Approaches for Ecosystem Services Valuation for the Gulf of Mexico After the Deepwater Horizon Oil Spill Interim Report (2012) / Chapter Skim
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1 Physiographic, Oceanographic, and Ecological Context of the Gulf of Mexico
1 Physiographic, Oceanographic, and Ecological Context of the Gulf of Mexico
Pages 31-54
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From page 31... ...
Thus, we begin our report with an overview of the geographic, oceanographic, and ecological setting of the GoM. It is only within this context that we can properly identify appropriate approaches for delineating, quantifying, and valuing the impact of the Deepwater Horizon Mississippi Canyon-252 (DWH)
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From page 32... ...
The organic debris, particulates, and dissolved nutrients introduced into the Gulf by these riv ers ensured high primary productivity, high carbon-content sediments, and abundant hydrocarbon resource rocks. The subsidence of the basin along with the massive sediment loads provided by river input created the appro priate burial conditions (pressure and heat)
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From page 33... ...
The annual average freshwater discharge of 580 km3 enters the northern GoM through two main distributaries: the Mississippi River delta southeast of the city of New Orleans, Louisiana, and the Atchafalaya River delta ~200 km to the west on the central Louisiana coast (Meade, 1995)
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From page 34... ...
The largest decrease in suspended sediments occurred after 1950, when the natural sources of sediments in the drainage basin were cut off from the Mississippi River mainstem by the construction of large reservoirs on the Missouri and Arkansas rivers (Meade and Parker, 1985; NRC, 2008a; Blum and Roberts, 2009)
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From page 35... ...
are available from land-based coastal sites as well as offshore buoys. The primary sources of data are archived at the National Data Buoy Center (NDBC)
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From page 36... ...
SOURCE: Image created by committee usingFigure 1-2 data from NOAA's National Data Buoy Center, station 42001 Bitmapped (http://www.ndbc.noaa.gov/station_page.php? station=42001)
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From page 37... ...
. Deepwater Circulation In the east-central Gulf, ocean currents in the upper 1,000 m of the water column are often dominated by the Loop Current, a warm ocean current that eventually joins the Gulf Stream (Figure 1.3)
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From page 38... ...
. Some are generated by the strong shear found along the periphery of the Loop Current and LCE but others form along additional fronts, as demonstrated by the eddy separating colder and fresher shelf and slope waters (Figure 1.3)
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From page 39... ...
Regardless of the location, winds are a factor especially during tropical cyclones or winter storms. The transfer of wind energy through the water column is dramatically affected by stratification induced by solar heating and the substantial freshwater discharge from the
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From page 40... ...
The Loop Current sets up a large-scale sea-level gradient along the shelf that models suggest can generate substantial southerly currents. • On the Mississippi-Alabama shelf, the discharge from the Mobile Tombigbee, Pascagoula, Pearl, and Mississippi rivers are an impor tant influence on near-surface stratification, which in turn affects the transfer of wind through the water column.
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From page 41... ...
Habitat mapping, therefore, proceeds with the use of alternative criteria. Among the numerous alternatives in use, one requires narrowing actual biotic surveys to a few indicator species (e.g., mangrove habitat, fish habitat, brown pelican habitat, red snapper habitat, cold coral habitat, etc.)
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From page 42... ...
One thing is most certain, the more a seemingly homogeneous habitat is studied, the more complex it is shown to be. Inshore Habitats of the GOM Inshore habitats of the northern GoM range from uplands through in tertidal areas and wetlands to open bodies of water in bays and lagoons sheltered from the open Gulf by barrier island formations or emptied through tidal passes and open connections with Gulf waters.
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From page 43... ...
In sandier protected bay and lagoon settings, submerged seagrass meadows are common where water clarity is suitable for their growth. Common sea grasses in the northern Gulf are turtle grass (Thalassia testidinum)
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From page 44... ...
These coastal habitats provide shelter and food resources for fishes, crustaceans, and shellfish. Wetlands are widely recognized for their capacity to remove nutrients and pollutants from overlying waters, in effect improving water quality, recycling reactive nitrogen to N2 gas and reducing the potential for eutro phication, defined as the increase in the rate of primary production and accumulation of resulting organic carbon in an aquatic system (modified Rabalais, 2004 and Nixon, 1995)
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From page 45... ...
These hard banks support diverse communities of tropical and subtropical plants, invertebrates, and fishes and are considered to be sensitive habitats. The structures that rise a few meters above the surrounding seafloor, such as a series of shoals off the Atchafalaya River delta, provide refugia from seasonal bottom-water hypoxia on the northern Gulf of Mexico.
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From page 46... ...
, but must return to the surface to breath. Throughout the water column and deep seafloor, microbes are contributing to the larger marine ecosystem by returning nutrients through their metabolic functions.
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From page 47... ...
Changes in trophic levels of global and regional catches are considered by the Food and Agriculture Organization (2002) as a better reflection of trends in fisheries than the proportion of fish stocks that are reported as depleted, overexploited, fully exploited, and moderately exploited (Food and Agriculture Organization, 2002)
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From page 48... ...
. Microbes dominate the global ocean, both in terms of numerical abundance (averaging 106 per milliliter of seawater for an estimated total of 1030 in the global water column)
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From page 49... ...
Grouper and snapper various offshore commercially and recreationally important Atlantic croaker Micropogonias undulatus indicator species American oyster Crassostrea virginica commercial coastal fishery; indicator species Blue crab Callinectes sapidus commercial coastal fishery Spiny lobster Panulirus argus southern Gulf commercial fishery Pink conch Eustrombus gigas regulated recreational fishery Spotted sea trout Cynoscion nebulosus northern Gulf recreational fishery Red drum Sciaenops ocellatus northern Gulf recreational fishery Red snapper Lutjanus campecheanus northwestern Gulf recreational fishery Bottlenose dolphin Tursiops truncatus well known by public; keystone species American alligator Alligator mississippiensis keystone species American crocodile Crocodylus acutus keystone species Smooth cordgrass Spartina alterniflora keystone species Saltmeadow cordgrass Spartina patens keystone species Common reed Phragmites australis indicator species Maidencane Panicum hemitomon indicator species SOURCE: Derived from Fautin et al., 2010. widespread occurrence of marine microbes, their ability to reproduce rapidly when conditions allow, and the functional redundancy built into their communities mean that environmental changes and anthropogenic impacts do not imperil the existence of specific groups, such as those that recycle nutrients, degrade hydrocarbons, or provide chemosynthetically derived food for higher organisms at hydrocarbon seeps.
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From page 50... ...
. Major occupations in the northern Gulf of Mexico region as reported in 2010 include oil and gas drilling, water transportation-related industries, and leisure and hospitality, the latter particularly related to gaming and ca See http://www.census.gov/geo/landview/lv6help/coastal_cty.pdf.
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From page 51... ...
. In 2008, 165 processing plants and 229 wholesale plants employed nearly 10,000 workers that supported the commercial fishery.6 In addition, the recreational fishing industry supports employment in coastal counties (Adams et al., 2004)
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From page 52... ...
In the northern GoM, the Mississippi River shaped, and continues to shape, the coastal areas with sediment-rich waters continuously reforming the landscape into the Mississippi and Atchafalaya river deltas. The Gulf's oceanic environment is largely determined by wind and currents, which respectively establish the regional weather patterns and serve as an important transit system for pollutants and runoff throughout Gulf waters.
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From page 53... ...
The effects of the oiling are currently being assessed in many habitats, across complex food webs, with regard to short- and long-term impacts, as altered biogeochemical cycling, and in relationship to ecosystem functioning. Some GoM ecosystems and processes are well known, but knowledge in many cases may be sparse.
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