We evaluated landscape associations related to heron and egret colony site selection and the productivity of successful great blue heron (Ardea herodias) and great egret (Ardea alba) nests. The study was based on annual observations (1991–2005) at 45 colony sites known to be active within 10 km of historic tidal marshes of northern San Francisco Bay. The analyses focused on a priori models analyzed within 1, 3, 5, 7, and 10 km of colony sites, using the areal extents of several NOAA land cover types (Landsat images, 2000–2002), number of wetland patches, and total wetland edge as predictor variables. A comparison of landscape characteristics surrounding colony sites with those surrounding randomly selected, unoccupied sites revealed the primary importance of estuarine emergent wetland and open water within 1 km of colony sites. Increased productivity in successful great blue heron nests was associated with more estuarine emergent wetland, open water, and low-intensity development, and less grassland, but was not differentially related to the extent of habitat available within any particular distance from colony sites. The productivity in successful great egret nests was associated with variation in habitat extent at larger spatial scales, especially within 10 km of heronies, with nests producing more young at sites surrounded by more estuarine emergent wetland and low-intensity development, less open water and palustrine emergent wetland, and more patches of wetland habitat. To estimate landscape foraging patterns, we used aircraft to track the flights of great egrets departing from heronries and used the observed flight distances, colony sizes, and the regional distribution of wetland habitat to model regional foraging densities. Results suggested that increasing the extent of wetland feeding areas for herons and egrets might improve reproductive performance in colony sites up to 10 km away, increase foraging by herons and egrets in created or restored wetlands within 3–10 km of sites, and enhance nest abundance at colony sites within 1 km of restoration sites. Regional maps based on the distribution of colony-sites and predictions of landscape influences on colony site selection, nest productivity, and foraging dispersion, suggested areas potentially suitable for colonization.

Tree islands, forested islands in an herbaceous freshwater wetland landscape, are a major landscape feature in the Florida Everglades. The vegetation communities on the heads of 31 tree islands, including eight islands with recreational camp structures, were assessed throughout Water Conservation Area 3 to determine their composition, structure, and distribution across the landscape. The islands were a sample of the most elevated islands in the local landscape. Measures of forest canopy (> 3 m) and sub-canopy (1–3 m) structure and composition, including cover, species richness, number of exotics, and total canopy basal area were ordinated onto six hydrologic variables estimated from the South Florida Water Management Model (v5.5) simulation from 1984 to 1997, and history of recent fire. Ordination allowed identification of four island groups: Group A, higher islands, most with camp structures, low or no canopy structure, high level of fire history, driest hydrology, and largest number of exotic species in canopy; Group B, variable canopy development including many plots without canopy cover, some fire history, and exotics in sub-canopy; Group C, highest islands with well developed canopy structure and no canopy exotics; and Group D, low elevation islands, wettest hydrology, no exotics, and deep peat soils. Cluster analysis of the vegetation cover data was used to identify sub-canopy and canopy communities of the island groups. Our results indicated that the forest canopy of elevated tree islands is similar throughout the central Everglades and that differences in tree island forest composition and structure were the result of local differences in island topography, hydrology, direct human disturbance, and past fire history. Canopy composition and structure were strongly correlated with extreme wet or dry hydrologic events rather than mean or median annual water levels. Fern species were also found to be a ubiquitous component of the sub-canopy. The results of this study identify potentially successful species and provide some basic guidelines for restoring the forest head communities of degraded tree islands.

Seed dispersal is an important process for plants, but may be particularly important for plants occurring in spatially isolated habitats like wetlands. Variation in the geographic distribution of wetland plant species may be strongly influenced by their ability to use waterbirds, particularly waterfowl to enhance dispersal. We used controlled feeding and germination experiments to investigate recovery, retention time, and germination for the seeds of 10 wetland plant species (Chenopodium album, Digitaria ischaemum, Echinochloa colonum, Echinochloa crusgalli, Eleocharis palustris, Panicum dichotomiflorum, Polygonum lapathifolium, Polygonum pensylvanicum, Rumex crispus, and Scheonoplectus maritimus) and compared how these metrics varied with seed characteristics. We fed a known number of seeds to captive raised mallards (Anas platyrhynchos) and collected fecal samples every 4 hours for 48 hours; all recovered seeds were planted in seedling trays and watched for 60 days to monitor germination. We conducted 10 trials and fed each seed species in each trial, and included germination controls of non-consumed seeds. Overall, 19.0 ± 1.8% (mean ± SE) of seeds were recovered and of recovered seeds 7.6 ± 1.2% germinated. Recovery ranged from 1.9 ± 0.6% in D. ischaemum to 51.0 ± 4.7% in S. maritimus and germination ranged from < 0.5% in D. ischaemum to 28.5 ± 5.7% in R. crispus. Recovery and germination were not related to seed size or mass (p > 0.5) but recovery was positively correlated with seed fiber content (r²  =  0.44, p  =  0.04). Control seeds germinated better than fed seeds for all species except S. maritimus, where fed seeds germinated better. Germination percentage declined with gut retention time for four of seven species. We suggest despite the large differences in viable seeds recovered, mallards may be important dispersers for the seeds of most species we studied and hypothesize that observed variation may be attributable to different plant strategies that relate to reproductive tactics and habitat type.

Functional assessment is important to determine whether restored and created wetlands are similar to natural ones. We investigated ecosystem processes (decomposition, biomass production) and some aspects of biogeochemical cycles (plant uptake of nitrogen and phosphorus, litter N immobilization) in a population of natural and created (mitigation) wetlands. Our goals were to quantify ecosystem processes and compare some biological and physical characteristics, in order to assess the relative performance of created wetlands. The biological and biogeochemical characteristics of the natural and created sites were substantially different. Decomposition rates for both in-situ and control litter and tissue nutrient concentrations were higher in the natural wetlands, with final decomposition rate constant values (k (d⁻¹)) averaging 0.009 for natural and 0.006 for restored sites over approximately a one-year incubation period. Aboveground biomass production was also significantly higher in the natural sites, averaging 347 g m⁻² compared to 209 g m⁻². Concentrations of soil percent organic carbon, percent nitrogen, and plant available P (µgP g soil⁻¹) were significantly higher in the natural sites. Lower soil nutrient content in the created wetlands appears to propagate through the system resulting in low tissue nutrient levels, less biomass accumulation, and slower rates of decomposition.

Testate amoebae are unicellular micro-organisms whose hydrological sensitivity and good preservation in peats make them valuable proxies for past peatland surface wetness, and therefore climate. Previous testate amoebae transfer functions have been spatially restricted with no studies from Asia. To derive a transfer function, a sequence of samples was extracted from an ombrotrophic peatland in Turkey and amoebae counted. The internal structure of the data was explored using principal components analysis and relationships with the environmental data tested by redundancy analyses. Transfer function models were developed using a variety of techniques. As in other regions, depth to water table is the most important control on amoebae community composition. Transfer function performance was initially poor, primarily due to the inclusion of samples from areas of the site that had been heavily affected by peat cutting and had distinctly different amoebae communities. Model performance is improved by selective sample exclusion, reducing jack-knifed root mean square error of prediction to 7.1 cm. The model was tested using an initial palaeoecological data-set. Overlap with the training set was limited, although a hydrological reconstruction using this model produces similar results to a transfer function derived from northern European peatlands. This study provides the first testate amoebae transfer function from Asia and demonstrates that hydrological preferences of many of the key taxa are consistent across a large area of the Northern Hemisphere. The transfer function will allow detailed palaeoclimate reconstruction from this peatland, adding to our knowledge of Holocene climatic change in southwest Asia.

Accurate characterization of wetland condition at a regional or watershed scale requires an assessment that includes both a quantity and quality component. A probabilistic sampling design can facilitate the implementation of such assessments through its ability to extrapolate results from a random sample of wetlands to the entire population of wetlands over a large geographic area. In 2003 an assessment of the quantity and quality of depressional wetlands in the Redwood River watershed was conducted using a probabilistic sampling design. The number and cumulative area of depressional wetlands in the watershed was estimated relative to the National Wetland Inventory (NWI) by evaluating 146 randomly selected sites. However, limitations of the study design only allowed quantification of wetland loss over the ∼20-year period (c.1980–2003) following the acquisition of aerial imagery used to produce the NWI in this region. Wetland quality was assessed in 40 randomly selected sample sites using plant and macroinvertebrate indices of biological integrity (IBI). Depressional wetlands included in the NWI have experienced an estimated 56% reduction in number, equivalent to a 21% decrease in area, in the watershed over the last 20 years. Of the remaining wetland area, an estimated 91% was impaired. Thus, management practices with the goal of increasing suitable habitat for native wetland plant and animal communities should focus on restoration of drained wetlands as well as improvement of existing wetlands to maximize outcomes.

This paper presents a decision-tree method for identifying mangroves in the Pearl River Estuary using multi-temporal Landsat TM data and ancillary GIS data. Remote sensing can be used to obtain mangrove distribution information. However, serious confusion in mangrove classification using conventional methods can develop because some types of land cover (e.g., agricultural land and forests) have similar spectral behaviors and distribution features to mangroves. This paper develops a decision-tree learning method for integrating Landsat TM data and ancillary GIS data (e.g., DEM and proximity variables) to solve this problem. The analysis has demonstrated that this approach can produce superior mangrove classification results to using only imagery or ancillary data. Three temporal maps of mangroves in the Pearl River Estuary were obtained using this decision-tree method. Monitoring results indicated a rapid decline of mangrove forest area in recent decades because of intensified human activities.

Vernal pools are small depressional wetlands found in seasonal climates throughout the world. In California, they are among the few ecosystems still dominated by native flora and are critical habitat for numerous endemic and rare species. In this study, we show that geology is a dominant control on the physical and chemical hydrology of contrasting vernal pools on clay-rich and hardpan soils, the two most common types of vernal pools in the Central Valley, California. The vernal pools on clay-rich soils formed on alluvium derived primarily from sedimentary and metasedimentary rocks of marine origin and deposited in relatively low-gradient environments. The clay-rich soils are fine grained and moderately to strongly saline and sodic. The vernal pools on clay-rich soils are perched surface-water systems in which surface waters are relatively saline, sodic, and turbid and in which primary productivity may be nitrogen and light limited. The vernal pools on hardpan soils formed on alluvium derived primarily from coarse-grained igneous rocks and deposited in relatively high-gradient environments. Surface soils are coarse grained and underlain by a clay-rich argillic horizon and a silica- and iron-cemented duripan. The vernal pools on hardpan soils are surface-water and perched ground-water systems in which surface waters are relatively fresh and non-turbid and in which primary productivity may be phosphorus limited. While surficially similar, these vernal pools differ in their physical and chemical hydrology, and therefore should be treated differently in resource conservation, restoration, and management efforts.

An intermountain playa wetland preserve in Colorado's San Luis Valley was studied to assess how its current hydrologic function compares to its natural hydrologic regime. Current hydrologic conditions were quantified, and on-site effects of off-site water use were assessed. A water-budget model was developed to simulate an unaltered (i.e., natural) hydrologic regime, and simulated natural conditions were compared to observed conditions. From 1998–2002, observed stream inflows accounted for ≥ 80% of total annual water inputs. No ground water discharged to the wetland. Evapotranspiration (ET) accounted for ≥ 69% of total annual water loss. Simulated natural conditions differed substantially from current altered conditions with respect to depth, variability, and frequency of flooding. During 1998–2002, observed monthly mean surface-water depth was 65% lower than under simulated natural conditions. Observed monthly variability in water depth range from 129% greater (May) to 100% less (September and October) than simulated. As observed, the wetland dried completely (i.e., was ephemeral) in all years; as simulated, the wetland was ephemeral in two of five years. For the period 1915–2002, the simulated wetland was inundated continuously for as long as 16 years and nine months. The large differences in observed and simulated surface-water dynamics resulted from differences between altered and simulated unaltered stream inflows. The maximum and minimum annual total stream inflows observed from 1998–2005 were 3.1 × 10⁶ m³ and 0 m³, respectively, versus 15.5 × 10⁶ m³ and 3.2 × 10⁶ m³ under simulated natural conditions from 1915–2002. The maximum simulated inflow was 484% greater than observed. These data indicate that the current hydrologic regime of this intermountain playa differs significantly from its natural hydrologic regime, which has important implications for planning and assessing conservation success.

Freshwater marshes are often subject to severe disturbance from seasonal drying (dry-downs) and frequently have distinct food webs relative to other freshwater systems. Subtropical marshes in the Florida Everglades have a unique trophic structure characterized by low nutrients, high standing stocks of algae in the form of floating and benthic periphyton mats, low standing stocks of primary and secondary consumers (omnivorous small fishes, tadpoles, and large macroinvertebrates), and very low standing stocks of tertiary consumers (large fishes). To account for this trophic structure, two hypotheses have been proposed: 1) high algal standing stocks result from top-down control over omnivores (small fishes, tadpoles, and macroinvertebrates) by large fishes, or 2) that the physical and biotic structure of periphyton mats impedes grazing. We conducted caging experiments before and after the dry season to delineate interactions among species influencing trophic structure in these marshes. Treatments included a refuge cage that was accessible to omnivores but excluded large fishes, an open cage accessible by omnivores and large fishes, and an omnivore exclusion cage designed to exclude fishes, tadpoles, and large macroinvertebrates. The physical and biotic structure of mature periphyton mats mediated direct and indirect interactions of omnivores and large fishes. More omnivores used the refuge treatment compared to the open treatment, likely to avoid large fishes, leading to a trophic cascade where abundance of epiphytic algae was reduced. Reductions in epiphytic algae were especially pronounced after the dry season when neonate sailfin molly were the dominant omnivore. We did not find comparable reductions of periphyton-mat biomass in the refuge treatment, suggesting that edible forms within these mats gain an associative refuge from grazers. Reduced grazing on edible algae in mature periphyton mats may explain the high standing stocks of algae characteristic of Everglades marshes.

Cranberry agriculture is a major land use in parts of the New Jersey Pinelands, USA. We compared the composition of genus-level macroinvertebrate assemblages collected from three habitats (muck, vegetated muck, and woody debris) in 12 New Jersey Pinelands blackwater streams draining forest, abandoned-cranberry bogs, and active-cranberry bogs and evaluated whether variations in macroinvertebrate assemblages were related to differences in land uses within the associated drainage basins. All 12 streams were relatively slow moving and acidic, with low conductance values and dissolved-oxygen concentrations. Muck was the dominant substrate at most stream sites. Many of the taxa that we encountered are adapted to lentic habitats, slow-moving lotic habitats, or low-oxygen environments. Macroinvertebrate composition differed significantly between the active-cranberry streams and the other two stream types and was associated with a complex environmental gradient represented by variations in dissolved oxygen, temperature, specific conductance, stream width, and woody debris. Overall, the effect of stream type appeared to overshadow that of the three different habitats. Although we cannot conclude that subtle between-site differences in dissolved oxygen were responsible for variations in community composition, many of the genera associated with the forest and abandoned-bog/active-cranberry ends of the community gradient are reported to have contrasting tolerances to low-oxygen levels. The relationship between reduced canopy cover and both lower woody-debris cover and higher stream temperatures, which can influence dissolved-oxygen levels, was most likely related to forest-canopy removal associated with historic- and active-cranberry agriculture.

The seasonal dynamics in habitat characteristics of temporary freshwater pools were studied in relation to hydroperiod and geographical location for a set of 36 pristine pools in and around the Kiskunság National Park (Hungary). The pools were geographically distributed over three clusters and their hydroperiod varied from seven to more than 18 weeks. Biweekly to monthly monitoring started two weeks after inundation (March) and lasted until most pools were dry again (July). Throughout the season, nutrient concentrations and conductivity increased in all study pools. Algal biomass increased after short hydroperiod pools were already dry, resulting in an increase in the amount of suspended solids and turbidity in pools with a relatively long hydroperiod. Both the longer inundation period and conditions later in the season may have contributed to the stronger algal growth in these pools. Oxygen was not depleted towards the end of the season, potentially due to growing algae and vegetation. The high buffering capacity of the water may have contributed to the near constant pH levels through time. Pools in one of the clusters were typically more turbid, less vegetated, and had higher amounts of suspended matter when compared to pools in the two other clusters. Temporary pool characteristics were related to local environmental conditions and seasonal dynamics differed according to the duration of inundation.

Anthropogenic activities affect self-organization in wetlands, in turn affecting spatial patterns of soil properties such as pH, nutrient concentrations, and soil organic matter content. To better understand the effects of anthropogenic disturbance in wetlands, we examined soil patterns in wetlands subject to a gradient of human impact. Four cypress domes in north Florida representing reference/unmanaged, forest plantation, improved pasture, and urban land uses were sampled (n  =  60 site⁻¹) for soil pH, organic matter (OM), and total phosphorus (TP). Mean values varied significantly both within and among sites, with low pH, SOM, and TP at minimally impacted and plantation sites, and high values at pasture and urban sites. Within-site variability was large for SOM and TP in all sites (average coefficient of variation  =  48% and 62%, respectively), and small for pH (average CV  =  7%). Strong radial patterns for SOM and TP in minimally impacted and plantation sites were observed. In contrast, at pasture and urban sites linear/quadratic trends in pH were observed. We quantified spatial patterns by soil property for each site, observing significant structure (long range, low nugget:sill) for TP and SOM in minimally impacted and forest plantation sites. We infer a transition from endogenous to exogenous drivers with increasing anthropogenic influence. Our findings indicate that, for pH, a small number of samples (n < 3 for characterization within 10% of true mean) are needed, while more (n  =  11–33) are needed for SOM and TP; sampling density requirements increase with the scale of spatial structure. Our results allow the definition of the necessary sampling intensity and design to achieve effective monitoring.

Short-term methane and carbon dioxide flux rates were measured in two created, experimental marshes in the Midwestern U.S. over a two-year period (2004–2005) in which hydrologic conditions were manipulated to simulate flood-pulse and steady-flow conditions. Gas flux rates were measured in three distinct wetland zones: continuously inundated areas; edge zones with emergent macrophytes; and edge zones in which emergent macrophytes were removed. Methane fluxes between years were not significantly different in edge zones with and without emergent vegetation, but were twice as high in continuously inundated zones during the steady-flow year compared to the flood pulsed year. There was no apparent relationship between emergent vegetation and methane flux, as mean flux rates were not significantly different in either year in edge zones where emergent vegetation was removed, compared to edge zones containing emergent vegetation. Continuously inundated wetland zones emitted methane from summer through fall, while in edge zones methane fluxes were only substantial in spring and summer. Neither daytime rates of carbon dioxide uptake or nighttime rates of respiration were significantly different between the years for any wetland zone. When CO₂ flux rates (daytime uptake plus nighttime respiration) were normalized for solar radiation and day length, solar efficiency was found to be comparable between the steady flow and pulsed years. Methane fluxes were more strongly affected than carbon dioxide fluxes by the differences in hydrology, but only in the deeper areas of the wetlands.

The fundamental role of hydrology in determining HGM classification and function leads to the assumption that any test of regionalization might do well to begin with a comparison of hydrologic variation within regional subclasses across a geographical or landscape continuum. This paper deals with only the basic hydrologic comparisons between New York, Pennsylvania, and Virginia for similarly classified wetlands in all three regions. Water levels for headwater floodplain wetlands varied substantially between the New York region and the Pennsylvania and Virginia regions; the latter regions were very similar. The same pattern was evident for slope wetlands across the three regions, but there was no significant difference in water levels for riparian depressions. Based upon the hydrologic data alone, it seems that applying the classification outside of central Pennsylvania had mixed results; it worked well south to Virginia and less well north to New York. One substantial influence in New York was the presence of beaver (Castor canadensis) that greatly influenced almost every watershed we worked in. Furthermore, climate differences between the three regions may also have a large impact – the New York sites were subject to much more snow than sites further south.

I analyzed two sets of the same 583 vegetation plots (0.25–10 m²) and 97 plant taxa sampled in 1993 and 2001 in the Peace-Athabasca Delta (PAD), northern Alberta, Canada. Cluster analyses and Bray-Curtis ordinations were used to examine relationships between environmental and biological factors and wetland community changes over a flood-drawdown cycle. While water regime was key to explaining variation in the vegetation, the vegetation gradients were complex. Vegetation structure, bison grazing, and landscape attributes such as distance to nearest major river, relative elevation, and geographic location within the PAD also played significant roles in explaining variation in the vegetation. Autocorrelations among physical and biological factors indicate that the physical and biological regimes were integrated. The importance of environmental and biological variables in explaining vegetation variation changed from pre- to post-flood. The 1993 and 2001 vegetation matrices were positively associated, indicating that by 2001 the vegetation had returned to a state similar to that of 1993. Overall, 35% of the plots remained within the same cluster type from 1993 to 2001. Eight of the 25 cluster groups and 53% of all plots occupied the middle of environmental and biological gradients. There was a higher diversity of wet graminoid communities than there was of dry woody communities. Species turnover, unpredictable processes, and overlap in ecological tolerances impart an irreducible stochasticity to the vegetation at the plot scale. The future of the PAD's vegetation and biota are uncertain due to the combined effects of climate change, wildfire, exotic species, water allocations, and discharge of contaminants and saline waters from the tar sands industry. Other than in areas of local infestation, weeds remain a minor cause for concern but without a transition to cooler, moister conditions, weeds may rise in dominance and affect the future of the ecosystem.

It has been hypothesized that tiger salamanders (Ambystoma tigrinum) in fishless aquatic habitats are functional equivalents of planktivorous fish. I tested this idea in a series of fishless prairie wetlands (“potholes”) in southwestern Manitoba by comparing macroinvertebrate community structure and phytoplankton standing crop across a gradient of gray tiger salamander (A. tigrinum diaboli Dunn) abundance, and in the presence and absence of tiger salamanders. Estimates of tiger salamander abundance included both adult and larval forms. Separate analyses yielded similar results. First, across a set of 45 potholes sampled over two years, I found that as tiger salamander abundance increased, aquatic insect abundance decreased and phytoplankton standing crop increased. Second, for a subset of seven potholes that had tiger salamanders one year but not the other, reverse trophic structure patterns were observed. For all analyses, abundances of mostly herbivorous and detritivorous macroinvertebrates (e.g., Gastropoda, zooplankton) were unrelated to tiger salamander abundance suggesting that either aquatic food web relationships in prairie potholes are complex or the link between tiger salamanders and phytoplankton standing crop may partly be a function of nutrient recycling rather than only direct predator-prey interaction. These results support the idea that effects of tiger salamanders on the trophic structure of prairie potholes mimic those of planktivorous fish.

We investigated the effects of river floodpulses on the water chemistry and diatom assemblages in a floodplain wetland. During the two year study period (November 2003–September 2005), the river and wetland exhibited three periods of surface hydrologic connectivity. The impacts of flooding depended on flood magnitude and duration. Both the long/high magnitude and short/high magnitude floods thoroughly mixed river and wetland waters, with conductivity, total nitrogen, and total phosphorus in the wetland decreasing to levels similar to the river. In contrast, the short/low magnitude flood did not mix water chemistry. Wetland conductivity, total nitrogen, and total phosphorus remained elevated. Changes in algal biomass followed changes in water chemistry with the high magnitude floods producing conditions unfavorable for algal growth. Algal biomass decreased in the wetland coinciding with the two high magnitude floods. Increases in algal biomass coincided with the short/low magnitude flood. Wetland and river water column diatom assemblages were dominated by periphytic taxa. The diatom assemblage in the river and wetland were distinct, except during the short/high magnitude flood. During this period, floodwaters brought diatoms into the wetland and both systems were dominated by planktonic centric taxa. Similar diatom taxa were observed in the wetland water column assemblage and the assemblage collected in settling chambers, although their relative abundances varied. Shifts in the settling diatom assemblage coincided with periods of flooding, indicating that river floodwaters leave a discernable signal within this assemblage. Our findings indicate that caution should be exercised when using diatom-based bioassessment in frequently flooded wetlands as the wetland diatom assemblage is influenced by river floodwaters and changes may depend on the duration and magnitude of flooding.

The diversity and resultant habitat value of wetland plant communities in the Laurentian Great Lakes are dependent on water-level fluctuations of varying frequency and amplitude. Conceptual models have described the response of vegetation to alternating high and low lake levels, but few quantitative studies have documented the changes that occur. In response to recent concerns over shoreline management activities during an ongoing period of low lake levels in lakes Superior, Michigan, and Huron that began in 1999, we analyzed a quantitative data set from Saginaw Bay of Lake Huron collected from 1988 to 1993 during a previous lake-level decline to provide the needed information on vegetation responses. Transects were established that followed topographic contours with water-level histories that differed across a six-year period, ranging from barely flooded to dewatered for varying numbers of years to never dewatered. Percent cover data from randomly placed quadrats along those transects were analyzed to assess floristic changes over time, document development of distinct plant assemblages, and relate the results to lake-level changes. Ordinations showed that plant assemblages sorted out by transects that reflect differing water-level histories. Distinction of assemblages was maintained for at least three years, although the composition and positioning of those assemblages changed as lake levels changed. We present a model that uses orthogonal axes to plot transects by years out of water against distance above water and sorted those transects in a manner that matched ordination results. The model suggests that vegetation response following dewatering is dependent on both position along the water level/soil moisture gradient and length of time since dewatering. This study provided quantitative evidence that lake-level fluctuations drive vegetative change in Great Lakes wetlands, and it may assist in making decisions regarding shoreline management in areas that historically supported wetlands.

Short term nitrogen uptake dynamics in the marshes of the southern Everglades, USA, were determined through implementation of a field mesocosm and isotopic enrichment method. The approach was tested using six mesocosms, three enriched with a 300‰ ¹⁵N tracer, Ca(NO₃)₂ (± 98% ¹⁵N) and three unenriched mesocosms. This ¹⁵N tracer technique allowed the determination of nitrogen fluxes between key ecosystem components. The in situ mesocosm experiment was conducted in a freshwater marl prairie marsh habitat for a period of 21 days. Macrophytes (Cladium jamaicense), periphyton, soil, and consumers (Gambusia holbrooki) were sampled at prescribed intervals to determine the optimal sampling periods necessary to capture peak ¹⁵N tracer uptake. Over the course of the study period, ¹⁵N tracer was detected in all ecosystem components sampled except for soils. Periphyton exhibited the most rapid initial ¹⁵N tracer uptake, with an increase of 3.86‰ to 7.79‰ (± 1.70) only 5 minutes after tracer addition. Periphyton¹⁵N signatures continued to increase to 16.49‰ (± 6.45) and 108.15‰ (± 49.40) after 10 minutes and 6 hours, respectively. Increased ¹⁵N signatures were also noted in the macrophyte and consumer components, with peak tracer uptake values occurring in aboveground macrophyte tissue at t  =  9 day (26.62‰ (± 5.00)), the belowground macrophyte tissue at t  =  15 day (22.01‰ (± 5.83)), and in consumers at t  =  15 day (297.09‰ (± 127.36)). Tracer uptake by the soil component was minimal with no significant amount of tracer being detected in any of the three soil layers sampled (0–1, 1–5, and 5–10 cm). This testing of the in situ mesocosm and ¹⁵N isotopic enrichment approach provides a foundation for further experimentation with the method at this and other wetland study sites.

Landscape changes were examined in the Peace-Athabasca Delta, northern Alberta, Canada for the period 1945 to 2001 in 24 randomly chosen study areas. Proportions of the landscape covered by four community types (open water, marshes and meadows, shrub communities, and forests) were determined on airphotos from five periods. Progressive, retrogressive, and oscillatory changes were observed. Variation in cover was about 4–10 times greater than net change. Median rates of both increase and decrease were about 0.2% to 0.6% of the landscape per year. There was evidence of temporal stability in some areas, while in other areas, a dynamic mosaic existed. Local or short-term changes were often large (> 1% per year), but averaged over the entire delta, or over time, net changes were small. Net changes were the lowest in forests and the highest in marshes. Succession between open water and marshes and between marshes and willows were common. Forest showed little evidence of transition to other types. Oscillatory changes in open water and marshes were typical. Open water, marshes, and willows changed at similar rates and more rapidly than did forest. Succession from open water and marsh communities toward willow communities and forests is to be expected at centennial scales. In a naturally oscillating system, trends appear or disappear as temporal and spatial scales change. Short duration studies, or those of limited spatial extent, may provide inaccurate estimates of vegetation change in a large dynamic delta. Interactions between drivers such as isostatic rebound, sedimentation, and avulsions mean that the Peace-Athabasca Delta will remain dynamic.

Annual species contribute significantly to the standing biomass of tidal freshwater marshes, but they tend to be distributed unevenly along the elevation gradient, with higher surface elevations supporting greater densities of annual species. We explored the generation of this pattern by evaluating how different life history stages of annual species are related to elevation and to each other. In 2006, we counted seedlings emerging from the seed bank under optimal greenhouse conditions, as well as seedlings and mature stems of annual species in 38 plots located at different elevations in a tidal freshwater marsh near Alexandria, Virginia, USA. Annual species seedling and mature stem density increased with elevation of the marsh surface, but seed density did not change with elevation. Seeds of annual species germinated in saturated rather than flooded conditions (4.50 ± 0.54 versus 1.66 ± 0.26 species/greenhouse container ± SE). Germination and survival from seedling to mature stem affected density of annual species across an elevational gradient, but the relative importance of either process differed by species. Amaranthus cannabinus was common and frequent in the seed bank (68% of all plots), and seed density increased with elevation, but seedlings and mature stems were infrequent at any elevation (21% and 5%, respectively), suggesting that germination is limiting its recruitment to standing vegetation. In contrast, Bidens laevis was uncommon in the seed bank (18% of all plots), but was frequently observed as seedlings and mature stems (55% and 34%, respectively). We therefore conclude that B. laevis recruitment was limited by its ephemeral seed bank. Impatiens capensis density did not appear to be limited by germination or survival to maturity as density of the species was high at all life history stages. Rather, its strong positive relationship with elevation at all life stages shows that I. capensis is limited by water inundation, particularly in spring when seeds require oxygen to germinate. Overall, we show that annual species increase in density at higher elevations in a tidal freshwater marsh, but that recruitment of each species may be limited by different intrinsic and extrinsic processes.

The determination of the anisotropic and heterogeneous character of the saturated hydraulic conductivity (K_s) of wetland soils is technically challenging, but is crucial for the accurate quantification of flow and transport processes. We modified a laboratory method to determine K_s both in the vertical (K_s,v) and horizontal directions (K_s,h), and tested it on the same undisturbed peat samples using a constant head upward flow permeameter. The first results showed that K_s,v was greater than K_s,h in the majority of samples from two profiles of a degraded fen peat, indicating that K_s was anisotropic. In conclusion, the described method was suitable to determine K_s,v and K_s,h and can be recommended to estimate the anisotropy of K_s in wetland soils.

Above- and belowground biomass of the macrophyte Schoenoplectus maritimus was measured in Camargue (Rhône delta, southern France) using destructive and non-destructive sampling methods. Our aim was to validate whether non-destructive sampling could be used for long-term monitoring of marshes subjected to grazing by cattle and Greylag geese (Anser anser). Height and diameter explained more than 95% of the variation in shoot biomass but the allometric models differed between 2002 and 2003 for the grazed marsh and between the grazed and ungrazed marshes in 2003. This indicates that a generalized model could not be derived and that specific models would have to be established for each marsh. However, we determined that sampling 20 shoots per marsh would be sufficient to establish accurate models. Allometric models underestimated aboveground biomass obtained by destructive sampling and we thus computed correction factors. Total belowground biomass was adequately predicted by the aboveground biomass although the precision of the relationship varied between marshes and years. We concluded that non-destructive sampling can be used to estimate biomass of S. maritimus but that the technique must be adjusted for each study.

The Okavango Delta in Botswana is one of the world's most valuable wetland resources. The diverse and complex nature of the Okavango Delta in terms of its natural resources, the wide range of users and uses, the diversity of managers, and the array of national laws, policies and guidelines, regional and international conventions, and agreements and protocols are all factors that dictate the need and determine the context for an integrated management planning process for the Delta. Development of an integrated management plan for the Okavango Delta began in 2002 and was completed in 2007. The approach to the planning process was based on the main principle of strengthening ownership through accountability and active participation of all stakeholders during both development and implementation of the plan, with local communities being considered as particularly important role players in the planning process. The process of developing a management plan was divided into three phases: planning, implementation, and review. This paper describes the planning phase, which ended in 2007. The challenge remains to ensure that implementation and review of the plan occurs.

The golden apple snail (Pomacea maculata Perry) is an invasive species that lays its eggs out of water but is otherwise aquatic. To investigate this behavior and potential management techniques, we conducted experiments to examine the physical effects of immersion and underwater egg predation on hatching success. Predation on submerged eggs by P. maculata adults reduced hatching success by ∼99%. In predator-free conditions, hatching success was reduced 75% by immersion in water and was negatively correlated with time submerged. Our results suggest that both underwater egg predation and low immersion tolerance may be exploited to limit the spread of P. maculata.