Downstream Plain Research Articles

Flood Risk Mapping of Kankai Basin: A Case Study of Shivasatakshi Municipality and Kankai Municipality

Floods are probably the most frequent, widespread, and disastrous hazards in the world. It causes loss of life, casualties, financial loss, and displacement. Heavy monsoons, fragile geography, and constructions along the embankments cause the river to flood. The increase of population and squatter settlement of landless people living at the bank of the river has tremendous pressure on encroachment of flood plain making them vulnerable to flood damage. This study aims to develop HEC-RAS models for the Kankai River basin for preparation of 1D flood plain maps, vulnerability, risk assessment of RCC building in Shivasatakshi Municipality ward 10, and Kankai Municipality ward 4. Flood frequency analysis for 2, 10, 25, 50, 100, 200 and 1000 years return was carried out by Log Pearson III, Gumbel and Log Normal method based on maximum instantaneous flow recorded at Mainachuli station. The result of flood frequency analyzed by Log Normal method for 2, 10, 25, 50, 100, 200 and 1000 years return period floods shows higher among the results obtained using different methods. The flooding impact of the Kankai River being a large catchment with braided river form inundates vast downstream flood plain regions during high flood levels. With numerous people living along the river and downstream plains, flood risk is predominately high in the Kankai River catchment. With increasing flood intensity, higher flood depth increases and lower flood depth decreases. The inundation of a large area of Shivasatakshi Municipality ward 10 and Kanaki Municipality ward 4 at the bank of the Kankai river indicates that human lives and the physical infrastructure will be more vulnerable to flood disasters in the future. According to a study, the largest areas affected by floods with return periods of 2, 10, 25, 50, 100, 200, 1000 years, respectively, are 1843.24 ha, 1967.96 ha, 2016.32 ha, 2049.48 ha, 2079.64 ha, 2109.4 ha and 2176.08 ha of the whole basin. As a result, the study may help in future disaster planning and management.

Effects of elevation and geomorphology on cadmium, lead and chromium enrichment in paddy soil and rice: A case study in the Xiangtan basin of China

The distributions of heavy metals in paddy fields and rice along river valleys were studied to explore the key factors affecting the accumulation of heavy metals in the upstream terraces and downstream plains. Results from 975 sampling sites showed that elevation, growing season and soil organic matter (OM) had significant effects on the content of Cd and Pb in topsoil and rice. The content of Cd (0.47–0.66 mg kg−1) and Pb (49.9–68.6 mg kg−1) in paddy fields with low elevation (30–60 m) in the downstream plains was significantly higher than the content of Cd (0.29–0.38 mg kg−1) and Pb (43.9–56.3 mg kg−1) in the upstream terraces with high altitude (60–90 m). In the double-rice production area, late rice generally produced grains with higher Cd and Pb content than early rice. Soil Cd was positively increased with the content of OM, especially in the downstream plains. When elevation was used for principal component analysis, plains with low elevation were grouped together with high content of total and soluble Cd, OM and Pb in soil, as well as high content of Cd and Pb in late rice. Altitude is one of the key factors affecting Cd content in rice. Although content of Cr (93.7–138.0 mg kg−1) was significantly higher than that of Cd and Pb in soil, content of Cr was lower than that of Cd in rice. These results indicate that paddy fields with elevation of 30–60 m in the downstream plains had high risk to produce late rice with Cd and Pb content exceeding the food safety standard 0.2 mg kg−1, which may be resulted from the driving force of runoff on soil soluble Cd and Pb from terraces to alluvial plains in river valleys.

Modeling streamflow response under changing environment using a modified SWAT model with enhanced representation of CO2 effects

Study regionHaihe River Basin (HRB) in North China Plain. Study focusChanges in streamflow due to climate change and human activities are highly uncertain. An improved Soil and Water Assessment Tool (SWAT) model equipped with a dynamic CO2 input method was used to quantify the environmental change impacts on streamflow in the HRB. Streamflow changes were analyzed based on 22 bias-corrected CMIP6 GCMs under SSP1-2.6, SSP2-4.5, SSP3-7.0, and SSP5-8.5 during two 30-year periods of the middle (2041–2070) and end (2071–2100) of the 21st century relative to the historical period (1971–2000). New hydrological insights for the regionLong-term simulations of annual streamflow in the HRB demonstrated substantial discrepancies between the dynamic and constant CO2 input methods under the SSP1-2.6 and SSP5-8.5 scenarios, which highlighted the importance of using the dynamic CO2 input method for streamflow simulations. Spatio-temporal analysis using the improved SWAT model revealed that streamflow generally increased under four emission scenarios compared to the historical period. In the HRB, annual streamflow in the downstream plains was higher than in the upstream mountains, and this was more evident under the highest emission scenario of SSP5-8.5. Monthly streamflow showed considerable intra-annual variability that was generally greater from July to November. The strongest increment in streamflow was projected in the SSP3-7.0 and SSP5-8.5 scenarios, indicating that flood risk would possibly increase in the late 21st century.

The characteristic and seasonal variation of mesoscale convective systems' precipitation overNorth China

AbstractUsing an iterative rain‐cell tracking method to identify and track mesoscale convective system (MCS) precipitation during the warm seasons (May–October) of 2015–2020, we reveal the seasonal variation in the spatiotemporal distribution, rainfall characteristics, and the life cycle of MCS precipitation in different months over North China. Notable MCS precipitation centers are located around mountain slopes and downstream areas. The diurnal peak of MCS rainfall is manifested as a southeastern delay from afternoon in mountainous regions to midnight or morning over downstream plains. In May and June, MCS rainfall is distributed on the hillside of Taihang–Yan mountains and the Shandong Peninsula. MCS precipitation gets an early evening peak on mountain slopes and a nocturnal maximum over the North China Plain (NCP). In July and August, the MCS activities extend to NCP, and another MCS precipitation center exists over the Luliang Mountains in western North China, under the seasonal march of the monsoon flow. The local diurnal peaks to the east of 114°E are generally later than in May and June, and MCS precipitation gets a peak during midnight to early morning over the NCP. MCSs in July and August feature the strongest intensity. In September and October, the MCS precipitation shifts to high terrain of the Taihang Mountains and its west, with an early afternoon peak. MCSs have the largest size and the fastest propagation speed in September and October, but with the weakest intensity. Compared with short‐lived MCSs, long‐lived MCSs have stronger precipitation intensity, larger rainfall area, and faster propagation speed. In addition, the life cycle of long‐lived MCS precipitation represents asymmetric development and decay. Long‐lived MCSs occur with more pronounced upper troposphere warming and low‐level anomalous southwesterlies. Meanwhile, higher specific humidity in the low‐ and mid‐level troposphere provides a more favorable environment for the maintenance of MCS precipitation.

Upstream, Downstream: Iron Mining in Early Modern Japan and the Uneven Spread of Environmental Protection

This article examines disputes over iron mining in early modern Japan (1600–1868), focusing on how and why some communities had greater say in stopping or permitting environmental harm. Well before Japan became the first non-Western society to industrialize, mountain miners in the southwestern region of Chūgoku developed increasingly effective technologies for extracting Japan’s most abundant source of iron—iron sand found in granite rock. But their hydraulic methods involved sending more than a billion cubic meters of tailings into the region’s rivers, wreaking downstream havoc, from ruined crops to tainted drinking water. When downstream people pushed to curtail mining, two important social factors came into play. First, across ironmaking river basins, and in contrast to better-known modern cases, more affluent downstream plains communities bore the brunt of the damage that poorer mountain miners caused. Indeed, miners used their villages’ relative poverty to galvanize official support to continue mining. At the same time, in negotiating compromises, upstream and downstream inhabitants of different river basins also arrived at sharply different standards of what constituted an acceptable level of mining. These differences depended on the complex political geography of early modern Japan, in which some jurisdictions had much greater authority than others. All told, these disputes both reaffirm and cut against more familiar patterns found in modern cases, foreshadowing the uneven spread of industry’s harms across the social landscape, while also reflecting the distinctive mining technology, political culture, and geography of this early modern society.

Risk assessment and validation of farmland abandonment based on time series change detection.

Farmland abandonment, a widespread phenomenon during land-use transition, leads to a cycling or vanishing evolution of farmland resources. As urbanization advances, an increasing number of agricultural laborers migrate from rural to urban areas, causing ongoing farmland abandonment. However, in contrast to the abandoned information extraction and driving mechanisms revelation, the potential risk of farmland abandonment has received insufficient attention. This study took Yangtze River Economic Belt of China as study area, selected multiple aspects to construct a risk assessment system for farmland abandonment, and applied time series change detection to verify the results. The results showed that (1) farmland abandonment risk, with a regional average value of 0.0978, has strong spatial heterogeneity, with high values clustering in Yunnan-Guizhou and Sichuan-Chongqing mountainous areas and low values distributed in the midstream and downstream plains and the Sichuan Basin. (2) The proportion of farmland area gradually decreased as the risk grade increased. Farmland, with low abandonment risk, occupied an area of 204,837 km2, constituting the highest percentage of 35.18% among the overall farmland, and was mainly distributed in the provinces of Jiangsu and Anhui. The area of farmland with high risk was 16,458 km2, only accounting for 2.83%, the majority of which was clustered in Sichuan and Yunnan provinces. (3) The Normalized Difference Vegetation Index (NDVI) time series change detection validated the reliability of the risk assessment system. Samples of farmland having low abandonment risk indeed had the lowest abandonment rate of 10%, and those which indicated high risk had the highest abandonment rate of 32%. We propose differentiated managements for farmland resources with high and low abandonment risk from the perspective of sustainable use. This study provides a more reasonable and scientific system for farmland abandonment risk assessment and helps to fill the research gap.

Tracking the sub-catchment of nutrient contributors: The case of a typical mixed hilly-plain watershed in China

As the inlet river of Poyang Lake, it is important to master the source of nitrogen and phosphorus concentration in water body of Le 'an River for the water environment safety management in Poyang Lake. Therefore, this study aimed to quantify the weight of nutrient loss contribution from each sub-catchment to the inlet estuary cross-section. A SWAT model was constructed to simulate total nitrogen (TN) and total phosphorus (TP) loss of Le 'an River Watershed in 1995-2020. A key parameter Ci was proposed to quantify the contribution values and weights of the nutrient load from the sub-catchment to the inlet estuary cross-section and identify the crucial contribution areas. The results showed that: (1) The emission intensity of the TN and TP at the confluence section the Le 'an River Watershed in the past 30 years is 16.54 Gg/yr and 3.69 Gg/yr. (2) Nutrient losses in the watershed exhibited clear spatial variability. The average intensity of TN and TP loss in the middle and downstream plains was 1.38 and 1.12 times higher than in the upstream hilly areas. (3) The weight of nutrient contribution in sub-catchments varied significantly in space, and the TN and TP from the highest contributive sub-catchment was 11.52 and 25.91 times of the lowest, respectively. Through the analysis of contribution values, sub-catchments of No. 15, 20, and 22 were identified as the nutrient crucial areas.

Groundwater Recharge Modeling under Water Diversion Engineering: A Case Study in Beijing

The influence of surface water resource exploitation and utilization projects on groundwater has been widely studied. Surface water diversion projects lead to a reduction in river discharge, which changes the recharge of groundwater systems. In this study, the numerical simulation method is used to predict the variation in groundwater level under different diversion scale scenarios. The Zhangfang water diversion project in Beijing, China, was chosen for the case study. The downstream plain area of the Zhangfang water diversion project is modeled by MODFLOW to predict the influence of reducing water diversion on the dynamic change in the groundwater level in the downstream plain area. The model results show that the difference in groundwater recharge and discharge on the downstream plain of Zhangfang is 9,991,900 m3/a, which is in a negative water balance state, and the groundwater level continues to decrease. Reducing the amount of water diverted by the Zhangfang water diversion project to replenish groundwater is beneficial to the rise of the groundwater level in the downstream plain area. The results indicate that the groundwater flow model in the downstream plain area of Zhangfang performed well in the influence assessment of surface water resource exploitation and utilization projects on groundwater. This study also provides a good example of how to coordinate the relationship between surface water resources and groundwater resources.

Effects of vegetation restoration on evapotranspiration water consumption in mountainous areas and assessment of its remaining restoration space

In mountainous areas with inadequate precipitation, anthropogenic vegetation restoration would increase evapotranspiration water consumption and decrease regional water yield, affecting downstream water use. Assessing vegetation restoration-related water consumption and future vegetation restoration potential is important for vegetation management in mountainous areas. However, it is still difficult to evaluate the impact of vegetation restoration on evapotranspiration water consumption and determine the appropriate restoration level. This study focused on the Haihe River Basin as a typical afforestation area in China with growing competition for water use between the upstream afforested vegetation and the downstream urban development. This study adopted the Penman-Monteith-Leuning evapotranspiration model with a de-trending data series method to analyze actual evapotranspiration and vegetation restoration potential. The results show that 1) the average precipitation in the mountainous areas of the Haihe River Basin and the actual evapotranspiration (AET) between 2000 and 2019 were 508 and 317 mm, respectively, while the precipitation, leaf area index (LAI), and actual evapotranspiration all showed an increasing trend in the past two decades with growth rates of 3.8 mm/yr, 0.0015(cm3/cm3)/yr, and 1.37 mm/yr, respectively; 2) in the past 20 years, vegetation restoration has cumulatively led to an actual evapotranspiration increase by 314, 269, 175, 429, 277, and 187 mm in the Luan-He Mountainous Basin (LHMB), Yong-Ding-He Mountainous Basin (YDHMB), Da-Qing-He Mountainous Basin (DQHMB), Bei-San-He Mountainous Basin (BSHMB), Zi-Ya -He Mountainous Basin (ZYHMB), and Zhang-Wei-He Mountainous Basin (ZWHMB), respectively; 3) the LAI maximum recovery level in the six sub-basins was deduced by using the linear fitting formula. When considering the replacement water of over-drafting groundwater in the downstream plain, the LHMB, YDHMB, ZYHMB, ZWHMB still have the potential for vegetation restoration, and the maximum LAI could be restored to 1.83, 1.30, 1.09, and 1.6 cm3/cm3, respectively. In summary, large-scale anthropogenic afforestation should consider the decrease in regional water yield to avoid the imbalance of ecological and human water use. This research method can be extended to other areas of water scarcity and provide a reference for mountain vegetation restoration to set a reasonable threshold.

Hydrological significance of Himalayan surface water and its management considering anthropogenic and climate change aspects

Water plays a key role in maintaining different ecosystem services. The anthropogenic and climate change impacts studies on Himalayan water resources has been trending in recent years. The Indian Himalayan region cover several states like Jammu & Kashmir, Ladakh (Union territory), Himachal Pradesh, Uttarakhand, Sikkim, Arunachal Pradesh and the hilly regions of Assam and West Bengal. Water resources in this region are the life support for humankind and rich biodiversity. Researchers has reported that the warming in the Himalayas is more than the global average, thereby climate change can affect significantly in the mountainous water resources so as the snow and glacial melt is the main lifeline of the perennial rivers’ flow. Almost every year, the heavy monsoon rainfall brings floods on the upstream highlands and then the downstream plains causing enormous human suffering, loss of property, loss of life, agricultural crops damage as well as increased economic losses. The main challenges being associated to the frequency and magnitude of extreme weather events like monsoon rainfall which leads to flash floods, landslides and debris flow; and then the drought during dry season also, has had huge impacts on regional water security. Human actions like economic development and population growth have also brought changes in land cover/use to Himalayan watersheds recently. As a result of farming, grazing, tree planting, urbanization, etc., the changes in land cover have altered the water balance and transformed the water-flow paths in the global hydrological cycle. In contrast to freshwater ecosystems, demand is high, but their supply is limited, also depend on the specific flow pattern of rivers. Although, with interference of various infrastructure development upstream results in changes in flow pattern downstream causing non-availability of water to support aquatic life and communities that depend on for livelihoods. Initiation of monitoring and observation system for water resources and use of appropriate hydrological model are preferable to better understand the hydrological processes of the Himalayas.

Preparation of Inundation Maps by Developing Unsteady Flow Model of Pamba River- Decision Support System for Disaster Management

Nowadays extreme rainfall events are more frequent across our country. Controlled releases from reservoirs would be necessitated to ensure the safety of dams and people downstream during extreme inflow. Mitigation measures are to be planned and preparedness actions to be taken effectively to reduce the impact of such catastrophe at downstream flood plains of reservoirs. Advance information on the extent of the area likely to be in undated consequent to releases from reservoirs is vital in developing an effective action plan for the timely evacuation of people. In the present study, it has been attempted to develop an unsteady flow model of the Pamba River in Kerala& the flood plain downstream for determining the area likely to be inundated corresponding to a largely controlled release in the tune of 900m3/s. The unsteady flow model is developed in HEC-RAS to study the flow behavior of flood wave caused by the flow hydrograph with peak 900m3/s as it propagates to the downstream plains. From the studies, it is found that the transformation of flow profile of flood wave can be better estimated using the HEC-RAS 2D flow model and the results can be used as important information in the decision-making process for Disaster Management Authorities.

Comammox Nitrospira within the Yangtze River continuum: community, biogeography, and ecological drivers

The recent discovery of comammox Nitrospira as complete nitrifiers has fundamentally renewed perceptions of nitrogen cycling in natural and engineered systems, yet little is known about the environmental controls on these newly recognized bacteria. Based on improved phylogenetic resolution through successful assembly of ten novel genomes (71–96% completeness), we provided the first biogeographic patterns for planktonic and benthic comammox Nitrospira in the Yangtze River over a 6030 km continuum. Our study revealed the widespread distributions and relative abundance of comammox Nitrospira in this large freshwater system, constituting 30 and 46% of ammonia-oxidizing prokaryotes (AOPs) and displaying 30.4- and 17.9-fold greater abundances than canonical Nitrospira representatives in water and sediments, respectively. Comammox Nitrospira contributed more to nitrifier abundances (34–87% of AOPs) in typical oligotrophic environments with a higher pH and lower temperature, particularly in the plateau (clade B), mountain and foothill (clade A) areas of the upper reach. The dominant position of planktonic comammox Nitrospira was replaced by canonical Nitrospira sublineages I/II and ammonia-oxidizing bacteria from the plateau to downstream plain due to environmental selection, while the dissimilarity of benthic comammox Nitrospira was moderately associated with geographic distance. A substantial decrease (83%) in benthic comammox Nitrospira abundance occurred immediately downstream of the Three Gorges Dam, consistent with a similarly considerable decrease in overall sediment bacterial taxa. Together, this study highlights the previously unrecognized dominance of comammox Nitrospira in major river systems and underlines the importance of revisiting the distributions of and controls on nitrification processes within global freshwater environments.

Using multivariate statistical techniques and geochemical modelling to identify factors controlling the evolution of groundwater chemistry in a typical transitional area between Taihang Mountains and North China Plain

AbstractIdentifying the key factors controlling groundwater chemical evolution in mountain‐plain transitional areas is crucial for the security of groundwater resources in both headwater basins and downstream plains. In this study, multivariate statistical techniques and geochemical modelling were used to analyse the groundwater chemical data from a typical headwater basin of the North China Plain. Groundwater samples were divided into three groups, which evolved from Group A with low mineralized Ca‐HCO3 water, through Group B with moderate mineralized Ca‐SO4‐HCO3 water, to Group C with highly saline Ca‐SO4 and Ca‐Cl water. Water‐rock interaction and nitrate contamination were mainly responsible for the variation in groundwater chemistry. Groundwater chemical compositions in Group A were mainly influenced by dissolution of carbonates and cation exchange, and suffered less nitrate contamination, closely relating to their locations in woodland and grassland with less pronounced human interference. Chemical evolution of groundwater in Groups B and C was gradually predominated by the dissolution of evaporites, reverse ion exchange, and anthropogenic factors. Additionally, the results of the inverse geochemical model showed that dedolomitization caused by gypsum dissolution, played a key role in the geochemical evolution from Group A to Group B. Heavy nitrate enrichment in most groundwater samples of Groups B and C was closely associated with the land‐use patterns of farmland and residential areas. Apart from the high loads of chemical fertilizers in irrigation return flow as the main source for nitrate contamination, the stagnant zones, flood irrigation pattern, mine drainage, and groundwater‐exploitation reduction program were also important contributors for such high mineralization and heavy NO3− contents in Group C. The important findings of this work not only provide the conceptual framework for the headwater basin but also have important implications for sustainable management of groundwater resources in other headwater basins of the North China Plain.

Multidisciplinary study with quantitative analysis of isotopic data for the assessment of recharge and functioning of volcanic aquifers: Case of Bromo-Tengger volcano, Indonesia

Study regionThe Bromo-Tengger volcanic aquifer system, (East Java, Indonesia). Study focusAndesitic volcanic aquifers in Indonesia are an important source of groundwater supply for the population. The artesian flow from high discharge springs facilitates the access for irrigation and drinking water but continuously flowing artesian wells exert an increasing pressure on the groundwater resource. Given the complexity of the volcanic edifice, a multidisciplinary approach including geological, hydrometeorological, hydrochemical and isotopic measurements was performed to characterise the hydrogeological functioning of the volcano’s northern flank. New hydrogeological insights for the regionTwo main hydrogeological systems are identified: a system with perched aquifers in the lava flows and pyroclastic complex, supplying low discharge springs or infiltrating to a deep flow system. The latter system is unconfined and provides groundwater to the downstream plain that hosts a confined multi-layer volcano-sedimentary aquifer. The joint implementation of a quantitative isotopic approach and a groundwater budget allows characterising aquifer recharge along the whole volcano flank. It is mainly controlled by the rainfall distribution that peaks around 1200 m elevation. The caldera basin on the top of the volcano has a very limited contribution to recharge. A conceptual hydrogeological model is proposed and compared to the main concepts of volcanic islands. This study is a first step for further scientific and management discussions to implement protection policies on the Bromo-Tengger aquifer system.

Classification and Estimation of Irrigation Waters Based on Remote Sensing Images: Case Study in Yucheng City (China)

The downstream plain of the Yellow River is experiencing some of the most severe groundwater depletion in China. Although the Chinese government has issued policies to ensure that the Yellow River can provide enough irrigation waters for this region, groundwater levels continue to decrease. Yucheng City was selected as a case study. A new method was designed to classify the cropland into various irrigated cropland. Subsequently, we analyzed data regarding these irrigated-cropland categories, irrigation norms, and the minimum amount of irrigation water being applied to cropland. The results showed that 91.5% of farmland can be classified as double irrigated (by both canal/river and well water), while 8.5% of farmland can be classified as well irrigated. During the irrigation season, the sediments brought in by the river have blocked portions of the canals. This has led to 23% of the double-irrigated cropland being irrigated by groundwater, and it is thus a main factor causing reductions in groundwater supply. These blocked canals should be dredged by local governments to mitigate local groundwater depletion. The method for classifying irrigated cropland from high-resolution images is valid and it can be used in other irrigated areas with a declining groundwater table for the sustainable use of groundwater resources.

The Third Atmospheric Scientific Experiment for Understanding the Earth–Atmosphere Coupled System over the Tibetan Plateau and Its Effects

AbstractThis paper presents the background, scientific objectives, experimental design, and preliminary achievements of the Third Tibetan Plateau (TP) Atmospheric Scientific Experiment (TIPEX-III) for 8–10 years. It began in 2013 and has expanded plateau-scale observation networks by adding observation stations in data-scarce areas; executed integrated observation missions for the land surface, planetary boundary layer, cloud–precipitation, and troposphere–stratosphere exchange processes by coordinating ground-based, air-based, and satellite facilities; and achieved noticeable progress in data applications. A new estimation gives a smaller bulk transfer coefficient of surface sensible heat over the TP, which results in a reduction of the possibly overestimated heat intensity found in previous studies. Summer cloud–precipitation microphysical characteristics and cloud radiative effects over the TP are distinguished from those over the downstream plains. Warm rain processes play important roles in the development of cloud and precipitation over the TP. The lower-tropospheric ozone maximum over the northeastern TP is attributed to the regional photochemistry and long-range ozone transports, and the heterogeneous chemical processes of depleting ozone near the tropopause might not be a dominant mechanism for the summer upper-tropospheric–lower-stratospheric ozone valley over the southeastern TP. The TP thermodynamic function not only affects the local atmospheric water maintenance and the downstream precipitation and haze events but also modifies extratropical atmospheric teleconnections like the Asia–Pacific Oscillation, subtropical anticyclones over the North Pacific and Atlantic, and temperature and precipitation over Africa, Asia, and North America. These findings provide new insights into understanding land–atmosphere coupled processes over the TP and their effects, improving model parameterization schemes, and enhancing weather and climate forecast skills.

Dramatic undercutting of piedmont rivers after the 2008 Wenchuan Ms 8.0 Earthquake.

Changes in river channel erosion or deposition affect the geomorphic evolution, aquatic ecosystems, and river regulation strategies. Fluvial processes are determined by the flow, sediment and boundary conditions, and it has long been expected that increasing sediment supply will induce aggradation. Here, based on thorough field surveys, we show the unexpected undercutting of the piedmont rivers influenced by the 2008 Wenchuan (Ms 8.0) Earthquake. The rivers flow from the Longmen Mountain with significant topographic relief to the flat Chengdu plain. In the upstreams, sediment supply increased because of the landslides triggered by the earthquake, causing deposition in the upstream mountain reaches. However, the downstream plain reaches suffered undercutting instead of deposition, and among those rivers, Shiting River was the most seriously affected, with the largest undercutting depth exceeding 20 m. The reasons for this unexpected undercutting are proposed herein and relate to both natural and anthropogenic causes. In addition, we also demonstrate, at least for certain conditions, such as rivers flowing from large-gradient mountain regions to low-gradient plain regions, that upstream sediment pulses may induce aggradation in upstream and degradation in downstream, causing the longitudinal profile to steepen to accommodate the increasing sediment flux.

Spatial distribution characteristics of carbon, nitrogen and phosphorous and pollution status evaluation of sediments in the Haihe River Basin, China.

Studying the distribution of carbon, nitrogen and phosphorus of sediments on a whole-watershed scale is important to the research and management of water resources in the Haihe River Basin (HRB). In this study, total organic carbon (TOC), total nitrogen (TN), and total phosphorus (TP) of 163 samples were investigated in the HRB. Based on these data, the pollution le-vels of sediments were assessed by using different quantitative indices. The results showed that the concentrations of TOC, TN, and TP in the HRB were heterogeneous at different locations. A decreasing trend of concentrations was found from downstream plains (e.g., the Beisihe River and the Heilonggang River) to mountain areas (e.g., the Yongdinghe River, the Beisanhe River, and the Luanhe River). In addition, the concentration of TOC in river sediments was higher than that of reservoir sediments. The statistical analyses showed that TN was significantly (P<0.01) correlated to TOC and TP, with a correlation coefficient of 0.704 and 0.250, respectively. The pollution level based on organic indices was classified as the clean level in the HRB. However, the areas with a relatively high pollution level were still found in some spots, such as the Beisihe River, and the Heilonggang River. Sediments of rivers and reservoirs were similar in the pollution intensity. The average C/N value of sediments in the HRB was 12.71, indicating that the TOC was derived from algae, phytoplankton flora and fauna, followed by higher plants. The C/N value of reservoir sediments was higher than that of river sediments, indicating that the contribution of terrigenous material inputs to TOC was larger in reservoirs than in rivers.

Impact of land use/land cover changes on ecosystem services in the 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.

Acclimation of winter wheat (Triticum aestivum, cv. Yangmai 13) to low levels of solar irradiance

Winter wheat is a grass species widely planted in northern and central China, where the increase of aerosols, air pollutants and population density are causing significant reduction in solar irradiance. In order to investigate the adaptation of winter wheat (Triticum aestivum L., cv. Yangmai 13) to low irradiance conditions occurring in the downstream plain of the Yangtze River (China), plants were subjected to four solar irradiance treatments (100%, 60%, 40%, and 20% of environmental incident solar irradiance). Significant increases in chlorophyll (Chl) and xanthophyll (Xan) pigments, and decreases in Chl a/b and Xan/Chl ratios were observed in plants under low light. Light-response curves showed higher net photosynthetic rates (P N) in fully irradiated plants, that also showed a higher light-compensation point. Shaded plants maintained high values of minimal fluorescence of dark-adapted state (Fo) and maximum quantum efficiency of PSII photochemistry (Fv/Fm) that assess a lower degree of photoinhibition under low light. Reduced irradiance caused decreases in effective quantum yield of PSII photochemistry (&Phi;PSII), electron transport rate (ETR), and nonphotochemical quenching coefficient (qN), and the promotion of excitation pressure of PSII (1 - qP). The activities of the antioxidant enzymes superoxide dismutase and peroxidase were high under reduced light whereas no light-dependent changes in catalase activity were observed. Thiobarbituric acid reactive species content and electrolyte leakage decreased under shaded plants that showed a lower photooxidative damage. The results suggest that winter wheat cv. Yangmai 13 is able to maintain a high photosynthetic efficiency under reduced solar irradiance and acclimates well to shading tolerance. The photosynthetic and antioxidant responses of winter wheat to low light levels could be important for winter wheat cultivation and productivity.