Many New England salt marshes remain tide-restricted or are undergoing tidal restoration. Hydrologic manipulation of salt marshes affects marsh biogeochemistry and vegetation patterns, but responses by fishes and decapod crustaceans (nekton) remain unclear. This study examines nekton habitat-use patterns in the tide-restricted Hatches Harbor salt marsh (Provincetown, Massachusetts) relative to a downstream, unrestricted marsh. Nekton assemblages were sampled in tidal creek, marsh pool, and salt marsh surface habitats. Pools and creeks were sampled every two weeks for one year to account for seasonal variability, and the marsh surface was sampled at two-week intervals in summer and fall. Density, richness, and community composition of nekton in creek and marsh surface habitats were similar between the unrestricted and restricted marsh, but use of pools differed drastically on the two sides of the tide-restricting dike. In 95% of the cases tested, restricted marsh habitats provided equal or greater habitat value for nekton than the same habitat in the unrestricted marsh (based on density), suggesting that the restricted marsh did not provide a degraded habitat for most species. For some species, the restricted marsh provided nursery, breeding, and overwintering habitat during different seasons, and tidal restoration of this salt marsh must be approached with care to prevent losses of these valuable marsh functions.

Results of long-term field studies of wetlands in four different hydrogeologic and climatic settings in the United States indicate that each has considerably different sources of water, which affects their response to climate variability and land-use practices. A fen wetland in New Hampshire is supplied almost entirely by ground water that originates as seepage from Mirror Lake; therefore, stream discharge from the fen closely follows the pattern of Mirror Lake stage fluctuations. A fen wetland in northern Minnesota is supplied largely by discharge from a regional ground-water flow system that has its recharge area 1 to 2 km to the east. Because of the size of this wetland's ground-water watershed, stream discharge from the fen has little variability. A prairie-pothole wetland in North Dakota receives more than 90 percent of its water from precipitation and loses more than 90 percent of its water to evapotranspiration, resulting in highly variable seasonal and annual water levels. A wetland in the sandhills of Nebraska lies in a regional ground-water flow field that extends for tens of kilometers and that contains numerous lakes and wetlands. The wetland receives water that moves through the ground-water system from the upgradient lakes and from ground water in local flow systems that are recharged between the lakes. The difference in sources of water to these wetlands implies that they would require different techniques to protect their water supply and water quality.

Small-scale spatial patterns in abundance on the salt marsh surface were examined by comparing microalgal pigment concentrations and densities of meiofauna and macrofauna between interculm and interplant microhabitats in low-elevation edge natural and created marshes of Galveston Bay, Texas, USA. The interculm microhabitat consisted of sediments located within clusters of Spartina alterniflora culms, and the interplant microhabitat was located between clusters of culms. Paired interculm and interplant sediment samples were taken from 16 marshes in both fall and spring. No significant differences were found in concentrations of chlorophyll a or pheophytin a between microhabitats. The biomass of macroorganic matter was significantly greater in the interculm microhabitat. The meiofauna was dominated by nematodes and the macrofauna by annelid worms and peracarid crustaceans. Mean densities of almost all meiofaunal and macrofaunal taxa were greater in interculm samples, although not all differences were statistically significant. No taxa had significantly greater densities in interplant samples. Although sampling techniques can affect results, these data agree with small-scale distributional data from other low-elevation, salt marsh habitats. The interculm microhabitat should be considered when sampling organisms in salt marshes, as well as the more typically sampled interplant microhabitat. The interculm microhabitat at Galveston occupied between 9.5 and 31.9% of the marsh surface.

At the scale of ecosystems and regions, numbers of nesting long-legged wading birds are often highly variable from year to year, and much of this variation is thought to reflect variation in production or availability of prey animals in wetlands. Based on observations during and following a severe drought in the Florida Everglades (1989–1992), we predicted that large nesting events would be more likely immediately following droughts than at other times. Using a 38-year history of wading bird nesting events in the Florida Everglades, we tested the hypothesis that “supranormal” annual nesting events (numbers of nests >1 standard deviation above the long-term mean) would occur more frequently during the period of up to two years after severe droughts (stages <1 standard deviation below the mean) than after non-drought years. Within this database, we identified 8 supranormal events and 8 severe droughts; 7 of the nesting events occurred immediately after a drought, and 7 of the droughts were followed by a supranormal nesting event. There was a highly significant association between the two types of events. Because many studies suggest that wading bird reproduction is food-limited, this result implies that post-drought conditions somehow result in exceptional productivity and/or availability of small fishes and macroinvertebrates. We propose two biological mechanisms for this pattern and suggest that rare, severe droughts in the Everglades are a forcing function for wading bird population cycles and large-scale movements through the action of pulsed productivity in the aquatic food web.

Although relationships of birds to patch area and habitat characteristics have been dominant themes in avian ecology over the past few decades, relatively little is known about these relationships in wetland-dominated landscapes of the Great Lakes coastline. During 1997 and 1998, we surveyed birds and measured habitat characteristics along transects in wet meadows associated with the northern Lake Huron shoreline (NLHS) in the Upper Peninsula of Michigan. Using a suite of multivariate techniques, we related abundance and presence/absence of individual species to wet meadow area and habitat characteristics. Nine species were positively associated with increasing wet meadow area, which underscores the importance of large wetlands to avian conservation in the region. Bird variables also were related to habitat characteristics. Higher values of bird variables were generally associated with a suite of characteristics: more robust and dense grass/sedge vegetation, structural diversity in the horizontal and vertical planes, and increased frequency of willow shrubs. Individual species that require particular aspects of these characteristics for nesting or foraging were associated with principal components containing those aspects. In the NLHS, large wet meadows that possess these characteristics would support the greatest diversity and benefit the majority of species. However, conservation efforts that focus only on these traits will not be sufficient for all species because habitat requirements for some species are very specific (e.g., open water for mallard), and for others, habitat preferences may change from year to year in response to lake-level changes. While our results provide important insights, continued research is needed to further the successful conservation and management of birds in Great Lakes coastal wetlands.

This study describes the results of wetland construction projects designed to offset wetland losses authorized under the wetland regulatory program of the Commonwealth of Massachusetts, including analysis of 391 project files identified in the study period between 1983 and 1994 and 114 field sites. Detailed comparisons of replacement plant communities were made with remnant impacted wetlands when these existed. Most projects in the study were relatively small, impacting less than 46.5 m² (500 ft²) of wetland. The majority of projects (54.4%) were not in compliance with the Massachusetts wetland regulations for a variety of reasons, including no attempt to build the project (21.9%), insufficient size or hydrology (29.8%), or insufficient cover of wetland plants (2.6%). Many of the projects constructed (64.9%) were smaller than required. The majority of constructed projects involved impacts to forested wetlands (71.1%). Most replication projects were designed to produce scrub/shrub systems (61.4%), but projects actually built produced no wetland (38.6%), wet meadows (36.8%), or some other wetland type (24.5%). The plant communities produced at replication sites differed significantly from the wetlands they were designed to replace in terms of number of species, cover, and species composition. The similarity of the replication site plant communities did not increase between projects that were new and projects up to 12-years old, indicating that impacted plant communities may not be replaced at most sites for many years, if at all. The completeness of the replication plan and the Order of Conditions (permit) affected the likelihood that a project complied with the regulations but not the level of similarity between the replicated and impacted plant communities. Larger projects constructed under variances from the Massachusetts Wetland Protection Act were much more carefully designed and were all in compliance with the regulations. However, their plant communities were not similar to those of the impacted wetlands they replaced. Variance projects generally provided replication of water quality and sediment control functions but not of wildlife habitat. The state's goal of no net wetland loss cannot be met unless the regulatory program succeeds in compensating for all authorized wetland impacts.

Plant communities of tidal freshwater marshes fluctuate in composition seasonally and among years, but the influence of changes in hydrology on vegetation of these systems has not been examined. We investigated the effects of hydrology on vegetation of tidal freshwater marshes along the Patuxent River in Maryland, USA with a two-year field experiment, a one-year greenhouse experiment, and a seed-bank experiment. In the field experiment, sections of marsh soil and vegetation (“sods”) were elevated 10 cm, lowered 10 cm, or placed level with the marsh surface to simulate different hydrologic regimes. In the greenhouse experiment, sods were raised 10 cm above water surface (nonflooded) or flooded by 10 cm of water in tanks continuously, and in two other treatments changed from nonflooded to flooded or vice-versa after the first 35 days. For the seed-bank experiment, soil samples were spread in a 1-cm-thick layer in pans subjected to flooding by 3.5–4 cm of water or nonflooded but moist conditions in the greenhouse, and emerging seedlings counted. We found that lowering marsh sods by 10 cm (i.e., wetter conditions) in the field reduced plant species richness by 26% compared to the sods placed level with the marsh surface, while raising sods by 10 cm (drier conditions) increased richness by 42%. Total stem length of a majority of the most common species, as well as for all species combined, was more than twice as great in raised sods as in lowered sods. We observed similar patterns in richness and total stem length in the greenhouse study, where continuously nonflooded sods had almost twice the richness and 55% greater total stem length as continuously flooded sods. Sods that were flooded initially and then shifted to nonflooded conditions had richness and total stem length similar to the continuously flooded sods, while sods that were nonflooded initially and then flooded had richness and total stem length intermediate to continuously nonflooded and continuously flooded sods. In the field and greenhouse studies, species that are annual or annnual/perennial were more inhibited by flooding than were perennials. In the seed-bank experiment, flooding reduced the number of species emerging by 50% and total densities of emerging seedlings by 80% compared to nonflooded conditions. Taken together, the results of the field, greenhouse, and seed-bank studies indicate that 3–10 cm of flooding can significantly reduce seedling recruitment and growth in many plant species of tidal freshwater marshes and result in lower plant diversity. The greenhouse study further indicates that shallow flooding early in the growing season can reduce the abundance of certain species, primarily annuals, for the remainder of the growing season, resulting in a less diverse community. These findings suggest that hydrology is a dominant environmental variable controlling interannual variation in plant species composition of tidal freshwater marshes. Additionally, this study suggests that small increases in frequency and duration of inundation, which might occur due to watershed land-use changes, sea-level rise, or land subsidence, will reduce the diversity of these plant communities.

Small seasonal ponds are abundant in many forest landscapes, yet they remain poorly understood in terms of their response to disturbance of the surrounding upland forest. The potential for such a response is large because of the small size and, hence, high perimeter-to-area ratios of most ponds. High perimeter-to-area ratio may increase the importance of functional connections with the surrounding forest, via exchange of energy, organisms, and materials. To better understand this connection, we studied 19 seasonal ponds across a 100-year chronosequence of single-cohort forests in northern Minnesota. Our objective was to see if there are distinct changes over time in select pond attributes, which may reflect alteration of functional linkages with the surrounding forest. In 1998 and 1999, we sampled hydroperiod, water depth and chemistry, canopy openness, grass, sedge, shrub, and coarse woody debris cover, coarse particulate organic matter (CPOM) flux, and macroinvertebrate and amphibian populations. We related these variables to stand age through regression. Stand age explained little variation for most variables. Responsive variables included canopy openness and CPOM flux. Canopy openness, in turn, was related positively to total macroinvertebrate abundance, sensitive taxon richness, and Haliplidae beetle and Physidae snail abundances. Calling wood frogs occurred more frequently under an open canopy and low CPOM flux. An open canopy, which occurs more often over ponds in younger than in older forest, likely results in increases in water and air temperatures and photosynthetically active radiation, all of which may influence resource availability and habitat suitability for some macroinvertebrates and amphibian taxa. Results from our exploratory study suggest that many characteristics of small seasonal ponds are unaffected by harvest of the adjacent upland forest, at least as detected through examination of a chronosequence. However, responsive variables may include several abiotic characteristics that provide mechanistic links to pond foodwebs

We characterized canopy disturbance patterns in a bottomland hardwood forest and identified linkages to tree species characteristics and interannual flooding patterns. We located 116 newly formed canopy gaps created by 136 gapmakers of 13 species. Over 83% of the gapmakers were snapped or uprooted (i.e., windthrow). The probability of any given gapmaker snapping or uprooting differed among years, species, and elevations. Neither wood properties nor diameter were major factors in determining the probability of snapping versus windthrow. Quercus texana, which had individuals with larger diameters-at-breast height than trees of other dominant species, was the most frequent gapmaker. The effects of elevation and flooding on the probability of snap versus windthrow seem to be tempered or amplified by interspecific rooting habits and tree morphology. Across species, windthrow occurred at lower elevations than snaps, and Q. texana and Q. lyrata showed differences in elevation between the two disturbance types. The total amount of area in newly-formed canopy gaps, as well as gap size, was relatively low compared to estimates for other forests. Our results suggest that natural disturbance patterns in bottomland hardwood forests are complex and are affected by the interactions among forest structure and composition and flooding patterns.

We examined the effects of beaver impoundments on the benthic macroinvertebrate assemblages of two small Appalachian streams, Mountain Run (Somerset County, Pennsylvania) and a tributary to Herrington Creek (Garrett County, Maryland). Benthic macroinvertebrate assemblages above the impoundments were compared with assemblages within the impoundments and 1 m, 10 m, and 100 m below the impoundments. The results of our study indicate that beaver affect both within-impoundment and downstream benthic macroinvertebrate assemblages. Taxonomic and functional changes in benthic macroinvertebrate assemblages of the beaver-altered streams were a result of direct (impoundment) and indirect (changes in temperature, water chemistry, plant growth) alterations of the stream environment.

Testate amoebae are common inhabitants of moist soils, wetland, and lacustrine habitats. They produce a decay-resistant test, or shell, which can be identified to species in most cases and recovered from sediments in quantities sufficiently large to permit estimation of relative abundance. The objectives of this study were to assess the potential of testate amoeba assemblages as paleoenvironmental and environmental indicators in two Lake Superior coastal wetlands and to determine if morphological variation in four common taxa (Arcella spp., Assulina spp., Centropyxis cassis type, and Nebela tincta-parvula-collaris group) is related to microenvironment. Study localities included ridge-swale wetland systems adjacent to Grand Traverse Bay and Tahquamenon Bay in the Upper Peninsula of Michigan. Testate amoeba assemblages from 74 microsites were compared with percent moisture, depth to water table, pH, porosity, depth of living moss, and associated moss and vascular plant species. Morphometric analysis (e.g., test length and aperture diameter) was conducted on 25 individuals from at least 10 microsites for each of the four selected taxa. Gradient analysis indicated that testate amoeba assemblages are primarily controlled by substrate moisture and pH, consistent with results from other regions. Transfer functions for pH and substrate moisture were developed using ‘jack-knifed’ validation procedures. Little relationship was found between microenvironmental parameters and morphological variation in the investigated taxa, except for the Nebela tincta-parvula-collaris group, where test size was significantly correlated with pH (r² = 0.68). Results indicate that wetland testate amoeba assemblages in these coastal wetland systems are sensitive environmental and paleoenvironmental indicators that can be used to monitor and reconstruct water-level or pH changes.

The faunal composition, richness, and their determinant factors were analyzed in a Mediterranean temporary pond located in NE Spain. The aquatic community was sampled weekly over 7 periods of flooding during 4 years (1996–1999). Composition of the pond community was found to be influenced by duration of the hydroperiod and, secondarily, by seasonality. Insects and crustaceans were the most well-represented types of fauna. The small numbers of species captured over all hydroperiods spend the dry periods in situ or have an important dispersal capacity. Comparison of the faunal composition of several temporary ponds of temperate latitudes confirms the great diversity of faunal groups found in temporary aquatic environments, and this richness is comparable to that found in permanent water bodies. The richness of these temporary ponds is related to flooded surface and to hydroperiod duration. The peculiarity of the fauna of temporary waters, together the deteriorating condition of those habitats, make it necessary for more active policies of preservation to be pursued.

Purple loosestrife (Lythrum salicaria) is an invasive wetland perennial that is thought to threaten the ecological integrity of North American wetlands by forming monotypic stands and altering the diversity of native wetland ecosystems. To determine if purple loosestrife infestation alters aquatic invertebrate communities, the abundance and size distribution of aquatic invertebrates associated with purple loosestrife were quantified during the spring and summer and compared to those within stands of two other commonly occurring emergents, cattail (Typha latifolia) and bulrush (Scirpus acutus). Aquatic invertebrates representing 10 taxa (classes or orders) were collected using four different sampling techniques. Individuals from each taxa were collected in all three vegetation types, although the size of the individuals of some orders was smaller in Lythrum. Measurements of water quality indicated no significant (p ≤ 0.05) differences among the three vegetation types, despite the fact that Scirpus tended to be established in deeper water than Lythrum. Results indicate that monotypic stands of purple loosestrife are not lacking in aquatic invertebrates; however, because our study was conducted in a mixed vegetation wetland at an intermediate stage of purple loosestrife infestation, our findings may not be representative of more extreme purple loosestrife invasions.

The Lower Mississippi Alluvial Valley (LMAV) originally supported at least 10 million ha of bottomland hardwood (BLH) forests. Many of these forests were wetlands and provided a diversity of values that were not recognized fully until at least one-half of the original forested area had been converted primarily to row-crop agriculture. Efforts to restore these forests have expanded in proportion to growing recognition of their unique values. This paper provides a summary resulting from a survey of BLH afforestation by all agencies and private entities in Arkansas, Louisiana, and Mississippi, the three states in the LMAV with the most restoration activity and, more specifically, by the U.S. Fish and Wildlife Service, the U.S.D.A. Natural Resources Conservation Service, and state wildlife management agencies, the three entities responsible for approximately 95% of the afforestation in this region. There is a promising trend in the annual increase of BLH afforestation across the LMAV. Approximately 71,000 ha have been planted with BLH species through 1998; however, this represents <1% of the BLH forests that have been lost, and afforestation does not ensure restoration of all ecological functions. No clear choice between planting stocks (bareroot seedlings or direct seeding) or among planting seasons (Fall, Winter, Spring, or Summer) is prevalent among those involved in BLH afforestation. Much of the early afforestation used oaks (Quercus spp.) to accelerate replacement of mast-bearing species. Recently, mixtures of species have been incorporated into afforestation regimes. More light-seeded species and a more diverse component of oak species have been planted to mimic a more natural regeneration process. Successful wide-scale afforestation is a critical link in restoration of functional BLH ecosystems in this region.

Difficulties in accurately calculating evapotranspiration (ET) in wetlands can lead to inaccurate water balances—information important for many compensatory mitigation projects. Simple meteorological methods or off-site ET data often are used to estimate ET, but these approaches do not include potentially important site-specific factors such as plant community, root-zone water levels, and soil properties. The objective of this study was to compare a commonly used meteorological estimate of potential evapotranspiration (PET) with direct measurements of ET (lysimeters and water-table fluctuations) and small-scale root-zone geochemistry in a natural and constructed wetland system. Unlike what has been commonly noted, the results of the study demonstrated that the commonly used Penman combination method of estimating PET underestimated the ET that was measured directly in the natural wetland over most of the growing season. This result is likely due to surface heterogeneity and related roughness effects not included in the simple PET estimate. The meteorological method more closely approximated season-long measured ET rates in the constructed wetland but may overestimate the ET rate late in the growing season. ET rates also were temporally variable in wetlands over a range of time scales because they can be influenced by the relation of the water table to the root zone and the timing of plant senescence. Small-scale geochemical sampling of the shallow root zone was able to provide an independent evaluation of ET rates, supporting the identification of higher ET rates in the natural wetlands and differences in temporal ET rates due to the timing of senescence. These discrepancies illustrate potential problems with extrapolating off-site estimates of ET or single measurements of ET from a site over space or time.

In the upper reaches of estuaries, the pulsing of nutrient inputs and salinity occurs on fine temporal and spatial scales. We investigated the supply and exchanges of N, P, and S along a salinity gradient in a Chesapeake Bay subestuary. Interactions among nutrients in surface water, sediment porewater, and shoots of the dominant marsh macrophyte Spartina alterniflora were also examined. The system was characterized by a spatial gradient in nutrient availability, with the low salinity region representing abundant allochthonous nitrogen and phosphorus inputs and minimal sulfur availability. Autochthonous production and consumption of nutrients were most important at the midpoint of the salinity gradient. These patterns were reflected in the N, P, and S content of S. alterniflora over one growing season. This brackish tidal creek system also had a gradient of temporal variability in levels of inorganic nitrogen, phosphorus, and sulfur. The higher salinity portion experienced the damping effect of waters of more constant nutrient composition, whereas the upper portion of the system was characterized by highly pulsed nutrient availability. Interchanges between nutrient pools were apparent throughout the system. Sediment, and even surface-water, concentrations of nutrients seemed to respond to plant root zone oxidation and uptake and release of nutrients. Porewater biogeochemical processes were linked to surface-water nutrient dynamics as well.

Needs for environmental information have led to more emphasis on surveys that assess changing environmental conditions. In order to obtain biological, physical, and chemical measures of environmental change, it is critical to obtain repeated access to research sites. Use of established survey methodology can improve access rates to private property in order to visit randomly selected research sites. Surveys initiated by the U.S. Environmental Protection Agency's Environmental Monitoring and Assessment Program (EMAP) were conducted in 1995 and 1996 in Eastern North Dakota to monitor environmental conditions in prairie wetlands. These surveys required written permission from landowners to access private property. A summary of survey research methods designed to improve access rates to sites on private property is presented. Approximately 20% of the landowners who granted access did so in response to telephone calls after attempts by mail failed. The data show that a disproportionate number of accessible sites were located on non-agricultural lands, particularly in 1996. Owners of sites where agricultural land abutted wetlands tended to deny access. This may introduce bias in the monitoring data. A weighting class adjustment procedure was applied to account for any nonresponse bias resulting from denied access. This procedure deals with the imbalance from denied access and at least partially returns a balance to the collected data.