Sanjiang Plain Research Articles

Study of artificial water replenishment for wetland restoration

AbstractThe degradation of wetlands has caused regional environment and climate problems in the Sanjiang Plain. To provide a reference for wetland protection and restoration, two artificial water replenishment schemes were designed and four indicators—water quantity, ammonia nitrogen, total nitrogen and total phosphorus—were chosen to analyse results simulated by an environmental fluid dynamics code model. Simulation results showed that the wetlands receive a suitable amount of water and reach a normal water elevation, and the concentration of most water quality indicators decreased. In addition, a fuzzy analytic hierarchy process was used to select the four indicators and 30 different combinations were designed. Following the fuzzy calculation, the comprehensive scores of 29 combinations showed that a scheme involving multiple replenishments is better than a scheme of a single replenishment. This study indicates that an effective method for restoring wetlands near or surrounding irrigation areas is rational allocation of water resources.

Responses of Soil Microbial Biomass and Enzyme Activities to Natural Restoration of Reclaimed Temperate Marshes After Abandonment

Restoration of reclaimed marshes has great effects on soil biological processes. However, the responses of soil microbial properties (microbial biomass and enzyme activities) to natural restoration of reclaimed marshes is poorly studied, especially in a long restoration chronosequence. This study assessed the responses of soil microbial properties to natural restoration and investigated the relationships between soil microbial properties and soil physico-chemical and plant properties. We selected a restoration chronosequence (1, 4, 8, 13, 17, 27 years) after farmland abandonment, a soybean field, and a natural marsh in Sanjiang Plain, northeast China. For each site, we analyzed the soil microbial biomass carbon and nitrogen (MBC and MBN), four enzymes (β-glucosidase, invertase, catalase, urease) activities, soil physico-chemical properties at 0–50 cm depths, and plant properties (biomass, height, and coverage). The MBC and MBN contents increased with restoration time, but MBN content slowed down after 8 years of restoration. After 27 years of restoration, the soil MBC and MBN contents were 15.7 and 3.2 times of those in the soybean field, but the largest contents of MBC and MBN in the restored sites were 7.78%, 27.76% lower than those in natural marshes, respectively. Moreover, soil enzyme activities and the geometric mean of enzymatic activities (GME) also increased with restoration but slowed down after 13 years of restoration. After 27 years of restoration, the GME was 2.9 times than that in the soybean field, but the largest GME in the restored sites was 31.15% lower than that in the natural marsh. MBC and MBN contents, soil enzyme activities, and GME had significant relationships with soil C:N ratio, organic carbon, nutrients (total nitrogen, available nitrogen, total phosphorus), bulk density, moisture content, pH, plant properties, (i.e. biomass, height, and coverage) (p < 0.01). Redundancy analysis revealed that soil C:N ratio, pH, moisture content, total nitrogen and phosphorus were main factors affecting MBC and MBN contents and enzyme activities. In conclusion, soil microbial properties can respond positively to the natural restoration process of the reclaimed marshes and were significantly correlated with specific parameters of soil physico-chemical and plant properties.

The Effect of Returning Farmland to Grassland and Coniferous Forest on Watershed Runoff—A Case Study of the Naoli River Basin in Heilongjiang Province, China

In the 1950s and 1970s, China implemented large-scale wasteland reclamation in the Sanjiang Plain in eastern Heilongjiang Province, which expanded the area of cultivated land. Cultivated areas alter the quantity of water resources, provide the ecological requirements of river basins, and promote the ecological health of land use. In this study, the grid-based Sacramento (GSAC) model was adopted to simulate various changes in arable land, grassland, cultivated land, and deciduous coniferous forest. Quantitative analysis of the influence of cultivated land change on runoff and under dry season flow was conducted. The results showed that the GSAC model attains a high certainty coefficient in the process of simulating the daily basin discharge and reproduces the daily basin discharge process well for many years. The annual runoff increased between 5.07 and 64.05% due to the return of farmland to grassland and coniferous forest. The return of farmland to grassland greatly impacted runoff. The slope of the grassland and coniferous forest converted from farmland was negatively correlated with the discharge in the basin outlet section. The lower the gradient threshold in the scenario of returning arable land to forest or grassland, the more arable land will be replaced by grassland or deciduous coniferous forest, which could result in more water production in the watershed. Among the different change scenarios, the average flow rate of cultivated land with a slope larger than 15° was the closest to the ecological water demand of the studied watershed. The land use mode of converting cultivated land with a slope larger than 15° into grassland is expected to promote the ecological health of the watershed.

Bioconcentrations and health risk assessment of heavy metals in crops in the Naoli River Basin agricultural area, Sanjiang Plain, China

Bioconcentrations and health risk assessment of heavy metals in crops in the Naoli River Basin agricultural area, Sanjiang Plain, China

Tracking Historical Wetland Changes in the China Side of the Amur River Basin Based on Landsat Imagery and Training Samples Migration

In the recent decades, development of agricultural and human settlements have severely affected wetlands on the China-side of the Amur River Basin (CARB). A long-term holistic view of spatio-temporal variations of the wetlands on the CARB is essential for supporting sustainable conservation of wetlands in this region. In this study, a training sample migration method along with Random Forest classifier were adopted to map wetland and other land covers from two key seasons image collections. The proposed classification method was applied to Landsat images, and a 30-m resolution dataset was obtained, which reflected the dynamic changes of historical wetland distribution on the CARB region from 1990 to 2010. As the accuracy assessments showed, land cover maps of the CARB had high accuracies. The classification results indicated that the wetland area decreased from 89,432 km2 to 75,061 km2 between 1990 and 2010, with a net loss of 16%, which was mainly converted to paddy field and dry farmland, and the changes were most obvious in Sanjiang Plain and Songnen Plain. This suggests that agricultural activities are the main cause of wetland loss. The results can provide reliable information for the research on wetland management and sustainable development of the society and economy in the CARB.

Aquatic invertebrate assemblages during the spring-thaw season in wetlands of Northeastern China

Identifying the character and importance of invertebrates in thawing wetlands is useful, since they are the main food resource for migratory waterfowl during spring. We investigated aquatic invertebrate composition in the spring-thaw and compared it with the summer in wetlands of the Sanjiang Plain, China. NMDS analysis showed that the composition of aquatic invertebrates in the spring-thaw is significantly different from in summer. Aquatic invertebrate diversity (including Shannon–Wiener index; Margalef’s species richness; Pielou’s evenness) was lower in the spring-thaw, and Network analyses indicated that it was a simpler community. Indicator species were different between spring-thaw and summer. The scraper functional feeding group (i.e., snails) dominated both seasons, but especially in the spring-thaw. Snails and other invertebrates such as asellid crustaceans abounded in spring, are rich in both calcium and protein, making them to be an especially important food source for migratory waterfowl. Therefore, the spring-thaw should be a focus when assessing aquatic invertebrate function for waterfowl production.

Importance of stopping groundwater irrigation for balancing agriculture and wetland ecosystem

The surge in agricultural water consumption to ensure food security in China has severely hampered the survival of wetland ecosystems. People ignore the importance of “lungs” in the process of meeting the needs for “stomach”. In this study, we quantified the direct and indirect impacts of agricultural water consumption on wetland plant species using Characterization Factors (CFs) and identified their contributions in the three historical periods in the Sanjiang Plain, China. The total potential losses of wetland plant diversity were calculated, and the wetland benefits were evaluated based on the “National Sustainable Agriculture Plan for 2030”. Results indicated that the direct impact of the amount of irrigation water on plant species enhanced, while the indirect impact of groundwater abstraction declined with a drop in one order of magnitude. However, the wetland plant diversity was more responsive to 1 m3 of groundwater abstraction than 1 m3 of irrigation water in all three periods. The agricultural water consumption resulted in more than 120 wetland plant species-eq potential loss from 1987 to 2018, where irrigation water contributed for 57% and groundwater abstraction behavior contributed for 43% loss. The plant diversity loss due to groundwater abstraction was avoidable. By 2030, the wetland plant diversity will be restored by 15.5% according to the national policy, almost all of which comes from the contribution of eliminating the groundwater use. The comprehensive implementation of surface water irrigation, as a practical alternative to groundwater source, is an effective approach to alleviate the contradiction of food security and wetland protection.

Reference evapotranspiration change in Heilongjiang Province, China from 1951 to 2018: The role of climate change and rice area expansion

It is of great significance to study the variation in reference evapotranspiration (ETo) and the factors that influence it to ensure the sustainable and efficient utilization of water resources. In this study, the spatio-temporal changes in ETo and rice areas as well as the relationship between them in Heilongjiang Province, China, from 1951 to 2018 were analysed by using trend, correlation and contribution analyses. The results showed that rice area expansion is an important factor affecting ETo changes. ETo in Heilongjiang Province decreased during the study period. The areas with high ETo in the Songnen and Sanjiang Plain showed a gradually shrinking trend. Climate change and rice area expansion both contributed to the decline in ETo. The decreases in sunshine duration and average wind speed in Heilongjiang Province were the main reasons for the decrease in ETo. Rice area in Heilongjiang province continued to increase at a rate of 0.54 × 105 ha yr−1. The expansion of rice area in Sanjiang Plain was the largest, followed by Songnen Plain. In response to the rice area expansion, the rise in average temperature slowed down, the average relative humidity was increased, while wind speed was reduced, which directly lead to the decrease in ETo. The effects of the transformation of different land types into rice fields on ETo were different. The cumulative effects of wetlands and dry fields conversion to rice fields on ETo were 7.67 mm yr−1 and − 20.15 mm yr−1 in Sanjiang Plain respectively.

Shrub encroachment balances soil organic carbon pool by increasing carbon recalcitrance in a temperate herbaceous wetland

In recent decades, temperate herbaceous wetlands have been widely experiencing shrub encroachment. By now, little has been known about whether such alteration in plant community would generate updated soil organic carbon (SOC) conservation strategies, and thus alter SOC dynamics. To assess the temporal dynamics of SOC stock and fractions after shrub encroachment into temperate herbaceous wetlands, we measured floor litter mass, fine root biomass, and SOC stock and fractions (i.e. labile C pool I, labile C pool II, and recalcitrant C pool) across the 0–50 cm soil profile in the open wetlands and shrub islands (Betula fruticose and Salix floderusii) with different basal diameter sizes (small, 10 ~ 15 cm; medium, 15 ~ 20 cm; and large, 20 ~ 30 cm) in the Sanjiang Plain of Northeast China. Regardless of shrub species, SOC stock initially decreased after shrub expansion, but gradually recovered to the initial level of herbaceous wetlands. Moreover, SOC stock correlated positively with fine root biomass, but showed no significant relationship with floor litter mass. The responses of SOC fractions to shrub expansion mainly occurred in the surface soils (0–15 cm), despite a slight change in recalcitrant C pool in 15–50 cm layer. In the surface soils, labile C pool decreased substantially, whereas recalcitrant C pool and recalcitrant index of SOC elevated with increasing shrub sizes. Shrub encroachment can recover SOC pool and enhance SOC recalcitrance in temperate herbaceous wetlands, and altered fine root biomass would account for shrub encroachment-induced SOC dynamics.

Variation of soil carbon and nitrogen storage in a natural restoration chronosequence of reclaimed temperate marshes

Wetland restoration significantly affects ecosystem carbon and nitrogen cycles by changing soil physicochemical properties and plant properties. To reveal the effect of wetland restoration on soil organic carbon (SOC) and total nitrogen (TN) storage, we measured the SOC and TN content and calculated their storage in a restoration chronosequence (1, 4, 8, 13, 17, 27 years) and compared them with those in a soybean field and a natural marsh, all in Sanjiang Plain, northeast China. Our results showed that the SOC and TN content and storage in the investigated sites increased with restoration time. However, the restoration rate was faster in the first 8 years but slowed down after 8 years of restoration. The SOC and TN content and storage decreased with soil depths in the eight sites. After 27 years of restoration, the carbon and nitrogen storage in the restored site was 2.8 and 1.9 times that in the soybean field, respectively. However, the SOC and TN storage in the 27-year restored site was 45.3% and 35.1% lower than that in the natural marsh, respectively. The SOC and TN content, bulk density, moisture content, clay, and plant belowground biomass significantly impact the SOC and TN storage (P < 0.01). This study indicates that marsh restoration contributes to the accumulation of SOC and TN, but the restoration of SOC and TN storage to the level of natural marshes may take decades.

Hydrological and palynological evidence of wetland evolution on the Sanjiang Plain (NE China) in response to the Holocene East Asia summer monsoon

The responding mechanism of wetland ecosystem to climate change is currently unclear due to a lack of long-term records incorporating multiple ecological factors. This paper presents a well-dated and multi-proxy cored record from a natural freshwater wetland developed in a paleo-pingo-related depression on the Sanjiang Plain. The study aims to reconstruct the wetland water-level and vegetational regimes during the past ~6.0 ka BP and discuss the wetland evolution response to the East Asian summer monsoon (EASM) circulation. The results show that a shallow-water lake with hygrophilous herbs developed in the depression with a strong EASM during ~6.0–4.5 ka BP. The paleolake was succeeded by a wetland with a lowered mean water level and an increase in tree cover controlled by the weakened EASM during the past 4.5 ka BP. Such an ecological lake-to-wetland transition corresponds well to the sharp decline of the EASM around 4.5 ka BP which has been well documented in various geological records across the EASM domain. During the wetland developing stage over the past 4.5 ka BP, the water-level and vegetational changes in the studied depression were also closely related to the EASM variations. The strengthened EASM usually generated higher water levels with more hygrophilous herbs around 4.0 ka BP, 3.5 ka BP, 3.0 ka BP, 2.0 ka BP, and 1.3 ka BP. Considering the prevalent EASM climate serving as the predominant water supply for the wetlands on the modern Sanjiang Plain, we suggest the EASM circulation has played a critical role in driving the wetland ecological evolution during the mid-to-late Holocene Epoch. The past 0.4 ka BP is an exception as the local Trees/Herbs ratio visibly increased with the declined water level, while the monsoonal precipitation shows no equivalent shift. The wetland evolution at this stage was attributed to human interference.

Wetland reclamation homogenizes microbial properties along soil profiles

Wetlands store approximately one-third of soil carbon (C) in terrestrial ecosystems, and the loss of C in wetlands has been accelerated by reclamation. However, how wetland reclamation affects microbial properties along soil profiles remains unclear. In this study, we sampled 100 cm soil cores from a wetland and an adjacent cropland that has been cultivated for 23 years to evaluate the impacts of land conversion on soil microbial community structure and soil element concentrations in the Sanjiang Plain, Northeastern China. The C and nitrogen (N) concentrations in microbial biomass declined exponentially with depth in both the wetland and cropland with different magnitudes. Continuous cultivation for 23 years tended to homogenized C, N, phosphorus (P), and sulfur (S) contents in soils and microbial biomass along the soil profile. Compared with the wetland, C and N in cropland soils were lower, and microbial biomass C, N, P and S were lower in surface soils (0–30 cm), while higher in both middle soils (40–70 cm) and deep soils (70–100 cm). Cultivation narrowed the C:N:P:S stoichiometry in soils and microbial biomass, with large changes in surface soils and minor changes in deep soils. The Bray-Curtis dissimilarity test confirmed the large changes in surface soils while minor changes in deep soils. After 23-years of cultivation the abundances of fungi and bacteria were significantly reduced by approximately 90% and 78% in surface soils, but the bacterial abundance was enhanced by approximately 2–3 times in middle soils, leading to a decreasing fungi:bacteria ratio along soil profile in cropland. Soil TC and pH were the predominant factors controlling the microbial composition in wetland. The homogenizing impact of wetland reclamation on microbial properties along soil profiles suggests the different responses of microbial and soil elements to human activities, indicating a critical need of differentiating microbes from soils when examining soil elements under a changing environment.

Interannual and Seasonal Variability of Greenhouse Gases and Aerosol Emissions from Biomass Burning in Northeastern China Constrained by Satellite Observations

Biomass burning is a major source of greenhouse gases (GHGs) and particulate matter (PM) emissions in China. Despite increasing efforts of fire monitoring, it remains challenging to quantify the variability in interannual and seasonal emissions of GHGs and PM from biomass burning. In this study, we investigated the biomass burning emissions in Northeastern China based on fire radiative power (FRP) obtained from the Visible Infrared Imaging Radiometer Suites (VIIRS) active fires datasets during the period 2012 to 2019. Our results showed that the average annual emissions from biomass burning in Northeastern China during 2012–2019 were: 81.6 Tg for CO2, 260.2 Gg for CH4, 5.5 Gg for N2O, 543.2 Gg for PM2.5 and 573.6 Gg for PM10, respectively. Higher levels of GHGs and PM emissions were concentrated in the Songnen Plain and Sanjiang Plain, the main grain producing areas in this region, and were associated with dense fire points. There were two emission peaks observed each year: after harvesting (October to November) and before planting (March to April). During this study period, the total fire emissions initially increased and then decreased in a fluctuating pattern, with emissions peaking in 2015, the year when more emission regulations were introduced. Crop straw was the major source of GHGs and PM among all kinds of biomass burning. Following more stringent controls on burning and the utilization of crop straw, the main burning season changed from autumn to spring. The proportion from spring burning increased from 20.5% in 2013 to 77.1% in 2019, with an annual growth rate of 20%. The results of this study demonstrate the effectiveness of regulatory control in reducing GHGs and PM emissions, as well as satellite fire observations as a powerful means to assess such outcomes.

Regional ecological risk assessment of multi-ecosystems under the disturbance of regional pole-axis system: a case study of the Tongjiang-Fuyuan region, China.

In this study, the regional pole-axis system (urban/town areas and multi-level roads) where human production and living activities are concentrated was recognized as the main regional ecological risk source space; in contrast, multi-type ecosystems, such as wetland/waterbody and forestland and cropland with significant ecosystem service provisioning function, were identified as the main regional ecological risk receptor spaces. Based on this regional ecological risk source/receptor space division scheme, related ecological risk source/receptor indicators were chosen to characterize the spatial heterogeneities of human activities and ecological capital distribution within the study area. Among them, the Defense Meteorological Program Operational Line-Scan System (DMSP/OLS) nighttime light intensity and normalized density of multi-level roads data were employed as regional ecological risk source indicators, whereas the ecosystem service value of multi-ecosystems was employed as a regional ecological risk receptor indicator. Then, combined with regional eco-environmental vulnerability indexes, a regional ecological risk assessment framework was established and practiced in the Tongjiang-Fuyuan region, a wetland-concentrated area of the Sanjiang Plain. The results showed that (1) the DMSP/OLS nighttime light intensity data matched the distribution of regional urban/town areas and farms well, and it was reasonable to employ this dataset to represent the scope of regional production-living land space; (2) regional ecological space, such as wetlands and forestlands, had a higher ecological risk grade; (3) because of their higher human disturbance severity and ecological vulnerability level, regional settlement points (county seats and farms) had the highest ecological risk, whereas agricultural land space, occupying the largest area of the region, had the lowest ecological risk level; and finally, (4) in terms of proportion, the low, medium, high, and very high risk grades accounted for 71.66%, 17.13%, 8.43%, and 2.78% of the study area, respectively. Based on the results, a series of approaches, which can be adopted to promote regional sustainable development of the Tongjiang-Fuyuan region, were discussed, such as spatial governance of wetlands by establishing nature reserves, coordination of economic exploitation activities within forestlands, setup of a spatial expansion boundary of urban/town/farm areas, and tradeoffs between production and ecology functions of croplands.

Ditches as important aquatic invertebrate habitats: a comparative analysis of their snail (Mollusca: Gastropoda) assemblages with natural wetlands

Wetlands and ditches are both common aquatic habitats in lowland landscapes of northeast China. However, most biodiversity management and research for aquatic organisms has focused on the biota of natural wetlands, and the invertebrate fauna of ditches has not been previously addressed. Because ditch habitats can be so extensive in some landscapes, their contribution could be substantial. To assess the contributions of ditches to invertebrate biodiversity, snail assemblages of natural wetlands, wetland ditches, and agricultural ditches in the Sanjiang Plain of northeastern China were compared. Snail assemblages of the three habitats all differed significantly from each other. Species richness and abundance of snail assemblages in wetland ditches was similar with natural wetlands. Although lower, species richness and abundance of snail assemblages in agricultural ditches still accounted for 22% and 52%, respcetively, of that in natural wetlands. Each of the three different habitats supported unique species, with 11 snail species being indicators of specific habitat types. Biota and Environment matching analysis (BEST) showed that pH in combination with dissolved oxygen were the most important environmental factors in explaining the dissimilarities of snail assemblages among the three different habitats. This study illustrates that both wetland ditches and agricultural ditches make contributions to aquatic invertebrate biodiversity in Sanjiang Plain. More attention should be paid to the importance of ditches as reservoirs for aquatic invertebrates, and the biota of ditches should be considered in the overall scope of biodiversity management and monitoring.

Spatial–Temporal Vegetation Dynamics and Their Relationships with Climatic, Anthropogenic, and Hydrological Factors in the Amur River Basin

Information about the growth, productivity, and distribution of vegetation, which are highly relied on and sensitive to natural and anthropogenic factors, is essential for agricultural production management and eco-environmental sustainability in the Amur River Basin (ARB). In this paper, the spatial–temporal trends of vegetation dynamics were analyzed at the pixel scale in the ARB for the period of 1982–2013 using remotely sensed data of long-term leaf area index (LAI), fractional vegetation cover (FVC), and terrestrial gross primary productivity (GPP). The spatial autocorrelation characteristics of the vegetation indexes were further explored with global and local Moran’s I techniques. The spatial–temporal relationships between vegetation and climatic factors, land use/cover types and hydrological variables in the ARB were determined using a geographical and temporal weighted regression (GTWR) model based on the observed meteorological data, remotely sensed vegetation information, while the simulated hydrological variables were determined with the soil and water assessment tool (SWAT) model. The results suggest that the variation in area-average annual FVC was significant with an increase rate of 0.0004/year, and LAI, FVC, and GPP all exhibited strong spatial heterogeneity trends in the ARB. For LAI and FVC, the most significant changes in local spatial autocorrelation were recognized over the Sanjiang Plain, and the low–low agglomeration in the Sanjiang Plain decreased continuously. The GTWR model results indicate that natural and anthropogenic factors jointly took effect and interacted with each other to affect the vegetated regime of the region. The decrease in the impact of precipitation to vegetation growth over the Songnen Plain was determined as having started around 1991, which was most likely attributed to dramatic changes in water use styles induced by local land use changes, and corresponded to the negative correlation between pasture areas and vegetation indexes during the same period. The analysis results presented in this paper can provide vital information to decision-makers for use in managing vegetation resources.

Quantitative Assessment of the Influences of Snow Drought on Forest and Grass Growth in Mid-High Latitude Regions by Using Remote Sensing

Global climate change, especially the snow drought events, is causing extreme weather events influencing regional vegetation growth and terrestrial ecosystem stability in a long-term and persistent way. In this study, the Sanjiang Plain was selected, as this area has been experiencing snow drought in the past two decades. Logistic models, combined with multisource remote sensing and unmanned aerial vehicle (UAV) data, as well as the meteorological data over the past 20 years, were used to calculate sixteen phenological periods and biomass. The results show that (1) over the past two decades, snow drought has been based on the snow accumulation and has been occurring more frequently, wider-ranging and more severely; (2) snow drought has advanced the forest start of season (SOS)/end of season (EOS) by 6/5 days, respectively; (3) if the snowfall is greater than 80% of a normal year, the SOS/EOS of grass is postponed by 8/6 days; conversely, if it is less than 80%, the SOS/EOS are advanced by 7/5 days; and (4) biomass decreased approximately 0.61%, compared with an abundant snowfall year. Overall, this study is the first to explore how snow drought impacts the phenological period in a mid-high latitude area, and more attention should be paid to these unknown risks to the ecosystem.

Study on Hydrologic Effects of Land Use Change Using a Distributed Hydrologic Model in the Dynamic Land Use Mode

It is reasonable to simulate the hydrologic cycle in regions with drastic land use change using a distributed hydrologic model in the dynamic land use mode (dynamic mode). A new dynamic mode is introduced into an object-oriented modularized model for basin-scale water cycle simulation (MODCYCLE), a distributed hydrologic model based on sub-watersheds, and the hydrological response unit (HRU). The new mode can linearly interpolate data for the years without land use data and consistently transfer HRU water storage between two adjacent years after a land use data update. The hydrologic cycle simulation of the Sanjiang Plain in China was carried out from 2000 to 2014 in the dynamic mode using land use maps of 2000, 2005, 2010, and 2014. Through calibration and validation, the performance of the model reached a satisfactory level. Replacing the land use data of the calibrated model using that of the year 2000, a comparison model in the static land use mode (static mode) was built (i.e., land use unchanged since 2000). The hydrologic effects of land use change were analyzed using the two models. If the land use pattern remained unchanged from 2000, despite the average annual runoff increasing by 4% and the average annual evapotranspiration decreasing by 4% in this region only, the groundwater storage of the plain areas in 2014 would increase by 4.6 bil. m3 compared to that in 2000, rather than the actual decrease of 4.7 bil. m3. The results show that the fluxes associated with groundwater are obviously more disturbed by land use change in the Sanjiang Plain. This study suggests that the dynamic mode should be used to simulate the hydrologic cycle in regions with drastic land use change, and the consistent transfer of HRU water storage may be considered in the dynamic mode.

Soil physicochemical properties drive the variation in soil microbial communities along a forest successional series in a degraded wetland in northeastern China.

The Sanjiang Plain is the biggest freshwater wetland locating in northeastern China. Due to climate change and human activities, that wetland has degraded to a successional gradient from the original flooded wetland to dry shrub vegetation and a forest area with lower ground water level, which may result in changes in soil microbiologic structure and functions. The present study investigated the microbial diversity and community structure in relation to soil properties along that successional gradient. The soil physico‐chemical properties changed significantly with degradation stage. The Shannon diversity index of both soil bacteria (5.90–6.42) and fungi (1.7–4.19) varied significantly with successional stage (both p < .05). The community structures of soil bacteria and fungi in the early successional stages (i.e., the wetland) were significantly determined by water content, total nitrogen, and available nitrogen concentrations in soils, while those in the later successional stages (i.e., forests) were significantly structured by soil organic carbon, soil pH, and available phosphorus concentrations. These results suggest that the soil microbial structure is mainly determined by soil properties rather than by plant community such as plant species composition along successional stages.

Variations in the diversity of the soil microbial community and structure under various categories of degraded wetland in Sanjiang Plain, northeastern China

AbstractUnderstanding the changes in microbial community composition in wetlands affected by different types of degradation can help enrich theoretical knowledge about wetland degradation. However, studies of the relative role of microorganisms under different types of degradation of wetlands are rare in wetland ecology. Because of agricultural development, a large volume of groundwater has been extracted from the Sanjiang Plain over the last few decades, which has caused wetland degradation. To provide information for the development and protection of this wetland ecosystem, investigations into the processes of wetland degradation are important. The aim of the present work was to assess the impacts of wetland degradation on soil microbial communities under four different types of wetlands degradation in the Sanjiang Plain: swamp meadow (SW), meadow wetland (MW), paddy farmland (PF), and cropland (CL). Both 16S and ITS rRNA gene amplicon sequencing were used to evaluate the diversity and composition of bacteria and fungi. A total of 638,758 effective 16S rRNA and 916,211 valid internal transcribed spacer rRNA gene sequences were obtained, which were classified into 11 fungal and 40 bacterial phyla. The dominant fungal and bacterial phyla were Ascomycota and Proteobacteria, respectively. In addition, wetland degradation increased the relative abundances of Chloroflexi and Gemmatimonadetes, but the relative abundances of Proteobacteria and Verrucomicrobia significantly decreased. The bacterial Shannon index of SW was lower than those of the other investigated sites. Fungal diversity showed no significant differences for different types of degraded wetlands. In addition to wetland degradation, different reactions of the dominant microbial phyla and their diversity were clearly coorelated with total phosphorus (TP), total potassium (TK), available potassium (AK), and soil organic matter (SOM), which formed essential criteria that influenced the soil microbial communities. Wetland degradation resulted in the decrease of soil nutrient and the decline of the abundance of dominant phylum in soil bacterial and fungal communities. These changes can be used as an early warning signal for the degrading wetland of the Sanjiang Plain.