Reference Wetlands Research Articles

Effects of industrial effluent on wetland macroinvertebrate community structures near a wastewater treatment facility

Macroinvertebrate communities and environmental variables were examined in wetlands near an industrial wastewater treatment facility to assess impacts from exposure to historical effluents. Baseline wetland assessments were required prior to cleanup of contaminated sediments at the facility. The study included wetlands historically exposed to direct effluent discharge, wetlands exposed to current effluent discharge (at the time of sampling), and reference wetlands. Wetlands were sampled in June, July, and September 2018 using a new macroinvertebrate community monitoring protocol (“Wetland CABIN”) developed by Environment and Climate Change Canada. Macroinvertebrates were counted and identified to Family level. Data were qualitatively analyzed using pie charts and nonmetric multidimensional scaling, as well as quantitatively with the Shannon-Weiner diversity index, the Berger-Parker index and using pollution sensitivity values. Correlations using Spearman rho were also calculated between indices and measured environmental variables. Wetlands near the treatment facility were not significantly different compared to reference sites. Macroinvertebrate communities near the treatment facility appeared to be relatively unimpacted by historical effluent inputs. The Wetland CABIN protocol may be a useful monitoring tool for assessing wetland macroinvertebrate community structure because it allows for standardized approaches to be used to compare temporal changes at contaminated sites or spatially between sites.

Correction to A Framework for Identifying Reference Wetland Conditions in Highly Altered Landscapes

A Correction to this paper has been published: https://doi.org/ https://doi.org/10.1007/s13157-021-01447-0

A Framework for Identifying Reference Wetland Conditions in Highly Altered Landscapes.

This paper arose from collaboration and discussions over the past years between the authors about what wetlands should be restored to in landscapes that have been intensively altered due to human activities over many centuries and where reference conditions are lacking. It is not intended as an in-depth review of the thinking about reference conditions, but as an opinion paper, with the goal of stimulating discussions about wetland restoration approaches, particularly in regions around the world with highly altered landscapes where restoration of wetlands has been gaining traction only relatively recently. We first explain why the thinking on reference wetlands is biased towards North America, where large areas exist with wetlands that are relatively unimpacted by anthropogenic activities. We then argue that in regions with few unimpaired wetlands those of fair condition may still be good enough to be used as reference wetlands, and that restored and created wetlands should be considered as well.

Molecular profiles of naphthenic acid fraction compounds from mine lease wetlands in the Athabasca Oil Sands Region

Naphthenic acid fraction compounds (NAFCs) are a toxicologically relevant component of oil sands process-affected materials (OSPM). For the first time, we report on differences in the concentrations and distribution of NAFCs from wetlands on an Athabasca oil sands mine site with varied histories of solid and liquid OSPM input. Sampling locations included natural and naturalized reference wetlands, a reclaimed tailings pond, wetlands supplemented with OSPM, opportunistic wetlands, and tailings ponds. Samples were prepared using solid-phase extraction, and analyzed by high-resolution Orbitrap mass spectrometry; NAFC concentrations and characteristics were evaluated for all locations. The NAFCs from tailings ponds were dominated by O3-NAFCs and classical naphthenic acids (NAs; i.e., O2 species) with double bond equivalences of 3 and 4. Reference wetlands had no dominant species, and relatively little NAFC content. The heteroatomic species in opportunistic wetlands were dominated by highly-oxidized NAFC species, where Σ [O3:O6] species constituted 55–75% of the assignable spectrum and 3–4% NAs; in tailings ponds NAs constituted 47–51%. A relatively young (4-year-old) wetland built on a former tailings pond had NAFC concentrations between 65 and 80 mg/L, and NAs constituted 47% of the assignable spectrum. There was thus little apparent oxidation of NAFCs at this young wetland. The composition of NAFCs from one wetland (≥15 years old) supplemented with OSPM contained a greater proportion of oxidized species than tailings, suggesting NAFC transformation therein. These data suggest that while NAFCs are persistent in some wetlands, there is preliminary evidence for oxidation in mature wetlands.

Perspectives on Maximizing Coastal Wetland Restoration Outcomes in Anthropogenically Altered Ecosystems

When restoring coastal wetlands, approaches can vary in construction technique, planting strategy, and site placement within an anthropogenically altered landscape comprising both relict wetlands and developed habitat. Constructed marshes are often composed of discrete terraces or mounds formed with excavated sediments, or beneficial uses (BU) dredge material can be used to fill continuous areas to emergent marsh elevation. Either construction approach can be seeded or planted with native species, or colonization can occur naturally. Sites can vary in the degree of hydrological isolation due to the presence of structures (e.g., roads or buildings) that limit connectivity to other marsh areas. Data collected across multiple sites on the upper Texas (USA) coast were used to assess how coastal wetland restoration “success,” measured as emergent plant cover, biomass, and species richness, was influenced by the localized configuration of individual restoration sites and by the placement of each site within a landscape matrix of reference wetlands and developed areas. Plant biomass and cover in BU marshes were similar to reference conditions and up to 70% higher than in excavated formations, regardless of planting technique or location in the landscape. Species richness was highest at the reference sites and lowest at planted beneficial uses sites, but none of the restoration sites had species assemblages similar to reference areas. Restoration outcomes were relatively robust to anthropogenic alterations of the landscape. Individual restoration sites were highly dissimilar from each other, and although some had very low (< 20%) emergent plant cover, these sites provided habitat for aquatic wildlife. This analysis demonstrates the importance of utilizing a range of restoration approaches within the broader landscape to achieve desirable ecosystem-level restoration outcomes.

Persistent effects of underground longwall coal mining on freshwater wetland hydrology

More than half of global wetlands have been lost because of anthropogenic disturbance, with the trend of decline continuing in the 21st century. While much of this loss relates to changes in surface flows, groundwater is also critical to sustaining wetland hydrology. Underground longwall mines extract coal seams, in turn fracturing the overlying stratigraphy, influencing aquifer connectivity and affecting surface flows via subsidence disturbance. Crucially, this subterranean disturbance may disrupt the hydrological processes that sustain freshwater wetlands at the surface. Here we present a new designed empirical study that compares the persistence of soil moisture after a rainfall event in wetlands subject to underground longwall coal mining to that in unmined reference wetlands. Accelerated Failure Time models showed that mined wetlands were persistently drier, retained water for shorter durations and exhibited less spatial differentiation than unmined wetlands. This quantitative evidence of severe, persistent hydrological change following resource extraction reinforces earlier observations and has important implications for biodiversity and provision of ecosystem services to a large urban population. If Ecologically Sustainable Development (ESD) outcomes and effective deployment of the mitigation hierarchy are to be achieved in line with current legislative and policy paradigms, our results highlight the need for more emphasis on impact avoidance and minimisation than restoration or offsetting to protect water and biodiversity values. Given severe constraints on restoration success, greater emphasis on avoidance in mine design and approval processes offers realistic opportunities for an improved balance between sustaining irreplaceable public assets and short-term benefits from non-renewable resource extraction.

Case study: On hydrological function improvement for an endemic plant habitat in Gangcheon wetland, Korea

Wetlands are one of the most important ecosystems for the biodiversity of plants and animals. Especially, Gangcheon wetland in NamHan river, Korea is a very valuable one because Aster altaicus var. uchiyamae, which is one of endemic plants is inhabited. However, Gangcheon wetland was impaired by a river improvement project called ‘Four Major Rivers Project’. After the project, Gangcheon wetland restoration work was performed, for the rehabilitation of wetland functions but the habitat of Aster altaicus var. uchiyamae could not be restored. Actually, Aster altaicus var. uchiyamae can grow in a habitat made by mixing of gravel and sand from flood inundation of the river but there was no inundation after the project because of the rise of levee height. Therefore, this study evaluated wetland functions using Hydrogeomorphic(HGM) approach and analyzed flood inundation using HEC-GeoRAS model after the project for diagnosis of the functions and the habitat. Then we proposed a plan to improve the functions of Gangcheon wetland as a habitat for Aster altaicus var. uchiyamae. The reference wetland is Gangcheon wetland before the project and the wetland functions after the project were compared with the reference one. As a result of the function assessment, hydrological, biogeochemical, and plant habitat functions were deteriorated. The study wetland has three zones of A, B, and C for Aster altaicus var. uchiyamae habitats and particularly, hydrologic functions for zone C which is poor as the habitat should be improved. In particular, the habitat of Aster altaicus var. uchiyamae was adversely affected by the decrease in inundation depth and water level of the river. These hydrologic functions should be improved and the levee height be lowered for obtaining more proper habitat of Aster altaicus var. uchiyamae. This suggestion might be helpful for establishment of the habitat of Aster altaicus var. uchiyamae. Also, it could be expected that the overall function of Gangcheon wetland will be improved because biogeochemical and plant habitat functions are rehabilitated by the improved hydrological function.

Contaminant characterization in wetland media surrounding a pulp mill industrial effluent treatment facility

Three media (sediment, surface water, and dragonfly larvae tissue) were collected from wetlands surrounding an industrial effluent treatment facility prior to closure. Samples were analyzed for metals, total mercury, and polychlorinated dibenzo-p-dioxins/polychlorinated dibenzofurans (PCDD/PCDF) concentrations. Sediment and surface water concentrations were compared to provincial and federal guidelines, as well as reference wetland concentrations. Exceedances of arsenic, cadmium, chromium, copper, zinc, and PCDD/PCDF guidelines were found in deeper areas of wetlands historically contaminated from effluent, as well as wetlands exposed to current effluent inputs. Composite Libellulidae samples were collected from wetlands, and comparisons were made to reference tissue concentrations + 20%. Elevated As, Cu and Pb tissue concentrations were measured at two site wetlands, but total mercury (THg) and PCDD/PCDF reference tissue concentrations were higher than wetlands near the effluent treatment facility. Spearman rho tests identified a significant correlation between sediment and tissue Pb concentrations and between surface water and sediment THg concentrations. Results suggest relatively low ecological risk to macroinvertebrates within wetlands near the effluent treatment facility from current effluent inputs, and highlight strengths and weaknesses of federal and provincial guidelines.

An evaluation of water quality at Sandhill Wetland: implications for reclaiming wetlands above soft tailings deposits in northern Alberta, Canada

The experimental Sandhill Wetland is the first permanent reclamation of a composite tailings deposit, and annual water quality monitoring is of specific interest for evaluating and predicting long-term reclamation performance. Here, we present water chemistry monitoring data obtained from Sandhill Wetland (years 2009–2019) and compare results to twelve natural reference wetlands and to environmental quality guidelines for Alberta surface waters. By comparing water quality at Sandhill Wetland and natural sites to established guidelines, we can begin to document the natural background water quality of wetlands in the region and examine if guideline exceedances are seen in natural undisturbed environments, or appear only at active reclamation sites. At Sandhill Wetland the dominant ions in near-surface water were bicarbonate, sulfate, chloride, sodium, calcium, and magnesium. Since the first growing season concentrations for these ions have increased annually, causing concurrent increases in electrical conductivity. In year 2019, water chemistry at Sandhill Wetland was most comparable to regional saline fens, systems that exhibit elevated electrical conductivity and high sodicity. Near-surface water at Sandhill Wetland exceeded water quality guidelines for three substances/properties (dissolved chloride, iron, and total alkalinity) in the most recent year of monitoring. The saline fen natural sites also exceeded water quality guidelines for the same chemical substances/properties, suggesting guideline exceedances are a norm for some natural wetland site types in the region. Of note, in each year of monitoring at Sandhill Wetland, dissolved organic compounds evaluated in sub- and near-surface water were below detection limits.

Plant Diversity and Soil Properties at Different Wetland Restoration Stages along a Major River in the Arid Northwest of China

Agricultural activity is widely recognized as one of the leading drivers of natural wetland loss in many parts of the world. The suitability of farmland abandonment as the wetland restoration has not been well studied in arid regions. The plant growth, community structure and soil property were examined in three farmlands abandoned for 2 (W2), 6 (W6) and 15 (W15) years and reference wetland (Wr) in the Zhangye National Wetland Park in Gansu province. The results showed that the plant abundance, soil organic carbon, total nitrogen, soil water content increased and pH value decreased along the wetland restoration stages. Shannon-Wiener diversity and Pielou’s evenness index moved towards natural wetland with increasing time of farmland abandonment, the plant community composition of the three abandoned farmlands also changed from annual to perennial dominant species. The farmland abandonment is conducive to improve soil nutrients and quality. Soil and vegetation facilitated one another in the abandonment stages. Thus, farmland abandonment is rational for wetland restoration. The mechanism of interaction between plant and soil can be used to guide wetland restoration of abandoned farmland.

The Third Generation of Pan-Canadian Wetland Map at 10 m Resolution Using Multisource Earth Observation Data on Cloud Computing Platform

Development of the Canadian Wetland Inventory Map (CWIM) has thus far proceeded over two generations, reporting the extent and location of bog, fen, swamp, marsh, and water wetlands across the country with increasing accuracy. Each generation of this training inventory has improved the previous results by including additional reference wetland data and focusing on processing at the scale of ecozone, which represent ecologically distinct regions of Canada. The first and second generations attained relatively highly accurate results with an average approaching 86% though some overestimated wetland extents, particularly of the swamp class. The current research represents a third refinement of the inventory map. It was designed to improve the overall accuracy (OA) and reduce wetlands overestimation by modifying test and train data and integrating additional environmental and remote sensing datasets, including countrywide coverage of L-band ALOS PALSAR-2, SRTM, and Arctic digital elevation model, nighttime light, temperature, and precipitation data. Using a random forest classification within Google Earth Engine, the average OA obtained for the CWIM3 is 90.53%, an improvement of 4.77% over previous results. All ecozones experienced an OA increase of 2% or greater and individual ecozone OA results range between 94% at the highest to 84% at the lowest. Visual inspection of the classification products demonstrates a reduction of wetland area overestimation compared to previous inventory generations. In this study, several classification scenarios were defined to assess the effect of preprocessing and the benefits of incorporating multisource data for large-scale wetland mapping. In addition, the development of a confidence map helps visualize where current results are most and least reliable given the amount of wetland test and train data and the extent of recent landscape disturbance (e.g., fire). The resulting OAs and wetland areal extent reveal the importance of multisource data and adequate test and train data for wetland classification at a countrywide scale.

Restoration of retired agricultural land to wetland mitigates greenhouse gas emissions

Retired farmland restoration is increasingly seen as a valuable opportunity to improve ecosystem functions in sensitive regions. For example, with expected mass retirement of cranberry farms in New England, there is increasing interest in restoring retired cranberry farms back to wetlands. To understand how restoration of retired cranberry farms to wetland ecosystems influences climate‐related ecosystem functions, we assessed methane and carbon dioxide emissions from different post‐farming management options, including an actively farmed cranberry bog, young and old retired cranberry bogs, young and old restored cranberry bogs, and a natural reference bog. In addition to methane and carbon dioxide, we measured key soil properties influential in greenhouse gas flux, including soil organic matter, moisture, pH, redox potential, and bulk density. Greenhouse gas flux differed significantly by site type, with the restored systems functioning similarly to the natural reference wetland while retired sites had fluxes similar to the actively farmed site. The older restored site had significantly lower emissions of both methane and carbon dioxide than the newly restored site, indicating that over a larger time scale, restored systems may transition from net carbon dioxide sources to sinks. Overall, the results of this study suggest that in addition to the many other ecological benefits, the restoration of wetlands may also play a role in climate change mitigation through their ability to store carbon.

Use of Remote Sensing and Field Data to Quantify the Performance and Resilience of Restored Louisiana Wetlands

Typical goals of wetland restoration efforts are to conserve, create, or enhance wetland structure, and to achieve wetland function that approaches or exceeds natural conditions. Measuring wetland establishment, condition, and resilience can be difficult, especially because monitoring wetland function has traditionally been time-intensive, costly, and often required repeat field-based surveys. Remote sensing provides novel collections of data and facilitates rapid assessments of wetland landscapes, land cover, species/habitat composition, change detection, degradation, diversity, as well as system threats and pressures. A combination of remotely collected and in situ vegetation data were used in conjunction with landscape metrics and vegetative indices. These data were used to evaluate and compare changes and trends in condition, function and resilience of restoration sites and reference wetlands in southwest Louisiana, USA. Results of this work show the restored wetlands reached structural and functional equivalency to reference wetlands after approximately three to ten years post-construction. With adequate maturity, the restored wetlands outperformed the reference wetlands, having higher percentage of land, land aggregation, aboveground vegetation productivity and floristic quality. Supplementing traditional field-based methods with remote sensing applications provided enhanced metrics for inventorying and monitoring of wetland resources, forecasting of resource condition and stability, and adaptive management strategies.

Spatial distribution of soil organic carbon and total nitrogen in disturbed Carex tussock wetland

Disturbance affects the ecological structure and function of wetland ecosystems by altering plant and soil properties. To identify the response of soil carbon and nitrogen to wetland disturbance, this study was conducted in three disturbed and two reference Carex tussock wetlands in Momoge National Natural Reserve, China. The content and stocks of soil organic carbon (SOC) and total nitrogen (TN) were determined to investigate the effects of disturbance on their spatial distribution. Generally, SOC and TN content and stocks gradually decreased with increasing soil depth except for in reference tussock wetlands that had an accumulation peak at 11–20 cm. In disturbed tussock wetlands, a significantly higher SOC content was observed in the top 10 cm of soil, while in disturbed and reference wetlands, no significant differences were found in SOC content and stocks, or in TN levels, in deep soil. Additionally, soil organic carbon and nitrogen were significantly correlated with soil water content (SWC), bulk density, soil porosity, and soil respiration (SR). Redundancy analysis revealed that SWC and SR were major determinants of soil carbon and nitrogen. These findings clarified the dynamic changes of soil carbon and nitrogen of disturbed wetland, which is highly significant for accurate estimation of wetland carbon and nitrogen reserves.

Modified hydrogeomorphic approach for estimating quantitative change of riverine wetland functions

HydroGeoMorphic (HGM) approach could examine relatively more details for wetland functions. However, HGM cannot be utilized in assessing the functional improvement of wetlands because it is limited to evaluating the similarity between the reference and the target wetlands. Therefore, this study proposes the Modified HydroGeoMorphic (MHGM) approach for considering better functions of target wetlands. The values of Index of Function (FCI) and variables in HGM are in the range of 0.0 to 1.0 and so, in MHGM, we redefine the values of variables in 0.0 to 2.0 to find a better function for the target wetland. Based on the monitored variables, FCIs for the wetland functions were estimated and the functions of dynamic surface and subsurface water storage, spatial structure of habitat, and maintaining the distribution and abundance of vertebrates in Imjin riverine wetland as a target wetland showed better FCIs than those of Hwapo which is a reference. This means that MHGM reflects an actual change in FCI, leading to a more favorable evaluation of the target compared to the reference wetland. This indicates that MHGM considers actual functional progress of wetlands by improving HGM's limitations in assessing change.

Evaluating the realized niche and plant–water relations of wetland species using experimental transplants

Wet meadows are a common focus of wetland restoration efforts, and the species within them often exist within a restricted range of water levels. Unfortunately, many restored wetlands have higher water levels and more open water than naturally occurring reference wetlands, and many are invaded and dominated by species of Typha. Most studies evaluating the optimal water level for plant species use observational methods, yet experimental methods are required to understand the breadth of a species’ niche. We used experimental transplants of Carex pellita, a common wet meadow sedge used in restoration in the interior of the USA, and Typha latifolia, a species of cattail which invades many restored wetlands, to test whether higher water levels in a restored wetland were prohibitive to the target sedge species. Physiological and growth measurements were collected on both species. We found that C. pellita grew as well or better when transplanted into the ponded water levels, while T. latifolia had reduced growth when transplanted into the relatively drier meadow conditions. Interestingly, C. pellita was able to adjust its Turgor Loss Point in response to changing water levels. Only recently the assumption of a constant Turgor Loss Point for each species has been questioned. Our results provide evidence that wet meadow species have a broader hydrologic niche than previously thought, and their ability to make physiological adjustments in response to changing water levels may allow them to thrive in areas with widely varying water levels.

Marsh bird occupancy of wetlands managed for waterfowl in the Midwestern USA.

Marsh birds (rallids, bitterns, and grebes) depend on emergent wetlands, and habitat loss and degradation are the primary suspected causes for population declines among many marsh bird species. We evaluated the effect of natural wetland characteristics, wetland management practices, and surrounding landscape characteristics on marsh bird occupancy in Illinois during late spring and early summer 2015–2017. We conducted call-back surveys following the North American Standardized Marsh Bird Survey Protocol three times annually at all sites (2015 n = 49, 2016 n = 57, 2017 n = 55). Across all species and groups, detection probability declined 7.1% ± 2.1 each week during the marsh bird survey period. Wetlands managed for waterfowl (ducks, geese, and swans) had greater occupancy than reference wetlands. Marsh bird occupancy increased with greater wetland complexity, intermediate levels of waterfowl management intensity, greater proportions of surface water inundation, and greater proportions of persistent emergent vegetation cover. Wetland management practices that retain surface water during the growing season, encourage perennial emergent plants (e.g., Typha sp.), and increase wetland complexity could be used to provide habitat suitable for waterfowl and marsh birds.

A comparison of wetland characteristics between Agricultural Conservation Easement Program and public lands wetlands in West Virginia, USA.

In West Virginia, USA, there are 24 conservation easement program wetlands enrolled in the Agricultural Conservation Easement Program (ACEP). These wetlands are located on private agricultural land and are passively managed. Due to their location within fragmented agricultural areas, wetlands enrolled in ACEP in West Virginia have the potential to add wetland ecosystem services in areas that are lacking these features. We evaluated ACEP wetlands compared to reference wetlands on public land in West Virginia by using surrounding land cover, vegetative cover, and wetland features and stressors such as the presence or absence of erosion, upland inclusion, algal mats, and evidence of impacts from the surrounding landscape as surrogate measurements of wetland function on 13 ACEP wetlands and 10 reference wetlands. ACEP wetlands had higher percentages of tree coverage and a higher proportion of agricultural land in the areas immediately surrounding the wetland. Reference wetlands had higher percent coverage of emergent vegetation and had a higher proportion of forest in the immediate landscape. Our findings suggest that ACEP wetlands provide valuable early successional and forested wetland cover in a state that is largely forested. Because of this, it is important to maintain and even expand ACEP in West Virginia to continue providing a valuable source of early successional wetland habitat.

A Macroinvertebrate Multimetric Index for the Bioassessment of Wetlands Adjacent to Agriculture Fields in the Sanjiang Plain, China

Adjacent intensive agriculture disturbs the natural condition of wetlands. However, to assess the effect of this agriculture on wetlands, few studies have used indices based on aquatic invertebrates. Multi-metric indices (MMIs) have been successfully used to assess freshwater ecosystems worldwide and are an important management tool, but little is known about their applicability in the Sanjiang Plain, Northeast China. In this study, we developed a MMIs for aquatic invertebrates to assess freshwater wetlands in this region. The aquatic invertebrate assemblages were sampled in 27 wetlands in the Sanjiang Plain that included those in natural reserves and those affected by adjacent, intensive agriculture. Twenty-four candidate metrics were initially reviewed and screened before four core metrics were selected: total number of taxa, number of Hemiptera taxa, proportion of Gastropoda, and proportion of predators. Mann-Whitney U tests, Box and Whisker plots, correlation analyses, and redundant metric tests were used to assess the ability of metrics to distinguish among reference and impaired wetlands. Four ordinal rating categories for wetland were defined: poor, fair, good, and excellent. Of the impaired freshwater wetlands, 76.2% were in poor or fair categories. The MMIs was robust in discriminating reference wetlands from impaired wetlands and therefore have potential as a biomonitoring tool to assess the condition and to guide the restoration efforts of freshwater wetlands in Northeast China.

Species‐specific responses to wetland mitigation among amphibians in the Greater Yellowstone Ecosystem

Habitat loss and degradation are leading causes of biodiversity declines, therefore assessing the capacity of created mitigation wetlands to replace habitat for wildlife has become a management priority. We used single season occupancy models to compare the occurrence of larvae of four species of pond‐breeding amphibians in wetlands created for mitigation, wetlands impacted by road construction, and unimpacted reference wetlands along a highway corridor in the Greater Yellowstone Ecosystem, United States. Created wetlands were shallow and had less aquatic vegetation and surface area than impacted and reference wetlands. Occupancy of barred tiger salamander (Ambystoma mavortium) and boreal chorus frog (Pseudacris maculata) larvae was similar across wetland types, whereas boreal toads (Anaxyrus boreas) occurred more often in created wetlands than reference and impacted wetlands. However, the majority of created wetlands (&gt;80%) dried partially or completely before amphibian metamorphosis occurred in both years of our study, resulting in heavy mortality of larvae and, we suspect, little to no recruitment. Columbia spotted frogs (Rana luteiventris), which require emergent vegetation that is not common in newly created wetlands, occurred commonly in impacted and reference wetlands but were found in only one created wetland. Our results show that shallow created wetlands with little aquatic vegetation may be attractive breeding areas for some amphibians, but may result in high mortality and little recruitment if they fail to hold water for the entire larval period.