The requirement of Section 305(b) of the Clean Water Act (CWA) that all waters of the U.S. be assessed every two years has been historically ignored for wetlands, even though they are included in the definition of “waters of the U.S.” This paper presents the use of a landscape and rapid assessment to describe the wetland resource and assess wetland condition in the Upper Juniata watershed in central Pennsylvania, USA. A Floristic Quality Assessment Index (FQAI) is used to calibrate and refine the landscape and rapid assessments. The landscape assessment defined ecological condition of sites in terms of the degree of departure from reference standard condition (i.e., wetlands in predominantly forested settings). Criteria for condition categories were based on the literature or best professional judgment and resulted in more than half of the area of the resource being rated in high or the highest condition, while about 12% was rated in low condition. The rapid assessment adjusts the landscape assessment by accounting for the presence of stressors and the ameliorating effects of a buffer. This resulted in a 38% decrease in the proportion of wetland area in the highest and high condition categories and almost quadrupled the area in low condition. Classification and Regression Tree (CART) analysis was used to evaluate 1) whether the results of the landscape and rapid assessments correspond to those from the more quantitative data in FQAI and 2) whether the condition categories established for the landscape and rapid assessments agree with those established using FQAI. CART results indicate that our initial delineation of condition categories for the landscape and rapid assessments should be more stringent. However, it appears that the rapid assessment does a better job of gauging the factors important to wetland condition, as measured by FQAI, than the landscape assessment. This work can serve as a template for wetland monitoring and assessment and reporting as required by the U.S. Clean Water Act. Overall, such monitoring provides information that can be used to target areas for attention or protection, prioritize sites for restoration, design restoration projects, and choose best management practices.

This paper reports on the ecological status of wetlands in the Upper Juniata watershed in Pennsylvania, USA, as determined by employing the hydrogeomorphic (HGM) approach. HGM assessment provides a measure of the potential functional performance of a single wetland for up to 11 functions, depending on the subclass. Functional Capacity Index (FCI) scores calculated for each function range between a score of 1 (indicates the site is performing at optimum levels) and a score of 0 (indicates the site is not performing the function). Mean scores for all functions for the wetland resource in the Upper Juniata ranged from 0.48–0.63, except for Long-term Surface-Water Storage (0.39) and Characteristic Hydrology (0.85). Cumulative Distribution Function (CDF) plots were fairly linear over most of the distribution for all functions, indicating that the FCI scores were evenly distributed over the population. Several of the plots flattened at the upper and/or lower ends of the curves, indicating that a very small proportion of the wetland area had the highest and lowest scores. Clustering of the 69 riverine and slope sites using the FCI scores from the three functions with the most well-developed models resulted in the formation of four Functional Status Groups (FSGs). Groups 1 and 2 represented relatively high functioning groups of sites. They were differentiated by an exceptionally high Plant Community Function in Group 1 that differed significantly from the low value in Group 2. FSG's 3 and 4 represented relatively low functioning groups of sites and were differentiated by a significantly high Vertebrate Community Function in Group 3. We defined three reference domains (Natural, Agricultural, and Developed) based on predominant land cover. Sites of any given FSG were distributed across the reference domains, but there were some differences in distribution. Sites in the Natural Domain were much more likely to be in the higher functioning FSGs, while the Agricultural Domain was dominated by sites with an overall low level of functioning. Sites in the Developed Domain are equally distributed across the four FSGs. In summary, we demonstrated how HGM assessment might be employed to describe the functional status of the wetland resource in a watershed. We also demonstrated how the results of the assessment could be (1) used to evaluate the efficacy of the models comprising the HGM assessment and (2) combined with other data to identify relationships that could be used to develop management approaches.

A multi-level approach to wetland assessment and monitoring has been developed to incorporate information from multiple spatial scales and varying levels of effort. In this approach, wetland condition is evaluated in an intensive assessment through detailed, on-site measurement of physical and biological condition, and is inferred in a landscape assessment from a wetland's landscape setting characterized with available spatial data. This study assessed a comprehensive set of landscape metrics to improve an existing landscape assessment using wetland condition measures from the Upper Juniata intensive assessment data. On-site measures of wetland state (n = 10) were compared with landscape metrics (n = 47) measured at multiple spatial scales using Pearson's correlation coefficients. Landscape metrics enhanced the existing landscape assessment if they were correlated with condition metrics not correlated with the existing landscape assessment. Finally, landscape metrics identified through the correlation analysis were used to place sites in categories of condition based on the Floristic Quality Assessment Index (FQAI) using classification and regression tree analysis (CART). Results showed the existing landscape assessment metric is correlated with multiple measures of wetland state. The study identified landscape metrics that could enhance the existing landscape assessment, including measures of near-stream land use measured at an upstream scale, the percent of agriculture on steep slopes in a 250-m-radius circle or upstream area, and a measure of interior forest measured at a 250-m landscape circle or an upstream scale. Finally, the CART analysis showed the prediction of the FQAI was significantly (p < 0.001) improved by the addition of the landscape metrics identified in this study.

The hydrogeomorphic (HGM) approach to wetland assessment was combined with the Environmental Monitoring and Assessment Program (EMAP) survey design procedures to evaluate the condition of non-tidal riverine and flats wetlands in the Nanticoke River watershed (Delaware and Maryland, USA). We found degradation of wetland functions below reference standard levels for the majority of wetlands in both classes. Wetland condition was also related to the level of disturbance in both wetland classes. In flats, the most common disturbances were associated with hydrologic and vegetation modifications. Flat wetlands with low HGM function scores for the Plant Community and Habitat functions had almost all been converted from hardwood forest to Loblolly pine plantations. Most modifications associated with riverine wetlands were associated with stream channelization. Results of this study demonstrate that a site-specific and reference-based approach to assessment (i.e., the HGM method) can successfully be applied at the scale of an entire watershed if it is combined with a sampling approach that allows sites to be selected without geographic bias. The approach can also be used to determine if wetland functions vary from one sub-basin to another, and results of this project can be used by managers to begin to develop strategies for restoration of wetland functions at the watershed scale.

One beneficial service of wetland ecosystems is the improvement of water quality through nitrogen (N) removal. However, one important N-removal process, denitrification, can produce the atmospheric pollutant nitrous oxide (N₂O). Wetland biogeochemical functions, such as N processing, can be assessed by the hydrogeomorphic (HGM) approach using a suite of simple field observations made in a single visit to a wetland. HGM assessments score functions on a scale of 0–1 where 1 equals the functionality of an undisturbed reference standard wetland and 0 equals the functionality of a completely degraded wetland. We compared seasonal measurements of potential denitrification, N₂O emissions, and related soil characteristics to HGM assessments of nine non-tidal riverine wetlands and seven flats wetlands in the Nanticoke River watershed in Delaware and Maryland, USA. Denitrification potential, measured as denitrification enzyme activity (DEA), was higher in riverine wetlands than in flats. DEA increased with increases in percent water-filled pore space, pH, ammonium concentration, and the percentages of N and organic carbon. DEA decreased with increases in oxidation-reduction potential (E_h) and water-table depth. The difference in DEA between riverine and flats wetlands was attributable to the differences in the correlated soil characteristics. N₂O emission rates were higher on average in riverine wetlands than in flats, but the difference was not statistically significant. N₂O emission rates were generally less predictable than DEA and showed only weak correlations with pH, water-table depth, and the percentage of water-filled pore space when data from riverine wetlands and flats were combined. HGM biogeochemistry function scores ranged from 0.18 to 1 for the riverine wetlands and from 0.24 to 0.98 for the flats. The scores did not correlate with N₂O emission or DEA, except for summer DEA in flats, which increased with increasing score. Wetland alterations that increase soil moisture relative to reference standard conditions decrease biogeochemistry and hydrology function scores but increase DEA. Biogeochemistry function scores would more closely reflect denitrification potential if the scoring incorporated measurements of soil characteristics that correlate with DEA.

We developed relationships for estimating wetland condition from remotely sensed data and digital maps. Assessment methods relying on maps rather than field sampling (level 1 assessment) are often expert systems summarizing the best professional judgments of wetland scientists. We instead developed level 1 assessment relationships by statistically analyzing results from field sampling. The field campaign applied the hydrogeomorphic (HGM) functional assessment approach to sample 143 freshwater flat and riverine wetlands in the Nanticoke River watershed, Maryland and Delaware, USA. Functional condition index (FCI) scores for five wetland functions were calculated from the field observations. We used geographic information system (GIS) analysis of digital maps to derive candidate landscape indicators for the sampled points. We tested which indicators correlated strongly with the field condition scores, and then we used stepwise multiple regression and regression tree analysis to identify the most effective combinations of landscape metrics for predicting the condition measurements. The best multiple regressions combined information from land-cover, road, and stream maps, especially a stream map resolving natural stream reaches from channelized or ditched reaches. For riverine wetlands, we obtained statistically significant regressions explaining 63%–85% of the variance of measured FCI scores for all five HGM functions (hydrology, biogeochemistry, habitat, plant community, and landscape). Comparable models for flat wetlands were also statistically significant but explained less (48%–54%) of the variance. Regression tree analysis produced more parsimonious models than did stepwise multiple regression. A tree model explained the same amount of variability as the multiple regression model for two flat and two riverine functions, but the tree model explained less variability for two flat and three riverine functions. Our level 1 relationships can be applied to estimate condition scores for unsampled wetlands and to provide confidence limits for those estimates. The uncertainty in predicting a condition scores for individual assessment points is high for most HGM functions, but the models can still help prioritize field visits to select sites for management action. Confidence limits are narrower for predicting mean scores across many wetlands, so the relationships are more powerful for predicting average wetland condition across an assessment area, such as a watershed.

Probability-based sample surveys are increasingly being used to assess natural resource condition, yet many of the techniques commonly used in survey sampling are not well known to environmental scientists. Here we discuss several techniques from survey sample methodology that can substantially increase the efficiency of a sample (lower the variance for the same sample size), make the survey more cost-effective, or adjust the analysis to accommodate difficulties in implementation, such as lack of access to all sample sites. The techniques are illustrated with two surveys that were designed to assess wetland condition: one in the Juniata watershed in Pennsylvania, USA, and one in the Nanticoke watershed in Maryland and Delaware, USA.

Nine field indicators were identified for evaluating the hydrologic, biogeochemical, and/or habitat functioning of stream channels, riparian zones, or both. We ranked condition from “relatively unaltered” to “severely altered” for each of the identified indicators based on the range of conditions actually encountered among reference sites in the Coastal Plain of North Carolina, USA. The rankings provided a framework for developing a narrative used for scoring condition of the indicators at the scale of a reach (100-m-long × 60-m-wide segment). Reach condition was then derived by aggregating indicator scores, which were weighted by the number of functions with which each indicator was affiliated. Watershed-scale assessments were conducted by sampling randomly chosen first- to fourth-order reaches within stream networks at the density of approximately one 100-m reach per 1.0 km² of watershed drainage area. We used the association between indicators and hydrologic, biogeochemical, and habitat functions to obtain aggregated, weighted scores for channel and riparian zone condition. We used both aggregated network scores and mean indicator scores to compare condition among stream networks. At a reach scale, scores of indicators suggest strategies for restoration. At the watershed scale, aggregate scores showed differences among stream networks that could be used to prioritize restoration efforts and monitor change over time.

We analyzed 40 existing wetland rapid assessment methods that were developed for a variety of purposes, including informing regulatory decisions and local land use planning, and reviewed them for their potential to assess ecological integrity or condition. Four evaluation criteria were used. We determined if the method 1) can be used to measure condition, 2) is truly rapid, 3) includes a site visit, and 4) can be verified. This resulted in six methods being selected for evaluation relative to a conceptual model describing the core elements of a wetland assessment method, including universal indicators of soil, hydrology, and biotic communities, as well as regional indicators. An additional nine methods were kept for ideas on indicators, scoring, or regionalization. From this review, we identified five general areas that need to be addressed when adapting existing methods or developing new methods to assess condition: 1) definition of the assessment area, 2) treatment of wetland type, 3) approaches to scoring, 4) consideration of highly valued wetland types or features, and 5) procedures for validation with comprehensive ecological data. With scoring in particular, we present the advantages of a method that produces a single integrative score. Development of a rapid assessment method can assist those interested in incorporating condition assessment into their programs because they require less time in the field and less taxonomic expertise than more quantitative methods, which can lead to significant cost savings and increased sample sizes.

Several salt marsh plant species can oxygenate soils through their aerenchymous tissue and thereby facilitate the growth of neighboring species. Such positive interactions remain poorly understood for tidal freshwater marshes, yet may explain why species adverse to submerged roots are able to thrive in these marshes. Field observations showed a positive association between Typha angustifolia L. and Impatiens capensis Meerb., the two co-occuring dominant species in our study system, suggesting either that T. angustifolia facilitates I. capensis or that both species respond to environmental gradients the same way without interacting directly. We tested the facilitation hypothesis in a greenhouse experiment that measured the growth response of I. capensis with and without T. angustifolia as a neighbor species. Both species affected reduction-oxidation potential of the substrate, but facilitation of I. capensis was not observed. Typha angustifolia depleted soil nutrients in experimental mesocosms and negatively affected belowground root growth but not aboveground biomass of I. capensis; however, nutrient replenishment by tidal flushing may decrease the likelihood for competition in natural systems. Our greenhouse study suggests that abiotic conditions, dispersal events, or competitive biotic interactions, and not facilitation, are predominantly influencing the distribution of these two species in tidal freshwater marshes. Indeed, field measurements demonstrate that both species are positively associated with marsh surface elevation, which is related to frequency and length of water inundation of the marsh surface.

Grazing and burning are commonly applied practices that can impact the diversity and biomass of wetland plant communities. We evaluated the vegetative response of wetlands and adjacent upland grasslands to four treatment regimes (continuous idle, fall prescribed burning followed by idle, annual fall cattle grazing, and rotation of summer grazing and idle) commonly used by the U.S. Fish and Wildlife Service. Our study area was Grays Lake, a large, montane wetland in southeastern Idaho that is bordered by extensive wet meadows. We identified seven plant cover types, representing the transition from dry meadow to deep wetland habitats: mixed deep marsh, spikerush slough, Baltic rush (Juncus balticus), moist meadow, alkali, mesic meadow, and dry meadow. We compared changes in community composition and total aboveground biomass of each plant cover type between 1998, when all units had been idled for three years, and 1999 (1 yr post-treatment) and 2000 (2 yr post-treatment). Analysis using non-metric multidimensional scaling indicated that compositional changes varied among cover types, treatments, and years following treatment. Treatment-related changes in community composition were greatest in mixed deep marsh, Baltic rush, and mesic meadow. In mixed deep marsh and Baltic rush, grazing and associated trampling contributed to changes in the plant community toward more open water and aquatic species and lower dominance of Baltic rush; grazing and trampling also seemed to contribute to increased cover in mesic meadow. Changing hydrological conditions, from multiple years of high water to increasing drought, was an important factor influencing community composition and may have interacted with management treatments. Biomass differed among treatments and between years within cover types. In the wettest cover types, fall burning and grazing rotation treatments had greater negative impact on biomass than the idle treatment, but in drier cover types, summer grazing stimulated biomass production. Our results illustrate the spatial and temporal complexity of the transition between dry meadow and wetland habitats, and variable interactions among plant communities, treatments, and annual wetland conditions.

Flooding and sedimentation are two of the dominant disturbances that influence tree species composition and succession in floodplain forests. The importance of these disturbances may be most notable during the germination and establishment phases of plant succession. Channelization of most alluvial systems in the southeastern United States has caused dramatic and systematic alterations to both hydrologic and sedimentation processes of floodplain systems. We determined the influence of these altered abiotic processes on the germination and growth of two common floodplain tree species: swamp chestnut oak (Quercus michauxii Nutt.) and overcup oak (Q. lyrata Walt.). Flood durations of 0 days, 15 days, and 30 days prior to germination was a factor in germination, but the effect varied by species. For instance, overcup oak, which has a higher tolerance to flooding than swamp chestnut oak, had higher germination rates in the flooded treatments (15-day x̄ = 78% and 30-day x̄ = 85%) compared to the non-flooded treatment (x̄ = 54%). In contrast, germination rates of swamp chestnut oak were negatively affected by the 30-day flood treatment. Sediment deposition rates of 2 cm of top soil, 2 cm of sand, and 8 cm of sand also affected germination, but were secondary to flood duration. The main effect of the sediment treatment in this experiment was a reduction in above-ground height of seedlings. Our study provides evidence for the importance of both flooding and sedimentation in determining tree species composition in floodplain systems, and that tolerance levels to such stressors vary by species.

Marsh terracing is used to restore coastal wetlands by converting shallow nonvegetated bottom to intertidal marsh. Terraces are constructed from excavated bottom sediments, and are commonly arranged in a checkerboard pattern of square cells with open corners to form terrace fields. In 1999, terrace cells of three sizes (large = 122 m sides with 1.30 ha ponds; medium = 61 m sides with 0.29 ha ponds; small = 30 m sides with 0.06 ha ponds) were incorporated into a restoration project constructed at Galveston Island State Park, Texas, USA. This restoration project provided an opportunity to examine how nekton populations and the cost effectiveness of terracing projects vary with cell size. We compared nekton density and biomass (as measures of habitat value) in marsh and open water habitat types among the three cell sizes of the terrace fields. We also compared the habitat value of these terrace fields with the area before project construction, with nearby nonvegetated bottom, and with natural marsh habitat. Nekton abundance and biomass increased substantially in the project area following restoration by marsh terracing. An analysis of post-construction samples detected few statistically significant differences in animal density and biomass among cell sizes or between the terraced areas and adjacent natural habitats. Within terrace cells, density, biomass, and species richness were generally higher in marsh vegetation than over nonvegetated bottom. Using these post-construction density data, GIS, and population models for selected fishery species, we show that populations of most fishery species increase as cell size decreases. However, as cell size decreases, the cost of terrace construction increases much faster than population size. Therefore, terrace fields constructed of medium or large cells would be more cost effective in providing fishery habitat than would terraces composed of small cells.

Accurate, efficient, and repeatable mapping of changes in wetlands and riparian areas (referred to collectively as wetlands) is critical for monitoring human, climatic, and other effects on these important systems. We used Landsat-based satellite imagery from 1988 and 2001 to map changes in wetland ecosystems in the Gallatin Valley of southwest Montana. Stochastic gradient boosting (SGB) was used to classify the 2001 image, and change vector analysis (CVA) was used to identify locations where wetland areas might have changed between 1988 and 2001. These potentially changed locations again were classified for the 1988 Landsat image using SGB. Areas of change constituted 3.4% of the study area, thus only this small percentage of the image was reclassified for the 1988 image. Overall change detection accuracy was 76%, although changes along the periphery of wetland boundaries and in areas of smaller upland inclusions were not distinguished as well as other changes. Overall accuracies of the SGB wetland classification maps were 81% for 1988 and 86% for 2001. CVA significantly reduced the number of pixels involved in the historical image classification compared to conducting independent classifications, thus reducing the potential for compounding classification errors in unchanged areas.

Although most investigations of clonal plants have focused on negative aspects of interactions with neighbors, some studies have shown positive effects of clonal plants on other species, especially clonal plants with a compact, or phalanx, growth habit. For example, several plant species have been observed to grow directly upon tussocks of the freshwater rush Juncus effusus L., and the phenology of those species appeared to correlate with seasonal dynamics of the Juncus canopy. The present experimental study was conducted to enable distinction among four aspects of the Juncus tussock microhabitat: 1) collapse of the Juncus canopy, typical of summer conditions, 2) springtime pre-collapse erect architecture of the Juncus canopy, 3) availability of a living tussock platform in the absence of a canopy, and 4) simple physical provision of an elevated, organic surface for colonization in the form of artificial rooting platforms. Several species responded to particular features of the Juncus effusus canopy; three of those species, Boehmeria cylindrica, Leersia oryzoides, and Lonicera japonica, were identified as facilitated species in previous research on facilitation by Juncus. Particular features of the Juncus tussocks that appeared to correlate with increased cover of colonizing species were Juncus canopy height, tussock basal diameter, and relative water depth atop the tussock. Thus, results of this experimental study support conclusions from prior work on facilitation by Juncus effusus and other tussock-forming species regarding the importance of tussock physical structure in providing sites for plant colonization in freshwater wetlands.

Channelization of alluvial systems alters the functions and processes of floodplain ecosystems. In the loess belt region of western Tennessee and northern Mississippi, channelization, the geology of the region, and past land-use practices have resulted in geomorphic readjustments of streams and the formation of valley plugs. Valley plugs completely block stream channels with sediment and debris, and can result in greater deposition rates on floodplain surfaces. We used dendrogeomorphic techniques to quantify floodplain sediment deposition rates from the last 100 years. The data were used to determine the spatial and temporal patterns of sedimentation in floodplains affected by channelization and the subsequent formation of valley plugs and in floodplains along unchannelized streams. We measured sediment accumulation by coring trees for age determination and measuring depth to the root collar of 63 trees at unchannelized sites and 214 trees at channelized valley plug sites. Mean floodplain deposition rates were greater at valley plug sites (x̄ = 1.71 ± 0.08 cm/yr) compared to rates at unchannelized sites (x̄ = 0.31 ± 0.02 cm/yr). The formation of valley plugs in channelized streams also affected the spatial and temporal patterns of sedimentation. Increases in deposition rates at the valley plug sites occurred approximately 30 years ago and corresponds to the timing of regional activities including: channelization projects, increases in agricultural activity, and the termination of stream dredging projects.

Invasive plants are a growing concern worldwide for conservation of native habitats. In endangered wet meadow habitat in the Upper Midwestern United States, reed canary grass (Phalaris arundinacea) is a recognized problem and its prevalence is more widespread than the better-known invasive wetland plant purple loosestrife (Lythrum salicaria). Although resource managers are concerned about the effect of reed canary grass on birds, this is the first study to report how common wet meadow birds use habitat in relation to reed canary grass cover and dominance. We examined three response variables: territory placement, size of territories, and numbers of territories per plot in relation to cover of reed canary grass. Territory locations for Sedge Wren (Cistothorus platensis) and Song Sparrow (Melospiza melodia) were positively associated with reed canary grass cover, while those for Common Yellowthroat (Geothlypis trichas) were not. Only Swamp Sparrow (M. georgiana) territory locations were negatively associated with reed canary grass cover and dominance (which indicated a tendency to place territories where there was no reed canary grass or where many plant species occurred with reed canary grass). Swamp Sparrow territories were positively associated with vegetation height density and litter depth. Common Yellowthroat territories were positively associated with vegetation height density and shrub cover. Song Sparrow territories were negatively associated with litter depth. Reed canary grass cover within territories was not associated with territory size for any of these four bird species. Territory density per plot was not associated with average reed canary grass cover of plots for all four species. Sedge Wrens and Song Sparrows may not respond negatively to reed canary grass because this grass is native to wet meadows of North America, and in the study area it merely replaces other tall lush plants. Avoidance of reed canary grass by Swamp Sparrows may be mediated through their preference for wet areas where reed canary grass typically does not dominate.

Wetlands are the intermediate between terrestrial and open water systems, and are thus fundamentally tied to changes in water table. Under normal climate conditions, wetlands may experience short periods of water scarcity through seasonal variations in precipitation or surface water run-off. However, during anomalous drought episodes, wetland plants may experience elevated water stress resulting in considerable decreases of both productivity and survival. Despite the intricate relationship between wetland macrophytes and water supply, little is known about the physiological responses of these plants to short-term water deficits. Therefore, the purpose of this study was to evaluate the effects of simulated drought on plant water relations in five herbaceous wetland species (monocots Carex alata, Juncus effusus, Peltandra virginica, and dicots Saururus cernuus, Justicia americana). In general, plant response to water deprivation may include drought avoidance (e.g., changes in stomatal conductance, leaf area, and leaf orientation) and/or drought tolerance (maintaining cell turgor through osmotic adjustments or cell wall elasticity). In this study, simulated drought resulted in significant decreases in xylem water potential (Ψ_xylem) for all five species, suggesting that these plants were physiologically affected by water deficit. Four of the five species showed outward signs of drought avoidance, including significant reductions in transpiration (C. alata, P. virginica, J. americana, and S. cernuus) and decreases in leaf area (P. virginica and J. americana). Interestingly, while adjustments in transpiration were observed for most plants during the dry period, no significant changes in water use efficiencies (WUE) were detected until after water repletion. Notably, two species (C. alata and P. virginica) had enhanced WUE as water availability returned to pre-drought conditions. Water deficits also promoted drought tolerance responses in all five species, as indicated by a change in bulk modulus of elasticity ([Private character epsilon]; all species) and decreased osmotic potential (Ψ_π; P. virginica). Taken as a whole, this study reveals two contrasting drought tolerance strategies in wetland herbs. While four of the species alter [Private character epsilon] to generate declines in Ψ, P. virginica favored decreases in osmotic potential (as indicated by decreases in Ψ_π at full saturation and at turgor loss point).

The heterogeneous nature and widespread anthropogenic impacts to wetlands in the Willamette Valley, Oregon, pose challenges to bioassessment of these systems. The purpose of this study was to examine diatom species patterns in relation to environmental variables in wetlands, and to compare a diatom-based wetland classification to a hydrogeomorphic (HGM) wetland classification. Surface sediment diatoms, water quality, physical habitat, and surrounding land use characteristics were assessed for 92 wetlands. A total of 419 taxa were identified. Taxa richness was high (mean = 54, range 15–94) and dominance by a single taxon at a site was low (mean = 27%, range 7%–78%). Assemblages were dominated by tychoplanktonic taxa (e.g., Staurosira construens) and periphytic taxa (e.g., Fragilaria capucina and Achnanthidium minutissimum). Non-metric multidimensional scaling and correlational analysis showed that diatom assemblages were correlated with water depth, summer and winter total phosphorus, soluble reactive phosphorus, and turbidity. Diatom-based classification of wetlands produced four statistically significant groups that corresponded to within-wetland water depth, nutrient levels, and turbidity. Diatom-based wetlands classification did not agree with a priori HGM classification. Diatom assemblages and common species were similar between depressional and riverine-impounded wetlands. Our results suggest that, despite regional heterogeneity in both diatom assemblages and environmental conditions, diatoms can be useful indicators of water quality and habitat conditions in riverine and depressional wetlands. HGM classification may be too coarse to elucidate patterns of diatom community structure and conditions of the habitat in these anthropogenically-impacted wetlands.

More than 25,000 playa wetlands are embedded in the Southern High Plains (SHP), USA. The SHP is one of the most intensively cultivated areas in the world and, as a result, the function of playas has been altered by deposition of eroded sediments. We monitored water levels in 33 playas in summer 2003 to examine the influence of land use (cropland vs. native grassland) and playa characteristics (playa area, watershed size, starting water level, volume loss, sediment depth, percent playa vegetation cover, and soil texture zone) on water loss rate and hydroperiod (consecutive days a playa held measurable surface water). Multiple regression models (selected using Akaike's Information Criterion) indicated that land use, percent playa vegetation cover, and soil texture zone were important factors explaining water loss rate while starting water level and land use were important in explaining hydroperiod. Playas with cropland watersheds have lost their hydric soil-defined volume due to sedimentation, which results in an increase in water surface area and evaporation, and possibly infiltration, thus shortening hydroperiod. Hydroperiod was not related to playa area. Based on hydroperiod, small playas should receive the same conservation consideration as larger playas. Future research should examine transpiration rates in playas within grassland and cropland landscapes.

Hydrologic models aid in describing water flows and levels in wetlands. Frequently, these models use a specific yield conceptualization to relate water flows to water level changes. Traditionally, a simple conceptualization of specific yield is used, composed of two constant values for above- and below-surface water levels and neglecting the effects of soil capillarity and land surface microtopography. The effects of capillarity and microtopography on specific yield were evaluated at three wetland sites in the Florida Everglades. The effect of capillarity on specific yield was incorporated based on the fillable pore space within a soil moisture profile at hydrostatic equilibrium with the water table. The effect of microtopography was based on areal averaging of topographically varying values of specific yield. The results indicate that a more physically-based conceptualization of specific yield incorporating capillary and microtopographic considerations can be substantially different from the traditional two-part conceptualization, and from simpler conceptualizations incorporating only capillarity or only microtopography. For the sites considered, traditional estimates of specific yield could under- or over-estimate the more physically based estimates by a factor of two or more. The results suggest that consideration of both capillarity and microtopography is important to the formulation of specific yield in physically based hydrologic models of wetlands.

We characterized biota in two unfragmented and two fragmented mangrove-lined tidal creeks on Andros Island, Bahamas, in May 2003, to examine particular effects of tidal creek fragmentation by road blockage. Total number of plant and fish species was significantly different between fragmented and unfragmented creeks, and species composition was significantly different both between unfragmented and fragmented creeks, and between downstream and upstream areas within fragmented creeks. More reef-associated, economically important and ecologically critical plant, macroinvertebrate, and fish species were observed in unfragmented tidal creeks, while fragmented creeks contained: 1) plant species typical of higher elevation estuarine habitat, 2) terrestrial and aquatic macroinvertebrate species typical of upland habitats, 3) macroinvertebrate species adapted to low flow, and 4) temperature-and saline-tolerant macroinvertebrate and fish species. Furthermore, fragmented tidal creeks had different size distributions of common organisms, e.g., smaller sizes of two economically important fish species (Lutjanidae). This study suggests that fragmentation of tidal creeks and the subsequent loss of hydrologic connectivity influences the diversity and composition of aquatic flora and fauna, and may considerably inhibit nursery function and other ecosystem services provided by these coastal systems. These data also provide a baseline with which community- and ecosystem-level responses to restoration of hydrologic connectivity in fragmented tidal creeks will be assessed.

Historically, depressional wetlands have been viewed as small, closed basins without a naturally integrated inter-wetland surface drainage system. In this view, landscape-level connectivity is limited to surface water as overland flow. Contrasting with this view, conceptual prairie pothole ground-water models have relied on ground-water connectivity to explain inter-wetland differences in salinity, duration of inundation, and vegetation structure. To help clarify this contrast, we compared differences in hydrology, ground-water connectivity, near-surface soil moisture, geomorphology, water chemistry, and vegetation community structure and productivity for a suite of depressional wetlands in an intermontane prairie of western Montana. We compared depressional wetlands with and without temporary (< 4 wk) surface-water and/or soil-water connections. Connected wetlands had significantly smaller catchments, but stored more water, stored water longer, and had higher specific conductance than did isolated wetlands. Connected wetlands also had higher net primary productivity and a different plant community composition than did isolated wetlands. Comparisons of study site hydrology, water chemistry, and soil development found strong evidence for no ground-water exchange among any of the wetlands. The absence of ground water connection among these intermontane depressional wetlands emphasizes the importance of temporary surface-water and soil-water connections in depressional wetland ecology, as well as the need to understand the landscape scale variation of dissolved solutes and the distribution, abundance, and productivity of wetland plants among depressional wetlands and across wetland landscapes.

Marsh management is used to improve the quality of wetland habitats for a variety of waterfowl and other waterbirds. However, alien plants, such as alligatorweed (Alternanthera philoxeroides (Mart.) Griseb.), may impact success of marsh management by competing with and displacing important native plants. In managed marshes, we tested effects of application rate (high, medium, and low) and timing (April and July) of two herbicides (triclopyr amine and imazapyr) on controlling alligatorweed and restoring native plants. In the year of treatment, imazapyr controlled alligatorweed better than triclopyr amine when applied in April, but the herbicides were equally effective when applied in July. High application rate of herbicides in April controlled alligatorweed better than the low application rate, but application rates of herbicides in July did not influence control. In the year of treatment, application of triclopyr amine resulted in greater native plant biomass than imazapyr. High application rate of herbicides in April resulted in greater native plant biomass in the year of treatment than low application rate, but native plant biomass did not differ among rates of herbicides applied in July. One year after treatment, the high application rate of herbicides resulted in less alligatorweed than the low application rate, and July applications of either herbicide generally controlled alligatorweed better than April applications. Application of imazapyr in July resulted in greater biomass of native plants one year after treatment than either imazapyr or triclopyr amine applied in April. This study demonstrates that single herbicide applications can be effective at controlling alligatorweed, and that these applications can have immediate and longer-term benefits for restoring native plants to managed marshes.

Human development pollutes runoff and ground water. Temporary pools are good habitats to study the influence of general non-point source pollution because they are created by runoff and ground water, among other processes, which, in northern Ohio, can contain substances accumulated over the winter. Furthermore, little information on land-use effects on temporary pools exists. To ascertain if general human activities influenced the water quality of northern Ohio temporary pools, monthly measurements of pH, dissolved oxygen, temperature, conductivity, and depth were monitored from March–June 2004 in 30 dispersed pools of the Cuyahoga River basin, Ohio, USA. Nutrient measurements for most pools were taken in May and June 2004. Pools were located in ten sub-watersheds containing differing percentages of geographic information system (GIS)-delineated urban/suburban and agricultural lands. General water quality characteristics of northern Ohio temporary pools were variable, both spatially and temporally. Nutrient levels were generally low (oligotrophic). Spearman rank correlation coefficients between the characteristics and percent land-use showed that conductivity and percent agriculture were positively correlated, while depth and percent urban were negatively correlated. Temporally, dissolved oxygen and depth showed fairly strong seasonal decreases from March–June. Some measurements from pools in mostly natural sub-watersheds suggested poor water quality. Although large-scale (watershed) land-use influences can affect the physicochemical nature of temporary pools, local anthropogenic influences, both past and present, probably also affect the quality of temporary pool wetlands.

The richness and ecological roles of yeasts in peatlands are largely unknown. This paper presents a review of the literature on yeasts in peatlands and also provides new data with species isolated from peatlands in Saskatchewan, Canada, and West Siberia, Russia. To date, 75 yeast taxa have been reported from peatlands, including 46 identified species and 29 isolates identified only to genus or not at all. This represents 5%–10% of known yeasts and about 10% of all peatland fungi. Cryptococcus, Candida, Pichia, and Rhodotorula are the most prevalent genera, accounting for 58% of known peatland yeast species. We obtained 34 isolates from western Canadian and West Siberian bog and fen peat, including 12 identified species and eight unidentified taxa. Identified taxa comprised mostly species of Candida, Cryptococcus, and Rhodotorula. Unidentified taxa were described based on physiology and morphology. Globally, more species have been reported from bogs than fens (41 vs. 13 taxa), and the species composition differs between the two peatland classes. The effect of depth within the acrotelm on yeast abundance and species composition varies among peatlands. Physiological profiling of the yeasts from our study showed that they can use (poly)saccharides (primarily D-glucose, maltotriose, n-acetyl glucosamine, trehalose, and sucrose), organic acids (primarily D-gluconic acid, fumaric acid, malic acid, and succinic acid), sugar alcohols (primarily D-arabitol, D-mannitol, and D-sorbitol), glycosides (primarily arbutin and salicin), and amino acids (primarily L-glutamic acid) as carbon and nitrogen sources. Based on these profiles, yeasts likely access simple polymers that leach from senesced and/or dead plant materials in peatlands and probably play important roles during the initial stages of organic matter decomposition.