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Sanjiang Plain is the largest marsh distribution area of China, and marshes in this region significantly affect regional carbon cycle and biodiversity protection. The vegetation phenology of marsh significantly affects the energy exchange and carbon cycle in that region. Under the influence of global climatic change, identifying the changes in phenology and their responses to climatic variation in marshes of Sanjiang Plain is essential for predicting the carbon stocks of marsh ecosystem in that region. Using climate and NDVI data, this paper analyzed the spatiotemporal variations in the start (SOS), end (EOS), and length (LOS) of vegetation growing season and explored the impacts of climatic variation on vegetation phenology in marshes of Sanjiang Plain. Results showed that the SOS advanced by 0.30 days/a, and EOS delayed by 0.23 days/a, causing LOS to increase significantly (p <.05) by 0.53 days/a over marshes of Sanjiang Plain. Spatially, the large SOS advance and EOS delay resulted in an obvious increasing trend for LOS in northern Sanjiang Plain. The rise of spring and winter temperatures advanced the SOS and increased the LOS, and the rise in temperature in autumn delayed the EOS in marshes of Sanjiang Plain. Our findings highlight the necessity of considering seasonal climatic conditions in simulating marsh vegetation phenology and indicate that the different influences of climatic variation on marsh vegetation phenology in different regions should be fully considered to assess the marsh ecosystem response to climatic change in Sanjiang Plain. [ABSTRACT FROM AUTHOR]

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Drought is a natural disaster that profoundly impacts all parts of the environment. Drought forecasting could provide technical support for drought risk prevention. This paper explored and compared the forecasting abilities of the autoregressive integrated moving average (ARIMA) in statistics, the wavelet neural network (WNN) and the support vector machine (SVM) in machine learning for drought forecasting in the Sanjiang Plain, China. The models used in this paper are based on the standard precipitation evapotranspiration index (SPEI) on the 12-month timescale. The SPEI was calculated using precipitation and temperature data collected during the period 1979–2016 from seven meteorological stations in the study area. Then, the SPEI series were predicted with the ARIMA, WNN and SVM models separately. The coefficient of determination (R2), mean-squared error (MSE), Nash–Sutcliffe efficiency coefficient (NSE) and Kolmogorov–Smirnov (K–S) distance, which is a nonparametric measure, were used to evaluate the performance of all models. A comparison between the raw data and predictions illustrates that the R2 and NSE values of the WNN model were 0.837 and 0.831, respectively; those of the SVM model were 0.833 and 0.827, respectively; and those of the ARIMA model were both > 0.9. Moreover, the ARIMA model had smaller MSE and K–S distance values than those of the other two models. Further, analysis of variance showed that the ARIMA model exhibited an obvious advantage over the other two models when forecasting drought in the Sanjiang Plain, China. Therefore, the method used for drought forecasting depends not only on the object of the data series but also on the underlying concepts of the models or algorithms and is a choice that should be made with caution. [ABSTRACT FROM AUTHOR]

Groundwater is subjected to contamination threats from human activities, such as agriculture, especially long-term farming in the Sanjiang Plain, China. Identifying the sources and distribution of pollution is essential for its reasonable prevention and control. In this study, we analysed the chemical characteristics of 389 samples at 60 shallow groundwater monitoring points from 2011 to 2015 in the Sanjiang Plain using traditional hydrochemical methods, water quality assessment, Pearson's correlation, and principal component analysis (PCA). Although groundwater type in this area was predominantly HCO3-Ca·Mg, three forms of nitrogen pollution (ammonia, nitrate, and nitrite) were all detected in this area. The interaction of natural geochemical and anthropogenic factors during hydrochemical formation is confirmed by the high coefficients of variation and Gibbs plots of the main ions in the water. The overall shallow groundwater situation was described as good, with more than 40% and 90% of groundwater samples suitable for drinking and irrigation according to the quality assessment, respectively. The proportion of poor water quality in the wet season was higher than that in the dry season. NO3-N and NH3-N were identified as the major anthropogenic pollutants in the study area. Results from Pearson's correlation and principal component analysis shows two main pollutants fall into two chemical controlling factors together with natural chemical parameters, which implies that the migration and transformation of pollutants may have affected the overall hydrochemical characteristics of the regional groundwater. Therefore, findings from this paper can provide insight into the chemical evolution of groundwater in response to long-term agricultural activities and can help contribute to better management of groundwater resources and agricultural sustainable development. [ABSTRACT FROM AUTHOR]

The Holocene hydrological regime on the Heixiazi Island is critical for understanding the evolution of the East Asian summer monsoon (EASM) for the island's climate-sensitive location on the northern fringe of the EASM domain. In this paper, a marsh depression on the central island was selected to reconstruct the locally hydrological variation and to discuss its indications for the Holocene EASM evolution. This work is based on multi-proxy (magnetic susceptibility, grain size, loss-on-ignition, and carbonate content) analyses of 22 modern sedimentary samples with a water-level gradient of 0–66 cm and 100 cored sedimentary samples covering last ~ 9.0 ka BP. The proxies' hydrological significance was previously interpreted by the 22 modern samples using linear regression equations to construct their relationships to water-level changes. Among these proxies, the magnetic susceptibility, carbonate content, as well as the Md and sand fraction of grain size exhibit high-level relationships against the water-level changes with R2 > 0.6. Thus, these four proxies' linear-regression equations were selected and used on the 100 cored samples, and the Holocene water-level changes in the studied depression were quantitatively reconstructed. It shows that two relatively high water-level stages with strengthened EASM occurred during 8.0–4.5 ka BP and 3.0–1.4 ka BP, which were alternated by three low water-level stages with declined EASM during ~ 9.0–8.0 ka BP, 4.5–3.0 ka BP, and 1.4–0 ka BP, respectively. Among these fluctuations, the highest water-level stage with most strengthened EASM which is defined as the Holocene Monsoon Maximum occurred during 6.4–4.5 ka BP. Such a new evolution pattern of the EASM can be further supported by a large variety of records from monsoon-margin regions. We suggest the Holocene EASM evolution was generally associated with the thermal conditions in both the inner Eurasia landmass and the West Pacific Ocean, with an exception of the weak EASM before 8.0 ka BP due to the enhanced Siberia High with the dominance of the Eurasia ice sheet in the early Holocene. [ABSTRACT FROM AUTHOR]

Soil management significantly affects the soil labile organic factors. Understanding carbon and nitrogen dynamics is extremely helpful in conducting research on active carbon and nitrogen components for different kinds of soil management. In this paper, we examined the changes in microbial biomass carbon (MBC), microbial biomass nitrogen (MBN), dissolved organic carbon (DOC), and dissolved organic nitrogen (DON) to assess the effect and mechanisms of land types, organic input, soil respiration, microbial species, and vegetation recovery under Deyeuxia angustifolia freshwater marshes (DAMs) and recovered freshwater marsh (RFM) in the Sanjiang Plain, Northeast China. Identifying the relationship among the dynamics of labile carbon, nitrogen, and soil qualification mechanism using different land management practices is therefore important. Cultivation and land use affect intensely the DOC, DON, MBC, and MBN in the soil. After DAM soil tillage, the DOC, DON, MBC, and MBN at the surface of the agricultural soil layer declined significantly. In contrast, their recovery was significant in the RFM surface soil. A long time was needed for the concentration of cultivated soil total organic carbon and total nitrogen to be restored to the wetland level. The labile carbon and nitrogen fractions can reach a level similar to that of the wetland within a short time. Typical wetland ecosystem signs, such as vegetation, microbes, and animals, can be recovered by soil labile carbon and nitrogen fraction restoration. In this paper, the D. angustifolia biomass attained natural wetland level after 8 years, indicating that wetland soil labile fractions can support wetland eco-function in a short period of time (4 to 8 years) for reconstructed wetland under suitable environmental conditions. [ABSTRACT FROM AUTHOR]

Different types of vegetation occupy different geomorphology and water gradient environments in the Sanjiang Plain, indicating that the soil moisture dynamics and water balance patterns of the different vegetation communities might differ from each other. In this paper, a lowland system, perpendicular to the Nongjiang River in the Honghe National Nature Reserve (HNNR), was selected as the study area. The area was occupied by the non-wetland plant forest and the typical wetland plant meadow. The Microsoft Windows-based finite element analysis software package for simulating water, heat, and solute transport in variably saturated porous media (HYDRUS), which can quantitatively simulate water, heat, and/or solute movement in variably-saturated porous media, was used to simulate soil moisture dynamics in the root zone (20-40 cm) of those two plant communities during the growing season in 2005. The simulation results for soil moisture were in a good agreement with measured data, with the coefficient of determination ( R) of 0.44-0.69 and root mean square error (RMSE) ranging between 0.0291 cm/cm and 0.0457 cm/cm, and index of agreement ( d) being from 0.612 to 0.968. During the study period, the volumetric soil moisture content of meadow increased with the depth and its coefficient of variation decreased with the depth (from 20 cm to 40 cm), while under the forest the soil moisture content at different depths varied irregularly. The calculated result of water budget showed that the water budget deficit of the meadow was higher than that of the forest, suggesting that the meadow is more likely to suffer from water stress than the forest. The quantitative simulation by HYDRUS in this study did not take surface runoff and plant growth processes into account. Improved root water uptake and surface runoff models will be needed for higher accuracy in further researches. [ABSTRACT FROM AUTHOR]

Deyeuxia angustifolia is a dominant species in the Sanjiang Plain, the largest freshwater marsh wetland in China. However, this species has declined because of great environment changes. In the effects of sea-level rise and greenhouse gas, magnitude and frequency of flood and rate of deposit in wetland increased greatly. Thus, in this paper, effects of soil environment (soil type, burial depth, water depth and oxygen concentration) on seed germination of D. angustifolia were investigated. Both soil type and burial depth affected seedling emergence. Seedlings emerged through 1-, 2-, 4-mm sand, and at 1-and 2-mm mud. Regardless of soil, seedling emergence time increased and emergence percentage decreased with increasing burial depth. For example, seedlings started to emerge on the 4th day and the final emergence percentage was 30% when covered with1-mm mud, whereas the initial emergence time was on the 6th day and the final emergence percentage was only 8% when covered with 2-mm mud. At the same burial depth, emergence percentage was higher in sand than in mud. Increasing water depth inhibited seed germination. Germination percentage in 2-cm water level (20%) was 1.2 times higher than that in 12-cm water level (9%). Oxygen concentration also affected germination. In the 21% oxygen concentration, germination was started on the 2nd day and the germination percentage was 36%, while seed started to germinate on the 4th day and the germination percentage was only 3% at the 7% oxygen concentration. These data indicate that seed germination of D. angustifolia was highly sensitive to soil type, burial depth, water depth, oxygen concentration, and these responses may be an explicit indication of maladjustment to environment changes, and an important reason accounting for the decline of this species in the Sanjiang Plain. [ABSTRACT FROM AUTHOR]

A comprehensive and integrative view of East Asian monsoon evolution during the Holocene is still under debate, and additional high-resolution proxy records from climatically sensitive locations are requisite to solve this complex issue. In this paper, we present three well-dated mud/peat cores from a paleo-pingo depression in the Sanjiang Plain, a climatically sensitive region to monsoon variation, to reveal the paleoenvironmental history of the wetland and discuss the regional impacts from monsoon evolution. A paleolake developed in the study area before 5.5 ka BP, and a peatland initiated thereafter consequent upon the gradual shrinking of the paleolake. This transition lasted until 4.5 ka BP, when the paleolake changed entirely to a wetland. Considering the prevalent monsoon climate in the Sanjiang Plain, we suggest that the lake-to-wetland transition from 5.5 to 4.5 ka BP indicates a rapid decline of the East Asian summer monsoon in addition to autogenic basin infilling processes. Such a remarkable monsoon weakening event has been documented across northern China, and we associate this with ocean–atmosphere interactions throughout low-latitude regions. [ABSTRACT FROM AUTHOR]

• Constructing a three-layer large system for irrigation water allocation. • Balancing water supply and demand between farmland, irrigation areas and regions. • Farmer income, allocation equity, engineering and regional economy coordination. • Optimal water allocations for crops, canals and large irrigation areas. • Fluctuations in water supply affect water distribution of different scales. Reasonable and optimal allocation of irrigation water is of great significance to improve agricultural water use efficiency for large-area agricultural irrigation systems. To solve the problems of large agricultural production scale, unreasonable water distribution structure, many rivers in the region and large changes in runoff volume, this paper takes the Sanjiang Plain in Heilongjiang Province, China, as the research object to develop an efficient and accurate water optimal allocation method. First, the runoff volume of many rivers in the region was obtained through the ARIMA-SVM-BP combined runoff prediction model, based on which a 'regional-irrigation district-farmland' multilayer multiobjective water resource cooperative deployment system model was established to achieve the synergistic enhancement of farmers' interests and the economic-social and regional economic-engineering volume of the irrigation district. The joint optimization method, fuzzy mathematical planning, and large system decomposition-coordination coupling were used to solve the multilayer multiobjective regulation system. The results show that the optimal agricultural water allocation volumes for the current year (2020) and the forecast year (2025) of 37 irrigation districts in the Sanjiang Plain are 3.61 × 109 m3 and 3.89 × 109 m3, saving 17% of water and resulting in a 24% decrease in the agricultural water use ratio compared with the actual situation, respectively. In the process of repeated coordination of the large system, the water distribution error is controlled within 1%. The fairness of water distribution in the multilayer system was improved by 34.7% while obtaining high economic benefits. The method proposed in this study helps the coordinated regulation and planning of multiple water sources in large agricultural irrigation areas, improves the ability of water distribution in irrigation areas to cope with different levels of incoming water, and promotes the sustainable development of regional irrigated agriculture. [ABSTRACT FROM AUTHOR]

Purpose: The soil microbial community is an important bioactive component of terrestrial ecosystems. Its structural and functional diversity directly affects carbon and nitrogen processes. This study aimed to investigate the variations in the diversity and composition of soil bacterial communities in a wetland with different nitrogen deposition conditions. Methods: A long-term simulated nitrogen deposition experiment was conducted in the Ecological Locating Research Station of the Institute of Nature and Ecology of Heilongjiang Academy of Sciences. Three different treatments were evaluated, including low nitrogen (LK; 40 kg N·hm-2·a-1), high nitrogen (HN; 80 kg N·hm-2·a-1), and control (CK; 0 kg N·hm-2·a-1). Bacterial 16S rDNA was then sequenced and analyzed using the next-generation sequencing technology. Result: Higher levels of N deposition resulted in an α-diversity increase followed by a decrease, with significant reductions in the HN treatment. Simulated nitrogen deposition resulted in changes in the structure and abundance of bacterial communities in wetland soils. The dominant phyla in all three plots were Proteobacteria and Acidobacteria. Compared with CK, the relative abundance of Chloroflexi increased significantly under the HN treatment (P < 0.05), whereas the relative abundance of Firmicutes and Bacteroidetes decreased significantly (P < 0.05). Nitrogen input changed the composition and relative abundance of the bacterial community, which was possibly due to N-induced soil acidification. Conclusion: This study thus provides a theoretical basis for predicting the effects of atmospheric nitrogen deposition on soil microorganisms, as well as changes in the wetland ecosystem in Sanjiang Plain. [ABSTRACT FROM AUTHOR]

Land use and land cover change (LUCC) has been increasingly recognized as having important effects on climate systems. Paddy fields, one kind of artificial wetland, have seen a significant increase in the Sanjiang Plain, China since 2000 and have become the most typical LUCC at the regional scale. Against this background, in this paper, we discuss the effects of this artificial wetland increase on surface temperature, in addition to its driving mechanisms. Firstly, the spatiotemporal variations of land surface temperature (LST) and its two driving variables (albedo and latent heat flux (LE)) in the Sanjiang Plain are analyzed and assessed based on remote sensing observation information from 2001 to 2015. Our results from both spatial distribution difference and time series analysis show that paddy field expansion led to day-time cooling and night-time warming over the study area. However, the LST changes show different characteristics and magnitudes in the spring (May to June) compared to the other months of the growing season (July to September). The daytime cooling trend is found to be −0.3842 K/year and the warming trend at night 0.1988 K/year during the period 2001 to 2015, resulting in an overall cooling effect in May and June. In July–September, the LST changes have the same sign but a smaller magnitude, with a −0.0686 K/year temperature trend seen for the day-time and a 0.0569 K/year increase for the night-time. As a consequence, a pronounced decrease in the diurnal temperature range is detected in the growing season, especially in spring. Furthermore, albedo and LE are demonstrated to be very sensitive to land use changes, especially in the earlier periods of the growing season. Correlation analysis between LST and albedo and LE also indicates the dominant role played by evapotranspiration in paddy fields in regulating local temperature. [ABSTRACT FROM AUTHOR]

Summary: Wetlands are important dissolved organic carbon (DOC) reservoirs, and principal sources of DOC to the fluvial environment, constituting a significant linkage between land and ocean in the context of global carbon cycle. The Sanjiang Plain, a floodplain in Northeastern China that encompasses numerous natural freshwater wetlands, has been experiencing extensive building of drainage ditches and thus elevated degradation of wetlands. This paper investigated DOC, dissolved inorganic carbon (DIC), and dissolved total carbon (DTC) in soil, the surface ponding and rivers from natural wetlands and the degraded wetland, and also in an artificial drainage ditch in the Sanjiang Plain during the growing season (May to October) of 2009. Seasonal averaged DOC concentrations were greater in soil and the surface ponding of the degraded riparian wetland than those originating from the natural riparian wetlands (i.e. Bielahong, Yalv and Nongjiang riparian wetlands). Seasonal averaged DIC concentrations in the surface ponding of the degraded wetland increased by 1.76, 0.59 and 2.05 times, compared to those in the Bielahong, Yalv and Nongjiang riparian wetlands, respectively. Similar to dissolved carbon dynamics in the field sites, the seasonal averaged DOC concentration in the degraded marshy river showed higher value (10.36±1.99mg/L), compared to those in the pristine marshy rivers. Seasonal DIC concentrations followed a trend as the degraded marshy river (15.09±2.43mg/L) – the artificial ditch (12.52±1.61mg/L) – pristine marshy rivers on average (8.53±0.96mg/L). Seasonal mean DTC concentration in the artificial ditch showed higher values than that in the natural marshy rivers, while seasonal mean DTC concentration in the degraded marshy river was greater than that in the artificial ditch. Further, seasonal DOC and DIC dynamics were similar in the artificial ditch and the degraded marshy river. These qualitative changes in the dissolved carbon dynamics in our study might have important implications that the impact of building of artificial ditches on dissolved carbon of waters more fully reflected in increases of dissolved carbon resulting from wetland degradation rather than increases in the artificial ditch itself. [Copyright &y& Elsevier]

The transport characteristics of phosphorus in soil and the assessment of its environmental risk have become hot topics in the environmental and agricultural fields. The Sanjiang Plain is an important grain production base in China, and it is characterised by serious land use change caused by large-scale agricultural exploitation. Agricultural inputs and tillage management have destroyed the soil nutrient balance formed over long-term conditions. There are few studies on non-point source phosphorus pollution in the Sanjiang Plain, which is the largest swampy low plain in a mid-high-latitude region in China. Most studies have focused on the water quality of rivers in marsh areas, or the export mechanism of phosphorus from specific land uses. They were conducted using experimental methods or empirical models, and need further development towards mechanism models and the macro-scale. The question is how to find a way to couple processes in phosphorus cycling and a distributed hydrological model considering local hydrological features. In this study, we report an attempt to use a distributed phosphorus transport model to analyse non-point source total phosphorus pollution from different land uses and soil types on the Sanjiang Plain. The total phosphorus concentration generally shows an annually increasing trend in the study area. The total phosphorus load intensity is heterogeneous in different land use types and different soil types. The average total phosphorus load intensity of different land use types can be ranked in descending order from paddy field, dry land, wetlands, grassland, and forestland. The average total phosphorus load intensity of different soil types can be ranked in descending order: paddy soil, bog soil, planosol, meadow soil, black soil, and dark brown earth. The dry land and paddy fields account for the majority of total phosphorus load in the study area. This is mainly caused by extensive use of phosphate fertilizer on the cultivated land. This has important implications for future agricultural management and non-point source control in this agricultural area of the mid-high latitude region. [ABSTRACT FROM AUTHOR]

Sanjiang Plain has undergone dramatic land degradation since the 1950s, which has caused negative effects on ecosystems services and sustainability. In this study, we used trajectory analysis as well as the Lorenz curve, Gini coefficient and relative land use suitability index (R) to analyze spatiotemporal changes of land degradation from 1954 to 2013 and to make a preliminary estimation of the role of human activities in observed environmental changes using a five-stage LULC data. This study also explored the effect of land degradation on the values and structure of ecosystem services. Our results indicated that more than 70% of marsh area originally present in the study area has been lost, whereas less than 30% was preserved. Dry farmland and paddy increased rapidly at the expense of marsh, forest and grassland. Land use structure became more unsuitable during the past 60 years. Compared with natural factors, human activities played a dominant role (89.67%) in these changes. This dramatic land degradation caused the significant loss of ecosystem services values and the changes in the structure of ecosystem services. These results confirmed the effectiveness of combining temporal trajectory analysis, the Lorenz curve/Gini coefficient and the R index in analyzing spatiotemporal changes in progressive land degradation. Also, these findings highlight the necessity of separating dry farmland from paddy when studying land degradation changes and the effects on ecosystem services in regions where dry farmland has often been converted to paddy. [ABSTRACT FROM AUTHOR]

The Sanjiang Plain (SJP) wetland is the largest freshwater marshland in China. Peatlands were initiated early and are widely distributed across the SJP and form a large carbon (C) pool. Consequently, there is a growing interest in understanding past, present, and future peatland dynamics. Most studies on peatland dynamics have been carried out on boreal and subarctic region; however, there are limited data about peatland dynamics on temperate region, such as SJP wetland, which is sensitive to climate change and human disturbance. Here, we presented a data synthesis of basal peat ages, peatland area, and peat C accumulation rate in the SJP to examine Holocene peatland dynamics and climate sensitivity, along with total C storage and their future fate. We show that peatland initiation in the SJP started in the early Holocene, but the most intense period of peatland initiation occurred during the late Holocene, when the climate was colder and drier than the early and mid-Holocene. And the C accumulation rate also continued to increase during the late Holocene. Our results suggest that insolation and monsoon intensity as well as the local topographic characteristics and hydrology during the late Holocene in the SJP might have played an important role in causing the highest rates of peatland initiation and C accumulation. Based on the Second National Wetland Resources Survey data, we estimated that the total peatland covered an area of about 10,520 km2 on the SJP and currently stores ~0.26 Pg C. However, human activities, together with the widespread warming on the SJP over the past 60 years, not only reduce the area of wetlands but also have switched it from being a net C sink to a significant C source. [ABSTRACT FROM AUTHOR]

Rice is a primary staple food for the world population and there is a strong need to map its cultivation area and monitor its crop status on regional scales. This study was conducted in the Qixing Farm County of the Sanjiang Plain, Northeast China. First, the rice cultivation areas were identified by integrating the remote sensing (RS) classification maps from three dates and the Geographic Information System (GIS) data obtained from a local agency. Specifically, three FORMOSAT-2 (FS-2) images captured during the growing season in 2009 and a GIS topographic map were combined using a knowledge-based classification method. A highly accurate classification map (overall accuracy = 91.6%) was generated based on this Multi-Data-Approach (MDA). Secondly, measured agronomic variables that include biomass, leaf area index (LAI), plant nitrogen (N) concentration and plant N uptake were correlated with the date-specific FS-2 image spectra using stepwise multiple linear regression models. The best model validation results with a relative error (RE) of 8.9% were found in the biomass regression model at the phenological stage of heading. The best index of agreement (IA) value of 0.85 with an RE of 13.6% was found in the LAI model, also at the heading stage. For plant N uptake estimation, the most accurate model was again achieved at the heading stage with an RE of 11% and an IA value of 0.77; however, for plant N concentration estimation, the model performance was best at the booting stage. Finally, the regression models were applied to the identified rice areas to map the within-field variability of the four agronomic variables at different growth stages for the Qixing Farm County. The results provide detailed spatial information on the within-field variability on a regional scale, which is critical for effective field management in precision agriculture. [ABSTRACT FROM AUTHOR]

Surface water and groundwater are the main water resources used for drinking and production. Assessments of the relationship between surface water and groundwater provide information for water resource management in Sanjiang plain, Northeast China. The surface water (river, lake, and wetland) and groundwater were sampled and analyzed for stable isotopic ( δD, δO) composition, tritium, and chlorofluorocarbons concentrations. The local meteoric water line is δD = 7.3 δO-6.7. The tritium (T) and chlorofluorocarbon (CFC) contents in groundwater were analyzed to determine the groundwater ages. Most groundwater were modern water with the ages <50 years. The groundwaters in mountain area and near rivers were younger than in the central plain. The oxygen isotope ( δO) was used to quantify the relationship between surface water and groundwater. The Songhua, Heilongjiang, and Wusuli rivers were gaining rivers, but the shallow groundwater recharged from rivers at the confluence area of rivers. At the confluence of Songhua and Heilongjiang rivers, 88 % of the shallow groundwater recharged from Songhua river. The combination of stable isotopes, tritium, and CFCs was an effectively method to study the groundwater ages and interrelation between surface water and groundwater. Practically, the farmlands near the river and under foot of the mountain could be cultivated, but the farmlands in the central plain should be controlled. [ABSTRACT FROM AUTHOR]

Total mercury in soil, water, plant, insects, fishes and bird feathers were determined to study mercury distribution and accumulation in typical wetland ecosystems in the Sanjiang Plain, Northeast China. Results show that total mercury concentrations in soils of Deyeuxia angustifolia wetland and Carex lascarpa wetland are 0.046 mg/kg and 0.063 mg/kg, respectively. Total mercury concentration in water bodies is 0.053 μg/L on average. Of four plants studied, total mercury in moss is the highest with the mean of 0.132 mg/kg. Of 10 terrestrial insect species studied, total mercury in centipede ( Scolopendra spp.) is the highest with the mean of 0.515 mg/kg while total mercury in grasshopper ( Oxya spp.) bodies is the lowest. Total mercury concentrations in the herbivorous, omnivorous and predatory insects are 10.18 ng/g, 16.47 ng/g and 213.35 ng/g on average, respectively. Total mercury concentrations of the adult feather (549.88 ± 63.04 ng/g), nestling feather (55.15 ± 23.53 ng/g), and eggshell (22.05 ± 5.96 ng/g) of the Grey heron (Ardea cinerea) are higher than those of the Great egret (Egretta alba) (adult feather: 446.57 ± 90.89 ng/g; nestling feather: 32.99 ± 17.15 ng/g; eggshell: 21.02 ± 3.17 ng/g) in the wetlands of the Sanjiang Plain. The bioconcentration factors decrease in the order of piscivorous fish muscle > omnivorous fish muscle > herbivorous fish > insect. [ABSTRACT FROM AUTHOR]

From May 2005 to September 2006, the potential effects of marsh flooding regimes on the decomposition and nutrient (N, P) dynamics of Calamagrostis angustifolia litter were studied in the typical waterlogged depression in the Sanjiang Plain, Northeast China. The decomposition of C. angustifolia litter was related to four sites with different hydrologic regimes [F1 (perennial flooding, average water depth of 480 days was 40.14 ± 8.93 cm), F2 (perennial flooding 33.27 ± 6.67 cm), F3 (perennial flooding 23.23 ± 5.65 cm) and F4 (seasonal flooding 1.02 ± 1.09 cm)]. Results showed that flooding regimes had important effects on the litter decomposition, the decomposition rates differed among the four sites, in the order of F3 (0.001820d) > F1 (0.001210d) > F2 (0.001040d) > F4 (0.000917d), and the values in the perennial flooding regimes were much higher. Flooding regimes also had significant effects on the N and P dynamics of litter in decomposition process. If the perennial flooding regimes were formed in C. angustifolia wetland due to the changes of precipitation in the future, the litter mass loss would increase 23.28-48.88%, the decomposition rate would increase 13.41-98.47%, and the t would decrease 1.07 yr-4.50 yr. In the perennial flooding regimes, the net N accumulated in some periods, while the net P released at all times. This study also indicated that the changes of N and P content in the litter of the four flooding regimes were probably related to the C/N or C/P ratios in the litter and the N or P availability in the decomposition environment. If the nutrient status of the decomposition environment did not change greatly, the decomposition rates depended on the substrate quality indices of the litter. Conversely, if the nutrient status changed greatly, the decomposition rates might depend on the supply status of nutrient in the decomposition environment. [ABSTRACT FROM AUTHOR]

Agricultural activities, especially reclamation, are considered major threats to the wetland ecosystems in Sanjiang Plain, the largest concentrated area of the freshwater wetlands in China. In the past decades, the area of the cultivated land and its grain production have been increased at the cost of wetlands shrinkage. The large-scale land reclamation severely affected the ecosystems in this region. However, such effects at the regional scale are seldom evaluated quantitatively. We used three datasets of LANDSAT MSS and/or TM imagery to estimate the area changes and the transition of land use types from 1980 to 2000. We also valued changes in ecosystem services delivered by each land category using value coefficients published by Costanza et al. [Nature 387, 1997, 253–260]. Sensitivity analysis suggested that these estimates were relatively robust. Finally, the contribution of various ecosystem functions was ranked to the overall value of the ecosystem services in this study. According to our estimates, the total annual ecosystem service values in Sanjiang Plain have declined by about 40% between 1980 and 2000 ($156284–182572.18 million in total over 20 years). This substantial decline is largely attributed to the 53.4% loss of wetlands. For individual ecosystem functions, waste treatment, water supply and disturbance regulation account for more than 60% to the total ecological values. During those two decades, the contribution of disturbance regulation, cultural and recreation decreased, while the contribution of water regulation, nutrient cycling, food production, raw materials and climate regulation increased during the same period. We also put forward a few proposals concerning the future land use policy formulation and sustainable ecosystems. They are adjusting the ‘food first’ agricultural policy, establishing more nature reserves for wetlands, creating systems for the rational use of water, harnessing the degraded cultivated land and encouraging eco-tourism. [ABSTRACT FROM AUTHOR]

The area of well irrigation rice became more and more, so the crisis of groundwater appeared. Making the most of rainfall is an availability method in water saving irrigation, increasing water temperature and raising yield. Just based on this, through applying the theory of season random time series, according to the data of average monthly rainfall (1981-1999), the authors build up the forecasting model in the area of well irrigation rice in the Sanjiang Plain. Through contrasting with practical value, the model has good effect. So, it can be used in water irrigation management. [ABSTRACT FROM AUTHOR]