Extensive Salicornia beds along the Gulf of Kutchchh (northwest) and Tamilnadu (southeast) coasts were investigated with respect to vegetative structure and ambient environmental conditions. The width of the beds varied from approximately 5 m to 1000 m, depending upon the topography and tidal influence. The most extensive and healthy stands occurred in the regularly (20–50 tides month⁻¹) inundated intertidal zones. The width of Salicornia beds in the Gulf of Kutchchh was greater than those along the Tamilnadu coast due to greater (0.83–7.2 m) tidal amplitude and flat topography. The sediments from beds of the Gulf of Kutchchh were rich (4.9–16.9 % dry weight) in organic matter. The salt content in the sediments from Tamilnadu was relatively very low (0.08–0.1 % dry weight) compared to sediments from the Gulf of Kutchchh (0.48–0.78 % dry weight). Plant biomass, density, height, and frequency of occurrence in the more frequently inundated regions were greater than in the poorly or less frequently inundated intertidal regions. The average total biomass varied from 0.2 to 4.5 kg (dry weight) m⁻² and was mostly comprised of aboveground components. Peak biomass values of Salicornia were observed during September to February in the Gulf of Kutchchh, while along the southeast coast, they were observed during December to March. The growth of the S. brachiata seemed to be influenced primarily by the frequency of inundation, duration of atmospheric exposure at ebb tide, rainfall, and salinity and salt content of the ambient water and sediments, respectively. Average carbon and nitrogen content in the plants were estimated to be 21.7 ± 1.9 % and 0.8 ± 0.17 % (dry weight), respectively. The carbon content increased with increasing age of the plant, while protein content decreased. Constantly increasing anthropogenic pressures on coastal wetlands warrant immediate protection of S. brachiata and other obligate halophytes, which are either threatened /vulnerable or endangered.

The expansion of urban and agricultural activities in watersheds of the Midwestern USA facilitates the conversion of species-rich sedge meadows to stands of Phalaris arundinacea and Typha spp. We document the role of sediment accumulation in this process based on field surveys of three sedge meadows dominated by Carex stricta, their adjacent Phalaris or Typha stands, and transitions from Carex to these invasive species. The complex microtopography of Carex tussocks facilitates the occurrence of other native species. Tussock surface area and species richness were positively correlated in two marshes (r² = 0.57 and 0.41); on average, a 33-cm-tall tussock supported 7.6 species. Phalaris also grew in tussock form in wetter areas but did not support native species. We found an average of 10.5 Carex tussocks per 10-m transect, but only 3.5 Phalaris tussocks. Microtopographic relief, determined with a high-precision GPS, measured 11% greater in Carex meadows than Phalaris stands. Inflowing sediments reduced microtopographic variation and surface area for native species. We calculated a loss of one species per 1000 cm² of lost tussock surface area, and loss of 1.2 species for every 10-cm addition of sediment over the sedge meadow surface. Alluvium overlying the sedge meadow soil had a smaller proportion of organic matter content and higher dry bulk density than the buried histic materials. We conclude that sedimentation contributes to the loss of native species in remnant wetlands.

Time series of ground-water head at a mid-marsh site near North Inlet, South Carolina, USA can be classified into five types of forcing signatures based on the dominant water flux governing water-level dynamics during a given time interval. The fluxes that can be recognized are recharge by tides and rain, evapotranspiration (ET), seepage into the near surface soil from below, and seepage across the soil surface to balance either ET losses or seepage influxes from below. Minimal estimates for each flux can be made by multiplying the head change induced by it by the measured specific yield of the soil. These flux estimates are provide minimal values because ET fluxes resulting from this method are about half as large as those estimated from calculated potential evapotranspiration (PET), which place an upper limit on the actual ET. As evapotranspiration is not moisture-limited at this regularly submerged site, the actual ET is probably nearly equal to PET. Thus, all of the other fluxes are probably twice as large as those given by this method. Application of this method shows that recharge by tides and rain only occurs during spring and summer when ET exceeds upward seepage from below and is thereby able to draw down the water table below the marsh surface occasionally. During fall and winter, seepage of fresh water from below is largely balanced by seepage out of the soil into overlying tidal water or into sheet flow during tidal exposure. The resulting reduction in soil water salinity may thereby enhance the growth of Spartina in the following spring.

Improving our knowledge of regeneration processes in riparian woodlands could help guide restoration projects by enhancing the natural regeneration potential of riparian tree species. In western Europe, Populus nigra, is a major component of riparian woodlands, but the spatial extent of this species has decreased due to river management activities. In this study, the timing of Populus nigra seed dispersal and variations in seed germinability through time were monitored. An experiment was also devised to measure both seed germination and seedling survival in changing hydrologic conditions. The seed dispersal period lasted 12 weeks along the Garonne River. Individual poplar trees displayed variations in seed release patterns. On average, seed germinability remained rather low and close to 28%. However, large differences in germinability were observed between trees and over time. A continuously wet substrate was the most favorable condition for germination and seedling survival. A change from wet to submerged conditions increased germination and reduced seedling survival. In the case of a change from either wet or submerged to dry conditions, there was no survival possible if the dry conditions persisted more than one week. Substrate type had a significant effect on germinability only in moderate moisture conditions. Populus nigra tolerates decreases in the optimum minimum flow if coupled with at least a brief rise in river level on a weekly basis.

Florida apple snails (Pomacea paludosa) apparently have only a limited tolerance to wetland drying events (although little direct evidence exists), but their populations routinely face dry downs under natural and managed water regimes. In this paper, we address speculation that apple snails respond to decreasing water levels and potential drying events by moving toward refugia that remain inundated. We monitored the movements of apple snails in central Florida, USA during drying events at the Blue Cypress Marsh (BC) and at Lake Kissimmee (LK). We monitored the weekly movements of 47 BC snails and 31 LK snails using radio-telemetry. Snails tended to stop moving when water depths were < 10 cm; however, there was no apparent effect of water depth on distance traveled in water depths >10 cm. Snails moved along the greatest positive depth gradient (i.e., towards deeper water) when they encountered water depths between 10 and 20 cm. Snails tended to move toward shallower water in water depths ≥50 cm, suggesting that snails were avoiding deep water areas such as canals and sloughs. Of the 11 BC snails originally located in the area that eventually went dry, three (27%) were found in deep water refugia by the end of the study. Only one of the 31 LK snails escaped the drying event by moving to deeper water. Our results indicate that some snails may opportunistically escape drying events through movement. The tendency to move toward deeper water was statistically significant and indicates that this behavioral trait might enhance survival when the spatial extent of a dry down is limited. However, as water level falls below 10 cm, snails stop moving and become stranded. As the spatial extent of a dry down increases, we predict that the number of snails stranded would increase proportionally. Stranded Pomacea paludosa must contend with dry marsh conditions, possibly by aestivation. Little more than anecdotal information has been published on P. paludosa aestivation, but it is a common adaptation among other apple snails (Caenogastropoda: Ampullaridae).

We measured the amount and distribution of macroinvertebrates and seeds in four wetland habitats (short emergent, seasonal open water, semipermanent/permanent open water, and saltgrass [Distichlis spicata]) used by breeding ducks and shorebirds at a wetland complex in the San Luis Valley, Colorado, USA. Density of macroinvertebrates did not differ among habitats or sampling periods (P = 0.45), but dry mass, crude protein, and gross energy production were greater (P < 0.05) in short emergent than in other habitats. These differences were largely due to the greater dry mass of gastropods in short emergent than in other habitats. Total seed density, dry mass, crude protein, and gross energy differed among habitats and periods with interaction effects (P <0.01). Although seed abundance varied among habitats and sampling periods, abundance was greatest in short emergent during all sampling periods. Breeding waterbirds consumed a variety of macroinvertebrates and seeds on the study area. Patterns of abundance among habitats of macroinvertebrates and seeds consumed by six waterbird species were not consistent with patterns of foraging habitat use by most ducks and shorebirds at this wetland complex. Our results indicate that estimates of food or nutrient abundance are useful in assessing the functional role of broad habitat types, but factors other than food abundance also influence avian selection of wetland foraging habitats.

Where wetlands receive urban runoff, Typha spp. and other invasive plants often displace the native vegetation. We tested the ability of nutrients (N and P) to increase vegetative growth of T. × glauca (a hybrid of T. latifolia and T. angustifolia). In the greenhouse, 17 treatments revealed that T. × glauca required both N and P for growth, and total leaf length was most stimulated where a higher proportion of P was added (7N:1P vs. 14N:1P, with N constant and P changed), regardless of concentration (the High treatment was 4× the Low treatment). In Gardner Marsh (Madison, Wisconsin, USA), we set up 28 plots (1 × 6 m) that bisected the boundary between sedge meadow (graminoids) and T. × glauca, and we added a common lawn fertilizer (9N:1P:4K) at high (62.5 g/m²), medium (31.3 g/m²), low (15.6 g/m²), and control (0 g/m²) rates on five dates, with n=7 plots/treatment. After one growing season, fertilizer addition increased T. × glauca ramet density, height, and biomass, especially where the sedge meadow graminoids were initially dominant. Aboveground biomass of T. × glauca in the high nutrient addition treatment (1029 ± 256.1 g/m²) was more than double that for control plots (431 ± 80.52 g/m²) overall, with the greatest percent increase in sedge meadow subplots. In contrast, native graminoids (mostly Carex spp.) did not respond to treatment, either in biomass or percent cover. Typha × glauca allocated nutrients to both growth and storage, as indicated by higher N and P concentrations in leaves, shoot bases, and rhizomes in plots with high nutrient addition. Because fertilizing the marsh enhanced the shoot growth of T. × glauca but not native graminoids, and because the 7N:1P treatment stimulated growth in the greenhouse, we suggest that wetland managers focus on reducing P inflows to urban wetlands. Fertilizer additions below those recommended by the manufacturer for new lawns (5× that of our highest treatment) should be more economical and have fewer impacts on receiving wetlands.

The Columbia Wastewater Treatment Wetland (“Columbia Wetland”) is a constructed cattail wetland in the Missouri River floodplain outside Columbia, Missouri, USA. The wetland receives mixed primary and secondary effluent (≈60,000 m³ d⁻¹, BOD₅ ≈30 mg L⁻¹, TSS ≈13 mg L⁻¹, NH₄-N ≈8 mg L⁻¹) from a conventional treatment plant. During its first 6 years of operation (October 1994 through November 2000), the wetland received loadings of BOD₅, COD, and NH₄-N averaging 50, 83, and 12 kg ha⁻¹ d⁻¹, respectively, of which averages of 74%, 30%, and 17%, respectively, were removed from the effluent. TSS (mean loading = 21 kg ha⁻¹ d⁻¹) frequently increased in the wetland due to erosion and disturbance by waterfowl, but TSS removal efficiency increased with time and the development of macrophyte biomass and averaged 30% by 1998. The wetland typically removed >97% of fecal coliforms and fecal streptococcus, 36% of TN and 4% of TP. In comparison to other large treatment wetlands, BOD removal by the Columbia Wetland has been exceptionally efficient.

A distinctive feature of the Nhecolândia, a sub-region of the Pantanal wetland in Brazil, is the presence of both saline and freshwater lakes. Saline lakes used to be attributed to a past arid phase during the Pleistocene. However, recent studies have shown that saline and fresh water lakes are linked by a continuous water table, indicating that saline water could come from a contemporary concentration process. This concentration process could also be responsible for the large chemical variability of the waters observed in the area. A regional water sampling has been conducted in surface and sub-surface water and the water table, and the results of the geochemical and statistical analysis are presented. Based on sodium contents, the concentration shows a 1: 4443 ratio. All the samples belong to the same chemical family and evolve in a sodic alkaline manner. Calcite or magnesian calcite precipitates very early in the process of concentration, probably followed by the precipitation of magnesian silicates. The most concentrated solutions remain under-saturated with respect to the sodium carbonate salt, even if this equilibrium is likely reached around the saline lakes. Apparently, significant amounts of sulfate and chloride are lost simultaneously from the solutions, and this cannot be explained solely by evaporative concentration. This could be attributed to the sorption on reduced minerals in a green sub-surface horizon in the “cordilhieira” areas. In the saline lakes, low potassium, phosphate, magnesium, and sulfate are attributed to algal blooms. Under the influence of evaporation, the concentration of solutions and associated chemical precipitations are identified as the main factors responsible for the geochemical variability in this environment (about 92 % of the variance). Therefore, the saline lakes of Nhecolândia have to be managed as landscape units in equilibrium with the present water flows and not inherited from a past arid phase. In order to elaborate hydrochemical tracers for a quantitative estimation of water flows, three points have to be investigated more precisely: (1) the quantification of magnesium involved in the Mg-calcite precipitation; (2) the identification of the precise stoichiometry of the Mg-silicate; and (3) the verification of the loss of chloride and sulfate by sorption onto labile iron minerals.

Canopy disturbance is a major factor affecting forest structure and composition and, as a result of habitat alterations, can influence insect communities. We initiated a field study to quantify the effects of canopy disturbance on aerial insect abundance and distribution within a bottomland hardwood forest along the Cache River, Arkansas, USA. We used passive flight-intercept traps to sample insects in canopy gap and forest interior habitats from May to July in 1996, 1997, and 1998. The hydrologic conditions of our study site varied among years: 1996 was relatively dry, 1997 incurred a long-duration flood, and 1998 was moderately wet. Of the 34,000 Homopterans collected, many groups were distributed in a non-uniform manner among years and between habitats. Total Homopterans, two families of Homopterans, and six morphospecies were more abundant in canopy gaps than interior forest. Many Homopteran taxa were least abundant in 1997 following almost six months of flooding. Alternatively, relatively large Homopteran abundances were associated with the dry conditions of 1996 and the moderately wet conditions of 1998. Differences in Homopteran abundance among years and habitats may be related to differences in vegetation density. Canopy gaps supported more vegetation cover than the interior forest in all but the first sampling interval. In addition, similar to Homopteran abundance, vegetation density was lower in 1997 than in 1998. These results demonstrate that natural disturbance and flooding contribute to Homopteran abundance and distribution patterns in bottomland hardwood forests of the south central United States.

Riparian forest ecosystems are important for their high productivity of biomass, their biodiversity, and ecological services including control of floods and erosion, removal of nutrients from agricultural runoff, alleviation of pollution effects, and as habitats for birds and mammals. Intermittent cycles of flooding by meandering streams followed by soil drainage are essential for regeneration, optimal growth, preservation of biodiversity, and sustainability of these valuable ecosystems. The straightening of river channels and disruption of intermittent river flow by dams lead to decreases in downstream forest productivity and ecological services, reflecting arrested forest regeneration, suppression of tree growth, and early tree mortality. These responses result from inadequate seed supplies and poor seedbeds, as well as deficiencies of ground water and mineral nutrients. Water deficits in downstream forest trees induce dysfunctions in photosynthesis and mineral nutrition, which lead to growth inhibition and plant mortality. Very few bottomland forest species can withstand extended soil inundation. Hence, prolonged upstream flooding by interruption of river flow is followed by massive losses of biomass as a result of poor seed germination, arrested plant growth, and accelerated mortality of trees. The adverse impacts of flooding on upstream forests are associated with physiological dysfunctions induced by soil anaerobiosis. These include changes in respiration, photosynthesis, protein synthesis, mineral nutrition, and hormone relations, together with increased exposure to a variety of phytotoxic compounds. There is urgent need for developing more integrated and holistic flood-management policies that will recognize the need for protecting and restoring valuable riparian forests while also meeting other flood-control objectives.

A three-year study of aboveground biomass and nutrient dynamics in twelve restored depressional wetlands of different ages demonstrated significant annual variability among sites. Annual variations appeared to be primarily due to differences in hydrologic conditions over the three years of the study. Differences among wetlands were not related to time since restoration. When data for all sites were combined, annual differences in biomass and most measurements of nutrients (concentrations and standing stocks) did not, however, differ significantly. These results suggest that differences that are measured at individual wetland sites may be less important at the landscape level. Biomass decreased from the outer temporary to inner submersed zone, and there were few differences among wetlands when the temporary, seasonal, and submersed zones were compared. Nutrient concentrations in the plant biomass increased from the temporary zone to the submersed zone, resulting in few differences in nutrient standing crops across zones. Results from this study demonstrate that some measurements of restoration success (i.e., biomass production) should be used cautiously because they are likely to be highly variable among sites and across years and thus may be of limited use in post-restoration monitoring. Other ecosystem parameters (e.g., nutrient concentrations of biomass) are much more constant spatially and temporally, indicating that nutrient cycling processes in vegetation were established quickly following restoration. Nutrient characteristics of wetland vegetation thus may be a useful metric for evaluating restoration success or failure.

This study was carried out on a neglected component of wetlands: the picoplankton community. We analyzed the picoplanktonic community patterns and their related environmental factors in a hypertrophic semi-arid wetland located in Central Spain (Las Tablas de Daimiel National Park, TDNP). We determined the bacterial and autotrophic picoplankton (APP) abundance over a three-year period (1996: the end of a long drought period and 1997–1998: after flooding) in five sites of the wetland. The overall range of bacterial abundance was 0.2 × 10⁶ to 10 × 10⁶ cells/ml. The annual mean abundance increased in the wettest 1997. APP was composed mainly by coccoid phycocyanin-containing cyanobacteria, with the greatest abundance up to 25 × 10⁵ cells/ml. The annual mean also increased considerably in wetter 1997–98. Despite the large APP biomass in some sites, its percentage of total phytoplankton biomass was low (the annual average did not exceed 1.5%). We observed spatial heterogeneity in the picoplankton fraction depending on the fluctuating hydrology: bacteria tends to spatial homogeneity after flooding while APP showed only similarity among the output sites. Among the considered predictive variables (temperature, phosphorus, nitrogen, zooplankton, phytoplankton) of the picoplanktonic dynamics, temperature was the most closely correlated to picoplankton, especially to bacterial abundance. Further, in two factorial, coupled-hierarchical laboratory experiments (constant temperature), we searched for control mechanisms of picoplankton. We tested (a) the trophic cascade hypothesis by analyzing the effect of presence/absence of mosquitofish (experiment 1) or directly modifying the zooplanktonic community (experiment 2) and (b) the bottom-up regulation by altering the nutrient conditions (presence/absence of sediment in experiment 1; reducing the nutrient content in experiment 2). Bacterioplankton failed to show any behavior related to trophic cascade direct effects, while nutrients increased its abundance. APP was affected positively by nutrients and negatively by zooplankton grazing.

Interest by land-management and regulatory agencies in using biological indicators to detect wetland degradation, coupled with ongoing use of this approach to assess water quality in streams, led to the desire to develop and evaluate an Index of Biotic Integrity (IBI) for wetlands that could be used to categorize the level of degradation. We undertook this challenge with data from coastal wetlands of the Great Lakes, which have been degraded by a variety of human disturbances. We studied six barrier beach wetlands in western Lake Superior, six drowned-river-mouth wetlands along the eastern shore of Lake Michigan, and six open shoreline wetlands in Saginaw Bay of Lake Huron. Plant, fish, and invertebrate communities were sampled in each wetland. The resulting data were assessed in various forms against gradients of human disturbance to identify potential metrics that could be used in IBI development. Our results suggested that the metrics proposed as potential components of an IBI for barrier beach wetlands of Lake Superior held promise. The metrics for Lake Michigan drowned-river-mouth wetlands were inconsistent in identifying gradients of disturbance; those for Lake Huron open embayment wetlands were yet more inconsistent. Despite the potential displayed by the Lake Superior results within the year sampled, we concluded that an IBI for use in Great Lakes wetlands would not be valid unless separate scoring ranges were derived for each of several sequences of water-level histories. Variability in lake levels from year to year can produce variability in data and affect the reproducibility of data collected, primarily due to extreme changes in plant communities and the faunal habitat they provide. Substantially different results could be obtained in the same wetland in different years as a result of the response to lake-level change, with no change in the level of human disturbance. Additional problems included limited numbers of comparable sites, potential lack of undisturbed reference sites, and variable effects of different disturbance types. We also evaluated our conclusions with respect to hydrologic variability and other major natural disturbances affecting wetlands in other regions. We concluded that after segregation of wetland types by geographic, geomorphic, and hydrologic features, a functional IBI may be possible for wetlands with relatively stable hydrology. However, an IBI for wetlands with unpredictable yet recurring influences of climate-induced, long-term high water periods, droughts, or drought-related fires or weather-related catastrophic floods or high winds (hurricanes) would also require differing scales of measurement for years that differ in the length of time since the last major natural disturbance. A site-specific, detailed ecological analysis of biological indicators may indeed be of value in determining the quality or status of wetlands, but we recommend that IBI scores not be used unless the scoring ranges are calibrated for the specific hydrologic history pre-dating any sampling year.

In tidal marshes of the northeast US, replacement of native cattail (Typha angustifolia) by the common reed (Phragmites australis) is widespread, and reed is often the target of removal efforts. Reed sequesters nearly twice the amount of nitrogen per unit marsh area in living aboveground tissue compared to cattail. Microbial decay processes immobilize additional nitrogen or return this organic nitrogen to the pool of inorganic nitrogen. We compared microbial growth during decay of standing and fallen litter of cattail and reed. Shoots of both plants were collected at the time of peak live biomass and then periodically throughout litter decomposition. Litter was analyzed for mass loss, nitrogen content, and biomass and production of fungi and bacteria. There were statistically significant but small differences in litter-associated microbial biomass and production between these two plants. Microbial production on both litter types was dominated by fungi, accounting for > 99% of the total. Living fungal biomass (estimated from ergosterol) associated with reed and cattail litter averaged 6.1 and 8.2 mg fungal C/g litter dry mass, respectively, and fungal nitrogen accounted for roughly 25% of the total nitrogen associated with litter. Detrital nitrogen standing stocks/m² were greater for reed than cattail throughout the first 2.5 years of decay. Therefore, the ability of reed litter to support decomposer growth is only somewhat lower and nitrogen retention is greater than for one of the plants it replaces. These differences are probably insufficient to argue for aggressive control of reed in tidal wetlands.

Understanding the primary productivity of salt marshes requires accurate estimates of biomass. Unfortunately, these estimates vary enough within and among salt marshes to require large numbers of replicates if the averages are to be statistically meaningful. Large numbers of replicates are rarely taken, however, because they involve too much labor. Here, we present data on a fast, non-destructive method for measuring aboveground biomass of Spartina alterniflora and Phragmites australis that uses only the average height of the five tallest shoots and the total density of shoots over 10 cm tall. Collecting the data takes only a few minutes per replicate, and calculated values for biomass compare favorably with destructive measurements on harvested samples.