Eutrophication and Sedimentation Patterns in Complete Exploitation of Water Resources Scenarios: An Example from Northwestern Semi-arid Mexico

Water requirements to supply human needs lead water stakeholders to store more water during surplus periods to fulfil the demand during – not only – scarcity periods. At the reservoirs, mostly those in semi-arid regions, water level then fluctuates extremely between rises and downward during one single year. Besides of water management implications, changes on physical, chemical and biological dynamics of these drawdown and refilling are little known yet. This paper shows the results, throughout a year, on solids, nutrients (N and P), chlorophyll-a, and sedimentation changes on the dynamics, when the former policy was applied in a reservoir from the semi-arid Northwestern Mexico. Water level sinusoidal trend impinged changes on thermal stratification and mixing, modifying nutrient cycling and primary producer responses. According to nitrogen and phosphorus concentration as well as chlorophyll-a, reservoir was mesotrophic, becoming hypertrophic during drawdown. Nutrient concentrations were high (1.22 ± 0.70 and 0.14 ± 0.12 mg P l⁻¹), increasing phosphorus and lowering N:P significantly throughout the study period, although no intensive agricultural, no urban development, neither industrial activities take place in the watershed. This suggests nutrient recycling complex mechanisms, including nutrient release from the sediment–water interface as the main nutrient pathway when shallowness, at the same time as mineralization, increases. Outflows controlled nitrogen and phosphorus availability on the ecosystem while organic matter depended on river inflows. As on other subtropical aquatic ecosystems, nitrogen limited primary productivity (Spearman correlation R = 0.75) but chlorophyll-a seasonal pattern showed an irregular trend, prompting other no-nutrient related limitants. Shallowness induced a homogeneous temporal pattern on water quality. This observed temporal variability was mainly explained statistically by changes on solids (mineral and organic), chlorophyll-a and flows (62.3%). Annual sedimentation rates of total solids ranged from 11.73 to 16.29 kg m⁻² year⁻¹ with organic matter comprising around 30%. N:P ratio on sedimentation rates were as high as could be expected in a resuspension dominated ecosystem, and spatially inverse related with N:P ratio on bottom sediments. Distance from river inlet into the reservoir reveals a marked spatial heterogeneity on solid and nitrogen sedimentation, showing the system dependence on river inflows and supporting resuspension as the main phosphorus pathway. Accretion rates (2.19 ± 0.40 cm year⁻¹) were not related to hydrological variability but decreased with the distance to the river input. Total sediment accumulation (9,895 tons km⁻² year⁻¹) denotes siltation as other serious environmental problem in reservoirs but possibly not related with operational procedures.     

Seeking calm water: Exploring policy options for India's water future

This paper seeks to identify some promising policy options which could be part of a strategic and holistic effort to address India's future water challenges. Significant increases in agricultural water productivity would be a major factor in reducing the need for developing new water sources. Crop diversification, appropriately targeted to account for the present agricultural systems and available water resources, will increase productivity. Furthermore, much more emphasis needs to be placed on effective management of the groundwater resources through renewed efforts to enhance artificial recharge and conservation. Also, efforts should be revived to improve the existing surface irrigation systems. In particular, systems could be reconfigured to provide a more reliable water supply and allow effective community level management, where appropriate. Finally, while some of the increasing demands from domestic and industrial users will be met by the development of groundwater and reallocation of water from the agricultural sector, this will not be sufficient. Given that such conditions are emerging in states with high economic growth and relatively water scarce basins, this will require the further development of water resources. In some cases, these conditions along with the demand for reliable water for high value crops, will be part of the justification for inter‐basin transfers.     

The mountain-lowland debate: deforestation and sediment transport in the upper Ganga catchment

The Himalaya-Gangetic Plain region is the iconic example of the debate about the impact on lowlands of upland land-use change. Some of the scientific aspects of this debate are revisited by using new techniques to examine the role of deforestation in erosion and river sediment transport. The approach is whole-of-catchment, combining a history of deforestation with a history of sediment sources from well before deforestation. It is shown that deforestation had some effect on one very large erosional event in 1970, in the Alaknanda subcatchment of the Upper Ganga catchment, but that both deforestation and its effects on erosion and sediment transport are far from uniform in the Himalaya. Large magnitude erosional events occur for purely natural reasons. The impact on the Gangetic Plain of erosion caused by natural events and land cover change remains uncertain.     

Release and sedimentation behaviors of biochar colloids in soil solutions

The release of biochar colloids considerably affects the stability of biochar in environment. Currently, information on the release behavior and suspension stability of biochar colloids in real soil solutions is scarce. In this study, 20 soils were collected from different districts in China and the release behavior of biochar colloids and their suspension stability in soil solutions were systematically examined. The results showed that both pyrolysis temperature and biomass source had important effects on the formation of biochar colloids in soil solutions. The formation amount of biochar colloids from low pyrolysis temperatures (400 °C) (average amount of 9.33–16.41 mg/g) were significantly higher than those from high pyrolysis temperatures (700 °C) (average amount of less than 2 mg/g). The formation amount of wheat straw-derived biochar colloids were higher than those of rice straw-derived biochar colloids probably due to the higher O/C ratio in wheat-straw biochar. Further, biochar colloidal formation amount was negatively correlated with comprehensive effect of dissolved organic carbon, Fe and Al in soil solutions. The sedimentation curve of biochar colloids in soil solutions is well described by an exponential model and demonstrated high suspension stability. Around 40% of the biochar colloids were maintained in the suspension at the final sedimentation equilibrium. The settling efficiency of biochar colloids was positively correlated with comprehensive effect of the ionic strength and K, Ca, Na, and Mg contents in soil solutions. Our findings help promote a deeper understanding of biochar loss and stability in the soil-water environment.     

The effects of drainage basin geomorphometry on minimum low flow discharge: the study of small watershed in Kelang River Valley in Peninsular Malaysia

This study investigate the relationships between genomorphometric properties and the minimum low flow dischare of undisturbed drainage basins in the Taman BukitCahaya Seri Alam Forest Reserve,Peninsular Malaysia.The drainage basins selected were third-order basins so as to facilitate a common base for sampling and performing an unbiased statistical analyses.Three levels of relationships were observed in the study.Significant relationships exised between the genomorphometric properties as shown by the correlation network analysis;secondly,individual geomorphometric properties were observed to influence minimum flow discharge;and finally,the multiple regression model set up showed that minimum flow discharge(Qnub)was dependent of basin area(AU),stream length(LS),maximum relief(Hmax),average relief (HAV) and stream frequency(SF).These findings further enforced other studies of this nature that drainage basins were dynamic and functional entities whose operations were governed by complex interrelationships occurring within the basins.Changes to any of the geomorphometric properties would influence their role as basin regulators thus influencing a change in basin response.In the case of the basin‘s minimum low flow,a change in any of the properties considered in the regression model influenced the “time to peak”of flow.A shorter time period would mean higher discharge,which is generally considered the prerquisite to flooding.This research also conclude that the role of geomorphometric properties to control the water supply within the stream through out the year even though during the drought and less precipitations months .Drainage basins are sensitive entities and any deterioratons involve will generate reciprocals and response to water supply as well as the habitat within the areas.     

长江经济带典型流域重化产业环境风险及对策

长江经济带工业企业密集,环境风险点多,产业结构和布局不合理造成累积性、叠加性和潜在性的生态环境问题突出,制约了其持续健康发展.根据自然资源、社会经济和产业发展特征,选择3个典型流域（区域）（即重化产业最密集、人口最密集,重化产业布局性矛盾最突出的长江湖口以下干流区域;重大调水工程下游减水河段与涉水产业重点发展的汉江流域;生态系统脆弱的喀斯特地貌区与磷矿资源开发强度高的乌江流域）进行分析,并识别流域重化产业发展可能带来的环境风险问题及其演变趋势.基于保障“清洁长江”与“安全长江”建设的总体目标,按照“守底线、优格局、提质量、保安全”的调控思路,提出长江经济带典型流域重化产业绿色发展的优化调控对策和差别化生态环境保护与环境风险防控建议,为推动长江经济带的实施精准治理提供支撑,主要包括:①长江湖口以下干流区域以保障人居环境安全为目标,以各类工业园区为抓手优化布局,提升区域环境风险防控能力建设,研究制定长江沿岸地区持久性有机污染物控制对策;②汉江流域以流域环境承载力为硬约束,从国家产业政策战略高度调整汉江中下游的产业发展战略,严格控制高耗水和水污染产业的持续发展;③乌江流域以保障下游库区水质为目标,严控喀斯特地貌区域新增磷化工产能,研究喀斯特地貌区实施磷化工产业废水特别排放限值.      

Stream Communities Along a Catchment Land-Use Gradient: Subsidy-Stress Responses to Pastoral Development

When native grassland catchments are converted to pasture, the main effects on stream physicochemistry are usually related to increased nutrient concentrations and fine-sediment input. We predicted that increasing nutrient concentrations would produce a subsidy-stress response (where several ecological metrics first increase and then decrease at higher concentrations) and that increasing sediment cover of the streambed would produce a linear decline in stream health. We predicted that the net effect of agricultural development, estimated as percentage pastoral land cover, would have a nonlinear subsidy-stress or threshold pattern. In our suite of 21 New Zealand streams, epilithic algal biomass and invertebrate density and biomass were higher in catchments with a higher proportion of pastoral land cover, responding mainly to increased nutrient concentration. Invertebrate species richness had a linear, negative relationship with fine-sediment cover but was unrelated to nutrients or pastoral land cover. In accord with our predictions, several invertebrate stream health metrics (Ephemeroptera–Plecoptera–Trichoptera density and richness, New Zealand Macroinvertebrate Community Index, and percent abundance of noninsect taxa) had nonlinear relationships with pastoral land cover and nutrients. Most invertebrate health metrics usually had linear negative relationships with fine-sediment cover. In this region, stream health, as indicated by macroinvertebrates, primarily followed a subsidy-stress pattern with increasing pastoral development; management of these streams should focus on limiting development beyond the point where negative effects are seen.     

基于ENSO发展过程的中国夏季降水时空变化特征

利用1961—2019年中国地面降水月值格点数据,结合趋势分析、合成分析及T检验等气候诊断方法,对中国夏季降水时空变化特征进行分析,进而探讨不同类型ENSO事件对应夏季降水规律。结果表明：20世纪60—90年代末,长江、淮河夏季降水波动增加,海河降水持续下降,符合“南涝北旱”空间特征;21世纪后,除淮河夏季降水下降之外,其他流域降水均呈增加趋势;对于不同ENSO发展类型而言,以厄尔尼诺为主导的事件,副高脊线西伸增强,中国夏季多雨区集中在江淮地区,由南向北呈现“中间涝,南北旱”的空间格局;以拉尼娜为主导的事件中,副高脊线东移、控制面积缩小,中国夏季降水在胡焕庸线两侧、华南降水明显偏少;对于两种转换型事件而言,当前冬发生厄尔尼诺、夏季转为拉尼娜时,副高西伸且面积扩大,中国夏季降水偏多;反之,副高东移且面积缩小,中国夏季降水整体偏少。     

CONFLICT AND COOPERATION OVER INTERNATIONAL FRESHWATER RESOURCES: INDICATORS OF BASINS AT RISR1

ABSTRACT: In this paper we seek to identify historical indicators of international freshwater conflict and cooperation and to create a framework to identify and evaluate international river basins at potential risk for future conflict. We derived biophysical, socioeco‐nomic, and geopolitical variables at multiple spatial and temporal scales from GIS datasets of international basins and associated countries, and we tested these variables against a database of historical incidents of international water related cooperation and conflict from 1948 to 1999. International relations over freshwater resources were overwhelmingly cooperative and covered a wide range of issues, including water quantity, water quality, joint management, and hydropower. Conflictive relations tended to center on quantity and infrastructure. No single indicator—including climate, water stress, government type, and dependence on water for agriculture or energy—explained conflict/cooperation over water. Even indicators showing a significant correlation with water conflict, such as high population density, low per capita GDP, and overall unfriendly international relations, explained only a small percentage of data variability. The most promising sets of indicators for water conflict were those associated with rapid or extreme physical or institutional change within a basin (e.g., large dams or internationalization of a basin) and the key role of institutional mechanisms, such as freshwater treaties, in mitigating such conflict.     

影响活性污泥沉降因素及设计沉淀池应注意问题的探讨

通过理论和实验，对影响活性污泥沉降的多方面因素，进行了详细分析；并对设计沉淀池应注意的问题进行了探讨．