Breton Sound Estuary Research Articles

Patterns and Mechanisms of Wetland Change in the Breton Sound Estuary, Mississippi River Delta: A Review

Patterns and Mechanisms of Wetland Change in the Breton Sound Estuary, Mississippi River Delta: A Review

Engaging coastal community members about natural and nature-based solutions to assess their ecosystem function

Hazards in coastal ecosystems, such as flooding and land loss, demand natural and nature-based solutions from local communities due to the protective and non-protective services they provide when compared with traditionally engineered approaches. In this context, natural solutions are those that consider conserving existing habitats whereas nature-based solutions are those created by humans. These solutions support important coastal ecosystem functions, such as nutrient uptake, fisheries habitat, soil carbon storage, and surge attenuation. Our main research questions were: (1) Based on community engagement, what are the possible natural and nature-based solutions to address coastal hazards in Breton Sound Estuary, Louisiana? and (2) How do these community co-designed nature-based solutions support various ecosystem functions? To help answer these questions, we leveraged the competency group methodology to incorporate the local needs and traditional ecological knowledge of community stakeholders into collaborative ecosystem modelling. In total, fifteen members regularly met five times over an eight-month period to design nature-based solutions to address coastal hazards. Two nature-based solutions, created marshes and restored ridges, were identified most frequently by the competency group (>75% occurrence) in a final survey. Associated ecosystem functions of the identified solutions were assessed with simulation models to determine future ecosystem functions of nutrient uptake, fisheries habitat, soil carbon storage, and surge attenuation after 20 years. By adding created marshes to an ecosystem, our model results indicate slight increases in nutrient uptake, likely increases to fisheries habitat and soil carbon storage capacity, as well as storm surge attenuation in some areas following ridge restoration. Quantifying these ecosystem functions with management actions has been limited and is needed to assess how natural and nature-based solutions impact local communities and resource users. This novel approach to modeling ecosystem-based solutions through a collaborative modeling process with researchers and residents can be applied elsewhere to assess the viability of natural and nature-based solutions.

Elevating local knowledge through participatory modeling: active community engagement in restoration planning in coastal Louisiana

Numerical modeling efforts in support of restoration and protection activities in coastal Louisiana have traditionally been conducted externally to any stakeholder engagement processes. This separation has resulted in planning- and project-level models built solely on technical observation and analysis of natural processes. Despite its scientific rigor, this process often fails to account for the knowledge, values, and experiences of local stakeholders that often contextualizes a modeled system. To bridge this gap, a team of natural and social scientists worked directly with local residents and resource users to develop a participatory modeling approach to collect and utilize local knowledge about the Breton Sound Estuary in southeast Louisiana, USA. Knowledge capture was facilitated through application of a local knowledge mapping methodology designed to catalog local understanding of current and historical conditions within the estuary and identify desired ecological and hydrologic end states. The results of the mapping endeavor informed modeling activities designed to assess the applicability of the identified restoration solutions. This effort was aimed at increasing stakeholder buy-in surrounding the utility of numerical models for planning and designing coastal protection and restoration projects and included an ancillary outcome aimed at elevating stakeholder empowerment regarding the design of nature-based restoration solutions and modeling scenarios. This intersection of traditional science and modeling activities with the collection and analysis of traditional ecological knowledge proved useful in elevating the confidence that community members had in modeled restoration outcomes.

Predicting the impacts of Mississippi River diversions and sea-level rise on spatial patterns of eastern oyster growth rate and production

There remains much debate regarding the perceived tradeoffs of using freshwater and sediment diversions for coastal restoration in terms of balancing the need for wetland restoration versus preserving eastern oyster (Crassostrea virginica) production. Further complicating the issue, climate change-induced sea-level rise (SLR) and land subsidence are also expected to affect estuarine water quality. In this study, we developed a process-based numerical modeling system that couples hydrodynamic, water quality, and oyster population dynamics. We selected Breton Sound Estuary (BSE) (∼2740km2) in the eastern Mississippi River Deltaic Plain since it is home to several of the largest public oyster seed grounds and private leases for the Gulf coast. The coupled oyster population model was calibrated and validated against field observed oyster growth data. We predicted the responses of oyster population in BSE to small- (142m3s−1) and large-scale (7080m3s−1) river diversions at the Caernarvon Freshwater Diversion structure planned in the 2012 Coastal Master Plan (Louisiana) under low (0.38m) and high (1.44m) relative sea-level rise (RSLR=eustatic SLR+subsidence) compared to a baseline condition (Year 2009). Model results showed that the large-scale diversion had a stronger negative impact on oyster population dynamics via freshening of the entire estuary, resulting in reduced oyster growth rate and production than RSLR. Under the large-scale diversion, areas with optimal oyster growth rates (>15mg ash-free dry weight (AFDW) oyster−1wk−1) and production (>500g AFDWm−2yr−1) would shift seaward to the southeastern edge of the estuary, turning the estuary into a very low oyster production system. RSLR however played a greater role than the small-scale diversion on the magnitude and spatial pattern of oyster growth rate and production. RSLR would result in an overall estuary-wide decrease in oyster growth rate and production as a consequence of decreased salinities in the middle and lower estuary because rising sea level likely causes increased stage and overbank flow downstream along the lower Mississippi River.

A Modeling Study of the Impacts of Mississippi River Diversion and Sea-Level Rise on Water Quality of a Deltaic Estuary

Freshwater and sediment management in estuaries affects water quality, particularly in deltaic estuaries. Furthermore, climate change-induced sea-level rise (SLR) and land subsidence also affect estuarine water quality by changing salinity, circulation, stratification, sedimentation, erosion, residence time, and other physical and ecological processes. However, little is known about how the magnitudes and spatial and temporal patterns in estuarine water quality variables will change in response to freshwater and sediment management in the context of future SLR. In this study, we applied the Delft3D model that couples hydrodynamics and water quality processes to examine the spatial and temporal variations of salinity, total suspended solids, and chlorophyll-α concentration in response to small (142 m3 s−1) and large (7080 m3 s−1) Mississippi River (MR) diversions under low (0.38 m) and high (1.44 m) relative SLR (RSLR = eustatic SLR + subsidence) scenarios in the Breton Sound Estuary, Louisiana, USA. The hydrodynamics and water quality model were calibrated and validated via field observations at multiple stations across the estuary. Model results indicate that the large MR diversion would significantly affect the magnitude and spatial and temporal patterns of the studied water quality variables across the entire estuary, whereas the small diversion tends to influence water quality only in small areas near the diversion. RSLR would also play a significant role on the spatial heterogeneity in estuary water quality by acting as an opposite force to river diversions; however, RSLR plays a greater role than the small-scale diversion on the magnitude and spatial pattern of the water quality parameters in this deltaic estuary.

Sediment Deposition at the Caernarvon Crevasse during the Great Mississippi Flood of 1927: Implications for Coastal Restoration

During the 1927 Mississippi flood, the levee was dynamited downstream of New Orleans creating a 2 km wide crevasse that inundated the Breton Sound estuary and deposited a crevasse splay of about 130 km2. We measured sediment deposition in the splay that consisted of a silty-clay layer bounded by aged peat below and living roots above. Based on coring, we developed a map of the crevasse splay. The clay layer ranged from 2 to 42 cm thick and occurred 24 to 55 cm below the surface. Bulk density of the clay layer decreased and soil organic matter increased with distance from the river. 210Pbexcess and 137Cs dating an age of ~1926–1929 for the top of the layer. During the flood event, deposition was at least 22 mm·month−1—10 times the annual post-1927 deposition. The crevasse splay captured from 55% to 75% of suspended sediments that flowed in from the river. The 1927 crevasse deposition shows how pulsed flooding can enhance sediment capture efficiency and deposition and serves as an example for large planned diversions for Mississippi delta restoration.

Analysis of Environmental Factors Influencing Salinity Patterns, Oyster Growth, and Mortality in Lower Breton Sound Estuary, Louisiana, Using 20 Years of Data

ABSTRACT La Peyre, M.K.; Geaghan, J.; Decossas, G., and La Peyre, J.F., 2016. Analysis of environmental factors influencing salinity patterns, oyster growth, and mortality in lower Breton Sound Estuary, Louisiana, using 20 years of data. Freshwater inflow characteristics define estuarine functioning by delivering nutrients, sediments, and freshwater, which affect biological resources and ultimately system production. Using 20 years of water quality, weather, and oyster growth and mortality data from Breton Sound Estuary (BSE), Louisiana, we examined the relationship of riverine, weather, and tidal influence on estuarine salinity, and the relationship of salinity to oyster growth and mortality. Mississippi River discharge was found to be the most important factor determining salinity patterns over oyster grounds within lower portions of BSE, with increased river flow associated with lowered salinities, while easterly winds associated with increased salinity were less influential. These patterns were consis...

Assessing shoreline exposure and oyster habitat suitability maximizes potential success for sustainable shoreline protection using restored oyster reefs.

Oyster reefs provide valuable ecosystem services that contribute to coastal resilience. Unfortunately, many reefs have been degraded or removed completely, and there are increased efforts to restore oysters in many coastal areas. In particular, much attention has recently been given to the restoration of shellfish reefs along eroding shorelines to reduce erosion. Such fringing reef approaches, however, often lack empirical data to identify locations where reefs are most effective in reducing marsh erosion, or fully take into account habitat suitability. Using monitoring data from 5 separate fringing reef projects across coastal Louisiana, we quantify shoreline exposure (fetch + wind direction + wind speed) and reef impacts on shoreline retreat. Our results indicate that fringing oyster reefs have a higher impact on shoreline retreat at higher exposure shorelines. At higher exposures, fringing reefs reduced marsh edge erosion an average of 1.0 m y−1. Using these data, we identify ranges of shoreline exposure values where oyster reefs are most effective at reducing marsh edge erosion and apply this knowledge to a case study within one Louisiana estuary. In Breton Sound estuary, we calculate shoreline exposure at 500 random points and then overlay a habitat suitability index for oysters. This method and the resulting visualization show areas most likely to support sustainable oyster populations as well as significantly reduce shoreline erosion. Our results demonstrate how site selection criteria, which include shoreline exposure and habitat suitability, are critical to ensuring greater positive impacts and longevity of oyster reef restoration projects.

Phytoplankton Community Shifts and Harmful Algae Presence in a Diversion Influenced Estuary

River water entering estuaries affects the physical and chemical environment at irregular intervals creating a highly dynamic aquatic habitat. Phytoplankton are important primary producers in estuaries that respond quickly to their changing environment. Over a 12-month period, the phytoplankton response was examined in terms of biomass, abundance, community composition, and potential phycotoxin production to seasonal changes in river input entering the Breton Sound Estuary in Louisiana. Chlorophyll a (chl a) measurements estimated phytoplankton biomass and light microscopy identified phytoplankton abundance and community composition. Phycotoxins were measured using ultra-sensitive enzyme-linked immunosorbent assay (ELISA). During the study period, chl a and cell abundances exhibited an inverse relationship with the seasons, which were determined by temperature and diversion input rates. The community was dominated by cyanobacteria for most of the year, mainly corresponding to the warm-low flow season. For the rest of the year, cyanobacteria decreased while chlorophytes and centric diatoms increased to approximately equal contributions. Overall, the phytoplankton community composition was most commonly moderated by temperature, salinity, and dissolved inorganic nitrogen (DIN) availability using BIO-ENV. Microcystins (MCs) were detected throughout the year ranging from below detection to 2.92 μg MCs l−1. MC levels were highest during the warm-low flow season and toward the lower estuary. The detection of MCs for the first time in the Breton Sound Estuary illustrates a potential risk to human health and economically important estuarine food webs.

A numerical study of vegetation impact on reducing storm surge by wetlands in a semi-enclosed estuary

Coastal wetlands play a unique role in extreme hurricane events. The impact of wetlands on storm surge depends on multiple factors including vegetation, landscape, and storm characteristics. The Delft3D model, in which vegetation effects on flow and turbulence are explicitly incorporated, was applied to the semi-enclosed Breton Sound (BS) estuary in coastal Louisiana to investigate the wetland impact. Guided by extensive field observations, a series of numerical experiments were conducted based on variations of actual vegetation properties and storm parameters from Hurricane Isaac in 2012. Both the vegetation-induced maximum surge reduction (MSR) and maximum surge reduction rate (MSRR) increased with stem height and stem density, and were more sensitive to stem height. The MSR and MSRR decreased significantly with increasing wind intensity. The MSRR was the highest with a fast-moving weak storm. It was also found that the MSRR varied proportionally to the expression involving the maximum bulk velocity and surge over the area of interest, and was more dependent on the maximum bulk surge. Both MSR and MSRR appeared to increase when the area of interest decreased from the whole BS estuary to the upper estuary. Within the range of the numerical experiments, the maximum simulated MSR and MSRR over the upper estuary were 0.7m and 37%, respectively.

Spatial and Temporal Variations in Nutrients and Water-Quality Parameters in the Mississippi River-Influenced Breton Sound Estuary

ABSTRACT Lundberg, C.J.; Lane, R.R., and Day, J.W., Jr., 2014. Spatial and temporal variations in nutrients and water-quality parameters in the Mississippi River-influenced Breton Sound estuary. The purpose of this study is to investigate the long-term temporal and spatial nutrient patterns in the Breton Sound estuary, an estuarine wetland complex in coastal Louisiana that is highly influenced by the Caernarvon river diversion. A water-quality data set spanning 8 years of monthly sampling was analyzed. Analysis of salinity mixing diagrams indicates the estuary to be a source of ammonium and chlorophyll a, and a sink for nitrate, total nitrogen, and total suspended sediments. The estuary served as either a source or sink for phosphate, total phosphorus, and silicate depending on season. The NOx loading rate ranged from 1.1 g N m−2 y−1 during fall to 4.9 g N m−2 y−1 during spring, with an overall mean of 3.5 g N m−2 y−1. Nitrate removal efficiency varied seasonally, with highest efficiency during the fall (...

Simulating Fish Movement Responses to and Potential Salinity Stress from Large‐Scale River Diversions

AbstractRiver diversions are a major but controversial management approach to restoring coastal wetlands and mitigating offshore oil spills in the northern Gulf of Mexico. One of the controversies concerns the potential displacement of and salinity stress on commercially and recreationally important fish species in response to the widespread and prolonged freshening of habitat. We developed a coupled hydrodynamics–fish movement model and applied it to the Caernarvon diversion located in the Breton Sound estuary, Louisiana. Hydrodynamics model output was used as input to the individual‐based fish movement model. The period of model simulation was from April 1 to July 1, 2010. We simulated three diversion scenarios: baseline, pulse, and oil spill mitigation. We first used field data from Bay Anchovy Anchoa mitchilli and showed that the model predicted downestuary shifts similar to those observed in field studies under large diversions. We then defined generic low‐ and intermediate‐salinity fish species and simulated each under the three diversion scenarios. Compared with the baseline diversion scenario, more than 50% of the intermediate‐salinity individuals moved about 15 km farther downestuary under the pulse diversion scenario and moved more than 35 km under the oil spill mitigation diversion scenario. The effects of the diversions on the low‐salinity species were evidenced by individuals becoming more dispersed (i.e., spreading out downestuary) and more exposed to bursts of too high salinity. Our conclusions agreed with those from earlier field and modeling analyses that focused on average (rather than transitory) fish responses.Received November 4, 2013; accepted November 7, 2013

Ammonification and denitrification rates in coastal Louisiana bayou sediment and marsh soil: Implications for Mississippi river diversion management

The Caernarvon Diversion directs Mississippi River water into coastal marshes in the Breton Sound Estuary. Elevated nitrogen levels in the Mississippi River water result in nutrient loading to these coastal marsh systems and consequently to the coastal ocean. The goal of this study is to determine the potential nitrate removal rates for two different substrates. Bayou sediments represent the low flow conditions, when the water is constrained within the canals with high potential for transport to the coastal ocean. The marsh soil represents the high flow diversion events when flood water inundates up into the marshes. We sought to remove the plant effect by using cores containing bayou sediment and marsh soil, removing all roots and flooding with a water column containing 2mg NO3-NL−1. Water column nitrate and ammonium concentration were monitored over 9d. Net nitrate loss in bayou sediments was 9.5±1.5mg Nm−2d−1 while the nitrate loss was significantly less at 7.2±0.9mg Nm−2d−1 in the marsh soil. A comparison of nitrate reduction rates in vegetated and non-vegetated marsh soils indicated that the rate of denitrification increased tenfold in vegetated soils. This increase could be attributed to the “plant effect”. Our results suggest that operating diversions on the high flow end of the spectrum would promote nitrate delivery over the vegetated marsh rather than flowing only through canals. Flooding of the vegetated marsh maximizes the potential for removal of riverine nitrate and limits delivery of nitrate to the coastal ocean, thereby mitigating expressions of eutrophication including algal blooms and hypoxia.

Vegetation and Soil Dynamics of a Louisiana Estuary Receiving Pulsed Mississippi River Water Following Hurricane Katrina

We monitored wetland biomass, decomposition, hydrology, and soil porewater chemistry at the Breton Sound estuary, which receives Mississippi River water from the Caernarvon river diversion structure. The estuary was in the direct path of hurricane Katrina in 2005, which caused a dramatic loss of wetlands in the upper basin. From March 2006 to October 2007, we made duplicate measurements at three distance classes from the diversion structure along the estuarine gradient as well as at a reference area, designated Near (N1&2), Mid (M1&2), Far (F1&2), and Ref (R1&2). Above- and belowground live biomass, porewater nutrients (NOx, NH4, and PO4), salinity, sulfide, and soil Eh were measured every 2 months. Water level was monitored with gauges. Above- and belowground decomposition was measured using the litterbag (both) and cotton strip (belowground only) methods. Analysis of porewater parameters showed that stress factors affecting biomass production (porewater salinity, sulfide, flooding, and redox potential) were generally low to moderate, while measurable porewater nutrient concentrations occurred at all sites. Aboveground end of season live (EOSL) standing crop in October ranged from 423 g/m2 at site M2 to 1,515 at site F1, and was significantly greater at site N1 than at sites N2, M1, or M2. Aboveground EOSL biomass during this study was significantly lower than previously measured in 1999, 2000, and 2001. Peak belowground biomass ranged from 8,315 g/m2 at site R2 to 17,890 g/m2 at site N1, which is among the highest reported in the literature, and there were significant increases throughout the study, suggesting recovery from hurricane Katrina. The decomposition bag data did not indicate any significant differences; however, the cotton strip decomposition rate was significantly lower at the lowest depth. Wetland surface vertical accretion ranged from 0.49 cm/year at N2 to 1.24 cm/year at N1, with site N1 significantly greater than N2, M1, F2, and R1, and site N2 significantly less than all other sites except site R1. These findings show that marsh productivity and stability is related to a number of factors and no one factor can explain the impacts of the hurricanes.

Diverted Mississippi River sediment as a potential phosphorus source affecting coastal Louisiana water quality

Mississippi River water and associated sediment are seasonally diverted into Louisiana coastal basins to restore historic hydrologic and salinity regimes and to slow or reverse the widespread wetland loss. More river diversions are planned; however, very little research has been conducted on the potential source of phosphorous (P) of these sediments transported by the Mississippi River into the coastal areas through these diversions. In addition, the sediments have the potential to undergo changes in redox status when these significant flooding events occur. Therefore, we examined the effect of sediment redox condition on P release from newly deposited Mississippi River sediment. Sediment was collected from Big Mar Lake, the receiving water body of the Caernarvon diversion structure, through which river water is diverted into the Breton sound estuary. Sediment suspensions were incubated in the laboratory under reducing conditions, and the relation of redox conditions to P release was determined. Soluble reactive P (SRP), dissolved organic P (DOP), Fe, and Mn concentrations increased with decreasing sediment redox potential. The SRP and DOP concentrations increased 32 - and 8-fold during 20 days of anaerobic conditions. The increase in SRP and DOP availability was significantly correlated to an increase in ferrous iron with no significant relationship with Al, Ca, or Mg. While the vast majority of studies on nutrients associated with the Mississippi River diversions have focused on excess inorganic nitrogen forms (primarily NO3) in the river water, this study is one of the first to demonstrate that upon reduction associated with prolonged flooding, the diverted Mississippi River suspended sediment can be a significant source of available P to the coastal basin.

Landscape-Scale Analysis of Wetland Sediment Deposition from Four Tropical Cyclone Events

Hurricanes Katrina, Rita, Gustav, and Ike deposited large quantities of sediment on coastal wetlands after making landfall in the northern Gulf of Mexico. We sampled sediments deposited on the wetland surface throughout the entire Louisiana and Texas depositional surfaces of Hurricanes Katrina, Rita, Gustav, and the Louisiana portion of Hurricane Ike. We used spatial interpolation to model the total amount and spatial distribution of inorganic sediment deposition from each storm. The sediment deposition on coastal wetlands was an estimated 68, 48, and 21 million metric tons from Hurricanes Katrina, Rita, and Gustav, respectively. The spatial distribution decreased in a similar manner with distance from the coast for all hurricanes, but the relationship with distance from the storm track was more variable between events. The southeast-facing Breton Sound estuary had significant storm-derived sediment deposition west of the storm track, whereas sediment deposition along the south-facing coastline occurred primarily east of the storm track. Sediment organic content, bulk density, and grain size also decreased significantly with distance from the coast, but were also more variable with respect to distance from the track. On average, eighty percent of the mineral deposition occurred within 20 km from the coast, and 58% was within 50 km of the track. These results highlight an important link between tropical cyclone events and coastal wetland sedimentation, and are useful in identifying a more complete sediment budget for coastal wetland soils.

Hydrodynamic response of the Breton Sound estuary to pulsed Mississippi River inputs

Pulsed re-introduction of Mississippi River water into the deltaic plain has been proposed as a wetland restoration strategy for coastal Louisiana. In this study, the hydrodynamic response of the Breton Sound estuary to a two-week pulse of Mississippi River water via the Caernarvon river diversion structure was investigated using a barotropic, three-dimensional, Finite-Volume Coastal Ocean Model (FVCOM). The numerical model was driven by tidal and subtidal forcing at the open Gulf boundary, freshwater discharge from the Caernarvon river diversion structure, as well as wind stress at the water surface. After successfully validating the model with field observations, three numerical experiments were run to assess the response of current, water level, and marsh flooding to different diversion discharge scenarios. The three scenarios considered were: a pulsed scenario of ∼200 m 3 s −1 corresponding to the actual diversion discharge in March 2001, a constant discharge scenario of 40 m 3 s −1 corresponding to the annually averaged discharge of 2001, and a scenario with no discharge. Numerical simulation results indicated that constant 40 m 3 s −1 discharge caused little change in wetland inundation comparing to the no discharge case and, thus, inter-exchange between deep channels and the wetlands was not improved by this rate of diversion discharge. In contrast, the two-week ∼200 m 3 s −1 discharge caused enhanced water exchange between wetlands and adjacent water bodies, substantially increasing water velocity in the bayous and channels of the upper estuary. These effects occurred in the estuary to about 20–25 km from the diversion structure, and caused a noticeable increase in down-estuary residual current with a significant reduction of local estuarine residence times for the whole estuary. Beyond 30 km from the diversion structure, the impact of high water discharge was small and the hydrodynamics was mostly controlled by tides and wind.

Relating large-scale climate variability to local species abundance: ENSO forcing and shrimp in Breton Sound, Louisiana, USA

Climate creates environmental constraints (filters) that affect the abundance and distri- bution of species. In estuaries, these constraints often result from variability in water flow properties and environmental conditions (i.e. water flow, salinity, water temperature) and can have significant effects on the abundance and distribution of commercially important nekton species. We investigated links between large-scale climate variability and juvenile brown shrimp Farfantepenaeus aztecus abundance in Breton Sound estuary, Louisiana (USA). Our goals were to (1) determine if a tele- connection exists between local juvenile brown shrimp abundance and the El Nino Southern Oscilla- tion (ENSO) and (2) relate that linkage to environmental constraints that may affect juvenile brown shrimp recruitment to, and survival in, the estuary. Our results identified a teleconnection between winter ENSO conditions and juvenile brown shrimp abundance in Breton Sound estuary the follow- ing spring. The physical connection results from the impact of ENSO on winter weather conditions in Breton Sound (air pressure, temperature, and precipitation). Juvenile brown shrimp abundance effects lagged ENSO by 3 mo: lower than average abundances of juvenile brown shrimp were caught in springs following winter El Nino events, and higher than average abundances of brown shrimp were caught in springs following La Nina winters. Salinity was the dominant ENSO-forced environ- mental filter for juvenile brown shrimp. Spring salinity was cumulatively forced by winter river dis- charge, winter wind forcing, and spring precipitation. Thus, predicting brown shrimp abundance requires incorporating climate variability into models.

The impacts of re-introducing Mississippi River water on the hydrologic budget and nutrient inputs of a deltaic estuary

Most wetlands of the Mississippi deltaic plain are isolated from riverine input due to flood control levees along the Mississippi River. These levees have altered hydrology and ecology and are a primary cause of massive wetland loss in the delta. River water is being re-introduced into coastal basins as part of a large-scale ecological engineering effort to restore the delta. We quantified freshwater, nitrogen, and phosphorus inputs to the Breton Sound Estuary for three climatically different years (2000, 2001, and 2002). Water budgets included precipitation, potential evapotranspiration, the diversion, stormwater pumps, and groundwater. Precipitation contributed 48–57% of freshwater input, while the diversion accounted for 33–48%. Net groundwater input accounted for less than 0.05% of freshwater inputs. Inputs of ammonium (NH 4-N), nitrate (NO 3-N), total nitrogen (TN), and total phosphorus (TP) were determined for each of the water sources. Atmospheric deposition was the most important input of NH 4-N (57–62% or 1.44 × 10 5–2.32 × 10 5 kg yr −1) followed by the diversion. The diversion was the greatest source of NO 3-N (67–83%, 7.78 × 10 5–1.64 × 10 6 kg yr −1) and TN (60–71%). The diversion contributed 41–60% of TP input (1.17 × 10 5–2.32 × 10 5 kg yr −1). Annual loading rates of NH 4-N and NO 3-N were 0.17–0.27 and 1.2–2.3 g N m −2 yr −1, respectively, for the total basin indicating strong retention of nitrogen in the basin. Nitrogen retention through denitrification and burial was estimated for the upper basin.

Restoration of the annual flood pulse in Breton Sound, Louisiana, USA: habitat change and nekton community response

Riverine pulse events are hypothesized to benefit estuarine nekton resources by mak- ing high-quality habitat available for exploitation; however, few studies focus on the actual nekton use of this ephemerally flooded habitat during the flood pulse event. We evaluated the effects of pulsed freshwater flow on nekton density, biomass, diversity and community assembly through 2 winter/spring (February and March) experimental high-flow riverine discharge events in the upper reaches of the Breton Sound estuary, Louisiana, USA in 2005. Nekton were caught with a 1 m 2 drop sampler at flooded vegetated marsh sites in areas both receiving (inflow) and not receiving (refer- ence) pulsed freshwater flow. Inflow marsh sites had significantly greater water depth and were flooded for over twice as long as reference marshes. Significantly higher nekton density and biomass were found at flooded inflow marsh sites than reference marsh sites. Nekton communities were sim- ilar and dominated by estuarine resident species (Palaemonetes paludosus, Heterandria formosa, Gambusia affinis, Lucania parva, Poecilia latipinna, Cyprinodon variegatus). The C-score metric (EcoSim) indicated that while initial colonization (1 to 3 d) of flooded sites was random, species assembly following longer-term flooding (7 to 10 d) suggested non-random colonization (p < 0.0001; EcoSim) and supported the coexistence principle. Despite significant coexistence, subtle differences in community assembly were seen among the resident guild, with evidence of segregation driven by water depth (p = 0.002; canonical correspondence analysis).