Effect of time on consistent and repeatable macrophyte index for wetland condition

The vegetation portion of the Florida Wetland Condition Index (FWCI), an index of biological integrity, provided consistent and repeatable measures of condition at eighteen wetlands sampled in two consecutive growing seasons. The sample wetlands reflected a gradient of adjacent land use from non-impacted reference areas to wetlands imbedded within silviculture, cattle pasture and residential areas. Wetlands were described as herbaceous depression (n = 6), forested depression (n = 5) and forested strand or floodplain wetlands (n = 7), and represented different states of succession. Even though the wetlands were unique from one another and occurred across a large geographic area in Florida, the FWCI results calculated for all the wetlands were representative of adjacent land use impacts and not sensitive to natural variation. During the duration of this study, changes in weather from drought to tropical storm conditions, as well as management activities such as fire and herbivory, impacted wetlands. These effects were apparent in the change of species composition between sampling periods; 23–56% of species were different when resampled. Even though composition changed, the proportion of indicators remained consistent. The resulting condition scores suggested a one-to-one relationship between sampling periods.     

Immature mosquitoes in agricultural wetlands of the coastal plain of Georgia,U.S.A.: Effects of landscape and environmental habitat characteristics

This study is the first to report on the relationships between immature mosquitoes (larvae and pupae) and landscape and environmental habitat characteristics in wetlands associated with row crop agriculture. Indicator species analysis (ISA) was used to test for associations among mosquito species and groups of wetland sites with similar Landscape Development Intensity (LDI) values. Results indicated that Anopheles quadrimaculatus, Culex erraticus, and Psorophora columbiae were associated with agricultural wetlands (LDI > 2.0), whereas Anopheles crucians and Culex territans were associated with forested reference wetlands (LDI < 2.0) in both wet and dry years. The species fidelity to wetland type, regardless of the hydrologic regime, demonstrates these species are robust indicators of wetland condition. Data on immature mosquito assemblages were compared to selected landscape and environmental habitat variables using Akaike's Information Criterion (AIC_c) model selection. LDI indices, dissolved oxygen concentration, the proportion of emergent vegetation, and the proportion of bare ground in wetlands were important factors associated with the selected mosquito species. These results indicate that LDI indices are useful in predicting the distributions of disease vectors or other nuisance mosquito species across broad geographic areas. Additionally, these results suggest mosquitoes are valuable bioindicators of wetland condition that reflect land use and hydrologic variability.     

Temporal stability of vegetation indicators of wetland condition

Vegetation indices are widely employed to evaluate wetland ecological condition, and are expected to provide sensitive and specific detection of environmental change. Most studies evaluate the performance of condition assessment metrics in the context of the data used to calibrate them. Here we examined the temporal stability of the Florida Wetland Condition Index (FWCI) for vegetation of depressional forested wetlands by resampling sites in 2008 that were previously sampled to develop the FWCI in 2001. Our objective was to determine if FWCI, a composite of six vegetation-based metrics, provides a robust measure of condition given inter-annual variation in environmental conditions (i.e., rainfall) between sampling periods. To that end, we sampled 22 geographically isolated wetlands in north Florida that spanned a wide land use/land cover intensity gradient. Our results suggested the FWCI is robust. We observed no significant paired difference in FWCI across or within land use categories, and the relationship between FWCI in 2001 and 2008 was strong (r² = 0.88, p < 0.001). This was despite surprisingly high composition change. Mean Jaccard community similarity within sites between years was 0.30, suggesting that most of the herbaceous taxa were replaced, possibly because of different antecedent rainfall conditions or sampling during different phenological periods; both are contingencies to which condition indices must be robust. We did observe some evidence of convergence toward the mean in 2008, with the fitted slope relating 2001 and 2008 FWCI scores significantly below one (0.63, 95% CI = 0.53–0.73). The most variable FWCI component metric was the proportional representation of obligate wetland taxa, suggesting that systematic changes may have been induced by different hydrologic conditions prior to sampling; notably, however, FWCI computed without this component still exhibited a slope significantly less than 1 (0.72, 95% CI = 0.61–0.88). Moreover, there was evidence that species lost from reference sites (higher condition) were replaced by taxa of lower floristic quality, while species lost from agricultural sites (consistently the lowest condition land use category) were replaced by species of higher quality. A significant positive association between FWCI and the ratio of coefficients of conservatism (CC) of species lost to those gained suggests some overfitting in FWCI development. However, despite modest evidence of overfitting, FWCI provides temporally consistent estimates of wetland condition, even under conditions of substantial taxonomic turnover.     

Mosses in Ohio wetlands respond to indices of disturbance and vascular plant integrity

We examined the relationships between an index of wetland habitat quality and disturbance (ORAM score) and an index of vascular plant integrity (VIBI-FQ score) with moss species richness and a moss quality assessment index (MQAI) in 45 wetlands in three vegetation types in Ohio, USA. Species richness of mosses and MQAI were positively associated with ORAM and VIBI-FQ scores. VIBI-FQ score was a better predictor of both moss species richness and MQAI than was either ORAM score or vegetation type. This result was consistent with the strict microhabitat requirements for many moss species, which may be better assessed by VIBI-FQ than ORAM. Probability curves as a function of VIBI-FQ score were then generated for presence of groups of moss species having the same degree of fidelity to substrate and plant communities relative to other species in the moss flora (coefficients of conservatism, CCs). Species having an intermediate- or high degree of fidelity to substrate and plant communities (i.e., species with CC ≥ 5) had a 50% probability of presence (P₅₀) and 90% probability of presence (P₉₀) in wetlands with intermediate- and high VIBI-FQ scores, respectively. Although moss species richness, probability of presence of species based on CC, and MQAI may reflect wetland habitat quality, the 95% confidence intervals around P₅₀ and P₉₀ values may be too wide for regulatory use. Moss species richness, MQAI, and presence of groups of mosses may be more useful for evaluating moss habitat quality in wetlands than a set of “indicator species.”     

A candidate vegetation index of biological integrity based on species dominance and habitat fidelity

Indices of biological integrity of wetlands based on vascular plants (VIBIs) have been developed in many areas of the USA and are used in some states to make critical management decisions. An underlying concept of all VIBIs is that they respond negatively to disturbance. The Ohio VIBI (OVIBI) is calculated from 10 metrics, which are different for each wetland vegetation class. We present a candidate vegetation index of biotic integrity based on floristic quality (VIBI-FQ) that requires only two metrics to calculate an overall score regardless of vegetation class. These metrics focus equally on the critical ecosystem elements of diversity and dominance as related to a species’ degree of fidelity to habitat requirements. The indices were highly correlated but varied among vegetation classes. Both indices responded negatively with a published index of wetland disturbance in 261 Ohio wetlands. Unlike VIBI-FQ, however, errors in classifying wetland vegetation may lead to errors in calculating OVIBI scores. This is especially critical when assessing the ecological condition of rapidly developing ecosystems typically associated with wetland restoration and creation projects. Compared to OVIBI, the VIBI-FQ requires less field work, is much simpler to calculate and interpret, and can potentially be applied to all habitat types. This candidate index, which has been “standardized” across habitats, would make it easier to prioritize funding because it would score the “best” and “worst” of all habitats appropriately and allow for objective comparison across different vegetation classes.     

Constructing multimetric indices and testing ability of landscape metrics to assess condition of freshwater wetlands in the Northeastern US

Using data collected for the Environmental Protection Agency's (EPA) 2011 National Wetland Condition Assessment (NWCA), we developed separate multimetric indices (MMIs) for vegetation, soil, algae taxa, and water to assess condition of freshwater wetlands in the northeastern US. This study represents the first attempt at developing multiple biotic and abiotic MMIs of wetland condition over this large of an area, and is only possible because of the high quality data collected by the NWCA. We chose metrics that distinguished between reference and most disturbed sites, had a signal:noise ratio > 2, and were not strongly correlated with other metrics, latitude, or longitude. The vegetation and soil MMIs were the best performing indices, with good separation between reference and most disturbed sites, and included commonly used condition metrics (e.g., pH and P concentration for soil, and percent cover of exotic species for vegetation). The algae MMI was the weakest index, with considerable overlap between reference and most disturbed sites. For areas smaller than our study, algae taxa may be suitable for wetland MMIs. However, in our study area, many algae taxa followed strong latitudinal or longitudinal gradients, and could not be considered for the algae MMI. Small sample size and several metrics with a high signal:noise ratio were the major limitations of the water MMI. We also examined how well landscape (level 1) and rapid assessment (level 2) metrics predicted MMIs using random forest regression. Agricultural land use surrounding wetlands was an important predictor for all four MMIs, although the soil, algae and water MMI models performed best when intensive (level 3) vegetation metrics were also included in the random forest regression models. Based on these results, we recommend wetland assessment programs employ a combination of landscape and rapid assessment monitoring at many sites, along with level 3 monitoring at a subset of sites. We developed these MMIs to evaluate freshwater wetland condition for a long-term monitoring program in Acadia National Park. These MMIs are also applicable to a range of wetland types covering 11 states in the northeastern United States and can be calculated using a downloadable spreadsheet that calculates and rates each MMI using raw metric values.     

Methane emissions in Danish riparian wetlands: Ecosystem comparison and pursuit of vegetation indexes as predictive tools

The present study was conducted to (i) investigate parameters influencing the fluxes of the greenhouse gas methane (CH₄) in Danish riparian wetlands with contrasting vegetation characteristics and (ii) develop models relating CH₄ emissions to soil and/or vegetation parameters integrating the spatial and temporal variability in the fluxes. Fluxes of CH₄ were monitored in 12 wetland plots over a year using static chambers, yielding a dataset with more than 800 measured fluxes of CH₄. Yearly emissions of CH₄ ranged from −0.2 to 38.3 g CH₄-C m⁻² year⁻¹, and significant effects of groundwater level, soil temperature (10 cm depth), peat depth, sulfate, nitrate, and soil carbon content were found. Two methods based on easily available environmental parameters to estimate yearly CH₄ emissions from riparian wetlands are presented. The first uses a generalized linear model (GLM) to predict yearly CH₄ emissions based on the humidity preference of vegetation (Ellenberg-F), peat depth and degree of humification of the peat (von Post index). The second method relies solely on plant species composition and uses weighted-average regression and calibration to link the vegetation assemblage to yearly CH₄ emission. Both models gave reliable predictions of the yearly CH₄ fluxes in riparian wetlands (modeling efficiency > 0.35). Our findings support the use of vegetation, possibly in combination with some soil parameters such as peat depth, as indicator of CH₄ emission in wetlands.     

Testing a Passive Revegetation Approach for Restoring Coastal Plain Depression Wetlands

Restoration of coastal plain depressions, a biologically significant and threatened wetland type of the southeastern United States, has received little systematic research. Within the context of an experimental project designed to evaluate several restoration approaches, we tested whether successful revegetation can be achieved by passive methods (recruitment from seed banks or seed dispersal) that allow for wetland "self-design" in response to hydrologic recovery. For 16 forested depressions that historically had been drained and altered, drainage ditches were plugged to reestablish natural ponding regimes, and the successional forest was harvested to open the sites and promote establishment of emergent wetland vegetation. We sampled seed bank and vegetation composition 1 year before restoration and monitored vegetation response for 3 years after. Following forest removal and ditch plugging, the restored wetlands quickly developed a dense cover of herbaceous plant species, of which roughly half were wetland species. Seed banks were a major source of wetland species for early revegetation. However, hydrologic recovery was slowed by a prolonged drought, which allowed nonwetland plant species to establish from seed banks and dispersal or to regrow after site harvest. Some nonwetland species were later suppressed by ponded conditions in the third year, but resprouting woody plants persisted and could alter the future trajectory of revegetation. Some characteristic wetland species were largely absent in the restored sites, indicating that passive methods may not fully replicate the composition of reference systems. Passive revegetation was partially successful, but regional droughts present inherent challenges to restoring depressional wetlands whose hydrologic regimes are strongly controlled by rainfall variability.     

High altitude montane wetland vegetation classification of the Eastern Free State,South Africa

Wetlands occur where biotic and abiotic conditions combine to create unique habitats and plant assemblages. These systems have anaerobic or hydric soil resulting from waterlogging and are found across all nine biomes in South Africa. Wetlands can thus be regarded as hosting azonal vegetation. On Platberg, the freshwater wetlands are embedded within the Grassland Biome forming distinct units. Platberg wetlands were surveyed and described to explain and document vegetation of this inselberg. Additional aims were to elucidate Afro-montane floristic links with the Drakensberg Alpine Centre, and provide data for conservation management. The study site is located in the Eastern Free State, South Africa, on edge of the Great Escarpment. It is one of an archipelago of more than 20 inselbergs stretching north from the Drakensberg. A total of 51 sample plots (30 m²) were located in a randomly stratified manner within the wetland units to include all variations in the vegetation. The data was analysed using the TWINSPAN classification algorithm, refined by Braun-Blanquet procedures. The analysis showed the wetlands divided into five communities, six sub-communities and six variants. The wetland communities had an average of 13.56 species per relevé, ranging from 7 to 29 species per sample plot. Numerous floristic links with the Drakensberg Alpine Centre, the Cape Floristic Region and the Grassland biome were found. Platberg shows vegetation and hydrogeological affinity with low altitude freshwater and the high altitude Lesotho Mires of the Drakensberg Alpine Centre. A list of high altitude wetland species was compiled.     

Estimation of wetland vegetation height and leaf area index using airborne laser scanning data

Wetland vegetation is a core component of wetland ecosystems. Wetland vegetation structural parameters, such as height and leaf area index (LAI) are important variables required by earth-system and ecosystem models. Therefore, rapid, accurate, objective and quantitative estimations of wetland vegetation structural parameters are essential. The airborne laser scanning (also called LiDAR) is an active remote sensing technology and can provide accurate vertical vegetation structural parameters, but its accuracy is limited by short, dense vegetation canopies that are typical of wetland environments. The objective of this research is to explore the potential of estimating height and LAI for short wetland vegetation using airborne discrete-return LiDAR data.The accuracies of raw laser points and LiDAR-derived digital elevation models (DEM) data were assessed using field GPS measured ground elevations. The results demonstrated very high accuracy of 0.09 m in raw laser points and the root mean squared error (RMSE) of the LiDAR-derived DEM was 0.15 m.Vegetation canopy height was estimated from LiDAR data using a canopy height model (CHM) and regression analysis between field-measured vegetation heights and the standard deviation (σ) of detrended LiDAR heights. The results showed that the actual height of short wetland vegetation could not be accurately estimated using the raster CHM vegetation height. However, a strong relationship was observed between the σ and the field-measured height of short wetland vegetation and the highest correlation occurred (R² = 0.85, RMSE = 0.14 m) when sample radius was 1.50 m. The accuracy assessment of the best-constructed vegetation height prediction model was conducted using 25 samples that were not used in the regression analysis and the results indicated that the model was reliable and accurate (R² = 0.84, RMSE = 0.14 m).Wetland vegetation LAI was estimated using laser penetration index (LPI) and LiDAR-predicted vegetation height. The results showed that the vegetation height-based predictive model (R² = 0.79) was more accurate than the LPI-based model (the highest R² was 0.70). Moreover, the LAI predictive model based on vegetation height was validated using the leave-one-out cross-validation method and the results showed that the LAI predictive model had a good generalization capability. Overall, the results from this study indicate that LiDAR has a great potential to estimate plant height and LAI for short wetland vegetation.     

Vegetation Communities of 20-year-old Created Depressional Wetlands

Many studies have chronicled the early development of vegetation in wetlands created as mitigation for wetland impacts; however, very few studies have followed the floristics of wetlands that are more than 10 years post-creation. This article reports the results of vegetation composition and structural analysis within eleven 20-yr-old created non-tidal, emergent wetlands. Vegetation and inundation were sampled in 173 plots within 11 wetlands during the 1992 and 1994 growing seasons. A drought occurred in 1993, thus analyses characterized vegetative response and included weighted average (weighted by the tolerance of the species to excess soil moisture), species richness, species composition, and life history strategy. Weighted average and species richness increased in 7 and 10 of the 11 sites, respectively. There was little change among most species including Typha latifolia and Scirpus cyperinus, the two species with highest importance values (IV). However, among the top 10 species ranked by IV, two aquatic species decreased and a facultative species increased. Only one of the 10 most important species, Eleocharis obtusa, was an annual and only one, Salix nigra, was a woody perennial and the IV of both species declined during the study. After 20 years, a transition from annual to perennial graminoid life histories is suggested; however, succession from emergent to shrub–scrub or forested wetland is not indicated.     

Vegetation Monitoring of Created Dune Swale Wetlands, Vandenberg Air Force Base, California

A monitoring program was established on San Antonio Terrace at Vandenberg Air Force Base to compare vegetation development at two created wetland sites and six nearby natural wetlands. The reference wetlands were chosen to represent a range of habitats in dune swale wetlands on the Terrace. Vegetation in the reference wetland plant communities varies from low-growing herbaceous marsh species with open canopies to closed canopies dominated by shrub or tree species. Transects and plots for long-term vegetation monitoring were established in all the wetlands, stratified by plant communities in the reference wetlands and by geomorphic location in the newly created wetlands. Quantitative vegetation and environmental data were collected at all the sites; measures included species distributions, species cover, and topographical elevations. Over the first three years of monitoring, variations in groundwater depth at different geomorphic locations in the created wetlands resulted in a variety of physical conditions for plant growth. In the first year, more than 100 plant species were observed, the majority being natives. During the next two years, species richness at the created wetland sites remained relatively stable and was higher than at the reference sites. Statistical comparisons of vegetation parameters by analysis of variance and hierarchical clustering exhibited patterns of increasing similarity between the created and reference wetlands. Long-term monitoring will be continued to track the progress of vegetation at the created sites, and to assess their development relative to the reference wetlands.     

Patterns of vegetation and soil properties in a beaver-created wetland located on the Coastal Plain of Virginia

This study investigated vegetation and soil properties in a beaver-created freshwater wetland located on the Coastal Plain of Virginia near Washington, DC. We focused on the associations among floristic quality, soil physicochemistry, denitrification, and hydrologic conditions of the wetland to understand links between the effects of beaver engineering and ecosystem function. The floristic quality assessment index (FQI) and denitrification are two important indicators often used to examine overall habitat quality and ecosystem functioning of a wetland. Samples were collected from ten plots (10 m × 10 m each) in August 2014. Vegetation attributes included total percent cover, species richness (S), diversity, FQI, and prevalence index (PI). Soil attributes included organic matter (OM), total carbon, total nitrogen, gravimetric moisture (GM), pH, bulk density (D_b), and denitrification potential (DP). FQI was greater in the higher of the two standing water level categories, where D_b was lower, and was negatively associated with D_b but no other soil nutrient properties. DP was positively associated with soil nutrients, OM, and GM, but not with measured vegetation attributes nor standing water levels. We found higher soil GM, lower plant community PI, and lower plot S in this study compared to our previous study, with no changes to other vegetation or soil attributes, indicating enduring beaver activity and a resilient plant community. The outcome of the study includes regression models that best explain the association between structural and functional attributes of the ecosystem, which can be applicable to the study of other beaver-created wetlands. The study also provides partial evidence for the notion that low-lying areas dug out by beaver positively impact the FQI of wetlands.     

Marsh wetland degradation risk assessment and change analysis: A case study in the Zoige Plateau,China

Wetlands play an important role in regional development and environmental protection. Under the impact of natural and artificial factors, the plateau wetlands have degenerated and even disappeared, resulting in serious problems for society and the ecological environment. It is necessary to establish a reasonable risk assessment method to evaluate the risk of wetland degradation, and then to analyze changes in the range and features of risk. For this work, the Zogie Plateau wetland was selected as the study area. For this site, a wetland degradation risk assessment method was established based on the conceptual model of Ecological Risk Assessment (ERA). The method included nine indicators used to analyze the wetland hazard index, wetland vulnerability index, and wetland degradation risk synthetically. From the spatial-temporal pattern, the wetland degradation risk was analyzed using data from 2000 to 2014. The calculated results revealed the following: (1) from 2000 to 2014, the wetland hazard index (WHI) showed a trend of increase, the value of which increased from 0.29 to 0.42, with a growth rate of 44.83%. Similarly, the wetland vulnerability index (WVI) significantly increased from 0.30 to 0.54, with a growth rate of 80%. Over the same time, the total wetland area decreased from 3910.25 km² to 2777.38 km², a reduction of 28.97%. (2) Using the equidistant method, the risk value was divided into three risk grades. The wetland degradation risk in the whole region is increasing, and the risk rank has changed from the low risk zone (0.092) to the medium risk zone (0.25). The degradation risk becomes greater with distance from the center to fringe areas.     

Landscape hydrogeomorphic conditions determine structure and species composition of an ephemeral floodplain wetland

Wetlands are major sources of habitat heterogeneity, with certain environmental variables controlling wetland structure and composition. There is very little information on the heterogeneity of ephemeral floodplain wetland patch mosaics and how hydrogeomorphic circumstance affects composition and structure. Structure (wetland size) and composition (herbaceous species) are two attributes of an ephemeral wetland that are easily quantifiable using a moving window analysis. The moving window analysis is a statistical technique that identifies significant changes in parameters (i.e., structure and composition) along gradients. An analysis of changes in wetland structure and composition longitudinally identified two hydrogeomorphic types and laterally delineated wetland boundaries. The wide–flat type had a wide (131.2 ± 50.4 m) wetland patch and a mean lateral slope of 0.008 ± 0.003, in contrast the narrow–deep type had a significantly smaller (80 ± 40.2 m) and steeper (0.048 ± 0.06) wetland patch. Changes in hydrogeomorphology had distinct effects on the species composition of the wetland. Facultative wetland species such as Sporobolus pyrimidalis and Ischaemum afrum were associated with the wide–flat type, while, the narrow–deep type was characterized by more obligate, flood dependent species such as Phragmites australis, Mariscus congestus, and Eriochloa meyeriana. Internally, the structure and composition of ephemeral wetlands on the northern plains of Kruger National Park were spatially heterogeneous and correlated to hydrogeomorphic conditions, that are identifiable when examined at the wetland scale. Results add knowledge to wetlands as sources of landscape heterogeneity and highlight how environmental variation can result in increases in wetland heterogeneity.     

Comparison of created and natural freshwater emergent wetlands in Connecticut (USA)

Five three- to four-year old created palustrine/emergent wetland sites were compared with five nearby natural wetlands of comparable size and type. Hydrologic, soil and vegetation data were compiled over a nearly two-year period (1988-90). Created sites, which were located along major highways, exhibited more open water, greater water depth, and greater fluctuation in water depth than natural wetlands. Typical wetland soils exhibiting mottling and organic accumulation were wanting in created sites as compared with natural sites. Typha latifolia (common cattail) was the characteristic emergent vegetation at created sites, whereas a more diverse mosaic of emergent wetland species was often associated with Typha at the natural sites. Species richness was slightly higher in created (22–45) vs. natural (20–39) wetlands, but the mean difference (33 vs. 30) was not significant. Nearly half (44%) of the 54 wetland taxa found at the various study sites were more frequently recorded at created than natural wetlands. The presence of mycorrhizae in roots of Typha angustifolia (narrow-leaved cattail) and Phragmites australis (common reed) was greater at created than natural wetlands, which may be related to differential nutrient availability. Wildlife use at all sites ranged from occasional to rare, with more sightings of different species in the natural (39) than created (29) wetlands. The presence of P. australis and introduced Lythrum salicaria (purple loosestrife) may pose a threat to future species richness at the created sites. One created site has permanent flow-through hydrology, and its vegetation and wildlife somewhat mimic a natural wetland; however, the presence of P. australis and its potential spread pose an uncertain future for this site. This study suggests the possibility of creating small palustrine/emergent wetlands having certain functions associated with natural wetlands, such as flood water storage, sediment accretion and wildlife habitat. It is premature to evaluate fully the outcome of these wetland creation efforts. A decade or more is needed, emphasizing the importance of long term monitoring and the need to establish demonstration areas.     

湿地土壤种子库与地上植被相似性关系研究评述

土壤种子库与地上植被的关系是土壤种子库研究的重要组成部分。当前,湿地生态系统面临严重威胁,研究湿地土壤种子库和地上植被关系既可以加强对土壤种子库和植物群落特征的认识,又可以为湿地保护与管理提供理论指导。检索了科学引文索引扩展版(SCIE)数据库中收录的1900—2012年间研究湿地土壤种子库与地上植被关系的文献,通过分析土壤种子库与地上植被的Srensen相似性系数,结果发现:不同湿地类型的土壤种子库和地上植被的相似性存在显著差异,河流湿地中两者的相似性最小;不同植被类型中土壤种子库与地上植被的相似性差异显著:草本群落的相似性大于乔木群落;不同气候带的湿地中两者的相似性也存在显著差异,其中亚热带地区相似性最小。总结了湿地种子库与地上植被相似性关系的时空变化特征。二者的相似性通常随着植物群落的演替而减小,在空间上也随着环境梯度而变化。分析了两者关系的影响因素,如种子传播、环境条件和繁殖策略等。对研究中存在的问题及发展方向提出建议。     

Economic values and dominant providers of key ecosystem services of wetlands in Beijing,China

This study estimates the economic values of and the dominant contributors to five key ecosystem services of wetlands in Beijing, by using the wetland inventory data in 2014 and economic valuation methods. Results indicate that the 51,434 ha of wetlands in Beijing annually provide 2.07 billion m³ of flood regulation, 944.01 million m³ of water provision, 42,154 tons of chemical oxygen demand (COD) purification, 3.03 PJ of heat absorption, and 9587 ha of habitat. Their economic values are estimated to be 15.89 billion RMB, 1.19 billion RMB, 169 million RMB, 421 million RMB, and 1.08 billion RMB in 2014 (RMB: Chinese currency, US$1 = RMB 6.14), respectively. The total values of five key wetland ecosystem services reach 18.76 billion RMB. In addition, the reservoir and river wetlands in Miyun, Yanqing, Fangshan, Huairou, and Mentougou Districts contribute 78% of key ecosystem services, whereas the urban wetlands in Xicheng, Dongcheng, Haidian, Chaoyang, and Tongzhou Districts more conveniently serve densely local people, hence they should be given particular attentions. In this paper, we develop the valuation methods of wetland ecosystem services, and recommend diversified strategies, regulations, and programs to protect the remaining wetlands in Beijing. This work can also provide a reference for the valuating of wetland ecosystem services for other urban-rural areas.     

A comparison of soil carbon pools and profiles in wetlands in Costa Rica and Ohio

Wetlands are large carbon pools and play important roles in global carbon cycles as natural carbon sinks. This study analyzes the variation of total soil carbon with depth in two temperate (Ohio) and three tropical (humid and dry) wetlands in Costa Rica and compares their total soil C pool to determine C accumulation in wetland soils. The temperate wetlands had significantly greater (P < 0.01) C pools (17.6 kg C m⁻²) than did the wetlands located in tropical climates (9.7 kg C m⁻²) in the top 24 cm of soil. Carbon profiles showed a rapid decrease of concentrations with soil depth in the tropical sites, whereas in the temperate wetlands they tended to increase with depth, up to a maximum at 18–24 cm, after which they started decreasing. The two wetlands in Ohio had about ten times the mean total C concentration of adjacent upland soils (e.g., 161 g C kg⁻¹ were measured in a central Ohio isolated forested wetland, and 17 g C kg⁻¹ in an adjacent upland site), and their soil C pools were significantly higher (P < 0.01). Among the five wetland study sites, three main wetland types were identified – isolated forested, riverine flow-through, and slow-flow slough. In the top 24 cm of soil, isolated forested wetlands had the greatest pool (10.8 kg C m⁻²), significantly higher (P < 0.05) than the other two types (7.9 kg C m⁻² in the riverine flow-though wetlands and 8.0 kg C m⁻² in a slowly flowing slough), indicating that the type of organic matter entering into the system and the type of wetland may be key factors in defining its soil C pool. A riverine flow-through wetland in Ohio showed a significantly higher C pool (P < 0.05) in the permanently flooded location (18.5 kg C m⁻²) than in the edge location with fluctuating hydrology, where the soil is intermittently flooded (14.6 kg C m⁻²).     

Community congruence of plants,invertebrates and birds in natural and constructed shallow open-water wetlands: Do we need to monitor multiple assemblages?

Biomonitoring is a common means of evaluating wetlands. It is based on the premise that the community composition of one taxonomic group is indicative of overall biology and the underlying environmental conditions at a wetland. To be a good bioindicator, there must be adequate concordance between the indicator group and other biotic assemblages. Otherwise, multi-assemblage monitoring is necessary to glean a complete picture of wetland condition. In 32 sites ranging from reference wetlands to stormwater retention ponds, we evaluated concordance in community composition among the six most commonly monitored wetland assemblages: waterfowl, wetland dependent songbirds, aquatic macroinvertebrates, and plants in the wet meadow, emergent, and open-water vegetation zones. We also assessed agreement in environmental correlates among these six assemblages and investigated the impact of human disturbance on cross-assemblage concordance. We found that cross-assemblage concordance was positive (p < 0.03 in 14 of 15 pair-wise comparisons, p = 0.06 in 15th case), but relatively low (Mantel R values 0.11–0.37), suggesting that the assemblages are mediocre surrogates for one another. Yet, we found very strong agreement among environmental correlates of the six assemblages, especially along the first axis of assemblage-specific ordinations (mean Spearman rho = 0.923), indicating that despite low concordance, the six assemblages are likely responding to the same environmental gradients. Thus, while a single assemblage may not serve as a surrogate for the other assemblages, it should yield an adequate estimate of underlying environmental conditions and the degree of disturbance. Most important among the environmental correlates were sediment and water nutrient levels, shoreline slope, and the size of wet meadow and emergent vegetation zones. Perhaps most interestingly, we found that the strength of cross-assemblage concordance was greatest in reference wetlands and was lower (p ≤ 0.05) in constructed wetlands. This implies that cross-assemblage concordance present in undisturbed sites may not persist in disturbed wetlands where several of these cross-assemblage relationships deteriorate. Furthermore, a general change in cross-assemblage concordance may itself be indicative of human disturbance in wetlands.