Wetlands In China Research Articles

Estimation of Soil Organic Carbon Storage in Palustrine Wetlands, China.

Wetlands regulate the balance of global organic carbon. Small changes in the carbon stocks of wetland ecosystem play a crucial role in the regional soil carbon cycle. However, an accurate estimation of carbon stocks is still be debated for China’s wetlands ecosystem due to the limitation of data collection and methodology. Here, we investigate the soil organic carbon (SOC) storage in a 1-m depth in China’s palustrine wetlands. A total of 1383 sample data were collected from palustrine wetlands in China. The data sources are divided into three parts, respectively, data collection from published literature, data from books, and actual measurement data of sample points. The results demonstrate that there is considerable SOC storage in China’s palustrine wetlands (9.945 Pg C), primarily abundant in the northeast, northwest arid and semi-arid as well as Qinghai-Tibet Plateau regions. The SOC density in per unit area soil was higher in the wetland area of northeast, southwest and Qinghai-Tibet plateau. Within China terrestrial scale, the temperature and precipitation differences caused by latitude were the main environmental factors affecting the organic carbon content. Furthermore, except for the southeast and south wetland region, SOC content decreased with depth.

Dynamics of bacterioplankton community structure in response to seasonal hydrological disturbances in Poyang Lake, the largest wetland in China.

Bacterioplankton communities play a critical role in biogeochemical cycling in freshwater environments, but how the hydrological regime impacts the assembly of bacterioplankton communities remains unclear. This study examined differences in bacterioplankton community structures between wet (July and September) and dry (October and November) seasons in two consecutive years (2016 and 2017) in Poyang Lake, the largest seasonal freshwater lake in China. Our results revealed no overall difference in bacterioplankton compositions and their predicted functions among spatially separated sites. However, bacterioplankton communities did show significant temporal shifts, mainly between samples in November and other months. Transitions from the dry to the wet season were observed in October in both sampling years. Meanwhile, insignificant spatial but significant temporal differences were also found for physicochemical variables. Moreover, redundancy analysis indicates that compared with water depth, water temperature was found to better explain changes in the bacterioplankton community. These findings consistently indicate that the bacterioplankton community in Poyang Lake is relatively less sensitive to annual hydrology shifts than water temperature and nutrient conditions.

Quantifying expansion and removal of Spartina alterniflora on Chongming island, China, using time series Landsat images during 1995–2018

The rampant encroachment of Spartina alterniflora into coastal wetlands of China over the past decades has adversely affected both coastal ecosystems and socio-economic systems. However, there are no annual or multi-year epoch maps of Spartina saltmarsh in China, which hinders our understanding and management of Spartina invasion. In this study, we selected Chongming island, China, where Spartina saltmarsh had expanded rapidly since its introduction in the 1990s. We investigated phenology of Spartina, Phragmites and Scirpus saltmarshes, and the time series vegetation indices derived from Landsat images showed that Spartina saltmarsh did not green-up in April–May and stayed green in December–January, which differed from the phenology of Phragmites and Scirpus saltmarshes. We developed a pixel- and phenology-based algorithm that used time series Landsat data to identify and map Spartina saltmarsh, and we applied it to quantify the temporal dynamics (expansion and removal) of Spartina saltmarsh on Chongming island during 1995–2018. The resultant maps showed that Spartina saltmarsh area on Chongming island increased from ~4 ha in 1995 to ~2067 ha in 2012 but dropped substantially to ~729 ha in 2016 after a large-scale ecological engineering project (US$ 186 million) was started to remove Spartina during 2013–2016. Chongming island still had ~1315 ha Spartina saltmarsh in 2018, and majority of it was distributed outside the Chongming Dongtan National Nature Reserve, which could serve as the sources for reinvasion in the near future. This study demonstrates the feasibility of using time series Landsat images, pixel- and phenology-based algorithm, and GEE platform to identify and map Spartina saltmarsh over years in the region, which is useful to the management of invasive plants in coastal wetlands.

Driving Forces Analysis of Non-structural Carbohydrates for Phragmites australis in Different Habitats of Inland River Wetland

Habitat variation in non-structural carbohydrates (NSC) reflects the resource allocation trade-offs for clonal plants, and its driving force analysis embodies the ecological adaptation strategy of clonal plants to heterogeneous environments. In this paper, the reed (Phragmites australis) in the northwestern inland wetlands of China, as a typical example of clonal plants, was used as the research object. The content and distribution of NSC in reeds and their response characteristics to soil environmental factors were compared under three different environmental gradients with wet, salt marsh and desert habitats. The results showed: (1) the content of NSC and starch gradually increased and the content of soluble sugar gradually decreased from wetland to desert habitats, and the ratio of soluble sugar to starch increased significantly (p < 0.05), which demonstrated that reeds converted more NSC into starch to adapt to harsh environments as the environment changed. (2) Reeds tended to invest more NSC in underground architectures to achieve survival and growth with the increase in environmental stress, providing the evidence that NSC were transferred from leaf to rhizome, and root, stem and rhizome received more soluble sugar investment. The ratio of soluble sugar to starch of reed stem and rhizome increased significantly with the increasing content of soluble sugar and the decreasing content of starch, and more starch was converted into soluble sugar to resist the harsh environment. (3) Soil water, soil bulk density and salinity were the main driving forces for the NSC content and the distribution characteristics of reeds using the relative importance analysis. The study results clarified the habitat variation law, and the main environmental driving forces of NSC for reeds in inland river wetlands, which provided the significant references for enriching the ecology research theory of clonal plants and protection measures in the fragile and sensitive wetlands in arid regions.

Tracking Changing Evidences of Water in Wetland Using the Satellite Long-Term Observations from 1984 to 2017

Wetlands have been degrading and reducing under the influences of human activity and climate change. Landsat long-term observations can help us better track the changing evidences of wetland habitats that would be valuable for guiding the restoration and conservation of wetland. In this study, we demonstrated the results of tracking the changing evidence of wetland habitats using Landsat observations from 1984 to 2017 through the case study of Baiyangdian wetland in China. We extracted the open water and classified the wetland habitats using collected 190 scenes from Landsat observations. As a result, we found that the yearly variations of wetland present phasic changes in three phases: 1988–1998, 1999–2011 and 2013–2017. The landscape of wetland habitats presented during 1989–1999 mostly show us the natural spatial pattern with less human disturbance traces compared to that during 2013–2017. The water environment, moreover, changed for the better after the 2010s, which indicated the encouraging effects of the environmental restoration project implemented from the year 2010. The current landscapes of wetland habitats, however, present lots of linear belts that are blocking the water cycles and ecological channels of aquatic plants and animals in the wetland. The areas in the northwestern wing and around the northeastern edge of the wetland are changing to be drier due to cropping activities and are at risk of wetland loss. These historical changing evidences could be a guideline for planning and designing restoration for the wetland.

Analyzing Water Dynamics Based on Sentinel-1 Time Series—a Study for Dongting Lake Wetlands in China

In China, freshwater is an increasingly scarce resource and wetlands are under great pressure. This study focuses on China’s second largest freshwater lake in the middle reaches of the Yangtze River—the Dongting Lake—and its surrounding wetlands, which are declared a protected Ramsar site. The Dongting Lake area is also a research region of focus within the Sino-European Dragon Programme, aiming for the international collaboration of Earth Observation researchers. ESA’s Copernicus Programme enables comprehensive monitoring with area-wide coverage, which is especially advantageous for large wetlands that are difficult to access during floods. The first year completely covered by Sentinel-1 SAR satellite data was 2016, which is used here to focus on Dongting Lake’s wetland dynamics. The well-established, threshold-based approach and the high spatio-temporal resolution of Sentinel-1 imagery enabled the generation of monthly surface water maps and the analysis of the inundation frequency at a 10 m resolution. The maximum extent of the Dongting Lake derived from Sentinel-1 occurred in July 2016, at 2465 km2, indicating an extreme flood year. The minimum size of the lake was detected in October, at 1331 km2. Time series analysis reveals detailed inundation patterns and small-scale structures within the lake that were not known from previous studies. Sentinel-1 also proves to be capable of mapping the wetland management practices for Dongting Lake polders and dykes. For validation, the lake extent and inundation duration derived from the Sentinel-1 data were compared with excerpts from the Global WaterPack (frequently derived by the German Aerospace Center, DLR), high-resolution optical data, and in situ water level data, which showed very good agreement for the period studied. The mean monthly extent of the lake in 2016 from Sentinel-1 was 1798 km2, which is consistent with the Global WaterPack, deviating by only 4%. In summary, the presented analysis of the complete annual time series of the Sentinel-1 data provides information on the monthly behavior of water expansion, which is of interest and relevance to local authorities involved in water resource management tasks in the region, as well as to wetland conservationists concerned with the Ramsar site wetlands of Dongting Lake and to local researchers.

Use of aquaculture ponds by globally endangered red-crowned crane (Grus japonensis) during the wintering period in the Yancheng National Nature Reserve, a Ramsar wetland

Conversion of natural wetlands to artificial wetlands is a global phenomenon that leads to loss of natural habitats for waterbirds, while these alternative wetlands may buffer the adverse effects of natural wetlands loss by providing waterbirds with suitable habitats. Yancheng National Nature Reserve (YNNR), a Ramsar wetland in China, is the largest wintering area for the globally endangered red-crowned crane (Grus japonensis). A remarkable part of natural wetlands within the YNNR has been reclaimed into aquaculture ponds in recent decades. In order to better understand the utilization of aquaculture pond by cranes and identify beneficial management actions, we investigated the wintering crane occurrence in ponds and quantified pond characteristics as mainly influence factors from November to March in 2017–2018 and 2018–2019. A total of 198 ponds were measured (91 in 2017–2018 and 107 in 2018–2019), out of which 42 ponds were found to be used by 48 groups of cranes (16 in 2017–2018 and 32 in 2018–2019). Family groups with 2–4 individuals of cranes were mostly encountered (91.7%) of all the group types. Wintering crane abundance in the aquaculture ponds was higher in 2018–2019 (105 individuals) than that in 2017–2018 (59 individuals). Five factors including water depth, species abundance, species richness, structures and distance to road were identified to influence use of ponds by cranes. However, crane occurrence was significantly associated with only water depth. This study recognized aquaculture ponds as a potential habitat for red-crowned crane. Efforts should be channeled into the sustainable development and maintenance of aquaculture ponds. More specifically, we recommended appropriate management practices to benefit wintering cranes by sequential harvesting of aquaculture ponds, maintaining aquaculture ponds in the buffer zone and keeping the water at a low level.

Effects of dam impoundment on the soil seed bank in a plateau wetland of China

Dam impoundment, which rapidly changes hydrologic regimes and greatly alters aquatic environments, plays a critical role in the seed germination and seedling growth of wetland plants, especially influencing their seed banks. In this study, a soil seed bank experiment was carried out along a water level gradient for the Lake Lashi wetland in the Northwest Yunnan Plateau of China. The objectives of this study were to determine the effect, driver and dynamic mechanism of dam impoundment on the soil seed bank of plateau wetlands using partial least squares (PLS) regression and chaotic dynamic methods. The results showed that the soil seed bank had significant differences in seed density, species composition, and water ecotype of the plant species between the flood zone (perennially flooded area, seasonally flooded area, and flood plain area) and nonflood zone (control area) in the plateau wetland. The seed bank density was obviously lower in the perennially flooded area and higher in the seasonally flooded area and flood plain area, with values that were 39.88%, 153.53%, and 146.47% that of the control area, respectively. After dam impoundment, the number of plant species gradually increased; however, the dominance of the dominant species became less obvious, and the species diversity indices decreased significantly, e.g., by 15.47% for the Simpson diversity index and 72.39% for the Shannon Wiener diversity index. Our study showed that dam impoundment has made the Lake Lashi wetland complex chaotic ecosystem switch between order and disorder through self-organization and that the species composition of the soil seed bank continuously experienced self-adaptation. These results provide a reference for scientific evaluations of the effects of dam impoundment on wetland ecosystems and provide guidance for the protection and management of plateau wetland ecosystems.

Multi-temporal characterization of land surface temperature and its relationships with normalized difference vegetation index and soil moisture content in the Yellow River Delta, China

Land surface temperature (LST) is an important indicator of resource and environment changes in coastal wetlands and exhibits considerable spatiotemporal variations under multiple influences of intensive land–sea interaction and various human activities. Revealing the multi-temporal characteristics of LST and its relationships with normalized difference vegetation index (NDVI) and soil moisture content (MC) in coastal wetlands is important for identifying the LST variations under complex factors, the heat effects of different human exploitations, and the corresponding changes in vegetation and soil water conditions. The Yellow River Delta, a typical and important coastal wetland in China, was selected to demonstrate the study. Remote sensing and field investigation served as the data source, and the LST spatiotemporal patterns and their intrinsic correlations with NDVI and MC in the last 30 years and across different seasons were analyzed. Results indicated that LST spatial distributions varied in different years and seasons. In 1987, LST was low along the Yellow River and high in alongshore areas; in 2016, LST was distinctly low in most of the alongshore areas and high in urban and industrial areas. Across seasons, LST differences between alongshore and inner areas were more distinct in spring that in the other seasons, and LST in urban and industrial areas was especially higher than that in other areas in summer. Among different land covers, salt pond generated cool island effect, whereas urban and industrial areas generated heat island effect. Significant correlations were observed between LST and NDVI at regional scale and among LST, NDVI, and MC at site scale, and their relationships varied in different land cover types across different times. The changes in shorelines, land covers, and vegetation and soil conditions jointly determined the LST spatiotemporal patterns, and human activity has been the main driving factor.

Seasonal and interannual variability of surface energy fluxes and evapotranspiration over a subalpine horizontal flow wetland in China

Jiuzhaigou Valley, a subalpine river valley located in the transition zone between the Tibetan Plateau and the Sichuan Basin, is characterized by fragile ecosystems, strong climate change, and high-intensity human activities which might have changed the energy and water exchange of the wetlands. However, little is known about the seasonal and interannual variability of the surface fluxes and their driving forces in these wetlands owing to the lack of long-term continuous observations. We studied the dynamics of surface fluxes and their controlling factors based on the five-year data collected from July 2013 to April 2019. Our results showed that: (1) the dominant turbulent flux in this ecosystem shifted from sensible heat flux (H) in the frozen period to latent heat flux (LE) in the non-frozen period, especially in the growth period. This fluctuation, which was also reflected by Bowen ratio, highlighted the seasonality of precipitation in the monsoon climate. (2) The energy partitioning with each year was similar across years: LE accounted for approximately 58% of the net radiation, while H accounted for 41% and ground heat flux accounted for 1%. (3) Although the annual precipitation fluctuated between 870 mm and 1089 mm, the interannual fluctuations in evapotranspiration (ET) were less than 41 mm. (4) The wetland ET was predominantly driven by atmospheric demand and was limited to some extent by physiological factors. We then concluded that official management efforts by the local government to increase vegetation cover as well as climate change may lead to an increase in wetland ET, and this change will likely affect local hydrology, climate and the existence of this unique hydrological landscape.

Spatial Patterns and Spatial Autocorrelations of Wetland Changes in China During 2003-2013

Wetlands play an important role in maintaining ecosystem functions. Wetlands in China have suffered intensive human disturbance, especially before 2000, resulting in great losses and degradation. Therefore, two national wetland resource surveys were carried out by the Chinese government during 1998-2003 and 2008-2013 to determine the status of wetlands, understand their dynamics, and provide substantial data that can aid scientific wetland conservation. Based on the survey data, the spatial pattern and spatial autocorrelation were explored using the standard deviation ellipse as well as global and local spatial autocorrelation statistics. GIS mapping was employed to display the results via the visualization of the spatial patterns and relationships. Results indicate that:① Changes in the wetlands of China are significant and exhibit obvious regional differences. The center of the ellipse of the total wetlands has moved to the west, and the degree of spatial differentiation between natural wetlands and artificial wetlands is increasing. There is no significant spatial autocorrelation for changes in artificial wetlands. ② The changes in natural wetlands are significantly spatially autocorrelated and clustered, which are identified by global Moran's I and local Moran's I. The hotspots of natural wetland change are concentrated primarily in Qinghai, Tibet, and Sichuan. The individual hotspot is in Inner Mongolia and the cold spot is in Henan. The difference in spatial autocorrelation between natural and artificial wetland changes indicates that natural wetland changes have shown spatial continuity, while artificial wetland changes have shown strong spatial randomness. ③ Some useful spatial associations are used to delineate wetland conservation effects. Then, three major or five minor effective protection management regions are identified. Wetland conservation efforts should be continuously strengthened and improved, especially in the middle-lower Yangtze River region of central China. The use of Moran statistics helps to reveal spatial autocorrelation and identify the conservation effects in wetland changes, which can provide a basis for decision-making in regional wetland conservation and management systems.

Higher fluxes of C, N and P in plant/soil cycles associated with plant invasion in a subtropical estuarine wetland in China

Invasion of plants in wetland ecosystems is often associated with changes in litter decomposition and in nutrient use, uptake and cycling between invasive and native plants. We studied litter decomposition rates, N and P release and elemental composition and stoichiometry during the invasion of Phragmites australis and Spartina alterniflora into native Cyperus malaccensis wetlands in the Minjiang River estuary (China). Aboveground litter in mono-specific stands decomposed faster for Cyperus malaccensis than for Spartina alterniflora and for Phragmites australis. Cyperus malaccensis litter decomposed slower under the stands of both invasive species. In contrast, the litter of both invasive species decomposed faster under Cyperus malaccesis stands. We observed that the invasion of these species was associated with an increased rate of aboveground litter decomposition and large absolute amounts of C, N and P released from the litter when litter from invasive species was mixed with that of native species. Our results suggest that the large nutrient release from litter during early stages of the invasion favored invasive species with larger size and higher nutrient-uptake capacity than the native species.

Complete Genome Sequence Analysis of the Cold-active Siphoviridae Bacteriophage from Pseudomonas fluorescens

Phages are considered the most abundant and diverse biological entities on Earth. Although many phages have been isolated, most of this diversity remains completely unexplored. Recent advances in genome sequencing, however, have provided unprecedented glimpses into the virosphere. The lytic cold-active Siphoviridae bacteriophage VW6S, infecting the host Pseudomonas fluorescens W-6, was isolated from the Napahai plateau wetland in China. The newly sequenced phage VW6S contained double-stranded DNA with a genome size of 37,917 bp, an overall GC content of 56.90% and 52 open reading frames (ORFs). The genome was organized into several modules containing genes for packaging, structural proteins, replication/transcription, and cell lysis. The sequence contained 16 transcription terminators, no tRNAs. The lysis cassette of VW6S consisted of 4 proteins (holin protein, lysin protein and 2 putative spanins). This is the first report on cold-active SiphoviridaePseudomonas fluorescens bacteriophage genome sequencing.

Speciation and migration of heavy metals in sediment cores of urban wetland: bioavailability and risks.

To examine the status and risk of heavy metal pollution in an urban wetland in China, the distribution and speciation of chromium (Cr) and other metals (Cd, Cu, Pb, and Zn) were examined. We investigated the impact of three major land uses (residential and industrial (RI), orange plantation (OP), and mixed OP and RI (OPRI)) on the heavy metal characteristics using sediment cores (0-60cm below water/sediment interface) collected in Sanyang Wetland, China. It was found that all the metals (Cr, Cd, Cu, Pb, and Zn) had lower concentrations in the top layers but higher contents in the bottom layers of sediments. Species of metals in sediments were dominated by their secondary phase (i.e., exchangeable and carbonate bound, Fe-Mn bound and organic bound) with relatively low contents of primary phase (i.e., residual form), except for Cr in RI affected river sediments that had a relatively high content of primary phase (20.97-36.07%). The ratio of secondary phase to primary phase (RSP) and risk assessment code (RAC) methods were applied to assess environmental risk. The results implied that the metal mobility and bioavailability could significantly cause urban wetland environmental quality decline, and thus enhanced strategies should be required to target the capture and removal of metals.

Exotic Spartina alterniflora invasion changes temporal dynamics and composition of spider community in a salt marsh of Yangtze Estuary, China

Spiders play important roles in regulating arthropod populations in terrestrial ecosystems. However, the impact of exotic plant invasion on the spider community is still poorly understood, especially in salt marsh systems, which are especially susceptible to this invasion. The exotic Spartina alterniflora has widely invaded the coastal wetlands of China, and this study aims to evaluate such effects on the spider diversity and community composition in the Jiuduansha wetland of Yangtze Estuary. To do this, for a one-year period, we have collected spiders from the marsh surface (SMS) as well as spiders from the plant foliage surface (SPFS) respectively in S. alterniflora-dominated marshes (SDM) and native Phragmites australis-dominated marshes (PDM) in Jiuduansha. Results showed S. alterniflora invasion generally had a positive effect on the biodiversities of both SMS and SPFS, but actually changed the seasonal fluctuation of species richness and abundance of SMS. According to principal component analysis, community compositions of SMS and SPFS were different between SDM and PDM. Specially, SMS community composition exhibited more obvious temporal patterns in PDM than in SDM. The Bray-Curtis dissimilarity index between SDM and PDM varied more between sampling months in SMS than in SPFS. Based on canonical correspondence analysis, tidal elevation significantly affected community compositions of SMS and SPFS in SDM. In contrast, for spiders in PDM, tidal elevation had a weakened effect on SMS community composition. This may be explained by the different distribution of the two plants at high and low tidal levels. In summary, our study suggests that S. alterniflora invasion has changed the temporal dynamic and composition of the spider community in the Jiuduansha wetland. In future research, it should be highlighted that variations in habitat characteristics and ecological niches of spiders are important in mediating the invasive effects of exotic plants on the native spider community.

Valuation of Wetland Ecosystem Services in National Nature Reserves in China’s Coastal Zones

Wetlands provide ecosystem services for regional development, and, thus, have considerable economic value. In this study, a combination of evaluation methods was carried out to evaluate the wetland ecosystem services provided by national nature reserves in 11 coastal provinces/municipalities in China. We constructed a literature database containing 808 observations (over 170 papers) on field-scale research for wetlands in China’s coastal zones. Using this literature database, as well as land use (LU) data, net primary productivity (NPP), and statistical data, and digital elevation model (DEM) data, we established a valuation framework and database for nine important ecosystem services of the 13 wetland types in the study area. After the large-scale academic literature review, the ordinary kriging offered by Geostatistical Analyst tools was used to interpolate the physical dimensions of the unmeasured locations. The results showed that: 1) the wetland ecosystem services in 35 national nature reserves have a total value of 33.168 billion USD/year; 2) the values of wetland ecosystem services revealed considerable spatial variability along China’s coastal zones; and 3) assessments provide additional insights into the trade-offs between different ecosystem services and wetland types. The valuation framework and database established in this study can contribute to the mapping of wetland ecosystem services in coastal zones.

National wetland mapping in China: A new product resulting from object-based and hierarchical classification of Landsat 8 OLI images

Spatially and thematically explicit information of wetlands is important to understanding ecosystem functions and services, as well as for establishment of management policy and implementation. However, accurate wetland mapping is limited due to lacking an operational classification system and an effective classification approach at a large scale. This study was aimed to map wetlands in China by developing a hybrid object-based and hierarchical classification approach (HOHC) and a new wetland classification system for remote sensing. Application of the hybrid approach and the wetland classification system to Landsat 8 Operational Land Imager data resulted in a wetland map of China with an overall classification accuracy of 95.1%. This national scale wetland map, so named CAS_Wetlands, reveals that China’s wetland area is estimated to be 451,084 ± 2014 km2, of which 70.5% is accounted by inland wetlands. Of the 14 sub-categories, inland marsh has the largest area (152,429 ± 373 km2), while coastal swamp has the smallest coverage (259 ± 15 km2). Geospatial variations in wetland areas at multiple scales indicate that China’s wetlands mostly present in Tibet, Qinghai, Inner Mongolia, Heilongjiang, and Xinjiang Provinces. This new map provides a new baseline data to establish multi-temporal and continuous datasets for China’s wetlands and biodiversity conservation.

Surface Energy Flux Changes and Budget in a Typical Coastal Reed Wetland (Liaohe Delta, China)

Jia, Q.; Zhou, L.; Yu, W.; Wang, X.; Wen, R., and Xie, Y., 2020. Surface energy flux changes and budget in a typical coastal reed wetland (Liaohe Delta, China). Journal of Coastal Research, 36(5), 1005–1012. Coconut Creek (Florida), ISSN 0749-0208.Coastal wetlands are located between the continents and oceans, and their surface energy flux changes and budget play an important role in regulating regional climate. Liaohe Delta is a typical coastal reed wetland in China. The latent heat, sensible heat, and net radiation flux of reed wetlands in Liaohe Delta were studied for four consecutive years (2012–2015) on the basis of the eddy correlation system. The average annual accumulation of latent heat flux was 1525.39 MJ m–2, with a large seasonal variation. The latent heat flux was positive, and the peak value did not exceed 320 W m–2 in the daytime. The latent heat flux increased with the increase of temperature each day. The annual average sensible heat flux was 550.96 MJ m–2, with the minimum sensible heat in June and July, and the daily average change peak did not exceed 160 W m–2. The annual net radiation accumulation was 2868.32 MJ m–2, and the net radiation in winter decreased. The maximum value of net radiation in summer reached 622 W m–2. Latent heat flux accounted for 41%–63% of solar radiation, followed by storage flux, and sensible heat flux had the lowest value. This typical reed wetland has a strong water vapor regulation ability. These results contribute to research on land surface processes in wetlands.

Mapping coastal wetlands of China using time series Landsat images in 2018 and Google Earth Engine

Coastal wetlands, composed of coastal vegetation and non-vegetated tidal flats, play critical roles in biodiversity conservation, food production, and the global economy. Coastal wetlands in China are changing quickly due to land reclamation, aquaculture, industrialization, and urbanization. However, accurate and updated maps of coastal wetlands (including vegetation and tidal flats) in China are unavailable, and the detailed spatial distribution of coastal wetlands is unknown. Here, we developed a new pixel- and phenology-based algorithm to identify and map coastal wetlands in China for 2018 using time series Landsat imagery (2798 ETM+/OLI images) and the Google Earth Engine (GEE). The resultant map had a very high overall accuracy (98%). There were 7474.6 km2 of coastal wetlands in China in 2018, which included 5379.8 km2 of tidal flats, 1856.4 km2 of deciduous wetlands, and 238.3 km2 of evergreen wetlands. Jiangsu Province had the largest area of coastal wetlands in China, followed by Shandong, Fujian, and Zhejiang Provinces. Our study demonstrates the high potential of time series Landsat images, pixel- and phenology-based algorithm, and GEE for mapping coastal wetlands at large scales. The resultant coastal wetland maps at 30-m spatial resolution serve as the most current dataset for sustainable management, ecological assessments, and conservation of coastal wetlands in China.

Effect of hydrological variation on vegetation dynamics for wintering waterfowl in China’s Poyang Lake Wetland

Poyang Lake wetland of China, with designated national nature reserves, is one of the most important habitats for waterfowl in the world. During the wintering season, it is home to various rare and endangered species with abundant plant resources. However, extensive disturbances from both global climate change and human activities, such as the construction of hydroelectric dams, have exerted severe impacts on the hydrological regime and the vegetation dynamics in this region. To evaluate the suitability of the habitat for wintering waterfowl, it is necessary to monitor the spatio-temporal changes of vegetation over the protected wetland, and explore the potential environmental driving factors of the changes during the past decades. In this study, the time-series MODIS Enhanced Vegetation Index (EVI) data from 2000 to 2018, were used to analyze the seasonal dynamics and interannual tendencies of vegetation coverage over the wintering period from October to January. The results showed that the largest monthly mean EVI generally occurred in November, and was related to the quantity of wintering waterfowl in Poyang Lake wetland. The mean EVI in November had a lagged response to both temperature and accumulated precipitation. Long-term trend analysis revealed that the average EVI of the reserve increased significantly in the winters since the new millennium. Over the past 18 years, the hydrological regime, particularly the water area, is recognized as the dominant environmental factor determining the interannual variation of EVI. From 2010 onwards there was also an increasing influence of temperature. These analyses would help in the creation of appropriate management strategies to protect the habitat of wintering waterfowl in Poyang Lake wetland.