Estuarine Wetlands Research Articles

Pattern evolution and impact factor of Jiuduansha Wetland at the Yangtze Estuary during 1989-2020

Affected by the changes of drainage basin and marine environment and human activities, estuarine wetland is fragile, sensitive, and complex in evolution. Jiuduansha Wetland is the largest estuarine shoal wetland in the Yangtze Estuary, and is undergoing rapid changes due to the reduction of sediment inputs and the invasion of alien species Spartina alterniflora. In this study, the changes of Jiuduansha Wetland from 1989 to 2020 were analyzed through remote sensing interpretation, field investigation, and topographic data analysis. The impacts of watershed sediment reduction and S. alterniflora invasion on Jiuduansha Wetland were analyzed based on the hydrological data of Datong station and the invasion history of S. alterniflora. The results showed that the total area of Jiuduansha Wetland (above -5 m) first increased and then decreased since 1991, reaching its maximum in 2005 (421.16 km2). The area of tidal flat wetland (above 0 m) and wetland vegetation increased continuously from 1989 to 2020, with 1.5 times and 47.1 times increases, respectively. The decreases of sediment supply led to a decrease in the total area of Jiuduansha Wetland (above -5 m) and a decrease growth rate of tidal flat wetland area above 0 m and vege-tation area. The invasive species S. alterniflora had expanded rapidly, occupied the space of native species, and became the dominant species in Jiuduansha Wetland since it was introduced in 1997. Sediment reduction and S. alterniflora invasion had led to the rapid changes of Jiuduansha Wetland structure. In order to avoid the degradation of ecological service, wetland protection and restoration should be taken to maintain the stability and health of Jiu-duansha Wetland.

Soil Bacterial Community Structure in Different Micro-Habitats on the Tidal Creek Section in the Yellow River Estuary

Tidal creeks have attracted considerable attention in estuary wetland conservation and restoration with diverse micro-habitats and high hydrological connectivity. Bacterial communities act effectively as invisible engines to regulate nutrient element biogeochemical processes. However, few studies have unveiled the bacterial community structures and diversities of micro-habitats soils on the tidal creek section. Our study selected three sections cross a tidal creek with obviously belt-like habitats “pluff mudflat – bare mudflat – Tamarix chinensis community – T. chinensis-Suaeda salsa community– S. salsa community” in the Yellow River estuarine wetland. Based on soil samples, we dissected and untangled the bacterial community structures and special bacterial taxa of different habitats on the tidal creek section. The results showed that bacterial community structures and dominant bacterial taxa were significantly different in the five habitats. The bacterial community diversities significantly decreased with distance away from tidal creeks, as well as the dominant bacteria Flavobacteriia and δ-Proteobacteria, but in reverse to Bacteroidetes and Gemmatimonadetes. Moreover, the important biomarkers sulfate-reducing bacteria and photosynthetic bacteria were different distributions within the five habitats, which were closely associated with the sulfur and carbon cycles. We found that the bacterial communities were heterogeneous in different micro-habitats on the tidal creek section, which was related to soil salinity, moisture, and nutrients as well as tidal action. The study would provide fundamental insights into understanding the ecological functions of bacterial diversities and biogeochemical processes influenced by tidal creeks.

Considering the influence of land use/land cover on estuarine biotic richness with Bayesian hierarchical models.

The composition of land use/land cover (LULC) in coastal watersheds has many implications for estuarine system ecological function. Land use/land cover can influence allochthonous inputs and can enhance or degrade the physical characteristics of estuaries, which in turn affects estuaries' ability to support local biota. However, these implications for estuaries are often poorly considered when assessing the value of lands for conservation. The focus of research regarding terrestrial and estuarine interfaces often evaluates how LULC may stress estuarine ecosystems, but in this study we sought to understand how LULC may both positively and negatively affect estuaries using measures of observed biotic richness as proxies for estuarine function. We investigated the influence of LULC on estuarine biotic richness with Bayesian hierarchical models using multiple geospatial data sets from 33 estuaries and their associated watersheds along the Gulf of Mexico coastal region of the United States. We designed the hierarchical models with observed species richness of three functional groups (FGs) (i.e., pelagic fishes, forage fishes, and shrimp) from fishery-independent trawl surveys as response variables. We then set salinity and water temperature as trawl-specific covariates and measures of influence from six LULC classes as estuary-specific covariates and allowed the models to vary by estuary, trawl program, salinity, and temperature. The model results indicated that the observed richness of each FG was both positively and negatively associated with different LULC classes, with estuarine wetlands and forested lands demonstrating the strongest positive influences on each FG. The results are generally consistent with past studies, and the modeling framework provides a promising way to systematically quantify LULC linkages with the biotic health of estuaries for the purposes of potentially valuing the estuarine implications of land conservation.

Sediment Nitrate Dissimilatory Reduction Processes along a Salinity Gradient in an Estuarine and Coastal Wetland, China

Nitrate (NO3−) dissimilatory reduction processes (denitrification, anammox and dissimilatory NO3− reduction to ammonium (DNRA)) in estuarine and coastal ecosystems play a crucial role in regulating reactive nitrogen loadings. However, nitrate reduction process rates and relative proportions along the estuarine salinity gradient remain poorly understood. Here, denitrification, anammox and DNRA were explored simultaneously along a salinity gradient in Yangtze Estuary based on nitrogen isotope-tracing experiments. Measured denitrification, anammox and DNRA process rates were in the range of 2.33–28.21 nmol g−1 h−1, 0.43–1.87 nmol g−1 h−1 and 0.28–0.74 nmol g−1 h−1, respectively, with a large spatio-temporal variation. The changes in these nitrate reduction process rates were mainly affected by the TOC, TN, NH4+ and NOx− concentrations, rather than salinity and related functional gene abundance. Denitrification dominated the total NO3− reduction process (67.52 to 93.85%), while anammox (3.67 to 25.01%) and DNRA (2.48 to 11.21%) also played a substantially important role in nitrate reduction. The proportions of denitrification to gross nitrate reduction in high-salinity areas were generally lower than those in freshwater, but the opposite was true for DNRA. Overall, our study reported the simultaneous observation of nitrate dissimilatory reduction processes along the salinity gradient of the estuary and highlighted that changes in sediment environmental variables affected by human activities can alter the distribution patterns of NO3− reduction processes.

Tidal variation and litter decomposition co-affect carbon emissions in estuarine wetlands

Estuarine wetlands play important roles in the regional and global carbon cycle as well as greenhouse gas emissions; however, the driving factors and potential carbon emissions mechanisms are unclear. Here, the carbon emission fluxes were investigated in situ from different vegetated areas in the Chongming wetlands. The results showed that the highest methane (CH4) and carbon dioxide (CO2) emissions of 178.1 and 21,482.5 mg∙m−2∙min−1 were in Scirpus mariqueter and Phragmites australis dominated areas, respectively. A series of microcosms was strategically designed to simulate the influence of tidal variation on carbon emissions and the litter decomposition on daily- and monthly-timescales in estuarine wetlands. All added litter promoted CH4 and CO2 emissions from the wetland soils. The CH4 and CO2 emission fluxes of the S. mariqueter treatment were higher (367.7 vs. 108.4; 1607.9 vs. 1324.3 mg∙m−2∙min−1) than those of the P. australis treatment without tidal variation on a monthly timescale, due to the higher total organic carbon (TOC) content of S. mariqueter. The decomposition of litter also released a large amount of nutrients, which enhanced the abundance of methane-producing archaea (MPA) and methane-oxidizing bacteria (MOB). However, the tidal water level was negatively correlated with CH4 and CO2 emission fluxes. The CH4 and CO2 emission fluxes in the S. mariqueter treatment at the lowest tide were 556.02 and 604.99 mg∙m−2∙min−1, respectively. However, the CH4 and CO2 emission fluxes did not change significantly on the daily timescale in the S. mariqueter treatment without tidal variations. Therefore, the prolonged timescales revealed increases in litter decomposition but a decrease in the contribution of tidal variations to carbon emissions in estuarine wetlands. These findings provide a theoretical basis for evaluating the carbon cycle in estuarine wetlands.

Biogeochemical behavior of P in the soil and porewater of a low-salinity estuarine wetland: Availability, diffusion kinetics, and mobilization mechanism

Estuarine wetlands, which typically store large amounts of phosphorus (P), are experiencing increased salinity as well as changed environmental factors caused by rising sea levels. In this study, the seasonal dynamics of P speciation, availability, and biogeochemical couplings with iron (Fe)-sulfur (S) in soil and porewater were measured in a low-salinity estuarine wetland using in situ high-resolution diffusive gradients in thin films (DGT) and dialysis (HR-Peeper) techniques. The diffusion kinetics and resupply capacity of P from the soil phase to solution were simulated using a DGT-induced fluxes in soils (DIFS) model. The transition from freshwater to brackish wetlands reduced soil P pools and shifted to more recalcitrant speciation. The concentration of DGT-labile P across the soil-water profiles ranged from 0.002 to 0.039 (mean: 0.015) mg L−1, which increased with increasing salinity in both the field and mesocosm experiments. The distributions of labile and soluble P showed high heterogeneity across the profiles, and there were some sharp peak values below the soil-water interface (SWI), which significantly increased the concentration and lability of P. The strong coupling between labile P and Fe (S) provided direct evidence for the coexistence of iron reduction (IR) and sulfate reduction (SR) in the estuary, while IR might predominate in P mobilization in the brackish environment because of higher labile Fe concentrations and stronger Fe-P couplings. The diffusion fluxes of P were positive at both sites, demonstrating that the kinetics of P were from the soils to the overlying water. Higher R and k-1 values fitted in the DIFS model implied that a stronger resupply capacity and desorption rate and thus faster remobilization kinetics of P occurred with increasing salinity. Our findings indicated that increased salinity (even at low levels) can alter the desorption rate and resupply capacity of soil P in estuarine wetlands and accelerate P remobilization and release by regulating the IR and SR processes, thereby leading to the deterioration of water quality.

Effects of simulated precipitation changes on plant community characteristics of wetland in the Yellow River Delta, China

Under the changing climate scenario, changes in precipitation regimes are expected to alter soil water and salinity conditions, with consequences on the characteristics of plant community in estuarine wetland. Here, we used a six-year (2015-2020) precipitation manipulation experiment to examine how plant community characteristics responded to precipitation changes in the Yellow River Delta. The results showed that soil electrical conductivity significantly decreased, while soil moisture significantly increased with increasing precipitation. Precipitation changes altered plant community composition. Increased precipitation reduced the absolute dominance of Suaeda glauca and Suaeda salsa, but increased that of Triarrhena sacchariflora and Imperata cylindrica. Shannon index and Margalef richness index of plant community significantly increased with increasing precipitation. Compared with the control, both decreased and increased precipitation decreased the plant community abundance, frequency and coverage. The treatment of 60% increased precipitation significantly decreased plant community frequency by 54.9%, while the 60% decreased precipitation, 40% decreased precipitation, 40% increased precipitation and 60% increased precipitation treatment significantly decreased plant abundance by 38.9%, 33.8%, 35.8% and 45.7%, respectively. The aboveground biomass significantly increased with increasing precipitation, but aboveground plant biomass under 60% increased precipitation treatment being lower than that reducing under 40% increased precipitation treatment, probably due to the negative effects of flooding stress. In addition, Margalef richness index had a significantly positive relationship with aboveground biomass. Aboveground biomass, Shannon diversity index, Margalef richness index, and Simpson diversity index were negatively related to soil electrical conductivity, and aboveground plant biomass was positively related to soil moisture. Our results revealed that precipitation changes regulate growth characteristics, species composition, and diversity of plant community by altering soil water and salinity conditions in a coastal wetland.

Soil Organic Carbon Storage, Active Component Contents, and Stability Along a Flooding Gradient in the Tidal Wetland of the Jiulong River Estuary

Flooding is one of the key environmental factors affecting the carbon sequestration potential of estuarine tidal flat wetlands. In order to reveal the effect of flooding on soil carbon (C) sinks in estuarine tidal wetlands, we investigated and analyzed the soil organic carbon (SOC) storage, the contents of active SOC components, and SOC stability indicators across a tidal flat in the Jiulong River estuary in southeast China. The results showed that the SOC storage gradually decreased by 54% with the increase in flooding frequency. The change pattern of microbial biomass carbon (MBC), dissolved organic carbon (DOC), and liable organic carbon (LOC) followed the change pattern of the SOC storage. With the increase in flooding frequency, DOC/SOC and LOC/SOC increased by 80% and 26%, respectively, whereas MBC/SOC decreased by 29%. As flooding frequency increased, particulate organic carbon (POC) and mineral-associated organic carbon (MAOC) contents decreased by 81% and 35%, respectively. The decreases in POC contents were correlated with the increases in soil pH, whereas the decreases in MAOC contents were associated with the decline in clay contents. Soil carbon stability index (CSI) increased by 246% with increasing flooding frequency. These combined results indicated that SOC storage decreased, but SOC stability increased, with the increased flooding frequency. Mineral-bound organic carbon was the main protection mechanism for the SOC stability, which was of great significance to the soil C sink of the estuarine tidal wetlands.

Spatially explicit estimation of soil organic carbon stock of an estuarine mangrove wetland of eastern India using elemental analysis and very-fine resolution satellite data

BackgroundThis study estimated the total soil organic C (SOC) stock of the wetland influence zone of Bichitrapur mangroves in eastern India in a spatially explicit manner. Both spatial and vertical distribution of SOC densities with respect to land use/land cover (LULC) pattern were assessed. Subsequently, some site-specific management strategies were forwarded towards enhancement of C sequestration potential.MethodsThe changing patterns of LULC within the wetland influence zone of the site were analyzed using Landsat TM (30 m) and Pleiades-1A (2 m) imageries from 1988 to 2018. Point-specific SOC measurement was done using samples taken from four core-depth intervals (viz. D1: 0–20 cm, D2: 20–40 cm, D3: 40–70 cm, D4: 70–100 cm) at 89 locations belonging to different LULC categories. Spatial interpolation was applied on this point-based data to produce SOC density and stock models as a whole and at all core-depths. Relationships between SOC density, core-depth and present LULC were evaluated through multivariate statistical analyses.ResultsThe LULC transformations during last three decades suggested the gradual growth of mangrove plantations as well as agricultural and aquacultural activities. Most amount of SOC was concentrated in D1 (37.17%) followed by D3 (26.51%), while D4 had the lowest (10.87%). The highest mean SOC density was observed in the dense mangrove patches (248.92 Mg ha−1) and the lowest mean was in the Casuarina plantations (2.78 Mg ha−1). Here, Spline method emerged as the best-fit interpolation technique to model SOC data (R2 = 0.74) and estimated total SOC stock of the entire wetland influence zone as 169,569.40 Mg and the grand mean as 125.56 Mg ha−1. Overall, LULC was inferred as a major determinant of SOC dynamics with a statistically significant effect (p < 0.001), whereas no such inference could be drawn for soil core-depth.ConclusionsThe C sequestration potential of sites such as the present one could be increased with appropriate zone-wise plantation strategies, restriction on the land conversion to aquaculture and promotion of ecotourism. Periodic monitoring through integration of geospatial techniques and elemental analyses would be immensely beneficial in this regard.Graphic

Optimization of plant harvest and management patterns to enhance the carbon sink of reclaimed wetland in the Yangtze River estuary

Estuarine wetlands are often located in economically developed and densely populated estuarine deltas, which are frequently disturbed and threatened by human activities. Reclamation, as an important way to alleviate the demand for local land resources, can lead to habitat destruction of natural coastal wetlands and weakening of ecological service functions, including carbon sink capacity. Research has shown that poor plant growth and weakened carbon fixation were the main reasons for the reduced carbon sequestration in a reclaimed wetland. This study aimed to examine the impacts of plant management on the improvement or restoration of carbon sink function in Chongming Dongtan reclaimed wetland, located in the Yangtze River Estuary, China. A management pattern that could effectively enhance the carbon sink function of the reclaimed wetland was selected based on analyses of the effects of different plant harvesting and management patterns (no harvesting, harvesting without returning to the field, direct straw return, and charred straw return) on the plant growth, carbon fixation, and soil respiration, combined with whole-life-cycle carbon footprint evaluation from straw harvest to field return. Compared with no harvesting, the aboveground biomass of direct straw return and charred straw return increased by about 12.3% and 15.5%, respectively (P < 0.05). Simultaneously, straw charring released the least amount of CO2 (1.94 μmol m−2 s−1) and inhibited degradation of soil organic carbon through affecting its microbial community structure. Moreover, considering the carbon budget of different patterns, the charred straw return pattern also most effectively enhanced the carbon sink function and thus could be used for subsequent improvement of carbon sequestration in reclaimed wetlands.

Spatiotemporal Dynamics of Bacterial Taxonomic and Functional Profiles in Estuarine Intertidal Soils of China Coastal Zone.

Bacteria play an important role in regulating carbon (C), nitrogen (N), and sulfur (S) in estuarine intertidal wetlands. To gain insights into the ecological and metabolic modes possessed by bacteria in estuarine intertidal wetlands, a total of 78 surface soil samples were collected from China's coastal intertidal wetlands to examine the spatial and seasonal variations of bacterial taxonomic composition, assembly processes, and ecological system functions through shotgun metagenomic and 16S rRNA gene sequencing. Obvious spatiotemporal dynamic patterns in the bacterial community structure were identified, with more pronounced seasonal rather than spatial variations. Dispersion limitation was observed to act as a critical factor affecting community assembly, explaining approximately half of the total variation in the bacterial community. Functional bacterial community structure exhibited a more significant latitudinal change than seasonal variability, highlighting that functional stability of the bacterial communities differed with their taxonomic variability. Identification of biogeochemically related links between C, N, and S cycles in the soils showed the adaptive routed metabolism of the bacterial communities and the strong interactions between coupled metabolic pathways. Our study broadens the insights into the taxonomic and functional profiles of bacteria in China's estuarine intertidal soils and helps us understand the effects exerted by environmental factors on the ecological health and microbial diversity of estuarine intertidal flats.

Soil characteristics and ecological thresholds of Suaeda salsa wetlands

ABSTRACT Suaeda salsa is an annual euhalophyte in estuarine wetlands. Soil properties of wetlands have an important influence on S. salsa growth. Therefore, the soil ecological thresholds is valuable for the restoration of degraded S. salsa wetlands. The objectives of this present study were to analyze the soil physicochemical properties and evaluate the soil ecological thresholds in the typical degraded areas for S. salsa growth. Soil text components became coarser with increased sand contents and less clay contents, as the higher degree of wetland degradation. Meanwhile, the salt contents in different soil depths gradually increased with the increased degree of degradation of wetlands. Evident changes in soil water content, organic matter content, and cations concentrations were not observed, while the concentrations of these factors were higher in the soil layer of 0–10 cm than those in the 20–30 cm. The soil pH in the 0–10 cm soil layer was lower than that in the 20–30 cm. The content of the three available nutrients did not change evidently with the increasing degree of degradation. The optimum thresholds of soil salinity and water content were 7.073–16.613 g/kg and 31.8–63.2%, respectively.

Different stochastic processes regulate bacterial and fungal community assembly in estuarine wetland soils

The long-standing challenge in microbial ecology is to quantify the relative importance of deterministic and stochastic processes in controlling the community structures through space and time. Deterministic processes are important when the environmental selection and species interactions are strong, whereas stochastic processes may dominate when there is large number of neutral births, death, speciation of microorganism. The existing studies are still lacking in understanding how these two processes structure microbial communities in an ecosystem whose environmental gradients change sharply at a very short geographic scale, such as in the fresh-saltwater transition zone. Here, we investigated the bacterial and fungal assembly processes in topsoil (0–10 cm) in a wetland transect with fresh-saltwater transition zone in the Yellow River Estuary, China, by calculating beta-mean-nearest taxon distance (βMNTD), beta nearest taxon index (βNTI) and Raup–Crick index. We found that stochastic processes primarily shaped the two communities. The bacterial assembly was controlled by homogenizing dispersal and dispersal limitation within and across the wetland transect, respectively. The fungal assembly, on the other hand, was mostly regulated by undominated processes, which are processes induced by weak selection/dispersal, diversification, and drift. Dispersal limitation had more pronounced effects on the bacterial diversity and cooccurrence in comparison with the effects of undominated processes on the fungal community. Nevertheless, environmental factors, such as pH, salinity and C/N, explained ∼30% (p < 0.01) of compositional variations with more explanatory power for bacteria than fungi. Our study highlights the different types of stochastic processes in regulating bacterial and fungal communities along the short natural environmental gradients.

Spartina alterniflora invasion has a greater impact than non-native species, Phragmites australis and Kandelia obovata, on the bacterial community assemblages in an estuarine wetland

The invasion of Spartina alterniflora poses a serious threat to the sustainability of native ecosystems worldwide. However, compared with other non-native plants (e.g., Phragmites australis and Kandelia obovata), how Spartina alterniflora invasion influences the community structure of bacteria and their assembly processes and functionality remains elusive. Here, we characterized the diversity, community structure, assembly processes and functional guilds of bacteria underneath five plant species and a bare tidal flat at three soil depths in an estuarine wetland. We found that plant species played a more important role than soil depth in mediating the bacterial community structure. Compared with bare tidal flats, the native species Cyperus malaccensis, rather than Scirpus triqueter, significantly changed the bacterial community structure. However, S. alterniflora invasion increased bacterial alpha diversity and significantly altered the bacterial community structure by enriching Chloroflexi, Bacteroidetes and Firmicutes while reducing Acidobacteria, Nitrospirae and Gemmatimonadetes. The invasion of P. australis and translocation of K. obovata had less pronounced effects on the bacterial community structure. Total carbon, total nitrogen and salinity were the key environmental factors mediating the bacterial community structure. Overall of all the non-native plant species, the invasion of S. alterniflora increased the relative importance of stochastic processes in the assembly of bacterial communities, and shifted the bacterial functional profiles by stimulating sulfur cycling groups and suppressing nitrogen cycling groups. Altogether, our results suggest that S. alterniflora invasion has a greater effect than P. australis invasion or K. obovata translocation on the profiles and assembly processes of the bacterial communities, with important implications for soil biogeochemical processes in coastal wetlands.

Stopover use of a large estuarine wetland by dunlins during spring and autumn migrations: Linking local refuelling conditions to migratory strategies.

Migratory strategies dictate stopover ecology, particularly concerning decisions of when, where and how long to stop, and what to do at stationary periods. In birds, individuals stop primarily to replenish energy stores, although the functions of stopover events vary among and within species, particularly between pre- and post-breeding seasons. Here, we combined plasma metabolite levels and haematological parameters to compare refuelling rates and physiological state within (early, mid, late) and between (spring, autumn) migratory periods, aiming to identify potentially different migratory strategies in a shorebird, the dunlin Calidris alpina, using a key stopover site in Iberia. Plasma triglycerides and β-hydroxybutyrate concentrations did not differ between seasons, and small differences were found in haematological profiles (higher haemoglobin and hematocrit levels in spring). Similar refuelling rates and physiological status suggests a single migratory strategy in spring and autumn. During both seasons, dunlins arrive at the Tagus estuary with medium-to-high fuel loads, indicating they do not engage in prolonged fuelling. This agrees with a skipping migratory strategy, where birds fly short-to-medium distances while fuelling at moderate rates along a network of sites. Although we may expect late spring migrants to experience stronger pressures to optimally schedule migratory events, we found no significant differences in physiological profiles among early, mid and late migrants. Unexpectedly, such differences were found in autumn: early birds showed the highest triglycerides and haemoglobin levels and lowest β-hydroxybutyrate concentrations. These results denote enhanced refuelling rates and blood oxygen-carrying capacity in early autumn migrants, which is typical of jumpers, i.e., birds travelling with larger fuel loads and performing fewer stops. Our study adds substantially to previous knowledge of stopover ecology in migratory shorebirds in the East Atlantic Flyway. Importantly, it indicates that the Tagus estuary is a high-quality stopover site for intermediate fuelling. Yet, understanding non-fuelling stopping functions is needed to ultimately inform conservation planning.

Plant Species-Driven Distribution of Individual Clades of Comammox Nitrospira in a Subtropical Estuarine Wetland.

Plant species play a crucial role in mediating the activity and community structure of soil microbiomes through differential inputs of litter and rhizosphere exudates, but we have a poor understanding of how plant species influence comammox Nitrospira, a newly discovered ammonia oxidizer with pivotal functionality. Here, we investigate the abundance, diversity, and community structure of comammox Nitrospira underneath five plant species and a bare tidal flat at three soil depths in a subtropical estuarine wetland. Plant species played a critical role in driving the distribution of individual clades of comammox Nitrospira, explaining 59.3% of the variation of community structure. Clade A.1 was widely detected in all samples, while clades A.2.1, A.2.2, A.3 and B showed plant species-dependent distribution patterns. Compared with the native species Cyperus malaccensis, the invasion of Spartina alterniflora increased the network complexity and changed the community structure of comammox Nitrospira, while the invasive effects from Kandelia obovata and Phragmites australis were relatively weak. Soil depths significantly influenced the community structure of comammox Nitrospira, but the effect was much weaker than that from plant species. Altogether, our results highlight the previously unrecognized critical role of plant species in driving the distribution of comammox Nitrospira in a subtropical estuarine wetland.

Composition of water sources and transformation relationship between surface water and groundwater in the Fenhe River estuarine wetland of the middle Yellow River

水源动态补给和转化是影响湿地水文过程及其生态效应的重要机制，在黄河流域生态保护和高质量发展的战略背景下，开展沿黄湿地多水源组成分析及转化关系研究，是揭示干旱半干旱区水量转化及湿地生态系统演变机制的关键.本文根据山西省汾河入黄口湿地的水文节律变化特征，选择2019年旱季（5月）、主汛期（7月）和汛末（9月）作为典型时期，分析了降雨、土壤水、地下水与河水氢氧同位素组成，研究了湿地水分的补给来源，并结合端元混合模型揭示了不同时期地表水与地下水的转化关系.结果发现，不同水体¹⁸O和D组成存在明显差异，均值总体表现为降雨 > 土壤水 > 汾河水 > 汾河流域地下水 > 黄河水的变化特征，表明黄河和流域地下水的侧向排泄对汾河下游径流和河口湿地水源补给具有重要贡献作用.进一步研究得出，旱季湿地地下水在近岸带主要受汾河水补给影响，随着远离汾河水体，主要受流域浅层地下水补给，并向黄河水转化，主汛期和汛末期，黄河水又侧向补给湿地地下水，并向汾河水转化，而湿地土壤水主要受降雨入渗和毛细上升水的影响.入黄口湿地的地表水-地下水存在季节变化的作用关系，旱季主要为汾河流域浅层地下水侧向补给汾河，补给贡献约为72%，然而主汛期，由于黄河倒灌补给导致汾河水位抬高，进而渗漏补给流域浅层地下水，补给比例约为69%，至于汛末期，黄河和流域地下水均向汾河排泄.本文研究结果对促进黄河流域生态保护和自然湿地生态建设具有重要的意义，可强化对河口湿地水资源组成和演变机制的深入理解.;Water supply and the conversion relationship among different water sources play an important role in affecting wetland hydrological processes and the associated ecological functions. Under the guidance of the national strategy of ecological protection and high-quality development of the Yellow River, exploring the conversion relationship among rainfall, surface water, and groundwater in the estuarine wetland of the Yellow River Basin is the key to reveal the mechanism of regional wetland system evolution and the water conversion processes in the arid and semi-arid area. In this study, we aim to investigate the characteristics of hydrogen and oxygen isotopes of rainfall, river water, groundwater, soil water in the Fenhe River estuarine wetland (the Yellow River) in May, July, and September during 2019. To achieve these objectives, the water sources composition of wetland in different hydrological periods was analyzed. In addition, the transformation relationship among rainfall, surface water, and groundwater was quantified using a mixed source model. The results show that the isotope composition of various water sources is distinctly different. The mean values of δD and δ¹⁸O for different water sources are in the order of rainfall, soil water, Fenhe River water, watershed groundwater, and the Yellow River water, demonstrating that the discharge of the Yellow River water and the watershed groundwater plays a prominent role in maintaining the downstream runoffs of Fenhe River and the wetland water sources. During the drought season, the wetland groundwater in the riparian zone is mainly supplied by Fenhe River. Because of the increased distance to Fenhe River, the wetland is mainly recharged by the shallow groundwater from the Fenhe River basin, and then discharges to the Yellow River. While the Yellow River water transformed to the wetland groundwater in high water level season. The wetland soil water is mainly recharged by the local rainfall and the wetland groundwater. The transformation relationship among rainfall, river water, and groundwater varies between different seasons. During the drought season, the shallow groundwater in Fenhe River basin discharges into the Fenhe River, with a contribution proportion of 78%. During the flood period, the Yellow River acts to restrict discharge from the Fenhe River, and the flow reversals occur as the Yellow River's strong blocking effect. Consequently, the watershed shallow groundwater is generally replenished by the Fenhe River water at high water level stage, and the proportions can reach up to approximately 69%. However, the Yellow River water, wetland groundwater, and the shallow watershed groundwater discharge to the surrounding Fenhe River channel during the falling water period. The outcomes of this paper are of great significance for national ecological conservation of the Yellow River Basin and the restoration of natural wetland, contributing to further understanding water resources composition and evolution mechanism in other similar estuarine wetlands.

干旱叠加海平面上升、氮负荷增加对河口潮汐沼泽生态系统净CO2交换的影响

PDF HTML阅读 XML下载 导出引用 引用提醒 干旱叠加海平面上升、氮负荷增加对河口潮汐沼泽生态系统净CO2交换的影响 DOI: 10.5846/stxb202106291727 作者: 作者单位: 作者简介: 通讯作者: 中图分类号: 基金项目: 福建省自然科学基金重点项目（2019J02008）；福建省林业科技项目（201916）；国家自然科学基金项目（41877335） Effects of combination of drought and sea-level rise, nitrogen enrichment on net ecosystem exchange of CO2 in an estuarine tidal marsh Author: Affiliation: Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:河口潮汐沼泽湿地是全球重要的蓝碳生态系统之一。海平面上升和氮负荷增加是入海河流河口湿地面临的两个主要环境问题。近年来，干旱事件频发，干旱及其与海平面上升、氮负荷增加的叠加将如何影响河口潮汐沼泽湿地生态系统净CO2交换，目前还未见报道。2020年夏秋，福建沿海经历了数月严重的气象干旱，这为揭示干旱对河口潮汐沼泽湿地生态系统净CO2交换量（NEE）和生态系统呼吸（ER）的影响提供了一个契机。分别于2019年8-10月（正常天气）和2020年8-10月（干旱天气），在闽江河口微咸水短叶茳芏沼泽湿地运用光合作用测定仪+箱法测定不同处理（对照、模拟海平面上升、模拟氮负荷增加、模拟海平面上升＋模拟氮负荷增加）短叶茳芏湿地生态系统NEE和ER，以期揭示气象干旱与海平面上升、氮负荷增加的叠加对河口沼泽湿地生态系统净CO2交换的影响。与正常天气相比，干旱天气下各处理（包含对照）的NEE均显著降低（P<0.05）；对照、海平面上升以及氮负荷增加处理样地的ER显著减少（P<0.05），海平面上升＋氮负荷增加处理ER显著增加（P<0.05）。NEE （负值）与光合有效辐射（PAR）与呈显著负相关（P<0.05）。研究发现，气象干旱降低了河口潮汐沼泽生态系统固碳规模，且这种固碳规模的降低在叠加海平面上升或氮负荷增加的情景下仍将存在。 Abstract:Estuarine tidal marsh is one of the coastal blue carbon ecosystems in the world. Sea level rise and nitrogen enrichment are two major global environmental issues facing by estuarine wetlands. In recent years, meteorological drought events often occurred. The influences of drought, and combination of drought and sea-level rise, and nitrogen enrichment on net ecosystem exchange (NEE) of CO2 of estuarine tidal marshes remain poorly studied. A novel approach using the weirs for in-situ manipulating sea level rise (including the increase of depth and duration of flooding) at relatively larger spatial scale was developed in the journal of Methods in Ecology & Evolution, however at present, the method has not been actually used in-situ to study effects of sea level rise on carbon cycle in coastal tidal marsh ecosystem. In our study, we improved the weirs and used them to manipulate the sea level rise (SR) treatment in-situ, and meanwhile applied in-situ experimental manipulations of control, nitrogen enrichment (NE), and SR+NE in a tidal brackish marsh of Cyperus malaccensis in the Minjiang River estuary, southeastern China. In summer and autumn of 2020, the meteorological drought occurred in the coastal zone of Fujian Province, which provided an opportunity to determine the effects of drought, the combination of drought and simulated sea-level rise, nitrogen enrichment on the NEE and ecosystem respiration (ER). From August to October in 2019 and 2020, the NEE and ER were measured using transparent static chamber (or black cloth shading)+Licor-6800 method. Compared with 2019 (normal year), the NEE under each treatment (including control) was significantly reduced in 2020 (drought year), and the ER in the control, the SR, and the NE was also significantly decreased in 2020. NEE was significantly negatively correlated with the photosynthetically active radiation (PAR). The results indicate that drought event can reduce net CO2 gain in estuarine tidal marshes, and this decrease still occurs under combination of drought and sea-level rise, nitrogen enrichment. 参考文献 相似文献 引证文献

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