Subsistence strategies during the Neolithic in the Nenjiang River basin, Northeast China

The Nenjiang River Basin, located in the northern part of Northeast China, is an important cultural region that has attracted much attention from academic communities. Previous studies demonstrated that hunting and gathering always dominate the subsistence for prehistoric populations in this region. Herein, we further investigate the evolution of dietary and economic strategies in the Late Neolithic and Bronze Age occupations at the recently excavated Honghe site of the Nenjiang River Basin by means of a multidisciplinary approach incorporating zooarchaeological and stable isotope analysis. The results of zooarchaeological approaches indicate that the Honghe populations rely extensively on hunting and fishing during the Late Neolithic (4500–4000 cal BP), consistent with the results of previous studies. Interestingly, by the Bronze Age (3100–2400 cal BP), animal husbandry develops as one main economic strategy, corresponding to the probable decline of hunting and fishing, which is different from the previous reports. In addition, based on the results of stable isotopic approaches, C3 plants are always prominent diets for animals and humans from the Late Neolithic to the Bronze Age, which signifies that crop agriculture does not appear to have been of primary importance during either of these eras, in contrast to the C4 agricultural tradition formed in the Neolithic Age of the southern part of Northeast China. The findings of this paper shed some more light on the evolution of human subsistence strategies in the Nenjiang River Basin.

Response of prehistoric human activity to environmental changes since 7,000 cal yr BP in Nenjiang River Basin, northeast China

The Nenjiang River Basin is an important foodstuff base and eco-environmental fragile area in Northeast China. With the rapid rise in human population, human-induced changes in land use/land cover form an important component of regional environment and ecosystem service change. At the local and regional level, the ecosystem service concept can act as a decision support tool for a stakeholder to reach sustainable land use management. However, the prevailing ecosystem service evaluation would produce a biggish warp when it is applied to concrete area. So, it is essential to evaluate ecosystem service change according to the local actuality. According to 1:250,000 land use/land cover maps of China and the adjusted equivalent value per unit area of ecosystem services in the Nenjiang River Basin, we evaluated the ecosystem service change of the river basin from 1980 to 2005. The forest and wetland, which are mainly located in the upstream mountainous area of the Nenjiang River Basin, were the two valuable land cover types, accounting for more than three quarters of the total ecosystem service value of the river basin. As for individual ecosystem service, besides the food production, all of the ecosystem service values declined from 1980 to 2005. The total decline of 2.43 billion USD was mainly due to the cultivation of grassland (14.34 % of the area in 1980) and wetland (4.62 % of the area in 1980) in the downstream plain. Due to the increase in population and the concomitant requirement of grain, the inconsistency between decision-making at the macro-level, and the objective of agricultural production at the micro-level, cultivated land was increased through zealous reclamation of grassland, marginal woodland, and even fallow land. Tremendous land use/land cover changes had caused great damages to the ecological environment such as land degradation and ecosystem service recession. So, the policies of the Grain for Green and Construction of Ecological Province projects should be well-implemented to optimize land use/land cover.

The Songhua River Basin (SRB) in Northeast China is one of the areas most sensitive to global climate change because of its high-latitude location. In this study, we conducted a modeling assessment on the potential change of water resources in this region for the coming three decades using the Soil and Water Assessment Tool (SWAT). First, we calibrated and validated the model with historical streamflow records in this basin. Then, we applied the calibrated model for the period from 2020 to 2049 with the projected and downscaled climatic data under two emission scenarios (RCP 4.5 and RCP 8.5). The study results show: (1) The SWAT model performed very well for both the calibration and validation periods in the SRB; (2) The projected temperatures showed a steady, significant increase across the SRB under both scenarios, especially in two sub-basins, the Nenjiang River Basin (NRB) and the Lower SRB (LSRB). With regard to precipitation, both scenarios showed a decreasing trend in the NRB and LSRB but an increasing trend in the Upper Songhua River Basin (USRB); and (3), generally, the hydrologic modeling suggested a decreasing trend of streamflow for 2020–2049. Compared to baseline conditions (1980–2009), the streamflow in the NRB and LSRB would decrease by 20.3%–37.8%, while streamflow in the USRB would experience an increase of 9.68%–17.7%. These findings provide relevant insights into future surface water resources, and such information can be helpful for resource managers and policymakers to develop effective eco-environment management plans and strategies in the face of climate change.

In the August of 1998, a big flood happened in Nenjiang River Basin, Northeast of China. The dike of Nenjiang River was breached in some places. A lot of houses and farmland were flooded. Economical loss is very heavy. On the other hand, in order to understand the whole effect of the flood and find proper flood management policy, the environmental effect of flood is studied. Results show that floodwater cleaned the Alkali soil, irrigated wetland, improved vegetation state and increased river flow in next years.

Incorporating private and working lands into protected area networks could mitigate the isolation state of protected areas (PAs) and improve the efficiency of conservation. But how to select patches of land for conservation is still a troublesome issue. In this study, the MaxEnt model and irreplaceability index were applied to guide marsh conservation in the Nenjiang River Basin, Northeast China. According to the high accuracy of the MaxEnt model predictions (i.e., the average AUC value = 0.933), the Wuyuer River and Zhalong marshes in the downstream reaches of Wuyuer River are the optimal habitat for the Red-crowned crane and migratory waterfowls. There are 22 marsh patches selected by the patch irreplaceability index for conservation, of which 12 patches had been included in the current network of protected areas. The other 10 patches of marsh (amounting to 1096 km2) far from human disturbances with high NDVI (up to 0.8) and close distance to water (less than 100 m), which are excluded from the existing network of PAs, should be implemented conservation easement programs to improve the protection efficiency of conservation. Specifically, the marshes at Taha, Tangchi, and Lamadian should be given priority for conservation and restoration to reintroduce migratory waterfowls, as this would lessen the current isolation state of the Zhalong National Nature Reserve.

Better investigation of extreme precipitation in large river basins is important for hydro-meteorological research and water resources management. Based on daily precipitation data from 17 national meteorological stations in Nenjiang River Basin (NRB) during 1959–2011, spatial-temporal characteristics and trends of seven extreme precipitation indices were analyzed in this study using Mann-Kendall non-parametric test and the ensemble empirical mode decomposition (EEMD) method. We found that almost all selected extreme precipitation indices declined in regionally averaged values, except maximum 5-day precipitation amount (Rx5day). Both extreme precipitation indices and their trends demonstrated spatial varieties. Generally, lower basin obtained less extreme precipitation and tended to be drier. But the amount and intensity of extreme precipitation in upper basin, where are more humid, are rising. Extreme precipitation indices presented apparent non-linear process with periodic oscillations of 1.63–1.94a for IMF1 to 25–31a for IMF4. The findings of this study are useful for the management of water resources in NRB, as well as provide reference information for precipitation evolution under climate change in other regions.

Reservoirs play an important role in responding to natural disasters (such as flood and drought) by controlling the runoff. With the climate changing, the frequency and intensity of flood and drought are likely to increase. Thus, the impact of reservoirs on runoff under climate change needs to be studied to cope with future floods and drought. In this study, the Nierji Reservoir located on the Nenjiang River Basin was chosen to explore the impact. The Nenjiany River Basin is the vital water source in the water resources transfer project in Northeast China. Climate change in Nenjiang River Basin was analyzed using the 1980 to 2013 climate observations. The results show that the temperature of the basin significantly (p < 0.05) increased while the precipitation significantly (p < 0.05) decreased. Based on the result, nine kinds of different climate scenarios were set up. For different climate scenarios, the Hydroinformatic Modeling System (HIMS) model and the HIMS model with the reservoir calculation module were used to simulate runoff during the no reservoir operation period (1980–2000) and reservoir operation period (2007–2013), respectively. The impact of reservoirs on runoff under climate change is studied. Results show that the Nierji Reservoir can effectively relieve the impact of climate change on downstream runoff. When temperature increases or precipitation decreases, there are larger differences in runoff over the non-flood period, especially during periods of no reservoir operation. Reservoir operation under climate change can provide reliability in drought protection.

The relationship between the water budget of wetlands and the water cycle process in local river basin is bidirectional. The recovery and function performance of the wetland are based on this relationship. Hydrological models are the effective tool to detecting this link. The distributed hydrologic model was the key supports in this study and was used to quantitative identify the change of water budget of the wetlands which was impacted by the water cycle evolution in Nenjiang River basin in Northeast China. The results indicated that precipitation, runoff and evapotranspiration both in the basin and wetlands present similar declining trend. The precipitation is the major recharge source, and the evapotranspiration is the primary output of wetlands. The value of mean change in storage of the wetlands is negative which is caused by the decrease of the area of wetlands. The results of land use pattern evolution change surface inflow in the wetlands in the basin scenarios simulation indicated. These results suggested that water budget of wetlands is influenced by water cycle in basin. And some reasonable measures for wetlands management should not only base on its features, but also pay attention to hydrological regime in basin.

Quantitative climatic reconstruction and prehistoric human subsistence strategy evolution since the mid-Holocene in Nenjiang river Basin, Northeastern China

The objectives of this study were to assess land use changes and their hydrological impacts in the Nenjiang River Basin (NRB). The Soil and Water Assessment Tool (SWAT) model was employed to evaluate the impacts of land use changes. The Cellular Automata-Markov model was used to predict a land use map in 2038. Streamflow under each land use state was simulated by the SWAT model. The results showed that there was a significant expansion of agriculture area at the expense of large areas of grassland, wetland, and forest during 1975–2000. The land use changes during the period of 1975 to 2000 had decreased the water yield (3.5%), surface runoff (1.7%), and baseflow (19%) while they increased the annual evapotranspiration (2.1%). For impacts of individual land use type, the forest proved to have reduced streamflow in the flood season (10%–28%) and increased surface runoff in the drought season (20%–38%). Conversely, grassland, dry land, and paddy land scenarios resulted in increase of streamflow during summer months by 7%–37% and a decrease of streamflow in the cold seasons by 11.7%–59.7%. When the entire basin was changed to wetland, streamflow reduced over the whole year, with the largest reduction during January to March. The 2038 land use condition is expected to increase the annual water yield, surface runoff and wet season flow, and reduce evapotranspiration and baseflow. These results could help to improve sustainable land use management and water utilization in the NRB.

Understanding streamflow changes under climate warming is critical for water resource management and disaster prevention in mid- and high-latitude regions. However, the factors driving streamflow changes remain unclear. This study investigated long-term streamflow trends, influencing factors, responses to climate change, and future flood risks in the Nenjiang River Basin, a typical mid-latitude region in Northeast China that is highly sensitive to droughts and floods. Using data from 1960 to 2016, we applied the Mann–Kendall trend and mutation tests and random forest models, and modeled streamflow responses to climate change to explore streamflow–climate interactions. Results showed significant warming (0.24–0.41 °C/decade, p < 0.05) and increased winter precipitation (0.77 mm/decade, p < 0.05), accompanied by declining annual and autumn streamflow (−6.03 and −3.62 mm/decade, p < 0.05), with abrupt shifts in 1963, 1996, and 2013. Climate change dominated streamflow changes, although human activities contributed 65% during 2013–2016. Streamflow responded more to precipitation than temperature, except in spring. Extreme floods occurred in 1960, 1998, and 2013. Scenario analysis (2021–2100) showed the highest flood frequency under the high-emission pathway (SSP5–8.5). These findings have crucial implications for water resource management, flood risk control, farming systems, and food security.

To understand the temporal and spatial variations of reference crop evapotranspiration (ET0) in Nenjiang River Basin, and clarify the effects of climatic factors on ET0, we calculated the daily ET0 of each station in Nenjiang River Basin from 1970 to 2019 by Penman-Monteith formula, analyzed the temporal variation trend and spatial distribution pattern of ET0. We further quantitatively examined the sensitivity of ET0 to meteorological factors by sensitivity analysis, and explored the contribution of meteorological factors to ET0 changes. The results showed that ET0 generally showed an insignificant decreasing trend during the study period in the Nenjiang River Basin. ET0 decreased in spring, summer, and autumn, but increased in winter, and decreased from southeast to northwest. ET0 had the highest sensitivity to relative humidity at both temporal and spatial scales. The sensitivity coefficients of mean temperature, relative humidity and wind speed increased gradually, while that of sunshine hours decreased gradually. ET0 was sensitive to mean temperature in northern Greater Khingan Mountains and Lesser Khingan Mountains, while to wind speed in southern Greater Khingan Mountains and Songnen Plain. Wind speed was the main factor affecting the change of ET0 in the whole year, spring, autumn, and winter. Sunshine hours was the main affecting factor in summer. The mean temperature and relative humidity had the greatest contribution to ET0 in the north of Greater Khingan Mountains and Lesser Khingan Mountains, and it was the wind speed in Songnen Plain.

This study examined hydrological and meteorological changes in China’s Nenjiang River Basin. Taking account of the physical processes in hydrology and meteorology revealed by the hydrological elements, we selected typical periods and sites for analysis on temperature (1951–2004), precipitation, and runoff data (1955–2005). Through some methods including improved cumulative curve method, the Sen slope estimation method, Mann-Kendall non-parametric test analysis, the Pettitt mutation point test and Spearman rank correlation test, and the spatiotemporal characteristics of hydrological and meteorological elements were evaluated. An innovative concept of the “centroid of precipitation” was proposed to analyze the spatial evolution tendency of precipitation. The results are concluded as follows: (1) the temperature began to show a rising trend during the 1960s and 1970s in Nenjiang River Basin in the twentieth century. The temperature had risen significantly by the 1990s. Furthermore, the temperature increased significantly at the coldest place and in the coldest month. (2) There was no significant trend change in the annual precipitation in the Nenjiang River Basin. However, monthly precipitation before the flood season (April) and after the flood season (October) exhibited a significant upward trend. The centroid of precipitation was concentrated in a compact spatial distribution in the main flood season but was dispersed relatively in the other months. (3) River runoff showed a downward trend year by year and exhibited a mutation in 1979. The spatial variation in runoff showed that the fluctuation of downstream runoff was greater than that in the upper reaches of the basin and that the runoff from the upstream to the downstream reaches gradually decreased. According to the M-K mutation point test, the Pettitt mutation point test, and the improved cumulative curve method, a mutation in annual runoff sequence occurred in 1979. These findings will be helpful for understanding evolution of hydrological changes and will be supportive for local water managers to deal with changing climate.

Ancient cattle DNA provides novel insight into the subsistence mode transition from the late Neolithic to Bronze Age in the Nenjiang River Basin