Restoring prairie pothole wetlands: does the species pool concept offer decision‐making guidance for re‐vegetation?

Question: Do regional species pools, landscape isolation or on‐site constraints cause plants from different guilds to vary in their ability to colonize restored wetlands? Location: Iowa, Minnesota, and South Dakota, USA. Methods: Floristic surveys of 41 restored wetlands were made three and 12 years after reflooding to determine changes in local species pools for eight plant guilds. The effect of landscape isolation on colonization efficiency was evaluated for each guild by plotting local species pools against distance to nearby natural wetlands, and the relative importance of dispersal vs. on‐site constraints in limiting colonization was explored by comparing the local species pools of restored and natural wetlands within the region. Results: Of the 517 wetland plant taxa occurring in the region, 50% have established within 12 years. The proportion of the regional species pool represented in local species pools differed among guilds, with sedge‐meadow perennials, emergent perennials and floating/submersed aquatics least represented (33‐36%) and annual guilds most represented (74‐94%). Colonization‐to‐extinction ratios suggest that floating/submersed aquatics have already reached a species equilibrium while sedge‐meadow and emergent perennials are still accumulating species. Increasing distance to nearest wetlands decreased the proportion of the regional species pool present in local pools for all guilds except native annuals and woody plants. The maximum proportion predicted, assuming no distance constraint, was comparable to the lowest‐diversity natural wetlands for most perennial guilds, and also lower than what was achieved in a planted, weeded restoration. Conclusions: A biotic constraints seem to limit the colonization of floating/submersed aquatics into natural or restored wetlands, whereas all other guilds are potentially constrained by dispersal or biotic factors (i.e. competition from invasive species). Using species pools to evaluate restoration progress revealed that immigration potential varies considerably among guilds, that local species richness does not necessarily correspond to immigration limitations, and that some guilds (e.g. sedge‐meadow perennials) will likely benefit more than others from being planted at restoration sites.     

三江平原恢复湿地土壤种子库特征及其与植被的关系

通过幼苗萌发法和样方调查相结合的方法对三江平原不同演替恢复阶段的种子库特征及其与植被的关系进行了研究。将开垦湿地、不同演替恢复阶段湿地以及天然湿地不同土壤层次(0-5、5-10 cm和根茎)的种子库在两种水分条件下(湿润、淹水10 cm)进行萌发处理。结果表明: 随着演替恢复阶段的进行, 种子库的结构和规模逐渐扩大, 地表群落表现出由旱生物种占优势的群落逐渐演变成以小叶章(Calamagrostis angustifolia)占优势的湿生群落的演替趋势。恢复7年湿地、恢复14年湿地、天然湿地土壤种子库萌发物种数分别为24种、29种、39种, 植被物种数为21种、25种、14种。湿地类型、水分条件和土壤层次均显著影响种子库萌发的物种数及幼苗数(p < 0.01)。种子库具有明显的分层现象, 天然湿地0-5 cm土层种子库种子萌发密度是5-10 cm土层的4倍左右, 而恢复湿地仅1.3倍左右, 且土层间萌发物种相似性系数较低。湿润条件下的萌发物种数显著高于淹水条件, 且两种水分条件下萌发物种的生活型不同。由于恢复时间较短, 不同演替恢复阶段的种子库与植被相似性维持在30%以下。湿地中根茎分蘖出大量的湿地物种, 对于小叶章等优势物种的繁殖具有重要作用。研究表明, 在开垦湿地退耕后的次生演替阶段, 种子库能够保持大量的湿地物种, 通过对湿地种子库与植被的关系研究, 能够为三江平原湿地群落演替与湿地恢复提供策略指导。     

内蒙古高原典型草原区河漫滩湿地植物群落退化表征

草原区河流河漫滩草甸是生物多样性表现最充分和生物生产力最高的地段, 但由于过度放牧利用, 绝大部分草甸处于退化状态。该文以锡林河流域中游的河漫滩草甸为研究对象, 比较分析了围封保育湿地与放牧退化湿地的群落组成、地上生物量, 以及共有植物种的植株高度、节间长、叶长、叶宽, 土壤含水量、容重, 群落地下根量及根的分布, 土壤微生物生物量碳、氮的变化。结果表明: 1)放牧使得湿地植物群落优势种发生变化, 原有湿生植物逐渐向旱生化转变, 同时地上及地下生物量明显降低。2)退化湿地的植物呈现显著小型化现象。3)放牧退化湿地的土壤含水量较围封保育湿地低, 其垂直分布及地下根的垂直分布也发生变化。在低河漫滩, 土壤水分随土层的增加而增加, 根量也趋于深层化。但在高河漫滩湿地, 土壤含水量接近典型草原, 根未出现深层化分布趋势。4)放牧践踏引起土壤容重和土壤紧实度增加。5)放牧使得低河漫滩湿地土壤微生物生物量增加, 而在过渡区及高河漫滩湿地, 放牧使得土壤微生物生物量碳、氮含量显著降低。     

Detecting soil and plant community changes in restored wetlands using a chronosequence approach

Wetland restoration aims to recreate or enhance valuable ecosystem services lost during wetland destruction. Regaining wetland ecosystem services depends on restarting basic wetland functions, like carbon (C) storage, which are unmeasured in many Wetlands Reserve Program (WRP) restoration sites. We collected soil and plant data from 17 WRP sites in western New York that were used for tillage or non-tillage agriculture and then actively restored as isolated depressional wetlands by excavating basins and disabling drainage systems. Sites had been restored for 0–15 years when sampled in August-October 2010. We analyzed data as chronosequences and tested whether soil and vegetation parameters in restored wetlands, over time, (1) departed from pre-restoration baselines, estimated using active agricultural fields paired to each WRP site, and (2) converged towards “natural” benchmarks, estimated from four naturally-occurring wetlands. Restored WRP soils remained similar to agricultural soils in organic matter, density, moisture, and belowground plant biomass across chronosequences, indicating negligible C storage and belowground development for 15 years following restoration. Soil changes were limited in sites restored after both tillage and non-tillage agriculture and throughout the upland meadow, emergent shoreline, and open-water habitat zones that characterize these sites. Many plant metrics like aboveground biomass matched natural wetlands within 15 years, but recovered inconsistently among tilled and untilled sites and across all habitat zones, suggesting land-use history impacts and/or zonation effects. Disparities in recovery times exists between vegetation, which can respond quickly to wetland restoration, and underlying soils, which show limited signs of recovery 15 years after being restored.     

A comparison of created and natural wetlands in Pennsylvania,USA

Recent research suggests that created wetlands do not look, or function, like the natural systems they are intended to replace. Proper planning, construction, and the introduction of appropriate biotic material should initiate natural processes which continue indefinitely in a successful wetland creation project, with minimal human input. To determine if differences existed between created and natural wetlands, we compared soil matrix chroma, organic matter content, rock fragment content, bulk density, particle size distribution, vegetation species richness, total plant cover, and average wetland indicator status in created (n = 12) and natural (n = 14)wetlands in Pennsylvania (USA). Created wetlands ranged in age from two to 18 years. Soils in created wetlands had less organic matter content, greater bulk densities, higher matrix chroma, and more rock fragments than reference wetlands. Soils in reference wetlands had clay loam textures with high silt content, while sandy clay loam textures predominated in the created sites. Vegetation species richness and total cover were both greater in natural reference wetlands. Vegetation in created wetlands included a greater proportion of upland species than found in the reference wetlands. There were significant differences in soils and vegetation characteristics between younger and older created wetlands, though we could not say older created sites were trending towards the reference wetland condition. Updated site selection practices, more careful consideration of monitoring period lengths, and, especially, a stronger effort to recreate wetland types native to the region should result in increased similarity between created and natural wetlands.     

Influence of macroinvertebrates and macrophytes on waterfowl utilization of wetlands in the Prairie Pothole Region of northwestern Wisconsin

Waterfowl and limnological data were monitored on Waterfowl Production Area (WPA) wetlands in northwestern Wisconsin over a 6-yr period (1983–88) to determine the impact of macroinvertebrates and macrophytes on waterfowl utilization. Interrelationships between limnological conditions and Waterfowl Breeding Pair Densities (BPDs reported as pairs/ha water surface) were analyzed using correlation and general linear model analysis techniques.Annual changes in waterfowl BPDs differed between wetlands according to differences in the structure of macrophyte communities and basin morphometry. The strength of associations differed between the two dominant waterfowl species. In a wetland dominated by dense stands of submersed vegetation, annual fluctuations in blue-winged teal (Anas discors) BPDs corresponded directly with changes in macrophyte biomass, but not with changes in macroinvertebrate density. In a nearby less densely vegetated wetland of similar water chemistry and trophic status, fluctuations in teal BPDs corresponded directly with changes in macroinvertebrate density, but not with changes in macrophyte biomass. These associations occurred despite a significant positive correlation between macroinvertebrates and macrophyte biomass in the latter habitat. Annual fluctuations in mallard (Anas platyrhynchos) BPDs were not correlated significantly with either macrophyte biomass or macroinvertebrate density in either wetland.     

Salvaged-Wetland Soil as a Technique to Improve Aquatic Vegetation at Created Wetlands in Wyoming,USA

Aquatic plants usually establish following wetland creation from a variety of mechanisms including animal transport, inflows from nearby wetlands, wind dispersal, and seed banks if they are available. However, at created wetlands that are isolated from natural wetlands, aquatic plant communities may not establish even after 10 or more years. One method of improving the establishment of aquatic plants is through the use of salvaged-marsh soils. Using this method, wetland soil from a donor site is collected and spread across the basin of the created wetland. When the proper hydrologic regime is reached at the created site, the seed bank from the donor soil is then present to take advantage of the uncolonized site. Over 1500 wetlands have been created in northeast Wyoming, USA from bentonite mining and most of them have not developed submersed and emergent plant communities due to isolation from plant sources. Our goal was to evaluate the effectiveness of using salvaged-wetland soil as a tool for improving plant growth at created wetlands. Our study took place at 12 newly created wetlands that were isolated from other wetlands by >5 km. Six wetlands were treated as reference wetlands, with no introductions of seeds or propagules. At the other six wetlands we spread ≈10–15 cm of salvaged soil from a donor wetland during the winter of 1999–2000. To identify the potential plants in donor soil, we collected 10 random samples from the donor wetlands and placed them within wetland microcosms in a greenhouse where they were treated to either moist-soil conditions (water at or just below the soil line) or submersed conditions (water levels maintained at 15–30 cm). Treatment wetlands were evaluated for plant growth during the fall of 2000 and 2001, whereas the greenhouse samples were grown for two growing seasons then harvested. Our results show that using salvaged wetland soil increases: (1) the number of plant species present at a wetland over time, (2) the total vegetation coverage in a treated wetland over time, and (3) the total plant biomass in a treated wetland. The species pool available in the salvaged wetland soil was limited to 10 obligate wetland species, but several of them are considered valuable to waterfowl and other wildlife. Furthermore, salvaged-wetland soil could be useful for ameliorating poor substrate conditions (i.e., bentonite) and improving conditions for the establishment of additional species. One concern with this technique is the introduction of invasive or exotic species that could form monocultures of undesirable plants (e.g., cattail [Typha spp.]); introducing more desirable species during the application of salvaged soil could reduce this probability. We believe incorporating salvaged-wetland soil during basin construction could be used to increase the value and productivity of created wetlands in this region.     

Incomplete recovery of plant diversity in restored prairie wetlands on agricultural landscapes

Restoration efforts are being implemented globally to mitigate the degradation and loss of wetland habitat; however, the rate and success of wetland vegetation recovery post‐restoration is highly variable across wetland classes and geographies. Here, we measured the recovery of plant diversity along a chronosequence of restored temporary and seasonal prairie wetlands ranging from 0 to 23 years since restoration, including drained and natural wetlands embedded in agricultural and natural reserve landscapes in central Alberta, Canada. We assessed plant diversity using the following structural indicators: percent cover of hydrophytes, native and non‐native species, species richness, and community composition. Our findings indicate that plant diversity recovered to resemble reference wetlands in agricultural landscapes within 3–5 years of restoration; however, restored wetlands maintained significantly lower species richness and a distinct community composition compared to reference wetlands located within natural reserves. Early establishment of non‐native species during recovery, dispersal limitation, and depauperated native seed bank were probable barriers to complete recovery. Determining the success of vegetation recovery provides important knowledge that can be used to improve restoration strategies, especially considering projected future changes in land use and climate.     

Plant traits in response to raising groundwater levels in wetland restoration: evidence from three case studies

Question: Is raising groundwater tables successful as a wetland restoration strategy? Location: Kennemer dunes, The Netherlands; Moksloot dunes, The Netherlands and Bullock Creek fen, New Zealand. Methods: Generalizations were made by analysing soil dynamics and the responsiveness of integrative plant traits on moisture, nutrient regime and seed dispersal in three case studies of re wetted vs. control wetlands with the same actual groundwater levels. Soil conditions included mineral (calcareous and non‐calcareous) soils with no initial vegetation, mineral soils with established vegetation and organic soils with vegetation. Results: The responsiveness of traits to raised groundwater tables was related to soil type and vegetation presence and depended on actual groundwater levels. In the moist‐wet zone, oligotrophic species, ‘drier’ species with higher seed longevity occupied gaps created by vegetation dieback on rewetting. The other rewetted zones still reflected trait values of the vegetation prevalent prior to rewetting with fewer adaptations to wet conditions, increased nutrient richness and higher seed longevity. Moreover, ‘eutrophic’ and ‘drier’ species increased at rewetted sites, so that these restored sites became dissimilar to control wetlands. Conclusions: The prevalent traits of the restored wetlands do not coincide with traits belonging to generally targeted plant species of wetland restoration. Long‐term observations in restored and control wetlands with different groundwater regimes are needed to determine whether target plant species eventually re vegetate restored wetlands.     

Wind dispersal in freshwater wetlands: Knowledge for conservation and restoration

Questions: For wetland plants, dispersal by wind is often overlooked because dispersal by water is generally assumed to be the key dispersal process. This literature review addresses the role of seed dispersal by wind in wetlands. Why is wind dispersal relevant in wetlands? Which seeds are dispersed by wind and how far? And how can our understanding of wind dispersal be applied to wetland conservation and restoration? Methods: Literature review. Results and conclusions: Wind is a widely available seed dispersal vector in wetlands and can transport many seeds over long distances. Unlike water, wind can transport seeds in all directions and is therefore important for dispersal to upstream wetlands and to wetlands not connected by surface water flows. Wind dispersal transports seeds to a wider range of sites than water, and therefore reaches more sites but with lower seed densities. Many wetland plant species have adaptations to facilitate wind dispersal. Dispersal distances increase with decreasing falling velocity of seeds, increasing seed release height and selective release mechanisms. Depending on the adaptations, seeds may be dispersed by wind over many km or only a few m. The frequency of long‐distance wind dispersal events depends on these adaptations, the number of produced seeds, the structure of the surrounding vegetation, and the frequency of occurrence of suitable weather conditions. Humans reduce the frequency of successful long‐distance wind dispersal events in wetlands through wetland loss and fragmentation (which reduce the number and quality of seeds) and eutrophication (which changes the structure of the vegetation so that seed release into the wind flow becomes more difficult). This is yet another reason to focus on wetland conservation and restoration measures at increased population sizes, prevention of eutrophication, and the restoration of sites at short distances from seed sources.     

Vegetation Similarity and Avifaunal Food Value of Restored and Natural Marshes in Northern New York

Measuring the success of wetland restoration efforts requires an assessment of the wetland plant community as it changes following restoration. But analyses of restored wetlands often include plant community data from only one time period. We studied the development of plant communities at 13 restored marshes in northern New York for 4 years, including 1 year prior to restoration and 3 years afterwards. Restored wetlands ranged in size from 0.23 to 1.70 ha. Four reference wetlands of similar basin morphology, soil type, and size (0.29–0.48 ha) that occurred naturally in the same area were studied as comparisons. Dike construction to restore hydrology disturbed the existing vegetation in some parts of the restored sites, and vegetation was monitored in both disturbed and undisturbed areas. Undisturbed areas within the restored sites, which were dominated by upland field grasses before restoration, developed wetland plant communities with lower wetland index values but comparable numbers of wetland plant species than the reference wetlands, and they lagged behind the reference sites in terms of total wetland plant cover. There were significantly more plant species valuable as food sources for wetland birds, and a significantly higher percent cover of these species, at the undisturbed areas of the restored sites than at the reference wetlands. Areas of the restored sites that were disturbed by dike construction, however, often developed dense, monospecific cattail stands. In general, the plant communities at restored sites became increasingly similar to those at the reference wetlands over time, but higher numbers of herbaceous plants developed at the restored sites, including food plants for waterfowl, rails, and songbirds. Differences in shrub cover will probably lessen as natural recolonization increases shrub cover at the restored sites. Natural recolonization appears to be an effective technique for restoring wetlands on abandoned agricultural fields with established plant cover, but it is less successful in areas where soil has been exposed by construction activity.     

滨海蓝碳湿地碳汇速率测定方法及中国的研究现状和挑战

滨海盐沼、红树林和海草床蓝碳湿地生态系统具有高效的固碳-储碳能力,准确测定滨海蓝碳湿地生态系统碳汇速率,对于评估滨海湿地碳中和能力、生态恢复新增碳汇规模及碳贸易至关重要。深入思考滨海蓝碳湿地生态系统碳汇定义的内涵,提出狭义碳汇和广义碳汇的概念,介绍沉积物碳累积+植被净初级生产力法以及生态系统碳通量收支法2个目前国际上应用最多的滨海蓝碳湿地碳汇速率测定方法,特别是深入分析作为开放系统的滨海盐沼生态系统和海草床生态系统碳汇速率测定面临的诸多问题与挑战,梳理中国红树林、滨海盐沼和海草床生态系统碳汇速率的测定结果及国家尺度滨海蓝碳湿地生态系统碳汇规模,最后提出中国在滨海蓝碳湿地碳汇速率测定实践中急需加强的基础研究领域,以期为科学地计量中国滨海蓝碳湿地生态系统碳汇速率与碳汇规模提供方法参考和技术支撑。     

Hydrologic similarity to reference wetlands does not lead to similar plant communities in restored wetlands

Few wetland restoration projects include long‐term hydrologic and floristic data collection, limiting our understanding of community assembly over restored hydrologic gradients. Although reference sites are commonly used to evaluate outcomes, it remains unclear whether restoring similar water levels to reference sites also leads to similar plant communities. We evaluated long‐term datasets from reference and restored wetlands 15 years after restoration to test whether similar water levels in reference and restored sites led to vegetation similarity. We compared the hydrologic regimes for three different wetland types, tested whether restored wetland water levels were different from reference water levels, and whether hydrologic similarity between reference and restored wetlands led to similarity in plant species composition. We found restored wetlands had similar water levels to references 15 years after restoration, and that species richness was higher in reference than restored wetlands. Vegetation composition was similar across all wetland types and was weakly correlated to wetland water levels overall. Contrary to our hypothesis, water table depth similarity between restored and reference wetlands did not lead to similar plant species composition. Our results highlight the importance of the initial planting following restoration and the importance of hydrologic monitoring. When the restoration goal is to create a specific wetland type, plant community composition may not be a suitable indicator of restoration progress in all wetland types.     

艾比湖湿地土壤有机碳及储量空间分布特征

土壤碳储量的研究是全球碳循环研究的热点,土壤碳库的变化对全球气候变暖、维护生态平衡都有着重要的意义。新疆的艾比湖湿地是干旱区典型的盐湖湿地,为探明该湿地有机碳特性及储量,选择艾比湖湿地1m深度的土壤作为研究对象,测试有机碳含量后,对艾比湖湿地土壤有机碳特性进行分析并分层定量测算有机碳储量,结果显示:(1)艾比湖湿地土壤有机碳整体偏低,随土层加深,含量依次递减的规律比较显著。湿地7种不同植被覆盖类型的土壤有机碳含量垂直空间变异性差异明显,其中荒漠河岸林、盐化草甸、小乔木荒漠大多属于强变异,而其它植被覆盖的土壤类型多属于中等变异。(2)艾比湖湿地7种不同植被类型土壤有机碳含量在相同土层的分布特征为:有机碳集中分布在浅表层(0—20 cm),从40 cm以下变幅缓慢,分布较为均匀。不同植被类型土壤有机碳在不同土层的分配比例差异比较明显,但表层(0—20 cm)大多占到30%以上。(3)艾比湖湿地土壤有机碳储量排序依次为小乔木荒漠盐化草甸干涸湖底灌木荒漠盐生灌丛荒漠河岸林寒湿性针叶林。湿地有机碳蓄积总量为7086862.83 kgC。上述研究结果可为新疆干旱区湿地生态系统恢复、保护与科学管理提供科技支撑。     

莫莫格扁秆藨草恢复湿地土壤种子库对长芒稗入侵的响应

湿地恢复过程中,时常有外来种或本地杂草入侵。土壤种子库作为未来植被的潜在种源,对湿地恢复效果具有重要的指示意义。在莫莫格国家级自然保护区,以恢复白鹤栖息地(扁秆藨草(Scirpus planiculmis)沼泽)为目的,进行了退化湿地的水文恢复;但退化湿地恢复2a后,一年生杂草长芒稗(Echinochloa caudata)在大部分区域成为建群种。以长芒稗入侵湿地和扁秆藨草自然湿地为研究对象,对比分析了长芒稗和扁秆藨草的土壤种子库及生长结实特征。结果表明,在自然湿地扁秆藨草种子库规模是长芒稗的18.42倍,而在恢复湿地长芒稗种子库大小是扁秆藨草的5.04倍。与自然湿地相比,扁秆藨草种子库密度在入侵湿地明显减少,但仍保留了一定量具有活力的种子(664.32±105.98)粒/m~2,这与研究区扁秆藨草较高的种子生产力(9210.4±1513.4)粒/m~2及种子较强的浮力(FP50=39.7d)有关,说明扁秆藨草具备通过种子库或水传播恢复的潜力。长芒稗土壤种子库密度在入侵湿地高达(3345.9±520.3)粒/m~2,明显高于自然湿地种子库规模(P0.01),说明恢复湿地受长芒稗入侵影响严重,这与长芒稗较高的种子生产力(7621.4±376.25)粒/m~2及较弱的种子浮力(FP0=5d)有关,同时也表明长芒稗通过水传播扩散的能力较弱。另外,研究区长芒稗平均高度超过1m,且盖度较大,不仅阻碍扁秆藨草种子的水播,也降低了到达地表的光照水平,从而抑制扁秆藨草更新。因此,在莫莫格受长芒稗入侵湿地,于开花结实前收获长芒稗地上植物体及凋落物应是限制长芒稗扩展、同时促进扁秆藨草恢复的有效措施。     

Soil amendments promote denitrification in restored wetlands

Wetlands perform important ecosystem functions, including improvement of water quality through the process of denitrification. To offset the negative environmental impact of replacing wetlands with agriculture and development, the United States has a policy requiring that losses in wetland area are compensated for through wetland restoration elsewhere. However, these restored wetlands may require decades to achieve functional equivalency to natural wetlands. We evaluated the efficacy of using carbon amendments during restoration to promote denitrification potential in four restored wetlands in central New York State, United States. The amendments were straw, topsoil, and biochar, chosen to range along a gradient of carbon lability. Soil samples collected 6 years after restoration were analyzed for denitrification potential and associated soil properties, including soil carbon and nitrogen, pH, microbial biomass carbon and nitrogen, carbon lability, and potential net nitrogen mineralization and nitrification. Compared to unamended control plots, denitrification potential was approximately 3 times higher in straw‐amended plots, 8 times higher in topsoil‐amended plots, and 11 times higher in biochar‐amended plots. Denitrification potential positively correlated with both soil organic carbon and microbial biomass nitrogen, suggesting that the use of soil amendments in restorations can help stimulate the development of denitrification potential by facilitating the suite of carbon and nitrogen cycling processes that underlie this function. However, denitrification potential in a nearby natural reference wetland was at least 50 times higher than it was in the restored wetland plots, highlighting the limitations of using wetland restoration to compensate for the loss of natural wetlands.     

排水对小兴安岭森林沼泽湿地溶解性有机碳和有效氮磷的影响

选取不同排水年限的兴安落叶松人工林湿地(1974年排水、1985年排水、1992年排水、2003年排水)和天然森林沼泽湿地(兴安落叶松沼泽湿地)为研究对象,探讨排水对小兴安岭森林沼泽湿地土壤溶解性有机碳(DOC)和有效氮磷的影响。结果表明,天然沼泽排水后,在土壤垂直剖面上,不同排水年限的森林湿地与天然沼泽湿地的土壤溶解性有机碳含量均呈递减变化。与天然森林沼泽湿地相比,排水湿地各土层DOC含量均显著低于天然沼泽湿地(P0.05)。天然森林沼泽,表层(0—10 cm)的土壤SOC含量、DOC/SOC、土壤有效氮含量均大于排水森林沼泽,但是有效磷含量却低于排水森林沼泽(P0.05)。在土壤表层(0—10 cm),排水年限与DOC、SOC、DOC/SOC、土壤有效氮呈显著性负相关,与有效磷呈显著性正相关(P0.05)。天然沼泽排水后,表层(0—10 cm)土壤的DOC含量与有效氮(铵态氮、硝态氮)含量成正比,与有效磷含量成反比(P0.05)。     

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.     

Waterbird habitat-selection during winter and spring in reclaimed coastal wetlands in Nanhui Dongtan, Shanghai

From December 2009 to May 2010 goose and duck (Anatidae) community censuses in winter and shorebird (Charadriiforms) community censuses in spring were conducted across three types artificial wetlands (urban lake wetland, restorative wetland, abandoned wetland) along the coast of Nanhui, Shanghai. Correlation analyses were undertaken between community indices and habitat factors. The results showed there were significant differences in the density of geese and ducks among the wetlands, but no difference in the number of species. The density of geese and ducks in the restorative wetland was 3.77 times that of abandoned wetland and 6.03 times that of urban lake wetlands. The number of species and density of shorebirds in restorative wetlands was 2.88 and 5.70 times that of abandoned wetlands. We found significant differences in the number and density of shorebird species between restorative and abandoned wetlands. The number of species density of geese and ducks and the Shannon-Wiener (H') index were positively correlated with water area. The number of species and H' were negatively correlated with vegetation area. The number of species, species density and H' and evenness were negatively correlated with vegetation coverage. H' was positively correlated with mean water level. The results showed that the number and density of shorebird species were positively correlated with bare muddy areas. Aquaculture ponds and paddy fields in reclaimed area is efficient sufficient compensation mechanism to maintain more water areas for waterbirds and to control vegetation expansion and maintain shorebird habitat after coastal reclamation.     

Setting reclamation targets and evaluating progress: Submersed aquatic vegetation in natural and post-oil sands mining wetlands in Alberta, Canada

Oil sands mining disturbs thousands of hectares of boreal landscape, about 65% of which is wetland. Its reclamation will constitute the largest wetland reclamation project in Canadian history. We developed a unified analytical framework that we used to set reclamation targets and evaluate reclamation progress using submersed aquatic vegetation (SAV). We sampled SAV in 38 minimally disturbed wetlands to establish a reference condition and compared this to SAV in 25 reclamation wetlands. We observed 26 taxa: all were native and five are regionally rare. Using a combination of ordination, clustering, and indicator species analysis, we identified seven SAV assemblages, distinguishable based on 10 indicator species. The assemblages found in wetlands contaminated by tailings had significantly fewer taxa. Using joint plots, we demonstrate that they differ in terms of environmental variables reflecting depth, slope, salinity, transparency, water and sediment nutrient levels, and alkalinity. Collectively, 74% of reference wetlands had SAV belonging to either marsh or fen-marsh assemblages that we consider suitable targets for reclamation. Having multiple reclamation targets avoids creating a homogenous post-mining landscape with low gamma diversity. Using complementary multivariate and categorical tests, we found that reclamation wetlands failed to support either of these dominant reference assemblages. Instead, every reclamation wetland supported one of five atypical SAV assemblages, each of which was uncommon (<10%) among reference wetlands. The analytical framework we developed can be applied to other ecosystems or taxa to develop targets for reclamation, to evaluate reclamation progress, and to identify environmental characteristics associated with reclamation targets.