co-Authors: Gregory M. Clark, Robert E. Broshears, Richard P. Hooper, Donald A. GoolsbyAbstract:: Chemical variability in the Mississippi River during water years 1989 to 1998 was evaluated using stream discharge and water-quality data in conjunction with the DAFLOW/BLTM hydraulic model. Model simulations were used to identify subbasin contributions of water and chemical constituents to the Mississippi River upstream from its confluence with the Ohio and the Mississippi River and at the Atchafalaya Diversion in Louisiana. Concentrations of dissolved solids, sodium, and sulfate at the Thebes site showed a general decreasing trend, and concentrations of silica and nitrate showed a general increasing trend as the percentage of discharge from the Mississippi River upstream from Grafton increased. Concentrations of most chemical constituents in the Mississippi River at the Atchafalaya Diversion exhibited a decreasing trend as the percentage of water from the Ohio River increased. Regression models were used to evaluate the importance of the source of water to the water chemistry in the Mississippi River at Thebes and the Atchafalaya Diversion. The addition of terms in regression equations to account for the percent of water from sub-basins improved coefficients of determination for predicting chemical concentrations by as much as nine percent at the Thebes site and by as much as 48 percent at the Atchafalaya Diversion site. The addition of source-water terms to regression equations increased the estimated annual loads of nitrate and silica delivered from the Mississippi River Basin to the Gulf of Mexico by as much as 14 and 13 percent, respectively.
-
Eutrophication: Nitrate flux in the Mississippi River
Nature, 2001Co-Authors: Gregory F. Mcisaac, Mark B. David, George Z. Gertner, Donald A. GoolsbyAbstract:Increased delivery of biologically available nitrogen to estuaries and coastal oceans in recent decades has been linked to eutrophication and seasonal hypoxia in the northern Gulf of Mexico1,2 and elsewhere3,4. We have developed a model that accounts for 95% of annual variation in delivery of nitrate to the Gulf of Mexico by the Mississippi River in 1960–98. Retrospective analysis indicates that this nitrate flux could have been reduced by 33% if the use of nitrogen-containing fertilizer in the Mississippi River basin had been cut by 12%.
-
Nitrogen flux and sources in the Mississippi River Basin.
Science of The Total Environment, 2000Co-Authors: Donald A. Goolsby, William A. Battaglin, Brent T. Aulenbach, Richard P. HooperAbstract:Abstract Nitrogen from the Mississippi River Basin is believed to be at least partly responsible for the large zone of oxygen-depleted water that develops in the Gulf of Mexico each summer. Historical data show that concentrations of nitrate in the Mississippi River and some of its tributaries have increased by factors of 2 to more than 5 since the early 1900s. We have used the historical streamflow and concentration data in regression models to estimate the annual flux of nitrogen (N) to the Gulf of Mexico and to determine where the nitrogen originates within the Mississippi Basin. Results show that for 1980–1996 the mean annual total N flux to the Gulf of Mexico was 1 568 000 t/year. The flux was approximately 61% nitrate as N, 37% organic N, and 2% ammonium as N. The flux of nitrate to the Gulf has approximately tripled in the last 30 years with most of the increase occurring between 1970 and 1983. The mean annual N flux has changed little since the early 1980s, but large year-to-year variations in N flux occur because of variations in precipitation. During wet years the N flux can increase by 50% or more due to flushing of nitrate that has accumulated in the soils and unsaturated zones in the basin. The principal source areas of N are basins in southern Minnesota, Iowa, Illinois, Indiana, and Ohio that drain agricultural land. Basins in this region yield 800 to more than 3100 kg total N/km 2 per year to streams, several times the N yield of basins outside this region. Assuming conservative transport of N in the Mississippi River, streams draining Iowa and Illinois contribute on average approximately 35% of the total N discharged by the Mississippi River to the Gulf of Mexico. In years with high precipitation they can contribute a larger percentage.
Menghua Wang - One of the best experts on this subject based on the ideXlab platform.
-
satellite observations of flood driven Mississippi River plume in the spring of 2008
Geophysical Research Letters, 2009Co-Authors: Menghua WangAbstract:[1] Satellite measurements from the Moderate Resolution Imaging Spectroradiometer (MODIS) on Aqua were used to quantify the Mississippi River plume following the intense rainfall and massive flood along the Mississippi River and its tributaries during the spring of 2008. The shortwave infrared (SWIR) atmospheric correction algorithm has been used to derive the total suspended matter (TSM) concentration and the spectral optical features of the Mississippi River plume. Following a significantly increased River discharge, the observed Mississippi River plume was considerably large relative to climatological monthly Mississippi River plume data, which were derived from the six-year MODIS-Aqua time series from 2002–2008. The areal coverage of the Mississippi River plume was double compared to the six-year mean value, with plume areal coverage of 5859, 4984, 4366, and 3050 km2 for the months of April, May, June, and July in 2008, respectively. Within the plume, significantly elevated TSM concentration was observed with the pronounced normalized water-leaving reflectance at the green, red, and near-infrared wavelengths in the northern Gulf of Mexico. Near the coast, the satellite-observed TSM concentration in April had increased approximately from the 20 mg/l six-year mean value to over 30 mg/l in the April of 2008.
-
Satellite observations of flood‐driven Mississippi River plume in the spring of 2008
Geophysical Research Letters, 2009Co-Authors: Menghua WangAbstract:[1] Satellite measurements from the Moderate Resolution Imaging Spectroradiometer (MODIS) on Aqua were used to quantify the Mississippi River plume following the intense rainfall and massive flood along the Mississippi River and its tributaries during the spring of 2008. The shortwave infrared (SWIR) atmospheric correction algorithm has been used to derive the total suspended matter (TSM) concentration and the spectral optical features of the Mississippi River plume. Following a significantly increased River discharge, the observed Mississippi River plume was considerably large relative to climatological monthly Mississippi River plume data, which were derived from the six-year MODIS-Aqua time series from 2002–2008. The areal coverage of the Mississippi River plume was double compared to the six-year mean value, with plume areal coverage of 5859, 4984, 4366, and 3050 km2 for the months of April, May, June, and July in 2008, respectively. Within the plume, significantly elevated TSM concentration was observed with the pronounced normalized water-leaving reflectance at the green, red, and near-infrared wavelengths in the northern Gulf of Mexico. Near the coast, the satellite-observed TSM concentration in April had increased approximately from the 20 mg/l six-year mean value to over 30 mg/l in the April of 2008.
Gregory F. Mcisaac - One of the best experts on this subject based on the ideXlab platform.
-
relating net nitrogen input in the Mississippi River basin to nitrate flux in the lower Mississippi River a comparison of approaches
Journal of Environmental Quality, 2002Co-Authors: Gregory F. Mcisaac, Mark B. David, George Z. Gertner, Donald A. GoolsbyAbstract:A quantitative understanding of the relationship between terrestrial N inputs and Riverine N flux can help guide conservation, policy, and adaptive management efforts aimed at preserving or restoring water quality. The objective of this study was to compare recently published approaches for relating terrestrial N inputs to the Mississippi River basin (MRB) with measured nitrate flux in the lower Mississippi River. Nitrogen inputs to and outputs from the MRB (1951 to 1996) were estimated from state-level annual agricultural production statistics and NO y (inorganic oxides of N) deposition estimates for 20 states that comprise 90% of the MRB. A model with water yield and gross N inputs accounted for 85% of the variation in observed annual nitrate flux in the lower Mississippi River, from 1960 to 1998, but tended to underestimate high nitrate flux and overestimate low nitrate flux. A model that used water yield and net anthropogenic nitrogen inputs (NANI) accounted for 95% of the variation in Riverine N flux. The NANI approach accounted for N harvested in crops and assumed that crop harvest in excess of the nutritional needs of the humans and livestock in the basin would be exported from the basin. The U.S. White House Committee on Natural Resources and Environment (CENR) developed a more comprehensive N budget that included estimates of ammonia volatilization, denitrification, and exchanges with soil organic matter. The residual N in the CENR budget was weakly and negatively correlated with observed Riverine nitrate flux. The CENR estimates of soil N mineralization and immobilization suggested that there were large (2000 kg N ha -1 ) net losses of soil organic N between 1951 and 1996. When the CENR N budget was modified by assuming that soil organic N levels have been relatively constant after 1950, and ammonia volatilization losses are redeposited within the basin, the trend of residual N closely matched temporal variation in NANI and was positively correlated with Riverine nitrate flux in the lower Mississippi River. Based on results from applying these three modeling approaches, we conclude that although the NANI approach does not address several processes that influence the N cycle, it appears to focus on the terms that can be estimated with reasonable certainty and that are correlated with Riverine N flux.
-
Eutrophication: Nitrate flux in the Mississippi River
Nature, 2001Co-Authors: Gregory F. Mcisaac, Mark B. David, George Z. Gertner, Donald A. GoolsbyAbstract:Increased delivery of biologically available nitrogen to estuaries and coastal oceans in recent decades has been linked to eutrophication and seasonal hypoxia in the northern Gulf of Mexico1,2 and elsewhere3,4. We have developed a model that accounts for 95% of annual variation in delivery of nitrate to the Gulf of Mexico by the Mississippi River in 1960–98. Retrospective analysis indicates that this nitrate flux could have been reduced by 33% if the use of nitrogen-containing fertilizer in the Mississippi River basin had been cut by 12%.
Richard P. Hooper - One of the best experts on this subject based on the ideXlab platform.
-
Evaluating the influence of source basins on downstream water quality in the Mississippi River
Journal of the American Water Resources Association, 2002Co-Authors: Gregory M. Clark, Robert E. Broshears, Richard P. Hooper, Donald A. GoolsbyAbstract:: Chemical variability in the Mississippi River during water years 1989 to 1998 was evaluated using stream discharge and water-quality data in conjunction with the DAFLOW/BLTM hydraulic model. Model simulations were used to identify subbasin contributions of water and chemical constituents to the Mississippi River upstream from its confluence with the Ohio and the Mississippi River and at the Atchafalaya Diversion in Louisiana. Concentrations of dissolved solids, sodium, and sulfate at the Thebes site showed a general decreasing trend, and concentrations of silica and nitrate showed a general increasing trend as the percentage of discharge from the Mississippi River upstream from Grafton increased. Concentrations of most chemical constituents in the Mississippi River at the Atchafalaya Diversion exhibited a decreasing trend as the percentage of water from the Ohio River increased. Regression models were used to evaluate the importance of the source of water to the water chemistry in the Mississippi River at Thebes and the Atchafalaya Diversion. The addition of terms in regression equations to account for the percent of water from sub-basins improved coefficients of determination for predicting chemical concentrations by as much as nine percent at the Thebes site and by as much as 48 percent at the Atchafalaya Diversion site. The addition of source-water terms to regression equations increased the estimated annual loads of nitrate and silica delivered from the Mississippi River Basin to the Gulf of Mexico by as much as 14 and 13 percent, respectively.
-
Nitrogen flux and sources in the Mississippi River Basin.
Science of The Total Environment, 2000Co-Authors: Donald A. Goolsby, William A. Battaglin, Brent T. Aulenbach, Richard P. HooperAbstract:Abstract Nitrogen from the Mississippi River Basin is believed to be at least partly responsible for the large zone of oxygen-depleted water that develops in the Gulf of Mexico each summer. Historical data show that concentrations of nitrate in the Mississippi River and some of its tributaries have increased by factors of 2 to more than 5 since the early 1900s. We have used the historical streamflow and concentration data in regression models to estimate the annual flux of nitrogen (N) to the Gulf of Mexico and to determine where the nitrogen originates within the Mississippi Basin. Results show that for 1980–1996 the mean annual total N flux to the Gulf of Mexico was 1 568 000 t/year. The flux was approximately 61% nitrate as N, 37% organic N, and 2% ammonium as N. The flux of nitrate to the Gulf has approximately tripled in the last 30 years with most of the increase occurring between 1970 and 1983. The mean annual N flux has changed little since the early 1980s, but large year-to-year variations in N flux occur because of variations in precipitation. During wet years the N flux can increase by 50% or more due to flushing of nitrate that has accumulated in the soils and unsaturated zones in the basin. The principal source areas of N are basins in southern Minnesota, Iowa, Illinois, Indiana, and Ohio that drain agricultural land. Basins in this region yield 800 to more than 3100 kg total N/km 2 per year to streams, several times the N yield of basins outside this region. Assuming conservative transport of N in the Mississippi River, streams draining Iowa and Illinois contribute on average approximately 35% of the total N discharged by the Mississippi River to the Gulf of Mexico. In years with high precipitation they can contribute a larger percentage.
George Z. Gertner - One of the best experts on this subject based on the ideXlab platform.
-
relating net nitrogen input in the Mississippi River basin to nitrate flux in the lower Mississippi River a comparison of approaches
Journal of Environmental Quality, 2002Co-Authors: Gregory F. Mcisaac, Mark B. David, George Z. Gertner, Donald A. GoolsbyAbstract:A quantitative understanding of the relationship between terrestrial N inputs and Riverine N flux can help guide conservation, policy, and adaptive management efforts aimed at preserving or restoring water quality. The objective of this study was to compare recently published approaches for relating terrestrial N inputs to the Mississippi River basin (MRB) with measured nitrate flux in the lower Mississippi River. Nitrogen inputs to and outputs from the MRB (1951 to 1996) were estimated from state-level annual agricultural production statistics and NO y (inorganic oxides of N) deposition estimates for 20 states that comprise 90% of the MRB. A model with water yield and gross N inputs accounted for 85% of the variation in observed annual nitrate flux in the lower Mississippi River, from 1960 to 1998, but tended to underestimate high nitrate flux and overestimate low nitrate flux. A model that used water yield and net anthropogenic nitrogen inputs (NANI) accounted for 95% of the variation in Riverine N flux. The NANI approach accounted for N harvested in crops and assumed that crop harvest in excess of the nutritional needs of the humans and livestock in the basin would be exported from the basin. The U.S. White House Committee on Natural Resources and Environment (CENR) developed a more comprehensive N budget that included estimates of ammonia volatilization, denitrification, and exchanges with soil organic matter. The residual N in the CENR budget was weakly and negatively correlated with observed Riverine nitrate flux. The CENR estimates of soil N mineralization and immobilization suggested that there were large (2000 kg N ha -1 ) net losses of soil organic N between 1951 and 1996. When the CENR N budget was modified by assuming that soil organic N levels have been relatively constant after 1950, and ammonia volatilization losses are redeposited within the basin, the trend of residual N closely matched temporal variation in NANI and was positively correlated with Riverine nitrate flux in the lower Mississippi River. Based on results from applying these three modeling approaches, we conclude that although the NANI approach does not address several processes that influence the N cycle, it appears to focus on the terms that can be estimated with reasonable certainty and that are correlated with Riverine N flux.
-
Eutrophication: Nitrate flux in the Mississippi River
Nature, 2001Co-Authors: Gregory F. Mcisaac, Mark B. David, George Z. Gertner, Donald A. GoolsbyAbstract:Increased delivery of biologically available nitrogen to estuaries and coastal oceans in recent decades has been linked to eutrophication and seasonal hypoxia in the northern Gulf of Mexico1,2 and elsewhere3,4. We have developed a model that accounts for 95% of annual variation in delivery of nitrate to the Gulf of Mexico by the Mississippi River in 1960–98. Retrospective analysis indicates that this nitrate flux could have been reduced by 33% if the use of nitrogen-containing fertilizer in the Mississippi River basin had been cut by 12%.