Salt marsh rhizosphere affects microbial biotransformation of the widespread halogenated contaminant tetrabromobisphenol-A (TBBPA)

Estuarine sediments are the repository for a wide range of contaminants. Anthropogenic impacts and variations in the belowground biomass of salt marsh plants potentially select for different sediment microbial communities with different functional capabilities, including the ability to biotransform anthropogenic contaminants. There are large differences in both root morphology and the amount of fine root biomass of Spartina alterniflora and Phragmites australis; Spartina is the species commonly used to replace Phragmites in northeastern US salt marsh restoration projects. Our study compared the effect of these two macrophyte species on sediment microbial communities responsible for the biotransformation of the halogenated flame retardant tetrabromobisphenol A (TBBPA). Sediments were obtained from contaminated and uncontaminated salt marsh field sites in New Jersey. Anaerobic methanogenic sediment microcosms were established and incubated for up to 130 days. TBBPA was reductively dehalogenated resulting in the transient formation of two intermediates, identified as tribromobisphenol A and dibromobisphenol A, and the formation and accumulation of bisphenol A (BPA) as the end product. Spartina sediments from both sites were found to dehalogenate TBBPA more rapidly than the Phragmites or unvegetated sediments, resulting in greater production of BPA. Microbial community diversity as measured by in situ sediment phospholipid fatty acid (PLFA) composition prior to TBBPA exposure, was found to be higher in the uncontaminated sediments; differences in microbial PLFA diversity were not seen in contaminated sediments associated with either the different plant species or unvegetated sediment. The results of this study demonstrate that these two plant species affected sediment microbial community function with respect to dehalogenation capabilities, even though the disturbed and undisturbed sediments varied in microbial community composition.     

Effects of Exotic Plant Species on Soil Properties in Hardwood Forests of New Jersey

Two exotic plant species, Berberis thunbergii and Microstegium vimineum, recently have invaded deciduous hardwood forests in the Northeast. We examined changes in soil properties that may be associated with this invasion in three parks in northern New Jersey. In each park, we collected soil and vegetation data along transects that were established across heavily infested areas and extended into uninvaded forest. The data were analyzed statistically by ANOVA and Canonical Correspondence Analysis (CCA). Significant differences were found between invaded and uninvaded plots in both soil and vegetation characteristics. Invaded areas have fewer oaks (Quercus spp.) in the canopy, and lack the native understory shrubs (Vaccinium spp.). The pH of soils in the invaded areas is significantly higher than in the uninvaded areas, and the litter and organic horizons are thinner. The data cannot show that the exotic species have caused these changes. However, the occurrence of contrasting soils in adjacent areas of native vegetation, with no evidence of differences in land-use history between areas, suggests that such a cause-and-effect relationship exists. We propose a feedback loop involving the exotic plants, and the presence of earthworms to explain these dramatic soil differences.     

Effects of Vegetation Removal and Urea Application on Iron and Nitrogen Redox Chemistry in Riparian Forested Soils

Riparian wetlands are subject to nitrogen enrichment from upgradient agricultural and urban land uses and also from flooding by nitrogen-enriched surface waters. The effects of this N enrichment on wetland soil biogeochemistry may be mediated by both the presence of plants and the presence of redox-active compounds, specifically iron oxides in the soil. Despite the extensive research on wetland N cycling, the relative importance of these two factors on nitrogen is poorly known, especially for forested wetlands. This study evaluates the responses of the N and the Fe cycles to N enrichment in a riparian forested wetland, contrasting vegetated field plots with plots where the vegetation was removed to test the role of plants. Furthermore, in vitro anaerobic incubations of the experimental soils were performed to track Fe chemical changes over time under anoxic or flooded conditions. Wetland soils treated with N in form of urea, as expected, had significantly higher amounts inorganic nitrogen. In the soils where vegetation was also removed, in addition to inorganic nitrogen pool, increase in organic nitrogen pool was also observed. The results demonstrate the role of vegetation in limiting the effects excess urea has on different soil nitrogen pools. Results from anaerobic incubation of the experimental soils demonstrated the effects of N enrichment on the wetland Fe cycle. The effects of excess nitrogen and the role of vegetation on the Fe cycle in riparian wetland soil became more evident during anaerobic incubation experiments. At the end of the field experiment, Fe concentrations in the soils under the treatments were not significantly different from the control soils at the 5% confidence level. However, during the anaerobic incubation experiment of soils collected at the end of the experiment from these plots, the N-enriched soils and the unvegetated soils maintained significantly elevated concentrations of reducible Fe(III) for the initial 2-week period of incubation, and the soils collected from the plots with both the treatments had the highest Fe(III) concentrations. After 20 days of incubation, however, the Fe(III) concentrations decreased to the similar concentrations in all the incubated soils. The study clarifies the roles vegetation play in mediating the effects of N enrichment and also demonstrates that N enrichment does affect wetland redox cycle, which has strong implications on ecosystem services such as water quality improvement.     

The effects of changes in land-use on swamps of the New Jersey Pine Barrens

A qualitative study was made of the vegetation of Pine Barrens swamps, in order to determine whether species composition is altered in sites draining developed lands. Thirty-two sites (half pristine) were examined, and at each, as complete as possible a list of species and relative abundances was compiled. Of a total of 177 species, 73 occurred only in developed sites, and 26 only in pristine sites. The remainder were recorded at both types of sites, but changed in frequency of occurrence. Developed sites tended to lose the herbaceous species characteristic of the region, and to suffer a decrease in the frequency of the characteristic shrub species. In their place, a diverse group of plants, including species from surrounding biogeographic regions, cosmopolitan species, and exotic species, invaded the developed sites; these invaders were mostly herbaceous, and included a large number of vine species. Because of this influx of new species, developed sites had greater species richness (mean of 34 species per site) than did the pristine sites (28 species per site). Polar ordination and an ANOVA of coefficients of community similarity showed that pristine sites were significantly more similar to each other (mean similarity 29%) than to the developed sites (inter-type similarity 20%). Thus, land use changes in the Pine Barrens substantially degraded the character of the region's wetlands.The results of the study suggest several general principles concerning the conservation of wetlands.     

Partitioning of lead in pristine and runoff-impacted waters from acidic wetlands in the New Jersey Pinelands

We have examined the roles of dissolved organic carbon (DOC) and pH in determining patterns of Pb fractionation in surface water from Sphagnum-dominated peatlands in undisturbed and urbanized watersheds of the Pinelands of New Jersey. In undisturbed wetlands, the water is highly acidic (pH 3.5) and has high concentrations of DOC; wetlands receiving urban runoff are less acidic and have lower concentrations of DOC. The effects of PH were separated from the effects of DOC by experimentally raising the pH of water from the undisturbed site to 6.0. A separation procedure was compiled from the literature to separate the soluble Pb fraction into labile (exchangeable on ion-exchange resin) and non-labile fractions, and the latter fraction was further separated into photo-oxidation-sensitive and insensitive fractions. In low pH, high DOC waters, 95% of added PbCl₂ remained soluble, and 56 to 80% of this Pb was labile (varying with contact time with the resin). In high-pH swamp waters, a smaller fraction (64 to 71%) remained soluble; the distribution of the soluble Pb among non-labile forms varied with the source of the water. Pb fractionation in runoff was quite different from that in runoff-impacted swamp water at the same pH, and may reflect differences in DOC and/or higher levels of Fe in the runoff.