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Emerging organic contaminants (EOCs) include a diverse group of chemical compounds, such as pharmaceuticals and personal care products (PPCPs), pesticides, hormones, surfactants, flame retardants and plasticizers. Many of these compounds are not significantly removed in conventional wastewater treatment plants and are discharged to the environment, presenting an increasing threat to both humans and natural ecosystems. Recently, antibiotics have received considerable attention due to growing microbial antibiotic-resistance in the environment. Constructed wetlands (CWs) have proven effective in removing many EOCs, including different antibiotics, before discharge of treated wastewater into the environment. Wastewater treatment systems that couple conventional treatment plants with constructed and natural wetlands offer a strategy to remove EOCs and reduce antibiotic resistant bacteria (ARB) and antibiotic resistance genes (ARGs) far more efficiently than conventional treatment alone. This review presents as overview of the current knowledge on the efficiency of different wetland systems in reducing EOCs and antibiotic resistance., (Copyright © 2020 Elsevier Ltd. All rights reserved.)

The relationship between nutrient removal and loading rate was examined using data from five forested wetlands in Louisiana that have received secondarily treated effluent from 3 to 60 years. Loading rates ranged from 0.65 to 26.80 g/m(2)/yr for total nitrogen and 0.18 to 8.96 g/m(2)/yr for total phosphorus. At loading rates below 20 g/m(2)/yr, total nitrogen concentrations in surface waters of Louisiana forested wetlands were reduced to background concentrations (i.e., < or =3 mg/l). Similarly, at loading rates below 2 g/m(2)/yr, total phosphorus concentrations were also generally reduced to background concentrations (i.e., < or =1 mg/l). These data demonstrate that freshwater forested wetlands can reduce nutrient concentrations in treated effluent to background concentrations present in relatively undisturbed wetlands. An understanding of the relationship between loading rates and nutrient removal in natural wetlands is important, particularly in Louisiana where discharges of fresh water are being used in ecosystem restoration.

Hurricanes Katrina and Rita showed the vulnerability of coastal communities and how human activities that caused deterioration of the Mississippi Deltaic Plain (MDP) exacerbated this vulnerability. The MDP formed by dynamic interactions between river and coast at various temporal and spatial scales, and human activity has reduced these interactions at all scales. Restoration efforts aim to re-establish this dynamic interaction, with emphasis on reconnecting the river to the deltaic plain. Science must guide MDP restoration, which will provide insights into delta restoration elsewhere and generally into coasts facing climate change in times of resource scarcity.

The fragility of the world's deltas is not solely a consequence of rising ocean waters. Human fresh water use is a predominant force behind receding coastlines. [ABSTRACT FROM AUTHOR]

Flood control levees cut off the supply of sediment to Mississippi delta coastal wetlands, and contribute to putting much of the delta on a trajectory for continued submergence in the 21st century. River sediment diversions have been proposed as a method to provide a sustainable supply of sediment to the delta, but the frequency and magnitude of these diversions needs further assessment. Previous studies suggested operating river sediment diversions based on the size and frequency of natural crevasse events, which were large (>5000 m 3 /s) and infrequent (active < once a year) in the last naturally active delta. This study builds on these previous works by quantitatively assessing tradeoffs for a large, infrequent diversion into the forested wetlands of the Maurepas swamp. Land building was estimated for several diversion sizes and years inactive using a delta progradation model. A benefit-cost analysis (BCA) combined model land building results with an ecosystem service valuation and estimated costs. Results demonstrated that land building is proportional to diversion size and inversely proportional to years inactive. Because benefits were assumed to scale linearly with land gain, and costs increase with diversion size, there are disadvantages to operating large diversions less often, compared to smaller diversions more often for the immediate project area. Literature suggests that infrequent operation would provide additional gains (through increased benefits and reduced ecosystem service costs) to the broader Lake Maurepas-Pontchartrain-Borgne ecosystem. Future research should incorporate these additional effects into this type of BCA, to see if this changes the outcome for large, infrequent diversions. [ABSTRACT FROM AUTHOR]

This research presents the initial results of the effects of hydrological restoration on forested wetlands in the Mississippi alluvial plain near Memphis, Tennessee. Measurements were carried out in a secondary channel, the Loosahatchie Chute, in which rock dikes were constructed in the 1960s to keep most flow in the main navigation channel. In 2008-2009, the dikes were notched to allow more flow into the secondary channel. Study sites were established based on relative distance downstream of the notched dikes. Additionally, a reference site was established north of the Loosahatchie Chute where the dikes remained unnotched. We compared various components of vegetation composition and productivity at sites in the riparian wetlands for two years. Salix nigra had the highest Importance Value at every site. Species with minor Importance Values were Celtis laevigata, Acer rubrum, and Plantanus occidentalis. Productivity increased more following the introduction of river water in affected sites compared to the reference. Aboveground net primary productivity was highest at the reference site (2926 ‡ 458.1 g·m-2 year-1), the intact site; however, there were greater increase at the sites in the Loosahatchie Chute, where measurements ranged from 1197.7 ‡ 160.0 g m-2 year-1 to 2874.2 ‡ 794.0 g·m-2 year-1. The site furthest from the notching was the most affected. Pulsed inputs into these wetlands may enhance forested wetland productivity. Continued monitoring will quantify impacts of restored channel hydrology along the Mississippi River. [ABSTRACT FROM AUTHOR]

The City of Hammond, Louisiana began discharging secondarily-treated municipal effluent into Four Mile Marsh in the northwestern Joyce wetlands during fall of 2006. At the time discharge began, these wetlands had been isolated from virtually all freshwater inflow from the surrounding watershed for over a half century, due primarily to the construction of canals and spoil banks. Immediately following effluent discharge in 2006, there was robust growth of herbaceous vegetation. By late fall 2007, the emergent wetlands in the immediate vicinity of the effluent discharge began to decline, and within months nearly the entire marsh south of the discharge pipe had converted to open water or mudflat. By 2010, there had been substantial recovery of the marsh. A number of hypotheses have been presented to explain the degradation of the marsh to open water and mudflats, including herbivory by the introduced rodent nutria ( Myocastor coypus ), excessive nutrients, reductions in above- and belowground biomass, increased soil decomposition due to high nutrients, prolonged inundation, toxicity, increased pH, and disease. Intensive field and mesocosm studies provide conclusive data that the marsh loss was primarily caused by nutria herbivory, and secondarily by waterfowl herbivory, and that recovery of the herbaceous vegetation occurred as a result of aggressive nutria control (>2000 eliminated). Marsh recovery has been most intensive near the point of discharge. Mature baldcypress growing in the area of discharge had growth rates that were five times those of trees not receiving effluent in the lower Joyce area and Maurepas swamp. Field and mesocosm studies show that nutrients increased both above- and belowground biomass and did not increase decomposition rates of herbaceous vegetation. Increased flooding due to lack of drainage from the area is hindering marsh recovery. [ABSTRACT FROM AUTHOR]

Abstract: We investigated two adjacent wetlands in the Lake Pontchartrain basin, one of which receives periodic input of Mississippi River water and one which does not, to gain insight into how isolation from river input impacts wetland loss in the Mississippi delta. The LaBranche (LB) wetlands bordering Lake Pontchartrain are severely degraded due to saltwater intrusion, subsidence, leveeing of the river, and hydrologic alterations including partial impoundment. Directly adjacent is the Bonnet Carré (BC) spillway, a geomorphically similar area that contains healthy baldcypress swamp. The spillway carries river water to the lake during high discharge years and has been opened eleven times in 80 years, with flows as high as 9000m3 s−1. The primary hydrologic difference between the two areas is the regular input of River water to the BC wetlands while the LB wetlands are isolated from the river. The interior of the LB wetlands is also isolated from sediment originating from Lake Pontchartrain. Long-term accretion, tree growth, and elevation were measured in these two wetland areas to determine impacts of riverine input. 137Cs accretion rates in the BC wetlands were 2.6–2.7cmyr−1, compared to 0.43 and 1.4cmyr−1, respectively, in the LB wetlands in areas without and with sediment input from Lake Pontchartrain. Baldypress growth in the BC averaged about 2.3mmringwidthyr−1, compared to 1.4mmyr−1 in LB. Trees are of relatively the same age due to lack of recruitment and widespread logging. Tree height, an indicator of site quality, is about 20% less at the LB sites compared to BC, even though the trees are approximately the same ages. The average wetland elevation in the BC wetlands was about one meter with some areas higher than two meters, and was significantly higher than elevations in the LB (average sea level and 0.3m, respectively, in areas with and without input from Lake Pontchartrain). [Copyright &y& Elsevier]

Abstract: Academicians and government officials have advocated incorporating ecosystem services into environmental policy-making processes. The State of Louisiana has adopted policy guidelines for using natural wetlands to assimilate nutrients in secondarily treated municipal effluent, thus utilizing ecosystem services of natural wetlands. We describe a case study for the city of Breaux Bridge, Louisiana, to discuss policy guidelines and assess ecological and financial benefits of this approach. In addition to water quality improvement, wetland assimilation provides additional ecosystem services, including increased vegetative productivity, surface accretion, and carbon sequestration. Financially, using wetland assimilation at Breaux Bridge generated an economic savings of $1.8 million in capital costs and annual savings of $72,116 for operation and maintenance costs, resulting in nearly $3 million savings over the lifetime of the project, due to its low capital expenditures and high energy efficiency, compared with a sand filtration method. When considering rapidly depleting non-renewable resources (e.g., fossil fuels) and challenging financial situations of small communities across the nation, wetland assimilation can be an important factor in designing sustainable communities. [Copyright &y& Elsevier]

A Tree Sparrow Passer montanus colony has now been in existence at Big Waters Nature Reserve for over fourteen years. The colony, located in a typical rural wetland habitat, became established in nest boxes originally provided for titmice and has since expanded to over thirty pairs. This account describes the development of the colony, and an analysis of data derived from monitoring breeding behaviour, productivity and the patterns of dispersal of juvenile and adult birds. The development of the colony over a fourteen-year period reverses an earlier trend for the Tree Sparrow as a declining species in the county and the colony may have formed the nucleus for the recent expansion of the Tree Sparrow in south-east Northumberland. [ABSTRACT FROM AUTHOR]

Abstract: From 1990 to 2004, we carried out a study on accretionary dynamics and wetland loss in salt marshes surrounding two small ponds in the Mississippi delta; Old Oyster Bayou (OB), a sediment-rich area near the mouth of the Atchafalaya River and Bayou Chitigue (BC), a sediment-poor area about 70km to the east. The OB site was stable, while most of the marsh at BC disappeared within a few years. Measurements were made of short-term sedimentation, vertical accretion, change in marsh surface elevation, pond wave activity, and marsh soil characteristics. The OB marsh was about 10cm higher than BC; the extremes of the elevation range for Spartina alterniflora in Louisiana. Vertical accretion and short-term sedimentation were about twice as high at BC than at OB, but the OB marsh captured nearly all sediments deposited, while the BC marsh captured <30%. The OB and BC sites flooded about 15% and 85% of the time, respectively. Marsh loss at BC was not due to wave erosion. The mineral content of deposited sediments was higher at OB. Exposure and desiccation of the marsh surface at OB increased the efficiency that deposited sediments were incorporated into the marsh soil, and displaced the marsh surface upward by biological processes like root growth, while also reducing shallow compaction. Once vegetation dies, there is a loss of soil volume due to loss of root turgor and oxidation of root organic matter, which leads to elevation collapse. Revegetation cannot occur because of the low elevation and weak soil strength. The changes in elevation at both marsh sites are punctuated, occurring in steps that can either increase or decrease elevation. When a marsh is low as at BC, a step down can result in an irreversible change. At this point, the option is not restoration but creating a new marsh with massive sediment input either from the river or via dredging. [ABSTRACT FROM AUTHOR]

Abstract: This study reports on the response of a tidal, freshwater forested wetland ecosystem to long-term input of secondarily treated municipal effluent from the City of Mandeville, LA. Measurements of hydrology, nutrients, and aboveground net primary productivity were made from September 1998 through March 2002. Accretion measurements were made in October 2000 and October 2004. The major hydrologic inputs to the system were the effluent, precipitation, and back water flooding from Lake Pontchartrain. Nutrient levels were generally low except in the immediate vicinity of the outfall. Mean net primary production of the freshwater forest system was significantly higher downstream of the effluent discharge (1202gm−2 yr−1) compared to the control site (799gm−2 yr−1). Downstream of the outfall, accretion rates were double the rate of relative sea level rise in the area. Removal efficiencies of N and P were as high as 75% and 95%, respectively. The relatively constant flow of secondarily treated municipal effluent buffered the downstream area from salinity intrusion during a region-wide drought. Re-direction of nutrient-enhanced effluents from open water bodies to wetland ecosystems can maintain plant productivity, sequester carbon, and maintain coastal wetland elevations in response to sea-level rise in addition to improving overall surface water quality, reducing energy use, and increasing financial savings. [Copyright &y& Elsevier]

Abstract: Louisiana has had a high rate of coastal wetland loss due mainly to the isolation of the Mississippi River from the deltaic plain. We conducted a feasibility analysis of using once-through, non-contact industrial cooling water for restoring subsiding forested wetlands in coastal Louisiana. We considered the impacts of heated water and high nutrient and sediment concentrations. River diversions introduce sediments and nutrients to stimulate the productivity and accretion of coastal wetlands. Since increases in sediments and nutrients can cause water quality problems, we analyzed the assimilative capacity of the swamp. Based on a loading rates analysis, we estimated that the following nutrient reductions would occur: 75% for NO3, 50% for TN, 60–75% for TP, and 100% for suspended sediments. Because of the concern of impacts from heated water, it is likely that the temperature of the cooling water will have to be decreased before discharge. Altering the duration and location of the discharge are ways to minimize the impact of temperature. We recommend that a pilot study be carried out to determine the effects of heated water on the functioning of the system, the retention of sediments and nutrients, and the impacts of different discharge scenarios. [Copyright &y& Elsevier]

Abstract: Nutrient dynamics, net aboveground primary productivity (NPP), and benthic macroinvertebrates were measured in a Louisiana tidal, freshwater forested wetland that received secondary treated effluent for 27 years. NO3, NH4, TKN, PO4, TP concentrations were measured at treatment and control sites. TKN (2.0–4.0mg/L), NH4–N (0.4–1.0mg/L) and NO3–N accounted for almost 75%, 25% and less than 1% of TN, respectively. PO4 (0.1–0.9mg/L) was about 50% of TP. TN and TP were reduced by 79% and 88%, respectively, as water flowed through the wetland, which is consistent with low loading rates of 9.4g N and 1.2g P/m2/yr. Litterfall was significantly greater in the treatment site (717g/m2/yr) than one of the control sites (412g/m2/yr). Stem growth (302–776g/m2/yr) was not statistically different among the sites. Total NPP was highest at treatment sites (1467 and 1442g/m2/yr) which were statistically higher than one of the control sites (714g/m2/yr). Total individuals, total species, and species richness of macroinvertebrates were greatest near the outfall and declined away from the discharge. In summary, long-term addition of secondarily treated municipal effluent resulted in a high level of nutrient retention, enhanced forest productivity, and minimal impact on benthic community structure. [Copyright &y& Elsevier]

Abstract: Nitrate-nitrogen retention as a result of river water diversions is compared in experimental wetland basins in Ohio for 18 wetland-years (9 years×2 wetland basins) and a large wetland complex in Louisiana (1 wetland basin×4 years). The Ohio wetlands had an average nitrate-nitrogen retention of 39g-Nm−2 year−1, while the Louisiana wetland had a slightly higher retention of 46g-Nm−2 year−1 for a similar loading rate area. When annual nitrate retention data from these sites are combined with 26 additional wetland-years of data from other wetland sites in the Basin Mississippi River (Ohio, Illinois, and Louisiana), a robust regression model of nitrate retention versus nitrate loading is developed. The model provides an estimate of 22,000km2 of wetland creation and restoration needed in the Mississippi River Basin to remove 40% of the nitrogen estimated to discharge into the Gulf of Mexico from the river basin. This estimated wetland restoration is 65 times the published net gain of wetlands in the entire USA over the past 10 years as enforced by the Clean Water Act and is four times the cumulative total of the USDA Wetland Reserve Program wetland protection and restoration activity for the entire USA. [Copyright &y& Elsevier]