We examine the carbon balance of North American wetlands by reviewing and synthesizing the published literature and soil databases. North American wetlands contain about 220 Pg C, most of which is in peat. They are a small to moderate carbon sink of about 49 Tg C yr⁻¹, although the uncertainty around this estimate is greater than 100%, with the largest unknown being the role of carbon sequestration by sedimentation in freshwater mineral-soil wetlands. We estimate that North American wetlands emit 9 Tg methane (CH₄) yr⁻¹; however, the uncertainty of this estimate is also greater than 100%. With the exception of estuarine wetlands, CH₄ emissions from wetlands may largely offset any positive benefits of carbon sequestration in soils and plants in terms of climate forcing. Historically, the destruction of wetlands through land-use changes has had the largest effects on the carbon fluxes and consequent radiative forcing of North American wetlands. The primary effects have been a reduction in their ability to sequester carbon (a small to moderate increase in radiative forcing), oxidation of their soil carbon reserves upon drainage (a small increase in radiative forcing), and reduction in CH₄ emissions (a small to large decrease in radiative forcing). It is uncertain how global changes will affect the carbon pools and fluxes of North American wetlands. We will not be able to predict accurately the role of wetlands as potential positive or negative feedbacks to anthropogenic global change without knowing the integrative effects of changes in temperature, precipitation, atmospheric carbon dioxide concentrations, and atmospheric deposition of nitrogen and sulfur on the carbon balance of North American wetlands.

Terminal mineralization of organic carbon (C) in northern peat soils usually produces more carbon dioxide (CO₂) than methane (CH₄), but the maintenance of microbial CO₂ production is unclear. Carbon dioxide production relies on oxygen (O₂) or alternative (to O₂) electron acceptors (NO₃⁻, Fe(III), SO₄²⁻). We examined rates of CO₂ production and CH₄ production in peat soils from two ombrotrophic bogs and two minerotrophic fens incubated in vitro with and without added glucose (an electron donor) and added electron acceptors. Soil interstitial water had dissolved NO₃⁻ (2–17 µmol L⁻¹) in three sites, and SO₄²⁻ (2–20 µmol L⁻¹) and Fe(III) (0.02–0.8 µmol L⁻¹) in all four sites. Peat soils incubated in vitro without added glucose or electron acceptors had rates of CH₄ production between 0.2 and 1.5 µmol g⁻¹ day⁻¹ and rates of CO₂ production between 8 and 17 µmol g⁻¹ day⁻¹. Added glucose increased CO₂ production in all of the peat soils, although adding an electron acceptor with glucose had no additional impact in the bogs. Nitrate plus glucose had the largest increase in CO₂ production in both fens, and SO₄²⁻ plus glucose enhanced CO₂ production in one fen. Added glucose alone or with O₂ or Fe increased CH₄ production in peat soil from the two bogs, whereas glucose plus SO₄²⁻ or NO₃⁻ inhibited CH₄ production. Glucose plus an electron acceptor inhibited CH₄ production in the forest fen but enhanced CH₄ production in sedge fen. Terminal electron acceptors did not universally divert C and electron flow away from CH₄ production and towards CO₂ production in these peat soils, and thus maintenance of CO₂ production is still uncertain, with no single explanation likely.

This study was conducted in two eutrophic shallow lakes (Lake Honda LH and Lake Nueva LN) that share geographic proximity but have contrasting hydrology, meteorology, biogeochemistry, and geomorphology. Our objective was to explore the inter-annual, seasonal, and daily variability in selected biological, physical, and chemical variables of these two systems. Although the study lakes demonstrated a notable inter-annual and seasonal variation in nutrient concentrations, water transparency was the only variable that was consistently more variable in LH than LN. The reason for the greater temporal variability in water transparency of LH is its major susceptibility to wind and rain events. The impact of wind events in this lake is favored by its shallowness and by its silty surface sediment; the high ratio of catchment area to lake area is responsible for the relatively higher susceptibility of LH to rain events than LN. By contrast, in the younger and deeper LN, ground-water discharge buffers certain water chemistry parameters such as conductivity, turbidity, and alkalinity. Interestingly, differences in turbidity and ground-water discharge do not seem to affect the variability in nutrient concentrations, which was similar between the lakes, although these factors may explain differences between the lakes in nutrient concentrations. This paper reveals that the unpredictability and frequency of events in Mediterranean aquatic ecosystems makes it necessary to increase data collection frequency to obtain more accurate simulations in water quality models.

Saltcedars (Tamarix ramosissima, T. chinensis, and their hybrids) have invaded riverways and lakeshores across the western USA and northern Mexico. In Montana, ornamental plantings of saltcedar have been hypothesized, to varying degrees, to be the origin of nearby, wild populations. To examine this hypothesis, we compared chloroplast and nuclear DNA sequences from 36 ornamental and 182 wild saltcedars from Montana, North Dakota, and Wyoming, USA. We found that ornamental and wild population genotype frequencies were highly dissimilar. Also, genotype frequencies of hypothetical propagule populations under scenarios of random mating, self-fertilization, and clonal reproduction in the ornamental population were highly dissimilar to the genotype frequencies of the wild populations. Assignment tests indicated that the majority of wild genotypes originated from other wild plants, not from ornamental plants. However, ornamental plants could not be excluded as contributors to wild populations because all chloroplast and nuclear haplotypes found in the ornamental plants were found at some frequency in the wild. These findings suggest that while ornamental saltcedars are not the sole source of wild saltcedar, they do have potential to contribute genetic material to an invasion or re-establish a population after existing wild saltcedars are removed.

We examined the effects of hydrology and nutrients on the food webs of ten coastal wetlands on Lake Superior, using published stable isotope food web data for three wetlands and original data from seven additional systems in order to span regional hydrologic and nutrient enrichment gradients. We used a dual-source isotope mixing model to estimate the proportion of carbon in fish that originated from planktonic versus periphytic invertebrates, and we related carbon source to 1) nutrient enrichment, 2) hydraulic residence time, and 3) an index of nutrient loading that incorporates residence time and nutrient concentrations. There was no relationship between nutrient enrichment and the proportion of planktonic versus periphytic C in fish. Proportion of planktonic C in fish increased significantly with hydraulic residence time (F  =  5.68, R²  =  0.42, p  =  0.044). Riverine wetlands generally had lowest proportions of planktonic C in fish, dendritic wetlands were intermediate, and lagoon wetlands had highest proportions. A regression between the loading index and planktonic C in fish was an improvement over the residence time regression (F  =  11.7, R²  =  0.59, p  =  0.009). We conclude that coastal wetland food webs are strongly affected by hydrology and further by nutrient enrichment. This work has implications for the development of food web-based ecological indicators of nutrient enrichment and the use of hydrology as a classification factor in the prediction of nutrient effects on food webs.

Riparian zones are especially dynamic due to occasional river floods that provide powerful physical disturbances. Northern Hemisphere riparian woodlands are often dominated by cottonwoods, and studies in semi-arid ecoregions have indicated associations between flood events and cottonwood colonization. Here, we investigated the association between a major flood and cottonwood recruitment along a mountain river in a humid, forested ecoregion. We investigated riparian processes and black cottonwoods (Populus trichocarpa) along the free-flowing Elk River in the Rocky Mountains of British Columbia between 1993 and 2005, a period with a 1-in-100 year flood in June 1995. We analyzed hydrology, floodplain conditions, and aerial photographs and monitored vegetation establishment and survival. We excavated cottonwood saplings to determine origin and considered spatial patterns of cottonwood colonization. Results revealed that the flood induced channel migration and abrupt avulsion that created extensive barren nursery sites. This enabled prolific cottonwood establishment, but few seedlings from the flood year survived. Survival increased in subsequent years, but mortality remained extensive due to sediment burial, scour by high flows and ice, and drought. The patterns of successful colonization revealed seedling safe sites, survivable locations with appropriate elevation relative to water (0.6 to 2.8 m above base stage) and geomorphic context (<5 cm scour and <40 cm deposition). By 2002, cottonwood saplings covered islands and bars created by the flood, and excavation revealed seedling origin, not from clonal fragments. Clonal root suckers were stimulated by flood scarification, expanding previously established groves. The study confirmed that a major flood enabled extensive cottonwood colonization, but the underlying processes were somewhat different than along adjacent rivers in semi-arid ecoregions. Along the Elk River, sediment erosion and deposition were predominant, producing patches of even-aged cottonwoods, in contrast to the arcuate banding along rivers in drier regions with finer sediments and progressive channel migration. Thus, water was less limiting in the humid ecoregion and geomorphic disturbance was the more vital component of the flood event.

Aerial photographs from 1978, 1990, and 1995 were used to measure historical land-cover changes in the accretion portion of the Lower Delta of the Paraná River in Argentina. Six land-cover types were identified and mapped according to the dominant physiognomy: rushes, marshes, seibo forest, mixed prairies of woody and herbaceous plants, vegetated lagoons, and a human land-use category resulting from anthropomorphic intervention (willow and poplar plantations and tourist or recreational areas). The occurrence and magnitude of changes in cover were estimated through Kappa indices, and transition matrices were calculated in order to represent all possible changes that occur in the landscape. The study area had an increase in island surface of 11.75% from 1978 to 1995. Although the delta is in an active accretion phase, the results indicate that the landscape shows moderate to little changes in the time period analyzed (General Kappa: 1978–1990: 0.75, 1990–1995: 0.79). Rushes are pioneer colonizers of banks, which later give rise to marshes or woody and herbaceous prairies and forests. Marshes and forests are stable systems. The pattern of change in islands does not follow a one-way sequence; on the contrary, two main pathways were identified. In the time period analyzed, human activity increased substantially to the detriment of marshes and native forests. Quantification of landscape-change processes allowed us to construct a probability model of land-cover change and compare our results to the predictions formulated in previous vegetation studies based on plant community analysis.

Assessing the success of created seasonal pools as mitigation for the loss of wooded wetlands is generally based on two or three years of monitoring. We monitored a wetland mitigation site in mid-coast Maine, USA, from 1999 to 2004 to track populations of wood frogs (Rana sylvatica) and spotted salamanders (Ambystoma maculatum) in three created seasonal pools. Our goal was to study breeding patterns for six years to assess if presence of breeding animals in the first three years corresponded with long-term reproductive success and to track changes in vegetation development and hydrology in the mitigated pools. Breeding effort (egg masses/female) and reproductive success (juveniles/egg mass) were assessed using full enclosure drift fence/pitfall trap arrays and egg mass counts. Breeding effort was similar in all three pools for both species. However, for wood frogs, reproductive success was inversely related to hydroperiod and highest in the single pool that successfully replicated the desired seasonal water regime. The other two pools developed permanent and semi-permanent hydroperiods, thereby supporting populations of green frogs (Rana clamitans). Green frog tadpoles within these pools preyed upon wood frog eggs and embryos, causing almost complete losses in the last four years of the study. While spotted salamander reproductive success was also reduced in the permanent pool, spotted salamanders were more successful at producing metamorphs in the presence of green frogs. Over the study period, common cattail (Typha latifolia) dominated the pools, and although wetland vegetation did develop, it was not typical of forested seasonal pools. Our work shows that the presence of breeding amphibians characteristic of seasonal pools in the first three years is not sufficient to determine reproductive success of target species in created pools. Hydrology and canopy cover are elements of critical concern if created pools are to support native amphibian communities associated with seasonal pools.

Terraced salt marsh restoration projects have been designed to maximize edge because the edges between habitat types have been shown to be the most productive locations in Spartina alterniflora salt marshes for nekton and benthic infauna. We compared terraced plots with reference plots to see how much edge was created. We also quantified the differences in the spatial patterns of the habitat in the plots. We found that reference marshes had significantly more habitat diversity and more total low marsh area. We also found that reference marshes had a greater absolute amount of low marsh edge. Yet, we found little difference between terraced restoration marshes and nearby reference marshes in Galveston Bay, Texas, USA in terms of the percent of all habitat-to-habitat edge-type combinations that were aquatic edge (water- or seagrass-to-low marsh interface), and much of the reference marshes' area was in core marsh areas that were not suitable for high fisheries production value. Terracing appears an efficient strategy for the sole purpose of creating aquatic edge for fisheries production but does not appear to match other aspects of reference marshes in terms of their habitat composition or spatial configuration. This study shows the potential for using spatial pattern analysis to monitor restoration projects in the future.

Elevations of six biological indicators of historic water levels and hydric soils at twelve isolated Taxodium ascendens dominated wetlands in west-central Florida, USA were compared with long-term surface-water elevations to evaluate use of the indicators for inferring wetland hydrology when adequate water-level data are unavailable. Indicators included the elevation of Lyonia lucida root crown bases, the inflection point at the angular change of T. ascendens buttress swellings, the lower limit of epiphytic bryophytes (moss collars) growing on T. ascendens trunks, the uppermost elevation of woody adventitious roots of Hypericum fasciculatum, ground elevations at the lowest Serenoa repens, and the ground elevation at the landward-most T. ascendens. Elevations of L. lucida, moss collars, and buttress swellings did not differ (p  =  0.29) and were higher in elevation than the other indicators and hydric soils. Based on wetland water-level records for a recent ten-year period, L. lucida, moss collars, and buttress swellings were inundated 2–3% of the time, other indicators were inundated 13–29% of the time, and hydric soils were inundated 38% of the time. The biological indicators examined can be associated with hydrologic patterns in cypress domes in west-central Florida and may be useful for inferring hydrologic regimes for other regional wetlands.

The presence of live and dead emergent vegetation alters the microbial metabolism of communities within the water column of prairie pothole wetlands. To demonstrate the effects, dissolved CH₄, dissolved O₂, plant densities, and litter densities were measured in transects from emergent vegetation to open water zones. O₂ concentrations were consistently lower and CH₄ concentrations consistently higher in emergent zones. Plant surface cover most likely interferes with gas flux across the air-water interface in the emergent zone, impeding O₂ transport into the water column and impeding CH₄ transport out of the water column. Either directly or indirectly, the presence of emergent vegetation may alter aerobic and anaerobic metabolism; since wet and dry cycles can result in emergent plant cover from nearly absent to nearly 100%, understanding these dynamics over the long-term will require studies over a range of wetland stages.

Eutrophication is still a water quality problem within many watersheds. The Lake Okeechobee Basin, Florida, USA, like many watersheds is impacted by eutrophication caused by excess phosphorus (P). To meet water quality criteria to reduce this impairment, several levels of information on P dynamics within the Basin are required. The use of biogeochemical indices to help determine P retention/release of different landscape units such as wetlands and streams provides useful information on P dynamics. The objective of our study was to determine P retention/release indices for a range of wetland soils and their adjacent stream sediments. We sampled several wetlands and adjacent streams within Okeechobee's Basin, which represented a range of P impacted systems. Regression analyses suggest that a single incubation of sediment/soil equilibrated at 1000 mg P kg⁻¹ was sufficient (> 96% of the time) to estimate maximum P sorption capacity (S_max). Using this single incubation, sampled wetlands had nearly twice the P sorption capacity (238 ± 21 mg P kg⁻¹) of stream sediments (146 ± 14 mg P kg⁻¹). Stream sediments also had a greater P saturation ratio (PSR) than wetland soils, indicating that sediment had a greater potential to release P. Phosphorus sorption under ambient P conditions (soil equilibrated with ambient site water) covaried best with P concentrations in site surface water and, as concentrations increased, P sorption also increased. Finally, we used soil P storage capacity (SPSC) to help estimate the ability of soils and sediments to retain additional P loadings and found that wetland soils had a greater ability to retain P. Phosphorus sorption was predicted equally well (> 73%) using either ammonium oxalate or 1 M HCl extractable Fe and Al. The use of indices to quantify P dynamics of different landscape units can inform watershed management and policies aimed at reducing P loads to receiving water bodies.

To gain a better understanding of the spatial patterns of denitrification potential and related soil properties in created (CW), restored (RW), and natural wetlands (NWs), four CW/RW-NW pairs in North Carolina, USA were sampled. These site pairs spanned a range of hydrogeomorphic (HGM) settings common in the Coastal Plain. It was hypothesized that denitrification enzyme activities (DEAs) and related soil properties of CW/RWs would have less spatial variability than DEAs and soil properties of NWs, as prior land-use and mitigation activities tend to homogenize soil properties. Cochran's C tests indicated that variances were significantly lower in CW/RWs than in NWs for most soil properties, and that for nitrate (NO₃-N), variances were significantly lower in CW/RWs across all HGM settings. Interpolated maps of the soil properties revealed homogeneous distributions of NO₃-N across the CW/RW plots compared to much more heterogeneous distributions of NO₃-N across the NW plots. Multiple stepwise regressions confirmed that either NO₃-N or soluble organic carbon were significant predictors of the DEA at each plot. Interpolated maps of predicted DEA generally showed similar patterns to those of NO₃-N. While some nitrate and DEA hotspots were observed in the CW/RWs, more were present in the NWs. These results indicated that spatial distributions of soil chemical properties and DEAs were considerably different in CW/RWs than in paired NWs. This is the first study to document such differences, suggesting that CWs and RWs with homogeneous soil chemical distributions may not develop the full range of soil biogeochemical processes that occur in NWs.

Multiple factors have caused rapid changes in coastal landscapes in the last half century. Coastal natural areas have been set aside to mitigate some of these changes for habitat preservation, among other goals. However, areas set aside for conservation are not exempt from these rapid changes. A major concern for coastal wetlands is the potential for habitat loss resulting from external land-use changes and sea-level rise, which essentially threaten these natural areas from all sides. In order to quantify these trends, we determined the types and rates of land-use/land-cover conversion in differing coastal sites in the U.S. along the northern Gulf of Mexico from the 1950s to the 1990s using existing National Wetlands Inventory (NWI) habitat data and Geographic Information Systems (GIS). All sites were located in protected areas and contained an intact marsh-to-forest transition. A buffer zone of ~2000 m around each site was also analyzed. Two sites, Mandalay National Wildlife Refuge (MNWR) and the Barataria Preserve Unit of the Jean Lafitte National Historical Park and Preserve (JLNHPP), were located on the Mississippi Deltaic Plain in Louisiana, while the other sites, Grand Bay National Estuarine Research Reserve (GBNERR) and Weeks Bay National Estuarine Research Reserve (WBNERR), were located on the Gulf Coastal Plain in Mississippi and Alabama, respectively. Results showed prevalent marsh loss across all sites in the study, although the rate and type of marsh conversion to other land-cover types varied between the Mississippi Delta sites and the Coastal Plain. In the Delta, marsh was converted to open water along shorelines and in internal patches, but the majority of marsh loss was attributed to scrub-shrub encroachment. In the Coastal Plain, marsh was lost more slowly overall, both along the shoreline and forest-marsh boundary. The main trend in the Coastal Plain was replacement of agricultural areas by forest. The buffers experienced an increase in anthropogenically-modified categories, except for a decrease in agricultural areas. Our study suggests that coastal transitions of the northern Gulf of Mexico have indeed experienced landward and seaward losses and that marsh areas are especially vulnerable. It appears that marshes are not keeping pace with the spatial shifts in the aquatic to terrestrial transition as sea level rises, although results in the Coastal Plain are less conclusive because major land-use changes dominate the trends.

Most aquatic habitats are temporally dynamic, and selection has favored diverse strategies to persist in the face of fluctuating environmental conditions. Isolated wetlands in the southeastern United States harbor high diversities of aquatic and semi-aquatic organisms. However, drought may render these wetlands temporarily unsuitable for many species, sometimes for years at a time. We studied the movement patterns and demography of seven species of semi-aquatic snakes at Ellenton Bay, an isolated 10-ha freshwater wetland in the Upper Coastal Plain of South Carolina, following complete drying of the bay during a drought from 2000 to 2003. Behavioral and population responses varied markedly among species. Cottonmouths (Agkistrodon piscivorus) migrated to and from the wetland annually, fared well, and reproduced during the drought. Banded watersnakes (Nerodia fasciata) suffered a dramatic population decline and apparently did not reproduce, while eastern green watersnakes (N. floridana) were locally extirpated. Black swamp snakes (Seminatrix pygaea) aestivated within the wetland and were less affected by the drought than Nerodia. Interspecific differences in response to drought demonstrate that conservation measures may affect species differently and highlight the importance of terrestrial habitat around wetlands for semi-aquatic reptiles.

We compared growth and survival performance of the detritivorous amphipod Hyalella azteca fed lab-conditioned leaves of either Typha angustifolia (narrow-leaf cattail), Phragmites australis (common reed) sprayed with the herbicide Glypro®, and unsprayed Phragmites in microcosms. Leaves were from plants varying in time of senescence. Herbicide application advanced plant senescence and death by ~3 months, whereas the other two leaf types senesced naturally. Amphipods grew, on average, ~100 µg d⁻¹, and amphipod growth was positively related to fungal biomass on leaves, suggesting that fungi were a key nutritive source. Average fungal biomass was significantly greater on herbicide-treated, early sensecent Phragmites (317 ± 43 µg ergosterol g⁻¹ dry wt.; mean ± 1 SE) and Typha (226 ± 39 µg ergosterol g⁻¹ dry wt.) than on naturally senescent Phragmites (114 ± 21 µg ergosterol g⁻¹ dry wt.). Leaf toughness, an indicator of unpalatability, was greatest on naturally senescent Phragmites leaves. Even so, amphipod growth, survival, and offspring numbers did not differ among litter types, probably because individuals were mainly eating surface biofilms rather than the actual leaf matter, and biofilm abundance was relatively high in all leaf treatments. We also quantified decay rates of each leaf type, and amphipod (Hyalella and Gammarus pseudolimnaeus) abundance in leaves in a Lake Erie coastal marsh (i.e., drowned river mouth) to relate amphipod performance and leaf properties in microcosms to natural patterns. Average rates of leaf breakdown (~10.3 mg d⁻¹ over 126 d) in coarse-mesh litterbags and amphipod numbers in litterbags were similar among leaf types. Leaf mass decreased by ~20% during October but slowed from November to January when amphipod abundance and water temperature sharply declined. An increase in leaf loss from February to March, when Hyalella numbers and water temperatures (~0.1°C) were low, coincided with river channel thawing and opening, suggesting that ice and sediment movement affected litter breakdown. The ability of amphipods to perform, and fungi to grow, equally well on reed and cattail implies that leaf detritus of these macrophytes plays a similar role in marsh detrital food webs.

A dynamic hydrologic model was developed for the Örtülüakar Marsh in Turkey to investigate the causes of water-level decreases observed since the 1990s and to explore potential remediation and sustainability options. Örtülüakar Marsh is a sub-system of the Sultan Marshes ecosystem, a large wetland complex consisting of freshwater marshes and salt-water lakes in the Develi Basin of south-central Turkey. The wetland has experienced significant seasonal and long-term water-level changes after the construction of an irrigation project in the catchment. The model uses a monthly time scale and solves the unsteady water-balance equation. Inputs from precipitation, overland flow, springs and ground water, and outputs due to evapotranspiration and surface flow are represented in the model. The model was calibrated to fit monthly water-level measurements from 1997 to 2003. Sensitivity analyses showed that the model is highly sensitive to evapotranspiration and ground-water inflow. Simulations of several water allocation options suggest that ground-water use should be reduced in the Develi Basin to halt the decline in water level in the Örtülüakar Marsh.

Estimates indicate that nearly half of the world's wetlands have been destroyed or altered as a result of human activities. However, studies investigating the impacts of land-use land cover change on wetlands have shown varied results. Furthermore, when assessing wetlands at the site level, landscape-scale wetland health conditions can go largely unnoticed. The objective of this paper was to investigate wetland quality changes resulting from land-use land cover alterations at a watershed scale. Landscape-pattern metrics were generated to examine changes in wetlands characteristics between 1978 and 2000 in the Muskegon River Watershed, Michigan, USA. Metrics quantifying composition, configuration, and fractal indication were generated and correlated with land-use land cover patterns and alterations. Results show ranging wetland stress with the mid-river portion of the watershed undergoing the highest fragmentation indicated by wetland patch dynamics. Landscape Shape Index, Fractal Dimension Index, and Interspersion and Juxtaposition Index metrics reflect similar spatial trends of decreasing wetlands quality. Agriculture and urban land-use composition had weak to moderate strength correlations with the Interspersion and Juxtaposition Index, respectively. The method was useful for identifying the spatial variability of wetland changes across watersheds and possible regions to focus management and monitoring efforts.

We evaluated a potential index for quantifying wetland floristic quality, based on the Floristic Quality Assessment Index (FQAI) developed and tested in other regions of the United States. Principal reasons for this study were 1) FQAI is based on plant species’ coefficients of conservatism, which are unavailable for most of the world and 2) FQAI value calculation mathematically neglects exotic (non-native) species. The index that we evaluated, termed the Floristic Assessment Quotient for Wetlands (FAQWet), incorporated components of total species richness, wetland affinity of species present, and the contribution of native versus exotic species to wetland vegetation quality. Thus, this index incorporated factors demonstrated to be influenced by the degree of human activity on the landscape while including both native and non-native plant species, and it used information that is readily available for most plant species encountered in wetlands of the United States. Adequacy of this index at representing perceived human influence on wetlands was evaluated by sampling vascular plant assemblages in 53 wetlands across northern Mississippi, USA. Correlation of FAQWet scores with semi-quantitative disturbance indicators suggested that FAQWet Index calculations weighted by proportion and frequency of native species performed best overall and were comparable with the currently used FQAI, although all indices displayed low correlation with indices of human activity. Analyses of individual components of the disturbance index, along with information on hydrogeomorphology and hydrologic alteration, helped account for some unexplained variation in the relationship between floristic quality and disturbance. For example, there were more exotic species and a lower overall degree of wetland affinity in vegetation of depressional wetlands than in lake fringe and riverine wetlands. The most important benefits of the FAQWet index in these studies were a lack of correlation with total plant species richness (unlike the FQAI), a stronger correlation with non-native species richness than was the case with the FQAI, and the ease of obtaining wetland indicator status and nativity status for FAQWet calculations. Results also highlighted the potential danger of ignoring exotic species in floristic assessments because of the relatively strong correlations of non-native species richness with human activity, hydrologic impairment, and floristic index scores.

Wetland surface elevation and vertical accretion were measured from 1996 to 1999–2000 using a sediment elevation table (SET) and feldspar marker horizons in nine paired wetlands receiving Mississippi River water from the Caernarvon, West Pointe a la Hache (WPH), and Violet river diversions. The Caernarvon study sites had wetland surface elevation change rates ranging from 0.16±0.31 to 0.42±0.21 cm y⁻¹. Vertical accretion ranged from 0.75±0.04 to 1.57±0.05 cm y⁻¹, and shallow subsidence ranged from 0.59 to 1.21 cm y⁻¹. Wetland surface elevation at the WPH study sites initially increased 2.3 to 3.3 cm during the first seven months of the study and then steadily decreased over the following year. The overall rate of elevation change ranged from 0.27±0.09 to 0.70±0.11 cm y⁻¹. Vertical accretion and shallow subsidence ranged from 1.24±0.08 to 1.84±0.07 cm y⁻¹ and 0.54 to 1.27 cm y⁻¹, respectively. The Violet sites lost elevation and had the highest subsidence rates in this study, most likely due to a combination of hydrologic alteration and low diversion discharge. Wetland elevation decreased throughout the study, with rates ranging from −1.10±0.24 to −2.34±0.41 cm y⁻¹. Vertical accretion and shallow subsidence rates at the Violet-Near and Far sites were 0.44±0.10 and 0.44±0.11 cm y⁻¹ and 2.78 to 1.54 cm y⁻¹, respectively. The Violet-Mid site wetland was burned in Winter 1999, leading to more than 4.0 cm decrease in material measured over the marker horizon and contributing to the lowest accretion rate measured in this study of 0.34±0.05 cm y⁻¹. Analysis of regional relative sea-level rise (RSLR) indicates that all Caernarvon sites and the WPH-Near and Mid sites are keeping pace with RSLR. This study indicates that the use of river diversions can be an effective coastal restoration tool, with efficiency related to the proximity to riverine source and degree of hydrologic alteration, quantity of river water released, and land uses of the receiving wetland basin. Landscape modifications such as spoil banks associated with oil and gas access canals negate the benefits of river water introduction by limiting wetland-water interaction and should be removed in conjunction with river diversion implementation for effective wetland restoration.

Wetlands often support a variety of juxtaposed habitat patches (e.g., grass-, shrub- or tree-dominated) differentially suited to support the inhabiting fauna. The proportion of available habitat types has been affected by human activity and consequently has contributed to degrading habitat quality for some species. The Florida apple snail (Pomacea paludosa) has drawn attention as a critical prey item for wetlands wildlife and as an indicator of wetlands restoration success in peninsular Florida, USA. An apparent contradiction has evolved wherein this species appears intolerant of drying events, but these disturbances may be necessary to maintain suitable habitat structure for apple snails. We recently reported that assertions regarding intolerance to dry downs in this species were inaccurate. Here, we compared snail density in habitats with (wet prairie) and without (slough) emergent macrophytes, as well as evaluating the effects of structural attributes within the broad wet prairie habitat type. Snail densities were greater in prairies relative to sloughs (χ² = 12.90, df = 1, P = 0.0003), often by a factor of two to three. Within wet prairie habitats, we found greater snail densities in Panicum hemitomon as compared to Eleocharis cellulosa (χ² = 31.45, df = 1, P = 0.0001). Significantly fewer snails were found in dense E. cellulosa as compared to habitats with lower stem density (χ² = 10.73, df = 1, P = 0.011). Our results indicate that wet prairie habitat supports greater snail densities than Nymphaea-dominated slough. Our results have implications for wetlands water management in that continuous inundation has been shown to convert wet prairie to slough habitat, and we suggest this should be avoided in support of apple snails and their predators.

Native riparian cottonwood (Populus deltoides) dominated habitats are declining throughout the southwestern United States and being replaced by the exotic salt cedar (Tamarix ramosissima, T. chinensis) dominated systems. Restoration efforts have often involved removing salt cedar and simulating or restoring overbank flooding timed with seed rain of cottonwood and willow (Salix spp.). Success is then often assessed by examining seedling densities of the native species and their known competitive superiority over salt cedar at this stage. We measured plots in the Middle Rio Grande Valley, New Mexico, USA that had been cleared of salt cedar a decade earlier, compared the initial seedling community to the established community, and determined variables important in predicting establishment of cottonwood. During the decade since establishment, the proportion of cottonwood and seep willow (Baccharis glutinosa) increased, while salt cedar and coyote willow (S. exigua) decreased. Proportion of community foliar volume changed little for salt cedar (17.0 to 17.6%), while it increased for cottonwood (25.5 to 63.3%). Cottonwood dominated (>70%) the overstory. Initially established woody stem density (all species) was the only predictor of the percent of cottonwood canopy cover a decade later as declining coyote willow allowed for greater cottonwood growth. No abiotic variables were important in predictions of subsequent cottonwood community establishment, probably because these variables were similar among sites in this active floodplain. High initial cottonwood and salt cedar seedling densities were related to lower cottonwood foliar volume and smaller individual tree diameters a decade later. Low initial densities of cottonwood allowed individuals to grow rapidly to a greater height, dominating the canopy. Restoration biologists should therefore consider areas that have low initial cottonwood seedling densities as potentially very successful if their goal is to produce a stand of large cottonwoods in a relatively short time.