During the unprecedented oil spill in the northern Gulf of Mexico between April and July 2010, ~8... more During the unprecedented oil spill in the northern Gulf of Mexico between April and July 2010, ~8 x 108 liters of crude oil and ~7 x 106 liters of dispersant were released into the water column in the Gulf of Mexico. Fluorescence excitation and emission matrix (EEM) techniques and CDOM measurements have been used in many studies to examine the
Millie, D. F.1, Fahnenstiel, G. L.2, Carrick, H. J.3, Lohrenz, S. E.4, & Schofield, O. M. E.5 1US... more Millie, D. F.1, Fahnenstiel, G. L.2, Carrick, H. J.3, Lohrenz, S. E.4, & Schofield, O. M. E.5 1USDA‐Agricultural Research Service, Sarasota, FL 34236, USA, 2NOAA‐Lake Michigan Field Station, Muskegon, MI 49441, USA, 3Institute of Marine Science, University of Southern Mississippi, Stennis Space Center, MS 39529, USA, 4Department of Biological Sciences, State University of New York at Buffalo, Buffalo, NY 14060, USA; 5Isttitute of Marine and Coastal Sciences, Rutgers University, 71 Dudley Road New Brunswick NJ 08901 USA,Sediment resuspension is an annually recurrent feature during spring holomixis in southern Lake Michigan. Relationships between resuspension events and phyt‐oplankton biomass, compositional dynamics, and pro‐duction were evaluated during 1998 and 1999. Increased water‐column light attenuation (KPAR) and suspended particulate matter (SPM) concentrations corresponded with resuspension events within nearshore regions. However, neither KPAR nor SPM corresponded with chlor...
Phosphorus (P) control is critical to mitigating eutrophication in aquatic ecosystems, but the ef... more Phosphorus (P) control is critical to mitigating eutrophication in aquatic ecosystems, but the effectiveness of controlling P export from soils has been limited by our poor understanding of P dynamics along the land‐ocean aquatic continuum as well as the lack of well‐developed process models that effectively couple terrestrial and aquatic biogeochemical P processes. Here, we coupled riverine P biogeochemical processes and water transport with terrestrial processes within the framework of the Dynamic Land Ecosystem Model to assess how multiple environmental changes, including fertilizer and manure P uses, land use, climate, and atmospheric CO2, have affected the long‐term dynamics of P loading and export from the Mississippi River Basin to the Gulf of Mexico during 1901–2018. Simulations show that riverine exports of dissolved inorganic phosphorus (DIP), dissolved organic phosphorus, particulate organic phosphorus (POP), and particulate inorganic phosphorus (PIP) increased by 42%, 53%, 60%, and 53%, respectively, since the 1960s. Riverine DIP and PIP exports were the dominant components of the total P flux. DIP export was mainly enhanced by the growing mineral P fertilizer use in croplands, while increased PIP and POP exports were a result of the intensified soil erosion due to increased precipitation. Climate variability resulted in substantial interannual and decadal variations in P loading and export. Soil legacy P continues to contribute to P loading. Our findings highlight the necessity to adopt effective P management strategies to control P losses through reductions in soil erosion, and additionally, to improve P use efficiency in crop production.
ABSTRACT Dissolved inorganic carbon (DIC), total alkalinity (TAlk), pH, DO, and nutrients were me... more ABSTRACT Dissolved inorganic carbon (DIC), total alkalinity (TAlk), pH, DO, and nutrients were measured in the Mississippi River plume during five cruises in spring, summer and fall. In contrast to other large rivers, both DIC and TAlk were higher in the river than in seawater and were removed along the mixing gradient between river and coastal water. In the intermediate salinity regions, the strong DIC removal was accompanied by strong nutrient removal, high dissolved oxygen (DO), high pH, and high chlorophyll a concentration. Net community production (NCP) rate estimated based on DIC and TAlk removal peaked during summer, and was among the highest observed for large river plumes. In summer and fall, 60-80% of the nutrient load from the Mississippi River was consumed in the plume, while only 30% of nutrient load was consumed in spring as the result of higher discharge, higher nutrient load, and lower productivity. Spatial and temporal changes in carbon and nutrient dynamics and NCP as well as a comparison with other large river plumes suggest that nutrient supply, light availability, temperature, and water residence time are the most important factors regulating NCP in this large river plume. Budget analysis suggests that the Mississippi River plume produces sufficient amount of labile organic carbon during March-June that meets the demand for developing the summer hypoxia of the northern Gulf of Mexico. CaCO3 precipitation is also likely, but the mechanism is still not clear.
ABSTRACT Increased nutrient loading in rivers globally has led to the formation of many hypoxic a... more ABSTRACT Increased nutrient loading in rivers globally has led to the formation of many hypoxic areas, or dead zones, in the associated ocean margins. Results from multiple cruises between 2006 and 2009 demonstrated that intensive biological CO2 fixation into organic carbon (OC) driven by tripling riverine nutrients in the Mississippi River plume has led to accompanying hypoxic and acidic conditions in the bottom waters of the northern Gulf of Mexico (nGOM). The remineralization of OC into CO2 in the bottom waters has amplified the ocean acidification there from 0.11 pH unit to 0.16, and has resulted in conditions approaching carbonate under-saturation. Further increases in atmospheric CO2 are predicted to lead to increasingly acidic and suboxic conditions in the nGOM bottom waters, making them unfit for carbonate shell bearing organisms.
Biological productivity in the northern Gulf is significantly affected by the Mississippi River. ... more Biological productivity in the northern Gulf is significantly affected by the Mississippi River. The freshwater discharge (577 km3 yr−1, approx 10% of the volume of water on the shelf) contains high concentrations of dissolved nutrients (100-150 μmol NO3 l−1). Flow is primarily constrained by prevailing winds to the continental shelf west of the Mississippi Delta. River plumes are regions of high phytoplankton stock (\u3e30 g Chi l−1) and production (5 g C m−2 d−1), high copepod stocks (nauplius concentrations \u3e1000 l−1) and high ichthyoplankton stocks (larval concentrations \u3e50 m−3). The high temperature of shelf waters assures high physiological rates, implying high rates of trophic transfer and high turnover rates. The primary fate of phytoplankton production is grazing by macrozooplankton and microzooplankton. However, sinking of phytoplankton and other organic material fuels the annual development of a band of hypoxic water along the Louisiana coast. Fisheries production is high; the northern Gulf supports the largest volume fishery in the United States, the Gulf menhaden, Brevoortia patronus. The Loop Current in its northernmost position affects shelf processes to the east of the Delta. Anticyclonic rings derived from the Loop Current occasionally impact on the Louisiana shelf west of the Delta but usually drift over to the western Gulf resulting in exchange of oceanic and shelf water off Texas
During the unprecedented oil spill in the northern Gulf of Mexico between April and July 2010, ~8... more During the unprecedented oil spill in the northern Gulf of Mexico between April and July 2010, ~8 x 108 liters of crude oil and ~7 x 106 liters of dispersant were released into the water column in the Gulf of Mexico. Fluorescence excitation and emission matrix (EEM) techniques and CDOM measurements have been used in many studies to examine the
Millie, D. F.1, Fahnenstiel, G. L.2, Carrick, H. J.3, Lohrenz, S. E.4, & Schofield, O. M. E.5 1US... more Millie, D. F.1, Fahnenstiel, G. L.2, Carrick, H. J.3, Lohrenz, S. E.4, & Schofield, O. M. E.5 1USDA‐Agricultural Research Service, Sarasota, FL 34236, USA, 2NOAA‐Lake Michigan Field Station, Muskegon, MI 49441, USA, 3Institute of Marine Science, University of Southern Mississippi, Stennis Space Center, MS 39529, USA, 4Department of Biological Sciences, State University of New York at Buffalo, Buffalo, NY 14060, USA; 5Isttitute of Marine and Coastal Sciences, Rutgers University, 71 Dudley Road New Brunswick NJ 08901 USA,Sediment resuspension is an annually recurrent feature during spring holomixis in southern Lake Michigan. Relationships between resuspension events and phyt‐oplankton biomass, compositional dynamics, and pro‐duction were evaluated during 1998 and 1999. Increased water‐column light attenuation (KPAR) and suspended particulate matter (SPM) concentrations corresponded with resuspension events within nearshore regions. However, neither KPAR nor SPM corresponded with chlor...
Phosphorus (P) control is critical to mitigating eutrophication in aquatic ecosystems, but the ef... more Phosphorus (P) control is critical to mitigating eutrophication in aquatic ecosystems, but the effectiveness of controlling P export from soils has been limited by our poor understanding of P dynamics along the land‐ocean aquatic continuum as well as the lack of well‐developed process models that effectively couple terrestrial and aquatic biogeochemical P processes. Here, we coupled riverine P biogeochemical processes and water transport with terrestrial processes within the framework of the Dynamic Land Ecosystem Model to assess how multiple environmental changes, including fertilizer and manure P uses, land use, climate, and atmospheric CO2, have affected the long‐term dynamics of P loading and export from the Mississippi River Basin to the Gulf of Mexico during 1901–2018. Simulations show that riverine exports of dissolved inorganic phosphorus (DIP), dissolved organic phosphorus, particulate organic phosphorus (POP), and particulate inorganic phosphorus (PIP) increased by 42%, 53%, 60%, and 53%, respectively, since the 1960s. Riverine DIP and PIP exports were the dominant components of the total P flux. DIP export was mainly enhanced by the growing mineral P fertilizer use in croplands, while increased PIP and POP exports were a result of the intensified soil erosion due to increased precipitation. Climate variability resulted in substantial interannual and decadal variations in P loading and export. Soil legacy P continues to contribute to P loading. Our findings highlight the necessity to adopt effective P management strategies to control P losses through reductions in soil erosion, and additionally, to improve P use efficiency in crop production.
ABSTRACT Dissolved inorganic carbon (DIC), total alkalinity (TAlk), pH, DO, and nutrients were me... more ABSTRACT Dissolved inorganic carbon (DIC), total alkalinity (TAlk), pH, DO, and nutrients were measured in the Mississippi River plume during five cruises in spring, summer and fall. In contrast to other large rivers, both DIC and TAlk were higher in the river than in seawater and were removed along the mixing gradient between river and coastal water. In the intermediate salinity regions, the strong DIC removal was accompanied by strong nutrient removal, high dissolved oxygen (DO), high pH, and high chlorophyll a concentration. Net community production (NCP) rate estimated based on DIC and TAlk removal peaked during summer, and was among the highest observed for large river plumes. In summer and fall, 60-80% of the nutrient load from the Mississippi River was consumed in the plume, while only 30% of nutrient load was consumed in spring as the result of higher discharge, higher nutrient load, and lower productivity. Spatial and temporal changes in carbon and nutrient dynamics and NCP as well as a comparison with other large river plumes suggest that nutrient supply, light availability, temperature, and water residence time are the most important factors regulating NCP in this large river plume. Budget analysis suggests that the Mississippi River plume produces sufficient amount of labile organic carbon during March-June that meets the demand for developing the summer hypoxia of the northern Gulf of Mexico. CaCO3 precipitation is also likely, but the mechanism is still not clear.
ABSTRACT Increased nutrient loading in rivers globally has led to the formation of many hypoxic a... more ABSTRACT Increased nutrient loading in rivers globally has led to the formation of many hypoxic areas, or dead zones, in the associated ocean margins. Results from multiple cruises between 2006 and 2009 demonstrated that intensive biological CO2 fixation into organic carbon (OC) driven by tripling riverine nutrients in the Mississippi River plume has led to accompanying hypoxic and acidic conditions in the bottom waters of the northern Gulf of Mexico (nGOM). The remineralization of OC into CO2 in the bottom waters has amplified the ocean acidification there from 0.11 pH unit to 0.16, and has resulted in conditions approaching carbonate under-saturation. Further increases in atmospheric CO2 are predicted to lead to increasingly acidic and suboxic conditions in the nGOM bottom waters, making them unfit for carbonate shell bearing organisms.
Biological productivity in the northern Gulf is significantly affected by the Mississippi River. ... more Biological productivity in the northern Gulf is significantly affected by the Mississippi River. The freshwater discharge (577 km3 yr−1, approx 10% of the volume of water on the shelf) contains high concentrations of dissolved nutrients (100-150 μmol NO3 l−1). Flow is primarily constrained by prevailing winds to the continental shelf west of the Mississippi Delta. River plumes are regions of high phytoplankton stock (\u3e30 g Chi l−1) and production (5 g C m−2 d−1), high copepod stocks (nauplius concentrations \u3e1000 l−1) and high ichthyoplankton stocks (larval concentrations \u3e50 m−3). The high temperature of shelf waters assures high physiological rates, implying high rates of trophic transfer and high turnover rates. The primary fate of phytoplankton production is grazing by macrozooplankton and microzooplankton. However, sinking of phytoplankton and other organic material fuels the annual development of a band of hypoxic water along the Louisiana coast. Fisheries production is high; the northern Gulf supports the largest volume fishery in the United States, the Gulf menhaden, Brevoortia patronus. The Loop Current in its northernmost position affects shelf processes to the east of the Delta. Anticyclonic rings derived from the Loop Current occasionally impact on the Louisiana shelf west of the Delta but usually drift over to the western Gulf resulting in exchange of oceanic and shelf water off Texas
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