Inefficacy of wetland legislation for conserving Quebec wetlands as revealed by mapping of recent disturbances

To minimize wetland losses, many jurisdictions have adopted a ‘mitigation sequence’ that requires compliance for permit delivery. This study evaluated the outcome of this sequence in the province of Quebec, Canada, during the 3 years following its adoption in 2006. A case study was then conducted in the St. Lawrence Lowlands (29,096 km²) to compare statistics on delivered permits with losses detected by detailed mapping of disturbances from two periods: 1990 to 2011 and 2006 to 2011. A total of 558 permits were issued, most of which (550) represented 2870 ha of disturbed wetlands; the remaining (8) corresponding to restoration projects. The mitigation sequence was applied for 323 of the permits, mainly with compensations. The type of action undertaken was registered for only 63 % of the compensations with a minimal fraction dedicated to wetland restoration (1 ha) and creation (14 ha), resulting in a net loss of 99 % of the impacted wetland areas. In the case study, 56,681 ha (19 %) of wetlands had been disturbed in the last two decades, of which 22,535 ha were disturbed between 2006 and 2011, mainly by agricultural and forestry activities. No permit was delivered for these two activities according to our compilation. The area disturbed following permit deliverance was about 17–30 times smaller than losses estimated by our detailed mapping, depending on the period considered. Preserving wetlands will require not only mandatory compliance with the mitigation sequence but also efforts to subscribe all types of industries to the process of permit delivery.     

Mitigation under Section 404 of the Clean Water Act: where it comes from, what it means

The requirement to mitigate impacts to wetlands and streams is a frequently misunderstood policy with a long and complicated history. We narrate the history of mitigation since the inception of the Clean Water Act Section 404 permit program in 1972, through struggles between the US Environmental Protection Agency and the US Army Corps of Engineers, through the emerging importance of wetland conservation on the American political landscape, and through the rise of market-based approaches to environmental policy. Mitigation, as it is understood today, was not initially foreseen as a component of the Section 404 permitting program, but was adapted from 1978 regulations issued by the Council on Environmental Quality as a way of replacing the functions of filled wetlands where permit denials were unlikely. EPA and the Corps agreed in 1990 to define mitigation as the three steps of avoidance, minimization, and compensation, principles which must be applied to permit decisions in the form of the environmental criteria in EPA’s 404(b)(1) Guidelines. Through the 1980s and 1990s, the compensation component of mitigation has become nearly the sole focus of mitigation policy development, and has been the subject of numerous guidance documents and memoranda since 1990. Avoidance and minimization have received far less policy attention, and this lack of policy development may represent a missed opportunity to implement effective wetland conservation.

Aquatic macroinvertebrate community responses to wetland mitigation in the Greater Yellowstone Ecosystem

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Compensating for wetland losses in the United States

Impacts of climate change on US wetlands will add to those of historical impacts due to other causes. In the US, wetland losses and degradation result from drainage for agriculture, filling for urbanization and road construction. States that rely heavily on agriculture (California, Iowa, Illinois, Missouri, Ohio, Indiana) have lost over 80% of their historical area of wetlands, and large cities, such as Los Angeles and New York City, have retained only tiny remnants of wetlands, all of which are highly disturbed. The cumulative effects of historical and future degradation will be difficult to abate. A recent review of mitigation efforts in the US shows a net loss of wetland area and function, even though 'no net loss' is the national policy and compensatory measures are mandatory. US policy does not include mitigation of losses due to climate change. Extrapolating from the regulatory experience, one can expect additional losses in wetland areas and in highly valued functions. Coastal wetlands will be hardest hit due to sea-level rise. As wetlands are increasingly inundated, both quantity and quality will decline. Recognition of historical, current and future losses of wetland invokes the precautionary principal: avoid all deliberate loss of coastal wetland area in order to reduce overall net loss. Failing that, our ability to restore and sustain wetlands must be improved substantially.     

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 (>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.     

Long-term development of tidal mitigation wetlands in Florida

Monitoring periods for compensatory wetland mitigation projects are relatively short, typically 3 to 5 years. Although forested wetlands may require decades to develop structural characteristics similar to those of natural systems, studies that describe long-term trends in site development are rare. Eighteen mitigation sites in Florida that had originally been sampled in 1988 were re-visited in 2005. Changes in mangrove community composition and stand structure occurring over this timeframe at ten of these sites are described and compared with other mangrove wetlands in Florida. Factors limiting development of the remaining sites are discussed. The continued persistence and development of the majority of these mitigation sites indicates that the mitigation process can be successful, at least in terms of compliance with the typical permit requirements. Basal area and height had increased at most sites, and some were difficult to visually distinguish from adjacent natural stands of mangroves. However, even after 13–25 years, stand structure in mangrove mitigation wetlands in Florida still differed from that of natural sites. Although the number of mangrove species was similar, mitigation sites had lower basal area and height than natural sites, and were more dense and complex than natural sites.     

The hydrogeomorphic approach to functional assessment of riparian wetlands: evaluating impacts and mitigation on river floodplains in the U.S.A.

1. The ’hydrogeomorphic‘ approach to functional assessment of wetlands (HGM) was developed as a synthetic mechanism for compensatory mitigation of wetlands lost or damaged by human activities. The HGM approach is based on: (a) classification of wetlands by geomorphic origin and hydrographic regime (b) assessment models that associate variables as indicators of function, and (c) comparison to reference wetlands that represent the range of conditions that may be expected in a particular region. In this paper, we apply HGM to riparian wetlands of alluvial rivers. 2. In the HGM classification, riverine wetlands are characterized by formative fluvial processes that occur mainly on flood plains. The dominant water sources are overbank flooding from the channel or subsurface hyporheic flows. Examples of riverine wetlands in the U.S.A. are: bottomland hardwood forests that typify the low gradient, fine texture substratum of the south-eastern coastal plain and the alluvial flood plains that typify the high gradient, coarse texture substratum of western montane rivers. 3. Assessment (logic) models for each of fourteen alluvial wetland functions are described. Each model is a composite of two to seven wetland variables that are independently scored in relation to a reference data set developed for alluvial rivers in the western U.S.A. Scores are summarized by a ’functional capacity index‘ (FCI), which is multiplied by the area of the project site to produce a dimensionless ’functional capacity unit‘ (FCU). When HGM is properly used, compensatory mitigation is based on the FCUs lost that must be returned to the riverine landscape under statutory authority. 4. The HGM approach also provides a framework for long-term monitoring of mitigation success or failure and, if failing, a focus on topical remediation. 5. We conclude that HGM is a robust and easy method for protecting riparian wetlands, which are critically important components of alluvial river landscapes.     

Aquatic macroinvertebrate assemblages in mitigated and natural wetlands

Many wetlands have been constructed in West Virginia as mitigation for a variety of human disturbances, but no comprehensive evaluation on their success has been conducted. Macroinvertebrates are extremely valuable components of functioning wetland ecosystems. As such, benthic and water column invertebrate communities were chosen as surrogates for wetland function in the evaluation of 11 mitigation and 4 reference wetlands in West Virginia. Mitigation wetlands ranged in age from 4 to 21 years old. Overall familial richness, diversity, density and biomass were similar between mitigation and reference wetlands (p > 0.05). Within open water habitats, total benthic invertebrate density was higher in reference wetlands, but mass of common taxa from water column samples was higher in mitigation wetlands (p < 0.05) Planorbidae density from benthic samples in emergent habitats was higher in reference than mitigated wetlands. Benthic Oligochaeta density was higher across open water habitats in mitigation wetlands. All other benthic taxa were similar between wetland types. Among the most common water column orders, Isopoda density was higher in reference wetlands, but Physidae density was higher in mitigation wetlands. Within mitigation wetlands, emergent areas contained higher richness and diversity than open areas. These data indicate that mitigation and reference wetlands generally support similar invertebrate assemblages, especially among benthic populations. The few observed differences are likely attributable to differences in vegetative community composition and structure. Mitigation wetlands currently support abundant and productive invertebrate communities, and as such, provide quality habitat for wetland dependent wildlife species, especially waterbirds and anurans.     

Landsat-based monitoring of annual wetland change in the Willamette Valley of Oregon,USA from 1972 to 2012

In Oregon’s Willamette Valley, remaining wetlands are at high risk to loss and degradation from agricultural activity and urbanization. With an increased need for fine temporal-scale monitoring of sensitive wetlands, we used annual Landsat MSS and TM/ETM+ images from 1972 to 2012 to manually interpret loss, gain, and type conversion of wetland area in the floodplain of the Willamette River. By creating Tasseled Cap Brightness, Greenness, and Wetness indices for MSS data that visually match TM/ETM+ Tasseled Cap images, we were able to construct a complete and consistent, annual time series and utilize the entire Landsat archive. With an extended time series we were also able to compare annual trends of net change in wetland area before and after the no-net-loss policy established under Section 404 of the Clean Water Act in 1990 using a Theil-Sen Slope estimate analysis. Vegetated wetlands experienced a 314 ha net loss of wetland area and non-vegetated wetlands experienced a 393 ha net gain, indicating higher functioning wetlands were replaced in area by non-vegetated wetland habitats such as agricultural and quarry ponds. The majority of both gain and loss in the study area was attributed to gains and losses of agricultural land. After 1990 policy implementations, the rate of wetland area lost slowed for some wetland categories and reversed into trends of gain in wetland area for others, perhaps representative of the success of increased regulations. Overall accuracy of land use classification through manual interpretation was at 80 %. This accuracy increased to 91.1 % when land use classes were aggregated to either wetland or upland categories, indicating that our methodology was more accurate at distinguishing between general upland and wetland than finer categorical classes.     

Designing Wetlands for Amphibians: The Importance of Predatory Fish and Shallow Littoral Zones in Structuring of Amphibian Communities

Under section 401 and section 404 of the Clean Water Act, permission to degrade existing natural wetlands in the USA may be conditional on restoring or creating ‘replacement’ wetlands. Success of wetland mitigation efforts in adequately replacing lost wildlife habitats depends on our good understanding of key ecological attributes that affect the structure of wetland faunal communities. We examined the effects of the presence of predatory fish, shallow vegetated littoral zone, emergent vegetation cover, wetland age and size on amphibian diversity in 42 replacement wetlands located in the Ohio’s North Central Tillplain ecoregion. We recorded 13 species of pond-breeding amphibians, and the average local species richness (α-richness) was 4.2 ± 1.7 species per site (range 1–7). There is strong evidence for the positive association between amphibian species richness and presence of a shallow littoral zone, and the negative association with presence of predatory fish. There was no evidence for the association between species richness and age, size, amount of forest cover within 200 m, nor the amount of emergent vegetation cover at the study sites. It is estimated that local species richness in wetlands with shallows was 1.76 species higher on average than in wetlands without shallows (95% CI from 0.75 to 2.76). The presence of predatory fish was associated with an average reduction in species richness by an estimated 1.21 species (95% CI from 0.29 to 2.11). Replacement wetlands were placed in areas with little or no existing forest cover, and amphibian species associated with forested wetlands were either rare (eastern newt, spotted salamander) or not present at all (marbled salamander, wood frog). In addition, we surveyed all replacement wetlands constructed under section 401 in Ohio since 1990, and found that predatory fish were present in 52.4% of the sites and that shallows were absent from 42.7% of the sites. Our results indicate that current wetland replacement practices could have a negative effect on the amphibian diversity within our region.     

Tracking wetland loss to improve evidence-based wetland policy learning and decision making

At the core of any evidence-based policy analysis are accurate data and the policy analytic capacity of government agencies to use these data to develop and measure metrics of policy success. This study evaluated the government’s policy capacity to manage wetlands in Alberta, Canada, by measuring and evaluating three policy metrics: (1) no net change of wetland area; (2) permitted versus unpermitted wetland loss; and (3) an information tracking system that provides credible regulatory oversight. Using a climate-corrected wetland loss inventory, we detected the loss of 242 wetlands, totaling 71 ha, in the Beaverhill subwatershed between 1999 and 2009. The majority of the losses occurred on land that were classified as ‘developed’ (urban and industrial) or ‘agriculture’. When wetland loss was compared to government-issued wetland permit data, we found that over 80 % of the wetland area was lost without a government permit. The wetland permit data also revealed serious problems with information tracking by both government and non-government agencies responsible for policy and regulatory oversight. In order to resolve these common policy failures, governments need to commit more resources towards acquiring, effectively managing, and freely sharing information that can be used to evaluate policy outcomes to ‘open up’ wetland management and decision making to include active participation from informal institutions, local governments, and the general public as a means to drive improved regulatory oversight.     

Carbon storage dynamics of temperate freshwater wetlands in Pennsylvania

Healthy wetlands play a significant role in climate change mitigation by storing carbon that would otherwise contribute to global warming, leading to the reduction of water and food resources as well as more extreme weather phenomena. Investigating the magnitude of carbon storage potential of different freshwater wetland systems using multiple ecological indicators at varying spatial scales provides insight and justification for selective wetland restoration and conservation initiatives. We provide a holistic accounting of total carbon values for 193 wetland sites, integrating existing carbon algorithms to rapidly assess each of the following carbon pools: above-ground, below-ground, soil, woody debris, shrub cover, and herbaceous cover. Aspects of soil, vegetation, and ecosystem characteristics and stressors were measured to obtain an overall understanding of the ecosystems ability to store carbon (long-term) along a gradient of human disturbance. Based on a review of the literature, methods were prioritized based on the initial data available from field measurements as well as their practicality and ease in replicating the process in the future. Lacustrine human impounded (88.7?±?18.0 tC/ha), riverine beaver impounded (116.2?±?29.4 tC/ha), riverine upper perennial (163.3?±?11.8 tC/ha), riverine lower perennial (199.2?±?24.7 tC/ha), riverine headwater complex (159.5?±?22.2 tC/ha), perennial/seasonal depression (269.6?±?42.4 tC/ha), and slope (162.2?±?14.6 tC/ha) wetland types were compared. Overall results showed moderate variability (9.33–835.95 tC/ha) for total carbon storage values across the wetland types, with an average total carbon storage of 174.6?±?8.8 tC/ha for all wetlands. Results show that carbon storage was significantly higher (p?=?0.002) in least disturbed wetland sites. Apart from perennial/seasonal depression wetlands, all reference standard wetlands had greater carbon storage, less disturbance impact, and a greater extent of forest cover than non-reference wetlands. Carbon storage values calculated were comparable to published literature.     

Vegetation,Invertebrate, and Wildlife Community Rankings and Habitat Analysis of Mitigation Wetlands in West Virginia

Numerous efforts have been made in West Virginia to construct and restore compensatory wetlands as mitigation for natural wetlands destroyed through highway development, timbering, mining, and other human activities. Because such little effort has been made to evaluate these wetlands, there is a need to evaluate the success of these systems. The objective of this study was to determine if mitigation wetlands in West Virginia were adequately supporting ecological communities relative to naturally occurring reference wetlands and to attribute specific characteristics in wetland habitat with trends in wildlife abundance across wetlands. Specifically, avian and anuran communities, as well as habitat quality for eight wetland-dependent wildlife species were evaluated. To supplement this evaluation, vegetation and invertebrate communities also were assessed. Wetland ranks were assigned based on several parameters including richness, abundance, diversity, density, and biomass, depending on which taxa was being analyzed. Mitigation wetlands consistently scored better ranks than reference wetlands across all communities analyzed. Canonical correspondence analysis revealed no correlations between environmental variables and community data. However, trends relating wetland habitat characteristics to community structure were observed. These data stress the need to maintain specific habitat characteristics in mitigated wetlands that are compatible with wildlife colonization and proliferation.     

Influence of physical processes on the design, functioning and evolution of restored tidal wetlands in California (USA)

The performance of two intertidal wetland mitigation projects constructed by the California Department of Transportation (Caltrans) in the Sweetwater Marsh National Wildlife Refuge (SMNWR) in San Diego Bay was evaluated over 5 years. Most of the Sweetwater wetland complex has been altered this century, including diking (with subsequent subsidence), filling, modification of the tidal regime, freshwater inflow and sediment fluxes. The mitigation project goals included a range of functional criteria intended to support two endangered bird species (light-footed clapper rail and California least tern) and one endangered plant (salt marsh bird's-beak). While the mitigation projects have achieved some of the performance criteria established in the regulatory permits (particularly, those related to fish), vegetation criteria for one of the bird species have not been met. The initial grading (in relation to local tidal datums) should support the target plant species, but growth has been less than required. Shortcomings of the habitat include elevated soil and groundwater salinity, low nutrient levels (especially nitrogen, which is readily leached from the coarse substrate), and eroding topography (where a single oversized and overly sinous channel and the lower-than-natural marshpalin result in high velocity surface water flow and erosion). The failure to achieve a large plain at low-marsh elevations highlights the importance of a more complete understanding of the relationship between the site physical processes (topography, hydrology, climate, geomorphology), substrate conditions, and biotic responses.Corresponding editor: R.E. Turner     

Use of monetary wetland value estimates by EPA Clean Water Act Section 404 regulators

U.S. Environmental Protection Agency wetland regulators appear to use monetary estimates of the societal value of wetlands relatively infrequently in Section 404 permit review, enforcement, and compensatory mitigation-related activities. While 52 % of surveyed EPA regulators had used such estimates at least once, only 3 % reported using them frequently. Forty-eight percent said they never used them. Survey respondents indicated that their use of such estimates is inhibited by a lack of relevant information, uncertainty about the scientific validity of estimates, and concerns about the scientific and legal defensibility of estimate use. Respondents said they would be more apt to use estimates in regulatory activities if they perceived agency approval for such use and had access to training and best practices. The barriers and inducements EPA regulators cited largely accord with the literature on the science-policy divide and with the argument that regulatory use of valuation estimates may be inappropriate because research in this arena is not sufficiently advanced.     

Influence of physical processes on the design,functioning and evolution of restored tidal wetlands in California (USA)

The performance of two intertidal wetland mitigation projects constructed by the California Department of Transportation (Caltrans) in the Sweetwater Marsh National Wildlife Refuge (SMNWR) in San Diego Bay was evaluated over 5 years. Most of the Sweetwater wetland complex has been altered this century, including diking (with subsequent subsidence), filling, modification of the tidal regime, freshwater inflow and sediment fluxes. The mitigation project goals included a range of functional criteria intended to support two endangered bird species (light-footed clapper rail and California least tern) and one endangered plant (salt marsh bird's-beak). While the mitigation projects have achieved some of the performance criteria established in the regulatory permits (particularly, those related to fish), vegetation criteria for one of the bird species have not been met. The initial grading (in relation to local tidal datums) should support the target plant species, but growth has been less than required. Shortcomings of the habitat include elevated soil and groundwater salinity, low nutrient levels (especially nitrogen, which is readily leached from the coarse substrate), and eroding topography (where a single oversized and overly sinous channel and the lower-than-natural marshpalin result in high velocity surface water flow and erosion). The failure to achieve a large plain at low-marsh elevations highlights the importance of a more complete understanding of the relationship between the site physical processes (topography, hydrology, climate, geomorphology), substrate conditions, and biotic responses.     

Constructed Wetland Habitat for American Avocet and Black-Necked Stilt Foraging and Nesting

Abstract In 1994, a 117-ha wetland was designed, constructed, and operated by the Tulare Lake Drainage District (TLDD), California, USA, to provide foraging and nesting habitat for American avocets (Recurvirostra americana) and black-necked stilts (Himantopus mexicanus). The wetland was operated seasonally in compliance with regulatory requirements to compensate for impacts to stilts, avocets, and other wildlife exposed to elevated selenium concentrations, fluctuating water levels resulting in nest flooding, and high nest-predation rates at the TLDD agricultural drainage evaporation basins. Water supply for the wetland was from low-selenium (typically <2 μg/L) saline agricultural drainage water, although the facility also had capability to blend and use freshwater and saline supplies. Coincident with wetland construction, 2 evaporation basins totaling 1,174 ha were physically modified and operated to discourage their use by shorebirds. In the first year of wetland operation (1995), American avocet and black-necked stilt nest construction at the wetland was 17.6 nests/ha. This compares to a preproject (1994) combined density of 1.9 nests/ha at the evaporation basins. From 1995 through 2004, annual nesting attempts by American avocets and black-necked stilts at the wetland averaged 2,896 per year (24.8 nests/ha). American avocets and black-necked stilts represented 91% of the nests observed at the wetland. Over the 10-year monitoring period, nest success at the wetland averaged 82% for American avocets and 75% for black-necked stilts. We estimated nest predation rates at the constructed wetland to be <1%. During the same period, American avocet and black-necked stilt nesting at the evaporation basins declined from 2,266 in 1994 to 9 in 2004. The constructed wetland has proven to be effective in attracting and providing suitable nesting habitat for large numbers of avocets and stilts. Results of this long-term study confirm the validity of management recommendations for American avocets and black-necked stilts and suggest that agricultural drainage can be successfully managed to provide highly productive managed wetlands.     

Recent areal changes in US forested wetlands

This study summarizes US Forest Service Resource Bulletin data to estimate forested wetlands areal changes. The Forest Resource Bulletins used field-data surveys to estimate the area of different forest land plant associations, including those that are typically defined as forested wetlands. The information includes changes since 1940 on national and state levels. These figures may help judge the success of some recent efforts by private and public agencies to protect wetlands.Forested wetland area decreased by about 3 million ha from 1960 to 1990. The percentage of forested wetlands lost (13%) was greater than for forest land (7%) for the past three decades. In the 1980s, Louisiana and North Carolina experienced the greatest losses (178,000 ha and 203,000 ha, respectively). In the same period, Maine, Montana, and South Carolina experienced the largest increases. The area of forested wetlands in the United States decreased over 700,000 ha (0.3%/yr) between 1980 and 1990.Corresponding Editor: R.E. Turner     

Can the use of zooplankton dormant stages from natural wetlands contribute to restoration of mined wetlands?

Wetlands are among the most diverse environments on the planet and are strongly threatened by human activities. Their restoration and/or mitigation of human impacts, therefore, relies on information that can aid to the management of impacted wetlands so that they return to a (semi-) natural state. We investigate in this study the relationship between dormant stages of zooplankton and clay removal in areas subjected to mining. We evaluate whether a gradual increase in topsoil addition from donor natural wetlands to the sediment of mined wetlands influenced the zooplankton community. Eight wetlands were sampled in the Sinos River floodplain, four natural and four mined. In the laboratory, four field sediment samples were incubated for zooplankton hatching in five treatments comprising sediments from: mined wetlands, natural wetlands, and three treatments containing mined sediments added with low (5%), medium (20%) and high (40%) quantities of sediment from natural wetlands. Hatching consisted of 61 individuals distributed across eight zooplankton taxa. Copepod nauplii were the most abundant (31.1%) followed by Epiphanes sp. (29.5%) and Ovalona glabra (16.4%). While natural wetlands provided 42.6% of the hatched zooplankton, mined wetlands had just 6.5%. Zooplankton richness and abundance were higher in natural wetland sediments compared with mined and added sediment wetlands. To some degree, the sediment soil donation from natural to mined wetlands was considered viable. As long as prior studies are performed to test the size and quality of the dormant banks present in the sediment of candidate donor wetlands, sediment from donor wetlands may aid in the establishment of a more diverse community in disturbed systems.

     

城市湖泊湿地温湿效应——以武汉市为例

选择武汉城市三环内主城区14块湖泊湿地为研究对象,采用小尺度定量测定的方法,研究城市湖泊湿地与温湿效应间的关系。结果表明:(1)城市湿地温度值与面积指数、距离指数呈显著负相关,与景观形状指数呈显著正相关(P0.05);湿度值与面积指数、距离指数、环境类型指数呈显著正相关,与景观形状指数呈显著负相关(P0.05)。其中面积指数的贡献值最大。(2)14块湖泊湿地的降温增湿效应排序为湖泊11—14湖泊6—10湖泊1—5。当湖泊湿地面积为9.2—12.2 hm2时,其降温增湿效应明显;当湖泊湿地面积为308.4hm2左右时,降温效应显著且趋于稳定,湖泊湿地面积为67.6hm2左右时,增湿效应显著且趋于稳定(P0.05)。当湖泊湿地面积达到临界值之后,多斑块离散型(Dispersive)湖泊湿地布局对整个城市环境的降温增湿效应更为显著。