PLFA Analyses of Microbial Communities Associated with PAH-Contaminated Riverbank Sediment

Sediment contaminated with polycyclic aromatic hydrocarbons (PAHs) is widely distributed in aquatic ecosystems. The microbial community structure of riverbank PAH-contaminated sediments was investigated using phospholipid-derived fatty acid (PLFA) analysis. Surface and subsurface riverbank sediment was collected from a highly contaminated site and from an uncontaminated site along the Mahoning River, OH. PAH concentrations, physical sediment characteristics, and other microbial community parameters (biomass as phospholipid phosphate (PLP) and activity) were also measured. PAHs were detected in all samples but were only quantifiable in the contaminated (250?μg/g?g(-1)) subsurface sediment. Subsurface samples from both locations showed very similar PLP values and distribution of PLFAs, with 27-37?% of the microbial community structure being composed of sulfate reducing and other anaerobic bacteria. Principal components analysis indicated no correlation between PAH contamination and PLFA diversity. Although PLP and phospholipid fatty acid measurements of bacterial communities did not reflect the environmental differences among sites, the highly PAH-contaminated sediment showed the highest measured microbial activity (reduction of 1,200?nmol?INT?g(-1)?h(-1)), likely from a population adapted to environmental pollutants, rates that are much higher than measured in many uncontaminated soil and sediment systems. These data warrant further investigation into community structure at the genetic level and indicate potential for bioremediation by indigenous microbes.     

Impact of Coal-Coking Effluent on Sediment Microbial Communities: a Multivariate Approach

The functional response to and recovery from coal-coking waste effluent was evaluated for sediment microbial communities. Twenty estimates of microbial population density, biomass, and activity were measured five times during a 15-month period. Significant effects on microbial communities were observed in response to both wastewater contamination and diversion of the wastewater. Multivariate analysis of variance and discriminant analysis indicated that accurate differentiation between uncontaminated and contaminated sediments required a minimum of nine estimates of community response. Total viable population density, ATP, alkaline phosphatase, naphthalene, and phenanthrene mineralization rates were found to be highly weighted variables in site discrimination. Lipid and glucose mineralization, nitrogen fixation, and sediment protein also contributed significantly to explaining variation among sites. Estimates of anaerobic population densities and rates of methane production contributed little to discrimination among sites in the environment examined. In general, total viable population density, ATP, and alkaline phosphatase activity were significantly depressed in contaminated sediments. However, after removal of this contamination, the previously affected sites demonstrated greater temporal variability but a closer approximation of the mean response at the control site. Naphthalene and phenanthrene mineralization did not follow the general trend and were elevated at the contaminated sites throughout the investigation. Results of the investigation supported the hypothesis that multiple functional measures of microbial community response are required to evaluate the effect of and recovery from environmental contamination. In addition, when long-term effects are evaluated, select physiological traits, i.e., polyaromatic hydrocarbon mineralization, may not reflect population and biomass estimates of community response.     

Relationships between Sediment Microbial Communities and Pollutants in Two California Salt Marshes

Salt marshes are important ecosystems whose plant and microbial communities can alter terrestrially derived pollutants prior to coastal water discharge. However, knowledge regarding relationships between anthropogenic pollutant levels and salt marsh microbial communities is limited, and salt marshes on the West Coast of the United States are rarely examined. In this study, we investigated the relationships between microbial community composition and 24 pollutants (20 metals and 4 organics) in two California salt marshes. Multivariate ordination techniques were used to assess how bacterial community composition, as determined by terminal restriction fragment length polymorphism and phospholipid fatty acid analyses, was related to pollution. Sea urchin embryo toxicity measurements and plant tissue metabolite profiles were considered two other biometrics of pollution. Spatial effects were strongly manifested across marshes and across channel elevations within marshes. Utilizing partial canonical correspondence analysis, an ordination technique new to microbial ecology, we found that several metals were strongly associated with microbial community composition after accounting for spatial effects. The major patterns in plant metabolite profiles were consistent with patterns across microbial community profiles, but sea urchin embryo assays, which are commonly used to evaluate ecological toxicity, had no identifiable relationships with pollution. Whereas salt marshes are generally dynamic and complex habitats, microbial communities in these marshes appear to be relatively sensitive indicators of toxic pollutants.     

Effects of Environmental Toxicants on Metabolic Activity of Natural Microbial Communities

Two methods of measuring microbial activity were used to study the effects of toxicants on natural microbial communities. The methods were compared for suitability for toxicity testing, sensitivity, and adaptability to field applications. This study included measurements of the incorporation of ¹⁴C-labeled acetate into microbial lipids and microbial glucosidase activity. Activities were measured per unit biomass, determined as lipid phosphate. The effects of various organic and inorganic toxicants on various natural microbial communities were studied. Both methods were useful in detecting toxicity, and their comparative sensitivities varied with the system studied. In one system, the methods showed approximately the same sensitivities in testing the effects of metals, but the acetate incorporation method was more sensitive in detecting the toxicity of organic compounds. The incorporation method was used to study the effects of a point source of pollution on the microbiota of a receiving stream. Toxic doses were found to be two orders of magnitude higher in sediments than in water taken from the same site, indicating chelation or adsorption of the toxicant by the sediment. The microbiota taken from below a point source outfall was 2 to 100 times more resistant to the toxicants tested than was that taken from above the outfall. Downstream filtrates in most cases had an inhibitory effect on the natural microbiota taken from above the pollution source. The microbial methods were compared with commonly used bioassay methods, using higher organisms, and were found to be similar in ability to detect comparative toxicities of compounds, but were less sensitive than methods which use standard media because of the influences of environmental factors.     

Modeling Taxa-Abundance Distributions in Microbial Communities using Environmental Sequence Data

We show that inferring the taxa-abundance distribution of a microbial community from small environmental samples alone is difficult. The difficulty stems from the disparity in scale between the number of genetic sequences that can be characterized and the number of individuals in communities that microbial ecologists aspire to describe. One solution is to calibrate and validate a mathematical model of microbial community assembly using the small samples and use the model to extrapolate to the taxa-abundance distribution for the population that is deemed to constitute a community. We demonstrate this approach by using a simple neutral community assembly model in which random immigrations, births, and deaths determine the relative abundance of taxa in a community. In doing so, we further develop a neutral theory to produce a taxa-abundance distribution for large communities that are typical of microbial communities. In addition, we highlight that the sampling uncertainties conspire to make the immigration rate calibrated on the basis of small samples very much higher than the true immigration rate. This scale dependence of model parameters is not unique to neutral theories; it is a generic problem in ecology that is particularly acute in microbial ecology. We argue that to overcome this, so that microbial ecologists can characterize large microbial communities from small samples, mathematical models that encapsulate sampling effects are required.     

Patterns in the Composition of Microbial Communities from a Subtropical River: Effects of Environmental,Spatial and Temporal Factors

Microbes are key components of aquatic ecosystems and play crucial roles in global biogeochemical cycles. However, the spatiotemporal dynamics of planktonic microbial community composition in riverine ecosystems are still poorly understood. In this study, we used denaturing gradient gel electrophoresis of PCR-amplified 16S and 18S rRNA gene fragments and multivariate statistical methods to explore the spatiotemporal patterns and driving factors of planktonic bacterial and microbial eukaryotic communities in the subtropical Jiulong River, southeast China. Both bacterial and microbial eukaryotic communities varied significantly in time and were spatially structured according to upper stream, middle-lower stream and estuary. Among all the environmental factors measured, water temperature, conductivity, PO₄-P and TN/TP were best related to the spatiotemporal distribution of bacterial community, while water temperature, conductivity, NO_x-N and transparency were closest related to the variation of eukaryotic community. Variation partitioning, based on partial RDA, revealed that environmental factors played the most important roles in structuring the microbial assemblages by explaining 11.3% of bacterial variation and 17.5% of eukaryotic variation. However, pure spatial factors (6.5% for bacteria and 9.6% for eukaryotes) and temporal factors (3.3% for bacteria and 5.5% for eukaryotes) also explained some variation in microbial distribution, thus inherent spatial and temporal variation of microbial assemblages should be considered when assessing the impact of environmental factors on microbial communities.     

Environmental Impacts and Scarcity Perception Influence Local Institutions in Indigenous Amazonian Kichwa Communities

Much of the literature on common-pool resources has focused on elucidating the social mechanisms and local institutions that lead to the regulation of common-pool resources. There is much less information about how management regimes translate into environmental impacts or how environmental impacts influence the emergence of management decisions. We use quantitative and qualitative methods to investigate the link between forest condition, agricultural change and the emergence of common-pool resource management regimes in two indigenous Kichwa communities in the Ecuadorian Amazon. We show that forest condition is linked to agricultural production and that the perception of common-pool resource scarcity influences the emergence of management regimes. We argue that population pressure, market forces and resource scarcity, which are usually associated with measures of agricultural change can also promote the emergence of common-pool resource management regimes.     

Microbial Diversity During Cellulose Decomposition in Different Forest Stands: I. Microbial Communities and Environmental Conditions

We studied the effect of forest tree species on a community of decomposers that colonize cellulose strips. Both fungal and bacterial communities were targeted in a native forest dominated by beech and oak and 30-year-old beech and spruce plantations, growing in similar ecological conditions in the Breuil-Chenue experimental forest site in Morvan (France). Microbial ingrowths from the 3rd to 10th month of strip decomposition (May to December 2004) were studied. Community composition was assessed using temperature gradient gel electrophoresis with universal fungal (ITS1F, ITS2) and bacterial (1401r, 968f) primers. Soil temperature and moisture as well as fungal biomass were also measured to give additional information on decomposition processes. Changing the dominant tree species had no significant influence in the number of decomposer species. However, decomposer community composition was clearly different. If compared to the native forest, where community composition highly differed, young monocultures displayed similar species structure for fungi and bacteria. Both species numbers and community composition evolved during the decay process. Time effect was found to be more important than tree species. Nevertheless, the actual environmental conditions and seasonal effect seemed to be even more determining factors for the development of microbial communities. The course and correlations of the explored variables often differed between tree species, although certain general trends were identified. Fungal biomass was high in summer, despite that species richness (SR) decreased and conversely, that high SR did not necessarily mean high biomass values. It can be concluded that the growth and development of the microbiological communities that colonized a model material in situ depended on the combination of physical and biological factors acting collectively and interdependently at the forest soil microsite.     

Functional and Structural Succession of Soil Microbial Communities below Decomposing Human Cadavers

The ecological succession of microbes during cadaver decomposition has garnered interest in both basic and applied research contexts (e.g. community assembly and dynamics; forensic indicator of time since death). Yet current understanding of microbial ecology during decomposition is almost entirely based on plant litter. We know very little about microbes recycling carcass-derived organic matter despite the unique decomposition processes. Our objective was to quantify the taxonomic and functional succession of microbial populations in soils below decomposing cadavers, testing the hypotheses that a) periods of increased activity during decomposition are associated with particular taxa; and b) human-associated taxa are introduced to soils, but do not persist outside their host. We collected soils from beneath four cadavers throughout decomposition, and analyzed soil chemistry, microbial activity and bacterial community structure. As expected, decomposition resulted in pulses of soil C and nutrients (particularly ammonia) and stimulated microbial activity. There was no change in total bacterial abundances, however we observed distinct changes in both function and community composition. During active decay (7 - 12 days postmortem), respiration and biomass production rates were high: the community was dominated by Proteobacteria (increased from 15.0 to 26.1% relative abundance) and Firmicutes (increased from 1.0 to 29.0%), with reduced Acidobacteria abundances (decreased from 30.4 to 9.8%). Once decay rates slowed (10 - 23 d postmortem), respiration was elevated, but biomass production rates dropped dramatically; this community with low growth efficiency was dominated by Firmicutes (increased to 50.9%) and other anaerobic taxa. Human-associated bacteria, including the obligately anaerobic Bacteroides, were detected at high concentrations in soil throughout decomposition, up to 198 d postmortem. Our results revealed the pattern of functional and compositional succession in soil microbial communities during decomposition of human-derived organic matter, provided insight into decomposition processes, and identified putative predictor populations for time since death estimation.     

Quantifying the Human Impacts on Papua New Guinea Reef Fish Communities across Space and Time

Describing the drivers of species loss and of community change are important goals in both conservation and ecology. However, it is difficult to determine whether exploited species decline due to direct effects of harvesting or due to other environmental perturbations brought about by proximity to human populations. Here we quantify differences in species richness of coral reef fish communities along a human population gradient in Papua New Guinea to understand the relative impacts of fishing and environmental perturbation. Using data from published species lists we categorize the reef fishes as either fished or non-fished based on their body size and reports from the published literature. Species diversity for both fished and non-fished groups decreases as the size of the local human population increases, and this relationship is stronger in species that are fished. Additionally, comparison of modern and museum collections show that modern reef communities have proportionally fewer fished species relative to 19^th century ones. Together these findings show that the reef fish communities of Papua New Guinea experience multiple anthropogenic stressors and that even at low human population levels targeted species experience population declines across both time and space.     

Environmental Factors Shape Sediment Anammox Bacterial Communities in Hypernutrified Jiaozhou Bay,China

Bacterial anaerobic ammonium oxidation (anammox) is an important process in the marine nitrogen cycle. Because ongoing eutrophication of coastal bays contributes significantly to the formation of low-oxygen zones, monitoring of the anammox bacterial community offers a unique opportunity for assessment of anthropogenic perturbations in these environments. The current study used targeting of 16S rRNA and hzo genes to characterize the composition and structure of the anammox bacterial community in the sediments of the eutrophic Jiaozhou Bay, thereby unraveling their diversity, abundance, and distribution. Abundance and distribution of hzo genes revealed a greater taxonomic diversity in Jiaozhou Bay, including several novel clades of anammox bacteria. In contrast, the targeting of 16S rRNA genes verified the presence of only “Candidatus Scalindua,” albeit with a high microdiversity. The genus “Ca. Scalindua” comprised the apparent majority of active sediment anammox bacteria. Multivariate statistical analyses indicated a heterogeneous distribution of the anammox bacterial assemblages in Jiaozhou Bay. Of all environmental parameters investigated, sediment organic C/organic N (OrgC/OrgN), nitrite concentration, and sediment median grain size were found to impact the composition, structure, and distribution of the sediment anammox bacterial community. Analysis of Pearson correlations between environmental factors and abundance of 16S rRNA and hzo genes as determined by fluorescent real-time PCR suggests that the local nitrite concentration is the key regulator of the abundance of anammox bacteria in Jiaozhou Bay sediments.Anaerobic ammonium oxidation (anammox, NH₄⁺ + NO₂⁻ → N₂ + 2H₂O) was proposed as a missing N transformation pathway decades ago. It was found 20 years later to be mediated by bacteria in artificial environments, such as anaerobic wastewater processing systems (see reference 32 and references therein). Anammox in natural environments was found even more recently, mainly in O₂-limited environments such as marine sediments (28, 51, 54, 67, 69) and hypoxic or anoxic waters (10, 25, 39-42). Because anammox may remove as much as 30 to 70% of fixed N from the oceans (3, 9, 64), this process is potentially as important as denitrification for N loss and bioremediation (41, 42, 73). These findings have significantly changed our understanding of the budget of the marine and global N cycles as well as involved pathways and their evolution (24, 32, 35, 72). Studies indicate variable anammox contributions to local or regional N loss (41, 42, 73), probably due to distinct environmental conditions that may influence the composition, abundance, and distribution of the anammox bacteria. However, the interactions of anammox bacteria with their environment are still poorly understood.The chemolithoautotrophic anammox bacteria (64, 66) comprise the new Brocadiaceae family in the Planctomycetales, for which five Candidatus genera have been described (see references 32 and 37 and references therein): “Candidatus Kuenenia,” “Candidatus Brocadia,” “Candidatus Scalindua,” “Candidatus Anammoxoglobus,” and “Candidatus Jettenia.” Due to the difficulty of cultivation and isolation, anammox bacteria are not yet in pure culture. Molecular detection by using DNA probes or PCR primers targeting the anammox bacterial 16S rRNA genes has thus been the main approach for the detection of anammox bacteria and community analyses (58). However, these studies revealed unexpected target sequence diversity and led to the realization that due to biased coverage and specificity of most of the PCR primers (2, 8), the in situ diversity of anammox bacteria was likely missed. Thus, the use of additional marker genes for phylogenetic analysis was suggested in hopes of better capturing the diversity of this environmentally important group of bacteria. By analogy to molecular ecological studies of aerobic ammonia oxidizers, most recent studies have attempted to include anammox bacterium-specific functional genes. All anammox bacteria employ hydrazine oxidoreductase (HZO) (= [Hzo]₃) to oxidize hydrazine to N₂ as the main source for a useable reductant, which enables them to generate proton-motive force for energy production (32, 36, 65). Phylogenetic analyses of Hzo protein sequences revealed three sequence clusters, of which the cladistic structure of cluster 1 is in agreement with the anammox bacterial 16S rRNA gene phylogeny (57). The hzo genes have emerged as an alternative phylogenetic and functional marker for characterization of anammox bacterial communities (43, 44, 57), allowing the 16S rRNA gene-based investigation methods to be corroborated and improved.The contribution of anammox to the removal of fixed N is highly variable in estuarine and coastal sediments (50). For instance, anammox may be an important pathway for the removal of excess N (23) or nearly negligible (48, 54, 67, 68). This difference may be attributable to a difference in the structure and composition of anammox bacterial communities, in particular how the abundance of individual cohorts depends on particular environmental conditions. Anthropogenic disturbance with variable source and intensity of eutrophication and pollution may further complicate the anammox bacterium-environment relationship.Jiaozhou Bay is a large semienclosed water body of the temperate Yellow Sea in China. Eutrophication has become its most serious environmental problem, along with red tides (harmful algal blooms), species loss, and contamination with toxic chemicals and harmful microbes (14, 15, 21, 61, 71). Due to different sources of pollution and various levels of eutrophication across Jiaozhou Bay (mariculture, municipal and industrial wastewater, crude oil shipyard, etc.), a wide spectrum of environmental conditions may contribute to a widely varying community structure of anammox bacteria. This study used both 16S rRNA and hzo genes as targets to measure their abundance, diversity, and spatial distribution and assess the response of the resident anammox bacterial community to different environmental conditions. Environmental factors with potential for regulating the sediment anammox microbiota are discussed.     

Oil Impacts on Marine Invertebrate Populations and Communities

It is likely that roughly one billion gallons of oil entersour oceans each year as a result of man's activities. Only 8%of this input is believed to derive from natural sources. Atleast 22% is intentionally released as a function of normaltanker "operational discharges," 12% enters from accidentaltanker spills and another 36% from runoff and municipal andindustrial wastes. Invertebrate populations and communities form the foundationfor marine ecosystems and are continually subjected to stressesfrom both chronic and acute oil toxicity. The diversity of invertebratetaxa represented in the marine environment exhibit a wide rangeof responses to oil. Mortality is an obvious impact resultingfrom catastrophic spills or even chronic toxicity. Sublethalimpacts on individuals are manifested by physiological, carcinogenicand cytogenetic effects. Impacts typically felt at the populationlevel involve changes in abundance, age structure, populationgenetic structure, reproduction and reduced recruitment potential.Community level impacts are typified by modified interactionsbetween competitors, predator/prey and symbionts. Most importantly,changes in community structure represented by altered trophicinteractions tend to produce the most dramatic alterations tonatural invertebrate assemblages. Invertebrate communities respond to severe chronic oil pollutionand/or acute catastrophic oil pollution in much the same way.Initial massive mortality and lowered community diversity isfollowed by extreme fluctuations in populationsof opportunisticmobile and sessile fauna (and flora). Oscillations in populationnumbers slowly dampen over time and diversity slowly increasesto original levels. The time over which these events occur dependson the type of oil, the extent of the initial contamination,habitat type, weather conditions, latitude, the species assemblagesrepresented and a myriad of other complex factors.     

The Influence of Age and Gender on Skin-Associated Microbial Communities in Urban and Rural Human Populations

Differences in the bacterial community structure associated with 7 skin sites in 71 healthy people over five days showed significant correlations with age, gender, physical skin parameters, and whether participants lived in urban or rural locations in the same city. While body site explained the majority of the variance in bacterial community structure, the composition of the skin-associated bacterial communities were predominantly influenced by whether the participants were living in an urban or rural environment, with a significantly greater relative abundance of Trabulsiella in urban populations. Adults maintained greater overall microbial diversity than adolescents or the elderly, while the intragroup variation among the elderly and rural populations was significantly greater. Skin-associated bacterial community structure and composition could predict whether a sample came from an urban or a rural resident ~5x greater than random.     

Microscale Analyses of the Formation and Nature of Microbial Biofilm Communities in River Systems

The review covers aspects of biofilm cultivation, laser scanning microscopy, molecular probes and digital image analyses. This is accomplished through an overview of selected studies which illustrate the application of the microscale approach and laser microscopy techniques to the study of river biofilms and the results obtained.     

Impact of Fumigants on Soil Microbial Communities

Agricultural soils are typically fumigated to provide effective control of nematodes, soilborne pathogens, and weeds in preparation for planting of high-value cash crops. The ability of soil microbial communities to recover after treatment with fumigants was examined using culture-dependent (Biolog) and culture-independent (phospholipid fatty acid [PLFA] analysis and denaturing gradient gel electrophoresis [DGGE] of 16S ribosomal DNA [rDNA] fragments amplified directly from soil DNA) approaches. Changes in soil microbial community structure were examined in a microcosm experiment following the application of methyl bromide (MeBr), methyl isothiocyanate, 1,3-dichloropropene (1,3-D), and chloropicrin. Variations among Biolog fingerprints showed that the effect of MeBr on heterotrophic microbial activities was most severe in the first week and that thereafter the effects of MeBr and the other fumigants were expressed at much lower levels. The results of PLFA analysis demonstrated a community shift in all treatments to a community dominated by gram-positive bacterial biomass. Different 16S rDNA profiles from fumigated soils were quantified by analyzing the DGGE band patterns. The Shannon-Weaver index of diversity, H, was calculated for each fumigated soil sample. High diversity indices were maintained between the control soil and the fumigant-treated soils, except for MeBr (H decreased from 1.14 to 0.13). After 12 weeks of incubation, H increased to 0.73 in the MeBr-treated samples. Sequence analysis of clones generated from unique bands showed the presence of taxonomically unique clones that had emerged from the MeBr-treated samples and were dominated by clones closely related to Bacillus spp. and Heliothrix oregonensis. Variations in the data were much higher in the Biolog assay than in the PLFA and DGGE assays, suggesting a high sensitivity of PLFA analysis and DGGE in monitoring the effects of fumigants on soil community composition and structure. Our results indicate that MeBr has the greatest impact on soil microbial communities and that 1,3-D has the least impact.     

Vegetation-Associated Impacts on Arctic Tundra Bacterial and Microeukaryotic Communities

The Arctic is experiencing rapid vegetation changes, such as shrub and tree line expansion, due to climate warming, as well as increased wetland variability due to hydrological changes associated with permafrost thawing. These changes are of global concern because changes in vegetation may increase tundra soil biogeochemical processes that would significantly enhance atmospheric CO₂ concentrations. Predicting the latter will at least partly depend on knowing the structure, functional activities, and distributions of soil microbes among the vegetation types across Arctic landscapes. Here we investigated the bacterial and microeukaryotic community structures in soils from the four principal low Arctic tundra vegetation types: wet sedge, birch hummock, tall birch, and dry heath. Sequencing of rRNA gene fragments indicated that the wet sedge and tall birch communities differed significantly from each other and from those associated with the other two dominant vegetation types. Distinct microbial communities were associated with soil pH, ammonium concentration, carbon/nitrogen (C/N) ratio, and moisture content. In soils with similar moisture contents and pHs (excluding wet sedge), bacterial, fungal, and total eukaryotic communities were correlated with the ammonium concentration, dissolved organic nitrogen (DON) content, and C/N ratio. Operational taxonomic unit (OTU) richness, Faith''s phylogenetic diversity, and the Shannon species-level index (H′) were generally lower in the tall birch soil than in soil from the other vegetation types, with pH being strongly correlated with bacterial richness and Faith''s phylogenetic diversity. Together, these results suggest that Arctic soil feedback responses to climate change will be vegetation specific not just because of distinctive substrates and environmental characteristics but also, potentially, because of inherent differences in microbial community structure.     

Impacts of Saltwater Incursion on Plant Communities,Anaerobic Microbial Metabolism,and Resulting Relationships in a Restored Freshwater Wetland

Saltwater incursion carries high concentrations of sea salts, including sulfate, which can alter anaerobic microbial processes and plant community composition of coastal freshwater marshes. We studied these phenomena in a recently restored wetland on the coastal plain of North Carolina. We measured water inundation patterns, porewater chemistry, microbial process rates, plant tissue chemistry and iron plaque on plant roots, and quantified plant community composition across a hydrologic and salinity gradient to understand the potential interactions between saltwater incursion and changes in microbial processes and plant communities. Plant communities showed no obvious response to incursion, but were structured by inundation patterns and plant growth form (for example, graminoid versus forb). Saltwater incursion increased chloride and sulfate concentrations in surface and porewater, and drove resulting spatial patterns in anaerobic microbial metabolism rates. Plots experiencing saltwater incursion had higher sulfate reduction rates and were dominated by graminoid plant species (for example, sedges, rushes, and grasses). Graminoid plant species’ roots had greater iron plaque formation than forb and submerged species, indicative that graminoid plant species are supplying more oxygen to the rhizosphere, potentially influencing microbial metabolism. Future studies should focus on how plant and microbial communities may respond to saltwater incursion at different time scales, and on parsing out the influence that plants and microbes have on each other as freshwater wetlands experience sea level rise.