Breton Sound Research Articles

Impact of Mississippi River freshwater reintroduction on enhancing marsh accretionary processes in a Louisiana estuary

To counteract extensive wetland loss a series of diversion projects have been implemented to introduce freshwater and sediment from the Mississippi River into Louisiana coastal wetlands. To keep pace with increases in water level due to subsidence Louisiana coastal marshes must vertically accrete through the accumulation of both organic matter and mineral sediment. The impact of Mississippi River freshwater diversion on enhancing vertical marsh accretion (mineral and organic matter accumulation) was examined in Breton Sound estuary, a coastal wetland experiencing marsh deterioration as result of subsidence and salt water intrusion. Using 137Cs dating and artificial marker horizons, increases in the rate of vertical marsh accretion were measured at marsh sites along a spatial gradient which has been receiving diverted water from the Mississippi River (Caernarvon diversion) since 1991. Vertical accretion and accumulation of mineral sediment organic matter and nutrients in the marsh soil profile, increased at marsh sites receiving freshwater and sediment input. Iron and manganese content of the marsh surface sediment were shown to be an excellent signature of riverine sediment deposition. Soil extractable phosphorus was higher and extractable sodium was lower at sites nearest freshwater and sediment input. Results demonstrated that freshwater diversion through sediment input and lowering of salinity will enhance marsh accretion and stability, slowing or reversing the rate of wetland loss.

ABSTRACT: Field Development Case Studies: Breton Sound Blocks 32, 33, and 36, Offshore Louisiana

ABSTRACT: Field Development Case Studies: Breton Sound Blocks 32, 33, and 36, Offshore Louisiana

Field Studies of Breton Sound Blocks 37, 39 and 49, Offshore Louisiana

Field Studies of Breton Sound Blocks 37, 39 and 49, Offshore Louisiana

Water Quality Analysis of a Freshwater Diversion at Caernarvon, Louisiana

Since 1991, Mississippi River water has been diverted at Caernarvon, Louisiana, into Breton Sound estuary. Breton Sound estuary encompasses 1100 km2 of fresh and brackish, rapidly subsiding wetlands. Nitrite + nitrate, total Kjeldahl nitrogen, ammonium, total phosphorus, total suspended sediments, and salinity concentrations were monitored at seven locations in Breton Sound from 1988 to 1994. Statistical analysis of the data indicated decreased total Kjeldahl nitrogen with associated decrease in total nitrogen, and decreased salinity concentrations in the estuary due to the diversion. Spring and summer water quality transects indicated rapid reduction of nitrite + nitrate and total suspended sediment concentration as diverted Mississippi River water entered the estuary, suggesting near complete assimilation of these constituents by the ecosystem. Loading rates of nitrite + nitrate (5.6–13.4 g m−2 yr−1), total nitrogen (8.9–23.4 g m−2 yr−1), and total phosphorus (0.9–2.0 g m−2 yr−1) were calculated along with removal efficiencies for these constituents (nitrite + nitrate 88–97%; total nitrogen 32–57%; total phosphorus 0–46%). The low impact of the diversion on water quality in the Breton Sound estuary, along with assimilation of TSS over a very short distance, suggests that more water may be introduced into the estuary without detrimental affects. This would be necessary if freshwater diversions are to be used to distribute nitrients and sediments into the lower reaches of the estuary, in an effort to compensate for relative sea-level rise, and reverse the current trend of rapid loss of wetlands in coastal Louisiana.

Holocene Geologic Framework of Lake Pontchartrain Basin and Lakes of Southeastern Louisiana : ABSTRACT

The Lake Pontchartrain Basin is a 12,170-km2 (4,700-mi2) watershed in southeastern Louisiana, stretching from the State of Mississippi on the north and east to the Mississippi River on the west and south, and to Breton Sound at the Gulf of Mexico. The Pontchartrain Basin is about 200 km along strike and 75 km along dip with modern lakes (Maurepas, Pontchartrain, and Borgne) covering the southern portion of the basin. Lake Pontchartrain and its adjacent lakes form one of the largest estuaries in the United States. Nearly 1.5 million people (one-third of the entire population of Louisiana) live in the 14 parishes within the Lake Pontchartrain Basin. The basin is bounded by incised Pleistocene terraces to north, the Mississippi River delta plain to the south/southwest, and the Pine Island barrier shoreline to the south/southeast. Over the last 150 years, urban growth of New Orleans and the north shore communities and associated exploitation of natural resources have severely altered the environmental quality of the basin. In 1994, the USGS began a multidisciplinary evaluation of the geology, geomorphology, coastal processes, and environmental quality of the Pontchartrain Basin for use by Federal, state and local officials in coastal management and restoration planning. Existing geological information has been integrated with newly acquired high-resolution seismic profiles (>700 line km), 76 vibracores, and more than 1000 samples for geochemical data to develop a geologic history and record of sediment distribution of the basin (Fig. 1). The Pontchartrain Basin has a complex depositional history controlled by sea-level change. Lake Pontchartrain originated as a result of sedimentary processes. During the late Wisconsin lowstand, the region was entrenched by rivers. A buried incised channel of the ancestral Mississippi River, identified from seismic profiles (see Fig. 2 A-A’), underlies the southern margin of Lake Pontchartrain. The incision is three to four km across, was cut to a depth of 40 m, and can be traced from west to east into Lake Pontchartrain (Fig. 3). Sea-level rise during deglaciation truncated the filled paleochannel and the surrounding region of the Pontchartrain Basin. The ravinement surface is a sharp contact with siderite nodules and has been identified from vibracores as the Pleistocene-Holocene contact. The late Pleistocene unit is typically described as a stiff, olive-gray to light grayish-yellow clay that is highly bioturbated. The burrows are fill with oxidized organics or sand and silt. The structure contour map (Fig. 3) of the Pleistocene surface shows the contact is shallow (near the sediment surface, 2 m below sea level) in northeast Lake Pontchartrain and deeper (20 m below sea level) to the southwest. Cross section B-B’ (Fig. 3) illustrates how the Pleistocene contact crops out along the northeast shore and dips to the southwest. Sea-level rise flooded the “Pontchartrain Embayment” and

Regional Chronostratigraphic and Depositional Hydrocarbon Trends in Offshore Louisiana State Waters: ABSTRACT

ABSTRACT Successful exploration for hydrocarbons in the Northern Gulf of Mexico basin requires a systematic understanding of hydrocarbon producing trends, sand body geometries and the geologic, engineering and reservoir parameters of the producing sands. This study forms part of the Offshore Atlas project in progress at the University of Texas at Austin, Bureau of Economic Geology, Texas, in cooperation with the U.S. Department of Interior, Minerals Management Service, and the Geological Survey of Alabama, and is aimed at achieving this goal. In this study, 26 chronozones were grouped into 12 sub-groups. The chronozones were defined on the basis of the benthic foraminiferal biostratigraphic zones and were correlated across the Gulf using well and seismic data and were projected from the Federal offshore into the State waters. The chronozones on each well log in the 22 cross sections constructed from West Cameron area eastward to the Chandeleur Sound, Breton Sound and Main Pass areas, were subdivided as applicable into four depositional groups consisting of aggradational, progradational, transgressive and submarine fan facies based primarily on SP log shapes. In the Louisiana State waters there are 92 fields containing 685 reservoirs. This includes 214 oil, 347 gas, 33 condensate and 91 combination type reservoirs. Total combined cumulative production is 1,44l,091,263 barrels of oil, 117,641,457 barrels of condensate and 11,802,821,997 thousand cubic feet of gas. Total assigned production (1977-1995) shows the progradational facies to be most productive yielding 51.69% oil, 93.84% condensate, and 77.47% gas. The aggradational facies sands produced 46.98% oil, 1.70% condensate and 15.76% gas. The submarine fan facies yielded 1.21% oil, 4.45% condensate, and 6.74% gas. Production from the transgressive facies sands was less than 0.2% of the total assigned production of oil, gas and condensate.

Sedimentation in Breton Sound and Effects of Mississippi River-Gulf Outlet: ABSTRACT

The Mississippi River-Gulf outlet is a channel 36 ft deep and 500 ft wide extending from a point south of Michoud, Louisiana, southeastward across the marshes and Breton Sound into the Gulf of Mexico. The outlet was constructed by the U.S. Army Corps of Engineers to provide additional access to the Port of New Orleans and thereby ease traffic on the Mississippi River. The channel crosses a delta lobe constructed when the Mississippi River flowed down a course east of its present course. The sedimentary environments and the features formed by the destruction of the now abandoned and subsiding lobe have a great influence on sedimentation in the outlet and, conversely, the outlet has had a profound effect on the environments on which it has been superimposed. The outlet has ncountered an excessive amount of shoaling in its Breton Sound reach. In an effort to determine the cause(s) of the shoaling and the source(s) of the shoal material, a study was made of the factors influencing sediment distribution in the Breton Sound area (e.g., tides, winds, spoil, and sediment distribution, salinity, current directions, and velocities). The principal source of the shoal material was determined to be the spoil dredged from the outlet itself which returns to the channel by density flow rather than by normal deposition of suspended material. End_of_Article - Last_Page 1827------------

Marginal Sediments of Mississippi Delta

Marginal Sediments of Mississippi Delta

Macro-Invertebrate Assemblages as Indicators of Sedimentary Environments in East Mississippi Delta Region

As a result of a study based on three years of biological sampling in the east Mississippi Delta region, eight macro-invertebrate assemblages are recognized, each characteristic of a specific sedimentary environment ranging from the Mississippi Delta marshes to the edge of the continental shelf northeast of the Delta proper. The eight assemblages and their corresponding environments are: (I) the delta marshes, (II) delta front and lower distributaries, (III) lower Breton Sound and lower pro-delta clayey slopes, (IV) upper Breton Sound, (V) inlets, or areas of strong currents, (VI) the shallow continental shelf of the Gulf of Mexico from 0 to 12 fathoms, (VII) the deeper part of the continental shelf from approximately 13 fathoms to 60 fathoms, and (VIII) the living oyster reefs of the shallow protected bays of the Delta region. The boundaries of these environments were established by plotting the distributions of both living and dead representatives of species of invertebrates furnishing hard parts plus the distributions of living soft-bodied animals which were so abundant as to characterize regions where animals with hard parts were scarce though present. Comparison of the distribution of the hydrographic factors with the physiography of the land-masses in this area with the macro-organism distributions made it possible to formulate criteria for the interpretation of ancient environments as far back as the Miocene on the Gulf and Atlantic coasts. Paleontologic literature shows that most of the present-day delta species have been found in the Pliocene, and most of the diagnostic forms have existed since the lower Miocene. The primary factors influencing distributions of these organisms are bottom type, salinity and temperature (especially the degree of variability), turbidity of the water, and currents. It was also found that comparative rates of deposition could be estimated by the ratio of the number of living to the number of dead, i equal-size samples. A series of marine bottom communities based on the community concept of European marine ecologists is recognized on the basis of the most abundant and widespread animals.

Ecology of Foraminifera in Southeastern Mississippi Delta Area

1. The Foraminifera are grouped into three principal biofacies and one in the Mississippi Delta area. a. The following species are confined to the marsh facies. Ammoastuta inepta (Cushman and McCulloch) Arenoparrella mexicana (Kornfeld) Leptodermella variabilis Parker Miliammina fusca (H. B. Brady) Trochammina macrescens H. B. Bradyb. The Breton Sound facies is characterized by the abundance of various species of Ammobaculites, and also by Ammoscalaria pseudospiralis (Williamson) and Gaudryina exilis Cushman and Bronnimann. Elphidium incertum mexicanum Kornfeld and E. matagordanum (Kornfeld) also are largely confined to this facies. c. The open-gulf facies is characterized by the following species. Bigenerina irregularis Phleger and Parker Bolivina lowmani Phleger and Parker Buccella hannai (Phleger and Parker) Buliminella cf. bassendorfensis Cushman and Parker Cibicidina strattoni (Applin) Epistominella vitrea Parker Nonionella atlantica Cushman N. opima Cushman Nouria polymorphinoides Heron-Allen and Earland Proteonina atlantica Cushman P. sp. A Virgulina pontoni Cushmand. The offshore subfacies is characterized by the following species which are either restricted to it or occur there in greater abundance than elsewhere. Bigenerina irregularis Phleger and Parker Cibicidina strattoni (Applin) Epistominella vitrea Parker Nouria polymorphinoides Heron-Allen and Earland Proteonina atlantica Cushman2. Facies transition areas a. The average boundary between the open-gulf and Breton Sound facies extends south from Breton Island to Main Pass. There is a mixing of many typical open-gulf and Breton Sound species through a zone 10-15 miles wide extending on either side of this boundary. b. The bays and other nearshore areas contain a Breton Sound fauna with marsh species.3. a. Distribution of the living population of the various species seems to show good correlation with the distribution of the dead population. This suggests little large-scale post-mortem transportation of the tests. b. The total living population varies from 1116/sample to 0/sample. The northernmost area generally has the smallest standing crop of Foraminifera, approximately 10-50/sample,End_Page 712------------------------------ the middle area averages approximately 100/sample, and the largest living populations occur at the inshore open-gulf stations. c. The per cent ratios between living and total populations are grouped into four types of frequency areas. These show a general correlation with presumed sedimentation rates.4. It is believed that the distributions of the Foraminifera facies in this east delta area reflect the average distributions of the open gulf, Breton Sound, and marsh-river water masses.