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Research about Mississippi Delta

Source-linked reports with geographic coverage including Mississippi Delta.

7 recordsLinked to original sources
USGS2019

Canals, backfilling and wetland loss in the Mississippi Delta

Canals and spoil banks have contributed significantly to high rates of wetland loss in the Mississippi delta. There has been relatively little research on management of canals and spoil banks and this needs to be a significant component of restoration of the delta. We analyze research on the role of backfilling canals in the context of delta restoration with special reference to Turner and McClenachan (2018) who state that if all canals were backfilled, it could significantly reduce or even reverse wetland loss and that most wetland loss is caused by canals. We agree with T&M that canals have been a significant cause of wetland loss in the Mississippi Delta and that removing spoil banks and backfilling canals should be an integral part of delta restoration. However, a number of factors need to be considered when choosing which canals to backfill including possible enhanced erosion due to exposure to wave action for newly created and remnant marsh, the current and future production history of oil and natural gas from canals, and other restoration activities in oil and gas fields. Turner and McClenachan’s analysis using wetland loss patterns in 15-minute quadrangles suggesting that canal density can explain most wetland loss in coastal Louisiana is flawed because of scale problems and other impacts of oil and gas activity. These impacts include subsurface induced subsidence and the impact of produced water and toxins on wetlands that are largely unrelated to surface alteration due to canals and spoil banks.

Louisiana↗
USGS2014

Nitrogen transport within an agricultural landscape: insights on how hydrology, biogeochemistry, and the landscape intersect to control the fate and transport of nitrogen in the Mississippi Delta

Nitrogen (N) is a ubiquitous contaminant throughout agricultural landscapes due to both the application of inorganic and organic fertilizers to agricultural fields and the general persistence of nitrate (NO 3 ) in oxygenated aqueous environments (Denver et al. 2010; Domagalski et al. 2008; Green et al. 2008; Coupe 2001; Nolan and Stoner 2000). In order to understand why excess N occurs various hydrologic systems (environments), it is important to consider potential sources, the locations of these sources in the watershed, and the timing of the application of sources with respect to the movement of water. To learn how to manage N in a watershed, it is necessary to identify and quantify flow paths and biogeochemical conditions, which ultimately combine to determine transport and fate. If sources, transport mechanisms, and biogeochemical controls were uniformly distributed, it would be possible to manage N uniformly throughout a watershed. However, uniform conditions are rare to nonexistent in the natural world and in the landscape altered for agricultural production. In order to adjust management activities on the landscape to have the greatest effect, it is important to understand the fate and transport N within the intersection of hydrology and biogeochemistry, that is, to understand the extent and duration of the hydrologic and biogeochemical controls as N is routed through and among each hydrologic compartment.

Mississippi Delta↗
USGS2010

Recent subsidence-rate reductions in the Mississippi Delta and their geological implications

The Mississippi Delta has long been characterized as an area of rapid subsidence; however, recent subsidence rates are substantially lower than previously reported. Tide-gauge records indicate that rates of relative sea-level rise were slow from 1947 until the mid-1960s, relatively fast from the mid-1960s until the early 1990s, and then slow since the early 1990s. These trends and rates are independently verified by repeat benchmark surveys and height monitoring at continuously operating geographic positioning system stations. Subsidence rates for the slow periods were a few millimeters per year, comparable to rates averaged over geological time scales that are attributed to natural processes such as shallow sediment compaction and deep crustal loading. The decadal pattern of slow, then rapid, then slow subsidence may be caused by natural deep-basin processes ( e.g., gravity gliding and salt migration), but it is more likely related to rates of hydrocarbon production that followed the same temporal trends. If accelerated subsidence was primarily induced by reservoir compaction and fault reactivation associated with fluid withdrawal that also accelerated in the 1960s and 1970s, then the recent reductions in subsidence rates likely reflect a balancing of subsurface stresses and a return to near preproduction conditions.

Arkansas, Louisiana, Mississippi↗
USGS2010

Quantifying large-scale historical formation of accommodation in the Mississippi Delta

Large volumes of new accommodation have formed within the Mississippi Delta plain since the mid-1950s in association with rapid conversion of coastal wetlands to open water. The three-dimensional aspects and processes responsible for accommodation formation were quantified by comparing surface elevations, water depths, and vertical displacements of stratigraphic contacts that were correlated between short sediment cores. Integration of data from remotely sensed images, sediment cores, and water-depth surveys at 10 geologically diverse areas in the delta plain provided a basis for estimating the total volume of accommodation formed by interior-wetland subsidence and subsequent erosion. Results indicate that at most of the study areas subsidence was a greater contributor than erosion to the formation of accommodation associated with wetland loss. Tens of millions of cubic meters of accommodation formed rapidly at each of the large open-water bodies that were formerly continuous interior delta-plain marsh. Together the individual study areas account for more than 440 × 10 6 × m 3 of new accommodation that formed as holes in the Mississippi River delta-plain fabric between 1956 and 2004. This large volume provides an estimate of the new sediment that would be needed just at the study areas to restore the delta-plain wetlands to their pre-1956 areal extent and elevations.

Mississippi Delta↗
USGS1989

Accretion and canal impacts in a rapidly subsiding wetland II: Feldspar marker horizon technique

Recent (6–12 month) marsh sediment accretion and accumulation rates were measured with feldspar marker horizons in the vicinity of natural waterways and man-made canals with spoil banks in the rapidly subsiding environment of coastal Louisiana. Annual accretion rates in a Spartina alterniflora salt marsh in the Mississippi deltaic plain averaged 6 mm in marsh adjacent to canals compared to 10 mm in marsh adjacent to natural waterways. The rates, however, were not statistically significantly different. The average rate of sediment accretion in the same salt marsh region for a transect perpendicular to a canal (13 mm yr −1 ) was significantly greater than the rate measured for a transect perpendicular to a natural waterway (7 mm yr −1 ). Measurements of soil bulk density and organic matter content from the two transects were also different. This spatial variability in accretion rates is probably related to (1) spoil bank influences on local hydrology; and (2) a locally high rate of sediment input from lateral erosion associated with pond enlargement. In a brackish Spartina patens marsh on Louisiana’s Chenier plain, vertical accretion rates were the same along natural and canal waterways (3–4 mm yr −1 ) in a hydrologically restricted marsh region. However, the accretion rates for both waterways were significantly lower than the rates along a nonhydrologically restricted natural waterway nearby (11 mm yr −1 ). The vertical accretion of matter displayed semi-annual differences in the brackish marsh environment.

Louisiana↗
USGS1976

Geotechnical description of four Mississippi Delta soil borings

The submerged portion of the Mississippi Delta complex forms an ideal natural laboratory to study the effects of rapid deposition. One of the most obvious of these effects is the mass movements of sediments. Slump and slide signatures, mudflow characteristics, and evidence for creep are all found in abundance on the delta platform. These types of features have been studied by Colemen and Wright (1974) with regard to form and by Garrison (1974) with regard to their spatial distribution. Assembling these authors' findings, it is clear that the entire offshore zone contiguous with the Mississippi River is a myriad of geological action. This situation is indeed stimulating to the sedimentologist, yet it represents a nightmare to the foundation engineer. Emplacing offshore structures in such an environment is a most difficult task, particularly since the high degree of local variability dictates that each case must be handled separately. It is under these circumstances that a marriage between geology and engineering is most fruitful, for determining the relationships between the sedimentological processes and the engineering properties is satisfying to parties from both disciplines. This, then, is the underlying objective of the Mississippi Delta research project. By investigating the instability in a geologic sense, it is hoped that many of the engineering problems will become more soluble and that extrapolation and prediction will become more realistic.

Mississippi Delta↗