Title page for ETD etd-11012004-115333

Type of Document Master's Thesis
Author Hyfield, Emily Christina Grace
Author's Email Address ehyfie1@lsu.edu
URN etd-11012004-115333
Title Freshwater and Nutrient Inputs to a Mississippi River Deltaic Estuary with River Re-Introduction
Degree Master of Science (M.S.)
Department Oceanography & Coastal Sciences
Advisory Committee
Advisor Name Title
John W. Day, Jr. Committee Chair
Dubravko Justic Committee Member
Enrique Reyes Committee Member
Robert Gambrell Committee Member
  • nutrient input
  • water budget
  • breton sound estuary
  • diversion
Date of Defense 2004-10-06
Availability unrestricted
In this study, I quantified freshwater and nutrient inputs in the Breton Sound estuary which is receiving freshwater reintroduction in an effort to restore deteriorating wetlands. Almost all wetlands of the Mississippi deltaic plain are isolated from riverine input due to flood control levees along the Mississippi River. This has altered water and nutrient budgets and is a primary cause of the massive wetland loss in the delta. Maintenance of the delta depends on a healthy, functioning ecosystem which includes riverine input.

The Breton Sound estuary is located southeast of New Orleans and until recently was hydrologically isolated from direct riverine input. In 1992, a freshwater diversion became operational at Caernarvon, LA that re-introduces freshwater, nutrients, and sediments from the Mississippi River into the estuary. Several inputs and losses were calculated for three annual (2000, 2001, and 2002) water budgets including precipitation (PPN), potential evapotranspiration (PET), the diversion, stormwater pumps, and groundwater. The inputs of ammonium (NH4-N), nitrate (NO3-N), total nitrogen (TN) and total phosphorus (TP) were determined for each of the water sources.

There was a different precipitation pattern for each of the years for which water and nutrient budgets were calculated. Precipitation contributed 48-57% of freshwater input while the diversion structure accounted for 33-48%. The net input of fresh groundwater was 3 to 4 orders of magnitude less than diversion input and precipitation. Atmospheric deposition was the largest contributor of NH4-N accounting for 62-72% of the total NH4 input followed by the diversion (total annual NH4-N input was 1.39x105 to 1.96x105 kg). NO3-N input to the estuary was an order of magnitude greater than NH4-N input. The diversion was the greatest source of nitrate to the study area (7.78x105 to 1.64x106 kg) contributing 77-88% of total nitrate input. The diversion contributed 1.26x106 to 2.10x106 kg of TN, representing 77-79% of TN input. The diversion contributed 81-98% of TP input and was an order of magnitude greater than precipitation and stormwater pumps combined. Annual loading rates of NH4-N and NO3-N were 0.16-0.22 and 1.6-2.2 gNm-2y-1, respectively. TN ranged from 1.9-3.2 gNm-2y-1 and TP ranged from 0.17-0.29 gPm-2y-1.

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