Sanjiang Plain Research Articles

Variations in ecosystem services in response to paddy expansion in the Sanjiang Plain, Northeast China

ABSTRACT The ecosystem of the Sanjiang Plain in China has dramatically changed in the past four decades. This study investigated the history of paddy field expansion in the Sanjiang Plain and discovered the ecosystem service variations in response to paddy expansion. Integrating a series of Landsat images, we obtained the paddy expansion history from 1976 to 2015. Then, we calculated ecosystem service values (ESVs) to estimate the ecosystem service variations caused by paddy expansion in the Sanjiang Plain. The results indicate that the paddy area increased from 404,789–2,598,449 ha during 1976–2015, leading to a decline in the total ecosystem service values by 11288.04 million dollars. The largest decline in ESVs in response to paddy expansion was caused by wetland reclamation (9998.54 million dollars). Apart from agricultural products and gas regulation functions, the ESVs provided by other functions all showed a declining trend. Paddy expansion in the Sanjiang Plain increased agricultural product function at the expense of the decline of other functions. In future management practices, the rational allocation of water resources and paddy distribution are necessary in order to achieve sustainable development of both water resources and agricultural production. Some suggestions including coculture systems, restoring habitats for aquatic species, farm management that fosters biodiversity in paddy fields are provided for future sustainability.

Spatiotemporal variation in vegetation spring phenology and its response to climate change in freshwater marshes of Northeast China

Understanding wetland vegetation phenology and its response to climate change is important to predict the changes of wetland vegetation in wetland regions. Using the NDVI and climate data, this work studied the spatiotemporal change of start date of vegetation growing season (SOS) and explored the possible effects of climate change on the SOS over freshwater marshes of Northeast China. The results showed that the SOS significantly advanced by 0.52 day per year throughout the freshwater marshes of Northeast China during 2001 to 2016. The significant advancing of SOS was mainly concentrated in freshwater marshes of the Khingan Mountains (the Greater Khingan Mountains and the Lesser Khingan Mountains) and central arid or semi-arid regions (Songnen plain and Liaohe plain) in Northeast China. By contrast, there were weak delay trends of SOS in freshwater marshes of Eastern Inner Mongolia region, and Sanjiang plain. We found that precipitation was a dominant factor determining the SOS in arid or semi-arid regions (Songnen plain and Liaohe plain), while temperature played a bigger role in determining the SOS in Sanjiang plain and three cold mountains of the Northeast China. During the study period, increasing precipitation in the winter and spring contributed to advancing SOS in Songnen plain and Liaohe plain; the decrease of temperature from December to April explain the delaying SOS in freshwater marshes of Sanjiang Plain; the weak warming of temperature between November and May account for the advancing SOS of freshwater marshes in three cold mountains. In freshwater marshes of cold and the most arid region of Northeast China (Eastern Inner Mongolia), the SOS was influenced by both precipitation and temperature. Decreasing precipitation between January and April, as well as temperature decreases in March and April explain the delay of SOS in freshwater marshes of Eastern Inner Mongolia region.

Ecosystem service decline in response to wetland loss in the Sanjiang Plain, Northeast China

In the last six decades, natural ecosystems in the Sanjiang Plain have undergone significant disturbance. Our study investigated wetland loss history and revealed the ecosystem service decline caused by wetland loss in this area. Based on multi-source data, we obtained wetland loss history since the mid-1950s. Then ecosystem service value (ESV) changes in response to wetland loss were estimated quantitatively in the Sanjiang Plain. Results indicate that wetland area declined by 73.3% (about 2.77 million ha) since 1954, mainly due to the transformation of wetlands to farmland. Wetland loss has reduced the ecosystem service value by $57.46 billion over the past six decades. The largest reduction in ESVs was due to agricultural expansion, especially that of dry farmland. Ecosystem services of all functions except agricultural product functions decreased in the past 60 years. Agricultural product functions increased at the expense of other functions. Wetland restoration and protection of existing wetlands are necessary to reduce the loss of ecosystem services as well as to promote sustainable development.

Methane emissions from typical paddy fields in Liaohe Plain and Sanjiang Plain, Northeast China

Methane is one of the most important greenhouse gases and is emitted from waterlogged rice regions. Eddy covariance was used to obtain long-term (2017–2018), high-frequency data for the CH4 flux at typical rice paddy fields in Sanjiang Plain and Liaohe Plain. This study examines the CH4 emission process, emission characteristics at different time scales and the intensity of different emission sources. The relationships between CH4 emissions and temperature and photosynthetically active radiation were also analysed. CH4 emissions from Sanjiang Plain and Liaohe Plain in 2017 were 26.77 and 16.17 g CH4 m−2year−1, respectively. The CH4 fluxes in 2017 and 2018 were similar; emissions were higher at the Sanjiang site in 2018. Peak CH4 emissions (daily average: 0.127 μmol CH4 m−2s−1) corresponded to the tillering stage in Sanjiang Plain. CH4 emissions peaks corresponding to the jointing–heading and mature stages at Liaohe Plain. Monthly CH4 emissions were highest in July. The daily averaged flux was 0.065 μmol CH4 m−2s−1 during the growing season. The field-transplanting stage exhibited the highest CH4 emissions. No CH4 was emitted during the greening–tillering stages. Emissions increased again during the jointing–heading stages to 0.102 μmol CH4 m−2 s−1, and then decreased gradually. A significant linear correlation was observed between PAR and the methane flux in Liaohe Plain. CH4 emissions in Sanjiang Plain were more sensitive to changes in temperature. The temperature coefficient value was highest from the sowing period to the green period. The CH4 flux at Sanjiang Plain depended on the stage of rice growth, the temperature, the degree of irrigation and drainage, and the soil pH. In November (during the non-growing season) at Liaohe Plain, a slight negative flux (a weak CH4 sink) was observed. CH4 emissions were also found to be inhibited in the growing season by increased soil alkalinity.

Impacts of Wetland Reclamation and Paddy Field Expansion on Observed Local Temperature Trends in the Sanjiang Plain of China

AbstractThe warming or cooling effects on regional climate in response to early land use change may be strengthened, weakened, or eliminated by the same or opposite effect in the subsequent land use/management period. Taking the Sanjiang Plain in China as our study area, this paper analyzed the surface temperature change due to land use/land management changes from the mid‐1950s to 2015, based on the land surface temperature response model and the observation minus reanalysis (OMR) method using remote sensing data, meteorological observation data, and reanalysis data. Results revealed a magnitude of monthly mean land surface warming up to 1.31 °C due to the land use change from wetland to rain‐fed farmland and a cooling effect of −1.32 °C caused by the land management change from rain‐fed farmland to paddy fields during the growing season. The trends were confirmed using OMR method. Land surface temperature change based on remote sensing data was divided into radiative and nonradiative forcing. The nonradiative processes play a dominant role in regulating the local surface temperature. The monthly mean temperature differences in response to land use changes differ greatly during the growing season. The temperature difference was greater in May and June (spring) than in July and August (summer). Our study shows that the land use impact on regional climate could be switched dramatically, and it would be basically consistent with the impact of natural wetlands before reclamation in our study area right now, which provides important information for mitigating and adapting to global climate change at regional scale.

Responses of soil respiration to nitrogen addition in the Sanjiang Plain wetland, northeastern China.

This study was designed to test the hypothesis that nitrogen (N) addition leads to enhanced soil respiration (SR) in nitrogen deficient marsh. Here, we report the response of SR to simulated N deposition in a temperate marsh of northeastern China from June 2009 to September 2011. The experiment included three-levels of N treatment (control: no N addition, Low-N: 4g N m-2 y-1, and High-N: 8 g N m-2 y-1). Our study showed various responses of SR to level and duration of N addition. Yearly SR was increased by 11.8%-15.2% (P<0.05) under Low-N addition during the three years, while SR showed a strong increase by 27.5% (P<0.05) in the first year and then decreased by 4.4% (P>0.05) and 15.4% (P<0.05) in the next two years under High-N addition. Soil respiration was positively correlated with soil temperature and negatively correlated with soil water content. High-N treatment reduced soil pH value (P<0.05). The negative response of SR to High-N addition in the following two years may attribute to lower microbial activity, microbial biomass and alteration in the microbial community due to lower soil pH, which consequently leads to decreased SR. Meanwhile, we found root biomass were increased under High-N addition. This implies that the increase of autotrophic respiration was lower than the decline of heterotrophic respiration in the following two years. Our findings suggest complex interactions between N deposition and SR, which is needed to be further investigated in the future studies.

Holocene mercury accumulation calibrated by peat decomposition in a peat sequence from the Sanjiang Plain, northeast China

Peatlands are ideal archives that are widely used to reconstruct historical Hg accumulation around the world. However, decomposition of peat soils leads to Hg enrichment or depletion in peat profiles. To evaluate the impact of peat decomposition on historical Hg accumulation records, a 7800-year peat sequence from the Shenjiadian peatland (SJD-2, Sanjiang Plain, northeast China) was selected in this study. Based on the degree of peat humification and a generalized additive model (GAM), Hg accumulation rates (Hg ARs) were reconstructed and calibrated from the middle Holocene onward. The results showed that the Hg concentrations in the SJD-2 peat profile ranged from 11.9 to 55.3 ng g−1 and that the Hg AR ranged from 0.4 to 7.0 μg m−2 yr−1; these values for both parameters were lower than their corresponding values observed in other peatlands around the world. Peat decomposition led to Hg depletion in peat soils to some extent, and the GAM could be used to evaluate the impact of peat decomposition on historical Hg ARs in peat sequences based on the degree of peat humification and calibration of Hg ARs. Before the Industrial Revolution, anthropogenic Hg sources caused the calibrated Hg ARs in the SJD-2 peat profile to slightly increase around 1300 cal yr BP. Similar to other regions around the world, the calibrated Hg AR on the Sanjiang Plain also obviously increased from 3 to 8 μg m−2 yr−1 after global Hg emissions began to increase during the Industrial Revolution.

1954-2015年三江平原沼泽湿地变化的区域分异及影响因素

PDF HTML阅读 XML下载 导出引用 引用提醒 1954-2015年三江平原沼泽湿地变化的区域分异及影响因素 DOI: 10.5846/stxb201802270394 作者: 作者单位: 吉林师范大学 旅游与地理科学学院,吉林师师范大学旅游与地理科学学院,吉林师师范大学旅游与地理科学学院 作者简介: 通讯作者: 中图分类号: 基金项目: 吉林省科技发展计划（20180101085JC）；吉林省社会科学基金项目（2018B175） Regional differentiation and factors influencing changes in swamps in the Sanjiang Plain from 1954 to 2015 Author: Affiliation: College of Tourist and Geoscience,Jilin Normal University,, Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:以湿地变化较为剧烈的三江平原为研究区域，结合GIS和RS技术，利用动态度、景观指数和地理探测器模型，在流域尺度上对1954-2015年三江平原沼泽湿地变化的区域分异及影响因素进行定量分析。结果表明：1954-2015年，三江平原各流域沼泽湿地面积呈现减少趋势，其中挠力河流域和同抚流域沼泽湿地面积丧失最多，安邦河流域、萝北流域和倭肯河流域沼泽湿地丧失速率较快；三江平原各流域沼泽湿地格局变化特征具有一定的差异性，倭肯河流域沼泽湿地斑块的集中化程度逐渐增强且破碎化程度逐渐减少，其他流域沼泽湿地的集中化程度逐渐减弱且破碎化程度增加，各子流域沼泽湿地斑块之间的连接性和稳定性均呈下降趋势，其中安邦河流域下降幅度最大，最能表现三江平原各子流域沼泽湿地景观格局变化的指数是斑块密度；人为干扰是影响三江平原各子流域沼泽湿地变化的主要因素，自然因素中对沼泽湿地变化影响最大的是地形地貌，其次是气温和降水量。 Abstract:We used the Sanjiang Plain where swamp changes have been more drastic as the research area. Regional differentiation and factors influencing the changes of in swamps in the Sanjiang Plain from 1954 to 2015 at the watershed scale were analyzed using the dynamic degree, landscape index, and Geodetector model, and by combining GIS and RS techniques. The results showed that from 1954 to 2015, the area of swamps in the Sanjiang Plain had a decreasing trend, in which, the loss of wetland area in the Naoli River and Tongfu Basins was the greatest, whereas in the Anbang River, Luobei River, and Weiken River Basins the loss was faster. The variation characteristics of the swamps pattern in each basin within the Sanjiang Plain had some differences. The concentration of patches in the swamps in the Weiken River Basin gradually increased and the degree of fragmentation gradually decreased, whereas the concentration of swamps in other basins gradually decreased and their degrees of fragmentation increased, and the connectivity and stability of swamp patches in all sub-basins showed a decreasing trend, in which, the Anbang River Basin showed the largest decline. The index that best demonstrated the change in the swamp landscape pattern in each sub-basin of the Sanjiang Plain was patch density. Human disturbance was the main factor affecting the changes in swamps in each sub-basin of the Sanjiang Plain. Among the natural factors, the most influence factors on the change of swamps were topography, followed by temperature and precipitation. 参考文献 相似文献 引证文献

三江平原碟形洼地-岛状林土壤氮磷空间分布及生态化学计量特征

PDF HTML阅读 XML下载 导出引用 引用提醒 三江平原碟形洼地-岛状林土壤氮磷空间分布及生态化学计量特征 DOI: 10.5846/stxb201808231793 作者: 作者单位: 吉林师范大学,唐山师范学院,吉林师范大学 作者简介: 通讯作者: 中图分类号: 基金项目: 国家自然科学基金项目（41271113）；吉林省科技厅项目（20180101085JC） Spatial distribution and ecological stoichiometric characteristics of nitrogen and phosphorus in soils from saucer-shaped depressions to island forests in the Sanjiang Plain Author: Affiliation: jilin normal university,tangshan normal university,jilin normal university Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:为阐明由碟形洼地-岛状林方向土壤养分的空间分布特征，选取非生长季中国科学院三江平原沼泽湿地生态试验站内的碟形洼地为研究对象，探讨土壤全氮和全磷含量及其化学计量比的空间分布特征及其影响因素。结果表明：由碟形洼地-岛状林方向，全氮、全磷和氮磷比在各样点的平均值分别呈"V "字、倒" N"字和"V"字型分布，土壤全氮、全磷与氮磷比含量的平均值分别为2278.11 mg/kg、820.50 mg/kg与2.44，变异系数为全氮（51.77%） > 氮磷比（36.07%） > 全磷（13.65%）。在0-50 cm土层内，全氮、全磷和氮磷比总体呈随土壤深度增加而逐渐降低的趋势，其中全氮主要集中于不同样点土壤的中上层，各样点的最高值均分布在土壤表层区域；全磷的富集深度与全氮相同，但在土壤20 cm深度各样点含量相近，后在20-50 cm深度内呈逐渐下降趋势；氮磷比在各样点的最高值与全氮和全磷分布总体一致，富集深度与两元素呈基本一致趋势。相关性分析表明，碟形洼地-岛状林方向土壤全氮与全磷之间均呈现出良好的相关关系，其中土壤有机质的分布，植物与水文状况、季节变化和土壤温度也在养分分布中起重要作用。 Abstract:In order to illuminate the spatial distribution characteristics of soil nutrients from saucer-shaped depressions to island forests, this paper chose the saucer-shaped depression within the wetland ecological test station on the Sanjiang Plain, part of the Chinese academy of sciences, as a study site during the non-growing season, and discusses the spatial distribution characteristics of total nitrogen (TN) content, total phosphorus (TP) content, and their stoichiometric ratios and influential factors. The results showed that the average TN, TP and N/P, respectively, displayed a tendency towards "V", inverted "N", and "V" type distributions in soil from saucer-shaped depression to island forests, the average of each was 2278.11 mg/kg, 820.50 mg/kg and 2.44 respectively, and the Coefficient of Variation (CV) was TN (51.77%) > N/P (36.07%) > TP (13.65%). In soil layers from 0 to 50 cm, TN, TP, and N/P decreased gradually with increasing soil depth, but TN was mainly concentrated in the upper middle layer of soil at the different points, and the highest values at all points were found in the surface area of soil. The enrichment depth of total phosphorus was the same as that of TN, but the content was similar at various points at the depth of 20 cm in the soil, and gradually decreased within the depth of 20-50 cm. The maximum value of N/P at various points was consistent with the distribution of TN and TP, and the enrichment depth was consistent with the two elements. The correlation analysis showed that TN and TP in soils both had a good correlation from saucer-shaped depressions to island forests, and the distribution of soil organic matter (SOM), plants, hydrological conditions, seasonal variation, and soil temperature played an important role in nutrient distribution. 参考文献 相似文献 引证文献

冻融作用对三江平原湿地土壤活性有机碳及酶活性的影响

PDF HTML阅读 XML下载 导出引用 引用提醒 冻融作用对三江平原湿地土壤活性有机碳及酶活性的影响 DOI: 10.5846/stxb201809121962 作者: 作者单位: 黑龙江省地理环境监测和寒区空间信息服务重点实验室,黑龙江省地理环境监测和寒区空间信息服务重点实验室,黑龙江省科学院自然与生态研究所;黑龙江省科学院自然与生态研究所,黑龙江省地理环境监测和寒区空间信息服务重点实验室,黑龙江省科学院 作者简介: 通讯作者: 中图分类号: 基金项目: 国家科技重大专项（2012ZX07201003-003）；"十三五"国家重点研发计划子课题（2016YFC0500405-03） Effects of freezing and thawing on soil active organic carbon and enzyme activity in the Sanjiang Plain wetlands Author: Affiliation: Key Laboratory of Remote Sensing Monitoring of Geographic Environment, College of Heilongjiang Province,,,,Heilongjiang Academy of Sciences Fund Project: National science and technology major project(No. 2012ZX07201003-003);The 13th five-year national key research and development planning projects (No. 2016YFC0500405-03) 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:为了研究冻融作用对不同类型土壤活性有机碳组分及酶活性的影响，选取三江平原未受干扰小叶章湿地（UDAW），干扰小叶章湿地（DDAW）和水稻田（RP）土壤（0-10 cm，10-20 cm和20-30 cm）进行室内冻融模拟实验。实验设置（-10-10℃）和（-5-5℃）两个冻融幅度。将经过3次、6次、10次和15次冻融循环处理后的土壤活性有机碳和酶活性分别与未经过冻融处理的FTC（0）对比。结果表明：冻融循环增加了3种湿地土壤可溶性有机碳（Dissolved Organic Carbon，DOC）浓度。随着活动层深度的增加，同一类型土壤DOC增量降低，不同类型土壤DOC增量为UDAW最高，其次是DDAW，RP增量最低。与此相反，冻融循环均降低了土壤微生物量碳（Microbial Biomass Carbon，MBC）浓度和纤维素酶、蔗糖酶和淀粉酶的活性。随着土壤深度的增加，冻融循环对MBC和3种酶活性的影响逐渐减弱，不同类型间MBC浓度和3种酶活性降低幅度为UDAW高于DDAW，RP降低幅度最小。冻融幅度对DOC浓度的影响为-5-5℃大于-10-10℃，而对MBC浓度和3种酶活性的影响则是-10-10℃大于-5-5℃。冻融次数显著影响土壤活性有机碳组分（DOC与MBC）及3种酶活性（P < 0.05）。随着冻融次数的增加，DOC浓度先升高后降低，MBC浓度和3种酶活性则先降低后升高。此外，UDAW和DDAW土壤活性有机碳组分和土壤酶活性显著正相关（P < 0.01），暗示DOC浓度的增加，MBC起着重要作用。而在RP土壤中，二者的相关性降低，或许与人类的强烈干扰有关。 Abstract:The aim of this study was to analyze the influence of freezing-thawing cycles (FTCs) on soil active organic carbon fractions and soil enzyme activity in different types of soils. To this end, a laboratory freezing-thawing simulation test was carried out using soil samples from undisturbed Deyeuxia angustifolia wetlands (UDAW), disturbed Deyeuxia angustifolia wetlands (DDAW), and rice paddy fields (RP) in Sanjiang Plain. Soil samples were taken from different layers of each soil type (0-10 cm, 10-20 cm, and 20-30 cm). Two FTC amplitudes, namely, (-10-10℃) and (-5-5℃), were tested. Soil samples were then processed during the 3rd, 6th, 10th, and 15th FTCs, and dissolved organic carbon (DOC), microbial biomass carbon (MBC) and enzyme activity was compared in relation to FTCs (0). The results demonstrated that, in the three wetland soils, the dissolved DOC concentration increased after freezing-thawing cycles. The DOC concentration in each type of soil decreased with soil depth. DOC concentration increased the most in UDAW, followed by DDAW, and then RP. In contrast, MBC concentration and cellulase, sucrose and amylase activity in the soils decreased after freezing-thawing cycles. The effects of FTCs on MBC and the aforementioned activity of the three enzymes gradually weakened with increases in soil depth. MBC concentration and the three enzymes activities presented the greatest reduction in UDAW, followed by DDAW, and then RP. The effects of FTCs on DOC concentration in soils under a FTC amplitude of -5-5℃ were greater than that under a FTC amplitude of -10-10℃, but the opposite phenomenon was observed with respect to the effects of FTCs on MBC concentration and the three enzymes. The number of FTCs had a significant influence on the active organic carbon fractions (DOC and MBC) and the three enzymes activities (P < 0.05). With an increasing number of FTCs, the DOC concentration was first observed to increase and then decrease, whereas the MBC concentration and the activity of the three enzymes first decreased and then increased. In addition, soil active organic carbon fractions in UDAW and DDAW were significantly and positively correlated with soil enzyme activity (P < 0.01), which suggests that MBC contributes to the increased DOC concentration in soils. This correlation was weak in RP soils, which might be related to greater human disturbance in these types of soils. 参考文献 相似文献 引证文献

Change in the Distribution of Phosphorus Fractions in Aggregates under Different Land Uses: A Case in Sanjiang Plain, Northeast China.

Phosphorus in agro-ecosystems has attracted much attention due to its impact on the nutrient supply of plants and the risk of loss of non-point source pollution. This study investigated the fraction distribution and release of phosphorus from soil aggregates structure under different land uses (rice, maize and soybean). The soil aggregates were characterized as large macro-aggregates (L-mac, >1 mm), small macro-aggregates (S-mac, 0.25–1 mm), micro-aggregates (MIC, 0.053–0.25 mm) and silt clay (SC, <0.053 mm) with the wet-sieving method. A sequential chemical extraction scheme was used to separate phosphorus into labile inorganic phosphorus (L-Pi), labile organic phosphorus (L-Po), moderately labile organic phosphorus (Ml-Po), iron-aluminum bound phosphorus (Fe.Al-P), calcium-magnesium bound phosphorus (Ca.Mg-P), humic phosphorus (Hu-P) and residual phosphorus (Re-P). Experimental results indicated that soil aggregates were mainly S-mac and MIC, followed by L-mac and SC, and they accounted for 52.16%, 25.20%, 14.23% and 8.49% in rice fields, 44.21%, 34.61%, 12.88% and 8.30% in maize fields, and 28.87%, 47.63%, 3.52% and 19.99% in soybean fields, respectively. Total nitrogen (TN), soil organic matter (SOM), Fe and Mn in soil aggregate fractions decreased with the reduction in soil aggregate grain-sizes. For phosphorus fractions (P-fractions), Fe.Al-P and Re-P tended to condense in L-mac and S-mac. MIC and SC were the primary carriers of Ca.Mg-P. Adsorption isotherm simulation results demonstrated that L-mac and S-mac have a strong capacity to retain phosphorus. In rice fields, phosphorus bioavailability and utilization rate were high. However, the P-fractions there were easily changed under aerobic-anaerobic conditions. Therefore, the risk of phosphorus loss during drainage should be given considerable attention.

Study on Soil Water and Heat Transport Characteristic Responses to Land Use Change in Sanjiang Plain

Water and heat transport is the focus of hydrological research in seasonal frost areas. Considering Sanjiang Plain as the study area, this study explored the influence of land use change on soil water and heat transport and the future trend of surface water and heat transport. The effects of land use change on soil water and heat transport were revealed using observation data from the Sanjiang Mire Wetland Experimental Station of the Chinese Academy of Sciences from the period of May 2016 to May 2017. The analysis found evident changes in the water and heat status of different land use types. During conversion from uplands to paddy fields, the surface soil moisture content increased, evapotranspiration increased by approximately 20%, surface infiltration decreased by about 50%, and surface heat flux increased. In a future climate change scenario, the change trend of soil water and heat condition was roughly consistent with the present situation, and the proportion of evapotranspiration of upland and paddy fields in precipitation decreased to 40% and 55%, respectively. These results can provide a theoretical basis for the rational utilization of land and water resources in Sanjiang Plain.

SMAP, RS-DTVGM, and in-situ monitoring: Which performs best in presenting the soil moisture in the middle-high latitude frozen area in the Sanjiang Plain, China?

Soil moisture is a core ecohydrological element in the middle–high latitude frozen area, which occupies approximately 30% of the global land area. The Sanjiang Plain, an important commercial grain production area, is the largest swampy low plain in a middle-high latitude frozen area in China. However, no published studies on this region have clarified the accuracy of soil moisture data from in-situ measurements; the performance of ecohydrological models are also unknown. In this study, we compared the ability of the SMAP product, a RS-DTVGM model, and two self-erected soil moisture monitoring stations to capture soil moisture information in the Sanjiang Plain by using the Triple Collocation method. Soil moisture data were collected for 642 continuous days, and the data period was divided into three frozen periods (FT) and two non-frozen (NFT) periods. Valid data supply rates of the three methods were also calculated and compared. From the Triple Collocation method, the root mean square error (RMSE) of the SMAP, model and in-situ monitoring data sets were 0.03, 0.08, and 0.05. The valid data supply rates of the SMAP product in the FT and NFT periods were 27.1% and 57.5%, respectively. The Pearson correlation coefficient between the SMAP product and the in-situ monitoring dataset was 0.301 for the FT period and 0.557 for the NFT period. The RS-DTVGM model had a data supply rate of 100%. The Pearson correlation coefficient for this model was 0.101 for the FT period, but reached 0.726 for the NFT period. For the three soil moisture data sets, the accuracy ranking in this middle-high latitude area was SMAP > in-situ monitoring > model simulation. Although neither SMAP nor the RS-DTVGM model could capture the real soil moisture information for the FT period, both could accurately simulate the soil moisture in the NFT period. The results from the RS-DTVGM model demonstrated a closer relationship with in-situ soil moisture measurement data relative to the SMAP method. The in-situ method provided accurate soil moisture data, but its application is limited by high cost. In the future, the data from the three methods should be assimilated together to measure soil moisture data with high accuracy and high spatial and temporal resolution in this important area.

Trend and Abrupt Regime Shift of Temperature Extreme in Northeast China, 1957–2015

Trend and an abrupt regime shift of temperature extremes were investigated based on diurnal data at 116 meteorological stations in the Northeast China region during 1957–2015. A total of 10 temperature indices divided into two categories: extremely cold and warm indices, were used in this study. The Mann–Kendall (MK) test was employed to evaluate the trend in temperature while changepoint, an R package for changepoint analysis, was used to detect changes in the mean levels of temperature extreme data series. The results of this study reveal that occurrence frequencies of the extreme cold night (TN10p) and extreme warm night (TN90p) have decreased and increased by −1.67 and 1.79 days/decade, respectively. Moreover, variations in temperature extremes have not been uniform with warming trends in minimum temperature being rapidly compared to maximum temperature extremes. The diurnal temperature range (DTR) depicted a remarkable decrease as a result of rapid warming in the minimum temperature. Warming in the region led to a reduction in the number of frost days (FD) and icing days (ID) and an increase in the number of growing season length (GSL) and tropical nights (Tr). Seasonally, TN10p largely decreased in winter and spring, while TNn and TN90p largely increased in winter and summer, respectively. Spatially, most of the stations with a significant warming trend in minimum temperatures were located in the Changbai Mountain, Greater Khingan Range, and Lesser Khingan Range. This implies that the mountainous regions are more sensitive and vulnerable to warming than the plain regions. On the contrary, most stations located in the Songnen Plain, Sanjiang Plain, and Liao River Plain displayed significant positive trend GSL and Tr. These climate extreme trends show that the region is experiencing warming which may have an impact on the hydrological process, ecological process, and agricultural production capacity.

Effects of Environmental Variables on Spatiotemporal Variations of Nitrous Oxide Fluxes in the Pristine Riparian Marsh, Northeast China

Nitrous oxide (N2O) is an important greenhouse gas, and the riparian marsh plays an important role in modulating atmospheric concentrations of N2O. To investigate the effects of environmental variables on spatiotemporal variations of N2O fluxes in the pristine riparian marsh, the static chamber-GC techniques were used to explore the spatiotemporal variations of N2O fluxes in Calamagrostis angustifolia swamp meadow marsh (CASMM), Ecotone wetland (EW) and Carex Schmidtii Meinsh. marsh (CSMM) along the pristine riparian in Sanjiang Plain during one year. During non-growing season (October, 2015 to April, 2016), the variability of N2O fluxes in the three marshes were not significantly different (P > 0.05). However, during growing season (May to October, 2016), both variability differences of N2O fluxes between CSMM and EW, and between CSMM and CASMM were significant (P < 0.01). Atmospheric temperature, soil NH4+-N content and soil volumetric moisture content were the driving factors during non-growing season. During growing season, soil NH4+-N and NO3−-N content were the driving factors among interactions of multiple environmental variables. CASMM and EW became the sinks of N2O during non-growing season but converted to the source of N2O during growing season. However, CSMM became all sink of N2O during every season.

Mapping Forest Cover in Northeast China from Chinese HJ-1 Satellite Data Using an Object-Based Algorithm.

Forest plays a significant role in the global carbon budget and ecological processes. The precise mapping of forest cover can help significantly reduce uncertainties in the estimation of terrestrial carbon balance. A reliable and operational method is necessary for a rapid regional forest mapping. In this study, the goal relies on mapping forest and subcategories in Northeast China through the use of high spatio-temporal resolution HJ-1 imagery and time series vegetation indices within the context of an object-based image analysis and decision tree classification. Multi-temporal HJ-1 images obtained in a single year provide an opportunity to acquire phenology information. By analyzing the difference of spectral and phenology information between forest and non-forest, forest subcategories, decision trees using threshold values were finally proposed. The resultant forest map has a high overall accuracy of 0.91 ± 0.01 with a 95% confidence interval, based on the validation using ground truth data from field surveys. The forest map extracted from HJ-1 imagery was compared with two existing global land cover datasets: GlobCover 2009 and MCD12Q1 2009. The HJ-1-based forest area is larger than that of MCD12Q1 and GlobCover and more closely resembles the national statistics data on forest area, which accounts for more than 40% of the total area of the Northeast China. The spatial disagreement primarily occurs in the northern part of the Daxing’an Mountains, Sanjiang Plain and the southwestern part of the Songliao Plain. The compared result also indicated that the forest subcategories information from global land cover products may introduce large uncertainties for ecological modeling and these should be cautiously used in various ecological models. Given the higher spatial and temporal resolution, HJ-1-based forest products could be very useful as input to biogeochemical models (particularly carbon cycle models) that require accurate and updated estimates of forest area and type.

Seasonal Local Temperature Responses to Paddy Field Expansion from Rain-Fed Farmland in the Cold and Humid Sanjiang Plain of China

Numerous studies have documented the effects of irrigation on local, regional, and global climate. However, most studies focused on the cooling effect of irrigated dryland in semiarid or arid regions. In our study, we focused on irrigated paddy fields in humid regions at mid to high latitudes and estimated the effects of paddy field expansion from rain-fed farmland on local temperatures based on remote sensing and observational data. Our results revealed much significant near-surface cooling in spring (May and June) rather than summer (July and August) and autumn (September), which was −2.03 K, −0.73 K and −1.08 K respectively. Non-radiative mechanisms dominated the local temperature response to paddy field expansion from rain-fed farmland in the Sanjiang Plain. The contributions from the changes to the combined effects of the non-radiative process were 123.6%, 95.5%, and 66.9% for spring (May and June), summer (July and August), and autumn (September), respectively. Due to the seasonal changes of the biogeophysical properties for rain-fed farmland and paddy fields during the growing season, the local surface temperature responses, as well as their contributions, showed great seasonal variability. Our results showed that the cooling effect was particularly obvious during the dry spring instead of the warm, wet summer, and indicated that more attention should be paid to the seasonal differences of these effects, especially in a region with a relatively humid climate and distinct seasonal variations.

Predictive ability of climate change with the automated statistical downscaling method in a freeze–thaw agricultural area

Precipitation and temperature in freeze–thaw agricultural area have different patterns under global warming. In this study, a statistical relationship between large-scale changes in climate variables and local weather data was built by applying an automated statistical downscaling (ASD) model in the Sanjiang Plain in China. We evaluated the prediction ability of the ASD model in terms of spatial–temporal changes in freeze–thaw agricultural area, and the temperature and precipitation changes in the twenty-first century under the representative concentration pathway 4.5 (RCP4.5) scenario were estimated. The results revealed that the explained variances in temperature were higher than 0.93 during the calibration and verification periods, which demonstrated good simulation capacity. The R2 of precipitation was acceptable due to the randomness and complexity of daily precipitation. Based on the Geophysical Fluid Dynamics Laboratory Earth System Model with the Generalized Ocean Layer Dynamics component (GFDL-CM3), the regional climate simulation provided good predictions. By 2100, the average, maximum and minimum temperatures in this area could increase by 2.0–2.5 °C, 2.5 °C and 2.5–4.0 °C, respectively. In terms of the spatial distribution, temperatures could increase faster in the northern region and slower in the central and southern regions. The warming trends in summer and winter were more significant than those in spring and autumn. There was no significant change in annual precipitation in the twenty-first century (increased approximately 10 mm by 2100). Precipitation decreased obviously in July and August (approximately 0.4 mm/day), and other months showed an increasing trend (approximately 0.5–0.9 mm/day). There will be large spatial variation of precipitation in the future changes. The results could serve as a reference for assessing non-point source pollution and agricultural management.

Changes of soil physical and chemical properties of albic soil in the meadow of Sanjiang Plain after rice planting.

The changes and renewal of soil quality are the criteria for judging agricultural development and soil management. The albic soil is the main paddy field soil in Sanjiang Plain. There is limited knowledge about the changes of soil quality after the dry field was changed into the paddy field. Taking albic soils from different years of rice planting as study objects, the changes of soil physical and chemical properties were investigated. The results showed that the total amount of soil organic carbon and reducing substances increased in the ploughing layer (16-23 cm thick) and the bottom ploughing layer (6-8 cm thick). The depth of ploughing layer gradually increased with the increases of rice planting years. There was no significant change after the bottom layer was changed into the paddy field. There was no significant difference in the subsoil layer (20 cm thick) compared with dryland. The Fe2+ and Mn2+ in the soil tended to migrate downward, but only to the plough bottom layer. The ratio of soil solid phase of the ploughing layer and the ploughing bottom layer increased after rice planting, with the ratio of soil solid phase of the ploughing bottom layer increased from 47.8% to 70.0% and the bulk density increased from 1.22 g·cm-3 to 1.77 g·cm-3. Decreases of the total amount of soil porosity, increases of the proportion of micropores, and cohesive leaching deposition in the albic soil were observed after rice planting. The changes of soil physical and chemical properties of albic soil after rice planting were generally consistent with the evolution of paddy soil except for several particularities.

Effects of Carbon Addition on Dissimilatory Fe(III) Reduction in Freshwater Marsh and Meadow Wetlands

The progress of dissimilatory iron(III) reduction is widespread in natural environments, particularly in anoxic habitats; in fact, wetland ecosystems are considered as “hotspots” of dissimilatory Fe(III) reduction. In this study, we conducted soil slurry and microbial inoculation anaerobic incubation with glucose, pyruvate, and soluble quinone anthraquinone-2,6-disulphonate (AQDS) additions in freshwater marsh and meadow wetlands in the Sanjiang Plain, to evaluate the role of carbon addition in the rates and dynamics of iron reduction. Dissimilatory Fe(III) reduction in marsh wetlands responded more quickly and showed twice the potential for Fe(III) reduction as that in meadow wetland. Fe(III) reduction rate in marsh and meadow wetlands was 76% and 30%, respectively. Glucose had a higher capacity to enhance Fe(III) reduction than pyruvate, which provides valuable information for the further isolation of Fe reduction bacteria in pure culture. AQDS could dramatically increase potential Fe(III) reduction as an electron shuttle in both wetlands. pH exhibited a negative relationship with Fe(III) reduction. In view of the significance of freshwater wetlands in the global carbon and iron cycle, further profound research is now essential and should explore the enzymatic mechanisms underlying iron reduction in freshwater wetlands.