Khanka Research Articles

Recent changes of water level in Lake Khanka and their consequences for its fisheries resources

Interannual variation of the water level in Lake Khanka is considered on satellite altimetry data; its extreme rising in recent years is noted, with the maximum in 2016. Using a simple balance model, contribution of the main components of its water balance to the modern rise is determined, as precipitation in its basin, evaporation, and water discharge through the Sungacha River. Growth of summer precipitation is defined as the main reason of the level rising. However, the water income to the lake does not correlate with the precipitation volume since 2010 that confirms the hypothesis about artificial influence on the water balance of Lake Khanka by its connection with the Mulin River (China) and worsening of the outflow through the Sungacha. As the result, the lake got additionally about 1.3 km3in 2014–2015 that promoted the level rise to the highest mark. But before and after this period, the water inflow was lower than its expected values, obviously because of its redistribution. Positive influence of the anomalous water level growth on total abundance of commercial fish species is shown. The high level is favorable for reproduction of phytophilic species (Cyprinus rubrofuscus), whereas abundance of pelagophilic species (Chanodichthys erythropterus) declines.

AMUR AND PRIMORYE

The annual review of seismicity of Amur and Primorye based on the data of permanent seismic stations of Sakhalin branch GS RAS and the data of other Russian and foreign seismological agencies for 2014 is made. A detailed description of the seismic situation in different areas of the region is given. For the first time the Sikhote-Alin area (№5), where an earthquake of intensity I0=5 occurred, has dominated by terms of the released seismic energy level. Three tangible earthquakes were recorded in the region during the year. The most significant of them (Imax=5) earthquake occurred on April 12 at 21h22m east of Lake Khanka, in the ter-ritory of Primorye. Previously this territory was in the state of a seismic calm. A comparative analysis of the seismic situation in 2014 with the data of long-term observations is carried out. In 2014 the seismic energy of crustal earthquakes released in the region was one of the lowest for the past 15 years (2000–2014), except for 2006. The level of deep focus seismicity in 2014 also has low indicators. According to the methodology for assessing the level of seismic activity, the SOUS*09 scale, in 2014 the territory of Amur and Primorye is characterized by a lower background level of seismic activity.

Growth and biological characteristics of pike perch Sander lucioperca (Linnaeus, 1758) in the Amur River

Linear and weight growth of pike perch in the Amur River estuary is considered using the data on age determined for 197 specimens. The growth is described by von Bertalanffy and Schmalhausen equations. Some biological parameters of pike perch as the maximum size, age of mass maturation, etc. are calculated using the age-differentiated coefficients of natural mortality. The growth and biological parameters of pike perch in the Amur estuary are compared with the same parameters of this species in the Amur River at Khabarovsk. Recently 3 ecological forms of pike perch are distinguished in the Amur basin: i) riverine ecotype self-redistributed from Lake Khanka, ii) lacustrine ecotype in the lower Amur River, and iii) highly productive semi-anadromous marime ecotype in the Amur estuary. The 3rd phase of pike perch acclimatization is observed now in the Amur estuary known as the «bloom» phase accompanied with prominent increasing of population abundance and individual growth rate acceleration. Pike perch prey in this area mainly on juveniles of non-anadromous and diadromous fish, or on pond smelt Hypomesus olidus during their concentration in the estuary in winter.

Modern state of aquatic biological resources of the Amur River basin and directions of their research

Current status of aquatic biological resources in the middle and lower parts of the Amur River basin, including Lake Khanka and the Amursky Liman, is assessed. Generally high abundance of the water organisms is noted, but a downward trend is revealed. In 2015–2019, the total annual catch in the basin by Russian fishermen changed between 15.9–69.6 . 103 t (on average 39.1 . 103 t), with the main portions of pacific salmons (31.9 . 103 t, or 81.6 % of total catch) and smelts (5.5 . 103 t, 14.1 %). After the peak in 2016, the salmons abundance in the Amur has decreased, particularly for summer chum salmon and pink salmon, the number of arctic rainbow smelt Osmerus dentex has decreased gradually in the last 3 years. The stocks of freshwater fish are generally stable, with a slight increase for some species. The program of fisheries research «Amur River Fishes» implemented for 2020–2024 includes intensifying of traditional monitoring of the stocks and their biological state, as well as organization of detailed comprehensive studies for key species. Improvement of data quality on status of the main stocks of pacific salmons, smelts, and freshwater fishes is planned, as the basis for fisheries forecasting. Besides, the program conducts quantitative assessment of the main components of the ecosystem (phyto- and zooplankton, macrozoobenthos, and fish) and their dependence on environmental changes. State of food base for the Amur fish will be evaluated, including the feeding of artificially reproduced juveniles of salmons and sturgeons. Results of these studies will allow to improve approaches to regulation of fishery and to promote development of fishery industry toward organization of effective fishery complex in the Amur River basin.

Результаты гидрохимического мониторинга озера Ханка в 2016–2018 годах

Представлены результаты гидрохимических исследований озера Ханка в 2016–2018 гг. В 2015–2016 гг. съемки проводились в период максимального уровня озера. С 2017 г. наблюдалось снижение его уровня. Пространственное распределение температуры воды в целом не менялось из года в год, но при этом изменялись значения температуры. Так, температура воды в 2018 г. в течение всего сезона была выше на 1–2°. Содержание питательных веществ и растворенного кислорода во многом зависело от стока бытовых отходов пос. Камень-Рыболов, стока вод с рисовых чеков, от интенсивности стока впадающих в озеро рек и продукционных процессов. Цветение фитопланктона происходило даже зимой подо льдом, что подтверждалось высоким содержанием растворенного кислорода (до 180 %) под слоем льда. Вместе с тем содержание кислорода зимой в 2016 г., когда уровень озера был самым высоким, было несколько ниже, чем в последующие годы. Подобные межгодовые изменения отмечались и в колебаниях концентрации кремния. Зимой биологическое потребление кислорода (БПК5) также было высоким (6.53 мл/л), что указывало на активное разрушение органических веществ. Питательные вещества меняли свое соотношение в течение года из-за различных источников их поступления в определенные сезоны. Но в целом их значения и соотношение не имели значительных межгодовых колебаний. Наибольшие концентрации минерального азота и фосфора наблюдались осенью, вероятно, из-за сброса воды с рисовых плантаций. Сделан вывод о том, что высокие значения концентрации питательных веществ, БПК5 и содержания взвешенных веществ характерны для озера Ханка и не были обусловлены повышением его уровня. The results of the hydrochemical investigations of the Lake Khanka in 2016–2018 are presented. In 2015–2016, the surveys were carried out in the period of maximum level of the Lake. From 2017, its level recession was observed. The spatial distribution of the water temperature has generally remained the same each and every year but, at that time, the temperature values have changed. So, for example, the water temperature for the entire length of season in 2018 was higher by 1–2°. The content of nutrients and dissolved oxygen has largely depended on the household waste flow of the Kamen-Rybolov settlement, water flows from the rice checks as well as on flow intensity of the rivers falling into the Lake and production processes. The phytoplankton bloom was observed even in winter under the ice which was confirmed by the high content of the dissolved oxygen (up to 180‰) under the ice layer. At the same time, in winter of 2016 when the Lake level was highest the content of oxygen was slightly lower than in the subsequent years. The similar interannual changes were also noted in the silicon concentrations. In winter, the biological oxygen demand (BOD5) was also high (6.53 ml/l), which has pointed to the active destruction of the organic matter. The nutrients have changed their proportions throughout the year due to different sources of their entry during particular seasons. However, their values and proportions had basically no considerable interannual fluctuations. The highest concentrations of the mineral nitrogen and phosphorus were observed in autumn, probably, due to water discharge from the rice paddies. The conclusion was drawn that the high concentrations of nutrients, BOD5 and content of the suspended substances are characteristic of the Lake Khanka and were not caused by rise in its level.

Nesting of the black-faced spoonbill (Platalea minor) (Pelecaniformes: Threskiornithidae) and the hybrid partner on the coasts of Khanka Lake (the Russian Federation)

At the east coast of Khanka Lake (Russian Federation) on May 15, 2020, an unusual pair of spoonbill was observed. One of the partners was a black-faced spoonbill; the second partner included features of both the black-faced spoonbill and the Eurasian spoonbill, which can be regarded as a hybrid. This pair had a nest with two eggs, which later hatched one chick with signs of a black-faced spoonbill.

Life-history traits and intra-cohort divergence of clearhead icefish (Protosalanx chinensis), indicating cannibalism increased fitness

Cannibalism is considered one of the causes of intra-cohort size divergence in fish and is usually believed to result in increased fitness in terms of survival and reproduction, but direct evidence of this is lacking. Population demographics of the clearhead icefish (Protosalanx chinensis) from Lake Xingkai (Khanka) were investigated for one year. Size-frequencies exhibited a bimodal distribution from July through January, where the population diverged into an upper and a lower modal group based on size. Stomach content analysis confirmed the occurrence of cannibalism, where fish belonging to the larger, upper modal group preyed upon those of the smaller, lower modal group. We found P. chinensis does not spawn until all of the oocytes have reached maturity and then a single spawning event occurs although the oocytes may develope asynchronously in the ovary. Upper modal group females matured slightly earlier than those of the lower modal group, and reproductive investment was considerably greater in the upper modal group than the lower modal group. The lower modal males made up the majority of the population after the spawning period, which meant they may have few opportunities to participate in reproduction. Therefore, piscivory and cannibalism of P. chinensis appears to have increased fitness of the fish belonging to the upper modal group and greatly reduced the fitness of those belonging to the lower modal group.

Critical period and pathways of water borne nitrogen loss from a rice paddy in northeast China

Rice paddy nitrogen (N) loss is a great concern leading to a high risk of receiving water pollution. Various models have been applied as practical tools for simulation of the nutrient loss amount, and pathways or yield change affected by management factors in previous studies. However, N loss features of rice paddies in northern regions have received less attention and few model simulation studies have combined crop yield and N loss to simultaneously meet the needs of yield maintenance and environmental protection. To consider benefits to local farmers and to assess the paddy N loss features and factors in northeast China, rice yields and water borne N losses in 2013–2017 were simulated using the APSIM-Oryza model applied to Xingkai Lake Farm. Different from subtropical regions, high field ridges and lower rainfall limit local paddy overflow occurrence except after unexpected storms after irrigation in dry years or serial rainfall events, which result in subsurface N loss during stages of tillering (Ti) to flowering (Fl) which comprise the dominant pathway accounting for 50.03–69.99% of the total water borne N loss. The correlation analysis results also indicate irrigation and the applied N amount more significantly affect local paddy N loss than does precipitation. In each year, stimulated by an increase in the applied N amount, increasing rice yield (symbolizing crop growth status) indicated N loss implicitly rose. But under similar applied N amount range, inter-annual N loss results showed weaker growth status result in a higher N loss. Based on local N loss features, nutrient conservation practices including planting density increase or side strip application, and net N loss reduction practices including intermittent or recycling irrigation are recommended to limit nutrient loss from a paddy field which would be helpful for optimization of local nutrient conservation and surrounding water environment protection.

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

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

Applied methods for remote sensing of the Earth in the interests of agriculture of Russian Far East

The paper presents the methods (procedures) of processing data from satellites of the Landsat series, for classification and evaluation of agricultural land used for rice cultivation in the area of Lake Khanka, Primorsky Krai. Opportunities for using various vegetation indices for analysis are described, as well as their complex combinations that ensure most accurate identification of the considered culture during the entire period of active vegetation. The developed procedures provided foundation for analysing the growth dynamics of crops innate to the Far East, where the potential for using satellite data for agricultural needs remains practically untapped.

Level of soil moisture determines the ability of Eisenia fetida to re-incorporate carbon from decomposed rice straw into the soil

Burning is the most common practice for rice straw disposal. Due to associated negative environmental and climatic effects, development of viable alternatives, preferably based on the natural functions of soil biota are needed. In the conditions of non-tropical rice-growing systems, where periods of flooding are very short, such an approach seems to be particularly promising. We carried out a mesocosm experiment to assess the possibility of using the model earthworm species Eisenia fetida (Savigny 1826) to decompose rice residues and control associated CO2 and CH4 emissions from paddy soils at different soil moisture levels. We filled 96 mesocosms with three types (32 each) of rice paddy soils collected in key regions of rice production in Russia: Krasnodarsky Krai (the Sea of Azov lowland, Calcic Phaeozems), the Republic of Kalmykia (the Volga river valley, Haplic Phaeozems) and Primorsky Krai (Khanka lake lowland, the Russian Far East, Umbric, Histic Fluvisols). We added 2.5 g dry rice straw in each mesocosm. The experiment had a full factorial design including three categorical factors: soil type (n = 3), soil moisture level (12, 25, 50 and 75% soil water holding capacity) and E. fetida earthworm addition (none and 4 individuals per mesocosm). The integral emission of CO2 across the observation period of 10 days significantly differed between moisture classes with the highest values at 25% (p < 0.05). Earthworm amendment had no effect on CO2 flux in all moisture treatments besides 75%, where it was positive. The detectable CH4 emissions were observed only at soil moisture levels of 50 and 75%. Earthworms strongly positively affected this parameter at 75% soil moisture level (p < 0.05). Carbon content after the experiment was significantly higher in the earthworm-inoculated microcosms only at the 25% moisture level. We conclude that E. fetida may positively contribute to carbon sequestration during rice straw degradation in the studied rice paddy soil types only under certain levels of substrate moisture (25% in our case). This highlights the importance of soil encountering abiotic conditions when developing climate-friendly systems for rice straw decomposition and carbon immobilization. It also suggests the potential of using E. fetida as a viable agent of biological rice straw recycling during the drained stages in non-tropical rice paddies or in artificial confinements.

Element composition of soils to assess the success of wetland restoration

AbstractThe main purpose of this study is to assess if wetland restoration is associated with a directional shift in soil element concentration toward the original prefarming status in the peatlands of northeastern China. The concentrations of 55 soil elements and related environmental factors including organic matter content, electrical conductivity, and pH were investigated in natural, restored, and farmed wetlands in the Xingkai Lake Watershed of northeastern China. All but four of the soil element concentrations varied by wetland type (natural, restored, and farmed wetlands), and the soil concentrations of 41 elements increased from natural to restored to farmed wetlands. Soil organic matter and electrical conductivity explained 87.8% and 3.3% of the variation in element concentration based on ordination analysis using redundancy analysis. Both nonmetric multidimensional scaling analysis and cluster analysis indicated that the restored wetlands had a higher similarity with the farmed wetlands than the natural wetlands. Our findings suggest that restoration led to an increase in soil organic matter content and shifts in level of element concentration that was more similar to natural wetlands. However, differences remained so that the biogeochemistry of restored wetlands was not the same as the original prefarming level. This information is very important for wetland restoration, because to be successful, not only biodiversity and hydrology, but also the soil element composition and biogeochemistry need to be restored. Our approach can be used to assess the success of wetland restoration.

The homeland of Proto-Tungusic inferred from contemporary words and ancient genomes.

The Tungusic languages form a language family spoken in Xinjiang, Siberia, Manchuria and the Russian Far East. There is a general consensus that these languages are genealogically related and descend from a common ancestral language, conventionally called 'Proto-Tungusic'. However, the exact geographical location where the ancestral speakers of Proto-Tungusic originated from is subject to debate. Here we take an unprecedented approach to this problem, by integrating linguistic, archaeological and genetic evidence in a single study. Our analysis of ancient DNA suggests genetic continuity between an ancient Amur genetic lineage and the contemporary speakers of the Tungusic languages. Adding an archaeolinguistic perspective, we infer that the most plausible homeland for the speakers of Proto-Tungusic is the region around Lake Khanka in the Russian Far East. Our study pushes the field forward in answering the tantalizing question about the location of the Tungusic homeland and in illustrating how these three disciplines can converge into a holistic approach to the human past.

Phylogenetic relationships and historical population reconstruction of Asian members of the genus Epischura (Copepoda, Calanoida)

We have reconstructed major demographic and phylogenetic events for two closely related copepod species: Epischura baikalensis Sars, 1900 (Copepoda, Calanoida), a key endemic species of the plankton community from Lake Baikal, and E. chankensis Rylov, 1928, a key zooplankton species from Lake Khanka. The reconstructions were based on the nucleotide sequences of mitochondrial DNA (mtDNA) cytochrome oxidase subunit 1 (CO1) using the BEAST software package and recently identified calibrations for the Baikal amphipods Gmelinoides fasciatus. The time span to a common ancestor for E. baikalensis and E. chankensis is 13.7 million years (95% confidence interval is 8.3–21.4 million years. Both species studied have experienced abrupt changes in the effective population size in the past. These changes are likely associated with climate and geological shifts in their habitat areas. For E.baikalensis, these changes can be associated with alternating glacier and interglacial periods as well as an increase in depth of Lake Baikal; for E. chankensis with formation and increase in the area of Lake Khanka, which was also due to climate and geological shifts in the Khanka basin.

Development of the system of transboundary protected areas in the Asian part of Russia

The task of preserving biotic and landscape diversity in the conditions of separation by administrative or state borders leads to organizing transboundary protected natural areas that are important for the preservation of the natural environment and formation of the entire natural complex sites. The article presents the results of scientific analysis of the current situation concerning the creation of transboundary protected areas, as well as examples of those existing in the Asian part of Russia and promising for creating. In 2019, there are interstate agreements with Mongolia, China and Kazakhstan, providing for the activities of five transboundary protected natural areas: “Altai”, “Dauria”, “the Amur Sources”, “Lake Khanka”, and “Ubsunur Depression”. Additionally, we indicate transboundary specially protected natural areas of the Asian part of Russia that are the most important for the future. Analysis of the current situation concerning the protection of nature in the border areas allows us to identify ten new territories that are well-known for high environmental importance. The well-studied and promising territories include: “Khentei-Chikoiski highlands”, “the Selenga”, “From Huvsgul to Lake Baikal”, “Sayan Cross”, “Saylyugem”, “Delger-Muren”, [[CHECK_DOUBLEQUOT_ENT]] the Amur Tiger and Leopard”, “Tumangan”, “South Kuril Islands”, and “Beringia”. Cooperation with such countries bordering with Russia as Kazakhstan, China, Mongolia, North Korea, Japan, and the United States is expected.

Current Geo-Ecological Problems Within the Lake Khanka Drainage Basin

A brief geographical description is provided for Lake Khanka and its drainage basin where the Russian part accounts for more than 90% of the area. Sixteen rivers on the Russian territory and eight rivers on the Chinese territory flow into the lake. Only one river, Sungacha, flows out of the lake; it is a border river and connects Lake Khanka with the Ussuri river. A historical analysis of the water level dynamics in Lake Khanka for the last 10 thousand years showed that rises of the lake water level, shore erosion, an increase in flood frequency and duration, and an increase of the degree of waterlogging of the valleys corresponded to warm climatic phases. The cold phases showed a decrease in hydraulicity of the rivers and in the lake level, and an enhancement in aeolian processes in the coastal zone of the lake and its river valleys. Seismic processes and changes in groundwater flow can also be responsible for changes in the lake water level. Morphostructural analysis indicates a potentially high seismic activity of this territory and risks of magnitude 8 earthquakes. In the 20th century, the natural processes of water level fluctuations in the lake began to be influenced by anthropogenic factors, such as the water withdrawal for irrigation of paddy fields and streamflow control. The territory of China within the Lake Malaya Khanka drainage basin is the home for extensive paddy systems which are supplied with water from the Muling river basin. The water is then directed to Lake Malaya Khanka, and through the drain facilities it enters Lake Khanka. In fact, an inter-basin transboundary water transfer is carried out, which can affect significantly the water level in the lake. Characteristics of the existing nature management practices in the Russian portion of the lake drainage basin, and also lake pollution assessments are given. The main geo-ecological problems in the Lake Khanka transboundary drainage basin associated with water level fluctuations, geodynamic processes and environmental pollution are identified. Geo-ecological problems are considered to mean changes in natural processes accompanied by the transformation of separate natural components and landscapes in general, and causing, as a rule, negative consequences for humans and for various forms of nature management. The primary and related components of the geo-ecological problems highlighted. The main directions of comprehensive research within the framework of cooperation between the People’s Republic of China and the Russian Federation in order to work out the plan for governance of sustainable nature management in the transboundary drainage basin of Lake Khanka are suggested.

Environmental Transboundary Territories of Siberia and the Far East

A specific feature of the term “transboundary” is defined, which is usually perceived as an opportunity to overcome the borders separating the territory, and is used as opposed to the “frontier” objects adjacent to the border but not crossing it. Transboundary interstate territories are discussed, where only regulated activities may be carried out, such as nature conservation in solving the problem of preserving biotic and landscape diversity where a poor involvement of border areas in economic activity ensures an adequate degree of ecosystem preservation. A possibility of establishing transboundary specially protected natural areas arises in the most significant (in terms of natural diversity conservation) areas adjacent to the borders of neighboring States. The main condition for the effective functioning of transboundary specially protected natural areas implies signing bilateral agreements or agreements between a large number of countries with the aim of developing joint scientific and tourist programs as well as weakening of border control. Issues related to the theoretical and practical substantiation of the establishment of transboundary specially protected natural areas are considered. As of the beginning of 2019, there are five such areas established in accordance with interstate agreements: “Altai”, “Dauria”, “Sources of the Amur”, “Lake Khanka” and “Ubsunur Depression”. The most important planned transboundary specially protected natural areas of the Asian part of Russia are also highlighted. The relatively well investigated areas include “Amur Tiger and Leopard”, “Delger-Muren”, “From Khubsugul to Baikal”, “Khentei-Chikoi Highland”, “Sailyugem”, “Sayan Junction”, “Selenga”, “Tumangan”, “Southern Kuriles”, and “Beringia”.

Landscape Pattern Changes in the Xingkai Lake Area, Northeast China.

Understanding landscape change is important for ecologically sustainable development. In this paper, we assessed the spatiotemporal variations of landscape pattern in the Xingkai Lake area using remote sensing data from 1982, 1995, 2000, 2005, 2010, and 2015. Landscape patterns of marshlands, paddy fields, dry farmlands, and their combinations were analyzed at class and landscape levels. We examined the stability of landscape types through principal component analysis based on class level indices for landscape types. The results indicated that marshland areas decreased significantly by 33.87% but paddy fields increased by 1.84 times from 1982 to 2015. The largest conversion of dry farmlands to paddy fields was 90.88 km2 during the period 2010–2015. In contrast, the largest conversion of paddy fields to dry farmlands was 86.03 km2 during the period 2000–2005. The difference in relative change revealed that dry farmlands had experienced a greater relative change than paddy fields since 2000. The interspersion and juxtaposition index decreased, while the number of patches grew. This showed that landscape fragmentation was increasing and the landscape pattern was becoming dispersed. Marshlands were more stable than paddy fields and dry farmlands across all time periods, except for the year 2005.

East Asian winter monsoon evolution since the late Pliocene based on a pollen record from Lake Xingkai, northeast Asia

AbstractA 328.58 m drill core (XK12) was recovered from lacustrine–alluvial sediments in the Xingkai Basin, northeast China, with the aim of obtaining a high-resolution pollen record of East Asian winter monsoon (EAWM) evolution since 3.6 Ma. An index based on the pollen record of thermophilous trees and terrestrial herbs is used as an indicator of winter temperature conditions controlled by the EAWM, at the glacial–interglacial scale. Primary age control was established based on lithostratigraphy and magnetostratigraphy, and then the pollen index was correlated to the LR04 global benthic δ18O record and finally tuned to Earth orbital obliquity to produce a high-resolution astronomical time scale. The pollen record indicates that the EAWM underwent two stepwise enhancements at 2.8 and 1.6 Ma. These events are consistent with paleoclimatic records of mean quartz grain size from the Chinese Loess Plateau, and they are also in accord with the initiation and intensification of Northern Hemisphere glaciation. Our findings suggest that the variability of the EAWM since 3.6 Ma was primarily controlled by changes in global ice volume and climatic cooling.

Comparative analyses of wetland plant biomass accumulation and litter decomposition subject to in situ warming and nitrogen addition.

The effects of climate warming on boreal wetland plant structure and carbon (C) sequestration on local scale may be overestimated. An in situ passive warming experiment manipulated by open-top chambers and artificial nitrogen (N) addition was deployed in a lacustrine wetland of Xingkai Lake for 3 consecutive years. The annual changes and allocations of the aboveground biomass of Glyceria spiculosa, and decomposition dynamics of the total litter and cotton strips as standard references were observed. Results showed that the aboveground biomass was significantly affected by warming and increased from 99.43 ± 10.59 g m-2 (ambient) to 112.02 ± 8.08 g m-2 (ca. +1 °C) and 117.21 ± 9.92 g m-2 (ca. +2 °C). N addition had a more positive effect on the annual aboveground biomass accumulations than warming, for the relative importance weights of N addition were 2.60 and 1.49 times greater than warming in 2011 and 2013 respectively. Their main effects on the allocations had significant interannual variations, and their interaction effects were dependent on organ and year. The decomposition constant (k-value) of the litter and cotton strips were 0.747 yr-1 and 2.057 yr-1, respectively. Compared to warming and N addition, the internal quality characterized by Lignocellulose index and soil organisms reflected by litterbag size played overwhelming role in decomposition dynamics, with 2 orders greater of relative importance weights in 2011 and 2012. Our results highlight the importance of interannual variation for differentiating the contributions of external and internal factors to boreal wetland plant biomass accumulation and decomposition. Given the asymmetric responses of accumulation and decomposition, the C storage in the litter would increase in long term.