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Abstract: General circulation models predict that Mississippi River runoff would increase 20% if the concentration of atmospheric CO2 doubles. This hydrologic change would be accompanied by an increase in winter and summer temperatures over the Gulf of Mexico coastal region of a 4.2oC and 2.2oC, respectively. Using a coupled physical-biological model, we examined the potential effects of climate variability on the Gulf of Mexico hypoxic zone. Model simulations suggest that increased freshwater inflow and surface oxygen cycling in the coastal waters of the northern Gulf of Mexico. In simulation experiments, a 20% increase in annual runoff of the Mississippi River, relative to a 1985-1992 average, resulted in a 50% increase in net primary productivity of the upper water column (0-10 m) and a 30 to 60% decrease in summertime subpycnoclincal oxygen content within the present day hypoxix zone. These model projections are in agreement with the observed increase in severity and areal extent of hypoxia during the Great Mississippi River Flood of 1993. 144. Justić, D., N. N. Rabalais and R. E. Turner. 2002. Modeling the impacts of decadal changes in riverine nutrient fluxes on coastal eutrophication near the Mississippi River Delta. Ecological Modeling 152: 33-46. Abstract: A mathematical model was used to link decadal changes in the Mississippi River nutrient flux to coastal eutrophication near the Mississippi River Delta. Model simulations suggest that bottom water hypoxia intensified about 30 years ago, as a probable consequence of increased net productivity and increased sedimentation of the organic material produced in situ in the upper water column. Model simulations also suggest that long-term increase in riverine nutrient fluxes has been responsible for this historical decrease in bottom layer oxygen concentrations. Importantly, model simulations are in good agreement with the available historical data from the northern Gulf of Mexico, and are additionally supported by the retrospective analyses of sedimentary records. Conclusively, this modeling study supports the hypothesis that riverine nutrient fluxes, via their influence on net productivity of the upper water column, play a major role in controlling the development of bottom water hypoxia and accumulation of organic carbon in coastal sediments. 145. Justić, D., N. N. Rabalais, and R. E. Turner (2003), Simulated responses of the Gulf of Mexico hypoxia to variations in climate and anthropogenic nutrient loading, Journal of Marine Systems, 42, 115-126. Abstract: A mathematical model was used to simulate monthly responses of the Gulf of Mexico hypoxia to variations in climate and anthropogenic nutrient loading over a 45-year period. We examined six hypothetical future scenarios that are based on observed and projected changes in the Mississippi River discharge, Mississippi River nitrate concentrations, and ambient water temperatures. In particular, we investigated the implications of a 30% decrease in the Mississippi River nitrogen flux, which was recently proposed by the Mississippi River Watershed/Gulf of Mexico Hypoxia Task Force as a measure to reduce the size of the hypoxic zone. Model simulations suggest that the frequency of hypoxia in the northern Gulf of Mexico is highly sensitive to variations in riverine nitrate flux, but also to variations in freshwater discharge and ambient water temperatures. A 30% decrease in the Mississippi River nitrate flux, for example, would reduce the frequency of hypoxia by 37%. Nevertheless, a 20% increase the Mississippi River discharge, which may occur under some climate change scenarios, would produce an increase in the frequency of hypoxia of the same magnitude. Thus, if the potential climatic variations are taken into account, a 30% decrease in the nitrogen flux of the Mississippi River may not be sufficient to accomplish the proposed hypoxia management goal. 146. Justić, D., N. N. Rabalais, R. E. Turner. 2003. Climate, hypoxia and fisheries: Implications of global climate change for the Gulf of Mexico hypoxic zone. In R. F. Kazmierczak, Jr. and L. J. Thibodeaux (eds.) Proceedings of the 2000 Louisiana Environmental State of the State Conference, available on line at the Department of Agricultural Economics & Agribusiness, Louisiana State University, http:www.agecon.lsu.edu/ESOS-V Proceedings/index.htm Abstract: A large-scale hypoxic zone (< 2 mg O2 l-1) in the coastal waters of the northern Gulf of Mexico, recently approaching 20,000 km2, overlaps with habitat and fishing grounds of commercial fish and shrimp species. Projections of general circulation models have indicated that the Mississippi River runoff would increase if atmospheric CO2 concentration doubles. A higher freshwater runoff would be accompanied by an increase in temperatures over the Gulf Coast region of 2 to 4oC. These two results are likely to affect water column stability, surface productivity and global oxygen cycling in the northern Gulf of Mexico, leading perhaps to an expanded hypoxic zone. This presentation is available in its entirety as a PDF. The link to the PDF is here: http://www.agecon.lsu.edu/ESOS-V%20Proceedings/pdf/JusticESOS-VProceedings.pdf 147. Justić, D., R. E. Turner and N. N. Rabalais. 2003. Climatic influences on riverine nitrate flux: Implications for coastal marine eutrophication and hypoxia. Estuaries 26: 1-11. Abstract: The average nitrate flux of the lower Mississippi River increased 3.3-fold between 1954-1967 and 1983-2000. During the same time period, the average nitrate concentration increased 2.3-fold while the average discharge increased 40%. Partitioning of the observed trend in nitrate flux among the two flux components, nitrate concentration and discharge, revealed that about 80% of the observed increase in flux could be explained by the increase in nitrate concentration. This indicates that a historical increase in the anthropogenic nutrient inputs has had a far greater impact on the lower Mississippi River nitrate flux than a change in climate. The influence of climatic factors on nitrate flux has been significant and may further increase as a result of global climate change. This argument is supported by two tines of evidence. The residual component of nitrate flux, obtained by removing a trend from the time series, is controlled primarily by the variability in discharge, i.e., climatic factors. Also, there is a highly significant relationship between discharge and nitrate concentration at the low end of the discharge spectrum (< 13,000 m(3) s(-1)). The differences in nitrate flux between flood and drought years are significantly larger than the variations in discharge. This makes the Mississippi River nitrate flux potentially sensitive to future changes in the frequency of extreme climatic events. Because of the importance of nitrate for the productivity of coastal phytoplankton, future climate change would likely have important implications for coastal marine eutrophication and hypoxia. 148. Justić, D., R. E. Turner and N. N. Rabalais. 2004. Perspectives for coastal marine hypoxia in a warmer world. Pp. 57-72 in G. L. Rupp and M. D. White (eds.), Proceedings of the 7th International Symposium on Fish Physiology, Toxicology and Water Quality, Tallinn, Estonia, May 12-15, 2003. EPA 600/R-04/049, U.S. Environmental Protection Agency, Ecosystems Research Division, Athens, Georgia. The complete proceedings of this symposium are available as a PDF: http://water.montana.edu/symposium/proceedings/default.htm 149. Justić, D., N. N. Rabalais and R. E. Turner. 2005. Coupling between climate variability and marine coastal eutrophication: historical evidence and future outlook. Journal of Sea Research 54: 25-35. Abstract: It is generally believed that coastal eutrophication is primarily controlled by the magnitude of anthropogenic nutrient loading and this cause-effect relationship is often used as a common explanation for the widespread eutrophication observed during the second half of the 20th century. This paper examines the coupling between climate variability and coastal cutrophication, and discusses how future changes in climate may affect nutrient fluxes to the coastal zone, nutrient ratios, phytoplankton production and the severity of hypoxia. We focus on the northern Gulf of Mexico, a coastal ecosystem dominated by inflow of the Mississippi River, where recorded decadal and interannual variations in the size of a large hypoxic zone (> 2 x 10(4) km(2)) provide examples of anthropogenic and climatic controls on eutrophication. Using a mathematical model, four hypothetical future climate scenarios were examined. The scenarios were based on projected changes in the Mississippi River discharge, nitrate flux, and ambient water temperatures, and the simulation results were compared to the standard model. The forcing functions in the standard model included the observed time-series of temperature, riverine freshwater discharge and nitrate flux over the 45-y period 1955-2000. In all four model scenarios, simulated frequency of hypoxia differed significantly from the standard model, ranging from a 58% decrease to a 63% increase. The Gulf of Mexico responses to climate-driven variations in freshwater inflow may not be representative for other coastal ecosystems. A comparison of the northern Gulf of Mexico and the Hudson River estuary revealed that the increased riverine freshwater inflow, which causes cutrophication in the northern Gulf of Mexico, improves trophic conditions in the Hudson River estuary. Hence, the degree to which coastal eutrophication will be affected by future climate variability will vary from one system to another, depending on the characteristics of the physical environment and the current eutrophication status. 150. Justić, D., N. N. Rabalais, and R. Eugene Turner. In press. Implications of Global Climate Change for Coastal and Estuarine Hypoxia: Hypotheses, Observations and Models for the Northern Gulf of Mexico. In Proceedings, 6th International Symposium, Fish Physiology, Toxicology and Water Quality, Hypoxia in the Aquatic Environment, La Paz, Baja California, Mexico, January 2001, EPA Rpt. No. EPA/600/R-02/097, Environmental Protection Agency, Ecosystems Research Division, Athens, Georgia. Abstract: Scientists from fifteen countries presented papers at the Sixth International Symposium on Fish Physiology, Toxicology, and Water Quality held in La Paz, Baja, Mexico, January 22-26, 2001. These Proceedings include 25 papers presented in sessions convened over four days. Papers addressed the effects of hypoxia and anoxia on the physiology of fishes and aquatic invertebrates as a global phenomenon, the role of adenosine as a universal promoter of fish survival under hypoxia, the effects of hypoxia on fish species, and the specific effects of hypoxia and anoxia in: temperate estuaries, the continental shelf, the deep sea environment, shallow eutrophic lakes, and the subtropical environment. Water quality papers included: general discussions on hypoxia, effects of anoxia on the marine sulfur cycle, effects of hypoxia/anoxia on major ion and redox chemistry, physical effects of anoxia on sediment biota morphology, hypoxia in the Gulf of California, effect of hypoxia on the ecological conditions of coastal estuaries, nonpoint source pollution effects on coastal hypoxia, modeling effects of climate change on hypoxia, and the use of euthrophication modeling to assess water quality and ecological endpoints. These proceedings are available in their entirety as a PDF: http://www.epa.gov/ATHENS/publications/reports/EPA_600_R02_097.pdf 151. Karlsen, A. W., T. M. Cronin, S. E. Ishman, D. A. Willard, R. Kerhin, C.W. Holmes and M. Marot. 2000. Historical trends in Chesapeake Bay dissolved oxygen based on benthic foraminifera from sediment cores. Estuaries, 23, 488-508. Abstract: Environmentally sensitive benthic foraminifera (protists) from Chesapeake Bay were used as bioindicators to estimate the timing and degree of changes in dissolved oxygen (DO) over the past five centuries. Living foraminifers from 19 surface samples and fossil assemblages from 11 sediment cores dated by Pb-210, Cs-131, C-14, and pollen stratigraphy were analyzed from the tidal portions of the Patuxent, Potomac, and Choptank Rivers and the main channel of the Chesapeake Bay. Ammonia parkinsoniana, a facultative anaerobe tolerant of periodic anoxic conditions, comprises an average of 74% of modern Chesapeake foraminiferal assemblages (DO = 0.47 and 1.72 ml l(-1)) compared to 0% to 15% of assemblages collected in the 1960s. Paleoecological analyses show that A. parkinsoniana was absent prior to the late 17th century increased to 10-25% relative frequency between approximately 1670-1720 and 1810-1900, and became the dominant (60-90%) benthic foraminiferal species in channel environments beginning in the early 1970s. Since the 1970s, deformed tests of A. parkinsoniana occur in all cores (10-20% of Ammonia), suggesting unprecedented stressful benthic conditions. These cores indicate that prior to the late 17th century, there was limited oxygen depletion. During the past 200 years, decadal scale variability in oxygen depletion has occurred, as dysoxic (DO = 0.1-1.0 mi l(-1)), perhaps short-term anoxic (DO < 0.1 mi l(-1)) conditions developed. The most extensive (spatially and temporally) anoxic conditions were reached during the 1970s. Over decadal timescales, DO variability scents to be Linked closely to climatological: factors influencing river discharge; the unprecedented anoxia since the early 1970s is attributed mainly to high freshwater now and to an increase in nutrient concentrations From the watershed. 152. Karlson, K., R. Rosenberg and E. Bonsdorff. 2002. Temporal and spatial large-scale effects of eutrophication and oxygen deficiency on benthic fauna in Scandinavian and Baltic waters – a review. Oceanogr. Mar. Biol. Ann. Rev., 40, 427-489. Abstract: Eutrophication has been an increasing ecological threat during the past 50 yr in many Scandinavian and Baltic marine waters. Large sedimentary areas are seasonally, or more or less permanently, affected by hypoxia and/or anoxia with devastating effects on the benthic macrofauna in, for example, the Baltic Sea, the Belt Seas and Oresund between Denmark and Sweden, the Kattegat and the Skagerrak coast towards the North Sea. In this review figures for the input of nitrogen and phosphorus to different sea areas are presented, and in several cases also changes of nitrogen and phosphorus concentrations in the water. The nutrient input is related to production levels, and related to macrobenthic infauna. Changes of dominant benthic species, abundance and biomass are presented in relation to both changes in organic enrichment and hypoxia and/or anoxia in time and space. Since the 1950s-60s, the benthic faunal biomass has increased in the Gulf of Bothnia as a result of increased organic enrichment. In the Aland Archipelago, the number of benthic species decreased since the 1970s but abundance and biomass increased. Drifting algae at the sediment surface has also been an increasing problem. The changes were caused by increasing eutrophication. In the Finnish Archipelago Sea, large-scale eutrophication has resulted in periodic bottom water hypoxia and drifting algal mats with negative effects on benthic fauna. In the Gulf of Finland, the benthic fauna has been negatively affected by hypoxic bottom water below 70 in depth since the 1960s, but with a period of improved oxygen conditions during 1987-94. In the Baltic Proper, large sea-bed areas of 70 000-100 000 km(2) below 70-80 in water depth have been more or less hypoxic and/or anoxic since the 1960s with no or reduced sediment-dwelling fauna. This process was a result of increased eutrophication and lack of larger inflows of oxygenated water from the Kattegat. Several coastal areas and larger basins in the southern Baltic (e.g. the Bornholm Basin, the Arkona Basin and the Kiel Bay), have, on occasions, been similarly negatively affected by hypoxic bottom water. Many sedimentary areas below similar to 17 in in the Danish Belt Seas have been affected by seasonal hypoxia since the 1970s with negative consequences for the bottom fauna. On the Danish Kattegat coast, the benthic fauna in the Limfjord, the Mariager fjord and the Roskilde fjord have been particularly negatively affected. In the southeast, open Kattegat, increased input of nutrients in combination with stratification have resulted in seasonal hypoxia since 1980 with negative effects on benthic animals and commercial fish species in most years. Several fjords on the Swedish and Norwegian Skagerrak coast have shown negative temporal trends in bottom water oxygen concentrations, and some of them lack benthic fauna in the deeper parts for several months or more. In this review the temporal development of bottom water hypoxia and/or anoxia is discussed and consequent possible losses of sediment-dwelling faunal biomass are roughly calculated. In total for the areas investigated, the worst years of hypoxia and/or anoxia combined may have reduced the benthic macrofaunal biomass by 3 million t. This loss is partly compensated by the biomass increase that has occurred in well-flushed organically enriched coastal areas. Tolerance of some Baltic species to hypoxia and/or anoxia is discussed and also their different strategies to cope with hypoxia and/or anoxia and H2S. 156. Lane RR, Day JW, Justić D, Reyes E, Marx B, Day JN, Hyfield E. 2004. Changes in stoichiometric Si, N and P ratios of Mississippi River water diverted through coastal wetlands to the Gulf of Mexico. ESTUARINE COASTAL AND SHELF SCIENCE 60 (1): 1-10. Abstract: During the spring of 2001, we monitored nutrient concentrations and stoichiometry of diverted Mississippi River water as it flowed through the Breton Sound estuary, Louisiana, USA. River water was discharged through a diversion structure at Caernarvon as a two-week pulse that peaked at 220 m(3) s(-1). There were reductions in observed concentrations of TN, TP, DIN, DIP and DSi, of up to 44%. 62%, 57%. 23%, and 38%, respectively, as water flowed through the estuary. TN, TP, DIN, DIP and DSi concentrations in the river were 137-140, 5.0-5.1, 104-153, 1.1-1.3 and 114-121 muM, respectively, and 36-122, 1.8-3.6, 13-119, 0.3-1.8 and 29-110 muM, respectively, at the Gulfward end member stations. The DSi:DIN ratio rose from 0.9 at the Caernarvon diversion to 2.6 at the Gulf end member station, while the DIN:DIP ratio fell from 107 to 26. This study shows that freshwater diversions can significantly alter riverine nutrient concentrations and ratios and reduce the overall amount of exported nitrogen. 157. Lawrence, G.B., Goolsby, D.A., Battaglin, W.A., and Stensland, G.J., 2000. Atmospheric nitrogen in the Mississippi River Basin - emissions, deposition and transport. Science of the Total Environment 248 (2-3): 101-113. Abstract: Atmospheric deposition of nitrogen has been cited as a major factor in the nitrogen saturation of forests in the north-eastern United States and as a contributor to the eutrophication of coastal waters, including the Gulf of Mexico near the mouth of the Mississippi River. Sources of nitrogen emissions and the resulting spatial patterns of nitrogen deposition within the Mississippi River Basin, however, have not been fully documented. An assessment of atmospheric nitrogen in the Mississippi River Basin was therefore conducted in 1998-1999 to: (1) evaluate the forms in which nitrogen is deposited from the atmosphere; (2) quantify the spatial distribution of atmospheric nitrogen deposition throughout the basin; and (3) relate locations of emission sources to spatial deposition patterns to evaluate atmospheric transport. Deposition data collected through the NADP/NTN (National Atmospheric Deposition Program/National Trends Network) and CASTNet (Clean Air Status and Trends Network) were used for this analysis. NOx Tier 1 emission data by county was obtained for 1992 from the US Environmental Protection Agency (Emissions Trends Viewer CD, 1985-1995, version 1.0, September 1996) and NH3 emissions data was derived from the 1992 Census of Agriculture (US Department of Commerce. Census of Agriculture, US Summary and County Level Data, US Department of Commerce, Bureau of the Census. Geographic Area series, 1995:1b) or the National Agricultural Statistics Service (US Department of Agriculture. National Agricultural Statistics Service Historical Data. Accessed 7/98 at URL, 1998. http://www.usda.gov/nass/pubs/hisdata++ +.htm). The highest rates of wet deposition of NO3- were in the north-eastern part of the basin, downwind of electric utility plants and urban areas, whereas the highest rates of wet deposition of NH4+ were in Iowa, near the center of intensive agricultural activities in the Midwest. The lowest rates of atmospheric nitrogen deposition were on the western (windward) side of the basin, which suggests that most of the nitrogen deposited within the basin is derived from internal sources. Atmospheric transport eastward across the basin boundary is greater for NO3- than NH4+, but a significant amount of NH4+ is likely to be transported out of the basin through the formation of (NH4)2SO4 and NH4NO3 particles--a process that greatly increases the atmospheric residence time of NH4+. This process is also a likely factor in the atmospheric transport of nitrogen from the Midwest to upland forest regions in the North-East, such as the western Adirondack region of New York, where NH4+ constitutes 38% of the total wet deposition of N. http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=10805230&dopt=Abstract 160. Levin, L. A., J. D. Gage, C. Martin and P. A. Lamont. 2000. Macrobenthic community structure within and beneath the oxygen minimum zone, northwest Arabian Sea. Deep-Sea Res. II, 47, 189-226. Abstract: Investigations of macrobenthos were carried out within and beneath the oxygen minimum zone (OMZ, < 0.5 ml l(-1)) during Fall 1994 on the Oman margin, NW Arabian Sea. Six stations (400, 700, 850, 1000, 1250 and 3400m) were characterized with respect to macrofaunal abundance, biomass, body size, taxonomic composition, diversity and lifestyles, and the relation of these parameters to environmental conditions. The OMZ (400-1000 m) was dominated by a dense (5818-19,183 ind m(-2)), soft-bodied assemblage consisting largely (86-99%) of surface-feeding polychaetes, Spionids and cirratulids dominated at the 400- and 700-m stations, paraonids and ampharetids at the 850- and 1000-m stations. Molluscs and most crustaceans were common only below the OMZ ( greater than or equal to 1250 m); a species of the amphipod Ampelisca was abundant within the OMZ, however. Both density and biomass were elevated within the OMZ relative to stations below but body size did not differ significantly among stations. The lower OMZ boundary (0.5 ml l(-1)) was not a zone of enhanced macrofaunal standing stock, as originally hypothesized. However, abundance maxima at 700-850m may reflect an oxygen threshold (0.15-0.20 ml l(-1)) above which macrofauna take advantage of organically enriched sediments. Incidence of burrowing and subsurface-deposit feeding increased below the OMZ, Species richness (E[S-100]), diversity (H') and evenness (J') were lower and dominance (R1D) was higher within than beneath the OMZ. Within-station (between-boxcore) faunal heterogeneity increased markedly below the OMZ. Surface sediment pigment concentrations and oxygen together explained 96-99% of the variance in measures of E[S-100], H' and J' across the transect; grain size and % TOC did not yield significant regressions. Pigments, assumed to reflect food availability and possibly oxygen effects on organic matter preservation, were negatively correlated with species richness and evenness, and positively correlated with dominance. The reverse was true for water depth. Macrobenthic patterns of calcification and lifestyle within the Oman margin OMZ (0.13-0.3 mi l(-1)) match the dysaerobic biofacies of paleo-environmental reconstruction models. 162. Liu, S. M., J. Zhang, H. T. Chen, Y. Wu, H. Xiong and Z. F. Zhang. 2003. Nutrients in the Changjiang and its tributaries. Biogeochem., 62, 1-18. Directory: sab sab -> Office of the administrator science advisory board sab -> History honours thesis, 1986 – 2013 sab -> University rankings new method sab -> Is a decision by world banks to step in and provide cut-price dollar funding to eurozone banks a credible solution to the debt crisis? The Environment Agency says a drought that has affected parts of England since June could last until next sab -> David A. Broniatowski Term Address Permanent Address sab -> Test Technology Standards Committee Update Rohit Kapur Mar 2008 Attendees sab -> Analysis: Aid or Immigration? 03 Oct 11 sab -> The deal to solve the eurozone's debt crisis is to be put to a referendum in Greece. Demonstrators outside St Paul's Cathedral are being told they have two days to leave or face legal action Download 0.67 Mb. Share with your friends:
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