Over the past several decades, populations of the common reed, Phragmites australis, have expanded rapidly in salt marshes of coastal North America, creating dramatic changes in community composition. Populations of Phragmites in coastal wetlands of the Great Lakes may similarly threaten the ecological integrity of these inland wetland communities. Strategies for the conservation of biodiversity in these wetlands should be informed by an understanding of both the recent trends and the historic role of Phragmites in these wetlands. A combination of paleoecological and genetic analyses was used to determine when Phragmites became established in a Lake Superior coastal wetland and whether the source of Phragmites was native or non-native populations. Radiocarbon-dated stratigraphic changes in the abundance of pollen and macroscopic plant remains were used to infer the timing of vegetation changes in the wetland. From about 1100–490 ¹⁴C yr ago, low water levels were associated with a lowland conifer forest with wetland swales at this site. At about 490 BP, conifers became less common, and peatlands became established at the site, perhaps in response to higher water levels in the wetland. There is no evidence that Phragmites grew at the site until the last several decades, suggesting that it is not native to this wetland and that its recent expansion may create significant changes in the wetland community. However, genetic data from chloroplast DNA sequences and microsatellite markers indicate that it is a variety that is native to North America and common throughout the Midwest. Our results suggest that human-induced changes in the landscape in combination with long-term environmental changes may play an important role in the expansion of native Phragmites populations.

Descriptive studies are an important first step in developing assessment models for regional wetland subclasses. Objectives of this study were to gather benchmark information on the composition and structure of vegetation from minimally impacted riparian forested wetland sites in Michigan, USA, and to determine if species composition of the breeding bird community and relative densities of individual species varied among riparian and adjacent upland forest zones. Plant species richness, dominance, and structure differed greatly between floodplain wetlands and uplands and were similar among zones within floodplain forests. Of 54 breeding bird species recorded through point count surveys (1998–99), 39 were observed in both floodplain and upland forests, while 11 were found only in floodplains and 4 solely in the uplands. Detectable patterns of avian density across riparian and upland forest zones were evident for 31 breeding species. Most species preferred areas closest to the river over other zones, although a few species were more prevalent within interior floodplains or uplands as compared to riverside forests. Forested riparian wetlands in this region act as essential breeding habitats for many avian species not often found in upland areas and are especially important for obligate riparian species and rare or declining breeding birds observed within our sites. These results are consistent with many studies across North America, where riparian forests have been found to support disproportionately large numbers of breeding bird species as compared to more xeric forests and other upland habitats.

Studies were undertaken on seeds of the summer annual mudflat species Ammannia coccinea and Rotala ramosior to determine the (1) effects of flooding during late autumn to late spring on dormancy break and (2) optimum temperature for dormancy break. At maturity in autumn, about 65–100% of the seeds of these species were dormant. Seeds of both species buried under flooded and under nonflooded conditions in a nonheated greenhouse germinated to 70–98% at 30(day)/15(night)°C and at 35/20°C the following June or July; seeds required light for germination. As dormancy break occurred, seeds of R. ramosior showed a decrease in the minimum temperature for germination, but those of A. coccinea did not. In another experiment, seeds buried under nonflooded conditions in the nonheated greenhouse were flooded in November, December, February, March, April, or May, and all flooded seeds and nonflooded controls were exhumed and tested in July. With few exceptions, seeds of both species flooded for short (May–July) or long (November–July) periods germinated to significantly higher percentages over a range of temperatures when exhumed in July than did seeds that had not been flooded. In a third experiment, seeds of both species were incubated on moist sand in darkness at 5, 15/6, 20/10, and 30/15°C for 0, 3, 6, 9, and 12 wk and then tested in light at 15/6, 20/10, 25/15, 30/15, and 35/20°C. The optimal temperature regime for dormancy break in seeds of R. ramosior and A. coccinea was 20/10 and 30/15°C, respectively. In the nonheated greenhouse, some dormancy break began in buried seeds of both species during late autumn and winter, and it continued as temperatures increased in spring and/or early summer. The ability of seeds of both species to come out of dormancy during flooding at field temperatures from late autumn to early summer means that seeds are nondormant when mudflats become dewatered in summer.

The chironomid fauna living on an exotic macrophyte, Eurasian water milfoil (Myriophyllum spicatum), was studied quantitatively for a year in experimental ponds constructed to simulate reservoir wetlands. A total of 10 species, 2 Orthocladiinae, 5 Chironominae, and 3 Tanypodinae, were recorded. Of these 10 chironomid species, Apedilum elachistum comprised 79% of all chironomid larvae collected on the plants. Annual production of A. elachistum was estimated by the size-frequency method to be 9.9 g dry mass/m²/yr for milfoil surface area, which is among the highest production estimates reported for a single species. Annual production/biomass was 79/yr. Laboratory-reared larvae required an average of 23 days at 15°, 16 days at 20°, and 11 days at 25 °C to complete their development from first instar to imago.

Numerous landscape depressions on the High Lava Plain of southeast Oregon, USA are ponded in most years, but their wetland status has not been examined closely. We applied the standard wetland criteria (hydrology, soils, and vegetation) to one such pool to evaluate whether the pool meets federal criteria as a jurisdictional wetland. Wetland hydrology was determined to be present based on data from piezometer and ponding observations. Soils were determined to be hydric based on hydrology, soil temperature, and redox potentials. Vegetation met wetland criteria according to the 50/20 rule. Vegetation was similar to that of California Northern Basalt Flow vernal pools. Oregon pools are locally called “upland playas,” but they fit the definition of vernal pools. Many southeast Oregon vernal pools are dug out as waterholes for livestock, increasing ponding depth and duration. Increased water availability can alter biological communities within pools and on surrounding semi-arid uplands. Effects due to grazing and excrement inputs have not yet been investigated. Vernal pools constitute distinct habitat sites within semi-arid landscapes and, therefore, probably play an important, and so far poorly understood, ecological role on the southeast Oregon steppe.

A cluster of artesian springs encircled by mounds of marsh and wet meadows was discovered near the equator in Kenya, East Africa. Each spring is capped by a dense fibrous root mat that covers a mound of clayey peat with a blister of water in the center. Individual mounds are ∼15 m wide, 1–2 m high, and affect an area of ∼50 m². The central water-blister volume is <1 m³. The arched semi-permeable vegetation cap appears to be buoyed upward by slow artesian flow that leaks through the cap and moves slowly away. Lush plant growth (Poaceae and Cyperaceae, algae, diatoms, and filamentous cyanobacteria) is supported even through the dry season (Dec.–Feb.). The term “artesian blister wetland” is proposed for this unusual marsh, which has not been described previously. Approximately 20 small, circular-to-oval artesian blister wetlands occur within a large spring and wetland complex (∼1.3 km²) that includes several freshwater Typha marshes fed by ground-water seeps. The springs discharge along a rift-related fracture system near the contact between volcanic bedrock and late Quaternary sediments. Cores (1–2 m) through the mounds revealed a dense root mat underlain by water in the center and a clayey peat that is locally pebbly at the base surrounding the blister. LOI in the clayey peat decreases from 75% at surface to ∼10% at 0.4–1.2 m. Blister water is cool, fresh, and dysaerobic (T = 30–33 °C; pH = 6.2–7.2; conductivity ∼600 ìS/cm; and DO = 50%; 0.6–3.5 mg/l). The spring/wetland mounds likely form by the blanketing of the land around the spring orifice with vegetation (paludification). Plants and cyanobacteria seem to trap sediment transported by surface run-off and wind. The mound grows with time, but its height is limited by the magnitude of the hydraulic head. These ecological niches are important freshwater resources for animals and humans in semi-arid environments.

Seed fall from the parental plant and subsequent dispersal by tidal water flow were investigated in Aeschynomene virginica (sensitive joint-vetch) in order to understand how these processes may affect local population regeneration and inter-population seed exchange. Local seed fall was estimated using seed traps around four isolated plants. Plots enclosed on all four sides by mesh fences were compared to plots with the streamside open to examine seed dispersal by water flotation. Seed flotation times and stream flow rates were then used to estimate the potential for water dispersal of seeds after they have fallen to the soil. Ninety-four percent of all seeds fell within 0.5 m of maternal plants, with an exponential decrease in dispersed seeds with distance from the base of parental plants. More seeds left open plots than completely enclosed plots, but there was no difference between the number of seeds leaving plots that had standing vegetation and those without vegetation. At least 50% of the seeds placed in water remained floating after 28.4 hours, and 5% remained floating after 81.8 hours. Water flow rates in wetlands where A. virginica occurs naturally may carry seeds over 2600 m from the maternal plant, representing a significant potential for water dispersal of seeds in this species. Seed movement out of patches may impact population dynamics of the patch from which the seeds leave. Dispersing seeds cannot contribute to the population in that patch the following season. Seed dispersal may also represent an important mechanism for a species such as A. virginica, which specializes in open, newly created habitats, to find and colonize new habitat patches.

Four wetland restoration sites in the Emeralda Marsh Conservation Area located in central Florida, USA were flooded between 1992 and 1994. Florida Fish and Wildlife Conservation Commission stocked largemouth bass in the flooded areas from 1992 to 1996. In 1996, organochlorine pesticides (OCPs) were measured in flooded soils and in black crappie, brown bullhead catfish, and largemouth bass from the four sites. Areas 5 and 7 had the highest concentrations of total residual OCPs in the flooded soils, including dieldrin (385 ± 241 μg/kg), sum of DDT, DDD, and DDE (7,173 ± 1,710 μg/kg), and toxaphene (39,444 ± 11,284 μg/kg). Sum of chlordane residuals was highest in area 5 (1,766 ± 1,037 μg/kg). ANOVA indicated significant differences in location and fish muscle tissue concentrations for chlordane residuals, DDT residuals, and dieldrin. Fish from areas 5 and 7 had the greatest concentrations of chlordane residuals, DDT residuals, and dieldrin, which corresponded to the higher soil concentrations in these two areas. OCPs in muscle tissue were below the U.S. Food and Drug Administration action limits for human consumption. For three-year-old bass collected from Area 5, mean concentrations of chlordane residuals, DDT residuals, and dieldrin were 15–17 times higher in ovary tissue and 76–80 times higher in fat tissue compared with muscle tissue. Mean toxaphene levels in bass ovary and fat tissues were 9 and 39 times higher, respectively, than in muscle tissues. Tissue OCP concentrations were consistent with site OCPs, regardless of fish species.

The capacity of Phragmites australis to extract nutrients from its environment and to store them in plant tissue was studied in an infiltration wetland used for wastewater treatment. The aims of the study were to estimate the contribution of plant uptake to the overall nutrient removal efficiency of the wastewater treatment system and to determine measures to enhance the nutrient removal efficiency. The functional response of Phragmites australis to nutrient addition was studied at two levels of nutrient availability by comparing a wetland used for wastewater treatment with a natural, undisturbed wetland. In the nutrient-rich wastewater wetland, biomass production, nutrient content of plant tissue, shoot/root ratios, and translocation rates were much greater than in the natural wetland. In contrast, plant nutrient-use efficiencies of both nitrogen and phosphorus were much lower in the wastewater wetland. The lower nutrient-use efficiencies were probably due to (1) lower nutrient productivity, which was probably due to self-shading resulting in a lower photosynthetic activity, and (2) lower mean nutrient residence time, which can be explained by a higher litter production (higher shoot and leaf turnover). In the wastewater wetland, harvesting during winter removed only 9% of the total nitrogen input and 6% of the total phosphorus input associated with the loading of wastewater. The low nutrient removal efficiency by aboveground plant harvesting is caused by translocation of nutrients from shoots and leaves to rhizomes and roots in autumn. Nutrient removal efficiency of the wastewater wetland could be enhanced by 40–50% by harvesting at peak nutrient storage levels in the aboveground plant parts in August or September.

We present a Hydrogeologic Setting (HGS) framework and the results of subsequent field evaluation for minerotrophic fens throughout New York State, USA. HGS uses a hierarchical approach to link landscape properties to local environmental gradient and, therefore, the plant communities that are associated with calcareous wetlands. This framework was organized into three general classes (i.e., chemical, physical, and spatial), which cumulatively represent the primary top-down factors driving fen occurrence. For 45 fen sites in the New York Natural Heritage Program (NYNHP) database, landscape setting was inferred based on review of published materials (e.g., geologic, topographic, soils maps, and reports). To examine the relationship between HGS and local environmental gradients, nested observation well clusters were placed in 30 of the fen sites. Environmental gradients were quantified in the field (e.g., water depth, pore water pH, temperature, and specific conductivity) and laboratory (e.g., dominant ion and major limiting nutrients concentrations). Statistical analyses were used to relate HGS to local environmental gradients, ecological community, and fen indicator species occurrence. Results suggest that known New York fens occupy distinct hydrogeologic settings, that HGS is significantly correlated to local environmental gradients, and that HGS and local environmental gradients are significantly related to fen ecological community and indicator species occurrence. We used this HGS framework for fens, but the rationale provided may be applied more broadly or narrowly to a range of ecosystem types.

We report the results of an intensive study of forest structure and composition across a 1.4-m elevation gradient from the top of a natural levee into the backswamp of Bayou Des Familles, Jean Lafitte National Park, Jefferson Parish, Louisiana, USA. At the southernmost edge of the great bottomland hardwood forest of the Lower Mississippi Alluvial Valley (LMAV), forests of the Bayou Barataria-Des Familles distributary are undergoing rapid subsidence with resulting increased flood frequency, depth, and duration. We used data from a 4.6-ha permanently marked plot to examine patterns of distribution and regeneration in forest trees. Non-metric multidimensional scaling ordination of 23 quadrats (20 x 100 m) from this plot showed variation in forest composition across this 1.4-m elevation gradient corresponding to bottomland hardwood forest Zones III (semipermanently flooded) through V (temporarily flooded). A comparison of the size-frequency distributions of common species in upper, middle, and lower sectors of the gradient revealed deficient and poor recruitment in Quercus virginiana, Acer negundo, Celtis laevigata, and Salix nigra and episodic regeneration in Liquidambar styraciflua, Taxodium distichum, and Quercus nuttallii. Recruitment of the exotic species, Sapium sebiferum, is occurring at the low end of the gradient, as well as in canopy gaps throughout the gradient. Logistic regressions of sapling (<10 cm dbh) and tree (≥10 cm dbh) size classes as a function of elevation showed that saplings of L. styraciflua, Q. nigra, and U. americana occur at higher elevations than do adult trees of the same species, evidence of the rate of hydrologic change in this forest. A fourth species, Acer rubrum, resprouts vigorously under rising water levels and may be an effective competitor with more light-demanding, flood-tolerant species at low elevations.

Coastal salt marshes in the northern Gulf of Mexico are often highly fragmented, with a large amount of marsh edge, the interface between the vegetated marsh surface and shallow open water. Nekton predators, including many juvenile fishery species, aggregate near this marsh edge, and benthic infaunal populations are a primary source of prey for many of these predators. We examined the fine-scale (1–10 m) distributions of benthic infauna in relation to the edge of a Texas, USA salt marsh. Every six weeks for nearly a year, we sampled marsh sediments at five locations: on nonvegetated bottom 1 m from the marsh edge and on the vegetated marsh surface at 1, 3, 5, and 10 m from the edge. Surface-dwelling annelid worms and peracarid crustaceans were most abundant in low-elevation sediments near the marsh edge for most sampling periods. Because the marsh slope varied within the study area, we could distinguish between correlative relationships with elevation and distance from the marsh edge. Distributions of common surface-dwelling species were often unrelated to elevation but almost always negatively related to distance from the marsh edge. Abundances of near-surface direct deposit feeders and omnivores were related to both distance from edge and elevation. In contrast to surface dwellers, densities of abundant subsurface deposit feeders (mainly oligochaetes) were frequently greatest in sediments located away from the marsh edge. Surface and near-surface dwelling infauna are an important prey resource for nekton, including many juvenile fishery species that concentrate near the marsh edge. Populations of these infaunal prey fluctuated seasonally, with the greatest densities occurring during winter and early spring when predator abundances are generally low. Infaunal densities decreased dramatically near the marsh edge from the late spring through early fall, and this decrease coincides with historically high seasonal densities of nekton predators. Our data suggest that there is a strong trophic link between infauna and nekton near the marsh edge and that this relationship contributes to the high fishery productivity derived from Gulf Coast marshes.

Water levels fluctuate widely in Carolina bay wetlands and most dry periodically. Aquatic organisms inhabiting these wetlands have the capacity to either resist desiccation or to recolonize newly flooded habitats. The objective of this study was to determine which invertebrates aestivate in the soil of dry Carolina bays and to describe how differences in habitat affect the composition of aestivating invertebrates. Eight Carolina bays located on the Savannah River Site (SRS) near Aiken, South Carolina, USA were examined for this study. Although all of the wetlands dried seasonally, three of the wetlands were relatively wet (inundated 47–92% of the year on average), one was intermediate, and four were relatively dry (inundated 20% of year on average). Sections of soil were removed from each bay during August and November when all sites were dry, placed into tubs, flooded, and covered with fine mesh. Invertebrates were sampled from the water biweekly for four weeks. Invertebrate assemblages were contrasted between naturally inundated bays and rehydrated samples, wetter and drier bays, August and November collections, and remnant ditches and the main basins. Common aestivating fauna included midges, dytiscid beetles, copepods, and cladocerans. The Jaccard's coefficient of similarity for invertebrates emerging from dry substrate and from naturally flooded wetlands (with both aestivators and colonizers) averaged 0.22. More taxa emerged from rehydrated samples from wetter bays than drier bays. Season affected which taxa emerged. Remnant ditches supported fewer taxa than basins. Aestivating invertebrates make up a significant component of Carolina bay fauna.

Impoundments create unnatural shorelines that differ from lake shorelines in patterns of water-level fluctuations, flow, sediment transport, and shoreline vegetation dynamics. Shoreline plant communities of impoundments in the American Southwest often become dominated by mature, senescent Populus and Salix, with few if any seedlings. The failure of native plant community replacement is exacerbated by the fact that Tamarix, a prolific invader, is abundant on regulated rivers and occupies extensive areas along the shores of impoundments. Efforts to replant natives within the drawdown zone surrounding Lake Mohave, a lower Colorado River impoundment bordering Nevada and Arizona, have not been successful. A greenhouse experiment was designed to examine the responses of cuttings of a native species, Salix gooddingii (Goodding willow), and the invasive species, Tamarix ramosissima (salt cedar), to different hydroperiods comparable to those influencing Lake Mohave riparian plant communities. Higher survival and greater biomass under saturated but not flooded soil conditions demonstrated that both Salix and Tamarix cuttings can prosper in soils within the exposed drawdown zone, provided that the shoots are not submerged. However, greater biomass of Tamarix under conditions favorable to the native Salix also indicates that Tamarix colonization will have to be controlled. This research substantiates that the physiological tolerances of native and invasive riparian plant species and the prevailing hydrodynamics of a waterway must be considered when attempting to restore native vegetation.

To understand how Scirpus mariqueter responds to the creek-forming disturbance, we examined the differences in morphology and biomass allocation of the species between creekside and inland communities in the Changjiang estuary. Rhizome length and branching intensity were significantly greater in the creekside communities than in the inland community, and they were positively correlated to each other in both kinds of communities, enabling the clones to colonize a larger area and exploit resources efficiently in the creekside habitats. The plants growing along the creekside decreased substantially in their sexual reproduction and allocated more biomass to corms and vegetative reproduction than the inland ones. The biomass allocation pattern of the creekside clones was assumed to be a conservative strategy adopted by the species under disturbance to enhance survivorship at a clone level. In addition, our results imply that reciprocal translocation of materials between parent and daughter ramets probably occurred in the clones within the creekside communities, indicating that clonal integration may play an important role in controlling the responses of S. mariqueter to disturbance. We concluded that the clonal plant S. mariqueter has a high capacity for tolerating tidal disturbances.

Activity of root phosphatase was examined in Cladium jamaicense (sawgrass) and Typha domingensis (cattail) grown under controlled conditions in Everglades peat with different inorganic P availabilities and flooding regimes. Cladium root phosphatase activity was significantly greater than for Typha when both were subjected to relatively low inorganic phosphorus concentrations (10 to 80 μg l⁻¹) in the interstitial water, indicating a greater potential for Cladium to use organic phosphorus compounds as a phosphate source. When inorganic phosphorus concentration was elevated (500 μg l⁻¹), internal root phosphate concentrations increased and root phosphatase activities decreased in both species to similar levels. Thus, root phosphatase activity in these species is induced by low ambient inorganic phosphate concentrations. The relatively greater ability of Cladium to hydrolyze organic phosphorus compounds indicates that it is physiologically better adapted to peat-based, low inorganic phosphorus conditions and helps explain this species' historic dominance in peat-based Everglades soils.