Physical Sciences and Mathematics Commons^™

From The River To The Gulf: An Investigation Of Biogeochemical Cycling In Wetland Soils And Coastal Shelf Sediments, Katie Bowes

LSU Master's Theses

Louisiana is home to 40% of the coastal wetlands in the lower 48 states, yet accounts for 80% of the coastal wetland loss in this region. This loss is attributed to decreased sediment supply, levee alteration, sea level rise, channelization, and subsidence. The levee system in Louisiana disconnected coastal wetlands from the main stem of the Mississippi River (MSR), reducing the amount of land-building sediment that reaches coastal wetlands. This disconnection also allows a greater percentage of river discharge, including agricultural contaminants and runoff, to flow into the northern Gulf of Mexico (NGOM).

The 2012 Coastal Master Plan proposed eight …

Effects Of Enhanced Efficiency Nitrogen Fertilizers On Agronomic Parameters And Loss Pathways In The Subtropical Mississippi Delta Region, Scott Michael Pensky

LSU Master's Theses

Minimizing nitrogen (N) loss is critical for improving N use efficiency (NUE) in crop production and reducing its effects on the environment. Management practices such as seasonal application timing of N fertilizers and the addition of enhanced efficiency N fertilizers (EENFs) were investigated for the high N requirement of the two most common cereal crops globally, corn (Zea mays L.) and wheat (Triticum aestivum L.), in the subtropical climate of Louisiana. Field research was established during the 2016 and 2017 seasons at the LSU Agricultural Center’s Dean Lee and Central research stations to examine the effect of different EENFs and …

Evaluation Of Controlled-Release Nitrogen And Potassium Fertilizer In Louisiana Sugarcane Production, Samuel Kwakye

LSU Master's Theses

Sugarcane (Saccharum spp) production is an integral part of Louisiana's economy. Proper fertilizer management, particularly nitrogen (N) and potassium (K), optimizes sugarcane production. An experiment was established in 2015 at the LSU AgCenter Sugar Research Station in St. Gabriel, Louisiana to: (1) assess the effect of N and K fertilizer sources on sugarcane yield and quality parameters, and (2) monitor the changes in inorganic N and K levels in the soil at different sugarcane growth stages. The experiment was arranged in a randomized complete block design on a Sharkey clay soil and complete randomized design on a Commerce …

A Multi-Scale Investigation Of Nutrient Dynamics In The Lake Pontchartrain Estuary And Basin, Eric Daniel Roy

LSU Doctoral Dissertations

Humans are responsible for global-scale alteration of nitrogen (N) and phosphorus (P) biogeochemical cycles to support food production. Increases in N and P inputs into soils and waste-streams has resulted in excessive nutrient loading to surface waters, including the Mississippi River, leading to eutrophication. Here I investigated N and P dynamics occurring in the Lake Pontchartrain Estuary and Basin. I measured two biogeochemical processes using intact sediment core incubations and quantified their importance in the context of nutrient-rich Mississippi River flood diversions through the Bonnet Carré Spillway. I show that diffusion of nitrate-N into sediments accounts for a substantial magnitude …

Decade-Scale Nutrient Enrichment Effects On Wetland Plant Community Structure, Function, And Stability, Sean A. Graham

LSU Doctoral Dissertations

Human activities have increased the supply of nitrogen (N) and phosphorus (P) to coastal waters worldwide, threatening coastal wetlands with excess nutrient loading and subsequent eutrophication. In this dissertation, I present results from two decade-scale fertilization experiments in a Sagittaria lancifolia dominated oligohaline marsh that examined the species-, community-, and ecosystem-level effects of nutrient enrichment. My objectives were to determine (1) which nutrient limits primary production, (2) how increased supply of the limiting nutrient affects plant community structure and function, both above- and belowground, and (3) whether nutrient over-enrichment compromises ecosystem stability. Overall, significant changes in plant growth occurred with …

Nitrogen And Carbon Export To The Gulf Of Mexico By The Atchafalaya River, A Major Distributary Of The Mississippi River, April Elizabeth Bryantmason

LSU Doctoral Dissertations

Summer hypoxia in the Northern Gulf of Mexico has been attributed to large nutrient inputs, especially nitrate-nitrogen, from the Mississippi-Atchafalaya River system. The 2008 Gulf Hypoxia Action Plan calls for river corridor wetland restoration to reduce nitrate loads, but it is largely unknown how effective riverine wetland systems in the lower Mississippi River (MR) are for nitrate removal. This dissertation research examined nitrate and carbon export from the Atchafalaya River (AR) to: (1) determine nitrate processing by a river swamp basin under varied seasons, (2) investigate nitrate retention and processing in the AR during a major flood event, and (3) …

Biomass And Mass Balance Isotope Content Of Mussel Seep Populations, Philip Martin Riekenberg

LSU Master's Theses

Cold seep mussels, Bathymodiolus childressi, are common cold seep constituents that form large populations at upper continental slope (500-1000 m) cold seep sites in the Northern Gulf of Mexico. These mussels utilize methane present through symbiotic relationships with methanotrophic bacteria. This study uses a coupled isotope technique to determine the relative incorporation of respiratory carbon in the shell as a measure of the availability of methane between different seep sites. This method indicates a higher abundance of methane at the Brine Pool site than at the Bush Hill site which appears significantly more resource limited and that changes in methane …

The Effect Of Habitat Change On Nutrient Removal In The Atchafalaya River Basin, Louisiana, Amy E. Scaroni

LSU Doctoral Dissertations

The Mississippi and Atchafalaya rivers are the major sources of freshwater and nutrients to the Gulf of Mexico. Increased nutrient loads from these rivers exacerbate eutrophication in coastal receiving waters and contribute to the large area of hypoxia that develops seasonally in the Gulf. Levees along the Mississippi River have reduced contact between the river and the historic floodplain; this limits the ability of floodplain wetlands to naturally mitigate excess nutrients. However, the Atchafalaya River diverges from the Mississippi 217 km from the Gulf and enters a large river floodplain with a widely spaced levee system. This enhances the ability …

Impact Of Urban Runoff On Phosphorus, Nitrogen, And Dissolved Oxygen In A Shallow Subtropical Lake, Ryan Mesmer

LSU Master's Theses

This research assessed the current conditions of water quality in a shallow subtropical lake, influenced by a highly developed urban environment. Specifically, the research focused on the dynamics of phosphorus, nitrogen, and dissolved oxygen, as well as the effects of stormwater runoff on lake water quality. Furthermore, the research quantified gross primary production, net primary production, and respiration in order to discern seasonal variation in lake metabolism. A water quality monitoring platform with multi-parameter probes was deployed in the center of University Lake on the Louisiana State University campus. A series of lake water quality parameters including dissolved oxygen (DO) …

Developing Tools To Identify Factors That Limit Production In Coastal Marshes, Vanessa Danielle Tobias

LSU Doctoral Dissertations

Marsh loss is a problem in many areas around the world. In Louisiana’s coastal marshes, where Spartina patens is the most common plant, restoration and management seek to slow wetland loss rates that average approximately 77.4 km2/year. To combat the problem, scientists and managers require tools to determine local causes and evaluate the effectiveness of management techniques. Current methods for identifying factors that limit productivity in marshes are too time-consuming or expensive for wide-spread, regular use. Critical values of elemental concentrations in plant tissue are widely used to diagnose mineral deficiencies and toxicities in agricultural crops, however. I used the …

A Century Of Land Use And Water Quality In Watersheds Of The Continental U.S., Whitney P. Broussard Iii

LSU Doctoral Dissertations

Human endeavors, particularly the agricultural and industrial activities of the last half century, now produce more biologically available nitrogen (N) than all other natural sources combined. The increased N availability can have consequences for the health of aquatic biota on the local, regional, and global scales. One manifestation of this problem is the formation of coastal hypoxic zones where terrestrial N loading creates eutrophic conditions in coastal waters. This dissertation examines a century of changes in land use and water quality to quantify the relationships between agricultural land use practices and riverine N yields in the Mississippi River Basin and …

Denitrification Enzyme Activity As An Indicator Of Nitrate Loading In A Wetland Receiving Diverted Mississippi River Water, Lisa Michelle Gardner

LSU Master's Theses

The Davis Pond freshwater diversion discharges nutrient-rich Mississippi River water to a 3,760 ha receiving marsh in upper Barataria Basin, LA. Excess nitrate in the Mississippi River has been linked to algal blooms and hypoxia in the Gulf of Mexico with potential to negatively impact Barataria Basin. We hypothesized that 1) soil denitrification enzyme activity (DEA) will increase with higher surface water nitrate concentrations, and 2) the spatial distribution of DEA in Davis Pond marsh will provide information about the extent nitrate loading at a specific discharge rate. Intact soil cores collected from the marsh received a continuous flow of …

Inorganic Nitrogen Transformations At High Loading Rates In An Oligohaline Estuary, R. Eugene Turner, Q. Dortch, Nancy N. Rabalais

Faculty Publications

A well-defined nitrogen retention and turnover budget was estimated for a shallow oligohaline lake (Lake Pontchartrain, Louisiana, USA). In 1997 a month-long diversion of the Mississippi River filled the Lake with highly concentrated river water (80 µM nitrate) and lowered the salinity to 0 psu within 2 weeks. After the spillway was closed the Lake mixed with estuarine tidal waters and came to equilibrium over 4 months with the riverine, atmospheric and offshore water nitrogen sources. A flushing rate of 1.78% d−1 was estimated by analyzing a plot of ln salinity versus time for the first 120 days after the …

Suspended Sediment, C, N, P, And Si Yields From The Mississippi River Basin, R. Eugene Turner, Nancy N. Rabalais

Faculty Publications

The annual loads of C,N,P, silicate, total suspended sediment (mass) and their yields (mass area−1) were estimated for six watersheds of the Mississippi River Basin (MRB) using water quality and water discharge records for 1973 to 1994. The highest load of suspended sediments is from the Missouri watershed (58 mt km2 yr−1), which is also the largest among the six major sub-basins. The Ohio watershed delivers the largest load of water (38%). The Upper Mississippi has the largest total nitrogen load (32%) and yield (1120 kg TN km2 yr−1). The loading of organic carbon, total phosphorus and silicate from the …

The Effects Of Nutrient Enrichment On The Decomposition Of Belowground Organic Matter In A Sagittaria Lancifolia - Dominated Oligohaline Marsh, Kristen Raye Laursen

LSU Master's Theses

Wetlands improve water quality through sedimentation and the uptake of excess nutrients. As human population increases in the coastal zone, wetlands receive greater nutrient inputs. These additional nutrients may accelerate microbial activity, leading to faster decomposition rates. This decomposition could exceed belowground organic matter production, resulting in a net reduction in soil organic matter accumulation and vertical marsh accretion. The effects of nutrient enrichment on belowground organic matter decomposition in subtropical marshes have received little attention. As such, this research examined the effects of four levels of nitrogen combined with two levels of phosphorus enrichment on belowground decomposition through the …

Global Patterns Of Dissolved N, P And Si In Large Rivers, R. Eugene Turner, Nancy N. Rabalais, D. Justic', Q. Dortch

Faculty Publications

The concentration of dissolved inorganic nitrogen (DIN), dissolved nitrate-N, Total-N (TN), dissolved inorganic phosphate (DIP), total phosphorus (TP), dissolved silicate-Si (DSi) and their ratios in the world's largest rivers are examined using a global data base that includes 37% of the earth's watershed area and half its population. These data were compared to water quality in 42 subbasins of the relatively well-monitored Mississippi River basin (MRB) and of 82 small watersheds of the United States. The average total nitrogen concentration varies over three orders of magnitude among both world river watersheds and the MRB, and is primarily dependent on variations …

The Impact Of Accelerating Land-Use Change On The N-Cycle Of Tropical Aquatic Ecosystems: Current Conditions And Projected Changes, J. A. Downing, M. Mcclain, R. Twilley, J. M. Melack, J. Elser, Nancy N. Rabalais, W. M. Lewis Jr., R. Eugene Turner, J. Corredor, D. Soto, A. Yanez Arancibia, J. A. Kopaska, R. W. Howarth

Faculty Publications

Published data and analyses from temperate and tropical aquatic systems are used to summarize knowledge about the potential impact of land-use alteration on the nitrogen biogeochemistry of tropical aquatic ecosystems, identify important patterns and recommend key needs for research. The tropical N-cycle is traced from pre-disturbance conditions through the phases of disturbance, highlighting major differences between tropical and temperate systems that might influence development strategies in the tropics. Analyses suggest that tropical freshwaters are more frequently N-limited than temperate zones, while tropical marine systems may show more frequent P limitation. These analyses indicate that disturbances to pristine tropical lands will …