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Abstract: Here we present results of an initial assessment of the impacts of a water diversion event on the concentrations and chemical composition of dissolved organic matter (DOM) and bacterioplankton community composition in Barataria Bay, Louisiana U.S.A, an important estuary within the Mississippi River Delta complex. Concentrations and spectral properties of DOM, as reflected by UV/visible absorbance and fluorescence, were strikingly similar at 26 sites sampled along transects near two western and two eastern areas of Barataria Bay in July and September 2010. In September 2010, dissolved organic carbon (DOC) was significantly higher (568.1–1043 μM C, x = 755.6 +/− 117.7 μM C, n = 14) than in July 2010 (249.1–577.1 μM C, x = 383.7 +/− 98.31 μM C, n = 14); conversely, Abs254 was consistently higher at every site in July (0.105–0.314) than in September (0.080–0.221), averaging 0.24 ± 0.06 in July and 0.15 ± 0.04 in September. Fluorescence data via the fluorescence index (FI450/500) revealed that only 30% (8 of 26) of the July samples had an FI450/500 above 1.36, compared to 96% (25 of 26) for the September samples. This indicates a more terrestrial origin for the July DOM. Bacterioplankton from eastern sites differed in composition from bacterioplankon in western sites in July. These differences appeared to result from reduced salinities caused by the freshwater diversion. Bacterioplankton communities in September differed from those in July, but no spatial structure was observed. Thus, the trends in bacterioplankton and DOM were likely due to changes in water masses (e.g., input of Mississippi River water in July and a return to estuarine waters in September). Discharge of water from the Davis Pond Freshwater Diversion (DPFD) through Barataria Bay may have partially mitigated some adverse effects of the oil spill, inasmuch as DOM is concerned. [Copyright &y& Elsevier]

The article discusses research investigating a multi-method comparison of surface water organic matter samples taken from the Atchafalaya basin in south-central Louisiana. Researchers isolated surface water organic matter (OM) from two distinct sites within the Atchafalaya basin using a combination of XAD-8 and XAD-4 non-ionic macroporous resins. The samples were then characterized by a suite of analytical methods, including elemental analysis, 13C cross polarization magic angle spinning nuclear magnetic resonance, and attenuated total reflectance Fourier transform infrared. Results of the study, including the similarity between the spectral and elemental signatures of the hydrophobia and transphilic acid fractions of the isolated OM for the various sites, are discussed.

Abstract: Significant amounts of pharmaceuticals are discharged into the environment through wastewater effluent. Sorption has been shown to be a significant aqueous removal pathway for many of these compounds. Competition between ciprofloxacin (CIP), ofloxacin (OFL) and norfloxacin (NOR) and their sorption to, and desorption from, a surrogate Louisiana wastewater treatment wetland soil were investigated to gain insight into the fate and transport of the pollutants within wastewater treatment wetlands. This study was undertaken in the context of a treatment wetland that continuously receives pharmaceuticals. Therefore it is important to understand the total capacity of this soil to sorb these compounds. Sorption to this treatment wetland soil was found to provide a major and potentially long-term removal pathway for these antibiotics from wastewater. Log K F values for all three compounds were between 4.09 and 3.90 for sorption and 4.24 and 4.05μg1−1/ n (cm3)1/ n g−1 for desorption. The compounds were sorbed in amounts ranging from 60% to 90% for high and low loading, respectively. The majority of the compounds were sorbed to the soil within the first 20h, indicating that treatment wetland may not need long retention times (weeks to months) in order to remove these compounds. Sorption K D values for competition (20ppm of each compound for 60ppm of total fluoroquinolones) ranged from 2300 to 3800cm3 g−1 which is between both the 20 (4300–5800cm3 g−1) and 60 (1300–3000cm3 g−1) ppm single compound K D values, indicating that there is competition between these three compound for sorption sites. Sorption and desorption data (single component and mixture) collectively provide the following evidence: (1) NOR and, to a lesser extent, CIP outcompete OFL for sorption sites, (2) OFL sorbes to its share of “quality” sorption sites, and (3) competition only occurs for lesser “quality” binding sites. [Copyright &y& Elsevier]

Marsh edge erosion results in soil organic matter (SOM) loss from coastal wetlands and is differentially affected by wind waves, soil properties, and vegetation cover. The degradation of SOM may make the marsh edge susceptible to erosion. The objective of this study was to investigate the effect of in situ biogeochemical degradations of SOM on marsh edge erosion using porewater spectroscopic analyses. Edge erosion was monitored at 12 transects in one of the highly eroding coastal basins of Louisiana. A total of 36 cores were collected at different distances from the edge of the marsh. Porewater was extracted and analyzed for dissolved organic carbon (DOC) and spectroscopic indicators. The north and west side had greater erosion rates (102.38 ± 5.2 cm yr−1) than east and south side (78.47 ± 3.3 cm yr−1). However, the north and east side had greater DOC and refractory carbon but less microbial activity indicating SOM degradation alone did not correlate to edge erosion. The intersecting trend between erosion rate and SOM degradation among four sides of the island indicates the complex nature of edge erosion drivers. The estuarine bottom indicators suggest the eroded SOM is not reburied but rather degraded and emitted back into the atmosphere as CO 2 , potentially contributing to global change. The coastlines projected to experience high sea-level rise in the coming century are vulnerable to losing a large amount of stored carbon in the absence of efficient mitigation measures. • Significant edge erosion is occurring at relatively "protected" islands. • In situ soil organic matter degradation did not well correlate to marsh edge erosion. • Drivers of edge erosion are complex including waves, soil properties, and organic matter degradation. • The eroded wetland soil organic matter is not reburied in the estuarine bottom. [ABSTRACT FROM AUTHOR]

• Aromatic dissolved organic matter and humification indicators increased with depth. • Bioavailable N and P at 1 m were at least five times greater than at surface. • Depth was a significant control on 18 of the measured 20 parameters. • Soil physicochemical properties were unaffected by erosion and saltwater incursion. • Novel assessment of erosion by biogeochemical, spectroscopic, physicochemical analysis. Coastal wetlands in Louisiana experience high rates of edge erosion due to combined eustatic sea level rise and coastal subsidence. This study sought to (1) evaluate site-specific spatial and temporal patterns in marsh edge erosion rates within Barataria Bay, LA, (2) develop an understanding of the physical and chemical properties of eroding soils through biogeochemical and spectroscopic characterization, and (3) evaluate interactions between erosion, saltwater incursion, and soil properties through a comparison of sites with different erosion rates and varying distances from the eroding edge. Replicate soil cores were collected at three distances inland (1 m, 3 m, 5 m) at three different sites (west, south, and north) to a depth of 1 m. Erosion rates were measured at each site, and soils were sectioned into 10 cm intervals for a total of 270 soil and porewater samples. Each soil sample was subjected to soil physicochemical analysis (bulk density, moisture content, organic matter content, and total carbon (C), nitrogen (N), and phosphorus (P)) as well as assessments of biogeochemical cycling (production of CO 2 , mineralization of N and P, and extractable nutrient concentrations). Porewater samples were analyzed to elucidate spectroscopic and fluorometric indicators of carbon quality (aromaticity, humification, lignin proportion, and C source). Erosion rates at the west, north, and south sites were 3.36 ± 0.4, 1.34 ± 0.2, and 0.58 ± 0.03 m yr−1, respectively. Neither erosional magnitude nor saltwater incursion was found to be significant predictors of any measured spectroscopic or biogeochemical parameters, though depth was a significant control on 18 of the measured 20 parameters. The top 30 cm were more biologically active (as indicated by greater mineralization of C, N and P) and were characterized by lower molecular weight porewater DOM with less aromaticity. Degree of humification and aromaticity of porewater DOM increased with both depth and distance inland. Concentrations of bioavailable N and P at 1 m depth were at least 5 times greater than surface concentrations, representing a pool of nutrients that could be exported into the coastal ocean with ongoing erosion. This study is the first to couple spectroscopic and biogeochemical measurements for the purpose of assessing soil and porewater physicochemistry within wetland soils and illustrates an as-yet unaccounted for potential for the export of labile C, N, and P into the coastal ocean. [ABSTRACT FROM AUTHOR]

The Mississippi River Flood of 2011 prompted the opening of the Bonnet Carré Spillway (BCS) in southeastern Louisiana to protect the City of New Orleans. The BCS diverted approximately 21.9 km(3) of river water into the oligohaline Lake Pontchartrain Estuary over the course of 43 days. We characterized estuarine dissolved organic matter (DOM) dynamics before, during, and after the diversion in order to better understand the biogeochemical dynamics associated with these immense freshwater inflows. Dissolved organic carbon (DOC) exhibited a large degree of variability during and after the period of elevated primary productivity that occurred following the diversion. Furthermore, DOC analysis provides limited insight into carbon cycling during these dynamic periods. In order to overcome the limitations of DOC, spectroscopic methods were used to gain insights into chemical composition dynamics. Both ultraviolet visible (A254, A350, SUVA254, spectral slope, and normalized UV/Vis) and fluorescence spectroscopy (excitation emission matrices and fluorescence and biological indices) were used to study the compositional changes of DOM over time. Collectively, our results document a perturbation in DOM chemistry in Lake Pontchartrain due to the diversion and a subsequent return toward pre-diversion conditions. Immediate increases in A350 indicate that BCS freshwater contained elevated concentrations of lignin of terrestrial origin. Ensuing declines in A350, along with changes in the fluorescence and biological indices, indicate that DOM rapidly became more microbial in composition. Our results provide insights into estuarine DOM dynamics relevant to systems receiving flood pulses of freshwater due to either hydrologic manipulation or precipitation events., (Copyright © 2014 Elsevier B.V. All rights reserved.)