Showing papers on "Wetland published in 2021"

Scientists' warning to humanity on the freshwater biodiversity crisis.

Abstract: Freshwater ecosystems provide irreplaceable services for both nature and society. The quality and quantity of freshwater affect biogeochemical processes and ecological dynamics that determine biodiversity, ecosystem productivity, and human health and welfare at local, regional and global scales. Freshwater ecosystems and their associated riparian habitats are amongst the most biologically diverse on Earth, and have inestimable economic, health, cultural, scientific and educational values. Yet human impacts to lakes, rivers, streams, wetlands and groundwater are dramatically reducing biodiversity and robbing critical natural resources and services from current and future generations. Freshwater biodiversity is declining rapidly on every continent and in every major river basin on Earth, and this degradation is occurring more rapidly than in terrestrial ecosystems. Currently, about one third of all global freshwater discharges pass through human agricultural, industrial or urban infrastructure. About one fifth of the Earth's arable land is now already equipped for irrigation, including all the most productive lands, and this proportion is projected to surpass one third by midcentury to feed the rapidly expanding populations of humans and commensal species, especially poultry and ruminant livestock. Less than one fifth of the world's preindustrial freshwater wetlands remain, and this proportion is projected to decline to under one tenth by midcentury, with imminent threats from water transfer megaprojects in Brazil and India, and coastal wetland drainage megaprojects in China. The Living Planet Index for freshwater vertebrate populations has declined to just one third that of 1970, and is projected to sink below one fifth by midcentury. A linear model of global economic expansion yields the chilling prediction that human utilization of critical freshwater resources will approach one half of the Earth's total capacity by midcentury. Although the magnitude and growth of the human freshwater footprint are greater than is generally understood by policy makers, the news media, or the general public, slowing and reversing dramatic losses of freshwater species and ecosystems is still possible. We recommend a set of urgent policy actions that promote clean water, conserve watershed services, and restore freshwater ecosystems and their vital services. Effective management of freshwater resources and ecosystems must be ranked amongst humanity's highest priorities.

Global blue carbon accumulation in tidal wetlands increases with climate change.

Abstract: Coastal tidal wetlands produce and accumulate significant amounts of organic carbon (C) that help to mitigate climate change. However, previous data limitations have prevented a robust evaluation of the global rates and mechanisms driving C accumulation. Here, we go beyond recent soil C stock estimates to reveal global tidal wetland C accumulation and predict changes under relative sea-level rise, temperature and precipitation. We use data from literature study sites and our new observations spanning wide latitudinal gradients and 20 countries. Globally, tidal wetlands accumulate 53.65 (95%CI: 48.52–59.01) Tg C yr−1, which is ∼30% of the organic C buried on the ocean floor. Modelling based on current climatic drivers and under projected emissions scenarios revealed a net increase in the global C accumulation by 2100. This rapid increase is driven by sea-level rise in tidal marshes, and higher temperature and precipitation in mangroves. Countries with large areas of coastal wetlands, like Indonesia and Mexico, are more susceptible to tidal wetland C losses under climate change, while regions such as Australia, Brazil, the USA and China will experience a significant C accumulation increase under all projected scenarios.

Extreme Drought in the Brazilian Pantanal in 2019–2020: Characterization, Causes, and Impacts

Abstract: The Pantanal region in South America is one of the world’s largest wetlands. Since 2019, the Pantanal has suffered a prolonged drought that has spelled disaster for the region, and subsequent fires have engulfed hundreds of thousands of hectares. The lack of rainfall during the summers of 2019 and 2020 was caused by reduced transport of warm and humid summer air from Amazonia into the Pantanal. Instead, a predominance of warmer and drier air masses from subtropical latitudes contributed to a scarcity of summer rainfall at the peak of the monsoon season. This led to prolonged extreme drought conditions across the region. This drought had severe impacts on the hydrology of the Pantanal. Hydrometric levels fell all along the Paraguay River. In 2020, river levels reached extremely low values, and in some sections of this river, transportation had to be restricted. Very low river levels affected the mobility of people and shipping of soybeans and minerals to the Atlantic Ocean by the Hidrovia -Parana-Paraguai (Parana-Paraguay Waterway). This study is directed to better understand the hydroclimatic aspects of the current drought in the Brazilian Pantanal and their impacts on natural and human systems. As a consequence of the drought, fires spread and affected natural biodiversity as well as the agribusiness and cattle ranching sectors. While fires had serious socioecological and economic consequences, we do not intend to investigate the effect of the downstream low-level waters on the Pantanal ecosystems or the drought in the risk of fire.

A review of constructed wetland on type, treatment and technology of wastewater

Abstract: The performance of constructed wetland depends upon the types of constructed wetland, vegetation, applied hydraulic load, and media used in the bed. This paper describes the review of constructed wetland on type, technology and treatment of various types of wastewater generated such as textile waste, dairy waste, industrial waste, piggery waste, tannery waste, petrochemical waste, municipal waste, etc. The review summarizes the types of constructed wetlands considering media, vegetation, removal efficiency, construction cost, maintenance cost and land area requirement using life cycle cost analysis. The review compares how and why constructed wetland is a better option as per treatment efficiency, their payback period and cost-effective with the other wastewater treatment technologies. Further, there is no proper guidelines for the selection of media and vegetation in the constructed wetland. It is found that Typha Latifolia and Phragmites Australis have a better removal efficiency than other species. Lightweight Expanded Clay Aggregate (LECA), saw dust, zero-valent iron and gravels can be effectively used as a media for the removal of organic matter, phosphorus, sulphate and arsenate. Constructed wetland with low Hydraulic Loading Rate (HLR) performs exceptionally well and can remove 80%–91% Biochemical Oxygen Demand (BOD), 60%–85% Chemical Oxygen Demand (COD) and 80%–95% Total Suspended Solids (TSS). It requires a very low operation and maintenance than others. This review on constructed wetland further suggests research and development related to land area, media, plants, engineering design and automation of treatment units.

Salinity controls soil microbial community structure and function in coastal estuarine wetlands.

Abstract: Soil salinity acts as a critical environmental filter on microbial communities, but the consequences for microbial diversity and biogeochemical processes are poorly understood. Here, we characterized soil bacterial communities and microbial functional genes in a coastal estuarine wetland ecosystem across a gradient (~5 km) ranging from oligohaline to hypersaline habitats by applying the PCR-amplified 16S rRNA (rRNA) genes sequencing and microarray-based GeoChip 5.0 respectively. Results showed that saline soils in marine intertidal and supratidal zone exhibited higher bacterial richness and Faith's phylogenetic diversity than that in the freshwater-affected habitats. The relative abundance of taxa assigned to Gammaproteobacteria, Bacteroidetes and Firmicutes was higher with increasing salinity, while those affiliated with Acidobacteria, Chloroflexi and Cyanobacteria were more prevalent in wetland soils with low salinity. The phylogenetic inferences demonstrated the deterministic role of salinity filtering on the bacterial community assembly processes. The abundance of most functional genes involved in carbon degradation and nitrogen cycling correlated negatively with salinity, except for the hzo gene, suggesting a critical role of the anammox process in tidal affected zones. Overall, the salinity filtering effect shapes the soil bacterial community composition, and soil salinity act as a critical inhibitor in the soil biogeochemical processes in estuary ecosystems.

Future impacts of climate change on inland Ramsar wetlands

Abstract: The 1971 Ramsar Convention promotes wetland conservation worldwide, yet climate change impacts on wetland extent and associated biodiversity are unclear. Hydrological modelling and soil moisture estimates are used to quantify climate change-driven shifts in wetland area across 1,250 inland Ramsar sites. We estimate that net global wetland area expanded during 1980–2014, but 47% of sites experienced wetland loss. By 2100, a net area loss of at least 6,000 km2 (about 1%) is projected. The number of sites with area loss over 10% will increase by 19–65% under low emissions, 148–243% under high emissions and ~16% with global mean warming of 2 °C relative to 1.5 °C. Sites most vulnerable to shrinkage are located in the Mediterranean, Mexico, Central America and South Africa—all seasonal waterbird migration hotspots. Our findings highlight that climate mitigation is essential for future Ramsar wetlands conservation, in addition to the minimization of human disturbance. Hydrological modelling is combined with soil moisture estimates to quantify climate change impacts on inland Ramsar wetlands. Net global changes are estimated to be modest, but individual sites with area reductions over 10% are projected to increase 19–243% by 2100, depending on emissions scenario.

Aboveground biomass and its spatial distribution pattern of herbaceous marsh vegetation in China

Abstract: Herbaceous marsh is the most widely distributed type of marsh wetland ecosystem, and has important ecological functions such as water conservation, climate regulation, carbon storage and fixation, and sheltering rare species. The carbon sequestration function of herbaceous marsh plays a key role in slowing climate warming and maintaining regional environmental stability. Vegetation biomass is an important index reflecting the carbon sequestration capacity of wetlands. Investigating the biomass of marsh vegetation can provide a scientific basis for estimating the carbon storage and carbon sequestration capacity of marshes. Based on field survey data of aboveground biomass of herbaceous marsh vegetation and the distribution data set of marsh in China, we analyzed the aboveground biomass and its spatial distribution pattern of herbaceous marsh on a national scale for the first time. The results showed that in China the total area of herbaceous marsh was 9.7×104 km2, the average density of aboveground biomass of herbaceous marsh vegetation was 227.5±23.0 g C m−2 (95% confidence interval, the same below), and the total aboveground biomass was 22.2±2.2 Tg C (1 Tg=1012 g). The aboveground biomass density of herbaceous marsh vegetation is generally low in Northeast China and the Tibetan Plateau, and high in central North China and coastal regions in China. In different marsh distribution regions of China, the average biomass density of herbaceous marsh vegetation from small to large was as follows: temperate humid and semi-humid marsh region (182.3±49.3 g C m−2)

How plants influence resilience of salt marsh and mangrove wetlands to sea-level rise

Abstract: This review evaluates the importance of plants and associated biological processes in determining the vulnerability of coastal wetlands to sea-level rise. Coastal wetlands occur across a broad sedimentary continuum from minerogenic to biogenic, providing an opportunity to examine the relative importance of biological processes in wetland resilience to sea-level rise. We explore how plants influence sediment accretion, elevation capital (vertical position in the tidal frame), and compaction or erosion of deposited material. We focus on salt marsh and mangrove wetlands, which occupy a similar physiographic niche and display similar physical and biological controls on resilience to sea-level rise. In both habitats, plants stabilize emergent mudflats and help sustain the wetland position in the tidal frame relative to ocean height through both surface and subsurface process controls on soil elevation. Plants influence soil elevations by modifying (1) mineral sediment deposition and retention, (2) organic matter contributions to soil volume, and (3) resistance to compaction and erosion. Recognition of the importance of plants in coastal wetland resilience to sea-level rise is key to accurate predictions about the future fate of salt marshes and mangrove forests and for development of effective management and restoration plans.

Rebound in China’s coastal wetlands following conservation and restoration

Abstract: The coastal zone of China has experienced large increases in population, economy and urbanization since the early 1980s. Many studies have reported the loss, degradation and fragmentation of coastal wetlands in China at local to regional scales. To date, at the national scale, our knowledge of the spatial distribution, inter-annual variation and multi-decadal trends of coastal wetlands in China remains very limited. Here we analysed ~62,000 Landsat-5, -7 and -8 images over the period 1984–2018 and generated maps of coastal wetlands for individual years in China at 30-m spatial resolution. We found that coastal wetland area significantly decreased between 1984 and 2011. We also found a substantial increase in saltmarsh area and a stable trend of tidal flat area since 2012, driven by reduced anthropogenic activities and increased conservation and restoration efforts. These coastal wetland maps for the period 1984–2018 are invaluable for improvement of coastal wetland management and sustainability in China. China’s coasts have become more populous and urbanized. This study finds a rebound in the area of coastal wetlands, reflecting recent conservation and restoration, with large losses between 1984 and 2011 followed by increases in saltmarsh area and stabilization of tidal flats.

FLUXNET-CH4: a global, multi-ecosystem dataset and analysis of methane seasonality from freshwater wetlands

Abstract: . Methane (CH4) emissions from natural landscapes constitute roughly half of global CH4 contributions to the atmosphere, yet large uncertainties remain in the absolute magnitude and the seasonality of emission quantities and drivers. Eddy covariance (EC) measurements of CH4 flux are ideal for constraining ecosystem-scale CH4 emissions due to quasi-continuous and high-temporal-resolution CH4 flux measurements, coincident carbon dioxide, water, and energy flux measurements, lack of ecosystem disturbance, and increased availability of datasets over the last decade. Here, we (1) describe the newly published dataset, FLUXNET-CH4 Version 1.0, the first open-source global dataset of CH4 EC measurements (available at https://fluxnet.org/data/fluxnet-ch4-community-product/, last access: 7 April 2021). FLUXNET-CH4 includes half-hourly and daily gap-filled and non-gap-filled aggregated CH4 fluxes and meteorological data from 79 sites globally: 42 freshwater wetlands, 6 brackish and saline wetlands, 7 formerly drained ecosystems, 7 rice paddy sites, 2 lakes, and 15 uplands. Then, we (2) evaluate FLUXNET-CH4 representativeness for freshwater wetland coverage globally because the majority of sites in FLUXNET-CH4 Version 1.0 are freshwater wetlands which are a substantial source of total atmospheric CH4 emissions; and (3) we provide the first global estimates of the seasonal variability and seasonality predictors of freshwater wetland CH4 fluxes. Our representativeness analysis suggests that the freshwater wetland sites in the dataset cover global wetland bioclimatic attributes (encompassing energy, moisture, and vegetation-related parameters) in arctic, boreal, and temperate regions but only sparsely cover humid tropical regions. Seasonality metrics of wetland CH4 emissions vary considerably across latitudinal bands. In freshwater wetlands (except those between 20∘ S to 20∘ N) the spring onset of elevated CH4 emissions starts 3 d earlier, and the CH4 emission season lasts 4 d longer, for each degree Celsius increase in mean annual air temperature. On average, the spring onset of increasing CH4 emissions lags behind soil warming by 1 month, with very few sites experiencing increased CH4 emissions prior to the onset of soil warming. In contrast, roughly half of these sites experience the spring onset of rising CH4 emissions prior to the spring increase in gross primary productivity (GPP). The timing of peak summer CH4 emissions does not correlate with the timing for either peak summer temperature or peak GPP. Our results provide seasonality parameters for CH4 modeling and highlight seasonality metrics that cannot be predicted by temperature or GPP (i.e., seasonality of CH4 peak). FLUXNET-CH4 is a powerful new resource for diagnosing and understanding the role of terrestrial ecosystems and climate drivers in the global CH4 cycle, and future additions of sites in tropical ecosystems and site years of data collection will provide added value to this database. All seasonality parameters are available at https://doi.org/10.5281/zenodo.4672601 (Delwiche et al., 2021). Additionally, raw FLUXNET-CH4 data used to extract seasonality parameters can be downloaded from https://fluxnet.org/data/fluxnet-ch4-community-product/ (last access: 7 April 2021), and a complete list of the 79 individual site data DOIs is provided in Table 2 of this paper.

Mangroves in arid regions: Ecology, threats, and opportunities

Abstract: Mangroves are one of the few woody ecosystems that grow in hot-arid climates. They can survive extreme conditions of low precipitation, high solar radiation, wide temperature fluctuations and hypersalinity. These unique mangroves have distinct geomorphology, hydrology, forest structure, tree physiology, and soil biogeochemistry. In this review, supported by field data from Australia and Mexico, we explore the characteristics of mangroves in arid climates of the world. These mangroves are mostly tide-dominated with freshwater flows restricted to groundwater and sporadic tropical storms. They form dense forests with stunted growth dominated mainly by trees of the genus Avicennia that co-occur with salt marshes in the high intertidal. Their soils have low nutrient and carbon concentrations, and high soil δ15 N and δ13C values compared to subhumid and humid mangroves. Mangroves in arid climates have relatively low human pressure due to sparse human settlements. Key threats to these mangroves, which often persist at the edge of their physiological tolerances, include extreme drought, reductions in groundwater inputs, altered hydrology, sea-level fluctuations and increases in nutrient loading. Restoration of mangroves in arid climates should focus on restoring their hydrology. Mangroves in arid zones are under-represented in global maps and assessment programs, as they may not be consistent with countries’ definition of “forests”. Improved global representation and understanding of the ecology of mangroves in arid climates could help sustain their valuable ecosystem services.

Rewetting does not return drained fen peatlands to their old selves.

Abstract: Peatlands have been drained for land use for a long time and on a large scale, turning them from carbon and nutrient sinks into respective sources, diminishing water regulation capacity, causing surface height loss and destroying biodiversity. Over the last decades, drained peatlands have been rewetted for biodiversity restoration and, as it strongly decreases greenhouse gas emissions, also for climate protection. We quantify restoration success by comparing 320 rewetted fen peatland sites to 243 near-natural peatland sites of similar origin across temperate Europe, all set into perspective by 10k additional European fen vegetation plots. Results imply that rewetting of drained fen peatlands induces the establishment of tall, graminoid wetland plants (helophytisation) and long-lasting differences to pre-drainage biodiversity (vegetation), ecosystem functioning (geochemistry, hydrology), and land cover characteristics (spectral temporal metrics). The Paris Agreement entails the rewetting of 500,000 km2 of drained peatlands worldwide until 2050-2070. A better understanding of the resulting locally novel ecosystems is required to improve planning and implementation of peatland rewetting and subsequent management. Whether rewetting leads to effective restoration of drained peatlands is unclear. Here the authors analyse a large number of near-natural and rewetted fen peatland sites in Europe, finding persistent differences in plant community composition and ecosystem functioning, and higher variance in the restored sites.

Evidence of microplastics in wetlands: Extraction and quantification in Freshwater and coastal ecosystems

Abstract: Microplastics are the emerging non-degradable pollutants in natural ecosystems. It impacts humans and wildlife, mainly aquatic species, by getting incorporated into the food chain due to their sizes (

The Boreal–Arctic Wetland and Lake Dataset (BAWLD)

Abstract: . Methane emissions from boreal and arctic wetlands, lakes, and rivers are expected to increase in response to warming and associated permafrost thaw. However, the lack of appropriate land cover datasets for scaling field-measured methane emissions to circumpolar scales has contributed to a large uncertainty for our understanding of present-day and future methane emissions. Here we present the Boreal–Arctic Wetland and Lake Dataset (BAWLD), a land cover dataset based on an expert assessment, extrapolated using random forest modelling from available spatial datasets of climate, topography, soils, permafrost conditions, vegetation, wetlands, and surface water extents and dynamics. In BAWLD, we estimate the fractional coverage of five wetland, seven lake, and three river classes within 0.5 × 0.5 ∘ grid cells that cover the northern boreal and tundra biomes (17 % of the global land surface). Land cover classes were defined using criteria that ensured distinct methane emissions among classes, as indicated by a co-developed comprehensive dataset of methane flux observations. In BAWLD, wetlands occupied 3.2 × 10 6 km 2 (14 % of domain) with a 95 % confidence interval between 2.8 and 3.8 × 10 6 km 2 . Bog, fen, and permafrost bog were the most abundant wetland classes, covering ∼ 28 % each of the total wetland area, while the highest-methane-emitting marsh and tundra wetland classes occupied 5 % and 12 %, respectively. Lakes, defined to include all lentic open-water ecosystems regardless of size, covered 1.4 × 10 6 km 2 (6 % of domain). Low-methane-emitting large lakes ( >10 km 2 ) and glacial lakes jointly represented 78 % of the total lake area, while high-emitting peatland and yedoma lakes covered 18 % and 4 %, respectively. Small ( km 2 ) glacial, peatland, and yedoma lakes combined covered 17 % of the total lake area but contributed disproportionally to the overall spatial uncertainty in lake area with a 95 % confidence interval between 0.15 and 0.38 × 10 6 km 2 . Rivers and streams were estimated to cover 0.12 × 10 6 km 2 (0.5 % of domain), of which 8 % was associated with high-methane-emitting headwaters that drain organic-rich landscapes. Distinct combinations of spatially co-occurring wetland and lake classes were identified across the BAWLD domain, allowing for the mapping of “wetscapes” that have characteristic methane emission magnitudes and sensitivities to climate change at regional scales. With BAWLD, we provide a dataset which avoids double-accounting of wetland, lake, and river extents and which includes confidence intervals for each land cover class. As such, BAWLD will be suitable for many hydrological and biogeochemical modelling and upscaling efforts for the northern boreal and arctic region, in particular those aimed at improving assessments of current and future methane emissions. Data are freely available at https://doi.org/10.18739/A2C824F9X (Olefeldt et al., 2021).

Assessment of the impact of LUCC on NPP and its influencing factors in the Yangtze River basin, China

Abstract: Land use and land cover change (LUCC) will directly affect the types, structures and functions of ecosystems, and then have important impact on vegetation net primary productivity (NPP). The evaluation of the spatio-temporal dynamic changes of LUCC and regional NPP, and assessing the impact of LUCC on NPP can facilitate the corresponding management of different environmental types of regions and provide scientific guidance for scientific development of ecological resources, and better restore and control the ecological environment, thus promoting rapid economic development. Using MODIS normalized difference vegetation index (NDVI) data and meteorological data from 2001 to 2018, combined with Carnegie-Ames-Stanford model (CASA), the regional NPP was estimated, and the influence of LUCC on NPP in Yangtze River basin from 2001 to 2018 and its causes were analyzed. The results showed that the area with a land cover and land use change account for 10.98% of the total study area in the past 18 years, and the most important change is the transformation from grassland to forest and grassland to crop/natural vegetation mosaic (NVM). Forests, wetlands, crop/natural vegetation mosaic, low vegetation cover (LVC) land, urban, and water bodies are growing. The forest land area increased the most and that of grassland decreased the most. Total NPP has increased by 53887.51GgC in the past 18 years, which was due to the combination effect of LUCC change and climate change.

Kernel low-rank representation with elastic net for China coastal wetland land cover classification using GF-5 hyperspectral imagery

Abstract: Wetland contains various ground objects with high spectral similarity. How to accurately distinguish complex classes has become a challenge in wetland land cover classification. In this paper, low-rank representation with elastic net (ENLRR) and the kernel version of ENLRR (KENLRR) are proposed for coastal wetland land cover classification by using Gaofen-5 (GF-5) hyperspectral data of China. The main idea of ENLRR is to combine elastic net with low-rank representation, which replaces rank function with the combination of nuclear norm and Frobenius norm when constraining the coefficient matrix. The KENLRR method considers nonlinear characteristics of hyperspectral data, where a neighborhood filter (NF) kernel function is adopted to map the original data space into a higher dimensional feature space for better classification. In the experiments, three typical coastal wetlands in China: Yellow River Delta, Jiangsu Dafeng Natural Reserve, and Yangtze River Delta (Nantong) are adopted, and the proposed methods and seven comparison methods are used to conduct wetland land cover classification. The experimental results demonstrate that the proposed ENLRR and KENLRR are effective in accurately distinguishing wetland ground objects and reliably mapping their distribution. More specifically, the KENLRR method can provide the best performance, and the OAs are 96.63%, 96.76% and 87.67% for the three wetlands, respectively. The land cover distributions and spatial patterns of the three wetlands are studied as well. Yellow River Delta is a typical estuarine wetland with abundant landscapes, Dafeng Nature Reserve is a coastal wetland with the block regular feature distribution in spatial, and Yangtze River Delta (Nantong) mainly includes river and flood plain, whose ecological environment is deeply affected by human activities.

Climate change : impact on coastal habitation

Abstract: Introduction, D. Eisma The World Heat Budget: Expected Changes, C.J.E. Schuurmans Recorded Sea Level Variability in the Holocene and Expected Future Changes, N.-A. Moerner Present and Future Sea Level: The Effects of Predicted Global Changes, E.C.F. Bird River Flux to the Sea: Impact of Human Intervention on River Systems and Adjacent Coastal Areas, J.D. Milliman and M. Ren Response of Estuaries to Climate Change, K.R. Dyer Effects of Sea Level Rise on Coastal Sedimentation and Erosion, J.T. Wells Sea Level Rise: A Worldwide Assessment of Risk and Protection Costs, F.M.J. Hoozemans and C.H. Hulsbergen Impact of Climatic Change on Coastal Cities, T.J. Deelstra Impact of Climate Change on the Ecology of Temperate Coastal Wetlands, Beaches, and Dunes, V. Noest, E. van der Maarel, and F. van der Meulen Impact of Climatic Change on Coral Reefs, Mangroves, and Tropical Seagrass Ecosystems, A.J. Edwards Impact of Climatic Change on Coastal Agriculture, R. Brinkman Index