DYNAMICS OF LITTER DECOMPOSITION AND SEASONAL DYNAMICS OF PHOSPHORUS IN DECOMPOSED RESIDUA OF Calamagrotis augustifolia IN THE WETLAND OF THE SANJIANG PLAIN

During the period of May to October in1999,systematical studies were giv en to the rate of decomposition of Calamagrostis angustifolia litter,the phosphorus content and weight in decomposed residua of litte r,and phosphorus content in the corresponding soil in the Sanjiang Plain.At the same time,the simulation models were listed in the paper.The results showed that the rate of we ight lost of decomposition of Calamagrostis angustifolia litter is 29.80%and the maximum of daily rate of weight lost i s 0.25%,which appeared in July.The c hange trend of phosphorus content an d weight in the decomposed residua of l itter is to reduce with the decomposing process,when it comes to the day of157,the decrement amount of the both were respectively 57.69mg /kg and 1.6199mg,which were 72.80%and 76.30%of its previous amount.In addition,th ere is a polynomial minus correlatio nship of phosphorus content between the variation in corresponding soil and the decomp osed residua of litter at the corresp onding period.The study will be help ful to further understand the process and mechanis m of biochemical cycling of nutrient elements in wetland ecosystems,in a ddition,it will also be helpful to the restoration and rebuilding of retrogressive wetlands and reasonable development and utilization of wetlands in the Sanjiang Plain.

A Macroinvertebrate Multimetric Index for the Bioassessment of Wetlands Adjacent to Agriculture Fields in the Sanjiang Plain, China

Adjacent intensive agriculture disturbs the natural condition of wetlands.However, to assess the effect of this agriculture on wetlands, few studies have used indices based on aquatic invertebrates.Multi-metric indices(MMIs) have been successfully used to assess freshwater ecosystems worldwide and are an important management tool, but little is known about their applicability in the Sanjiang Plain, Northeast China.In this study, we developed a MMIs for aquatic invertebrates to assess freshwater wetlands in this region.The aquatic invertebrate assemblages were sampled in 27 wetlands in the Sanjiang Plain that included those in natural reserves and those affected by adjacent, intensive agriculture.Twenty-four candidate metrics were initially reviewed and screened before four core metrics were selected: total number of taxa, number of Hemiptera taxa, proportion of Gastropoda, and proportion of predators.Mann-Whitney U tests, Box and Whisker plots, correlation analyses, and redundant metric tests were used to assess the ability of metrics to distinguish among reference and impaired wetlands.Four ordinal rating categories for wetland were defined: poor, fair, good, and excellent.Of the impaired freshwater wetlands, 76.2% were in poor or fair categories.The MMIs was robust in discriminating reference wetlands from impaired wetlands and therefore have potential as a biomonitoring tool to assess the condition and to guide the restoration efforts of freshwater wetlands in Northeast China.

Mercury Distribution and Accumulation in Typical Wetland Ecosystems of Sanjiang Plain,Northeast China

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.

Spatial Analysis of Land Use Change Effect on Soil Organic Carbon Stocks in Sanjiang Plain of China between 1980 and 2016

1 Introduction Marsh-wetland,as an important type of wetlands,is a synthetic natural ecosystem with rich soil organic carbon.The largest area of marsh-wetland was located in Sanjiang Plain in the Northeast China and obvious land use changes have occurred during the last 50 years with large area of marsh-wetland cultivated to farmland which had a big impact on soil organic carbon stock.In this study,spatial distributions of 0-20cm soil organic carbon sources and sinks in Sanjiang Plain were investigated from 1980 to 2016.

Impact of marsh changes on breeding cranes in Sanjiang Plain,northeastern China

In order to measure the impact of changes in the marsh on breeding Red-crowned Cranes (Grus japonensis) and White-naped Cranes (G.vipio) in the Sanjiang Plain,we conducted a complete crane súrvey in each of the summers of 2007 and 2008,and obtained information on the changes in its marsh through interpretation of satellite images in 1986,1995,2000 and 2005.A comparison between the 1984 and 2008 census shows that:1) the number of Red-crowned Cranes remained stable at about 300 birds,while the number of White-naped Cranes increased markedly; 2) the estimates of nests of Red-crowned cranes are close to the numbers of 1984,while approximately 90％ of the nests of these two crane species were distributed over five national nature reserves (NNRs); 3) the two crane species became more concentrated in three regions,i.e.,the Fuyuan Delta,the middle reaches of the Naoli and Qixing rivers,and the Xingkai Lake wetlands,rather as formerly in six regions.The area of the marsh decreased by 45％ within the 20-year period from 1986 to 2005.The major loss of the marsh area was in the form of a conversion to paddy fields and dry land,which can be primarily attributed to direct human activity under various economic and policy drivers.The disappearance of cranes in the Dulu and Abuqin rivers was induced by large-scale agricultural development.The fragmentation into and isolation of small areas of the marsh became increasingly more serious,which resulted in unsuitable condtions for crane breeding in small patches of the marsh.The number of cranes declined from 1984-1995 but had recovered remarkably by 2008,which may be due to theestablishment of a system of nature reserves,in place since 2000.The land ownership of the reserve plays a key role in maintaining the integrity of the wetland ecosystem,especially in Sanjiang,Honghe,Naolihe and Qixinghe NNRs,which together accommodated approximately 80％ of the population of cranes.However,we did not discover any nests at all in the provincial and municipal reserves,which may be attributed to high human disturbances in these areas.In the end,we propose some recommendations on reserve management.

Effects of Nitrogen Addition on Plant Functional Traits in Freshwater Wetland of Sanjiang Plain,Northeast China

To clarify the responses of plant functional traits to nitrogen(N) enrichment, we investigated the whole-plant traits(plant height and aboveground biomass), leaf morphological(specific leaf area(SLA) and leaf dry mass content(LDMC)) and chemical traits(leaf N concentration(LNC) and leaf phosphorus(P) concentration(LPC)) of Deyeuxia angustifolia and Glyceria spiculosa following seven consecutive years of N addition at four rates(0 g N/(m2·yr), 6 g N/(m2·yr), 12 g N/(m2·yr) and 24 g N/(m2·yr)) in a freshwater marsh in the Sanjiang Plain, Northeast China. The results showed that, for both D. angustifolia and G. spiculosa, N addition generally increased plant height, leaf, stem and total aboveground biomass, but did not cause changes in SLA and LDMC. Moreover, increased N availability caused an increase in LNC, and did not affect LPC. Thus, N addition decreased leaf C∶N ratio, but caused an increase in leaf N∶P ratio, and did not affect leaf C∶P ratio. Our results suggest that, in the mid-term, elevated N loading does not alter leaf morphological traits, but causes substantial changes in whole-plant traits and leaf chemical traits in temperate freshwater wetlands. These may help to better understand the effects of N enrichment on plant functional traits and thus ecosystem structure and functioning in freshwater wetlands.

The current status, threats and protection way of Sanjiang Plain wetland, Northeast China

The Sanjiang Plain is a vast area of alluvial floodplains and low hills in northeast Heilongjiang Province. It is the largest tract of wetlands in China and East Asia outside of Siberia. 28 wetland nature reserves exist on the Sanjiang Plain, and three of them have been listed as wetlands of international importance to water bird conservation by the Ramsar Convention Bureau. The wetlands of Sanjiang Plain are noteworthy for its rich biodiversity, but they continue to decline in area and deteriorate in quality currently. The main threats or constrains, immediate cause, root cause and required response are analyzed in this paper, and the four aspects opinion such as improvement of watershed management, enhancement of protection and restoration of habitats and biodiversity, alternative livelihoods of rural residents living in and near natural wetland reserve, and reinforcement of capacity building of natural reserves are brought forward as the effective measures for the Sanjiang Plain wetland protection.

Effect of Nitrogen and Phosphorus on Tissue Nutrition and Biomass of Freshwater Wetland Plant in Sanjiang Plain,Northeast China

Nitrogen (4, 10, 20 and 40g/m2) and phosphorus (1.2, 4.8 and 9.6g/m2) were applied to tanks to evaluating the effects of N and P additions on plant tissue nutrition and the biomass of two freshwater wetland plants in the Sanjiang Plain of Northeast China, namely Carex lasiocarpa and Carex meyeriana. For C. lasiocarpa, the total N concentration (TN) of plant tissues under the treatment of 10g/m2 was lower compared with the other N treatments. Initially, C. lasiocarpa exhibited a significant increase of biomass as compared with the control value, reaching the maximum of 31.20±4.01g/tank under the treatment of 10g/m2, and then dropped to 18.02±1.53g/tank under the treatment of 40g/m2. For C. meyeriana, TN generally increased with increasing amount of N applied. High N applied produced more aboveground biomass than low N applied. C. meyeriana, as the accompanying species, can adapt itself to the wetland enriched by N, and it may replace C. lasiocarpa as the dominant species of wetland. The total P concentration (TP) in tissues of C. lasiocarpa increased with P addition. The aboveground biomass of C. lasiocarpa increased with P addition, and it changed from 18.77±3.29g/tank to 46.03±3.95g/tank. However, TP of tissue may accelerate the C. meyeriana development under the treatment of 1.2g/m2. P accumulation contributes to the dominance of C. lasiocarpa but limits the production of C. meyeriana, and the latter may disappear gradually from the wetland enriched by P. Increased input of N and P might have an influence on wetland plant community composition and structure, so the effects of nutrient inputs and accumulation should be considered to protect the freshwater wetland.

Simulation Study on Purification Efficiency for Nitrogen in Different Types of Wetlands in Sanjiang Plain, China

The purification law of nitrogen in Deyeuxia angustifolia, Carex lasiocarpa and Deyeuxia angustifolia-Carex lasiocarpa combined wetland systems in the Sanjiang Plain, China was studied by field simulation experiment. The results indicate that the removal rates of TN, NH4^＋-N and NO3^--N in above three types of wetlands present an obvious logarithm growth trend along with the time. There are evident removal effects for NH4＋-N and NOa--N in water bodies of wetlands after the 30th day of experiment, with the removal rates over 80.0%, but the removal rate of TN is slightly low, being 63.1%-74.3%. NO3 -N is most quickly removed by the combined wetland, and NH4^＋-N by Deyeuxia angustifolia wetland. The removal speeds of TN by the three wetland systems are comparatively slow, of which the Deyeuxia angustifolia wetland is the fastest. In consideration of plant growth season, Deyeuxia angustifolia wetland has much more practical application value in purifying nitrogen. These results can provide references for the study on the purification function of wetlands and the control of non-point source pollution in Northeast China.

Temperature Variation of Jiamusi Region in Sanjiang Plain

[Objective] The study aimed at analysing the change characteristics of temperature in Jiamusi region of Sanjiang Plain.[Method] Based on temperature data of Jiamusi region in Sanjiang Plain from 1961 to 2010,including Jiamusi,Huanan,Fujin and Fuyuan station,we studied the change trends,abrupt climate change and abnormal years of temperature in Jiamusi region.[Result] Annual average temperature of Jiamusi region in Sanjiang Plain showed increasing trend,with the increase of 0.249-0.412 ℃/10 a.The order of annual average temperature in Jiamusi region was east> south> north> west.In addition,abrupt climate change of annual average temperature occurred in the early 1980s.Abrupt climate change of annual average temperature appeared in 1981 in Jiamusi,Huanan and Fujin,but in 1984 in Fuyuan.Annual average temperature in the mid-1960s and late 1960s was abnormally low in Jiamusi,Fujin and Huanan,while it was abnormally high in Huanan,Fuyuan and Jiamusi from 2007 to 2008,but Fujin in the early 1990s.Meanwhile,anomalies of seasonal average temperature in distinct regions appeared in various years.[Conclusion] The research could provide references for the prediction of temperature in Jiamusi region of Sanjiang Plain in furture.

Seasonal characteristics of Carex lasiocarpa biomass and nutrient accumulation in the typical wetland of Sanjiang Plain, China

Seasonal dynamics of above- and belowground biomass and nutrient characteristics （nitrogen, carbon, and phosphorus） of Carex lasiocarpa were investigated in the typical wetland of Sanjiang Plain, China from May 2007 to September 2008. The results show that the changes of aboveground biomass during the growing season are best described by the twice function curve model, whereas the changes of belowground biomass follow the exponential increase curve model. Both the organic carbon contents in the above- and belowground plant parts show significant positive linear correlations with the growing time, and the coefficients R2 are 0.983 and 0.746, respectively. The carbon accu-mulations of the above- and belowground plant parts during the growing season show the same dynamics as those of the biomass. However, the nitrogen contents and accumulation in C. lasiocarpa aboveground and belowground parts show exponential increase during the growing season. The dynamics of C. lasiocarpa phosphorus contents follows the twice function curve model, whereas the accumulation of phosphorus shows the linear increase. The ratios of C/N in different parts of C. lasiocarpa fit the negative linear relations with total nitrogen content in the growing season. Moreover, the ratios of C/P in C. lasiocarpa plant also fit the negative linear relations with total phosphorus content. The results show that nitrogen is the primary limiting nutrient for C. lasiocarpa growth as compared with carbon and phosphorus.

Influence of environment and substrate quality on the decomposition of wetland plant root in the Sanjiang Plain,Northeast China

The litterbag method was used to study the decomposition of wetland plant root in three wetlands along a water level gradient in the Sanjiang Plain,Northeast China.These wetlands are Calamagrostis angustifolia(C.aa),Carex meyeriana(C.ma)and Carex lasiocarpa (C.la).The objective of our study is to evaluate the influence of environment and substrate quality on decomposition rates in the three wetlands.Calico material was used as a standard substrate to evaluate environmental influences.Roots native to each we...

Distribution characteristics of dissolved organic carbon in annular wetland soil-water solutions through soil profiles in the Sanjiang Plain,Northeast China

Overwhelming evidence reveals that concentrations of dissolved organic carbon （DOC） have increased in streams which brings negative environmental impacts. DOC in stream flow is mainly originated from soil-water solutions of watershed. Wetlands prove to be the most sensitive areas as an important DOC reserve between terrestrial and fluvial biogeosystems. This reported study was focused on the distribution characteristics and the controlling factors of DOC in soil-water solutions of annular wetland, i.e., a dishing wetland and a forest wetland together, in the Sanjiang Plain, Northeast China. The results indicate that DOC concentrations in soilwater solutions decreased and then increased with increasing soil depth in the annular wetland. In the upper soil layers of 0-10 cm and 10-20 cm, DOC concentrations in soil-water solutions linearly increased from edge to center of the annular wetland （R^2 = 0.3122 and R^2 = 0.443）. The distribution variations were intimately linked to DOC production and utilization and DOC transport processes in annular wetland soil-water solutions. The concentrations of total organic carbon （TOC）, total carbon （TC） and Fe（II）, DOC mobility and continuous vertical and lateral flow affectext the distribution variations of DOC in soil-water solutions. The correlation coefficients between DOC concentrations and TOC, TC and Fe（II） were 0.974, 0.813 and 0.753 respectively. These distribution characteristics suggested a systematic response of the distribution variations of DOC in annular wetland soil-water solutions to the geometry of closed depressions on a scale of small catchments. However, the DOC in soil pore water of the annular wetland may be the potential source of DOC to stream flow on watershed scale. These observations also implied the fragmentation of wetland landscape could bring the spatial-temporal variations of DOC distribution and exports, which would bring negative environmental impacts in watersheds of the Sanjiang Plain.

Nitrogen cycling of atmosphere-plant-soft system in the typical Calamagrostis angustifolia wetland in the Sanjiang Plain,Northeast China

The nitrogen （N） distribution and cycling of atmosphere-plant-soil system in the typical meadow Calamagrostis angustifolia wetland （TMCW） and marsh meadow Calamagrostis angustifolia wetland （MMCW） in the Sanjiang plain were studied by a compartment model. The results showed that the N wet deposition amount was 0.757 gN/（m^2·a）, and total inorganic N （TIN） was the main body （0.640 gN/（m^2·a））. The ammonia volatilization amounts of TMCW and MMCW soils in growing season were 0.635 and 0.687 gN/m^2, and the denitrification gaseous lost amounts were 0.617 and 0.405 gN/m^2, respectively. In plant subsystem, the N was mainly stored in root and litter. Soil organic N was the main N storage of the two plant-soil systems and the proportions of it were 93.98% and 92.16%, respectively. The calculation results of N turnovers among compartments of TMCW and MMCW showed that the uptake amounts of root were 23.02 and 28.18 gN/（m^2·a） and the values of aboveground were 11.31 and 6.08 gN/（m^2·a）, the re-translocation amounts from aboveground to root were 5.96 and 2.70 gN/（m^2·a）, the translocation amounts from aboveground living body to litter were 5.35 and 3.38 gN/（m^2·a）, the translocation amounts from litter to soil were larger than 1.55 and 3.01 gN/（m^2·a）, the translocation amounts from root to soil were 14.90 and 13.17 gN/（m^2·a）, and the soil （0-15 cm） N net mineralization amounts were 1.94 and 0.55 gN/（m^2·a）, respectively. The study of N balance indicated that the two plant-soil systems might be situated in the status of lacking N, and the status might induce the degradation of C. angustifolia wetland.

Quantitative Simulation on Soil Moisture Contents of Two Typical Vegetation Communities in Sanjiang Plain,China

Different types of vegetation occupy different geomorphology and water gradient environments in the San- jiang Plain, indicating that the soil moisture dynamics and water balance patterns of the different vegetation communi- ties 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 quantita- tively 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 determi- nation （R2） of 0.44-0.69 and root mean square error （RMSE） ranging between 0.0291 cm3/cm3 and 0.0457 cm3/cm3, and index of agreement （d） being from I）.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.

Value Estimation of Greenhouse Gases Exchange in Wetland Ecosystem of Sanjiang Plain,China

The objective of this study is to quantify the values of greenhouse gases(GHGs) exchange in carbon equivalents of marshes and paddy fields in the Sanjiang Plain,Heilongjiang Province,China. We obtained the GHGs exchange values based on comparable price by calculating the carbon sequestration values and the GHGs emission values of marshes and paddy fields respectively in four periods of 1982,1995,2000 and 2005. It is noted that the GHGs emission values are always negative. In this study,the marshes areas decreased from 1438977.0 to 775,132.2ha and the paddy fields areas increased from 417195.8 to 934205.0ha. The values of GHGs exchange of marshes varied from 135877.156×106 to 136882.534×106 yuan(RMB) and those of paddy fields varied from 1006.256×106 to 2767.645×106 yuan. The GHGs exchange values of marshes decreased from 1982 to 2005 on the whole,reversely,those of paddy fields increased,but those in 2005 were lower than those in 2000. In different periods,the GHGs exchange values were always higher in marshes than in paddy fields. The contribution rate of GHGs exchange values per unit area of marshes was also very high in different periods,and the maximum was up to 98.35% in 2005. As far as the whole wetland ecosystem(including marshes and paddy fields) ,assuming a linear change in GHGs exchange values,it represented a cumulative increase of 20926.757×106 yuan from 1982 to 2005. By adding GHGs exchange values increased during those four periods,we obtained a cumulative net increase values of GHGs exchange of wetland ecosystem of 18200.860×106 yuan. The results will be useful for understanding the indirect services provided by marshes and paddy fields.

Response of Regeneration Diversity of Carex Lasiocarpa Community to Different Water Levels in Sanjiang Plain,China

The species diversity at the regeneration stage, inflenced by different water levels, is important for community composition in the later growing season.Regeneration diversity of Carex lasiocarpa community under different water levels was studied at two stages, recruitment and adult, in the Sanjiang Plain, Heilongjiang Province, China.The results showed that, at the two growing stages, important value of C.lasiocarpa population and species richness of the community decreased with the increasing water level, while the Simpson and Shannon-Wiener diversity indexes and Pielou evenness index increased.Under different water levels, community diversities were higher at the recruitment stage, while population important values of C.lasiocarpa were higher at the adult stage.Indexes in vegetation evaluation must be chosen prudentially for successful restoration and effective management of wetlands, and especially for wetland restoration, the optimal time should be selected according to the restoration objectives and costs.

Effects of Wetland Reclamation on Soil Nutrient Losses and Reserves in Sanjiang Plain,Northeast China

The carbon （C）, nitrogen （N） and phosphorus （P） variations of a temperate wetland soil under continuous cultivation for 40 yr were determined and evaluated in the Sanjiang Plain, Northeast China. The results showed that the soil organic carbon （SOC） and total nitrogen （TN） contents in each soil layer decreased sharply after cultivation for 2-3 yr, and exhibited minor differences after cultivation for 11 yr, which showed an exponential decline curve with the increase of cultivation years. The reduction rates of carbon and nitrogen reserves were 14.79% and 28.53% yr^-1 at the initial reclamation stages of 2-3 yr and then decreased to 2.02-3.08% yr^-1 and 1.98-2.93% yr^-1 after cultivation for 20 yr, respectively. Soil total phosphorus （TP） reserves decreased within cultivation for 5 yr, and then gradually restored to the initial level after cultivation for 17 yr. Both SOC and TN could be restored slightly when the farmland was left fallow for 8 yr after reclamation for 11 yr, whereas TP had no significant difference. These results demonstrated that wetland cultivation was one of the most important factors influencing on the nutrient fate and reserves in soil, which could lead to the rapid nutrient release and slow restoration through abandon cultivation, therefore protective cultivation techniques preventing nutrients from loss should be immediately established after wetland reclamation.

Mapping the fallowed area of paddy fields on Sanjiang Plain of Northeast China to assist water security assessments

Rice growth requires a large amount of water,and planting rice will increase the contradiction between supply and demand of water resources.Paddy field fllowing is important for the sustainable development of an agricultural region,but it remains a great challenge to accurately and quickly monitor the extent and area of fallowed paddy fields.Paddy fields have unique physical features associated with paddy rice during the flooding and transplanting phases.By comparing the differences in phenology before and after paddy field fllowing,we proposed a phenology-based fallowed paddy field mapping algorithm.We used the Google Earth Engine(GEE)cloud computing platform and Landsat 8 images to extract the fllowed paddy field area on Sanjiang Plain of China in 2018.The results indicated that the Landsat8,GEE,and phenology-based fllowed paddy field mapping algorithm can effectively support the mapping of fallowed paddy fields on Sanjiang Plain of China.Based on remote sensing monitoring,the total fallowed paddy field area of Sanjiang Plain is 91543 ha.The resultant fallowed paddy field map is of high accuracy,with a producer(user)accuracy of 83%(81%),based on validation using ground-truth samples.The Landsat-based map also exhibits high consistency with the agricultural statistical data.We estimated that paddy field fallowing reduced irigation water by 384-521 million cubic meters on Sanjiang Plain in 2018.The research results can support subsidization grants for fallowed paddy fields,the evaluation of fallowed paddy field effects and improvement in subsequent fallowed paddy field policy in the future.

Evapotranspiration Estimation Based on MODIS Products and Surface Energy Balance Algorithms for Land(SEBAL) Model in Sanjiang Plain,Northeast China

In this study,the Surface Energy Balance Algorithms for Land(SEBAL) model and Moderate Resolution Imaging Spectroradiometer(MODIS) products from Terra satellite were combined with meteorological data to estimate evapotranspiration(ET) over the Sanjiang Plain,Northeast China.Land cover/land use was classified by using a recursive partitioning and regression tree with MODIS Normalized Difference Vegetation Index(NDVI) time series data,which were reconstructed based on the Savitzky-Golay filtering approach.The MODIS product Quality Assessment Science Data Sets(QA-SDS) was analyzed and all scenes with valid data covering more than 75% of the Sanjiang Plain were selected for the SEBAL modeling.This provided 12 overpasses during 184-day growing season from May 1st to October 31st,2006.Daily ET estimated by the SEBAL model was misestimaed at the range of-11.29% to 27.57% compared with that measured by Eddy Covariance system(10.52% on average).The validation results show that seasonal ET from the SEBAL model is comparable to that from ground observation within 8.86% of deviation.Our results reveal that the time series daily ET of different land cover/use increases from vegetation on-going until June or July and then decreases as vegetation senesced.Seasonal ET is lower in dry farmland(average(Ave):491 mm) and paddy field(Ave:522 mm) and increases in wetlands to more than 586 mm.As expected,higher seasonal ET values are observed for the Xingkai Lake in the southeastern part of the Sanjiang Plain(Ave:823 mm),broadleaf forest(Ave:666 mm) and mixed wood(Ave:622 mm) in the southern/western Sanjiang Plain.The ET estimation with SEBAL using MODIS products can provide decision support for operational water management issues.