Nutrient status and retention in pristine and disturbed wetlands in Uganda: management implications

Wetlands in Uganda experience different forms of human pressure ranging from drainage for agriculture and industrial development to over harvesting of wetland products. In order to develop sustainable management tools for wetland ecosystems in Uganda and the Lake Victoria Region, water quality analyses were carried out in a rural undisturbed (pristine) wetland (Nabugabo wetland in Masaka) and two urban wetlands that are experiencing human and urban development pressure (the Nakivubo wetland in Kampala and Kirinya wetland in Jinja). The former wetland forms the main inflow into Lake Nabugabo while the other two border the northern shore of Lake Victoria, Uganda. Nabugabo wetland buffers Lake Nabugabo against surface runoff from the catchment, while Nakivubo and Kirinya wetlands provides a water treatment function for wastewater from Kampala City and Jinja town respectively, in addition to buffering Lake Victoria against surface runoff. Water quality was assessed in all the wetland sites, and in addition nutrient content and storage was investigated in the main plant species (papyrus, Phragmites, Miscanthidium and cocoyam) in Nakivubo and Kirinya wetlands. A pilot experiment was also carried out to assess the wastewater treatment potential of both the papyrus vegetation and an important agricultural crop Colocasia esculenta (cocoyam). Low electrical conductivity, ammonium–nitrogen and ortho-phosphate concentrations were recorded at the inflow into Nabugabo wetland (41.5 μS/cm; 0.91 mg/l and 0.42 mg/l respectively) compared to the Nakivubo and Kirinya wetlands (335 μS/cm; 31.68 mg/l and 2.83 mg/l and 502 μS/cm; 10 mg/l and 1.87 mg/l respectively). The papyrus vegetation had higher biomass in Nakivubo and Kirinya wetlands (6.7 kg DW m⁻²; 7.2 kg DW m⁻² respectively), followed by Phragmites (6.5, 6.7), cocoyams (6.4, 6.6) and Miscanthidium (4.0, 4.2). The papyrus vegetation also exhibited a higher wastewater treatment potential than the agricultural crop (cocoyam) during the pilot experiment (maximum removal degree of ammonium–nitrogen being 95% and 67% for papyrus and yams). It was concluded that urbanisation pressure reduces natural wetland functioning either through the discharge of wastewater effluent or the degradation of natural wetland vegetation. It is recommended that wetland vegetation be restored to enhance wetland ecosystem functioning and for wetlands that are not yet under agricultural pressure, efforts should be made to halt any future encroachment.     

Differences exist in bird communities using restored and natural wetlands in the Parkland region,Alberta, Canada

Wetland restoration is used to compensate for historic and ongoing wetland losses. We compared bird community composition in 24 restored wetlands and 36 natural wetlands in the Parkland region of Alberta. Natural wetlands ranged in exposure to agricultural activity and were binned into three classes (low, medium, and high disturbance). Although the abundance and average species richness of birds were similar between restored and natural wetlands (analysis of variance: p > 0.22), the avian community composition differed significantly among wetland types (multiresponse permutation procedure [MRPP]: A = 0.05, p < 0.001). The avifauna using restored wetlands was distinct from the avifauna using natural wetlands spanning a range of disturbance levels (A = 0.02–0.06; p ≤ 0.006). Notably, restored wetlands were surrounded by less shrub/forest cover and more open water than low‐disturbance, natural wetlands. The majority (58%) of species using the surveyed wetlands were not classified as wetland‐dependent. Interestingly, if only wetland‐dependent species are considered, the avifauna using restored wetlands is no longer distinctive (MRPP: A < 0.01, p = 0.187), although the abundance of wetland‐dependent birds was marginally higher in restored wetlands (n = 24) than in low‐disturbance, natural wetlands (n = 10; Tukey's honestly significant difference test: p = 0.041). Overall, restored wetlands had reduced beta diversity compared to natural wetlands, regardless of whether the avifauna were restricted to wetland‐dependent species or considered comprehensively. This draws into question the legitimacy of the assumption that restoration can fully offset continued losses of natural wetlands.     

Periphyton biomass and ecological stoichiometry in streams within an urban to rural land-use gradient

This study examined the effects land use on biomass and ecological stoichiometry of periphyton in 36 streams in southeastern New York State (USA). We quantified in-stream and land-use variables along a N–S land-use gradient at varying distances from New York City (NYC). Streams draining different landscapes had fundamentally different physical, chemical, and biological properties. Human population density significantly decreased (r = −0.739; P < 0.00001), while % agricultural land significantly increased (r = 0.347; P = 0.0379) with northing. Turbidity, temperature, conductivity, and dissolved Mg, Ca, SRP, pH, DOC, and Si significantly increased in more urban locations, but NO₃ ⁻ and NH₄ ⁺ did vary not significantly along the gradient. Periphyton biomass (as AFDM and Chl-a) in rural streams averaged one-third to one-fifth that measured in urban locations. Periphyton biomass in urban streams averaged 18.8 ± 6.0 g/m² AFDM and 75.6 ± 28.5 mg/m² Chl-a. Urban Chl-a levels ranging between 100 and 200 mg/m², are comparable to quantities measured in polluted agricultural streams in other regions, but in our study area was not correlated with % agricultural land. Periphyton nutrient content also varied widely; algal C varied >20-fold (0.06–1.7 μmol/mm²) while N and P content varied >6-fold among sites. Algal C, N, and P correlated negatively with distance from NYC, suggesting that periphyton in urban streams may provide greater nutrition for benthic consumers. C:N ratios averaged 7.6 among streams, with 91% very close to 7.5, a value suggested as the optimum for algal growth. In contrast, periphyton C:P ratios ranged from 122 to >700 (mean = 248, twice Redfield). Algal-P concentrations were significantly greater in urban streams, but data suggest algal growth was P-limited in most streams regardless of degree of urbanization. GIS models indicate that land-use effects did not easily fit into strict categories, but varied continuously from rural to urban conditions. We propose that the gradient approach is the most effective method to characterize the influence of land use and urbanization on periphyton and stream function.     

Tropical wetlands: seasonal hydrologic pulsing,carbon sequestration,and methane emissions

This paper summarizes the importance of climate on tropical wetlands. Regional hydrology and carbon dynamics in many of these wetlands could shift with dramatic changes in these major carbon storages if the inter-tropical convergence zone (ITCZ) were to change in its annual patterns. The importance of seasonal pulsing hydrology on many tropical wetlands, which can be caused by watershed activities, orographic features, or monsoonal pulses from the ITCZ, is illustrated by both annual and 30-year patterns of hydrology in the Okavango Delta in southern Africa. Current studies on carbon biogeochemistry in Central America are attempting to determine the rates of carbon sequestration in tropical wetlands compared to temperate wetlands and the effects of hydrologic conditions on methane generation in these wetlands. Using the same field and lab techniques, we estimated that a humid tropical wetland in Costa Rica accumulated 255 g C m⁻² year⁻¹ in the past 42 years, 80% more than a similar temperate wetland in Ohio that accumulated 142 g C m⁻² year⁻¹ over the same period. Methane emissions averaged 1,080 mg-C m⁻² day⁻¹ in a seasonally pulsed wetland in western Costa Rica, a rate higher than methane emission rates measured over the same period from humid tropic wetlands in eastern Costa Rica (120–278 mg-C m⁻² day⁻¹). Tropical wetlands are often tuned to seasonal pulses of water caused by the seasonal movement of the ITCZ and are the most likely to be have higher fire frequency and changed methane emissions and carbon oxidation if the ITCZ were to change even slightly.     

Aerial seed storage in <Emphasis Type="Italic">Melaleuca ericifolia</Emphasis> Sm. (Swamp Paperbark): environmental triggers for seed release

Aerial seed banks are potentially the main source of sexual recruitment for woody wetland plants. Whilst the importance of soil seed banks for the persistence and recruitment of wetland plants has been examined in many studies, the role of aerial seed banks has been largely neglected. We used seed traps and the seedling emergence technique to quantify the seed rain from aerial seed banks of the Swamp Paperbark Melaleuca ericifolia Sm. (Myrtaceae) in Dowd Morass, a Ramsar-listed, brackish-water wetland in south-eastern Australia. Nine plant species germinated from material collected in seed traps over 2004–2005, but emergents were dominated (80–97%) by M. ericifolia. The mean number of M. ericifolia emergents ranged from <1 to <100 seedlings m⁻² day⁻¹, and showed a peak in the summer–autumn period. Regression analysis showed a significant negative correlation (r ² = 0.738) between the number of M. ericifolia emergents and water depth. Water depth and salinity were negatively correlated (r ² = 0.819), and increases in the number of M. ericifolia emergents as water levels fell were also associated with high salinities. Increasing air temperature and vapour pressure deficit also stimulated seed release during periods of drying. This study is one of the first to demonstrate the importance of aerial seed banks for sexual recruitment in woody wetland plants and the release of seed in relation to environmental factors. Aerial seed banks warrant consideration alongside soil seed banks for the establishment and long-term survival of woody plants in wetlands. Handling editor: Luis Mauricio Bini     

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).     

Benthic diatom composition in isolated forested wetlands subject to drying: Implications for monitoring and assessment

The development of bioindicators for wetlands, especially ephemerally hydrated depressional and isolated wetlands, can be problematic because of seasonal changes in hydrology and target indicator organism biology. To determine if benthic diatoms could be used as a multi-season biological indicator of wetland condition in isolated forested wetlands of Florida, USA, 11 wetlands were sampled twice during a 5-month period, once when dry, then again when hydrated. Sites sampled when dry had significantly higher diatom taxa richness at genus and species levels. Non-metric multidimensional scaling and multiple response permutation process analyses resulted in no obvious or significant wet/dry grouping of species or genus level abundance data. Five of seven diatom metrics of the Florida Wetland Condition Index (FWCI) for depressional forested wetlands were significantly linearly correlated (p < 0.05), while only one of seven metrics (a dissolved oxygen indicator) had a significantly different mean in paired t-test analyses. The final FWCI was significantly correlated (Pearson's r = 0.85, p < 0.001) between wet and dry sites, and no difference was found in mean FWCI score between wet and dry sites (t = −1.98, p = 0.076), suggesting that with additional research, benthic diatoms may be used to monitor and assess wetland condition regardless of season or site hydrologic conditions.     

Discerning Fragmentation Dynamics of Tropical Forest and Wetland during Reforestation,Urban Sprawl,and Policy Shifts

Despite the overall trend of worldwide deforestation over recent decades, reforestation has also been found and is expected in developing countries undergoing fast urbanization and agriculture abandonment. The consequences of reforestation on landscape patterns are seldom addressed in the literature, despite their importance in evaluating biodiversity and ecosystem functions. By analyzing long-term land cover changes in Puerto Rico, a rapidly reforested (6 to 42% during 1940–2000) and urbanized tropical island, we detected significantly different patterns of fragmentation and underlying mechanisms among forests, urban areas, and wetlands. Forest fragmentation is often associated with deforestation. However, we also found significant fragmentation during reforestation. Urban sprawl and suburb development have a dominant impact on forest fragmentation. Reforestation mostly occurs along forest edges, while significant deforestation occurs in forest interiors. The deforestation process has a much stronger impact on forest fragmentation than the reforestation process due to their different spatial configurations. In contrast, despite the strong interference of coastal urbanization, wetland aggregation has occurred due to the effective implementation of laws/regulations for wetland protection. The peak forest fragmentation shifted toward rural areas, indicating progressively more fragmentation in forest interiors. This shift is synchronous with the accelerated urban sprawl as indicated by the accelerated shift of the peak fragmentation index of urban cover toward rural areas, i.e., 1.37% yr⁻¹ in 1977–1991 versus 2.17% yr⁻¹ in 1991–2000. Based on the expected global urbanization and the regional forest transition from deforested to reforested, the fragmented forests and aggregated wetlands in this study highlight possible forest fragmentation processes during reforestation in an assessment of biodiversity and functions and suggest effective laws/regulations in land planning to reduce future fragmentation.     

Developing a wetland IBI with statewide application after multiple testing iterations

An index of biotic integrity (IBI) is a frequently used approach for assessing the ecological integrity of streams with fish and macroinvertebrates the faunal assemblages most commonly used as indicator taxa. The IBI approach has been much less commonly applied to wetlands, despite the legal, policy and scientific need to assess wetland condition and develop ecological performance goals for wetland creation, restoration and enhancement. While some IBIs are sophisticated systems with statewide application that have undergone one or more testing iterations, many published IBIs are derived from single data sets of a single class of aquatic resource with limited geographic application. The State of Ohio initiated development of a wetland IBI using vascular plants in 1996. Sampling methods were investigated and ultimately a plot-based method was adopted. Potential attributes and different human disturbance gradients were evaluated in several studies. Ultimately, IBIs for emergent, forest and shrub dominated wetlands were developed. Data from the Vegetation IBI-emergent (VIBI-E) is presented to illustrate this process. Subsequent testing and refinement is a critical step in the development of a robust IBI with more than local application. Throughout its initial development (R² = 0.863, p < 0.001), first major testing iteration (R² = 82.2%, p < 0.001), second test iteration (R² = 75.0%, p < 0.001) and third test iteration (R² = 82.1%, p < 0.001), the VIBI-E has remained significantly correlated with the disturbance gradient. Eight of the original 10 metrics proposed continued to have significant and interpretable relationships with the disturbance gradient, with 4 metrics remaining completely unchanged, and 4 undergoing relatively minor modifications, and 2 being replaced. The VIBI-E and its component metrics were also evaluated against a new disturbance gradient (Landscape Development Index or LDI), derived from land use percentages within a 1 km radius of the wetlands, that was not used during VIBI-E development. The VIBI-E score and 9 of 10 metrics were significantly correlated with the LDI disturbance gradient providing separate confirmation of the VIBI. The Vegetation IBI-E consistently and reliably assessed wetland condition across the whole range of wetland types throughout Ohio's ecological regions.     

Phosphorus regulates stream injury by filamentous green algae,DO, and pH with thresholds in responses

Nutrient concentrations, benthic algal biomass, dissolved oxygen (DO), and pH were measured in 70 or more streams during spring and summer in the Illinois River Watershed (IRW), which crosses the Oklahoma and Arkansas (USA) border, to determine whether injury to streams occurred and if that injury was related to spreading poultry waste on fields. Definitions of injury were based on Oklahoma water quality regulations and scientific literature. Phosphorus and nitrogen concentrations were each independently related to poultry house density (PHD) in watersheds and percent urban land use in watersheds. In addition, phosphorus and nitrogen concentrations were unusually high compared to regions with similar geology and hydrology. Molar N:P ratios were high and indicated that phosphorus was the most likely limiting nutrient. Phosphorus concentrations, as well as PHD and urban land use, were related to algal biomass during spring, but were less related during summer. A threshold response in cover of stream bottoms by nuisance filamentous green algae (NFGA: Cladophora, Rhizoclonium, and Oedogonium) during spring was observed at 27 μg TP l⁻¹ using regression tree analysis. Great increases in average NFGA cover (from 4 to 36% cover) occurred with relatively small increases in TP concentration at the 27 μg TP l⁻¹ threshold. Average concentrations of DO, variability in DO, and pH during spring were positively related to TP, chlorophyll a, and NFGA cover. Minimum DO during spring and early morning DO during summer were negatively related to TP concentration. Spring pH and summer DO frequently violated water quality requirements for protecting biodiversity that were established by the state of Oklahoma. We conclude that poultry house operations as well as urban activities, independently and interactively, pollute IRW streams with phosphorus, which resulted in injury to aesthetic condition and the potential for injury of biodiversity.     

Comparisons of P-Yield,Riparian Buffer Strips,and Land Cover inSix Agricultural Watersheds

Riparian buffer strips may protect streams from phosphorus (P) pollution. We compared 2 years of daily P-yield (μg m⁻² day⁻¹) from six southeast Wisconsin watersheds with contrasting riparian buffer attributes. Of the variables measured, mean daily P-yield was most closely correlated with the variability in riparian patch size. Variability in P-yield was most closely correlated with characteristics of the riparian buffer, such as percent wetland land cover, riparian continuity, and stream sinuosity. During the most extreme events, mean P-yield was negatively correlated with the percentage of wetland land cover in the upland watershed. Correlations suggest that riparian continuity may influence P-loading in these watersheds. Our results corroborate the importance of continuity and uniformity of riparian buffers as moderators of P flow from upland agricultural lands into streams. Received 1 June 2001; accepted 5 February 2002.     

Influences of climate,hydrology, and land use on input and export of nitrogen in California watersheds

Human activities have greatly increased the input of biologically available nitrogen (N) from land-based sources to aquatic ecosystems; yet few studies have examined how human actions influence N export in regions with a strong seasonality in water availability. In this study, we quantified N inputs and outputs for 23 California watersheds and examined how climate, hydrology, and land use practices influenced watershed N export. N inputs ranged from 581 to 11,234 kg N km⁻² year⁻¹ among watersheds, with 80% of total input for the region originating from agriculture (inorganic fertilizer, manure, and legumes). Of the potential N sources examined, mean annual concentrations of dissolved organic N and dissolved inorganic N in study rivers correlated most strongly with manure N input (r ² = 0.54 and 0.53, respectively). Seasonal N export varied by basin and was correlated with climate, anthropogenic N inputs, and reservoir releases. Fractional export of watershed N inputs by study rivers annually was small (median of 8%) and scaled exponentially with runoff (r = 0.66). Collectively, our results show that anthropogenic activities have altered both the magnitude and timing of watershed N export in California and suggest that targeted management in specific locations and times of the year could reduce N export to downstream systems in the region.     

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.     

城市化背景下小微湿地景观动态变化及其驱动因素

小微湿地是指自然界在长期演变过程中形成的小型湿地。城市发展导致小微湿地大量消失，了解小微湿地景观动态变化特征及驱动因素是保护与管理小微湿地的重要基础。以合肥市包河区为研究区域，选取2006-2018年4期遥感影像，利用空间分析方法确定2006-2010年、2010-2014年、2014-2018年、2006-2018年4个时期小微湿地景观动态变化，基于300m×300m的网格单元，结合增强回归树和地理加权逻辑回归模型，分析13个预测变量与小微湿地损失之间的关系。结果表明：2006-2018年，小微湿地在整个研究区大范围减少，总面积下降了60.8%，斑块数量减少了60.5%，同时，小微湿地边缘复杂度降低，小微湿地间的空间距离增加，聚集程度降低。增强回归树模型显示，城市发展初期(2006-2010年)，周边用地类型(建设用地、旱地、林地和草地)变化是导致小微湿地损失的主要因素，中后期(2010-2018年)各类型土地利用变化的相对影响有不同程度的下降，斑块面积和坡度对小微湿地损失的驱动作用逐渐凸显。2006-2018年，建设用地变化(14.4%)、斑块面积(13.5%)、旱地变化(11.1%)、坡度(10.1%)、林地变化(8.5%)、草地变化(7.0%)是导致小微湿地损失的高重要性变量。地理加权逻辑回归模型揭示了高重要性变量对小微湿地损失影响的空间非平稳性特征，结果显示，除斑块面积系数的空间可视化无解释意义，其余高重要性变量对小微湿地损失的影响随地点的变化，贡献的大小和方向也有所不同。研究方法和结果可以为城市快速发展地区小微湿地的保护与管理提供理论支持。     

不同恢复措施对南滇池湿地冬季水禽多样性的影响

恢复受损湿地生态功能是国家湿地公园建设中的重要内容,修复措施的选用会对恢复效果产生重要影响。滇池是国内重要候鸟越冬区,受长期围垦以及城市扩张的影响,湖滨区域破坏严重,近年来湿地公园建设为滇池湖滨带恢复带来了契机,但各种恢复措施的效果仍有待明确。2017年冬季以昆明南滇池国家湿地公园及临近湿地为研究区域,设置了人工重建湿地、人工恢复湿地、自然恢复湿地以及自然湖泊湿地4个对照样区,基于冬季水禽多样性进行了湿地恢复效果评价,并从景观生态学角度对结果进行了分析。结果表明：自然湖泊湿地具有最高物种丰富度,其次为自然恢复湿地、人工恢复湿地和人工重建湿地。以Simpson多样性指数评价,自然恢复湿地的水禽多样性最高（0.60±0.03）,其次为自然湖泊湿地（0.46±0.04）和人工恢复湿地（0.34±0.04）,人工重建湿地水禽多样性最低（0.17±0.03）,由此可见自然恢复措施效果优于人工恢复和人工重建。从景观格局上分析,水禽多样性与道路面积（r=-0.735,P<0.01）、景观形状指数（r=-0.461,P<0.01）和景观分离度指数（r=-0.661,P<0.01）负相关,这也表明人为干扰程度、景观形状以及破碎化程度均会对水禽造成重要影响。建议在国家湿地公园规划和建设中,降低非湿地类景观尤其是道路对整体湿地景观的分割作用,提高湿地斑块的连接性和完整性以满足水禽的空间需求,对于湖泊型的湿地公园应加强对湖滨带沼泽生境的营造,以满足涉禽的生存需求,从而增加区域的鸟类多样性。     

Evaluation of Florida Palustrine Wetlands: Application of USEPA Levels 1, 2, and 3 Assessment Methods

Three categories of wetland assessment methods have been recognized by the United States Environmental Protection Agency, including Level 1—Landscape-scale Assessment; Level 2—Rapid Field Methods; and Level 3—Intensive Biological and Physico–Chemical Measures. This study incorporates wetland assessment methods for each assessment level, including the Level 1 Landscape Development Intensity (LDI) index, Level 2 Wetland Rapid Assessment Procedure (WRAP), and Level 3 Florida Wetland Condition Index (FWCI). Using a neighborhood analysis in Geographic Information Systems (GIS), an LDI index map was created using 1995 land use, creating a calculated LDI index value for each 30 m² area in Florida. Level 1–3 assessment procedures were employed at 193 palustrine emergent (n = 75) and forested (n = 118) wetlands. Significant correlations were found among the multiple Level 1–3 assessment procedures using the nonparametric Spearman’s correlation coefficient for pair-wise comparisons of LDI and WRAP, LDI and diatom FWCI, WRAP and diatom FWCI, LDI and macrophyte FWCI, WRAP and macrophyte FWCI, LDI and macroinvertebrate FWCI, and WRAP and macroinvertebrate FWCI (|r| > 0.50, P < 0.01). Defining the relationship between Level 1–3 assessment methods may be used to estimate the more intensive and species assemblage-specific Level 3 FWCI assessment scores for wetlands with Level 1 or Level 2 scores. Inferences can then be made as to wetland condition based on established correlations with intensive assessment methods.     

Greenhouse gas emissions and carbon sequestration potential in restored wetlands of the Canadian prairie pothole region

North American prairie pothole wetlands are known to be important carbon stores. As a result there is interest in using wetland restoration and conservation programs to mitigate the effects of increasing greenhouse gas concentration in the atmosphere. However, the same conditions which cause these systems to accumulate organic carbon also produce the conditions under which methanogenesis can occur. As a result prairie pothole wetlands are potential hotspots for methane emissions. We examined change in soil organic carbon density as well as emissions of methane and nitrous oxide in newly restored, long-term restored, and reference wetlands across the Canadian prairies to determine the net GHG mitigation potential associated with wetland restoration. Our results indicate that methane emissions from seasonal, semi-permanent, and permanent prairie pothole wetlands are quite high while nitrous oxide emissions from these sites are fairly low. Increases in soil organic carbon between newly restored and long-term restored wetlands supports the conclusion that restored wetlands sequester organic carbon. Assuming a sequestration duration of 33 years and a return to historical SOC densities we estimate a mean annual sequestration rate for restored wetlands of 2.7 Mg C ha⁻¹year⁻¹ or 9.9 Mg CO₂ eq. ha⁻¹ year⁻¹. Even after accounting for increased CH₄ emissions associated with restoration our research indicates that wetland restoration would sequester approximately 3.25 Mg CO₂ eq. ha⁻¹year⁻¹. This research indicates that widescale restoration of seasonal, semi-permanent, and permanent wetlands in the Canadian prairies could help mitigate GHG emissions in the near term until a more viable long-term solution to increasing atmospheric concentrations of GHGs can be found.     

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.     

Relationships among Amphibian Assemblage Structure,Wetland pH,and Forest Cover

A common mesofilter approach to conservation of biological diversity and ecosystem function used in agricultural and urban landscapes is maintenance of wetlands and an undisturbed terrestrial buffer surrounding wetlands. Although it is generally accepted that forest buffers protect wetland-associated biological diversity and ecosystem function, the effectiveness and optimal spatial extent of buffers is still an area of debate. During 2007 and 2008 we surveyed amphibians and environmental conditions associated with 54 depression wetlands on the Delmarva Peninsula of Maryland, USA, to examine the role of forest buffers and wetland characteristics in structuring amphibian communities. Forest cover within a 50-m buffer surrounding wetlands was correlated (r = −0.81) with wetland pH but no other wetland characteristics. Wetland pH, canopy cover, hydroperiod, and adjacent forest cover were important predictors of wetland use by individual amphibian species, with many species more likely to occur at wetlands that dried late in the hydrological year and with open canopies. At least one common species preferred circumneutral pH and several restricted-distribution species preferred lower pH (<5). Contrary to expectations, relationships between species occurrence and adjacent forest cover were negative. Our results suggest that current regulations that provide buffers of 30 m or less do not provide adequate protection of wetland water chemistry but that forest encroachment into wetlands may be a threat to the integrity of amphibian communities and should be the target of monitoring, future research, and management efforts. © 2021 The Wildlife Society.     

三江平原流域湿地景观破碎化过程研究

以流域为研究单元,利用历史图件和遥感数据资料及GIS技术,系统分析了该区典型流域50年来湿地景观的破碎化过程.结果表明,该区湿地景观破碎化在斑块个体和空间结构两方面变化极大.景观斑块个体变化主要表现为最大斑块、平均斑块面积不断缩小,斑块密度不断增大,斑块形状破碎化指数不断增大,景观内部生境面积破碎化指数不断上升;空间结构变化主要表现为湿地景观由初始基质景观逐渐变为河岸带景观;同时,随着农田面积逐渐扩大,隔离湿地斑体数量不断上升,隔离度不断增大;景观空间分布模式由“大陆-岛屿模式”向“卫星型模式”转变,最后变化为“完全隔离型模式”.导致该区湿地景观破碎化的主导因素是大规模的农业开发,反映了人类活动对湿地景观的巨大影响.