基于水土保持的流域生态环境需水研究

针对现有生态环境需水量的计算主要基于现状而导致其实用性不足的特点,提出了根据流域或区域对生态环境功能的需求来确定其生态建设规模并计算其生态环境需水量的思想。以位于黄土高原的安塞纸坊沟流域为例,针对该流域以水土流失为首要生态环境问题的特点,在已有的土壤侵蚀与土地利用结构关系研究的基础上,基于水土保持目标确定土地利用结构,进而计算出该流域的生态环境需水量,并对不同土地利用情景以及不同水土保持目标进行了对比分析。研究表明,综合考虑水土保持效益与生态环境用水代价,纸坊沟流域以允许土壤流失量1 000 t/(km²·a)为目标为宜,此时该流域生态环境需水量约为1.77×10⁶ m³,占该流域年降水总量的39.0%。通过与基于生态系统现状的计算结果相比较,说明提出的思想更为合理。     

Identifying sustainability challenges on land and water uses: The case of Lake Ziway watershed,Ethiopia

This paper firstly analyzes the land use - land cover (LULC) in Lake Ziway watershed (Ethiopia) and quantifies the changing patterns from 1973 to 2014 using Landsat images. Secondly, the paper estimates sediment yields using the Soil and Water Assessment Tool (SWAT model). It also assesses and estimates water abstraction from Lake Ziway using survey data. The study shows that the conversions from woodlands into agricultural lands and settlement areas are the major detected LULC changes. Of the total area of the watershed, agricultural lands and settlement areas together increased from 57% in 1973 to 75% in 2014 at the expense of woodlands whose areas decreased from 26.16% to 6.63% in the study periods. The study also shows that water abstraction and sediment loads are increasing at Lake Ziway watershed. The major driving forces behind these LULC changes and the impacts on the lake natural condition are anthropogenic factors such as population growth, land policy changes and deforestation. Increasing demands for more land and water resources, i.e., land for settlements and cultivation, wood for fuel and charcoals, and water for irrigation and municipal water supply, are the underlying causes for the observed changes on the watershed resources. Thus, if the existing scenarios of human pressures are left neglected without management interventions, severe watershed degradations will continue to further affect the watershed's resources including the hydrology. Therefore, responsible government institutions should start mobilizing the local communities along with providing financial and material supports for watershed rehabilitation through afforestation and soil and water conservation activities. Additionally, the free-access practices for water use should be replaced by user-charge policy to regulate water abstractions in order to adequately sustain the water level of Lake Ziway and its feeder rivers. In this respect, this study provides firsthand information to policy makers and planners to put in place a comprehensive land and water use plan and regulations against the unruly human actions in the watershed before irreversible losses might happen to Lake Ziway and its watershed resources.     

Groundwater arsenic contamination in Manipur,one of the seven North-Eastern Hill states of India: a future danger

Manipur State, with a population of 2.29 million, is one of the seven North-Eastern Hill states in India, and is severely affected by groundwater arsenic contamination. Manipur has nine districts out of which four are in Manipur Valley where 59% of the people live on 10% of the land. These four districts are all arsenic contaminated. We analysed water samples from 628 tubewells for arsenic out of an expected total 2,014 tubewells in the Manipur Valley. Analyzed samples, 63.3%, contained >10 μg/l of arsenic, 23.2% between 10 and 50 μg/l, and 40% >50 μg/l. The percentages of contaminated wells above 10 and 50 μg/l are higher than in other arsenic affected states and countries of the Ganga–Meghna–Brahmaputra (GMB) Plain. Unlike on the GMB plains, in Manipur there is no systematic relation between arsenic concentration and the depth of tubewells. The source of arsenic in GMB Plain is sediments derived from the Himalaya and surrounding mountains. North-Eastern Hill states were formed at late phase of Himalaya orogeny, and so it will be found in the future that groundwater arsenic contamination in the valleys of other North-Eastern Hill states. Arsenic contaminated aquifers in Manipur Valley are mainly located within the Newer Alluvium. In Manipur, the high rainfall and abundant surface water resources can be exploited to avoid repeating the mass arsenic poisoning that has occurred on the GMB plains.     

Relations between climatic–geomorphological parameters and sediment yield in a mediterranean semi-arid area (Sicily,southern Italy)

In the present work on-going research is discussed whose primary goal is to test some statistical methods to estimate the average yearly area-specific sediment yield (SSY). Using geomorphological and climatic parameters various multiple regression formulae have been set up based on SSY observed data from 16 catchments of Sicily. Three distinct techniques were adopted to select the parameters to be used in the equations: simple correlation, stepwise regression analysis and a supervised geomorphological–statistical correlation. The comparison of the results showed the effectiveness of the stepwise analysis, which led to a regression equation with a coefficient of determination (r ²) of 0.87. Nevertheless, even this methodology showed some elements of uncertainty that have caused, in some cases, appreciable differences between observed and predicted values (mean percentage error equal to 26%). These differences are likely either due to the hydraulic regime of most of Sicilian watercourses (typical of semi-arid regions) or to hidden factors (e.g., topography, human impact and concentrated erosion), which can greatly affect the processes of sediment production and transport. The study has pointed out the need to take into account a larger number of observations and to perform the analysis of relations between suitable variables and SSY at a more detailed time resolution.     

Identifying erosion hotspots and assessing communities' perspectives on the drivers,underlying causes and impacts of soil erosion in Toledo's Rio Grande Watershed: Belize

Erosion in the Rio Grande watershed of Belize, Central America results in widespread ecological impacts and significant economic costs. In this study, quantitative soil loss analysis and qualitative social surveys were integrated to identify erosion vulnerable areas or hotspots, and to analyze varying perspectives between communities near and far from erosion hotspots regarding the causes of erosion. The results of the quantitative analysis suggest that erosion hotspots are located in the upper-mid reaches of the watershed near the communities of Crique Jute, Naluum Ca, San Pedro Columbia and San Miguel. The Mann–Whitney U test identified significant difference in the ranking of erosion drivers (cattle ranching, logging, and clearing of slopes) between communities. Communities far from erosion hotspots (FEH) ranked cattle ranching and logging higher than communities near erosion hotspots as the main drivers of soil erosion (NEH and FEH, mean = 79.02, 105.92, (U) = 3055, p < 0.001 and mean = 84.9, 100.90, (U) = 3560.5 p < 0.05) respectively. On the other hand, communities near erosion hotspots (NEH) ranked clearing and planting on slopes higher than communities far from erosion hotspots as the main driver of soil erosion (NEH and FEH, mean = 107.03, 81.86, (U) = 3136.5, p < 0.001). The logistic regression model depicted that ethnicity, distance, gender, and employment were significant in explaining the data variability on the perceived implementation of erosion prevention techniques in the watershed (2LL = 208.585, X² = 49, df = 8, p < .001). This research provides significant information on the drivers, underlying causes and erosion vulnerable areas that will aid stakeholders to garner community support, develop and implement sustainable soil management practices. Moreover, the study highlights the need to implement cost-effective soil erosion prevention programs and to assess the loss of soil nutrients and agriculture productivity in the study site.     

Assessments of ecosystem service indicators and stakeholder's willingness to pay for selected ecosystem services in the Chure region of Nepal

The Chure region of Nepal—the area sandwiched between the hills in the north and the plains in the south—is considered an ecologically fragile, structurally weak, and highly erosion-prone region. The forest in the Chure region provides several ecosystem services to people living in the downstream areas. However, assessment and quantification of ecosystem services in this region are very limited. This study, conducted in a watershed of the Chure region of western Nepal, combined local users' perspectives with experts' opinions to identify and rank ecosystem services based on land use types, to investigate the downstream users' willingness to pay for ecosystem services, and to explore the socio-economic factors affecting their willingness to pay. The study found that forests offered the highest number of ecosystem goods and services in this area. Local people were familiar with 10 different ecosystem services provided by the watershed and ranked drinking water service at the top. The downstream beneficiaries would be willing to pay a higher amount for drinking water service than they were currently paying if the quality of the service and its sustainability were assured. The amount they were willing to pay for ecosystem services increased significantly with monthly income. The results of this study are useful for other areas in which an upstream–downstream linkage exists and the upstream communities play a crucial role in maintaining ecosystem functions and the resulting supply of ecosystem services to the downstream communities.     

Neural network modeling for regional hazard assessment of debris flow in Lake Qionghai Watershed, China

This paper presents a neural network (NN) based model to assess the regional hazard degree of debris flows in Lake Qionghai Watershed, China. The NN model was used as an alternative for the more conventional linear model MFCAM (multi-factor composite assessment model) in order to effectively handle the nonlinearity and uncertainty inherent in the debris flow hazard analysis. The NN model was configured using a three layer structure with eight input nodes and one output node, and the number of nodes in the hidden layer was determined through an iterative process of varying the number of nodes in the hidden layer until an optimal performance was achieved. The eight variables used to represent the eight input nodes include density of debris flow gully, degree of weathering of rocks, active fault density, area percentage of slope land greater than 25° of the total land (APL25), frequency of flooding hazards, average covariance of monthly precipitation by 10 years (ACMP10), average days with rainfall >25 mm by 10 years (25D10Y), and percentage of cultivated land with slope land greater than 25° of the total cultivated land (PCL25). The output node represents the hazard-degree ranks (HDR). The model was trained with the 35 sets of data obtained from previous researches reported in literatures, and an explicit uncertainty analysis was undertaken to address the uncertainty in model training and prediction. Before the NN model is extrapolated to Lake Qionghai Watershed, a validation case, different from the above data, is conducted. In addition, the performances of the NN model and the MFCAM were compared. The NN model predicted that the HDRs of the five sub-watersheds in the Lake Qionghai Watershed were IV, IV, III, III, and IV–V, indicating that the study area covers normal hazard and severe hazard areas. Based on the NN model results, debris flow management and economic development strategies in the study are proposed for each sub-watershed.     

流域地下水资源评价

本文提出了流域地下水资源评价的概念,并且讨论了“流域地下水资源”的组成,以及各部分量之间的内在联系,从而揭示了在全流域内地下水资源形成的过程,反映了开采资源与补给量、排泄量的关系。“流域地下水资源评价”主要服务于国土整治宏观决策与规划,它的计算数据既不重复,又不挂漏,具有高度可统计性;同时又能针对流域内不同单元提出具体的评价意见,对生产实践有较重要的指导意义。     

Geochemical and Mineralogical Studies of the Mylonite Xenoliths and Monzogranite Rocks at Wadi Abu Rusheid,South Eastern Desert,Egypt: Insights on the Genesis of Mineralization

Abu Rusheid area lie in the south of the Eastern Desert of Egypt and comprises (1) ophiolitic mélange, consisting of ultramafic rocks and layered metagabbros in metasedimentary matrix (2) cataclastic group, consisting of protomylonites, mylonites, ultramylonites and silicified ultramylonites (3) monzogranites (4) pegmatite pockets, quartz veins and post-granite dykes. Focus on the monzogranites and the xenoliths of mylonite rocks from the geochemical and mineralogical points of view introduces a new view about the genesis of the related mineralization. Geochemically, the monzogranites have a metaluminous character and were crystallized under moderate water-vapor pressure around 3 kb and temperatures of 750–800°C. The monzogranites are altered along strike-slip faults exhibiting propylitic, with slightly sodic metasomatism and record high radioactive measurements. The average uranium and thorium (U and Th) contents in fresh monzogranites, mylonite xenolith and altered monzogranites are (7.3, 21.20), (40.36, 94.82), (60.34 and 347.88 ppm), respectively. These high radioactivities are attributed to the presence of kasolite, uranothorite, cerite, fluorite, zircon, apatite and columbite. The mylonite xenolith is higher in radioactivity than the surrounding fresh monzogranites, reflecting U and Th enrichment before emplacement of the monzogranites, then the latter were subjected to right lateral strike-slip faulting with producing hydrothermal solution rich in Th and U.     

Insights from watershed simulations around the world: Watershed service-based restoration does not significantly enhance streamflow

Increased water yield and baseflow and decreased peak flow are common goals of watershed service programs. However, is the forest management often used in such programs likely to provide these beneficial watershed services? Many watershed service investments such as water funds typically change less than 10% of watershed land cover. We simulate the effects of 10% forest-cover change on water yield, low flow, and high flow in hydrologic models of 29 watersheds around the world. The forest-cover changes considered are: forest restoration from degraded natural lands or agriculture, forest conversion to agriculture, and forest conversion to urban cover. We do not consider grassland restoration by removal of alien tree species from riparian zones, which does increase water yield and low flow. Forest restoration from locally-predominant agricultural land resulted in median loss in annual water yield of 1.4%. Forest restoration reduced low flow and high flow by ∼3%. After forest restoration, low flow increased in ∼25% of cases while high flow and water yield declined in nearly all cases. Development of forest to agriculture or urban cover resulted in a 1–2% median increase in water yield, a 0.25–1% increase in low flow, and a 5–7% increase in high flow. We show that hydrologic responses to forest cover changes are not linearly related to climate, physiography, initial land cover, nor a multitude of watershed characteristics in most cases. These results suggest that enhanced streamflow watershed services anticipated from forest restoration or conservation of 10% or less of a watershed are generally modest.