Physical Sciences and Mathematics Commons^™

Comparison Of Continuous Records Of Near-Bottom Dissolved Oxygen From The Hypoxia Zone Along The Louisiana Coast, Nancy N. Rabalais, William J. Wiseman, R. Eugene Turner

Faculty Publications

Oxygen depletion is a seasonally dominant feature of the lower water column on the highly-stratified, riverine-influenced continental shelf of Louisiana. The areal extent of hypoxia (bottom waters ≤2 mg l−1 dissolved oxygen) in mid-summer may encompass up to 9,500 km2, from the Mississippi River delta to the upper Texas coast, with the spatial configuration of the zone varying interannually. We placed two continuously recording oxygen meters (Endeco 1184) within 1 m of the seabed in 20-m water depth at two locations 77 km apart where we previously documented midsummer bottom water hypoxia. The oxygen meters recorded considerably different oxygen conditions …

A Preliminary Mass Balance Model Of Primary Productivity And Dissolved Oxygen In The Mississippi River Plume/Inner Gulf Shelf Region, Victor J. Bierman Jr., Scott C. Hinz, William J. Wiseman Jr., Nancy N. Rabalais, R. Eugene Turner

Faculty Publications

A deterministic, mass balance model for phytoplankton, nutrients, and dissolved oxygen was applied to the Mississippi River Plume/Inner Gulf Shelf (MRP/IGS) region. The model was calibrated to a comprehensive set of field data collected during July 1990 at over 200 sampling stations in the northern Gulf of Mexico. The spatial domain of the model is represented by a three-dimensional, 21-segment water-column .grid extending from the Mississippi River Delta west to the Louisiana-Texas border, and from the shoreline seaward to the 30-60 m bathymetric contours. Diagnostic analyses and numerical experiments were conducted with the calibrated model to better understand the environmental …

Coastal Eutrophication Near The Mississippi River Delta, R. Eugene Turner, Nancy Rabalais

Faculty Publications

CHANGES in delivery of river-borne nutrients such as dissolved phosphate, nitrate and silicate, owing to land-use changes and anthropogenic emissions, are known to result in eutrophication1— enhanced phytoplankton blooms—and more severe hypoxic events2–1 in many enclosed bays and seas. Although similar ecological effects might be expected on continental shelves, the occurrence of such eutrophication has remained unresolved5. Here we present evidence of eutrophication of the continental shelf near the outflow of the Mississippi river, obtained by quantifying biologically bound silica (BSi) in diatom remnants within dated sediment cores. BSi accumulation rates are greatest in water depths of 20 to 50 …

A Rationale For Coastal Wetland Restoration Through Spoil Bank Management In Louisiana, Usa, R. Eugene Turner, E. M. Swenson, J. M. Lee

Faculty Publications

The rationale and outline of an implementation plan for restoring coastal wetlands in Louisiana is presented. The rationale for the plan is based on reversing the consequences of documented cause-and-effect relationships between wetland loss and hydrologic change. The main feature is to modify the extensive interlocking network of dredged spoil deposits, or spoil banks, by reestablishing a more natural water flow at moderate flow velocity (/sec). Guidelines for site selection from thousands of potential sites are proposed. Examples of suitable sites are given for intermediate marshes. These sites exhibit rapid deterioration following partial or complete hydrologic impoundment, implying a strong …

The Value Of Salt Marsh Edge Vs Interior As A Habitat For Fish And Decapod Crustaceans In A Louisiana Tidal Marsh, G. W. Peterson, R. Eugene Turner

Faculty Publications

Flume nets of various lengths and a 3-m seine were used to sample the fishes and macrocrustaceans using a flooded Louisiana salt marsh and the adjacent tidal creek. The experiment allowed for species-specific comparisons of the flooded marsh at the creek edge versus the interior. Of the 37,667 organisms collected in flume nets from January through November 1989, 89% were decapods (nine species) and 11% were fish (29 species). An additional 18,539 organisms (75% decapods and 25% fish) were collected from concurrent seine samples taken from July through November. Comparison of catches among different flume lengths and low tide versus …

Backfilling Canals To Restore Wetlands: Empirical Results In Coastal Louisiana, R. Eugene Turner, James M. Lee, Christopher Neill

Faculty Publications

Wetland restoration is largely a developing science and engineering enterprise. Analyses of results are too few and constrained to observations over a few years. We report here on the effectiveness of one restoration technique used sparsely in coastal Louisiana for several decades. Canals have been dredged in coastal Louisiana wetlands since 1938 for oil and gas exploration and extraction. These canals are typically dredged to 2.5 m depth and are 20 to 40 m wide. Canal lengths vary from 100 m to several 1000s m in the case of outer continental shelf pipeline canals that cross the wetlands.

Today, thousands …