scholarly journals Forces Driving the Morphological Evolution of a Mud-Capped Dredge Pit, Northern Gulf of Mexico

Water ◽  
2018 ◽  
Vol 10 (8) ◽  
pp. 1001 ◽  
Author(s):  
Jiaze Wang ◽  
Kehui Xu ◽  
Chunyan Li ◽  
Jeffrey Obelcz
Keyword(s):  
Gulf Of Mexico ◽  
Observational Data ◽  
Mississippi River ◽  
Numerical Models ◽  
Morphological Evolution ◽  
Suspended Sediments ◽  
Weather Conditions ◽  
Sediment Concentration ◽  
Northern Gulf Of Mexico ◽  
Island Restoration

Sandy sediments preserved as paleo-channel fill on the inner shelf, some of which are overlain by modern muds, have been mined for barrier island restoration along the northern Gulf of Mexico. These mined areas have been termed “mud-capped” dredge pits. The processes governing the morphological evolution of the pits are poorly constrained due to limited observational data. Physical oceanographic (e.g., currents and waves) and sedimentary data were collected at Sandy Point dredge pit offshore Plaquemines Parish, Louisiana in summer 2015. Currents outside the pit flowed southward and/or southeastward at speeds of 8–20 cm/s, while currents inside the pit had speeds less than 2 cm/s with no clear dominant direction. Wave heights detected inside the pit were less than 0.4 m. A high turbidity layer with suspended sediment concentration around 4 g/L was observed above the pit floor, and its thickness was ~0.5 m. With observational data as input, three 2–D numerical models were employed to predict pit morphological responses, including pit infilling, margin erosion and slope change. The model results suggest that resuspension events were rare on the seafloor adjacent to the pit under summer fair weather conditions. Modeled pit margin erosion was very limited. With little resuspension of seafloor sediment locally, weak margin erosion and stable pit walls, the dominant process governing pit evolution was infilling sourced by the deposition of suspended sediments from the Mississippi River plume.

scholarly journals Ensemble modeling informs hypoxia management in the northern Gulf of Mexico

2017 ◽  
Vol 114 (33) ◽  
pp. 8823-8828 ◽  
Author(s):  
Donald Scavia ◽  
Isabella Bertani ◽  
Daniel R. Obenour ◽  
R. Eugene Turner ◽  
David R. Forrest ◽  
...  
Keyword(s):  
Gulf Of Mexico ◽  
Mississippi River ◽  
Task Force ◽  
Weather Conditions ◽  
Nitrogen Loading ◽  
Load Reduction ◽  
Nutrient Inputs ◽  
Northern Gulf Of Mexico ◽  
Water Column Stratification ◽  
Hypoxic Area

A large region of low-dissolved-oxygen bottom waters (hypoxia) forms nearly every summer in the northern Gulf of Mexico because of nutrient inputs from the Mississippi River Basin and water column stratification. Policymakers developed goals to reduce the area of hypoxic extent because of its ecological, economic, and commercial fisheries impacts. However, the goals remain elusive after 30 y of research and monitoring and 15 y of goal-setting and assessment because there has been little change in river nitrogen concentrations. An intergovernmental Task Force recently extended to 2035 the deadline for achieving the goal of a 5,000-km2 5-y average hypoxic zone and set an interim load target of a 20% reduction of the spring nitrogen loading from the Mississippi River by 2025 as part of their adaptive management process. The Task Force has asked modelers to reassess the loading reduction required to achieve the 2035 goal and to determine the effect of the 20% interim load reduction. Here, we address both questions using a probabilistic ensemble of four substantially different hypoxia models. Our results indicate that, under typical weather conditions, a 59% reduction in Mississippi River nitrogen load is required to reduce hypoxic area to 5,000 km2. The interim goal of a 20% load reduction is expected to produce an 18% reduction in hypoxic area over the long term. However, due to substantial interannual variability, a 25% load reduction is required before there is 95% certainty of observing any hypoxic area reduction between consecutive 5-y assessment periods.

Validating the occurrence of Caribbean reef sharks, Carcharhinus perezi (Poey), (Chondrichthyes: Carcharhiniformes) in the northern Gulf of Mexico, with a key for sharks of the family Carcharhinidae inhabiting the region

Zootaxa ◽  
2011 ◽  
Vol 2933 (1) ◽  
pp. 65 ◽  
Author(s):  
WILLIAM B. DRIGGERS III ◽  
ERIC R. HOFFMAYER ◽  
EMMA L. HICKERSON ◽  
TIMOTHY L. MARTIN ◽  
CHRISTOPHER T. GLEDHILL
Keyword(s):  
Gulf Of Mexico ◽  
North Atlantic ◽  
Mississippi River ◽  
North Atlantic Ocean ◽  
Shark Species ◽  
Mississippi River Delta ◽  
The Bahamas ◽  
Northern Gulf Of Mexico ◽  
The Family ◽  
Reef Sharks

Among the sharks inhabiting the continental shelf waters of the western North Atlantic Ocean, those within the genus Carcharhinus are the most speciose (Castro 2011). Authoritative sources agree on the presence of twelve species of carcharhinids in the northern Gulf of Mexico; however, they disagree on the presence of a thirteenth species, C. perezi (Poey), in the region (Compagno 1984, Compagno 2002, McEachran & Fechhelm 1998, Castro 2011). While the range of C. perezi is well-documented to extend from the southeastern coast of Florida and the Bahamas to Brazil (Castro 2011), published records of C. perezi occurring in the northern Gulf of Mexico are limited to two sources. In their description of Eulamia springeri, a junior synonym of C. perezi, Bigelow & Schroeder (1944) place the species in the northern Gulf of Mexico based on “a somewhat shrivelled skin with head” from a specimen collected off the west coast of Florida that was reported by the authors to be “probably of this species.” Later, Springer (1960) reported the capture of a single specimen off the Mississippi River Delta in 1947; however, no detail of the capture was provided other than it being listed within a table summarizing shark species collected during exploratory fishing operations.

scholarly journals Extensive reproductive disruption, ovarian masculinization and aromatase suppression in Atlantic croaker in the northern Gulf of Mexico hypoxic zone

2011 ◽  
Vol 279 (1726) ◽  
pp. 28-38 ◽  
Author(s):  
Peter Thomas ◽  
Md. Saydur Rahman
Keyword(s):  
Gulf Of Mexico ◽  
Mississippi River ◽  
Aromatase Activity ◽  
Northern Gulf Of Mexico ◽  
Hypoxia Exposure ◽  
Hypoxic Zone ◽  
Seasonal Hypoxia ◽  
Reproductive Disruptions ◽  
Reproductive Disruption

The long-term impacts on marine ecosystems of the recent dramatic worldwide increase in the incidence of coastal hypoxia are unknown. Here, we show widespread reproductive disruption in Atlantic croakers collected from hypoxic sites approximately 120 km apart in the extensive northern Gulf of Mexico continental shelf hypoxic zone. Gonadal growth and gamete production were impaired in croakers from hypoxic sites compared with fish from reference normoxic sites east of the Mississippi River Delta. Male germ cells were detected in approximately 19 per cent of croaker ovaries collected in the hypoxic region, but were absent in ovaries from normoxic sites. In addition, the sex ratio was skewed towards males at the hypoxic sites. The masculinization and other reproductive disruptions were associated with declines in neuroendocrine function, as well as ovarian and brain expression of aromatase (the enzyme that converts androgens to oestrogens). A similar incidence of ovarian masculinization and decline in ovarian aromatase expression were observed in croaker after chronic laboratory hypoxia exposure, indicating that ovarian masculinization is a specific hypoxia response and is due to decreased aromatase activity. The results suggest severe reproductive impairment can occur over large coastal regions in marine fish populations exposed to seasonal hypoxia, with potential long-term impacts on population abundance.

scholarly journals Variations in primary production of northern Gulf of Mexico continental shelf waters linked to nutrient inputs from the Mississippi River

1997 ◽  
Vol 155 ◽  
pp. 45-54 ◽  
Author(s):  
SE Lohrenz ◽  
GL Fahnenstiel ◽  
DG Redalje ◽  
GA Lang ◽  
X Chen ◽  
...  
Keyword(s):  
Gulf Of Mexico ◽  
Primary Production ◽  
Continental Shelf ◽  
Mississippi River ◽  
Nutrient Inputs ◽  
Northern Gulf Of Mexico

Evolution and structure of a coastal squirt off the Mississippi River delta: Northern Gulf of Mexico

1996 ◽  
Vol 101 (C9) ◽  
pp. 20643-20655 ◽  
Author(s):  
Nan D. Walker ◽  
Oscar K. Huh ◽  
Lawrence J. Rouse ◽  
Stephen P. Murray
Keyword(s):  
Gulf Of Mexico ◽  
Mississippi River ◽  
River Delta ◽  
Mississippi River Delta ◽  
Northern Gulf Of Mexico

scholarly journals The ecosystem baseline for particle flux in the Northern Gulf of Mexico

Elem Sci Anth ◽  
2018 ◽  
Vol 6 ◽  
Author(s):  
S.L.C. Giering ◽  
B. Yan ◽  
J. Sweet ◽  
V. Asper ◽  
A. Diercks ◽  
...  
Keyword(s):  
Gulf Of Mexico ◽  
Mississippi River ◽  
Large Fraction ◽  
Combustion Products ◽  
Sediment Traps ◽  
Sedimentation Rates ◽  
Northern Gulf Of Mexico ◽  
Sinking Particles ◽  
Spilled Oil ◽  
Seep Site

Response management and damage assessment during and after environmental disasters such as the Deepwater Horizon (DWH) oil spill require an ecological baseline and a solid understanding of the main drivers of the ecosystem. During the DWH event, a large fraction of the spilled oil was transported to depth via sinking marine snow, a routing of spilled oil unexpected to emergency response planners. Because baseline knowledge of particle export in the Northern Gulf of Mexico and how it varies spatially and temporally was limited, we conducted a detailed assessment of the potential drivers of deep (~1400 m depth) particle fluxes during 2012–2016 using sediment traps at three contrasting sites in the Northern Gulf of Mexico: near the DWH site, at an active natural oil seep site, and at a site considered typical for background conditions. The DWH site, located ~70 km from the Mississippi River Delta, showed flux patterns that were strongly linked to the Mississippi nitrogen discharge and an annual subsequent surface bloom. Fluxes carried clear signals of combustion products, which likely originated from pyrogenic sources that were transported offshore via the Mississippi plume. The seep and reference sites were more strongly influenced by the open Gulf of Mexico, did not show a clear seasonal flux pattern, and their overall sedimentation rates were lower than those at the DWH site. At the seep site, based on polycyclic aromatic hydrocarbon data, we observed indications of three different pathways for “natural” oiled-snow sedimentation: scavenging by sinking particles at depth, weathering at the surface before incorporation into sinking particles, and entry into the food web and subsequent sinking in form of detritus. Overall, sedimentation rates at the three sites were markedly different in quality and quantity owing to varying degrees of riverine and oceanic influences, including natural seepage and contamination by combustion products.

Characterization of nutrient, organic carbon, and sediment loads and concentrations from the Mississippi River into the northern Gulf of Mexico

2007 ◽  
Vol 30 (5) ◽  
pp. 773-790 ◽  
Author(s):  
R. E. Turner ◽  
N. N. Rabalais ◽  
R. B. Alexander ◽  
G. McIsaac ◽  
R. W. Howarth
Keyword(s):  
Organic Carbon ◽  
Gulf Of Mexico ◽  
Mississippi River ◽  
Northern Gulf Of Mexico ◽  
Sediment Loads
Sign in / Sign up

Export Citation Format

Share Document