Indicators Of Wetland Condition Research Articles

Role of abiotic drivers on crab burrow distribution in a saltmarsh wetland

Crab burrows play an important role in saltmarsh wetlands and are a useful indicator of wetland condition. The spatiotemporal distribution of crab burrows varies considerably in tidal wetlands. However, the reasons for these variations are poorly understood, in part, due to the limited availability of comprehensive field data. Based on a two-year continuous observation at a tidal wetland in the northern Jiangsu Coast, China, this study explored the relationship between crab burrow density and environmental variables, including median grain size, water content, organic matter content, soil salinity, and elevation. Our results show that the distribution of crab burrows was unimodal across the shore in winter and spring (Nov-Apr) when air temperature was relatively low, while bimodal in summer and autumn (May-Oct) when temperature was relatively high. The density of crab burrows was larger at areas with higher water content, higher organic matter content, and lower soil salinity, while it was lower with stronger hydrodynamics and lower suspended sediment concentration. Crab burrows were more abundant in vegetated areas than in un-vegetated areas. A backward stepwise model selection was performed based on R-square and Akaike information criterion (AIC) to distinguish the main driving factors that determine crab burrow distribution. Results suggested that the principal driving factors were organic matter content and soil salinity in all the seasons, with the addition of water content in warm seasons. Overall, this study provides a comprehensive field dataset for a more in-depth understanding of crab burrow distribution and a scientific basis for sustainable management of tidal wetlands.

Evaluating the use of hyperspectral imagery to calculate raster-based wetland vegetation condition indicator

Abstract Field observations and measurements of wetland plants have traditionally been used to monitor and evaluate wetland condition; however, there has been increasing use of remote sensing applications for rapid evaluations of wetland productivity and change. Combining key aspects of field- and remote sensing-based wetland evaluation methods can provide more efficient or improved biological indices. This exploratory study set out to develop a raster-based Wetland Vegetation Condition Indicator system that used airborne hyperspectral imagery-derived data to estimate plant-community quality (via wetland classification and Coefficient of Conservatism) and vegetation biomass (estimated using the Normalized Difference Vegetation Index). The Wetland Vegetation Condition Indicator system was developed for three Lake Ontario wetland areas and compared to a field-based floristic quality index and a dominant-plant based Floristic quality indexdom. The indicator system serves as a proof-of-concept that capitalized on the spatial and spectral attributes of high-resolution imagery to quantify and characterize the quality and quantity of wetland vegetation. A Pearson correlation analysis showed moderate r values of 0.59 and 0.62 for floristic quality index and floristic quality indexdom, respectively, compared to the indicator method. The differences are potentially due to the spatial resolution of the imagery and the indicator method only accounting for the dominant plants within each assessment unit (pixel), therefore disregarding understory plants or those with low abundance. However, the multi-metric Wetland Vegetation Condition Indicator approach shows promise as an indicator of wetland condition by using remotely sensed data, which could be useful for more efficient landscape-scale assessments of wetland health, resilience, and recovery.

A national-scale vegetation multimetric index (VMMI) as an indicator of wetland condition across the conterminous United States

In 2011, the US Environmental Protection Agency and its partners conducted the first National Wetland Condition Assessment at the continental-scale of the conterminous United States. A probability design for site selection was used to allow an unbiased assessment of wetland condition. We developed a vegetation multimetric index (VMMI) as a parsimonious biological indicator of ecological condition applicable to diverse wetland types at national and regional scales. Vegetation data (species presence and cover) were collected from 1138 sites that represented seven broad estuarine intertidal and inland wetland types. Using field collected data and plant species trait information, we developed 405 candidate metrics with potential for distinguishing least disturbed (reference) from most disturbed sites. Thirty-five of the metrics passed range, repeatability, and responsiveness screens and were considered as potential component metrics for the VMMI. A permutation approach was used to calculate thousands of randomly constructed potential national-scale VMMIs with 4, 6, 8, or 10 metrics. The best performing VMMI was identified based on limited redundancy among constituent metrics, sensitivity, repeatability, and precision. This final VMMI had four broadly applicable metrics (floristic quality index, relative importance of native species, richness of disturbance-tolerant species, and relative cover of native monocots). VMMI values and weights from the survey design for probability sites (n = 967) were used to estimate wetland area in good, fair, and poor condition, nationally and for each of 10 ecoregion by wetland type reporting groups. Strengths and limitations of the national VMMI for describing ecological condition are highlighted.

Fine-scale spatial homogenization of microbial habitats: a multivariate index of headwater wetland complex condition.

With growing public awareness that wetlands are important to society, there are intensifying efforts to understand the ecological condition of those wetlands that remain, and to develop indicators of wetland condition. Indicators based on soils are not well developed and are absent in some current assessment protocols; these could be advantageous, particularly for soils, which are complex habitats for plants, invertebrates, and microbial communities. In this study, we examine whether multivariate soil indicators, correlated with microbial biomass and community composition, can be used to distinguish reference standard (i.e., high condition) headwater wetland complexes from impacted headwater wetland complexes in central Pennsylvania, USA. Our reference standard sites existed in forested landscapes, while our impacted sites were situated in multi-use landscapes and were affected by a range of land-use legacies in the 1900s. We found that current assessment protocols are likely underrepresenting sampling needs to accurately represent site mean soil properties. On average, more samples were required to represent soil property means in reference standard sites compared to impacted sites. Reference standard and impacted sites also had noticeably different types of microbial habitats for the two multivariate soil indices assessed, and impacted sites were more homogenized in terms of the fine-scale (i.e., 1 and 5 m) spatial variability of these indices. Our study shows promise for the use of multivariate soil indices as indicators of wetland condition and provides insights into the sample sizes and scales at which soil sampling should occur during assessments. Future work is needed to test the generalizability of these findings across wetland types and ecoregions and establish definitive links between structural changes in microbial habitats and changes in wetland soil functioning.

Plant functional traits as indicator of the ecological condition of wetlands in the Grassland and Parkland of Alberta, Canada

The analysis of functional trait-habitat relationships has been used to measure the degree to which environmental factors influence the assembly of ecological communities. In the Parkland and Grassland natural regions of Alberta, wetlands are embedded in a matrix of human modified landscapes. The extent and effects of land uses on the condition of these wetlands and plant assemblages remains largely unknown. We used the physico-chemical characteristics and plant functional traits collected in 322 wetlands as indicators of wetland condition. Plant functional traits included origin, life history, and habitat requirements. Physico-chemical characteristics at each wetland site were assessed and the intensity of land use quantified within a 250-meter buffer. Our analyses reveal that functional plant traits are impacted by surrounding land use intensity; the abundance of non-native (exotic), upland, and annual plants tend to increase with degree of agriculture. Wetlands in areas with abundant groundwater input (low isotopic oxygen-18 enrichment) tend to be associated with functional groups preferring stable hydrological conditions including perennials and upland species. This contrasts with wetlands with greater potential for evaporation which were shallower, had higher nutrient levels, and were positively associated with species tolerating higher levels of disturbances, such as annuals. Our study demonstrates how an understanding of plant functional trait-habitat relationship can provide a framework for linking the responses of taxonomically-unrelated plant species to the condition of wetlands, and ultimately be used as indicator of wetland condition.

A plant‐based index of biological integrity in permanent marsh wetlands yields consistent scores in dry and wet years

ABSTRACT Plant‐based assessments can contribute to wetland conservation and management by providing a standardized method to monitor biological communities in relation to human activity. One major challenge, however, is that their measurements must be fairly insensitive to temporal variation in community composition, which can be difficult since marsh plant communities are known to be influenced by natural climatic cycles. Variation in the scores for an index of biological integrity (IBI) was evaluated in relation to plant community changes that occurred between years with differing precipitation inputs throughout the growing season (dry: 240 mm in 2008, 198 mm in 2009; wet: 324 mm in 2010, 329 mm in 2011). Species composition and IBI scores were measured by sampling macrophytes in the centre of the wet meadow zone at 47 semi‐permanent to permanent natural and constructed marshes. Non‐metric multidimensional scaling (NMS) ordinations revealed that although plant community composition shifted between dry and wet years, IBI scores were sensitive to only 21% of the total inter‐annual variation in species composition. The first NMS axis was positively correlated with IBI scores (r = 0.85) as well as several environmental parameters (r2 > 0.2), including dissolved organic carbon, total nitrogen, potassium, shoreline slope, and salinity. The wet meadow IBI also yielded consistent scores between dry and wet years (Spearman's rho = 0.82; Wilcoxon z‐score = 0.53, P‐value = 0.60) and was able to distinguish a change in biological condition among sites against a backdrop of natural variation (F‐test = 3.0, P < 0.001). These findings provide support for the continued use of plants as indicators of wetland condition in permanent northern prairie marshes, providing that the range in water levels is moderate. Copyright © 2013 John Wiley & Sons, Ltd.

Macroinvertebrate Assemblages in Iowa Prairie Pothole Wetlands and Relation to Environmental Features

Macroinvertebrate assemblage characteristics and other biophysical features were measured in the open-water zone of 17 semipermanent/permanent prairie pothole wetlands in Iowa. Relations among variables were used to identify likely determinants of invertebrate abundance and diversity, and useful indicators of wetland condition (i.e., health). Abundant invertebrates included physid and planorbid snails, oligochaetes, leeches, caenid mayflies, corixid bugs, chironomid midges, and amphipods. Abundant taxa were distributed across multiple functional feeding and habit groups. Invertebrate densities and taxonomic diversity were positively associated with plant/coarse particulate organic matter (plant/CPOM) abundance, and negatively related to turbidity, water-column concentrations of nitrogen and phosphorus, and presence of large-bodied fishes. Results supported hypotheses that plant/CPOM was an important invertebrate resource, and that plant/CPOM abundance was reduced in turbid, hypereutrophic wetlands. Fish likely reduced invertebrate abundance and diversity through predation and/or cascading effects on plants, turbidity, and nutrients. Wetlands with high invertebrate abundance and diversity, abundant plant/CPOM, low turbidity and nutrient concentrations, presence of tiger salamanders (Ambystoma tigrinum), and absence of large-bodied fishes appeared to be in the best condition. These features should be routinely measured to effectively assess condition of Iowa prairie pothole wetlands. Additionally, eliminating non-native fish populations may be critical to improving condition of these wetlands.

Impact of urbanization on the water quality, fish habitat, and fish community of a Lake Ontario marsh, Frenchman’s Bay

Frenchman’s Bay is a barrier beach wetland with a highly urbanized watershed located east of Toronto, along the north shore of Lake Ontario. Degradation of water quality has reduced the historically large stand of emergent vegetation to fringe emergent beds to the north and south of the Bay. Altered hydrology and runoff from the urban watershed and a nearby major highway have resulted in poor water quality, and warmer waters at the northern site. By contrast, the southern site has considerably cleaner and cooler water, as it is influenced by exchange of good-quality water with Lake Ontario. These differences in water quality were reflected in the composition of the fish assemblages that were sampled at the two sites over a 2-year period. Comparisons with past studies indicate that the dominant fish community of Frenchman’s Bay has been relatively stable for the last 20 years. Scores for the Wetland Fish Index, an indicator of wetland condition, were significantly higher in the south site than in the north site, which corresponded to significant differences in Water Quality Index scores. Although the northern portion of Frenchman’s Bay shows clear signs of degradation, the southern portion contains important fish habitat for western Lake Ontario.

Testing the Floristic Quality Assessment Index as an Indicator of Wetland Condition

Testing the Floristic Quality Assessment Index as an Indicator of Wetland Condition

Indicators of wetland condition for the prairie pothole region of the United States.

We describe a study designed to evaluate the performance of wetland condition indicators of the Prairie Pothole Region (PPR) of the north central United States. Basin and landscape scale indicators were tested in 1992 and 1993 to determine their ability to discriminate between the influences of grassland dominated and cropland dominated landscapes in the PPR. Paired plots were selected from each of the major regions of the PPR. Among the landscape scale indicators tested, those most capable of distinguishing between the two landscapes were: 1) frequency of drained wetland basins. 2) total length of drainage ditch per plot, 3) amount of exposed soil in the upland subject to erosion, 4) indices of change in area of wetland covered by water, and 5) number of breeding duck pairs. Basin scale indicators including soil phosphorus concentrations and invertebrate taxa richness showed some promise: however, plant species richness was the only statistically significant basin scale indicator distinguishing grassland dominated from cropland dominated landscapes. Although our study found a number of promising candidate indicators, one of our conclusions is that basin scale indicators present a number of implementation problems. including: skill level requirements, site access denials, and recession of site access by landowners. Alternatively, we suggest that the use of landscape indicators based on remote sensing can be an effective means of assessing wetland integrity.