Vulnerability assessment of coastal wetlands in Minjiang River Estuary based on cloud model under sea level rise

The change of coastal wetland vulnerability affects the ecological environment and the economic development of the estuary area.In the past,most of the assessment studies on the vulnerability of coastal ecosystems stayed in static qualitative research,lacking predictability,and the qualitative and quantitative relationship was not objective enough.In this study,the“Source-Pathway-Receptor-Consequence”model and the Intergovernmental Panel on Climate Change vulnerability definition were used to analyze the main impact of sea level rise caused by climate change on coastal wetland ecosystem in Minjiang River Estuary.The results show that:(1)With the increase of time and carbon emission,the area of high vulnerability and the higher vulnerability increased continuously,and the area of low vulnerability and the lower vulnerability decreased.(2)The eastern and northeastern part of the Culu Island in the Minjiang River Estuary of Fujian Province and the eastern coastal wetland of Meihua Town in Changle District are areas with high vulnerability risk.The area of high vulnerability area of coastal wetland under high emission scenario is wider than that under low emission scenario.(3)Under different sea level rise scenarios,elevation has the greatest impact on the vulnerability of coastal wetlands,and slope has less impact.The impact of sea level rise caused by climate change on the coastal wetland ecosystem in the Minjiang River Estuary is mainly manifested in the sea level rise,which changes the habitat elevation and daily flooding time of coastal wetlands,and then affects the survival and distribution of coastal wetland ecosystems.

Spatiotemporal Dynamics of Coastal Wetlands and Reclamation in the Yangtze Estuary During Past 50 Years(1960s–2015)

Reclamation is one of the fastest-growing land use type developed in coastal areas and has caused degradation and loss of coastal wetlands as well as serious environmental problems. This paper was aimed at monitoring the spatiotemporal patterns of coastal wetlands and reclamation in the Yangtze Estuary during the 1960s and 2015. Satellite images obtained from 1980 to 2015 and topography maps of the 1960 s were employed to extract changes of reclamation and coastal wetlands. Area-weight centroids were calculated to identify the movement trend of reclamation and coastal wetlands. The results show that from the 1960 s to 2015, the net area of natural wetlands declined by 574.3 km^2, while man-made wetlands and reclamation increased by 553.6 and 543.9 km^2, respectively. During the five study phases, the fastest areal change rate natural wetlands was –13.3 km^2/yr in the period of 1990–2000, and that of man-made areas was 24.7 km^2/yr in the same period, and the areal change rate of reclamation was 27.6 km^2/yr in the period of 2000–2010. Conversion of coastal wetlands mainly occurred in the Chongming Island, Changshu City and the east coast of Shanghai Municipality. Reclamation was common across coastal areas, and was mainly attributed to settlement and man-made wetlands in the Chongming Island, Lianyungang City and the east coast of Shanghai Municipality. Natural wetlands turned into farmlands and settlement, and man-made wetlands gained from reclamation of farmlands. The centroid of natural wetlands generally moved towards the sea, man-made wetlands expanded equally in all directions and inland, and the centroid of reclamation migrated toward Shanghai Municipality. Sea level rise, erosion-deposition changes, and reclamation activities together determine the dynamics of the Yangtze Estuary wetlands. However, reclamation activities for construction of ports, industries and aquaculture are the key causes for the dynamics. The results from this study on the dynamics of coastal wetlands and reclamation are valuable for local government to put forward sustainable land use and land development plans.

Effects of Reclamation on Soil Carbon and Nitrogen in Coastal Wetlands of Liaohe River Delta,China

To evaluate the influence of wetland reclamation on vertical distribution of carbon and nitrogen in coastal wetland soils, we measured the soil organic carbon(SOC), soil total nitrogen(STN) and selected soil properties at five sampling plots(reed marsh, paddy field, corn field, forest land and oil-polluted wetland) in the Liaohe River estuary in September 2013. The results showed that reclamation significantly changed the contents of SOC and STN in the Liaohe River estuary(P < 0.001). The SOC concentrations were in the order: oil-polluted wetland > corn field > paddy field > forest land > reed marsh, with mean values of 52.17, 13.14, 11.46, 6.44 and 6.16 g/kg, respectively. STN followed a similar order as SOC, with mean values of 1351.14, 741.04, 632.32, 496.17 and 390.90 mg/kg, respectively. Interaction of reclamation types and soil depth had significant effects on SOC and STN, while soil depth had significant effects on SOC, but not on STN. The contents of SOC and STN were negatively correlated with pH and redox potential(Eh) in reed marsh and corn field, while the SOC and STN in paddy field had positive correlations with electrical conductivity(EC). Dissolved organic carbon(DOC), ammonium nitrogen(NH_4^+-N) and nitrate nitrogen(NO_3~–-N) were also significantly changed by human activities. NH_4^+-N and NO_3~–-N increased to different degrees, and forest land had the highest NO_3~–-N concentration and lowest DOC concentration, which could have been caused by differences in soil aeration and fertilization. Overall, the results indicate that reed harvest increased soil carbon and nitrogen release in the Liaohe River Estuary, while oil pollution significantly increased the SOC and STN; however, these cannot be used as indicators of soil fertility and quality because of the serious oil pollution.

Spatial distribution of heavy metals(Cu, Pb, Zn, and Cd)in sediments of a coastal wetlands in eastern Fujian, China

We investigated the spatial distribution （horizontal and vertical concentrations） of copper （Cu）, lead （Pb）, zinc （Zn）, and cadmium （Cd） in five wetland types （mudflat, aquaculture wetland, water area, farmland wetland and mangrove） from three areas （Ningde, Fuding, and Xiapu）, China. Cu concentrations in five wetland types descended in the order： farm wetland, mudflat, aquaculture, water area and mangrove. Pb concentrations decreased in the order： aquaculture, mangrove, farm wetland, mudflat, and water area. Zn content decreased in the order： farm wetland, water area, aquaculture, mudflat and mangrove, and Cd content decreased as follows： mangrove, aquacul- ture, water area, rnudflat, and farm wetland. Comparison of the concentrations of the same heavy metals in different areas showed that the highest Cu （63.75 mg kg-1） and Zn （152.32mgkg-1） concentrations occurred in Ningdecoastal wetlands; Pb （110.58 mg kg-1） and Cd （2.81 mg kg-1） contents were highest in Fuding wetlands, and the average contents of all heavy metals were very low in Xiapu wetlands. Examination of the vertical distribution showed that the Cu content was high in all mudflat layers; Pb and Cd concentrations were highest in aquaculture and mangrove wetlands, respectively, and Zn content was highest in farm wetlands. The spatial distribution of Cu and Zn contents for different areas decreased as follows： Ningde 〉 Fuding 〉 Xiapu, for Pb and Cd were most concentrated in Fuding coastal wetlands. Concentrations of Zn and Cu were highly correlated, while Zn and Cu were not significantly correlated with Pb.

Compound extreme inundation risk of coastal wetlands caused by climate change and anthropogenic activities in the Yellow River Delta,China

The coastal wetlands of the Yellow River Delta(YRD)in China are crucial for their valuable resources,environmental significance,and economic contributions.However,these wetlands are also vulnerable to the dual threats of climate change and human disturbances.Despite substantial attention to the historical shifts in YRD's coastal wetlands,uncertainties remain regarding their future trajectory in the face of compound risks from climate change and anthropogenic activities.Based on a range of remote sensing data sources,this study undertakes a comprehensive investigation into the evolution of YRD's coastal wetlands between 2000 and 2020.Subsequently,the potential fate of coastal wetlands is thoroughly analyzed through the Land Use/Cover Change(LUCC)simulation using System Dynamic-Future Land Use Simulation(SD-FLUS)model and the extreme water levels projection integrated future sea-level rise,storm surge,and astronomical high tide in 2030,2050,and 2100 under scenarios of SSP1-2.6,SSP2-4.5,and SSP5-8.5.Results revealed that YRD's coastal wetlands underwent a marked reduction,shrinking by 1688.72 km²from 2000 to 2020.This decline was mostly attributed to the substantial expansion in the areas of artificial wetlands(increasing by 823.78 km2),construction land(increasing by 767.71 km²),and shallow water(increasing by 274.58 km²).Looking ahead to 2030-2100,the fate of coastal wetlands appears to diverge based on different scenarios.Under the SSP1-2.6 scenario,the area of coastal wetland is projected to experience considerable growth.In contrast,the SSP5-8.5 scenario anticipates a notable decrease in coastal wetlands.Relative to the inundated area suffered from the current extreme water levels,the study projects a decrease of 6.8%-10.6%in submerged coastal wetlands by 2030 and 9.4%-18.2%by 2050 across all scenarios.In 2100,these percentages are projected to decrease by 0.4%(SSP2-4.5)and 27.1%(SSP5-8.5),but increase by 35.7%(SSP1-2.6).Results suggest that coastal wetlands in the YRD will face a serious compound risk from climate change and intensified human activities in the future,with climate change being the dominant factor.More effcient and forward-looking measures must be implemented to prioritize the conservation and management of coastal wetland ecosystems to address the challenges,especially those posed by climate change.

Seasonal response of nitrogen exchange fluxes to crab disturbance at sediment-water interface in coastal tidal wetlands

Coastal wetlands are hotspots for nitrogen(N)cycling,and crab burrowing is known to transform N in intertidal marsh soils.However,the underlying mechanisms remain unclear.This study conducted field experiments and used indoor control test devices to investigate the seasonal response of nitrogen to crab disturbance at the sediment-water interface in coastal tidal flat wetlands.The results showed that crab disturbance exhibited significant seasonality with large seasonal differences in cave density and depth.Due to crab disturbance,nitrogen fuxes at the sediment-water interface were much greater in the box with crabs than in the box without crabs.In summer,NH-N showed a positive flux from the sediment to the overlying water,but NO2-N and NOg-N showed positive fluxes from the sediment to the overlying water only in early stages.In winter,NH-N showed a positive flux from the sediment to the overlying water,but NO-N and NO,-N both exhibited positive and negative fluxes.These results indicated that the presence of crab burrows can cause the aerobic layer to move downward by approximately 8-15 cm in summer and directly promote nitrification at the sediment surface.

A numerical study of hydrodynamic characteristics and hydrological processes in the coastal wetlands during extreme events

Providing accurate predictions of extreme water levels through numerical simulation has become essential for disaster prevention and damage mitigation in coastal wetland areas.This study applies the FVCOM model to simulate storm surges caused by several typhoons in the Bohai Sea and the North Huanghai Sea.The vegetation drag force caused by salt marsh plants is inserted into the FVCOM model for model improvement with vegetation effect by integrating RS and GIS technologies.A parametric typhoon model is coupled with background wind fields derived to acquire the spatio-temporal variations of wind and pressure fields in the computational domain.The simulation results reproduce the extreme storm surges induced by typhoon events very well.The modeling results are compared by validating with literature results to examine the effect of vegetation on tidal waves in tidal mud flats.Moreover,the coupled model is also applied to explore storm surge attenuation and land intrusion during Typhoon Winnie in the wetlands of the Liao River Estuary.The simulation results indicate that salt marsh plants can reduce the flow current with little impact on tide flooding/ebbing in vegetated regions.Furthermore,the results show that typhoon presence increases the inundation depth and extendes the flood time in the tidal wetlands of the study region.The FVCOM model incorporating the method with vegetation drag force can provide new insights to understand the comprehensive impact of tidal wetland plants on hydrodynamic characteristics in the Bohai Sea and other waters,hence presents a more accurate quantification of the hydrological process of storm surge in the tidal wetlands.

Analysis of the contributions of human factors and natural factors affecting the vegetation pattern in coastal wetlands

Introduction:Accurate identification of the dominant factors affecting coastal wetlands can provide a reference for vegetation rehabilitation.In this study,quantitative analysis was performed on the Yancheng coastal wetland using ANOVA and geostatistical methods.Outcomes/other:The results indicated that in the directions perpendicular and parallel to the coastline,the soil moisture and salinity in the study area exhibited relatively significant(p<0.05)spatial variability.Vegetation in the southern experimental zone was in a low-moisture,low-salinity ecological niche,whereas vegetation in the northern experimental zone was in a high-moisture,high-salinity ecological niche.Soil salinity exhibited higher spatial variability than soil moisture,and it was most correlated with unvegetated mudflats,followed by areas with Spartina alterniflora,Suaeda glauca,and Phragmites australis.Discussion:The fitting of the semivariogram showed that the nugget and sill of the ratio were relatively low(<25%)for soil moisture and salinity in the northern experimental zone and northern buffer zone,whereas these values were relatively high(>75%)for soil moisture and salinity in the southern experimental zone and southern buffer zone.Conclusion:Compared with the northern study area,the contribution of human disturbance to the spatial heterogeneity of soil moisture and salinity in the southern study area is higher.

Analysis of intrinsic value and estimating losses of “blue carbon”in coastal wetlands:a case study of Yancheng, China

Introduction:Large stocks of“blue carbon”exist in the ecosystems of coastal wetlands.This paper presents a case study of the Chinese city of Yancheng.First,through field surveys and laboratory analysis,changes in the organic carbon(OC)content in typical plant communities throughout the study area are described in detail.Second,an OC burial rate and economic value model is constructed to analyze the composition of the carbon sink values.Outcomes/other:The results are as follows:Of the typical plant communities,Spartina alterniflora has the highest OC content(5.80 g·kg-1),followed by Suaeda glauca(4.78 g·kg-1)and Phragmites australis(3.76 g·kg-1);the contemporary OC sedimentation rates are 2.01,1.48,and 1.22 cm·yr-1,respectively.Spartina alterniflora communities have the highest annual average carbon sink value($418.74/ha)in the study area,followed by Phragmites australis($176.29/ha)and Suaeda glauca($101.54/ha).Discussion:As a result of both the expansion of the Spartina alterniflora area and coastal erosion,the total OC value since 1987 has displayed two-stage characteristics:it first increased and then decreased.Conclusion:In recent years,the annual average decline in OC value has ranged from approximately$82,100 to$123,100(reference:the Sweden carbon tax provided by the World Bank,130$/ton)

Sulfur mediated heavy metal biogeochemical cycles in coastal wetlands:From sediments,rhizosphere to vegetation

The interactions and mechanisms between sulfur and heavy metals are a growing focus of biogeochemical studies in coastal wetlands.These issues underline the fate of heavy metals bound in sediments or released into the system through sediments.Despite the fact that numerous published studies have suggested sulfur has a significant impact on the bioavailability of heavy metals accumulated in coastal wetlands,to date,no review article has systematically summarized those studies,particularly from the perspective of the three major components of wetland ecosystems(sediments,rhizosphere,and vegetation).The present review summarizes the studies published in the past four decades and highlights the major achievements in this field.Research and studies available thus far indicate that under anaerobic conditions,most of the potentially bioavailable heavy metals in coastal wetland sediments are fixed as precipitates,such as metal sulfides.However,fluctuations in physicochemical conditions may affect sulfur cycling,and hence,directly or indirectly lead to the conversion and migration of heavy metals.In the rhizosphere,root activities and microbes together affect the speciation and transformation of sulfur which in turn mediate the migration of heavy metals.As for plant tissues,tolerance to heavy metals is enhanced by sulfur-containing compounds via promoting a series of chelation and detoxification processes.Finally,to further understand the interactions between sulfur and heavy metals in coastal wetlands,some major future research directions are proposed.

ON THE DEVELOPMENT OF COASTAL VEGETATED WETLANDS IN CHINA

This paper discusses in detail the distributions, plant charactenstics and environmental conditions of the coastal vegetated wetlands in China. In contrast to most of fhe European and American salt marshes where Spartina is dominant, the China's ones are dominated by Suaeda in area. Given a great amount of fine sediments by rivers, China's coastal wetlands are accumulated rapidly. Ths factor combined with the human's ruthless reclaimation makes the marshes inmature. The vegetated wetlands are classified into four types, each having differential features in geomorphological background, deposits and vegetation.

Spatio-temporal variation of water salinity in mangroves revealed by continuous monitoring and its relationship to floristic diversity

Salinity is among the most critical factors limiting the growth and species distribution of coastal plants.Water salinity in estuarine ecosystems varies temporally and spatially,but the variation patterns across different time scales and salinity fluctuation have rarely been quantified.The effects of salinity on floristic diversity in mangroves are not fully understood due to the temporal and spatial heterogeneity of salinity.In this study,we monitored water salinity at an interval of 10-min over one year in three mangrove catchment areas representing the outer part,middle part,and inner part respectively of Dongzhai Bay,Hainan,China.The number of mangrove community types and dominant mangrove species of the three catchment areas were also investigated.We found that the diurnal variation and dry-season intra-month variation in water salinity were driven by tidal cycles.The seasonal variation in water salinity was mainly driven by rainfall with higher salinity occurring in the dry season and lower salinity occurring in the wet season.Spatially,water salinity was highest at the outer part,intermediate at the middle part,and lowest at the inner part of the bay.The intra-month and annual fluctuations of water salinity were highest at the middle part and lowest at the outer part of the bay.The number of mangrove community types and dominant species were lowest at the outer part,intermediate at the middle part,and highest at the inner part of the bay.These results suggest that the temporal variation of water salinity in mangroves is driven by different factors at different time scales and therefore it is necessary to measure water salinity at different time scales to get a complete picture of the saline environment that mangroves experience.Spatially,lower salinity levels benefit mangrove species richness within a bay landscape,however,further research is needed to distinguish the effects of salinity fluctuation and salinity level in affecting mangrove species richness.

Geographical Variation and Influencing Factors of Spartina alterniflora Expansion Rate in Coastal China

Biological invasion poses a huge threat to ecological security.Spartina alterniflora was introduced into China in 1979,and its arrival corresponded with negative effects on native ecosystems.To explore geographical variation of its expansion rate in coastal China,we selected 43 S.alterniflora sites from Tianjin Coastal New Area to Beihai.The area expansion rate,expansion rate paralleling and vertical to the shoreline were analysed based on Landsat images and field survey in 2015.Simple Ocean Data Assimilation(SODA)and climate data were collected to statistically analyse the influential factors of expansion rate.Results showed that significant difference of S.alterniflora area expansion rate among different latitude zones(P<0.01),increasing from 6.08%at southern(21°N–23°N)to 19.87% in Bohai Bay(37°N–39°N)along latitude gradient.There was a significant difference in expansion rate vertical to shoreline in different latitude zones(P<0.01)with the largest occurring in Bohai Bay(256m/yr,37°N–39°N),and showed an decreasing tendency gradually from north to south.No significant difference and latitudinal clines in expansion rate paralleling to shoreline were observed.Expansion rate had significant negative correlation with mean seawater temperature,the lowest seawater temperature,current zonal velocity and meridional velocity and presented a reducing trend as these biotic factors increased;however,they were not significantly correlated with the highest seawater temperature and mean seawater salinity.We identified significant correlations between expansion rate and annual mean temperature,the lowest temperature in January and annual precipitation,but there was little correlation with annual diurnal difference in temperature and the highest temperature in July.The rapid expansion rate in high-latitude China demonstrated a higher risk of potential invasion in the north;dynamic monitoring and control management should be established as soon as possible.

How Does the Blue C Stock Vary in Restored and Degraded Wetlands Across Land Cover Mosaics? Evidences from Medinipur Coastal Plain, India

Coastal wetlands are of paramount importance as major reservoirs of blue carbon(C),playing a crucial role in providing nature-based solutions to mitigate climatic changes.This research aimed to analyse the dynamics of total blue C(TBC)and its components;viz.soil organic C(SOC),below ground C,and above ground C;as well how they are influenced by land use/land cover(LULC)categories and wetland situations.Subsequently,study were identified as one restored wetland and another degraded wetland in the Medinipur Coastal Plain,India.The LULC categories were analyzed using Pleiades 1A and 1B satellite imagery,corresponding to the restored and degraded wetland,respectively.The quantification of SOC was based on point-specific sample data collected from both wetlands(nr=250;nd=84).Above ground biomass(AGB)was appraised employing allometric relationships involving field-measured dendrometric variables.Below ground biomass values were calculated using indirect allometric equations that take into account the AGB values.Integrating all the components,TBC stock of the restored and degraded wetlands were estimated at 246710.91 Mg and 7865.49 Mg,respectively.In the restored wetland,dense mangrove and open mangrove exhibited higher concentrations of blue C components,while other LULC categories demonstrated moderate to low densities.In the degraded wetland,the open mangrove category rechigh densities of C pools,whereas herbaceous vegetation,bare earth and sand,and waterbody exhibited lower concentrations.The results portrayed significant disparities(P<0.05)in blue C pools among different LULC categories in both wetlands.Furthermore,it was evident that wetland type and LULC category had notable(P<0.001)impacts on TBC dynamics,both individually and in combination.Overall,this research may aid in effective management of coastal wetlands as blue C sinks,emphasizing their significance as essential elements of climate mitigation strategies.

Phosphorus Behavior at Sediment-Water Interface in Coastal Wetland

[Objective] The aim was to explore the role of coastal wetlands in phosphorus fixation in the Yellow River Delta.[Method] The research analyzed phosphorus behavior at sediment-water interface by static water column test. [Result] The research concluded that phosphorus concentration was in the range of 0.051-0.322 mg/L in overlying water, and phosphorus was effectively removed by degradation and adsorption. The static water column test has demonstrated that phosphorus concentration of coastal wetlands plays the role of accumulation when phosphorus concentration is lower than 7 mg/L in overlying water of coastal wetlands. It is notable that substrates of overlying water all perform well in adsorption, and the adsorption reaches saturation if the concentration goes up to 10 mg/L. [Conclusion] Coastal wetlands would significantly adsorb and degrade phosphorus in overlying water, controlling phosphorus within a lower range.

Reclamation-oriented spatiotemporal evolution of coastal wetland along Bohai Rim,China

Coastal wetlands are located in the ecotone of interaction between the land surface and sea,and anthropogenic activities extensively interfere with these wetlands through the reclamation of large tidal wetlands and destruction of the function of the ecosystems.In this study,we investigated the dynamic evolutionary characteristics of the Bohai Rim coastal area over the past 40 years using the Modified Normalized Difference Water Index,the fractal dimension,object-oriented classification,the land-use transfer trajectory,and regression analysis.Additionally,we quantified and monitored the evolution of reclamation and analyzed the correlation between reclamation and coastal wetlands based on 99 Landsat-2,-5,and-8 images(at 60 m and 30 m spatial resolution) over the period 1980–2019.The results are as follows.(1) The coastline of the Bohai Rim increased by 1 631.2 km from 1980 to2019 with a zigzag variation.The artificial coastline increased by 2 946.1 km,whereas the natural coastline decreased by 90%.(2) The area of man-made wetlands increased by 3 736.9 km~2,the area of construction land increased by 1 008.4 km~2,and the natural wetland area decreased by 66%.The decrease of tidal flats is the main contributor to the decrease of natural wetland area(takes account for 91.1%).Coastal areas are affected by intense human disturbance,which was taken place across a large area of tidal flats and caused the landscape to fragment and be more heterogeneous.The coastal zone development activities were primarily concentrated in the southern Laizhou Bay,the Yellow River Delta,the Bohai Bay,the northern Liaodong Bay,and the Pulandian Bay.The solidified shorelines and increase in sea level have resulted in intertidal wetlands decreasing and impaired wetland ecology.(3) There is a good agreement between reclamation and the size of the coastal wetlands.Both land reclamation and the reduction in coastal wetland areas are significantly related to the population size,fishery output value,and urbanization rate.In summary,human activities,such as the construction of aquaculture ponds and salt pans,industrialization,and urbanization,are the primary forces that influence the environmental changes in the coastal region.This study is beneficial for establishing and improving the systems for the rational development and utilization of natural resources,and provides theoretical references for restoring wetland ecology and managing future reclamation activities in other coastal zone-related areas.

Spatial Variations in Depth-distribution of Trace Metals in Coastal Wetland Sediments from Quanzhou Bay,Fujian Province,China

Four short cores were obtained from the coastal wetland of the Quanzhou Bay,Fujian Province,China,and sediment samples were analyzed with a Mastersizer 2000 for grain size analysis and an Inductively Coupled Plasma Atomic Emission Spectrometer(ICP-AES) for trace metal analysis. The results of grain size analysis show that the wetland sediments are mainly composed of silt and clay,and the distribution of median grain size is affected by human activities obviously. The results of trace metal analysis show that the wetland sediments mainly originate from terrestrial materials in the Luoyangjiang River estuary and from contaminants discharged from adjacent rivers in Shuitou area. The heavy metal contamination in Luoyangjiang estuary decreased from 1984 to 2004 due to industry transformation,but has increased since 2004 because of the discharge of contaminants to the Jinjiang River and much living sewerage to the bay,and a large number of trace metals are trapped within Spartina alterniflora marsh.

Effect of Hydrological Connectivity on Soil Carbon Storage in the Yellow River Delta Wetlands of China

Hydrological connectivity has significant effects on the functions of estuarine wetland ecosystem.This study aimed to examine the dynamics of hydrological connectivity and its impact on soil carbon pool in the Yellow River Delta,China.We calculated the hydrological connectivity based on the hydraulic resistance and graph theory,and measured soil total carbon and organic carbon under four different hydrological connectivity gradients(Ⅰ0‒0.03,Ⅱ0.03‒0.06,Ⅲ0.06‒0.12,Ⅳ0.12‒0.39).The results showed that hydrological connectivity increased in the north shore of the Yellow River and the south tidal flat from 2007 to 2018,which concentrated in the mainstream of the Yellow River and the tidal creek.High hydrological connectivity was maintained in the wetland restoration area.The soil total carbon storage and organic carbon storage significantly increased with increasing hydrological connectivity fromⅠtoⅢgradient and decreased inⅣgradient.The highest soil total carbon storage of 0‒30 cm depth was 5172.34 g/m^(2),and organic carbon storage 2764.31 g/m^(2)inⅢgradient.The hydrological connectivity changed with temporal and spatial change during 2007‒2018 and had a noticeable impact on soil carbon storage in the Yellow River Delta.The results indicated that appropriate hydrological connectivity,i.e.0.08,could effectively promote soil carbon storage.

Combined influence of sedimentation and vegetation on the soil carbon stocks of a coastal wetland in the Changjiang estuary

Coastal wetlands play an important role in the global carbon cycle. Large quantities of sediment deposited in the Changjiang （Yangtze） estuary by the Changjiang River promote the propagation of coastal wetlands, the expansion of saltmarsh vegetation, and carbon sequestration. In this study, using the Chongming Dongtan Wetland in the Changjiang estuary as the study area, the spatial and temporal distribution of soil organic carbon （SOC） stocks and the influences of sedimentation and vegetation on the SOC stocks of the coastal wetland were examined in 2013. There was sediment accretion in the northern and middle areas of the wetland and in the Phragmites australis marsh in the southern area, and sediment erosion in the Scirpus mariqueter marsh and the bare mudflat in the southem area. More SOC accumulated in sediments of the vegetated marsh than in the bare mudflat. The total organic carbon （TOC） stocks increased in the above-ground biomass from spring to autumn and decreased in winter; in the below-ground biomass, they gradually increased from spring to winter. The TOC stocks were higher in the below-ground biomass than in the above-ground biomass in the P. australis and Spartina alterniflora marshes, but were lower in the below-ground biomass in S. mariqueter marsh. Stocks of SOC showed temporal variation and increased gradually in all transects from spring to winter. The SOC stocks tended to decrease from the high marsh down to the bare mudflat along the three transects in the order： P. australis marsh 〉 S. alterniflora marsh 〉 S. mariqueter marsh 〉 bare mudflat. The SOC stocks of the same vegetation type were higher in the northern and middle transects than in the southern transect. These results suggest that interactions between sedimentation and vegetation regulate the SOC stocks in the coastal wetland in the Changjiang estuary.

Validation of Global Evapotranspiration Product(MOD16) Using Flux Tower Data from Panjin Coastal Wetland,Northeast China

Recent advances in remote sensing technology and methods have resulted in the development of an evapotranspiration(ET) product from the Moderate Resolution Imaging Spectrometer(MOD16). The accuracy of this product however has not been tested for coastal wetland ecosystems. The objective of this study therefore is to validate the MOD16 ET product using data from one eddy covariance flux tower situated in the Panjin coastal wetland ecosystem within the Liaohe River Delta, Northeast China. Cumulative ET data over an eight-day period in 2005 from the flux tower was calculated to coincide with the MOD16 products across the same period. Results showed that data from the flux tower were inconsistent with that gained form the MOD16 ET. In general, results from Panjin showed that there was an underestimation of MOD16 ET in the spring and fall, with Biases of -2.27 and -3.53 mm/8 d, respectively(–40.58% and -49.13% of the observed mean). Results for Bias during the summer had a range of 1.77 mm/8 d(7.82% of the observed mean), indicating an overestimation of MOD16 ET. According to the RMSE, summer(6.14 mm/8 d) achieved the lowest value, indicating low accuracy of the MOD16 ET product. However, RMSE(2.09 mm/8 d) in spring was the same as that in the fall. Relationship between ET and its relevant meteorological parameters were analyzed. Results indicated a very good relationship between surface air temperature and ET. Meanwhile a significant relationship between wind speed and ET also existed. The inconsistent comparison of MOD16 and flux tower-based ET are mainly attributed to the parameterization of the Penman-Monteith model, flux tower measurement errors, and flux tower footprint vs. MODIS pixels.