Natural Wetland Ecosystems Research Articles

Vertical migration and distribution of added dissolved iron in Carex lasiocarpa marsh soil

Irrigating rice paddy fields with groundwater containing iron is standard practice for dry croplands replanted to rice in northeast China. To assess the impact of paddy field drainage on the receiving natural wetlands, vertical migration and distribution of dissolved iron in the soil–plant system with acidic dissolved iron addition were investigated in the Carex lasiocarpa marsh soil columns (diameter 35cm, height 65cm) of the Sanjiang Plain. The experiment was designed as four sequential stages: (1) iron-free leaching, (2) neutral iron addition using FeSO4 (100mgL−1 of iron concentration), (3) acidic iron addition using FeSO4 and HCl (200mgL−1 of iron concentration, pH adjusted to 3.56) and (4) iron-free leaching. After the experiment, the iron distribution within a natural wetland ecosystem was quantitatively observed. The results showed that pH and Eh in the soil columns were affected more by water table fluctuations than acidic addition. Effects of iron addition on the dissolved iron in soil solutions decreased with increasing soil depth, and the vertical migration rates in 20–30cm layer (AG horizon) and 30–50cm layer (G horizon) were 0.58 and 0.56mmmin−1, respectively. Doubling the iron addition did not increase the iron in soil solutions significantly. Only a small part of added iron (5.7%) drained out, while the majority was retained in soil (69.4%) and plant biomass (24.8%). Soil manganese and nitrogen were positively affected by acidic iron addition, while the effects on carbon and phosphorus were not significant.

Quantifying of Soil Denitrification Potential in a Wetland Ecosystem, Ochi Experiment Site, Japan

Nitrate contamination has become one of the most important issues for surface water and groundwater. N2O, with an increasing contribution to global warming, has been more and more attention by the IPCC recently. As well known, denitrification plays a major role in nitrogen cycle of aquatic ecosystems and operates at rates far below its potential under proper conditions. Sediments are the single largest pool of nitrogen in wetland ecosystems. During this process, facultative anaerobic bacteria transform nitrite into nitrogen gas which dissolves in the groundwater and diffuses into the atmosphere finally when it shows up with seepage or spring in the wetland. To seek a mechanistic understanding of N removal in natural wetland ecosystem, a case study was carried in terms of denitrification rate at the Ochi catchment, Chiba, Japan. In this study, samples of intact soil cores in 0–20cm were taken along the groundwater flow path, which including 2 samples in the unsaturated zone and 2 in saturated wetland ecosystem. Denitrification capacity of soil was quantified using acetylene (C2H2) inhibition/gas chromatography ECD method with time intervals of 0, 2, 6, 12, 24 h. Total—N and Total—C contents and amount of denitrifying bacteria were also analyzed. It is found that denitrification ability is low for all 2 samples in the unsaturated zone and high in saturated zone. Results show that N2O emission flux after C2H2—inhibition ranges from 0 to 1.17 gN m-2h-1, with an increase value prior 6 hours and slow down after that.

The impact of dissolved organic carbon on the spatial variability of methanogenic archaea communities in natural wetland ecosystems across China

Significant spatial variation in CH(4) emissions is a well-established feature of natural wetland ecosystems. To understand the key factors affecting CH(4) production, the variation in community structure of methanogenic archaea, in relation to substrate and external environmental influences, was investigated in selected wetlands across China, using denaturing gradient gel electrophoresis. Case study areas were the subtropical Poyang wetland, the warm-temperate Hongze wetland, the cold-temperate Sanjiang marshes, and the alpine Ruoergai peatland on the Qinghai-Tibetan Plateau. The topsoil layer in the Hongze wetland exhibited the highest population of methanogens; the lowest was found in the Poyang wetland. Maximum CH(4) production occurred in the topsoil layer of the Sanjiang Carex lasiocarpa marsh, the minimum was observed in the Ruoergai peatland. CH(4) production potential was significantly correlated with the dissolved organic carbon (DOC) concentration but not with the abundance or diversity indices of methanogenic archaea. Phylogenetic analysis and DOC concentration indicated a shift in the dominant methanogen from the hydrogenotrophic Methanobacteriales in DOC-rich wetlands to Methanosarcinaceae with a low affinity in wetlands with relatively high DOC and then to the acetotrophic methanogen Methanosaetaceae with a high affinity in wetlands with low DOC, or with high DOC but rich sulfate-reducing bacteria. Therefore, it is proposed that the dominant methanogen type in wetlands is primarily influenced by available DOC concentration. In turn, the variation in CH(4) production potential in the wetlands of eastern China is attributable to differences in the DOC content and the dominant type of methanogen present.

Bio‐mitigation of carbon following afforestation of abandoned salinized farmland

AbstractAs the global demand for food continues to increase, the displacement of food production by using agricultural land for carbon mitigation, via either carbon sequestration, bioenergy or biofuel is a concern. An alternative approach is to target abandoned salinized farmland for mitigation purposes. Australia, for example, has 17 million ha of farmland that is already or could become saline. At a representative, salinized, low rainfall (350 mm yr−1) site at Wickepin, Western Australia, we demonstrate that afforestation can mitigate carbon emissions through either providing a feedstock for bioenergy or second generation biofuel production and produce salt‐tolerant fodder for livestock. A range of factors markedly affect this mitigation. These include hydrological conditions such as salinity, site factors such as slope position and soil properties and a range of silvicultural factors such as species, planting density and age of the planting. High density (2000 stems ha−1) plantings of Eucalyptus occidentalis Endl. produced a mean total biomass of 4.6 t ha−1 yr−1 (8.5 t CO2‐e ha−1 yr−1) averaged over 8 years. Atriplex nummularia Lindl. produced a mean total biomass of 3.8 t ha−1 yr−1 (6.9 t CO2‐e ha−1 yr−1) averaged over 4 years and approximately 1.9 t ha−1 yr−1 of edible dry matter annually to 8 years of age. With differences in salt tolerance between E. occidentalis and A. nummularia, we propose an integrated approach to treating salinized sites that takes salinity gradients into account, replicates natural wetland ecosystems and produces both fodder and biomass. Continued mitigation is expected as the stands mature, assuming that growth is not affected by the accumulation of salt in the soil profile. Such carbon mitigation could potentially be applied to salinized farmland globally, and this could thus represent a major contribution to global carbon mitigation without competing with food production.

Assessing constructed wetland functional success using diel changes in dissolved oxygen, pH, and temperature in submerged, emergent, and open-water habitats in the Beaver Creek Wetlands Complex, Kentucky (USA)

We assessed the functional success of restored wetlands by determining if the patterns in dissolved oxygen (DO), temperature, and pH were similar to those conditions observed in natural wetlands. The Beaver Creek Wetlands Complex consists of dozens of marshes and ponds built in a former Licking River floodplain, in the hills of east Kentucky, USA. In natural wetland ecosystems, aquatic primary production is highest in emergent and submerged vegetations zones; where daybreak dissolved oxygen (DO) is often near zero, and DO may rise to well over 100% saturation past mid-day. Open-water areas, dominated by phytoplankton, have less dramatic diel DO fluctuations—often without pre-dawn anoxia. Compared to open water, temperatures fluctuate less dramatically in vascular vegetation, due to shading and suppression of wind and waves. Measurements of ecosystem metabolism (diel changes in DO and pH) in three aquatic habitats of the constructed wetlands (emergent vegetation, submerged vegetation, open water) were compared to these natural ideals. In Beaver Creek Wetlands, water temperature patterns were not as dramatic as in natural habitats, nor did they did follow a similar trend. Waters in emergent vegetation (29.5 °C) were warmest; submerged vegetation coolest (26.5 °C); open-water intermediate (27.4 °C). Diel DO and pH patterns were not similar to natural habitats. Highest net primary production (NPP) and gross primary production (GPP) were measured in emergent vegetation waters (mean GPP = 7.58 g m −2 d −1); lowest in submerged vegetation (mean GPP = 5.48 g m −2 d −1); and intermediate in open-water (mean GPP = 6.95 g m −2d −1). Diel pH changes were greatest in the highly productive emergent waters (median maximum daily difference of 0.36), and not as pronounced in submerged vegetation and open-water (median maximum change = 0.16 and 0.22, respectively). Water-column respiration was generally about double NPP. Like natural ecosystems, near anoxic DO concentrations were consistently measured in emergent and submerged plants before dawn; whereas open-water zones were generally >4 mg l −1. These restored wetland systems may need more time to be functionally equivalent to natural marshes.

Wetland Monitoring, Serving as an Index of Land Use Change-A Study in Samaspur Wetlands, Uttar Pradesh, India

Wetlands are among the most productive ecosystems in the world and any alterations might lead to changes in their bio-physical, socio-economic and climatic conditions. Wetland dynamics as an index of land use change were studied. Satellite remote sensing was utilized to understand the periodic and seasonal dynamics of Samaspur wetlands using Landsat and RESOURCESAT-1 temporal data. Index-based (i.e., Normalized Difference Water Index (NDWI) and Normalized Difference Vegetation Index (NDVI)) classification resulted in meaningful discrimination of wetland classes. Results indicate (i) effective water spread areas have increased to optimum capacity at 1990 due to the influence of Sharda canal, (ii) expansion of the agricultural area has led to reduction of the wetland buffer area, and (iii) increase in vegetation biomass due to pesticide-fertilizer runoff and sedimentation load. We also reiterate (i) free availability of the Landsat satellite data in public domain facilitating such monitoring studies and (ii) availability and utility of SWIR band information in wetland classification exercise. The study concludes that policy-driven measures have both long and short term impacts on land use and its natural wetland ecosystems; and the characterizing the later serves as indictor of the former and perhaps vice versa.

Source attribution of the changes in atmospheric methane for 2006–2008

Abstract. The recent increase of atmospheric methane is investigated by using two atmospheric inversions to quantify the distribution of sources and sinks for the 2006–2008 period, and a process-based model of methane emissions by natural wetland ecosystems. Methane emissions derived from the two inversions are consistent at a global scale: emissions are decreased in 2006 (−7 Tg) and increased in 2007 (+21 Tg) and 2008 (+18 Tg), as compared to the 1999–2006 period. The agreement on the latitudinal partition of the flux anomalies for the two inversions is fair in 2006, good in 2007, and not good in 2008. In 2007, a positive anomaly of tropical emissions is found to be the main contributor to the global emission anomalies (~60–80%) for both inversions, with a dominant share attributed to natural wetlands (~2/3), and a significant contribution from high latitudes (~25%). The wetland ecosystem model produces smaller and more balanced positive emission anomalies between the tropics and the high latitudes for 2006, 2007 and 2008, mainly due to precipitation changes during these years. At a global scale, the agreement between the ecosystem model and the inversions is good in 2008 but not satisfying in 2006 and 2007. Tropical South America and Boreal Eurasia appear to be major contributors to variations in methane emissions consistently in the inversions and the ecosystem model. Finally, changes in OH radicals during 2006–2008 are found to be less than 1% in inversions, with only a small impact on the inferred methane emissions.

Relation between methanogenic archaea and methane production potential in selected natural wetland ecosystems across China

Abstract. Methane (CH4) emissions from natural wetland ecosystems exhibit large spatial variability at regional, national, and global levels related to temperature, water table, plant type and methanogenic archaea etc. To understand the underlying factors that induce spatial differences in CH4 emissions, and the relationship between the population of methanogenic archaea and CH4 production potential in natural wetlands around China, we measured the CH4 production potential and the abundance of methanogenic archaea in vertical soil profiles sampled from the Poyang wetland in the subtropical zone, the Hongze wetland in the warm temperate zone, the Sanjiang marsh in the cold temperate zone, and the Ruoergai peatland in the Qinghai-Tibetan Plateau in the alpine climate zone. The top soil layer had the highest population of methanogens (1.07–8.29 × 109 cells g−1 soil) in all wetlands except the Ruoergai peatland and exhibited the maximum CH4 production potential measured at the mean in situ summer temperature. There is a significant logarithmic correlation between the abundance of methanogenic archaea and the soil organic carbon (R2 = 0.72, P < 0.001, n = 13) and between the abundance of methanogenic archaea and the total nitrogen concentrations (R2 = 0.76, P < 0.001, n = 13) in wetland soils. This indicates that the amount of soil organic carbon may affect the population of methanogens in wetland ecosystems. While the CH4 production potential is not significantly related to methanogen population (R2 = 0.01, P > 0.05, n = 13), it is related to the dissolved organic carbon concentration (R2 = 0.31, P = 0.05, n = 13). This suggests that the methanogen population might be not an effective index for predicting the CH4 production in wetland ecosystems. The CH4 production rate of the top soil layer increases with increasing latitude, from 273.64 μg CH4 kg−1 soil d−1 in the Poyang wetland to 664.59 μg CH4 kg−1 soil d−1 in the Carex lasiocarpa marsh of the Sanjiang Plain. We conclude that CH4 production potential in the freshwater wetlands of Eastern China is mainly affected by the supply of methanogenic substrates rather than temperature; in contrast, low summer temperatures at high elevations in the Ruoergai peatland of the Qinghai–Tibetan Plateau result in the presence of dominant species of methanogens with low CH4 production potential, which in turn suppresses CH4 production.

Plant Species Composition Can Be Used as a Proxy to Predict Methane Emissions in Peatland Ecosystems After Land-Use Changes

Land-use change in peatlands affects important drivers of CH4 emission such as groundwater level and nutrient availability. Due to the high spatial and temporal variability of such environmental drivers, it is hard to make good predictions of CH4 emissions in the context of land-use changes. Here, we used plant species composition as a stable integrator of environmental drivers of CH4 emissions. We used weighted averaging regression and calibration to make a direct link between plant species composition and CH4 flux in an effort to predict values of CH4 emission for a land-use gradient in two extensive peatland sites. Our predicted CH4 emissions showed good fit with observed values. Additionally, we showed that a quick characterization of vegetation composition, by the dominant species only, provides equally good predictions of CH4 emissions. The use of mean groundwater level alone for predicting emissions showed the same predictive power as our models. However, water level showed strong variability in time. Furthermore, the inverse relationship between water level and CH4 emission can lead to higher errors in predictions at sites with higher CH4 emission. The performance of our model was comparable with those of mechanistic models developed for natural wetland ecosystems. However, such mechanistic models require complex input parameters that are rarely available. We propose the use of plant species composition as a simple and effective alternative for deriving predictions of CH4 emissions in peatlands in the context of land-use change.

ESTIMATING THE LOCAL COST OF PROTECTING KOSHI TAPPU WILDLIFE RESERVE, NEPAL: A CONTINGENT VALUATION APPROACH

We estimate the compensation required by the local communities to forego access to the natural resources within the Koshi Tappu Wildlife Reserve (KTWR), Nepal using the contingent valuation method (CVM). In addition to contributing a CVM application from a seldom studied location to the literature, this case illustrates the sensitivity of WTA estimates to the analytical technique adopted. We analyze households’ willingness to accept (WTA) compensation using Tobit and double-hurdle regression models that account for the censored distribution of WTA and nested yes/no decision implicit in the WTA responses. The average WTA of a household residing in the vicinity of KTWR is estimated to be US $238, which amounts to nearly $ 1.64 million for the neighboring region. The results provide a basis to address local people’s concerns in the process of sustainable management of natural resources and wetland ecosystems in KTWR, Nepal.

Impacts on wetlands of large-scale land-use changes by agricultural development: the Small Sanjiang Plain, China.

The Small Sanjiang Plain (SSP), was formerly the largest wetland complex in China, located in the Northeastern part of Heilongjiang Province, China. Home to vast numbers of waterfowls, fish, and plants, the SSP is globally significant for biodiversity conservation. The loss and fragmentation of wetlands as a result agricultural development over 50 years has impacted wetland communities and their biodiversity. We used GIS to inventory large-scale land-use changes from 1950 to 2000, together with other statistical data. We found that 73.6% of the wetlands were lost due to agricultural development. Consequences of these land-use changes included: i) a rapid decline in waterfowl and plant species with the loss and fragmentation of natural wetlands and wetland ecosystem degradation; ii) greater variation in wetland water levels as the result of land-use changes over the years; iii) disruption of the dynamic river-floodplain connection by construction of drainage ditches and levees; and iv) a decrease in floodplain area that caused increased flooding peak flows and runoff. Here we show how these changes affect wetland biodiversity and impact important wetland species.

Phytoremediation in Wetland Ecosystems: Progress, Problems, and Potential

Assessing the phytoremediation potential of wetlands is complex due to variable conditions of hydrology, soil/sediment types, plant species diversity, growing season, and water chemistry. Conclusions about long-term phytoremediation potential are further complicated by the process of ecological succession in wetlands. This review of wetlands phytoremediation addresses the role of wetland plants in reducing contaminant loads in water and sediments, including metals; volatile organic compounds (VOC), pesticides, and other organohalogens; TNT and other explosives; and petroleum hydrocarbons and additives. The review focuses on natural wetland conditions and does not attempt to review constructed wetland technologies.Physico-chemical properties of wetlands provide many positive attributes for remediating contaminants. The expansive rhizosphere of wetland herbaceous shrub and tree species provides an enriched culture zone for microbes involved in degradation. Redox conditions in most wetland soil/sediment zones enhance degradation pathways requiring reducing conditions. However, heterogeneity complicates generalizations within and between systems.Wetland phytoremediation studies have mainly involved laboratory microcosm and mesocosm technologies, with the exception of planted poplar communities. Fewer large-scale field studies have addressed remediation actions by natural wetland communities. Laboratory findings are encouraging with regards to phytoextraction and degradation by rhizosphere and plant tissue enzymes. However, the next phase in advancing the acceptance of phytoremediation as a regulatory alternative must demonstrate sustained contaminant removal by intact natural wetland ecosystems.

Wetlands: Lifeline for people at the edge

Communities with livelihood strategies that combine subsistence agriculture with utilisation of wetland resources constitute a significant proportion of the population in developing countries. Their livelihood depends to a large extent on the productivity of the natural systems, in particular wetlands that provide a great variety of functions and benefits. This includes their role as hydrological buffers and the provision of food, water, construction materials, as well as many other products. In addition, wetlands may provide options for additional developments such as tourism. Many of the amenities, functions and values of wetlands are crucial, not only for the food security of these people, but also for the survival of their cultures.To safeguard and possibly enhance the benefits of development for many communities who subsist on wetlands it is imperative that the benefits of the natural wetland ecosystems including their values for subsistence economies are recognised when planning and implementing development projects. Unfortunately, the importance of wetlands for these communities has been and continues to be too often ignored. While developments may bring economic prosperity or improved food security for the urban populations, often it is the poorer and marginalised people who subsist at the edge of wetlands and who are not involved the development planning that suffer from the negative environmental impacts of such developments. For many of these communities the loss of the wetlands would be tantamount to losing their lifeline.Emerging integrated wetland and water resources management approaches offer mechanisms to involve all stakeholders, to reconcile otherwise conflicting interests and to incorporate in the development plans the intrinsic natural values of wetlands. International conventions (e.g. the Ramsar Convention, Convention on Combating Desertification), and current vision building initiatives (e.g. World Water Vision) contribute to and promote the development of integrated development of policies at the international, national and local levels.

Methane emissions from natural wetlands

Methane is considered one of the most important greenhouse gases in the atmosphere. Because of the strict anaerobic conditions required by CH4-generating microorganisms, natural wetland ecosystems are one of the main sources of biogenic CH4. The total natural wetland area is estimated to be 5.3 to 5.7 × 10(12) m(2), making up less than 5% of the Earth's land surface. However, natural wetland plays a disproportionately large role in CH4 emissions. Wetlands are likely the largest natural sources of CH4 to the atmosphere, accounting for about 20% of the current global annual emission. Out of the total amount of CH4 emitted, northern wetlands contribute 34%, temperate wetlands 5%, and tropical systems about 60%.Because of the unique characteristics and high productivity, wetland ecosystems are important in the global carbon cycle. Natural wetlands are permanently or temporarily saturated. Strict anaerobic conditions consequently develop, which allows methanogenesis to occur. But the thin oxic layer and the oxic plant rhizophere promote activity of CH4-oxidizing bacteria or methanotrophs. Thus, both CH4 formation and consumption in wetland systems are microbiological processes and are controlled by many factors. Eight of the controlling factors, including carbon supply, soil oxidation-reduction status, pH, temperature, vegetation, salinity and sulfate content, soil hydrological conditions and CH4 oxidation are discussed in this paper.

Study on wetland biodiversity in China

Wetland biodiversity means mainly the types of wetland ecosystem and biological species diversity. Biodiversity includes all species of plants, animals and microbes, all gene possessed by them and all ecosystems consisting of them and environment. According to the origin and genesis, China’s wetlands can be divided into natural wetland ecosystems including mires, lakeshores, bottomland, seashore, wet meadow, etc., and artificial wetland ecosystem including paddy field. Then based on geomorphological type, these ecosystems can be divided into 15 subsystems, then based on soil substrata and ecological niche conditions, they can be subdivided into 15 classes, finally according to construction species of plants, several types can be divided into. They are not only the expression of ecosystem diversity, but also the base for biological communities subsistence. This peculiar ecological niche provides a complex and perfect special habitat for various animal and plant communities. In this special habitat, there exist various biological types from monomolecular microbes to higher plants and animals, especially some endangered and rare plants and animals. According to the statistics, there are more than 300 species of birds in China wetlands, making up one-third of the total number of China’s birds. Wetlands not only good place for waterbirds living, but also the important environment on which wild animals and plant rely for existence. There are 65 species of mammals, 50 species of reptiles, 45 species of amphibious animals, 1040 species of fish, 825 species of higher plants, 639 species of angiosperm, 10 species of gymnosperm, 12 species of pteridophyte and 164 species of bryophyte investigated in China’s wetlands.

The use of freshwater wetlands as a tertiary wastewater treatment alternative

Freshwater wetlands can, in some circumstances, renovate added secondarily treated wastewater, thus providing an alternative to land or water disposal or expensive physical‐chemical treatment processes. This review summarizes North American studies in the contexts of ecosystem function and water quality changes, for both natural and artificial wetland ecosystems. All components of an ecosystem are involved in the alteration of the dissolved nutrient status and sediment content of the water. The results of recent studies are interpreted in terms of the principles of hydrology and nutrient cycling in wetlands. Initial uptake and alteration mechanisms involve sorption and microbial processes, such as denitrification. Peat soils provide a maximum condition for this rapid uptake. Detritus supports microbial populations and active periphyton, which coupled with other algae, represent a second temporary sink. The vascular plant community also represents nutrient storage which may be exploited by herbivores or de...