Distribution Of Wetlands Research Articles

Evolution Characteristics of Wetland Landscape Pattern and Its Impact on Carbon Sequestration in Wuhan from 2000 to 2020

The wetland ecosystem is an important organic carbon pool on earth, and rich carbon storage and high carbon density are present in wetland vegetation and soil. However, large areas of wetlands have been drained, the area of wetlands has shrunk, and the degree of fragmentation has intensified due to rapid urbanization in the past 20 years. Enhancing ecological carbon sequestration capacity is a key task of carbon peaking and neutrality, and studying the carbon sequestration function of urban wetland is urgently needed. In this work, the wetland in Wuhan was taken as the main research object. The landscape pattern index of Wuhan wetland was calculated and the evolution characteristics of landscape pattern were analyzed using the remote sensing image interpretation data from 2000 to 2020. CASA model was used to estimate the carbon sequestration of wetlands and explore the spatial and temporal distribution pattern of carbon sequestration. Spearman correlation was used to study the effects of different landscape pattern parameters on carbon sequestration. Results indicate the following: (1) From 2000 to 2020, the total wetland area in Wuhan has been reduced by 158.99 km2, among which the area of lakes, reservoirs and marshes decreased by 60.65 km2, 55.51 km2 and 41.77 km2, respectively. The density of wetland patches and the degree of fragmentation and irregularity increased, and the LPI, aggregation degree and diversity decreased. (2) In the past 20 years, the total carbon sequestration amount of wetland in Wuhan first decreased and then increased, among which the carbon sequestration in wetland was the lowest in 2010 (571,900 t). The amount of carbon sequestration in 2020 was the same as that in 2000, reaching 800,000 t. (3) A larger wetland area means more concentrated and denser distribution, more complex shape, more diverse type, and stronger carbon sequestration capacity for Wuhan wetland. On the contrary, the distribution of wetlands becomes more fragmented and regular, and the disordered planning leads to the reduction in wetland types in a unit area, which will decrease the carbon sink capacity of urban wetlands.

Nest‐site selection by cinnamon teal and other ground‐nesting ducks in Great Salt Lake wetlands

AbstractGround‐nesting ducks can reduce nest depredation by selecting nest sites where local physical structures or vegetation provide olfactory or visual concealment. We evaluated nest‐site selection by comparing duck nests to random sites during 2019 and 2020 in the impounded wetlands of Great Salt Lake (GSL), Utah, USA. During wet springs, most of the wetlands are underwater, leaving only the dams available as nesting substrate. We located the nests of 399 cinnamon teal (Spatula cyanoptera), 137 mallards (Anas platyrhynchos), and 162 gadwalls (Mareca strepera) on the dams. At nest and random sites, we measured overhead concealment, lateral concealment, average height of vegetation in the nest patch, standard deviation of vegetation height in the nest patch, tallest vegetation within 1 m of nest, dam width, and distance from the nest to the road along the center of the dam. We found that mallards and gadwalls did not select for any of these characteristics. Cinnamon teal selected for nest sites that had more overhead concealment. We also found mixed evidence that cinnamon teal selected nest sites where dams were wider. All species also favored heterogeneous patches of vegetation for nesting over homogenous ones. Duck nests had a clumped distribution in wetlands that contained colonies of American avocets (Recurvirostra americana), black‐necked stilts (Himantopus mexicanus), and common terns (Sterna hirundo), with nests located inside the colonies, but showed a random distribution in other wetlands. Prior to 1980, approximately half of the world's population of cinnamon teal nested in GSL wetlands, but since that time the nesting population has declined greatly. Given this decline, management actions should be conducted that will improve overhead cover and widen dikes within the species' nesting habitat.

Environmental Factors, Biomass, and Function of Wetlands

Wetlands are an important part of the biosphere. Wetlands not only impact the natural environment but also play vital roles in human life. This paper starts with the classification, distribution, and main functions of wetlands, then analyzes the relationship between wetlands and the biosphere from several aspects, including the factors that affect wetlands, the biomass of wetlands, the importance of wetlands for carbon storage, and the threats that wetlands may face. Based on previous research, wetlands can be impacted by environmental factors, such as water supply and temperature, and biological factors, including aboveground biomass and below-ground biomass. When interacting with these factors, wetlands can play crucial roles in the biosphere, such as facilitating the circulation of energy and materials and the storage of carbon. However, wetlands are facing threats. After analyzing the current state of wetlands, possible solutions are considered. Both research and society can make efforts to improve wetlands ecosystems. This report is significant for understanding the current situation and the direction of future development of wetlands. It is crucial to study the environmental factors affecting wetlands, considering the protection, improvement, and future development of wetland ecosystems depend on their surroundings to a great extent. Interactions between wetlands and the environment directly or indirectly determine the state of wetlands.

Evolution of Small and Micro Wetlands and Their Driving Factors in the Yangtze River Delta—A Case Study of Wuxi Area

Understanding the long-term dynamics and driving factors behind small and micro wetlands is critical for their management and future sustainability. This study explored the impacts of natural and anthropogenic factors on the spatiotemporal evolution of these areas in Wuxi area using the support vector machine (SVM) classification method and the geographic detector model based on Landsat satellite image data from 1985 to 2020. The results revealed that: (1) Natural wetlands were prominent in Wuxi area, with an average proportion of 70%, and although they exhibited a downward trend over the last ten years, the scale of natural small and micro wetlands increased 1.5-fold—from 4349.59 hm2 in 1985 to 10,841.59 hm2 in 2020. (2) The small and micro wetlands in Wuxi area had obvious seasonal variations, with most being 0.1–1 hm2 and 1–3 hm2, respectively. From the perspective of spatial distribution, they were primarily distributed in Yixing district, which accounts for 34% of Wuxi area. (3) The distribution of small and micro wetlands was systematically affected by natural and human activities. The main factors that affected the distribution of small and micro wetlands were the average annual temperature and GDP, with the interactions between all factors being nonlinear and bi-linear. The influences of natural factors on small and micro wetlands were weakened, with human activities steadily emerging as the dominant factor that affected their distribution. The results of this study can provide supportive data and a scientific basis for the ecological restoration and protection of wetlands.

Population demography of rare sedges (Eriophorum gracile and Carex livida) north of the Arctic Circle in Murmansk Region and climate change impacts

Species of Cyperaceae are little studied on the population level globally. Also in Murmansk Region, species from this family were not included in long-term population studies of rare plant species whereas other representatives from 21 families were put in [Blinova, 2009]. Experimental works with sedges is often neglected because of taxonomic difficulties and a lack of methods for study populations of this group [Kitamura et al., 2016; Sosnovska, Danylyk, 2017]. Such difficulties became obvious while the IUCN-red data book testing. Of rare sedges studied in this paper Eriophorum gracile is included in the regional Red data book [Kozhin, 2014] and Carex livida is in the Appendix of this book in the group Need of monitoring. 
 
 The Murmansk Region (6670 N), located in the north-eastern corner of Russian Fennoscandia, is a part of the Atlantic-Arctic zone of temperate belt with a rather mild climate. The region is very heterogeneous. Two latitudinal vegetation zones can be distinguished: tundra and taiga. So, many boreal plant species reach here their northern limit of distribution. Our field work has been conducted in the center part of the region in a recently found rich fen [Blinova, Petrovskij, 2014]. Both study species (Eriophorum gracile и Carex livida) have circumpolar distribution in wetlands of northern hemisphere [Hulten, Fries, 1986], and they are at the northern range in Murmansk Region [Kuzeneva, 1954; Chernov, 1954]. They are polycarpic perennials. An annual shoot has been selected as a counting unit (Fig. 1). In E. gracile only the number of generative shoots has been counted in the field. For non-destructive purposes, from herbarium data, the ratio between generative and vegetative shoots was defined as 1:1. The total population size for this species has been estimated from this ratio. In population of C. livida, the direct counting in the field has been done on 3-5 small plots (0.25*0.25 м2). Lately this value has been recalculated according to the area of population subset. Clusters and subsets have been distinguished in population structure according to suggested aggregation patterns of spatial structure in local plant populations [Blinova, 2018]. Marked population subsets have been monitored several times in the growing period in 2014-2016 years. In the field the boundaries and areas of rich fen and populations (including subsets) have been estimated with the help of GPS navigation device Garmin Dakota 20, in the lab all data are further processed using Garmin Software BaseCamp 4.2.5. Nomenclature for vascular plants is given according to S. K. Czerepanov [1995], for mosses after M. S. Ignatov O. M. Afonina [1992]. 
 
 Our results show that extremely low (0.2% for Eriophorum gracile) and relatively low (3.1% для Carex livida) population cover is characteristic for a large long-term monitored fen. Spatial aggregation of E. gracile population is structured on very small area (40 м2) whereas C. livida is established on relatively representative area (633 м2). E. gracile develops small population subsets (8 m2 on average) at a distance to next about 70 m in different parts of rich fen. Each such subset contains 9-10 mature individuals on average. C. livida has larger subsets (211 m2 on average) at 30 m away from the neighbor. The size of each subset makes c. 2500 generative shoots. The spatial population pattern of E. gracile shows isolated subsets with single clusters, whereas of C. livida represents isolated subsets with merged clusters. High fluctuations of population size and its subsets are revealed in E. gracile from year to year. The number of generative shoots and air temperature in the growing season (June-September) of the current year establish negative relationship.
 
 This study in one of the northernmost populations of Eriophorum gracile confirms other data from different parts of its distribution area that populations of this species are very fragmented and show high fluctuations in the number of generative shoots [Barr 1996; Ksermann, Moser, 1999; Dickenmann, Keel, 2004; Decker et al., 2006; Chatters, Sanderson, 2014]. An analysis of spatial structure of populations has been pointed out that anemochory of E. gracile could be a bottleneck for the population fitness in rich fens conditions, whereas baro- and hydrochory of C. livida promotes further seed germination and survival. Additionally, current climate-changed impacts could cause an extirpation of E. gracile from floristic composition of rich fens, whereas such a threat is minimal for C. livida. Both species need regional protection of their populations. An introduction into culture is essential for further ontogenetic studies and trigger examination of clonal division of labor.

Spatial–Temporal Evolution Monitoring and Ecological Risk Assessment of Coastal Wetlands on Hainan Island, China

Coastal wetlands are located at the intersection of land and sea and provide extremely important ecological services. The coastal wetlands of estuarine harbors are representative parts of the coastal wetlands. Changes that occur in estuarine harbor wetlands are microcosms of the changes occurring in the coastal wetlands more generally. The coastal wetlands of Hainan Island, China, are coastal wetlands typical of tropical islands and are extremely sensitive to climate change. In the context of global sea level rise, studying the characteristics of spatial and temporal distribution of coastal wetlands on Hainan Island, as well as changes in their vulnerability, could provide scientific and technological support to address the adverse effects of climate change. Using nine typical estuarine harbor wetlands as target areas, this study systematically studies the spatial–temporal evolution of coastal wetlands on Hainan Island from 1990 to 2020. The results suggest the following: (1) The total area of coastal wetlands has remained relatively stable, but the area of artificial wetlands, especially aquaculture ponds, has increased significantly. There is a clear spatial variability in the changes in mangrove wetlands, with a clear increase in the area of areas with a high degree of protection, such as Dongzhai Harbor (DZG). The area of the areas with a high intensity of human activity has been significantly reduced, such as Bamen Bay (BMG). (2) The overall ecological risk of coastal wetlands is low, with the average wetland risk index (WRI) of all harbors being below 0.15. The higher the degree of protection, the lower the ecological risk of the area, such as DZG. Human activities are the main factor causing increased ecological risk in wetlands. (3) Climate-change-induced sea level rise and the intensification of human activities are the main determinants of future trends in the spatial distribution of coastal wetlands and wetland ecosystem stability. The results of this study provide guidance on the conservation and restoration of coastal wetlands.

Wetland attributes significantly affect patterns of bird species distribution in the Sardinian wetlands (Italy): An uncertain future for waterbird conservation

Abstract The Sardinian wetlands belong to the Sardinia‐Corsica corridor of the central eastern Mediterranean bird flyway. They supply the food and shelter for many waterbird species and act as stopover sites during migratory journeys. Despite policies and laws of the European Union, the Sardinian wetlands are severely threatened by anthropic activities and ongoing climate change, making the condition of the associated avifauna critical. We (a) inventoried the avian metacommunity of the largest coastal wetlands in Sardinia during the summer period, (b) investigated the metacommunity structure, (c) quantified the effects of wetland attributes on avian diversity at species and guild level and (d) predicted future changes in species composition of this metacommunity. We recorded 60 bird species (of which 21 belonged to Annex I of the Birds Directive). The metacommunity structure resulted was significantly nested and non‐modular. Salinity negatively affected the presence of 48 species out of 60, followed by tourism pressure (44 species), wetland isolation (42 species) and water discharges (36 species). The mean water level resulting from artificial regulation for anthropic activities was too high for 63% of the species, which disadvantaged primarily small waders, species feeding on invertebrates and trans‐Saharan migrants. In addition, water‐level fluctuations (that would favour avian diversity) were prevented by artificial regulation during the summer period in many wetlands, producing further negative effects on the avifauna. We found 45% of the recorded bird species at risk of disappearance from this avian metacommunity. Synthesis and applications. Our study indicates that, as things stand, the avian metacommunity of the Sardinian wetlands is destined to experience reductions in the short term and mid‐term. This decline will be accelerated by increased saltwater intrusions due to sea‐level rise. Nevertheless, the nested and non‐modular structure of this avian metacommunity would allow for pro‐active conservation measures (e.g. restriction for tourism activities, construction of artificial dune cordons to minimize saltwater intrusions, water‐level regulation that keeps into account also the ecological requirements of waterbird species) to counteract the effects of current and future threats.

Elevation-based probabilistic mapping of irregularly flooded wetlands along the northern Gulf of Mexico coast

Irregularly flooded wetlands are found above the mean high water tidal datum and are exposed to tides and saltwater less frequently than daily. These wetlands provide important ecosystem services, such as providing habitat for fish and wildlife, enhancing water quality, ameliorating flooding impacts, supporting coastal food webs, and protecting upslope areas from erosion. Mapping irregularly flooded wetlands is challenging given their expansive coverage and dynamic nature. Furthermore, coastal wetlands are expected to change over the coming century due to sea-level rise and changes in the frequency and intensity of extreme storms. Consequently, coastal managers need baseline information on the spatial distribution of wetlands along with efficient and repeatable methods for observing changes. In this study, we used coastal wetlands from existing land use land cover data, best available lidar-derived digital elevation models, and Monte Carlo simulations to incorporate elevation uncertainty to create a probabilistic map of irregularly flooded wetlands along the northern Gulf of Mexico coast (USA). Our approach integrated findings from a review of coastal wetland elevation error in lidar datasets and an analysis of spatial autocorrelations of wetland elevation. We found a positive correlation (r = 0.563, p < 0.0001) when comparing the probability estimated from a digital elevation model and in situ elevation observations. The differences in probability had a mean bias error of −0.04 (i.e., digital elevation model-based probability tends to be slightly lower), a mean absolute error of 0.20, and a root mean square error of 0.26. Beyond this overall validation, we explored error metrics for land cover classes and lidar collection details. To quantify areal coverage of the probabilistic output, we classified the probability values into equal bins using an interval of 0.33. The areal coverage of the lowest probability bin (“unlikely”; probability ≤0.33) was separated into the upper and lower portions of the irregularly flooded wetland zone. Of the coastal wetlands along the northern Gulf of Mexico coast about 38% were classified as unlikely and low with the greatest coverage in south Louisiana and the Everglades and around 33% were classified as unlikely and high with the greatest coverage in the Everglades and Texas. The relative coverage within the highest probability bin (“likely”; probability >0.66) covered around 13%, with the greatest coverage in south Florida, south Louisiana, and Texas. The framework developed in this study can be transferred to other coastal wetland areas and updated to observe changes with sea-level rise.

Quantitative Responses of Active Ammonia-Oxidizing Archaea and Bacteria to the Biological and Abiotic Factors Across Functional gene Distribution in Coastal Wetlands

Quantitative Responses of Active Ammonia-Oxidizing Archaea and Bacteria to the Biological and Abiotic Factors Across Functional gene Distribution in Coastal Wetlands

A baseline study of polycyclic aromatic hydrocarbons distribution, source and ecological risk in Zhanjiang mangrove wetlands, South China

Polycyclic aromatic hydrocarbons (PAHs) are widespread environmental contaminants and pose a severe threat to human health. Here, 38 surface sediment samples collected from the Gaoqiao mangrove wetland in Zhanjiang, south China, were analyzed to determine 16 Environmental Protection Agency (EPA) priority PAHs. Total PAHs concentrations ranged from 33.5 µg/kg to 404.8 µg/kg with an average of 147.7 ± 77.7 µg/kg, inferring a moderate pollution level. Three and four-ring compounds dominated the PAHs composition patterns. Significant positive correlations were observed between the PAHs and the physicochemical properties of the sediments. According to the characteristic molecular ratio method, PAHs in sediments were mainly derived from combustion sources, including the incomplete combustion of liquid fossil fuels, grass, wood, and coal. The result based on the PMF model indicates that the primary combustion sources of PAHs are coal combustion, diesel-powered vehicles, biomass combustion and gasoline-powered vehicles, with a share of 39.01%, 25.21%, 12.72% and 10.48%, respectively. The petrogenic source contributes 12.58% PAHs to the sediments. The mean effects range median quotient (m-ERM-Q) and toxic equivalent method (TEQ) indicate a low comprehensive ecological risk of PAHs in the study area. Still, the evaluation results of effects range low (ERL) suggest that PAHs in the sediment would occasionally have adverse biological effects. Therefore, this situation demands attention and calls for protection strategies in the processes of urbanization and industrialization in south China.

Evaluation of wetland CH4in the Joint UK Land Environment Simulator (JULES) land surface model using satellite observations

Abstract. Wetlands are the largest natural source of methane. The ability to model the emissions of methane from natural wetlands accurately is critical to our understanding of the global methane budget and how it may change under future climate scenarios. The simulation of wetland methane emissions involves a complicated system of meteorological drivers coupled to hydrological and biogeochemical processes. The Joint UK Land Environment Simulator (JULES) is a process-based land surface model that underpins the UK Earth System Model (UKESM) and is capable of generating estimates of wetland methane emissions. In this study, we use GOSAT satellite observations of atmospheric methane along with the TOMCAT global 3-D chemistry transport model to evaluate the performance of JULES in reproducing the seasonal cycle of methane over a wide range of tropical wetlands. By using an ensemble of JULES simulations with differing input data and process configurations, we investigate the relative importance of the meteorological driving data, the vegetation, the temperature dependency of wetland methane production and the wetland extent. We find that JULES typically performs well in replicating the observed methane seasonal cycle. We calculate correlation coefficients to the observed seasonal cycle of between 0.58 and 0.88 for most regions; however, the seasonal cycle amplitude is typically underestimated (by between 1.8 and 19.5 ppb). This level of performance is comparable to that typically provided by state-of-the-art data-driven wetland CH4 emission inventories. The meteorological driving data are found to be the most significant factor in determining the ensemble performance, with temperature dependency and vegetation having moderate effects. We find that neither wetland extent configuration outperforms the other, but this does lead to poor performance in some regions. We focus in detail on three African wetland regions (Sudd, Southern Africa and Congo) where we find the performance of JULES to be poor and explore the reasons for this in detail. We find that neither wetland extent configuration used is sufficient in representing the wetland distribution in these regions (underestimating the wetland seasonal cycle amplitude by 11.1, 19.5 and 10.1 ppb respectively, with correlation coefficients of 0.23, 0.01 and 0.31). We employ the Catchment-based Macro-scale Floodplain (CaMa-Flood) model to explicitly represent river and floodplain water dynamics and find that these JULES-CaMa-Flood simulations are capable of providing a wetland extent that is more consistent with observations in this regions, highlighting this as an important area for future model development.

Classification, Distribution, Features, Biodiversity and Functions of Wetlands: A Review

Wetlands include a wide variety of habitats such as marshes, peatlands, floodplains, rivers and lakes and coastal areas such as salt marshes, mangroves and seagrass beds, but also coral reefs and other marine areas no deeper than 6 m at low tide, as well as human-made wetlands such as paddy lands, waste-water treatment ponds and reservoirs. According to Ramsar convention the wetlands are classified as three types viz., coastal/marine wetlands, inland wetlands and human made wetlands. According to UNCC, the estimated wetland cover of world is more than 1210 Million hectares and in that 13-18% are on the Ramsar List of Wetlands of International Importance, which are protected sites. In India 49 major wetland sites) are recognized as Ramsar sites of international importance. India has a variety of wetland ecosystem that support diverse and unique habitats because of diverse climatic condition and it is one amongst the 17 mega diverse countries. Total wetland area of Tamil Nadu is 9.02 lakh ha which is 6.92% of the geographic area and out of them Kancheepuram district is having highest total wetland area of about 8.91%.

Mountain Wetland Distributions Controlled by Landforms and Snow Depth at Quaternary Volcanoes in Northeastern Japan: Assessing the Vulnerability of Wetlands to Reduced Snowfall

Mountain Wetland Distributions Controlled by Landforms and Snow Depth at Quaternary Volcanoes in Northeastern Japan: Assessing the Vulnerability of Wetlands to Reduced Snowfall

The race for space: Modelling the landward migration of coastal wetlands under sea level rise at regional scale

Globally, sea-level rise (SLR) is a major environmental challenge for coastal ecosystems. Of particular concern are the impacts on intertidal wetlands, the loss of which would have detrimental consequences for both human and ecological communities. On the south-east Australian coast, case studies suggest that the future of intertidal wetlands will greatly depend on landward migration as surface accretion may not keep up with the predicted SLR in many estuaries. However, due to differences in geomorphological settings and land-use, estuaries vary in their capacity to accommodate lateral migration. Regional scale assessment of the lateral accommodation space is therefore critical for pre-emptive planning to conserve these valuable coastal ecosystems. In this study, we analysed wetland lateral accommodation space distribution within 110 estuaries under three SLR scenarios and three land management options on the New South Wales coast, south-east Australia. From the wetland distribution predictions, we calculated and mapped the lateral accommodation space in each estuary associated with each sea level and land use scenario. We further investigated the relationships between wetland migration capacity, intertidal hypsometry represented by elevation skewness, and estuary type within a Bayesian analysis framework. Our results showed that while a few large riverine estuaries dominated the state's total accommodation space, saline wetlands were at risk of disappearing from most intermittently closed-open estuaries if they cannot vertically accrete at the pace of SLR. These distinct responses to SLR are due to different elevation distributions. Furthermore, our assessment of land use adaptation options suggested that the promotion of landward migration without impairing other important ecosystems could be achieved by making low intensity land uses available within several riverine estuaries and barrier (open entrance) estuaries. Through identifying migration opportunities and barriers, the findings of the study could support regional scale adaptation strategies to ensure the sustainability of wetland-associated ecosystem goods and services.

Analysis of long-term wetland variations in China using land use/land cover dataset derived from Landsat images

Wetlands are one of the most productive ecosystems on earth and play an important role in maintaining ecological balance and regulating climate. In this paper, 30 m resolution land use/land cover (LULC) data (2000, 2005, 2010, 2015, 2020) were employed to analyze the characteristics of spatial and temporal changes in the distribution of wetlands in China and their evolution patterns in the last two decades. The results indicated that the total area of wetlands in China showed an increasing trend during 2000–2020. During the study period, provinces with more increase in wetland area were concentrated in Qinghai Province, Tibet Autonomous Region and Xinjiang Uygur Autonomous Region. And the provinces with more reduction in wetland area were mainly in Inner Mongolia Autonomous Region. The analysis of wetland change driving mechanism by introducing PLS-SEM model and GWR model found that good climate conditions as well as agricultural and economic conditions are favorable for wetland conservation in 2000–2020, while accelerated urbanization and population growth showed negative effects on wetland change. The spatial distribution pattern of wetland and NPP (Net Primary Production) changes showed spatial consistency in the extent of NPP changes and wetland transfer. The results of this study are intended to provide a basis for wetland conservation, rational use of wetland resources and scientific restoration in China.

Analysis of Spatial and Temporal Variability of Global Wetlands during the Last 20 Years Using GlobeLand30 Data

Knowing the distributions and changes in global wetlands and their conversion to other land cover types could facilitate our understanding of wetland development, causes of variations, and decision-making for restoration and protection. This study aimed to comprehensively analyze the changes in wetland distributions at global, continental, typical regional, and national scales and the conversions between wetlands and other land cover types in the last 20 years. This study used GlobeLand30 (GL30) data with a 30 m resolution for the years 2000, 2010, and 2020. The main findings of this study are as follows: (1) the area of wetlands continued to increase globally from 2000 to 2020, with a total increase of approximately 4%. Wetland changes from 2010 to 2020 were more significant than those from 2000 to 2010. The regions with significant wetland changes were mainly in the north middle- and high-latitude, and the equatorial middle- and low-latitude, and Oceania and North America were the continents with the highest increase and decrease, respectively; (2) the major conversion of wetlands was mainly natural land cover types, including forest, grassland, water, and tundra, and there were minor conversions due to human activities, including the conversion of wetlands to cropland (~4600 km2) and artificial land (~3400 km2); (3) from 2000 to 2020, the increase in global wetlands was uneven, while the decrease was nearly even at a national scale. Australia had the highest increase due to the conversions from grass, bare land, and water, and Canada had the highest decrease due to the conversion into tundra and forest. The analysis results could more comprehensively characterize the distributions and changes of global wetlands, which may provide basic information and knowledge for related research work and policymaking.

The Diurnal Variation Characteristics of Latent Heat Flux under Different Underlying Surfaces and Analysis of Its Drivers in The Middle Reaches of the Heihe River

The Latent Heat Flux (LE) is an important component of surface water heat transfer and hydrological cycle, and monitoring it is of great value for water resource management and crop water demand estimation. The Heihe River Basin has complex topography, which ensures better variable control in LE analysis. In this paper, the time series analysis and statistics of LE under different underlying surface conditions in summer were carried out by using the eddy correlation observation data in the Heihe River Basin, and the regression factors were analyzed. The results show that when the underlying surface types are greatly different, there are obvious differences in the daily distribution of LE, the daily variation trend of LE and the influencing factors. The range of diurnal distribution of LE in dune, Gobi and desert from −50 W/m2 to 100 W/m2. The diurnal LE distribution of vegetable fields, cornfields and wetlands were about 55% concentrated between −50 W/m2 and 100 W/m2. Temperature and carbon dioxide concentration (CO2) are the dominant factors affecting latent heat flux. Further analysis of temperature and CO2 is carried out by stepwise regression analysis, and multiple regression models are established. In terms of correlation and confidence, the results are better than the single factor fitting, which can better reflect the synergistic effect of temperature and CO2 on LE.

Characteristics and influencing factors of metal distribution in different wetlands of the Liaohe Delta, Northeastern China

Metal distribution in different wetlands under the complex influence of natural and anthropogenic activities in the Liaohe Delta was analyzed to better protect and manage delta areas. Ninety-six soil samples were collected from six wetland types, and the levels, depth distributions, risk, and influencing factors of metals (i.e., As, Cd, Cr, Ni, Cu, Pb, Zn, Mn, Al, and Fe) were analyzed. The results showed that the concentrations of As, Cd, Cr, Ni, Zn, and Al in more than 70% of the soil samples were higher than the background value of Liaoning Province. The concentration of As decreased with distance from the estuary, while that of Cr was higher downstream of Liaohe. The spatial distributions of Cd, Ni, Cu, Pb, and Zn were similar. The concentrations of most metals in the topsoil were higher than those in the subsoil. According to the Nemerow pollution index, higher pollution was observed in the area far away from the Liaohe River and Bohai Sea for the topsoil layer, while for the subsoil layers, higher pollution was observed in the area near the Liaohe estuary. The correlation analysis showed that the wetland type was clearly correlated with Cd, Cu, Al, and S. The concentrations of Cd, Pb, Zn, C, N, P, and S and the electrical conductivity obviously decreased with soil depth, while the concentration of Mn was positively correlated with soil depth. Mn was negatively correlated with total organic carbon (TOC), total nitrogen (TN), and total phosphorus (TP), whereas Cd, Pb, and Zn showed positive correlation with TOC, TN, and total sulfur (TS). The general linear model indicated that wetland type had a significant effect on As, Cd, Ni, Cu, Pb, Zn, Al, and Fe (p&amp;lt; 0.01), while depth had a significant effect on Cd, Cr, and Pb (p&amp;lt; 0.01). The findings of this work will contribute to pollution control and ecosystem health conservation of the Liaohe Delta.

Mapping African wetlands for 2020 using multiple spectral, geo-ecological features and Google Earth Engine

Wetlands provide numerous ecosystem services essential for biodiversity conservation, climate change mitigation, and human well-being. Nevertheless, there are still no complete and uniform wetland maps providing information on the location, distribution, size, and changing status of wetlands in Africa. In this study, we used 130,000 Landsat satellite images and 270,000 sampling points evenly distributed across Africa to classify wetlands with a random forest classifier based on the Google Earth Engine (GEE) cloud platform. This resulted in the first systematic and comprehensive map of existing wetlands in Africa that quantified the area and distribution of these wetlands at a spatial resolution of 30 m, with an overall wetland producer accuracy of 90.22 % and user accuracy of 95.74 %. To address the seasonal variation in African wetlands, we used a dynamic threshold segmentation method based on the Otsu method, which can extract the extent of wetlands under different periods more accurately based on Landsat time series and African phenology data. Our results show that the total African existing wetlands extent from 2019 to 2021 (here in 2020), was approximately 1,341,500 km2, excluding shallow marine waters, comprises 3.98 % of Africa's total land area. Of these wetlands, inland wetlands account for 81 %, and coastal wetlands account for 19 %. The wetlands in Africa were symmetrically distributed around the equator and decreased with increasing latitude, accounting for 97 % of the total wetland area being within the 20°N and 20°S latitudes. African marshes were highly dynamic, expanding by 92.22 % from the dry to wet season. Our study demonstrates the substantial potential of large data samples, multiple wetland classification features (spectral-temporal, topographic, and hydrological features), and random forest classification in GEE for large-scale wetland mapping. The resulting wetland maps provide new baseline data for large-scale monitoring of seasonal dynamics and long-term trends in African wetlands.

Automated extraction of map symbology from nineteenth century topographical maps by convolutional neural networks for understanding long-term changes in the extent and distribution of wetlands

Automated extraction of map symbology from nineteenth century topographical maps by convolutional neural networks for understanding long-term changes in the extent and distribution of wetlands