Wetland Expansion Research Articles

Holocene pollen records from a large shallow lake in East Asia: Complexity of climate changes, environmental variations, and human activities

The lack of consecutive Holocene sedimentary records in large shallow lakes poses a significant challenge for attaining a comprehensive understanding of long-term correlations among climate and environmental changes, as well as human activity worldwide. This paper presents detailed pollen records from a typical open Lake Baiyangdian which helped to reconstruct multiple environmental processes and human activities in North China during the Holocene, and to detect the complexity of the reconstruction results. The Baiyangdian area experienced a gradual expansion of wetlands since the early Holocene which then transformed into vast delta swamps due to the Holocene transgression of the Bohai Sea. The subsequent regression resulted in the degradation of the swamps and the formation of grassland 6,500–4,500 cal yr BP. The area quickly became a shallow lake after 4,500 cal yr BP, and then gradually expanded with the strengthening of river processes. The relatively warm mid-Holocene climate significantly accelerated the emergence of agriculture, notably the slash-and-burn cultivation after 6,500 cal yr BP, and the continuous intensification of agricultural activities after 4,000 cal yr BP. Human activity became a significant factor of the environmental change in the Baiyangdian Lake region since 2700 cal yr BP. Our results indicate that the Holocene pollen records from large shallow lakes are often complicated by sedimentary processes and human activity, and should be carefully considered when reconstructing past climatic and environmental changes.

Spatiotemporal Variation and Prediction of Carbon Storage in Terrestrial Ecosystems at Multiple Development Stages in Beijing City Based on the Plus and Integrated Valuation of Ecosystem Services and Tradeoffs Models

Terrestrial ecosystems play a critical role in the global carbon cycle, and their carbon sequestration capacity is vital for mitigating the impacts of climate change. Changes in land use and land cover (LULC) dynamics significantly alter this capacity. This study scrutinizes the LULC evolution within the Beijing metropolitan region from 1992 to 2022, evaluating its implications for ecosystem carbon storage. It also employs the Patch-Generating Land Use Simulation (PLUS) model to simulate LULC patterns under four scenarios for 2035: an Uncontrolled Scenario (UCS), a Natural Evolution Scenario (NES), a Strict Control Scenario (SCS), and a Reforestation and Wetland Expansion Scenario (RWES). The InVEST model is concurrently used to assess and forecast ecosystem carbon storage under each scenario. Key insights from the study are as follows: (1) from 1992 to 2022, Beijing’s LULC exhibited a phased developmental trajectory, marked by an expansion of urban and forested areas at the expense of agricultural land; (2) concurrently, the region’s ecosystem carbon storage displayed a fluctuating trend, peaking initially before declining, with higher storage in the northwest and lower in the central urban zones; (3) by 2035, ecosystem carbon storage is projected to decrease by 1.41 Megatons under the UCS, decrease by 0.097 Megatons under the NES, increase by 1.70 Megatons under the SCS, and increase by 11.97 Megatons under the RWES; and (4) the study underscores the efficacy of policies curtailing construction land expansion in Beijing, advocating for sustained urban growth constraints and intensified afforestation initiatives. This research reveals significant changes in urban land use types and the mechanisms propelling these shifts, offering a scientific basis for comprehending LULC transformations in Beijing and their ramifications for ecosystem carbon storage. It further provides policymakers with substantial insights for the development of strategic environmental and urban planning initiatives.

Surface-air exchanges of H2S and SO2 in an urban wetland in eastern China

Wetlands are widely recognized as hot spots for the emission or deposition of biogenic sulfur gases, including hydrogen sulfur (H2S) and sulfur dioxide (SO2), which significantly affect air quality and climate change. With the expansion of urban wetlands, it is critical to know the roles that urban wetlands played in atmospheric H2S and SO2 budget. In this study, the surface-air exchange fluxes of H2S and SO2 were measured by the Dynamic Flux Chamber (DFC) method in a typical urban wetland in eastern China from Sep 2022 to July 2023. It was found that the urban wetland did not have the expected high H2S emission, might be caused by the relatively high pH value and low sulfate concentration in the soil. Although H2S showed emission in the daytime of spring and summer, an overall H2S flux of −0.04 kg S ha−1 yr−1 was observed throughout the year. Meanwhile, the urban wetland presented a net sink of SO2, with a deposition flux of 0.14 kg S ha−1 yr−1. The negative peaks of SO2 flux corresponded to the suddenly elevated SO2 concentration in the ambient air especially in spring and winter. Through linear fitting of SO2 flux and concentration, the concept of SO2 “compensation point” was proposed. The compensation point is the concentration level at which the observed SO2 flux equals zero. The “compensation point” changed with the season and was related to temperature and humidity. The “compensation point” in summer and autumn were larger, being 2.37 ppb and 1.40 ppb, respectively, while they were 1.07 ppb and 0.86 ppb in spring and winter respectively. Our results suggest that the urban wetland expansion may have little risk of increasing air H2S but could act as a significant sink of SO2 with high SO2 concentration in the urban region.

Prediction of Land Use and Habitat Quality in Harbin City Based on the PLUS- InVEST Model

Analyzing the spatiotemporal evolution of urban land use and habitat quality can reveal the correlation between land use and habitat quality, aiding in rational urban land policies and high-quality ecological environment development. This study was based on land use transition matrices and an Intensity-Migration （IM） model to analyze the changes in land use in Harbin from 2000 to 2020. It combined the PLUS model to explore the driving factors of land use expansion for various land types and predicted land use scenarios for 2030 under natural development, ecological protection, farmland protection, and urban development scenarios. Finally, the InVEST model was used to complete the habitat quality analysis. The results indicated： ① The dominant land use types in Harbin were cropland, forest land, and grassland. From 2000 to 2020, there was a significant tendency of conversion into grassland, cropland, forest land, and artificial surfaces, with noticeable changes in land use intensity. Water bodies, bare land, and wetland types showed less conversion and tended to be restrictive. ② Elevation was the primary factor influencing the expansion of grassland, cropland, forest land, bare land, wetland, and water bodies. Socioeconomic factors were the main factor affecting the expansion of artificial surfaces. ③ Simulation of land use types in Harbin for 2030 under the four scenarios showed an increase in forest land area and a decrease in grassland area, with insignificant changes in wetland, water bodies, and bare land areas. Except for in the ecological protection scenario, the area of artificial surfaces increased, whereas cropland decreased. ④ Overall, habitat quality in Harbin improved from 2000 to 2020. ⑤ In 2030, the spatial pattern of habitat quality in Harbin remained consistent across all scenarios, showing an overall improvement in habitat quality. Under the ecological protection scenario, areas with low and medium habitat quality decreased, whereas areas with higher habitat quality increased, indicating a relatively significant improvement in habitat quality. The research results provide a scientific basis and insights for the development of ecological civilization and urban planning and construction in Harbin.

Enhanced Carbon Accumulation in China's New Coastal Wetlands Over the 21st Century

AbstractWetlands formed by natural sediment deposition account for a large proportion of new coastal lands, and these new wetlands usually have active ecosystems and obvious ecological effects. However, previous studies largely overlooked this sediment‐caused wetland expansion, and the spatiotemporal variation in these wetlands and future response to sea‐level rise (SLR) have not been determined. Here, we employed satellite observations to quantify the seaward expansion of coastal lands in China over the past two decades. A total land expansion of 6,651 km2 was found, and wetlands and artificial surfaces dominated, accounting for 32% and 25%, respectively. Subsequently, we utilized an integrated model to estimate the response of these new wetlands to SLR in the 21st century, that is, we estimated the wetland gain from sediment deposition and loss due to SLR. The results indicate that under the current condition of sediment availability, the area of China's new coastal wetlands is projected to increase by 200%–261% compared to that in 2020 based on four SLR scenarios, despite the unavoidable impact of SLR. These increases are accompanied by the continuous enhancement of carbon accumulation. Wetland changes are influenced by factors such as sediment deposition, SLR and storm surges, as well as the continued effect of local natural and anthropogenic factors. These results show the importance of understanding the ecological effects of new wetlands and constructing specific protection measures for sustainable development.

Wildfire-vegetation-climate-human interactions in the central Taiwan region during 17.3–2.0 cal kyr BP, inferred from sediments of Toushe Basin

In this study, a long-term relationship amongst wildfire, vegetation, climate, and human in the central Taiwan region, spanning from 17.3 to 2.0 cal kyr BP, is explored. To investigate this relationship, multiple proxy approaches were employed, including charcoal (CHAR and fire frequency), pollen data (Liew et al., 2006), magnetic susceptibility, and the carbon isotopic composition of organic carbon, along with the elemental ratio of total organic carbon to total nitrogen in the core sediments of the Toushe Basin, central Taiwan. From 17.3 to 14.5 cal kyr BP, the Toushe Basin experienced drier climate conditions, leading to high-intensity fires and reduced area of wetland. Between 14.5 and 11.5 cal kyr BP, a wetter climate corresponded with low-intensity fires and an increase in tree prevalence. From 11.5 to 5.0 cal kyr BP, the climate remained relatively stable with peaks of extreme wet phases, with frequent low-intensity fires promoting herbaceous plant growth. During the period from 5.0 to 2.0 cal kyr BP, wetter conditions persisted, but increased human activities likely intensified high-intensity fires, resulting in reduced tree and herbaceous plant populations and an expansion of wetlands, leading to complex impacts on the region's ecological dynamics. The pollen diversity index (PDI) and pollen richness index (PRI) showed that ecological diversity in the Toushe Basin decreased with high-intensity fires and increased with low-intensity fires, highlighting the complex interactions between natural and human factors during 17.3–2.0 cal kyr BP. In addition, this study showed a strong link between El-Niño events and increased wildfire activity in the Toushe Basin. El-Niño conditions, with reduced rainfall and increased dryness, likely heightened wildfire frequencies and intensity by lowering moisture levels and ignition thresholds. Increased lightning during these periods further exacerbated wildfires. This connection highlights El-Niño ‘s role in driving high-intensity fires, impacting the region's vegetation and ecological dynamics.

Remotely Sensed Changes in Qinghai–Tibet Plateau Wetland Ecosystems and Their Response to Drought

Wetland ecosystems in the Qinghai–Tibet Plateau are pivotal for global ecology and regional sustainability. This study investigates the dynamic changes in wetland ecosystems within the Chaidamu Basin and their response to drought, aiming to foster sustainable wetland utilization in the Qinghai–Tibet Plateau. Using Landsat TM/ETM/OLI data on the Google Earth Engine platform, we employed a random forest (RF) method for annual long-term land cover classification. Standardized precipitation evapotranspiration indices (SPEI3, SPEI6, SPEI9, and SPEI12) on different time scales were used to assess meteorological drought conditions. We employed a Pearson correlation analysis to examine the relationship between wetland changes and various SPEI scales. The BFASAT method was used to evaluate the impact of SPEI12 trends on the wetlands, while a cross-wavelet analysis explored teleconnections between SPEI12 and atmospheric circulation factors. Our conclusion is as follows: The wetlands, including lake, glacier, and marsh wetlands, exhibited a noticeable increasing trend. Wetland expansion occurred during specific periods (1990–1997, 1998–2007, and 2008–2020), featuring extensive conversions between wetlands and other types, notably the conversion from other types to wetlands. Spatially, lake and marsh wetlands predominated in the low-latitude basin, while glacier wetlands were situated at higher altitudes. There were significant negative correlations between the SPEI at various scales and the total wetland area and types. SPEI12 displayed a decreasing trend with non-stationarity and distinct breakpoints in 1996, 2002, and 2011, indicating heightened drought severity. Atmospheric circulation indices (ENSO, NAO, PDO, AO, and WP) exhibited varying degrees of resonance with SPEI12, with NAO, PDO, AO, and WP demonstrating longer resonance times and pronounced responses. These findings underscore the significance of comprehending wetland changes and drought dynamics for effective ecological management in the Chaidamu Basin of the Qinghai–Tibet Plateau.

Evolution of Wetland Patterns and Key Driving Forces in China’s Drylands

Wetlands within dryland regions are highly sensitive to climate change and human activities. Based on three types of land use data sources from satellite images and a spatial data analysis, the spatiotemporal characteristics of wetland evolution in China’s drylands and their relationship with human interference and climate change from 1990 to 2020 were analyzed. The results were as follows: (1) The wetlands within China’s drylands expanded, including rivers, lakes, and artificial wetlands, apart from marshes, which shrunk. Meanwhile, wetland fragmentation increased, with rivers being particularly severely fragmented. (2) Temperature and precipitation showed an increasing trend from 1990 to 2020 in China’s drylands. Lakes and rivers expanded with regional differences due to the uneven distribution of precipitation and rising temperature. (3) Human activities, more than climate change, became the key driving factor for the changes in wetland patterns in China’s drylands. The increased areas of farmland and grassland along with increased levels of drainage and irrigation activities led to the shrinkage of marshes and the fragmentation of rivers. The increase in the number of artificial reservoirs was the main reason for the expansion of artificial wetlands. This study clarifies the specific driving factors of different types of wetlands within China’s drylands, which is of great use for better protecting wetlands and the gradual restoration of degraded wetlands.

Land cover changes and comparison of current landscape metrics in a region of the Central Andes affected by population migration

ABSTRACT The Andes region has a rich history of environmental and human interactions that has shaped the landscape for millennia. Our study quantified the land cover changes in the districts of Huanta and Luricocha after the human population abandoned the region due to the armed conflict with Peruvian authorities (1980 – 1990) and their progressive return (1990 – 2020). We analysed satellite images of various resolutions, including Landsat-5 for the years 1986, 1990, 2000 and 2010; Landsat-8 for the year 2020, Sentinel-2 for the years 2017 and 2020; PeruSat-1 for the years 2017 and 2020, to assess the temporal change of land cover and landscape metrics. The classification was based on the pixel approach for Landsat images and Sentinel-2 with an average accuracy of 88.29% and 92.13% respectively, and an object-based (GEOBIA) approach for Perusat-1 images, with an average accuracy of 87.75%. The dominant coverages are high Andean grasslands, scrublands and croplands. According to the obtained data, high Andean grasslands and scrublands have decreased, which is associated with an increase in population over time. Likewise, there has been an increase in the area of lagoons and the expansion of nearby wetlands due to the construction of dams, driven by an increase in demand for water for human consumption and agriculture. However, areas with degraded soils, rocky outcrops, and forest plantations have expanded. The results suggest that abandoned agricultural lands did not recover quickly enough and more research and action is needed for restoration of the high-mountain ecosystem. Landscape metrics such as Edge Density (ED), Euclidean Distance to Nearest Neighbor (ENN) and Aggregation Index (AI) were calculated for different land cover (LC/LU) to characterize composition and structure, showing their variation at different spatial resolutions. This indicates that increasing spatial resolution makes it possible to better define the landscape characteristics.

Ecosystem health assessment and comparison of natural and constructed wetlands in the arid zone of northwest China

Wetlands in the arid zone of northwest China have ecological values such as climate regulation, water conservation, and biodiversity maintenance. However, in the context of global warming and economic development, the degree of natural and human interference in the wetlands has been increasing, and wetland health problems are becoming increasingly severe. The current comparative research on the ecosystem health evaluation of natural and constructed wetlands and their sustainable development in the arid zone of northwest China is not perfect, so we selected the natural (Dunhuang Xihu Wetland) and constructed wetlands (Suzhou District Wetland) as research objects. The ecosystem health evaluation system has been developed from 5 levels of the drive, pressure, state, impact, and response (DPSIR). The ecological health status and impact factors were evaluated for the two wetlands using socioeconomic data combined with remote sensing technology from 2000 to 2019. The results showed that 1) the ecological health of natural and constructed wetlands was in a medium healthy state, and the ecological health values of the wetlands showed a trend of decreasing and then increasing from 2000 to 2019, with 2005 as the turning point. The ecological health status of natural wetlands (0.46) was better than that of constructed wetlands (0.42). 2) The main reasons for the degradation of constructed wetlands (-3.20%) were the urban population expansion and blind agricultural reclamation of wetlands, while the degradation of natural wetlands (-6.45%) was dominated by extreme climatic conditions and overuse of water resources. These results provide case support and a theoretical basis for the conservation management and sustainable development of wetland ecosystems in the arid zone.

Dissolved organic carbon dynamics and fluxes in Mississippi-Atchafalaya deltaic system impacted by an extreme flood event and hurricanes: a multi-satellite approach using Sentinel-2/3 and Landsat-8/9 data

Transport of riverine and wetland-derived dissolved organic carbon (DOC) spanning tidal wetlands, estuaries, and continental shelf waters functionally connects terrestrial and aquatic carbon reservoirs, yet the magnitude and ecological significance of this variable and its spatiotemporal linkage remains uncertain for coastal deltaic regions, such as Mississippi River Delta Plain, which includes Mississippi (MR) and Atchafalaya (AR) rivers and estuaries with vast expanses of wetlands and coastal forests. We examined DOC dynamics and fluxes in this large river-dominated wetland-estuarine system for the period between 2019 and 2021 that included an extreme river flood event in 2019, two major hurricanes (Barry in 2019 and Ida in 2021), and cold front passage using an improved adaptive quasi-analytical algorithm (QAA-AD) applied to multi-satellite sensors (Sentinel 3A/B OLCI, Landsat-8/OLI and Sentinel-2A/B MSI) with varying spectral and spatial (10/30/300 m) resolutions. The DOC estimates from multi-satellite sensors in combination with water fluxes were used to assess DOC fluxes from two large rivers (MR and AR) and small channels across the delta plain. Overall, this system delivered a total of 6.7 Tg C yr-1(1 Tg = 1012g) into the estuarine zone and the northern Gulf of Mexico (nGoM) during 2019. High DOC fluxes from the AR (1.3 Tg C yr-1) and MR (4.5 Tg C yr-1) were associated with the extreme flood event in 2019. Hurricanes that occurred in the study period also contributed to the wetland and estuarine DOC fluxes into continental shelf waters; for example, the passage of Hurricane Barry in July 2019, delivered over a 3-day period ~1.33 ×109g DOC from Barataria Basin into the nGoM. Sentinel 2-MSI land and water classification revealed that Hurricane Ida eroded a total of 1.34×108m2of marshes in middle Barataria Basin, converting those habitats into open water with 3.0 m inundation depth and high DOC concentrations (16.4 mg L-1), a potentially large DOC source to the coastal waters. Overall, storms and flood events are major sources of DOC flux that facilitate transport of upstream carbon as well as transformation of carbon in the wetlands, through the conversion of vegetated wetland to open water.

Seasonal fluctuations of marsh wetlands in the headwaters of the Brahmaputra, Ganges, and Indus Rivers, Tibetan Plateau based on the adapted LandTrendr model

Marsh wetlands present a rich variety of ecosystem goods and services, including important carbon sinks, of great significance to changes in the global environment. However, seasonal responses of marsh wetlands remain understudied and poorly understood. Therefore, this study adapted the Landsat-based Detection of Trends in Disturbance and Recovery (LandTrendr) model using field and Landsat data during 1990–2017 to identify the seasonal and spatial variations in marsh wetlands in the headwaters of the Brahmaputra, Ganges, and Indus Rivers (HBGIR) and analyze the drivers of their spatiotemporal changes. The spatiotemporal change in the marsh wetlands was divided into the three stages of expansion (1990–1998), retreat (1998–2004), and stability (2004–2017). The marsh wetland area showed an increasing trend before 1998 and a stable and slightly increasing trend after 2004. The expansion area of the marsh wetlands was located in the reserves of Shiquanhe and Manasarovar and their surrounding areas. The marsh wetlands were subjected to the largest expansion in summer (114.45 km2), followed by spring (80.45 km2). The expansion of the marsh wetlands in summer was mainly driven by snow depth and temperature, with the strongest interaction factor of 0.6 between them. However, the retreat of the marsh wetlands was driven by the expansion of construction and cultivated lands in the HBGIR. Finally, the LandTrendr model modified in this study was useful for improving the change-detection accuracy of the marsh wetlands. This study provides an important theoretical basis for wetland protection and management for the Tibetan Plateau.

Three thousand years of anthropogenic impact and water management and its impact on the hydro-ecosystem of the Mérantaise river, Paris conurbation (France)

This article assesses the long-term hydro-sedimentary and ecological consequences of the urban pressure around Paris over the last 3000 years on the Mérantaise river. Using a geoarchaeological approach combining sedimentological, geochemical, palynological and geophysical investigations enabled us to identify the transformations of the hydrosystem and to discuss the consequences of the different types of pressure and to put the role of biophysical and historical legacies into perspective with respect to contemporary dynamics. Using two study sites, one a former pond (Mérancis), the other a former mill site (Ors mill), nine cores, two auger holes and four trenches dug in the valley floor and two electrical resistivity tomography (ERT) profiles, it was possible to reconstruct the geometry of the sedimentary deposits. Chronostratigraphy was based on 41 radiocarbon dates and the history of vegetation and anthropogenic activities was reconstructed from 42 pollen samples and non-pollen palynomorphs collected from the former pond site. Despite the expansion of wetlands in the valley bottom, the pollen data revealed strong agropastoral activities and cereal growing in the Iron Age and up until the end of the Middle Ages. For the first time, sedimentological data associated with pollen data revealed hemp retting activities from c. 675 CE. From the Late Middle Ages onwards, water management led to the creation of two ponds to feed water mills. Despite the persistence of wetlands, this study highlights the early onset of anthropogenic modifications and in particular, the start of organic pollution and eutrophication in the Early Middle Ages, attesting to early eutrophication of water quality and aquatic environments resulting from the transformation of agropastoral practices and hydraulic pressure around the largest European city during the last 1500 years, well before the inset of urban sprawl in the watershed.

Effect of wetland hydrological connectivity on runoff based on a basin comparison

Hydrological connectivity is of great significance to the protection of wetlands and the rational development of water resources. Climate change and overdevelopment have led to the reduction of the Zoige wetland area, the destruction of its ecosystem structure, and the severe degradation of wetland hydrological connectivity. This study proposes an analysis framework to explore the impact of hydrological connectivity on runoff based on the dynamic prediction of wetland spatial patterns and the quantification of wetland hydrological connectivity and nonlinear fitting; the Zoige wetland was selected for application and verification. Under the ecological protection scenario (Plan1), the wetland experienced an expansion of meadow wetland (MW); under the natural development scenario (Plan2), the degradation of shallow wetland (SW) is the most significant. The optimal threshold distances (TDs) for studying the hydrological connectivity in the Hei River basin (HRB) and Bai River basin (BRB) were 1200 m and 1800 m, respectively. The hydrological connectivity of the HRB was significantly greater, with a value that was approximately 30–50 times that of the BRB in the same year. The IIC and PC of the two basins gradually decreased during the historical period and showed increasing and decreasing trends under the Plan1 and Plan2 scenarios, respectively. The effect of wetland hydrological connectivity on runoff was significantly different in the two basins; wetlands developed extensively in the HRB, and connectivity had an inhibitory effect on the runoff and the runoff-generating efficiency of precipitation, while the wetland was even more fragmented in the BRB, and the increase in connectivity promoted the generation of runoff. Because biodiversity is sensitive to change, the patches in the middle reaches of the HRB and the lower reaches of the BRB are the areas that should receive the highest wetland protection priority in the future.

Rapid expansion of wetlands on the Central Tibetan Plateau by global warming and El Niño

Rapid expansion of wetlands on the Central Tibetan Plateau by global warming and El Niño

Deglacial records of terrigenous organic matter accumulation off the Yukon and Amur rivers based on lignin phenols and long-chain n-alkanes

Abstract. Arctic warming and sea level change will lead to widespread permafrost thaw and subsequent mobilization. Sedimentary records of past warming events during the Last Glacial–interglacial transition can be used to study the conditions under which permafrost mobilization occurs and which changes in vegetation on land are associated with such warming. The Amur and Yukon rivers discharging into the Okhotsk and Bering seas, respectively, drain catchments that have been, or remain until today, covered by permafrost. Here we study two marine sediment cores recovered off the mouths of these rivers. We use lignin phenols as biomarkers, which are excellently suited for the reconstruction of terrestrial higher plant vegetation, and compare them with previously published lipid biomarker data. We find that in the Yukon basin, vegetation change and wetland expansion began already in the early deglaciation (ED; 14.6–19 ka). This timing is different from observed changes in the Okhotsk Sea reflecting input from the Amur basin, where wetland expansion and vegetation change occurred later in the Pre-Boreal (PB). In the two basins, angiosperm contribution and wetland extent all reached maxima during the PB, both decreasing and stabilizing after the PB. The permafrost of the Amur basin began to become remobilized in the PB. Retreat of sea ice coupled with increased sea surface temperatures in the Bering Sea during the ED might have promoted early permafrost mobilization. In modern Arctic river systems, lignin and n-alkanes are transported from land to the ocean via different pathways, i.e., surface runoff vs. erosion of deeper deposits, respectively. However, accumulation rates of lignin phenols and lipids are similar in our records, suggesting that under conditions of rapid sea level rise and shelf flooding, both types of terrestrial biomarkers are delivered by the same transport pathway. This finding suggests that the fate of terrigenous organic matter in the Arctic differs on both temporal and spatial scales.

A new perspective on the impacts of Spartina alterniflora invasion on Chinese wetlands in the context of climate change: A case study of the Jiuduansha Shoals, Yangtze Estuary

Spartina alterniflora, an invasive plant, was introduced to the Chinese coastal zone in the early 90s. As an eco-engineering species, S. alterniflora not only alters saltmarsh species distributions, previously described as habitat degradation, but it also plays a vital role in coastal protection, especially for the development of recently emerged intertidal shoals. To provide a reference for coastal management under global change, we quantified the impact of the invasion process on provided ecological and coastal protection functions, exemplified at the emerging Jiuduansha Shoals (JDS) in the Yangtze Estuary. Results obtained by high-precision satellite monitoring and numerical modelling showed that the establishment and growth of S. alterniflora can exert considerable changes on local environment. The invasion of S. alterniflora to JDS wetland can be divided into three distinct phases, (1) establishment 1998–2003, (2) expansion 2003–2009, and (3) dominant 2009–2018 stages according to the changes in saltmarsh composition. Spatially, S. alterniflora continuously replaced Scirpus mariqueter, forcing S. mariqueter and Phragmites australis slowly to the lower and higher intertidal habitats, respectively. Notably, S. alterniflora expansion was the main driver that contributed to over 70 % of recent JDS wetland expansion even under sediment deficit conditions. Established S. alterniflora marsh (directly) dampens more waves because of aboveground stems, but it also causes more accretion and indirectly leads to higher “morphological” wave dampening. Thus, it increases coastal defense provided by the saltmarsh in the context of sea-level rise and strengthening storms. In conclusion, the role of S. alterniflora invasion to the local environment under global changes is controversial. For sustainable coastal management, we need context-dependent S. alterniflora management to maximize the benefit of coastal protection and minimize the impact on local ecology, especially in sediment-starving estuaries with expected coastline retreat.

FLOOD RISK ASSESSMENT, CLIMATE CHANGE ADAPTATIONS AND MITIGATION STRATEGIES OF COMMUNITIES IN EDO STATE, NIGERIA

Despite flooding being one of the most common and destructive natural hazards, the risk it poses is systematically underestimated and still increasing due to climate change and growing concentrations of people and assets in flood-prone areas. The study carried out a flood risk assessment, climate adaptation and mitigation strategies of communities in Edo State, Nigeria. With the aid of questionnaires and GIS techniques, the flood risk level of communities within Edo states were analysed by capturing all the components of flood risk which include exposure and vulnerability. All analysis was carried out using descriptive statistics and Analytical Hierarchy Process (AHP) to determine the extent of the communities’ flood. The extent of risk showed that 778 communities were captured in risk analysis, 503 (64.65%) of the communities were found within low flood risk level while 150 (19.28%) communities and 125 (16.07%) communities were found to be within medium and high flood risk level respectively. The climate variables showed some level of fluctuation while the adopted adaptation measures such as expansion of floodplain and wetlands was based on political will of administrators, and the measure was perceived less effective. There was high level of awareness about government mitigation measures in the area and the main mitigation measure by government is construction of drainage system which was perceived to be effective. It was therefore concluded that all the adopted attributes contributed to the establishment of flood risk of Edo State and was categories into high, medium and low flood risk level. Hence, there is need to intensify the planning and execution of disaster management programs with the support of the produced flood risk map.

Soil diazotrophic abundance, diversity, and community assembly mechanisms significantly differ between glacier riparian wetlands and their adjacent alpine meadows.

Global warming can trigger dramatic glacier area shrinkage and change the flux of glacial runoff, leading to the expansion and subsequent retreat of riparian wetlands. This elicits the interconversion of riparian wetlands and their adjacent ecosystems (e.g., alpine meadows), probably significantly impacting ecosystem nitrogen input by changing soil diazotrophic communities. However, the soil diazotrophic community differences between glacial riparian wetlands and their adjacent ecosystems remain largely unexplored. Here, soils were collected from riparian wetlands and their adjacent alpine meadows at six locations from glacier foreland to lake mouth along a typical Tibetan glacial river in the Namtso watershed. The abundance and diversity of soil diazotrophs were determined by real-time PCR and amplicon sequencing based on nifH gene. The soil diazotrophic community assembly mechanisms were analyzed via iCAMP, a recently developed null model-based method. The results showed that compared with the riparian wetlands, the abundance and diversity of the diazotrophs in the alpine meadow soils significantly decreased. The soil diazotrophic community profiles also significantly differed between the riparian wetlands and alpine meadows. For example, compared with the alpine meadows, the relative abundance of chemoheterotrophic and sulfate-respiration diazotrophs was significantly higher in the riparian wetland soils. In contrast, the diazotrophs related to ureolysis, photoautotrophy, and denitrification were significantly enriched in the alpine meadow soils. The iCAMP analysis showed that the assembly of soil diazotrophic community was mainly controlled by drift and dispersal limitation. Compared with the riparian wetlands, the assembly of the alpine meadow soil diazotrophic community was more affected by dispersal limitation and homogeneous selection. These findings suggest that the conversion of riparian wetlands and alpine meadows can significantly alter soil diazotrophic community and probably the ecosystem nitrogen input mechanisms, highlighting the enormous effects of climate change on alpine ecosystems.

Analysis of Spatial–Temporal Variations and Driving Factors of Typical Tail-Reach Wetlands in the Ili-Balkhash Basin, Central Asia

The Ili River Delta (IRD) is the largest delta in the arid zone of Central Asia. Since the 1970s, the entire delta system has undergone a series of changes due to climate change and the impoundment of the Kapchagay Reservoir upstream of the delta, triggering an ecological crisis. Wetlands play a crucial ecological role in biodiversity conservation. Most studies have mainly focused on the response of vegetation and soil microbial to ecological changes in the delta, ignoring the dynamic processes of wetlands changes. Hence, such changes in the IRD and the underlying mechanisms need to be investigated in depth. In this study, wetlands in the IRD from 1975 to 2020 were extracted based on Landsat images using the object-oriented method; changes in the wetland area, wetland landscape pattern, NDVI, and NPP were analyzed; and the contributions of natural and human factors to wetland evolution were quantified. The results indicated the following: (1) From 1975 to 2020, the wetland area of the IRD showed an increasing trend, and changes in the wetland area were mainly found in the middle part of the delta near the Saryesik Peninsula. (2) The wetland landscape pattern in the IRD changed markedly from 1975 to 2020. The dominant patches of the wetland in the middle of the delta continued to expand; the patch aggregation index (AI) increased, and the landscape fragmentation index (LFI) decreased. (3) From 2000 to 2020, the average annual normalized difference vegetation index (NDVI) and net primary productivity (NPP) in the IRD increased, which is consistent with the change in wetland expansion. (4) Inflow to the delta from the Ili River and the water level of Balkhash Lake are significantly correlated with the wetland area, which are the dominant factors driving wetland evolution; and water evaporation from the Kapchagay Reservoir and irrigation water diversion on the left bank of the reservoir obviously intensified the process of lake water level decline and wetland degradation during 1970 to 1985. These results can provide scientific background for making informed ecological protection decisions in the IRD under the impacts of climate change and human activities.