Important recent research accomplishments by NGI researchers, in collaboration with NOAA researchers, focus on the issues and resources of the Gulf with many of the tools and protocols transferrable to other coastal environs. Listed below are several examples of these successes with additional details available in the later project descriptions.
- Research results indicated that Barataria Bay estuary imports nitrogen and exports carbon to the coastal ocean. The annual Total Organic Carbon export is 109 million kg, or 57 gC m2 yr-1 when prorated to the total water area of the estuary. This carbon export is equivalent to a loss of 0.5 m of wetland soil horizon over an area of 8.4 km2, and accounts for about 34 % of the observed annual wetland loss in the estuary between 1978 and 2000. However, compared to the lower Mississippi River, the Barataria estuary appears to be a very small source of Total Organic Carbon for the northern Gulf of Mexico (2.7 % of riverine Total Organic Carbon), and is therefore unlikely to have a significant influence on the development of Gulf hypoxia. An interesting finding is that besides nutrients, wind appears to be an important controlling factor in productivity dynamics in Barataria Bay. Wind resuspends sediments that block light important for phytoplankton growth, but resuspension also liberates nutrients from sediment porewaters. When winds die down, as they usually do overnight, phytoplankton grow rapidly during daylight hours with P/R ratios of (gross productivity/respiration) in the 1-3 range.
- A Before-After-Control-Impact study demonstrated that nekton species biomass distributions changed significantly after the opening of the Caernarvon freshwater diversion 1991. The biomass of selected economically or ecologically important species showed an increase relative to the control (Micropterus salmoides, Micropogonias undulatus, Brevoortia patronus, Farfantepenaeus aztecus and Litopenaeus setiferus), and one was not affected (Cynoscion nebulosus). In addition, nekton species richness, abundance and the proportion of smaller individuals increased, indicating increased nursery function.
- To better understand the impacts of Mississippi River diversions on wetland restoration strategies, new data were analyzed to help budget what was happening to Mississippi River nitrate that was entering upper Breton Sound at Caernarvon. The data suggest that phytoplankton uptake is likely the major sink for nitrate at Caernarvon. The strongest biological uptake signals occurred in July at moderate residence times, and presumably moderate river flows. Macrophyte uptake probably is also very important in Lake Leary, accounting for the strong "estuarine filter" effect and about 100% nitrate removal unless diversion flows are very strong, as they were in April 2008.
- Consistent with the view that estuaries are generally highly productive systems, Breton Sound net productivity values are about 10x greater than average offshore values based on a model developed from averaging results from 24 hour incubations with results from field oxygen isotope measurements. For February – October 2009, Breton Sound phytoplankton productivity was about 2x higher in warmer than colder months where overall productivity averaged about 50 mmol C m-3/d and were sufficient to turnover and replace standing algal stocks about once every two days.
- Phycotoxins, including Microcystis, have now been detected in water samples in Breton Sound estuary, as well as primary and secondary consumers (chironomids, clams, blue crab and catfish), in two estuaries and coastal Louisiana illustrating the need for continued monitoring and research to discover the underlying factors that control toxin production. Finding phycotoxins in the estuary illustrates the potential for harmful effects on consumers and the entire food web.
- Relevant to understanding hazardous algal blooms, both field data and laboratory testing shows salinity as one of the major impacting factors in Vibrio proliferation. For example, a lower Barataria site with an annual average salinity of 18.7 g/L had an annual average putative Vibrio population of 277 CFU/100 mL in contrast to an average Vibrio population of 1 CFU/100 mL at an upper Barataria site with an average salinity of 0.15 g/L. Observations also demonstrated that freshwater pulse events in Breton Sound lowered Vibrio levels.
- Denitrification rates of the salt marsh soils in Breton Sound demonstrated a tolerance to salinity levels in the higher salinity range with no significant difference in rate for the 15 and 35 ppt treatments. However, freshwater salinity treatment led to a dramatic decrease in denitrification rates for the salt marsh soil. This result has consequences for any proposed very large diversion which would be capable of discharging very large amounts (50,000 - 150,000 cfs) of Mississippi River water. Under such hydraulic loading to the coastal wetlands, some nitrate would bypass the fresh marsh and would undergo little denitrification in the salt marsh environment. This increased inorganic N loading to the coastal ocean would have consequences for increased coastal hypoxia.
- Sampling continued at stations from Lower Pearl River estuary as well as in the Bay of Saint Louis, out into the Mississippi Sound and offshore to the 20 m isobath in the Mississippi Bight. This monitoring led to the discovery of seasonal hypoxia in the western Mississippi Bight after seasonal transition from horizontally to vertically stratified water column. These measurements show that hypoxia in the region leads to nutrient flux out of the benthos, and enhanced surface productivity, which can then lead to enhanced bottom hypoxia. Phosphate enhancement (N:P ratios < 1) in the Mississippi Sound was consistent with that originally found in the 1970s, but not appearing in the later literature.
- Data from NOAA's Coastal Change Analysis Program (C-CAP) program, distributed by the Coastal Services Center, and from the Landsat 5 Thematic Mapper satellite sensor were analyzed to investigate wetland loss patterns near the Caernarvon diversion due to hurricane storm surge. Before the 2005 hurricanes, wetland erosion occurred at a slow but steady pace throughout the region, from 0-2.4%. The most erosion was near the diversion in the freshwater region. After the 2005 hurricanes, land loss is evident throughout the basin. Both C-CAP and Landsat datasets show that, north of the Mississippi River Gulf Outlet, water coverage in the intermediate to saline regions increased from 1.5-3.7%. However, the freshwater regions increased as from 12.3-39.0%.The biggest proportional changes are in the diversion area. Hypotheses for this poor resiliency are currently being studied. The freshwater vegetation may be unable to withstand the shear stress from hurricane impacts on shallow low salinity root systems. Because of agricultural runoff into the Mississippi River, the Caernarvon's nutrient-rich waters contribute to "weaker" soils by lowering biomass, below ground production, and organic accumulation. Additionally, the bulk density of freshwater marsh (0.07 g cm-3) is much less than saline marsh (0.24 g cm-3). All these factors suggest freshwater vegetation is less hardy than its saline counterparts.
- Analysis of previously neglected invertebrate zooplankton taxa collected during SEAMAP Gulfwide surveys revealed that though the Gulf of Mexico is functionally designated as a single Large Marine Ecosystem for the purposes of ecosystem-based management, the diversity of biogeographic regimes within the Gulf ranges both longitudinally and over coastal-neritic-oceanic transitions. The northern Gulf of Mexico can be divided into three Large Marine Ecosystem sub-units corresponding to i) west Florida inner shelf, ii) northern River-dominated shelf, and iii) oligotrophic Gulf-wide. These sub-units can be further assessed by underlying drivers influencing productivity regimes across the northern Gulf namely salinity associated with river discharge, chlorophyll distribution and zooplankton biomass. Characterizing critical Large Marine Ecosystem subunits based on the differences found will help improve specific ecosystem model parameterizations planned for managing Gulf resources.
- A seasonal association was found between worldwide oceanic-atmospheric modes of variability, meteorological and hydrological conditions and displacement volumes of zooplankton in the northern Gulf of Mexico. The combination of Atlantic Multi-decadal Oscillation cold, North Atlantic Oscillation positive, and El Nino Southern Oscillation warm phases were associated with the stormy January to March winter weather (i.e., strong low pressure system, southern winds, and high moist air) of 1982, while the opposite phases of these modes of variability were related to the calm dry winter of 1999. The wet winter (high precipitation and surface runoff) of 1982 was further linked to high mean spring (April 24-May 26) displacement volumes of zooplankton, whereas the dry winter of 1999 was associated with low displacement volumes.
- NOAA and NGI co-sponsored and NGI researchers participated in several multi-agency workshops targeting multiple NOAA and Gulf state environmental agency priorities. The 2nd Annual Workshop to Coordinate Gulf of Mexico Hypoxic Zone Research was held March 31-April 1, 2011 in order to develop research plans, improve university, federal and state agency coordination of monitoring and modeling for the 2011 Gulf Hypoxic Zone and beyond and facilitate management of the Hypoxic Zone by identifying research findings for incorporation into the Gulf Hypoxia Task Force Annual Progress Report and Annual Operating Plans. The Operational Storm Surge Inundation Mapping Workshop was held March15-16, 2011 to develop a research plan of action including the understanding of available mapping techniques, their advantages and disadvantages, the validity of mapping from coarse models to higher resolution models, and the relationship between mapping and surge prediction uncertainty. The ultimate goal of this research plan is to identify the issues associated with the creation of operational inundation depth maps using high resolution data necessary for operational storm surge prediction. NGI provided follow up support to the Ecosystem Services Valuation workshop held June 16-18, 2010. That workshop developed a common definition of ecosystem services and identified and prioritized the ecosystem services most relevant to coastal and marine ecosystems in the Gulf of Mexico necessary for ecosystem based management in the Gulf. An ecosystem modeling workshop was held January 25-26, 2011 to develop consensus on a model framework to be used to develop a quantitative ecological relevant to northern Gulf coastal ecosystems including Barataria Bay, western Mississippi Sound, Perdido Bay, and Apalachicola Bay.