Sanjiang Plain Research Articles

Simulating Land-Use Changes and Predicting Maize Potential Yields in Northeast China for 2050.

Crop potential yields in cropland are the essential reflection of the utilization of cropland resources. The changes of the quantity, quality, and spatial distribution of cropland will directly affect the crop potential yields, so it is very crucial to simulate future cropland distribution and predict crop potential yields to ensure the future food security. In the present study, the Cellular Automata (CA)-Markov model was employed to simulate land-use changes in Northeast China during 2015–2050. Then, the Global Agro-ecological Zones (GAEZ) model was used to predict maize potential yields in Northeast China in 2050, and the spatio-temporal changes of maize potential yields during 2015–2050 were explored. The results were the following. (1) The woodland and grassland decreased by 5.13 million ha and 1.74 million ha respectively in Northeast China from 2015 to 2050, which were mainly converted into unused land. Most of the dryland was converted to paddy field and built-up land. (2) In 2050, the total maize potential production and average potential yield in Northeast China were 218.09 million tonnes and 6880.59 kg/ha. Thirteen prefecture-level cities had maize potential production of more than 7 million tonnes, and 11 cities had maize potential yields of more than 8000 kg/ha. (3) During 2015–2050, the total maize potential production and average yield decreased by around 23 million tonnes and 700 kg/ha in Northeast China, respectively. (4) The maize potential production increased in 15 cities located in the plain areas over the 35 years. The potential yields increased in only nine cities, which were mainly located in the Sanjiang Plain and the southeastern regions. The results highlight the importance of coping with the future land-use changes actively, maintaining the balance of farmland occupation and compensation, improving the cropland quality, and ensuring food security in Northeast China.

Soil Organic Carbon and Nitrogen Variations with Vegetation Succession in Passively Restored Freshwater Wetlands

Passive restoration after agricultural abandonment has been widely practiced to improve soil quality and recover the ecological functions of degraded wetlands. However, studies concerning the relationships between soil and vegetation during natural succession are still lacking. In this study, the variations of soil organic carbon (SOC) and total nitrogen (TN), as well as their relationships with soil and vegetation properties were evaluated in passively restored freshwater wetlands with a chronosequence (2, 4, 8, 13, 16, and 20 years) on the Sanjiang Plain, China. An adjacent natural wetland was chosen as a reference system. Results indicated that soil and vegetation in restored wetlands changed substantially overtime, and gradually came to resemble natural wetlands. SOC and TN contents in the 10–30 cm soil layers required less time to achieve a natural level than those in the 0–10 cm soil layers. They were significantly correlated with soil water content and conductivity, especially in the 0–10 cm layer. Moreover, SOC and TN storages were synergistically improved, and highly dependent on plant diversity, height, coverage, and biomass. These results suggest that passive restoration is an efficient measure for forming wetland plant communities after agricultural abandonment, and ultimately enhances SOC and TN accumulation in restored wetlands.

Relationship between relative growth rate and C:N:P stoichiometry for the marsh herbaceous plants under water-level stress conditions

It is well-known that relative growth rate (RGR) is closely related to C:N:P stoichiometry at the whole-plant level, yet it remains a misgiving to determine whether the growth-rate hypothesis is consistent between plant organs. Here, we examined RGR, C, N, P concentrations and their ratios of N:C, P:C, and N:P for four marsh herbaceous species (two gramineous species, Deyeuxia angustifolia and Glyceria spiculosa; two sedge species, Carex pseudocuraica and Carex lasiocarpa) grown in an increasing water level gradient (−5, 0, +5, and +15 cm relative to the soil surface) in the Sanjiang Plain of Northeast China. The applicability of the growth-rate hypothesis to leaf, stem, root, and total biomass was subsequently tested. With the increase of flooding stress, RGR and root mass ratio decreased to a certain degree for all species, whereas the above-ground biomass allocation was increased. The variation of N was much greater than that of P; hence the change in N:P ratios was determined mainly by N concentration. RGR was positively correlated with N concentration, N:C, and N:P for stem and total biomass when the data were pooled for all species but was negatively correlated with those for leaf and root organs. Furthermore, the theoretical predictions regarding the relationship between RGR and nutrient ratios were not always the case for each of the marsh herbs. Therefore, our results indicated that the organ-specific and species-specific for vascular plants should be carefully considered when using the theoretical association of growth rate with C:N:P stoichiometry.

The influences of the hydraulic gradient on the ecological characteristics of wetland vegetation communities in Sanjiang Plain, Northeast China

The influences of the hydraulic gradient on the ecological characteristics of wetland vegetation communities in Sanjiang Plain, Northeast China

Sources, Influencing Factors, and Pollution Process of Inorganic Nitrogen in Shallow Groundwater of a Typical Agricultural Area in Northeast China

As one of the largest agricultural areas, the Sanjiang Plain of Northeast China has faced serious inorganic nitrogen pollution of groundwater, but the sources and the formation mechanism of pollution in the regional shallow groundwater remain unclear, which constrains the progress of pollution control and agricultural development planning. An investigation on potential nitrogen sources, groundwater inorganic nitrogen compounds (NH4+, NO3−, NO2−), and topsoil total nitrogen concentration (TN) was conducted in a typical paddy irrigation area of Sanjiang Plain. Multivariate statistical analysis combined with geospatial-based assessment was applied to identify the sources, determine the governing influencing factors, and analyze the formation process of inorganic nitrogen compounds in shallow groundwater. The results show that the land use type, oxidation-reduction potential (Eh), groundwater depth, NO2− concentration, and electrical conductivity (EC) are highly correlated with the NO3− pollution in groundwater, while DO and Eh affected the distribution of NH4+ most; the high concentrations of NO3− in sampling wells are most likely to be found in the residential land and are distributed mainly in densely populated areas, whereas the NH4+ compounds are most likely to accumulate in the paddy field or the lands surrounded by paddy field and reach the highest level in the northwest of the area, where the fields were cultivated intensively with higher fertilization rates and highest values of topsoil TN. From the results, it can be concluded that that the NO3− compounds in groundwater originated from manure and domestic waste and accumulated in the oxidizing environment, while the NH4+ compounds were derived from N fertilization and remained steady in the reducing environment. NO2− compounds in groundwater were the immediate products of nitrification as a result of microorganism activities.

Aquatic invertebrate assemblages as potential indicators of restoration conditions in wetlands of Northeastern China

Wetland restoration has been implemented widely but evaluation of the effectiveness of wetland restoration has been limited. In this study, we aimed to investigate the utility of aquatic invertebrate assemblages as potential indicators of restoration condition in wetlands of the Sanjiang Plain, Northeastern China. Results from non‐metric multidimensional scaling analysis of invertebrate assemblages showed that study wetlands (n = 16) divided into two groups: natural wetlands and wetlands that have been restored for 4 years were classified as a group, and impaired wetlands and wetlands restored for only 1 year were classified into another group. After 4 years of recovery, 47.9% of invertebrate taxa found at the natural wetlands could also be found at the restored wetlands, primarily insects with aerial dispersal capabilities for rapid colonization. Indicator species analysis identified differences in community composition among wetland types, and Amphiagrion sp. and Bezzia sp. were indicators of the restored wetlands. In Northeastern China, aquatic invertebrate assemblages and certain indicator species may provide robust measures of wetland restoration. It is urgent for further exploration to monitor restored wetlands in the long‐time series and fully assess the efficiency of the restoration.

Spatial-temporal characteristics analysis of water resource system resilience in irrigation areas based on a support vector machine model optimized by the modified gray wolf algorithm

This study aims to address a series of problems with agricultural irrigation water shortages and the poor efficiency of irrigation water use in severely colder irrigation areas in China. For this purpose, a support vector machine model based on the improved gray wolf optimization algorithm (IGWO-SVM) was proposed to improve the accuracy of the evaluation of the resilience of the water resource system in the irrigation areas. The results showed that the overall resilience of the selected irrigation areas was U-shaped from 2007 to 2016. From a spatial perspective, the results revealed that the resilience level of the western Songnen Plain irrigation area was less robust than that of the eastern Sanjiang Plain irrigation area. A comparison with the SVM model and SVM models optimized by the gray wolf optimization algorithm (GWO-SVM) and the gravity search algorithm (GSA-SVM) showed that the mean square error of the IGWO-SVM model was reduced by 7.69%, 12.19%, and 25%; the R2 was 0.33%, 1.11% and 2.73%; and the accuracy was 2.32%, 4.74% and 16.03%, respectively. The running time of IGWO-SVM was 278.42 s, 498.63 s faster than those of GWO-SVM and GSA-SVM on average, respectively. The improvement in the results suggested that the IGWO-SVM model was stable and could be used to evaluate water resource system resilience.

Dissolved organic carbon loss from paddy fields by drainage and roles of common ions

Cations and anions exerted important effects on dissolved organic carbon (DOC) release and retention in arable soils. However, knowledge is limited on DOC loss from rice (Oryza sativa L.) paddies by drainage and its association with common ions under a conventional irrigation and drainage regime. This study aimed to investigate DOC dynamics in the soil-overlying water system and the synergistic behaviors of common ions (Na+, K+, Ca2+, Mg2+, Cl−, NO3− and SO42−) contributing to variations in DOC flux in drainage water at the pre-growing, vegetative and reproductive stages of rice cultivation in the Sanjiang Plain of NE China. Samples of overlying water and soil in three layers (0–20, 20–40, and 40–60 cm) were collected before drainage to evaluate variations of DOC and common ions across rice growing stages and to estimate DOC loss by drainage. Sorption experiments were conducted to determine DOC sorption capacities of surface soil (0–5 cm). Compared with the pre-growing stage, DOC concentrations in overlying water and soil significantly increased at the vegetative stage, while significant increases at the reproductive stage were merely in soil. Net movement of DOC was from soil to overlying water at the pre-growing and reproductive stages, and was close to equilibrium at the vegetative stage. Ca2+ and Mg2+ in surface soils (0–20 cm) displayed stronger capacities explaining DOC dynamics in the soil-overlying water system than the other common ions. As Ca2+ and Mg2+ in surface soils (0–20 cm) increased, DOC in the uppermost soil layers (0–20 and 20–40 cm) and overlying water increased, and DOC sorption capacities in surface soil were enhanced. DOC loss from paddy fields by drainage mainly occurred at the vegetative stage, occupying 62–83 % of the total, and much more attention ought to be paid to control drainage DOC loss during this period. In light of important roles of Ca2+ and Mg2+ in DOC dynamics and then DOC loss by drainage, appropriate measures with respect to addition of Ca2+ and Mg2+ could be taken into consideration in rice cultivation to alleviate paddy field DOC export.

Influence of wetland reclamation on land-surface energy exchange and evapotranspiration in the Sanjiang plain, Northeast China

Sustained, large-scale wetland reclamation of paddy fields has been implemented since the 1960s in the Sanjiang Plain, northeast China. The investigation of the effect of this reclamation on land-surface energy exchange and the local water cycle is important for evaluating the stability of regional water resources for future agriculture development and ecological conservation. This study used the eddy covariance method to measure evapotranspiration (ET) and dominant energy transport fluxes for two sites, a typical natural marsh and a paddy field, during the growing seasons of 2017–2018. The two sites showed similar total available energy, whereas the ratio of the latent to net radiative energy (LE/Rn) was substantially lower in the marsh (0.49) compared to the paddy field (0.81), indicating a considerable increase in ET energy consumption after wetland reclamation. The average ET rates of the marsh and paddy field were 2.3 mm d−1 and 3.6 mm d−1, respectively, throughout the growing season. Both the high Priestley-Taylor coefficient (αeq, 1.21 ± 0.20) and the decoupling factor (Ω) suggested Rn-limited conditions in the paddy field, whereas the controlling factor in the marsh changed from vapor pressure deficit (VPD) to radiation energy over the season. The greatest difference in ET occurred in spring due to the alteration in the hydrological environment, including a lowered standing water table and elevated water temperature in the paddy site. The differences in physiology and canopy shape between the paddy and marsh plants contributed largely to enhanced ET during the summer months. In total, alterations in the hydrological environment, canopy structure and plant physiology contributed to the increase in ET, suggesting a synthetic influence of marsh reclamation on surface energy and ET processes. Wetland reclamation increased water consumption through ET and altered the seasonal pattern of the energy balance. This process will inevitably result in increased deficits in regional water resources in the Sanjiang Plain.

Effects of Land Use Patterns on the Bacterial Community Structure and Diversity of Wetland Soils in the Sanjiang Plain

Changes in land use patterns can lead to changes in soil ecosystem function, and soil microbes could sensitively reflect soil quality and the evolution of different ecosystem functions. In order to study the impact of different land use patterns on microbial community structure, four typical land use patterns, including wetland (WL), meadow (MD), paddy field (Oryza sativa (OS)), and farmland (Zea mays(ZM)), were taken as research objects in Sanjiang Plain. The high-throughput sequencing technology based on bacterial 16S rRNA gene was used to study the community structure of soil bacteria and explore its relationship with soil environmental factors. For alpha diversity, it was found that soil bacterial Simpson index, Chao index, ACE index, and Shannon index in WL were the highest and lowest in OS, while no significant differences of soil bacterial diversity indices were observed among WL, ZM, and MD. The dominant bacterial groups under different land use types were Proteobacteria, Acidobacteria, Chloroflexi, Actinobacteria, and Actinobacteria, and soil bacterial community clearly differed among WL, MD, OS, and ZM. Soil water content, pH, soil organic carbon, total nitrogen, available nitrogen, total phosphorus, available phosphorus, NO3−-N, and soil moisture content had strong effects on soil bacterial community composition. In this perspective, it is well established that different land use patterns could affect microbial communities by changing soil environmental factors.

Dynamic changes in microbial communities and nutrient stoichiometry associated with soil aggregate structure in restored wetlands

Available information on interaction mechanisms between soil nutrient stoichiometry and microbial communities associated with soil aggregate structure in restored wetlands remains limited. As such, this study investigated water-stable aggregate structure using wet-sieving method and scanning electron microscope (SEM) in restored wetlands with a restoration duration of 0, 1, 2, 3, 5, 13 or 19 years, and their internal nutrient stoichiometry and microbial communities (phospholipid fatty acid analysis, PLFAs). The results showed that soil aggregate structure tended to be stable from the fifth restoration year. In the restored wetlands, General bacteria, Gram-positive bacteria (G+), and Gram-negative bacteria (G−) were the dominant components of soil microorganisms, which tented to condense in coarse-aggregates. The carbon-to-phosphorus (C:P) and nitrogen-to-phosphorus (N:P) ratios were higher in coarse-aggregates since C and N benefit from the physical protection. Redundancy analysis (RDA) results indicated that C:N ratio was primary environmental factors controlling the distribution of soil microbial communities. In the Sanjiang Plain, the soil organic carbon (SOC) decomposition was lower, and N was the primary nutrient limiting wetland restoration quality.

Shifts in bird ranges and conservation priorities in China under climate change.

Climate change is one of the most significant causes of species range shift and extinction. Based on a citizen science dataset of birds in China, the Bird Report, we developed a high-resolution map of bird species richness in China, and simulated the range shifts and area changes of the 1,042 birds through the year 2070 using three different General Circulation Models and two different Representative Concentration Pathways (RCPs, including RCP 2.6 and RCP 8.5). It was found that 241–244 (under different scenarios) bird species would lose a portion of their distribution ranges; and that most species in China would move to either higher elevations or northward. The other 798–801 species would experience range expansion. Compared to resident species (n = 516), migratory birds (n = 526) may undergo more limited range expansion but a longer range shift distance on average. The species diversity of birds will considerably increase in areas higher than 1,500 m in elevation under both RCPs. Conservation priorities with higher species richness were also identified using the Zonation model. The existing national nature reserves are not sufficient for protecting important bird habitats, especially after range shifts. Significant gaps in protected areas were observed in the northern Xinjiang, southern Tibet, Greater Khingan, Sanjiang Plain, Songnen Plain, northern Bohai Rim, and southeastern coastline areas. Many of these areas are characterized by high human populations and intensive development, and establishing sizable protected areas has become difficult. Inclusive conservation mechanisms that include restoring habitats in urban parks and sharing habitats in farmland areas, may be a feasible solution.

Land Surface Albedo Variations in Sanjiang Plain from 1982 to 2015: Assessing with GLASS Data

As a key parameter for indicating the fraction of surface-reflected solar incident radiation, land surface albedo plays an important role in the Earth’s surface energy budget (SEB). Since the Sanjiang Plain has been severely affected by human activities (e.g., reclamation and shrinking of wetlands), it is important to assess the spatiotemporal variations of surface albedo in this region using a long-term remote sensing dataset. In order to investigate the surface albedo climatology, trends, and mechanisms of change, we evaluated the surface albedo variations in the Sanjiang Plain, China from 1982 to 2015 using the Global LAnd Surface Satellite (GLASS) broadband surface albedo product. The results showed that: 1) an increasing annual trend (+0.000 58/yr) of surface albedo was discovered in the Sanjiang Plain based on the GLASS albedo dataset, with a much stronger increasing trend (+0.001 26/yr) occurring during the winter. Most of the increasing trends occurred over the cultivated land, unused land, and land use conversion types located in the northeastern Sanjiang Plain. 2) The increasing trend of land surface albedo in Sanjiang Plain can be largely explained by the changes of both snow cover extent and land use. The surface albedo in winter is highly correlated with the snow cover extent in the Sanjiang Plain, and the increasing trend of surface albedo can be further enhanced by the land use changes.

Soil Type and a Labile C Addition Regime Control the Temperature Sensitivity of Soil C and N Mineralization More than N Addition in Wetland Soils in China

Wetlands store a large amount of carbon (C) and many are vulnerable to potential global warming. It is critical to quantify the temperature sensitivity of soil nitrogen (N) and C mineralization in response to external labile C or N addition in different types of wetland. Through incubation experiments, the effects of temperature and the addition of N or C on soil C and N mineralization were tested using soils from the Sanjiang Plain wetland (SW), Zoigê alpine wetland (ZW), Yellow River estuary wetland (YW), and Baiyangdian Lake (BL). Our findings showed that temperature, available C and wetland type were dominant factors in the regulation of soil C loss, with soil C in SW and ZW being less stable and poorly resistant to increases in temperature. The response of net N mineralization to N addition showed regional differences. A lack of long-term effects of the deposition of N on soil mineralization suggested that there may be a particular N addition threshold level for changed C and N mineralization. It is predicted that an increase in labile C supply due to elevated carbon dioxide (CO2) and its interactions with wetland types will increase CO2 efflux more than N deposition in wetland soils.

Using Multisource Geospatial Data to Identify Potential Wetland Rehabilitation Areas: A Pilot Study in China’s Sanjiang Plain

Wetland rehabilitation, highlighted in the United Nations (UN) Sustainable Development Goals (SDGs), is imperative for responding to decreased regional biodiversity and degraded ecosystem functions and services. Knowing where the most suitable wetland rehabilitation areas are can strengthen scientific planning and decision-making for natural wetland conservation and management implementation. Therefore, we integrated multisource geospatial data characterizing hydrological, topographical, management, and policy factors, including maximum surface water coverage, farming time, anthropogenic disturbance, and wetland protection level, to identify potential wetland rehabilitation areas in the Sanjiang Plain (SJP), the largest marsh distribution and a hotspot wetland loss region in China. Our results indicate that a total of 11,643 km2 of wetlands were converted into croplands for agricultural production from 1990 to 2018. We estimated that 5415 km2 of the croplands were suitable for wetland rehabilitation in the SJP, of which 4193 km2 (77%) have high rehabilitation priority. Specifically, 63% of the potential areas available for wetland rehabilitation are dry croplands (3419 km2), the rest (37%) being paddy fields. We argue that the selected indicators and approach used in this study to determine potential wetland rehabilitation areas could guide their investigation, at either the provincial or national scale and would be beneficial to conservation and sustainable management of wetlands in the SJP.

Multi-element fingerprinting of soils can reveal conversion of wetlands to croplands

Little is known about the influence of conversion of wetlands to farmlands on concentrations and distribution of elements other than those most commonly studied, partly because of the lack of stratification in wetland soils. In this study, in the Sanjiang Plain in northeastern China, we determined the concentrations of 63 elements along soil profiles at three depths: 0–20 cm, 20–40 cm, and below the depth to which farmers would plow, at 40–60 cm, under four land uses: natural wetland, drained wetland, wetland converted to soybean field and subsequently to rice paddy field. Based on our previous work, we expected that changes in organic matter content would be an important factor affecting element concentrations, but that changes in land uses also led to decoupling of the influence of organic matter on elements. This would lead to other factors, such as changes in redox conditions, changes in hydrology and mixing of soils due to plowing, becoming more important factors affecting element distributions. Our study confirmed these expectations. Changes in organic matter content directly or indirectly affected many elements, explaining 67% of variation. Arsenic, cobalt, iron and nickel concentrations were dramatically higher and sulfur concentrations lower when wetland was converted to paddy field. Co and Ni were identified as potential chemical indicators of wetland conversion. Our research is the first to use multi-element fingerprinting to study effects of conversion of wetlands to croplands in China and showed that this relatively simple approach highlights the complexity of the many interacting factors in reclamation of wetland soils for agricultural uses.

DNA stable-isotope probing highlights the effects of temperature on functionally active methanotrophs in natural wetlands

Microbial methane (CH4) oxidation is a major global sink of CH4. Aerobic CH4-oxidizing bacteria (methanotrophs) represent a biological model system for CH4 consumption and is very sensitive to climate warming, but still poorly understood. Here we used DNA stable-isotope probing (SIP) coupled with high-throughput sequencing of 13C-DNA to compare active methanotrophs incubated at 10, 15, 20, and 25 °C in 13CH4-fed microcosms from two geographically distinct natural wetlands: Sanjiang Plain wetland in northeast China and Haibei wetland in Tibet Plateau. In both wetlands, CH4 oxidation potential was enhanced with increasing temperature. Community profiling revealed that type I methanotrophs dominated CH4 oxidation, although a small portion (2.76%–17.14%) of type II methanotrophs (Methylocystis, Methylosinus/Methylocystis) were significantly stimulated at 20 °C and 25 °C. 13C-labeled indicator species included Methylobacter, Methylocystis, and Methylosarcina species in Sanjiang Plain, and Methylobacter and Methylosarcina species in Haibei. Network analysis demonstrated positive co-occurrence of species between genera of Methylobacter, Methylosarcina, and Methylocystis with shifts in temperature, while interspecies interactions between Methylobacter and Methylomonas correlated negatively, and Methylobacter and Methylosinus/Methylocystis positively. Partial least squares path modeling illustrated that the direct effects of temperature on CH4 oxidation were stronger in northeast China than Tibet Plateau, and temperature could also indirectly influence CH4 oxidation via shifts in the methanotroph communities. Collectively, these results provide insights into how temperature could influence methanotrophy in natural wetlands under future climate scenarios.

Heavy metals exposure risk to Eurasian Spoonbill (Platalea leucorodia) in wetland ecosystem, Northeast China

Qixing River wetland is very representative of the marsh environment of Sanjiang Plain, northeast China. The wetland plays an important role in maintaining ecological service functions especially for protecting migratory birds. Despite Qixing River wetland being impacted by a number of diffuse and point sources of pollution (primarily from agricultural activities), a comprehensive survey of heavy metal exposure risk to migratory birds has never been undertaken. Identifying heavy metals exposure risk is significant for further improving the protection scheme of migratory birds. In the present study, the comprehensive water pollution index (WPI) and geo-accumulation index (Igeo) were calculated to assess the degree of contamination of water and sediments, respectively. Single-pollutant exposure metrics (HQ) were applied to measured concentrations in order to estimate the heavy metal exposure risk to migratory birds. In addition, an integrated hazard index (HI) was derived to assess the comprehensive risk of exposure to multiple heavy metals and associated risk threshold values calculated. The decreasing trends of average concentration of heavy metals were Zn > Cr > Ni > Cu > Pb > Cd in sediments and Zn > Cr > Pb > Ni > Cu > Cd in water. Concentrations of Cr were significantly elevated compared to the threshold of Aquatic Life Water Permissible Limits (AWPL) and Sediment Quality Guidelines (SGQ) (p < 0.01), thus may pose negative impacts to the aquatic ecological system. Values of WPI indicated ‘Clean’ status for more than 85% sampling sites with Zn accounting for 58% of the value of the WPI. Most of the sediment sampling locations were deemed to be ‘Clean’ or ‘Low’ status as defined by Igeo with Zn and Cd (mainly derived from agricultural sources) identified as the dominant indicators of pollution. Comprehensive exposure risk assessment indicated ‘Moderate’ risk (HI > 1) status for local populations of Eurasian Spoonbill. Despite the majority of heavy metals (except for Zn) being assigned ‘Clean’ or ‘Low’ pollution status, the elevated hazard quotient (HQ > 3) associated with Cr enhanced overall values of HI, especially for nestlings, indicating that current pollution control measures are insufficient for the protection of migratory birds. This study has supplemented current knowledge of the impacts of agriculture on wetland ecosystems and provides evidence that exposures of migratory birds to some heavy metals may exceed ‘safe’ levels. This study thus provides a scientific rationale for determining the safe feeding water depth for migratory birds.

Ecological risk assessment of wetland vegetation under projected climate scenarios in the Sanjiang Plain, China

Wetland ecosystems have comprehensive ecological functions and are sensitive to climate change. Under climate change, wetlands plant community productivity and diversity may be affected. In previous studies of wetlands, the effects of climate change have been primarily investigated using field observations, factor-controlled experiments, and mechanism analyses. However, the ecological risks to wetland communities under potential long-term climate change on a regional scale remain uncertain. The Sanjiang Plain is the largest area of natural marsh wetlands and the national ecological functions in China. In this study, the changes in plant productivity and diversity of wetland ecosystems in the Sanjiang Plain were simulated under different climate change scenarios (i.e., Representative Concentration Pathways, RCP 2.6, RCP4.5, RCP6.0, and RCP8.5), and the rank of spatiotemporal risk on a regional scale was estimated using a pressure–state–response model. Temperature and precipitation had average rates of increase of 0.44 °C/10a and 12.13 mm/10a, respectively, under different climate change scenarios to 2050. The fluctuation range in climatic factors was largest under the RCP8.5 scenario. On a long-term scale, compared with the base year of 2010, vegetation productivity increased significantly under the RCP2.6 scenario, remained almost constant under RCP4.5 and RCP6.0 scenarios, and decreased under the RCP8.5 scenario. In contrast to productivity, plant diversity increased under all four scenarios, but the range of increase gradually decreased with the increase in scenarios. Spatially, a fluctuation range change in precipitation was one of the important factors that caused high risks to regional wetlands. In the northwest of the Sanjiang Plain, most wetlands were assessed as high risk at level-3. In the other regions, the risks were lower with the values below level-2, and only a few places were assessed at risk level-3. In national wetland nature reserves, the northeast of the Qixing River, Xingkai Lake, and the Dongfanghong Marsh wetland area were ranked as high risk at level-3. These findings suggest that wetland protection and management should be focus on hydrological allocation and the potential ecological risks to national wetland nature reserves. However, a joint risk assessment of climate change and human activity should be conducted to provide a comprehensive reference for the protection and development of natural marsh wetlands.

Fluctuating water level effects on soil greenhouse gas emissions of returning farmland to wetland

Future climate change is predicted to have an important impact on regional precipitation patterns. Water level is an important factor influencing soil greenhouse gas emissions. However, the effect of small-scale water level fluctuations on soil greenhouse gas emissions from returning farmland to wetlands has been little studied. We collected soils of three lands from returning farmland to wetland with different restoration years and a natural wetland at the Honghe National Nature Reserve in Sanjiang Plain, China. Through indoor simulation experiments, we explored the characteristics of soil greenhouse gas (CO2, CH4, and N2O) emissions under fluctuating water levels. When the water level fluctuated between − 8 and 8 cm, the CO2 and N2O emissions decreased as the water level increased, but the CH4 emissions were highest when water level fluctuated between − 3 and 3 cm. The CH4 emissions tended to increase as laboratory time extended. Different gases react differently to water level fluctuations. The CO2 emissions contributed 78.90–96.48% of the total global warming potential of the GHG emissions. The results of this study indicate that during the process of returning farmland to wetland, more attention should be paid to the effects of CO2 emissions. An appropriately raised water level can effectively suppress the global warming potential of greenhouse gas emissions.