Impacts of Nutrient Loading on Mercury Fractionation and Mobility in an Estuarine Wetland in Nansi Lake,China

Total mercury is closely related to nutrient status in ecosystems. However, studies specifying the effects of various nutrient forms on the mobility of mercury are rare. In this study, three fractions of mercury (mobile, semi-mobile, and non-mobile) were examined in the soil of an estuarine wetland with excessive nutrient inputs in northern China. The wetland is located in the east route of China's South-to-North Water Transfer Project. Correlations between the three fractions of mercury and four nutrient parameters were analyzed. Results showed that toxic mobile and semi-mobile mercury comprised a great portion of total soil mercury in the studied wetland. Among the four nutrient parameters, ammonium nitrogen showed a significant negative correlation with mobile toxic mercury and was the principal nutrient component that influenced the mobility and toxicity of mercury. Nitrate nitrogen showed a positive correlation with mobile toxic mercury. Moreover, carbon/nitrogen ratio and soil acid were positively correlated with mercury mobility. Given that lower nitrogen loading is required in the watershed to ensure the water quality during the water transfer project, our study suggested that changes in nitrogen inputs might promote the mobility and bioavailability of mercury in the watershed. Thus, more attention should be provided to the potential hazard of mercury in the food web during the water transfer.     

Empirical evidence linking increased hydrologic stability with decreased biotic diversity within wetlands

Competing demands for water have resulted in many wetlands becoming either more permanently flooded or more permanently dry. It has been stated that such changes may lead to a loss of diversity in wetland communities; yet to date, this has not been tested experimentally. In this study, we experimentally test the hypothesis that increasing the hydrologic stability of wetlands results in reduced abundance, richness and diversity of aquatic biota emerging from wetland sediments. Sediment was collected from 19 wetlands that were divided into five groups (permanently flooded and wetlands that had been dry for 2, 7, 11 and 30 years). Aquatic plant communities germinating from the sediment of wetlands that had been permanently inundated and those that had been dry for 30 years had lower species richness and number of individuals than wetlands with intermediate flooding histories. For microfaunal communities, significantly less individuals but more taxa hatched from wetlands that had been permanently flooded or dry for 2 years than the other wetland groups. These results provide evidence of reduced biotic diversity as hydrological stability is increased under the common management scenarios of making wetlands more permanently wet or dry.     

River-wetland interaction and carbon cycling in a semi-arid riverine system: the Okavango Delta, Botswana

The Okavango River, in semi-arid northwestern Botswana, flows for over 400 km in a pristine wetland developed on a large (>22,000 km²) alluvial fan (Okavango Delta). An annual flood pulse inundates the floodplains of the wetlands and travels across the Delta in 4–6 months. In this study, we assess the effects of long hydraulic residence time, variable hydrologic interaction between river–floodplain–wetland and evapotranspiration on carbon cycling. We measured dissolved inorganic carbon (DIC) concentrations and stable carbon isotopes of DIC (δ¹³C_DIC) from river water when the Delta was not flooded (low water) and during flooding (high water). During low water, the average DIC concentration was 31 % higher and the δ¹³C_DIC 2.1 ‰ more enriched compared to high water. In the lower Delta with seasonally flooded wetlands, the average DIC concentration increased by 70 % during low water and by 331 % during high water compared to the Panhandle with permanently flooded wetlands. The increasing DIC concentration downriver is mostly due to evapoconcentration from transpiration and evaporation with increased transit time. The average δ¹³C_DIC between low and high water decreased by 3.7 ‰ in the permanently flooded reaches compared to an increase of 1.6 ‰ in the seasonally flooded reaches. The lower δ¹³C_DIC during high water in the permanently flooded reaches suggest that DIC influx from the floodplain-wetland affects river’s DIC cycling. In contrast, higher river channel elevations relative to the wetlands along seasonal flooded reaches limit hydrologic interaction and DIC cycling occurs mostly by water column processes and river-atmospheric exchange. We conclude that river-wetlands interaction and evapoconcentration are important factors controlling carbon cycling in the Okavango Delta.     

Factors influencing macroinvertebrate colonization of seasonal wetlands: responses to emergent plant cover

1. We conducted field experiments to examine factors influencing macroinvertebrate colonization of seasonally flooded marshes. Few macroinvertebrate species were found aestivating in soils within non-flooded wetlands indicating that most taxa colonize these marshes from other flooded habitats.
2. We manipulated amounts of salt grass ( Distichlis spicata ) to examine how emergent plant cover affects aerial colonization by macroinvertebrates. Areas mowed 3 weeks before flooding had low plant cover, areas mowed 5 and 9 weeks before flooding had medium and high plant cover, respectively, and non-mowed control areas had the most plant cover. Macroinvertebrate numbers and biomass were generally higher in mowed treatment areas than in control areas, but overall diversity was generally higher in high plant cover and control areas than in low plant cover areas.
3. Mosquitoes (Culicidae), brine flies (Ephydridae) and hover flies (Syrphidae) were positively correlated with amount of plant cover, and waterboatmen (Corixidae), midges (Chironomidae) and water scavenger beetles (Hydrophilidae) were negatively correlated with plant cover. Species assemblages changed seasonally among treatment areas because these taxa colonize wetlands at different times in the year.
4. These results demonstrate that invertebrate communities may be different within plant stands with heterogeneous amounts of emergent cover, and management practices that alter the structure of wetland vegetation can influence macroinvertebrate communities colonizing seasonal marshes.     

Wetland hydrologic class change from prior to European settlement to present on the Des Moines Lobe, Iowa

It has been hypothesized that wetland restoration policies have favored the restoration of the wettest classes of wetlands on the Des Moines Lobe of the prairie pothole region. To test this hypothesis we compared pre-drainage wetland distributions based on soils data and National Wetland Inventory (NWI) estimates of contemporary wetland distributions on the Des Moines Lobe. Based on the NWI data, the Des Moines Lobe today has only 3–4% of the wetland area that it had prior to the onset of drainage. On the basis of their soils, pre-drainage wetlands were predominantly temporarily flooded to saturated wetlands (84%), with only about 6% of the wetlands with water regimes classified as semi-permanently to permanently flooded. Depending on the interpretation of wetland modifiers on NWI maps, wetlands classified by the NWI as semi-permanent to permanently flooded make up more than 41% of the wetland area while wetlands with temporarily flooded to saturated water regimes account for 45–58% of the Lobe’s wetland area. The water regimes of contemporary wetlands when compared to their historic regimes suggest that many of today’s wetlands have different water regimes than they did prior to the onset of drainage. Because of the regional lowering of the groundwater table, many of today’s wetlands have drier water regimes, but some have wetter water regimes because they receive drainage tile inputs. Our results indicate that restoration has favored the wettest classes of wetlands and that temporarily to saturated wetland classes have not been restored in proportion to their relative abundance in the pre-drainage landscape.     

Hydrologic Regime Controls Soil Phosphorus Fluxes in Restoration and Undisturbed Wetlands

Many wetland restoration projects occur on former agricultural soils that have a history of disturbance and fertilization, making them prone to phosphorus (P) release upon flooding. To study the relationship between P release and hydrologic regime, we collected soil cores from three restoration wetlands and three undisturbed wetlands around Upper Klamath Lake in southern Oregon, U.S.A. Soil cores were subjected to one of three hydrologic regimes—flooded, moist, and dry—for 7.5 weeks, and P fluxes were measured upon reflooding. Soils from restoration wetlands released P upon reflooding regardless of the hydrologic regime, with the greatest releases coming from soils that had been flooded or dried. Undisturbed wetland soils released P only after drying. Patterns in P release can be explained by a combination of physical and biological processes, including the release of iron‐bound P due to anoxia in the flooded treatment and the mineralization of organic P under aerobic conditions in the dry treatment. Higher rates of soil P release from restoration wetland soils, particularly under flooded conditions, were associated with higher total P concentrations compared with undisturbed wetland soils. We conclude that maintaining moist soil is the means to minimize P release from recently flooded wetland soils. Alternatively, prolonged flooding provides a means of liberating excess labile P from former agricultural soils while minimizing continued organic P mineralization and soil subsidence.     

Seed bank potential of moist-soil managed wetlands in east-central Texas

Proper management techniques on moist-soil wetlands provide methods for enhancement of established wetlands, restoration of former wetlands, and creation of new wetland habitat. These techniques also create suitable wetland habitat for non-breeding waterfowl and other wetland dependent species during winter. To understand moist-soil managed wetland vegetative patterns, aspects such as plant species distribution, reproductive strategy, seed bank composition and viability should be thoroughly characterized. We investigated soil seed bank potential of moist-soil managed wetlands on Richland Creek Wildlife Management Area, Texas to determine which treatment (i.e., drawdown or flooded) produced the most desirable moist-soil plants. A total of 27 species germinated, producing 3,731 and 3,031 seedlings in drawdown and flooded treatments, respectively. There were also differences in stem densities between treatments of desirable and non-desirable species. Drawdown treatments had more seedlings germinate than flooded treatments, validating the notion that drawdown treatments provide favorable conditions for seed germination. Drawdown and flooding techniques, when properly timed, will allow managers to drive and directly influence managed wetland plant communities based on seed bank composition and response to presence or absence of water during the germination period.     

Methane emissions from tropical freshwater wetlands located in different climatic zones of Costa Rica

Wetlands are the largest natural source of the greenhouse gas methane to the atmosphere. Despite the fact that a large percentage of wetlands occur in tropical latitudes, methane emissions from natural tropical wetlands have not been extensively studied. The objective this research was to compare methane emissions from three natural tropical wetlands located in different climatic and ecological areas of Costa Rica. Each wetland was within a distinct ecosystem: (1) a humid flow‐through wetland slough with high mean annual temperatures (25.9 °C) and precipitation (3700 mm yr^?1); (2) a stagnant rainforest wetland with high mean annual temperatures (24.9 °C) and precipitation (4400 mm yr^?1); or (3) a seasonally wet riverine wetland with very high mean annual temperatures (28.2 °C) and lower mean annual precipitation (1800 mm yr^?1). Methane emission rates were measured from sequential gas samples using nonsteady state plastic chambers during six sampling periods over a 29‐month period from 2006 to 2009. Methane emissions were higher than most rates previously reported for tropical wetlands with means (medians) of 91 (52), 601 (79), and 719 (257) mg CH₄‐C m^?2 day^?1 for the three sites, with highest rates seen at the seasonally flooded wetland site. Methane emissions were statistically higher at the seasonally wet site than at the humid sites (P<0.001). Highest methane emissions occurred when surface water levels were between 30 and 50 cm. The interaction of soil temperature, water depth, and seasonal flooding most likely affected methanogenesis in these tropical sites. We estimate that Costa Rican wetlands produce about 0.80 Tg yr^?1 of methane, or approximately 0.6% of global tropical wetland emissions. Elevated methane emissions at the seasonally wet/warmer wetland site suggest that some current humid tropical freshwater wetlands of Central America could emit more methane if temperatures increase and precipitation becomes more seasonal with climate change.     

Hydrologic control of litter decomposition in seasonally flooded prairie marshes

The effect of seasonal inundation on the decomposition of emergent macrophyte litter (Scolochloa festucacea) was examined under experimental flooding regimes in a northern prairie marsh. Stem and leaf litter was subjected to six aboveground inundation treatments (ranging from never flooded to flooded April through October) and two belowground treatments (nonflooded and flooded April to August). Flooding increased the rate of mass loss from litter aboveground but retarded decay belowground. Aboveground, N concentration decreased and subsequently increased earlier in the longer flooded treatments, indicating that flooding decreased the time that litter remained in the leaching and immobilization phases of decay. Belowground, both flooded and nonflooded litter showed an initial rapid loss of N, but concentration and percent of original N remaining were greater in the nonflooded marsh throughout the first year. This suggested that more N was immobilized on litter under the nonflooded, more oxidizing soil conditions. Both N concentration and percent N remaining of belowground litter were greater in the flooded than the nonflooded marsh the second year, suggesting that N immobilization was enhanced after water-level drawdown. These results suggest different mechanisms by which flooding affects decomposition in different wetland environments. On the soil surface where oxygen is readily available, flooding accelerates decomposition by increasing moisture. Belowground, flooding creates anoxic conditions that slow decay. The typical hydrologic pattern in seasonally flooded prairie marshes of spring flooding followed by water-level drawdown in summer may maximize system decomposition rates by allowing rapid decomposition aboveground in standing water and by annually alleviating soil anoxia.     

Influences of riparian logging on plants and invertebrates in small,depressional wetlands of Georgia,U.S.A.

We studied 12 small, seasonally flooded, depressional wetlands on the Atlantic Coastal Plain of Georgia, U.S.A. Each wetland was embedded in stands of managed plantation pine. The pine trees surrounding each wetland had been harvested and replanted beginning in 1997 (2 sites), 1995 (2 sites), 1993 (1 site), 1988 (2 sites), 1984 (2 sites) or 1975 (3 sites). Regressions of various environmental variables with harvest histories indicated that those wetlands surrounded by smaller trees had greater light levels, water temperatures, pH, herbaceous plant cover and biomass, terrestrial invertebrate diversities and numbers, and water flea numbers, and lower water electrical conductivities and aquatic oligochaete numbers than those wetlands surrounded by more mature trees. Detected variations in hydroperiod, water depth, dissolved oxygen levels, sediment inputs, macrophyte diversity, periphyton biomass and densities of most aquatic invertebrates were not clearly correlated with past histories of peripheral tree harvest. This study suggests that harvesting trees around small wetlands initiates physical and ecological changes within the embedded habitats and that changes can persist for up to 15 years.     

Effects of soil moisture regimes on photosynthesis and growth in cattail (Typha latifolia)

Both waterlogging and water deficiency are major environmental factors affecting plant growth and functioning in many wetland and floodplain ecosystems across North America. Wetland plants possess various characteristics that enable them to survive and function in the intermittently flooded wetland environments, while their sensitivity to drought has received less attention. The present study quantified the photosynthetic and growth responses of cattail (Typha latifolia), an important species of freshwater wetlands, to a wide range of soil moisture regimes. In addition, changes in the efficiency of photosynthetic apparatus following initiation of the treatments were investigated. Under greenhouse conditions, seedlings were subjected to four soil moisture regimes: (1) drained (control), (2) continuous flooding, (3) periodic flooding, and (4) periodic drought. Results indicated that dark fluorescence yield was increased in response to periodic drought, while it showed decreases under continuous flooding. Net photosynthesis and stomatal conductance were enhanced by continuous flooding and periodic flooding. In contrast, these parameters exhibited reduction under periodic drought. In addition, leaf chlorophyll content was adversely affected by periodic drought. Recovery of net photosynthesis was noted, along with enhanced height growth, in both continuously and periodically flooded plants. Meanwhile, continuous flooding enhanced biomass production while periodic drought led to biomass reduction. Periodic drought also contributed to substantial reduction in root growth compared with shoot growth. Therefore, the combined photosynthetic performance and growth responses of cattail are likely to contribute to the ability of this species to thrive in flooded condition but be susceptive to periodic drought.     

科尔沁沙丘-草甸梯级生态系统土壤温室气体通量特征及其影响因素

采用静态箱-气相色谱法,对科尔沁半干旱地区典型的沙丘-草甸梯级生态系统中半流动沙丘和草甸湿地的温室气体(CO₂、CH₄、N₂O)通量进行了观测,分析了生长季温室气体的动态变化及其与环境影响因子的关系.结果表明: 生长季半流动沙丘和草甸湿地CH₄通量均整体表现为吸收,平均值分别为-52.7和-34.7 μg·m^-2·h^-1,介于-176.1～49.8 μg·m^-2·h^-1之间变化,8月22日半流动沙丘CH₄吸收值达到生长季最大值;8、9月降雨集中时段内草甸湿地CH₄通量表现为持续排放,与半流动沙丘呈明显差异.N₂O通量在7月21日达到生长季最大值,半流动沙丘N₂O通量的月均值表现为7月>8月>9月>6月>5月.土壤温湿度是影响CO₂和CH₄通量的关键因子,N₂O通量主要受土壤温度的影响.样地土壤温度敏感性(Q₁₀)表现为半流动沙丘(1.009)<草甸湿地(1.474),半流动沙丘土壤受到水分胁迫,导致其温室气体通量对土壤温度变化的敏感性明显低于草甸湿地.     

三江平原不同湿地类型土壤活性有机碳组分及含量差异

土壤活性有机碳对土壤干扰的反应较快,是土壤有机碳早期变化的敏感性指标。近50年来,三江平原湿地土壤有机碳库受农事活动影响较大。为了探讨不同湿地类型土壤活性有机碳主要组分土壤可溶性有机碳(Dissolved organic carbon,DOC)、微生物量碳(Microbial biomass carbon,MBC)和易氧化有机碳(Easily oxidized organic carbon,EOC)的分布差异及主要影响因子,选择了三江平原洪河自然保护区4种典型的湿地类型(小叶章+沼柳湿地、小叶章湿地、毛苔草湿地和芦苇湿地)为研究对象。分析了不同湿地类型土壤可溶性有机碳,微生物量碳和易氧化有机碳在0—30 cm土层内的分布特征和分配比例及其与有机碳、土壤养分和酶活性指标(蔗糖酶、纤维素酶和过氧化氢酶)之间的相关关系。结果表明:(1)4种湿地类型土壤DOC、MBC和EOC含量均随土层深度的增加而减少。不同湿地类型之间土壤活性有机碳含量在0—30 cm土层内存在显著性差异(P0.05),相对于长期淹水的毛苔草湿地和芦苇湿地而言,未淹水的小叶章+沼柳湿地和小叶章湿地具有较高的DOC,MBC和EOC含量。(2)土壤DOC、MBC和EOC占有机碳比例分别为0.27%—0.63%,1.27%—5.94%和19.63%—41.25%。土壤DOC所占比例呈先增后减的变化趋势,最大的比例均出现在10—20 cm。MBC所占比例在土壤剖面上则未表现出一致的变化规律,而EOC所占比例则随土层深度的增加而逐渐减少。(3)土壤DOC占SOC比例以小叶章湿地最高,MBC和EOC占SOC的比例则以小叶章+沼柳湿地最高。而长期淹水的毛苔草湿地和芦苇湿地则具有更低的DOC,MBC和EOC比例。(4)综合分析表明,4种湿地类型土壤DOC,MBC和EOC两两之间存在极显著相关性关系,它们除了与碳氮比相关性不显著外,与土壤有机碳,全氮,全磷养分和酶活性指标间相关性均达到极显著水平,尤其是与有机碳和全氮的相关性系数更高,此外DOC与纤维素酶,MBC与过氧化氢酶相关性更大。由此可见,土壤碳氮磷养分和酶活性是影响土壤活性有机碳组分分布的重要因素。     

Seed bank of seasonally flooded grassland: experimental simulation of flood and post-flood

Wetland seed banks comprise the propagules of plant species that have species-specific germination requirements for germination in either flooded or dry conditions. At the community level, wetland structure and succession during and after a seasonal flooding event depends upon the early life-history requirements of species, including germination under flooded and dry conditions. We examined the effects of simulated flood and post-flood scenarios on seedling emergence from a seed bank of seasonally flooded grassland in the Pantanal, Brazil. Field samplings were conducted in both wet and dry seasons, both of which were subject to flood and post-flood conditions. A total of 70 species emerged from the seed bank, dominated by Poaceae and Cyperaceae. Sixteen species were exclusive to the wet and one exclusive to the dry season. The richness of perennial species was higher under flood conditions, while the richness of annuals was greater post-flood. In general, the aquatic and amphibious species exhibited a significant germination response to flooding. Terrestrial species only germinated in post-flood conditions, with higher richness in the dry season. Four species had high seedling abundance in both treatments. The capacity of regeneration by seeds is high in these grasslands and can be increased by seasonal flooding and drawdown. In these seasonally flooded grasslands, we observed three main germination strategies: under flooded conditions, aquatic and amphibious species; post-flood conditions, an explosion of annual amphibious and terrestrial species; and in moist soil, perennial terrestrial species. The differential responses to flooding versus post-flood conditions help to maintain the structure and species richness in the community over time.     

Managed flooding can augment the benefits of natural flooding for native wetland vegetation

Managed flooding is increasingly being used to maintain and restore the ecological values of floodplain wetlands. However, evidence for its effectiveness is sometimes inconsistent and water available for environmental purposes often limited. We experimentally inundated a floodplain wetland (or “billabong”) in late spring by pumping water from its adjacent creek, aiming to promote the native wetland flora and suppress terrestrial exotics. Vegetation was surveyed before (spring) and after (late summer) the managed flood in the experimental billabong and in three control billabongs. Floodplain water levels were continuously monitored. Wet conditions caused two of the control billabongs to also flood, but to a lesser extent than the experimental billabong. We therefore assessed vegetation changes relative to flooding duration. With increasing flooding duration, the cover of wetland vegetation (amphibious and aquatic species) increased and the cover of terrestrial and exotic vegetation decreased, with these effects largest in the deliberately flooded billabong. Flooding durations greater than 20 days generally resulted in increased cover of wetland plants and restricted the growth of terrestrial plants. Reinstatement of more appropriate flooding regimes can thus promote native wetland plants, while suppressing terrestrial exotic species. Our study also provides evidence for the use of modest water allocations to augment the benefits of natural flooding in the maintenance and restoration of native wetland plant communities.     

不同水分条件下毛果苔草枯落物分解及营养动态

于2009年5月至2010年5月采用分解袋法,研究了三江平原典型湿地植物毛果苔草枯落物分解对水分条件变化的响应,探讨了典型碟形洼地不同水位下枯落物分解1a时间内的分解速率与N、P等营养元素动态。分解1a内,无积水环境下枯落物失重率为34.99%,季节性积水环境下为27.28%,常年积水环境下随水位增加枯落物失重率分别为26.99%与30.67%,表明积水条件抑制了枯落物的分解。枯落物的分解随环境变化表现出阶段性特征,分解0—122 d内随水位增加枯落物失重率分别为16.09%、24.25%、23.53%与26.60%,即生长季内积水条件促进了枯落物有机质的分解及重量损失。而随实验进行,分解122—360 d内随水位增加毛果苔草枯落物的失重率分别为18.90%、3.02%、3.46%、4.03%,即在非生长季土壤冻融期积水条件抑制了枯落物分解(P<0.05)。水分条件对毛果苔草枯落物N元素的影响表现为积水条件促进生长季内枯落物的N固定,水位最高处毛果苔草N浓度显著高于无积水环境(P<0.05)。但进入冻融期后积水环境下枯落物N浓度与含量降低;其中季节性积水限制了枯落物的N积累能力,至分解360d时与初始值相比表现出明显的N释放(P=0.01)。毛果苔草枯落物分解61d时P出现富集,其中积水条件下P的富集作用增强,但与水位不相关。分解1a后毛果苔草枯落物表现为P的净释放,不同水分条件下枯落物P元素损失没有明显差异(P>0.05)。     

A rapid assessment of anthropogenic disturbances in East African wetlands

The use of East African freshwater wetlands for agriculture has increased in recent decades, raising concerns about potential impacts on wetlands and the long-term sustainability of such land use trends. WET-health is an indicator-based rapid wetland assessment approach developed in South Africa. It allows determining the conditions of wetlands in four assessment modules (hydrology, geomorphology, vegetation, and water quality) by observing the degree of deviation of a wetland from its anticipated natural reference state. We tested the transferability of the WET-health concept for East African inland valley swamps and floodplain wetlands based on 114 assessment units at four study sites. Due to large wetland areas and different environmental settings in East Africa, we modified the original approach using a random selection of assessment units and an assessment scheme based on disturbance types (Appendices A and B). Estimated WET-health impact scores were matched with biophysical and socioeconomic variables using a generalized linear mixed model. Land use included largely undisturbed wetland units occurring side by side with seasonally cropped or grazed units, and drained, permanently cultivated units. A strong differentiation of impact scores between the four assessment modules was apparent with highest scores for vegetation and lowest scores for geomorphology. Vegetation and water quality responded most sensitively to land use changes. The magnitude of wetland disturbance is predominantly determined by management factors such as land use intensity, soil tillage, drainage intensity, and the application of agrochemicals and influences vegetation attributes and the provision of ecosystem services. The proposed modification of WET-health enables users to assess large wetland areas during relatively short periods of time. While further studies will be required, WET-health appears to be a promising concept to be applied to wetlands in East Africa and possibly beyond.     

Modern pollen deposition in wetlands of Majuli Island and its implication to decipher palaeoflood episodes in northeast India

The present study is the first attempt from any Indian wetland, where palynological data is assessed to understand the flooding histories of the Sakali and Duboi wetlands in the Majuli River Island, a part of the Indo-Burma hotspot. Palynological analyses of surface soil samples from these wetlands were carried out in order to explore the flooding histories of this island. The presence of extra-local taxa such as Rhododendron, Tsuga and Castanopsis, in the Sakali wetland is strongly suggestive of river water transportation and flooding on the Majuli Island in the recent past. In contrast, dominance of local arboreal taxa and low abundance or absence of extra-local pollen taxa in the Duboi wetland does not indicate flooding. Correspondence analysis (CA) was applied on the present dataset to reveal possible correlations between the surface samples of the wetlands and the major group of palynotaxa. The CA successfully discriminated the samples from the two wetlands and also marked strong correlations between flood indicators extra-local taxa with the samples of the Sakali wetland and local arboreal elements with the Duboi samples. The present result will not only provide a baseline for future palaeovegetation and palaeoclimate reconstructions, but will also help in deciphering palaeoflood episodes from these wetlands.