小集水区试验中三角堰量水问题的研究

对5种不同缺口角度的不完全收缩薄壁三角堰的出流特性进行了室内实验,得出了实验条条件下的流量系数经验公式和θ=90°堰的低水头(h<6cm)流量系数公式.通过理论分析和实测资料验证,指出了不能直接采用堰流公式得出小集水区的暴雨径流流量,并分析了野外观测的精度.     

喀斯特山区农村居民点“三生”空间耦合特征分析——以七星关区为例

为探究农村居民点“三生”空间之间的互动关系,以农村居民点斑块为研究单元,运用核密度估计和高斯两步移动搜索法分析了七星关区农村居民点及其“三生”空间分异特征,借助耦合协调度模型测算农村居民点“三生”空间及其两两之间的耦合度与协调度。结果表明:(1)七星关区农村居民点整体呈“大散居、小聚居”特征,其生活空间圈层结构突出,生产空间南北差异显著,生态空间则较为零散;(2)农村居民点“三生”空间功能呈现4种耦合度类型,5种耦合协调度类型,耦合协调状态服从“核心—边缘”模式;(3)农村居民点“三生”空间功能两两之间耦合协调状态呈现较强中心城区指向,其中生产—生态空间耦合协调状态较好,生活—生产、生活—生态空间较差。七星关区农村居民点“三生”空间耦合协调水平有待提升,需科学规划乡村“三生”空间,促进喀斯特山区乡村健康发展。     

IMPACTS OF LAND COVER CHANGE SCENARIOS ON STORM RUNOFF GENERATION: A BASIS FOR MANAGEMENT OF THE NYANDO BASIN,KENYA

The effects of conceptual land cover change scenarios on the generation of storm runoffs were evaluated in the Nyando Basin. The spatial scenarios represented alternatives that vary between full deforestation and reforestation. Synthetic storm events of depths 40, 60 and 80 mm were formulated according to the rainfall patterns and assumed to have durations corresponding to the runoff times of concentration. The Natural Resource Conservation Service–Curve Number model was used to generate runoff volumes within the sub‐catchments, which were subsequently routed downstream to obtain effects in the whole basin. The simulated land cover change impacts were evaluated relative to values obtained from the actual land cover state of the basin in the year 2000. From the results, an agricultural land cover scenario constituting of about 86 per cent of agriculture indicated increased runoff volumes in the entire basin by about 12 per cent. An agricultural‐forested land cover scenario with 40 and 51 per cent of forest and agriculture respectively revealed reduced runoff volumes by about 12 per cent. Alternatively, a scenario depicting a largely forested land cover state with about 78 per cent of forests reduced the runoff volumes by about 25 per cent according to the model estimates. Runoff volumes in the basin were also likely to reduce by about 15 per cent if the appropriate land cover scenario for the respective sub‐catchments were to be assumed for runoff management purposes. Considering the prevalent data uncertainty, the study effectively highlights the potential hydrological vulnerability of the basin. The results obtained can form a basis for appropriate catchment management of the area. Copyright © 2012 John Wiley & Sons, Ltd.     

Investigating the spatial distribution of soil erosion and deposition in a small catchment on the Loess Plateau of China, using Cs

An understanding of the spatial distribution of soil erosion and deposition in a catchment is important for designing soil and water conservation measures. Traditional monitoring techniques provide limited information on the spatial patterns of erosion and deposition. The fallout radionuclide ¹³⁷Cs was used to document rates and patterns of soil redistribution within a small (0.17 km²) gully catchment located near An'sai in Shaanxi Province, representative of the Loess Plateau of China. The local reference inventory was estimated to be 2266 Bq m⁻² and the ¹³⁷Cs inventories of 198 soil cores collected from the catchment, ranged from 0 to 3849 Bq m⁻². The coefficient of variation of the inventories of the individual cores was 0.85, reflecting the complex pattern of ¹³⁷Cs redistribution by soil erosion and deposition. Estimates of erosion rates derived from ¹³⁷Cs measurement ranged from less than 25 to 150 Mg ha⁻¹ year⁻¹, with about 70% of the net soil loss from the catchment coming from the gully area. The ¹³⁷Cs technique was shown to provide an effective means of documenting the spatial distribution of soil erosion and deposition within the small catchment.     

Sulphur isotope characteristics of two north Bohemian forest catchments

Sulphate concentrations and ³⁴S ratios were monitored in bulk precipitation, spruce throughfall, and soil water (depth of 30 and 90 cm) at ervená jáma (CER) and Naetín (NAC), two severely polluted sites in the Czech Republic, between December 1992 and September 1994. Throughfall [SO₄ ^2–], up to 80 mg L^–1 in winter and as low as 7 mg L^–1 in summer, was higher than [SO₄ ^2–] in bulk precipitation (annual average 6 mg L^–1). There was a distinct seasonaity in S isotope abundances, with lower ³⁴S_BULK in summer (+4 per mil CER, + 6 per mil NAC) and lower ³⁴S_TF in winter (+3 per mil CER, +4 per mil NAC). Wintertime ³⁴S_BULK was around +8 per mil at CER and +10 per mil at NAC, summertime ³⁴S_TF was close to +7 per mil at both sites. For only a 1- month period in spring, bulk precipitation S became isotopically lighter than throughfall S. Bulk precipitation data from CER were in good agreement with those from the nearby monitoring station Lesná (LES), typically differing by less than 10 mg L^–1 and 2 per mil in [SO₄ ^2–] and ³⁴S, respectively. Suction lysimeters (soil depth of 30 and 90 cm) yielded higher sulphate concentrations and lower ³⁴S ratios compared to both bulk and throughfall precipitation. Little seasonality was observed in [SO₄ ^2–] at 30 cm (around 40 mg L^–1); at 90 cm [SO₄ ^2–] was higher in winter (70 mg L^–1) than in summer (45 mg L^–1). ³⁴S at 90 cm was <+5 per=" mil=" in=" 1993=" and=" up=" to=" +7.5=" in=" 1994,=" lower=" in=" the=" first=" year=" and=" higher=" in=" the=" second=" year=" compared=" to=" the=" depth=" of=" 30=" cm.=" sulphur=" fluxes=" at=" cer=" and=" nac=" are=" characterized=" by=" distinct=" isotope=" compositions=" and=" can=" therefore=" be=" used=" to=" trace=" s=" pathways=" and=" transformations=" in=" the=" forest=">     

Proportions of subsurface drainages in large areas—methodological study in the Middle Mulde catchment (Germany)

High nitrogen (N) input to rivers requires measures for the reduction of diffuse N pollution. Beside the groundwater, artificial subsurface drainage systems are the main pathways of diffuse N input into rivers. Nevertheless, the N discharge via subsurface drainage systems is one of the main missing links for modeling, especially because of the lack of data bases of subsurface drainage areas. We introduce a method to calculate the normally unknown proportions of drained areas in arable lands improving the existing method by Behrendt et al. (2000). The method is applied for the catchment of Middle Mulde river (area: 2,700 km²) in Saxony/Germany. The data records of the mesoscale soil mapping are allocated to the subsurface‐drainage areas digitalized in representative areas using ARC/INFO GIS. In this way, it is possible to establish a differentiated record of the proportion of subsurface‐drainage area of each regional site type. The results were extrapolated to the entire area by transferring the proportions of subsurface‐drainage areas to areas where no information on drainage areas was available. The approach is well‐suited for future model approaches on a regional scale. By creating and integrating new data sets derived from modern GIS operations, the approach reduces the uncertainty of modeling N and water fluxes.     

闽南农业小流域土壤反硝化作用研究

土壤反硝化是流域土壤氮损失的重要途径之一。利用乙炔抑制培养法对五川流域内表层土壤的反硝化进行测定,研究发现,闽南农业小流域土壤具有较强的反硝化作用强度,在种植季节土壤平均反硝化作用强度为N 0.1 kg/(hm2.d),最高达到N 0.6 kg/(hm2.d),其中蔬菜地反硝化作用强于其他土地利用类型。反硝化作用同土壤的含水量、温度以及NO3-含量都存在有正相关关系,温度是流域土壤反硝化作用的最主要影响因子。五川流域土壤经由反硝化作用氮损失量占流域施肥量的16%,稍高于国内其他地区。     

Suitability of Watershed Models to Predict Distributed Hydrologic Response in the Awramba Watershed in Lake Tana Basin

Planning effective landscape interventions is an important tool to fight against land degradation and requires knowledge on spatial distribution of runoff. The objective of this paper was to test models that predict temporal and spatial distribution of runoff. The selected models were parameter‐efficient semi‐distributed watershed model (PED‐WM), Hydrologiska Byrans Vattenbalansavdelning integrated hydrological modeling system (HBV‐IHMS), and Soil and Water Assessment Tool (SWAT). We choose 7‐km² Awramba watershed in the Lake Tana basin with detailed hydrological information for testing these models. Discharge at the outlet, rainfall, and distributed information on infiltration rates, water table, and extent of the saturated area were collected from 2013 to 2015. The maximum saturated area was 6·5% of the watershed. Infiltration rates exceeded rainfall intensities 91% of the time. Hence, saturation excess runoff was the main runoff mechanism. Models were calibrated for the rainy seasons in 2013 and 2014 and validated for 2015. For daily flow validation, the PED‐WM model (Nash–Sutcliff efficiency, NSE = 0·61) outperformed HBV‐IHMS (NSE = 0·51) and SWAT (NSE = 0·48). Performance on monthly time step was similar. Difference in model behavior depended on runoff mechanism. In PED‐WM, saturation excess is the main direct runoff process and could predict the maximum extent of the saturated area closely at 6·9%. HBV‐IHMS model runoff simulation depended on soil moisture status and evapotranspiration, and hence was able to simulate saturation excess flow but not the extent of the saturated area. SWAT, where infiltration excess is the main runoff mechanism, could only predict the monthly discharges well. This study shows that prevailing runoff mechanisms and distribution of runoff source areas should be used for proper model selection. Copyright © 2016 John Wiley & Sons, Ltd.     

Complete versus partial macrophyte removal: the impacts of two drain management strategies on freshwater fish in lowland New Zealand streams

Complete macrophyte removal to maintain drainage performance in lowland streams can have a negative effect on resident fish communities, but few studies have quantified this impact. Moreover, limited research has been carried out exploring alternative approaches for macrophyte removal that minimise the impact on the resident fish community. The aims of this study were (i) to determine how the current practice of removing almost 100% of available macrophyte cover affects native fish populations in lowland New Zealand streams and (ii) to see whether this impact can be reduced by limiting macrophyte removal to alternating 50‐m sections of the waterway. Native fish populations were surveyed before and after experimental macrophyte removal for the following three treatments: (i) complete macrophyte removal, (ii) macrophyte removal from alternating 50‐m reaches and (iii) control with no macrophyte removal. Radiotelemetry was used to monitor the behavioural response of individual giant kokopu (Galaxias argenteus) to the different treatments. The results of this study suggest that current drain management practices reduce CPUE of fish by 60%. Although limiting macrophyte removal to alternating 50‐m sections did not minimise the community impacts of drain clearing, large giant kokopu did benefit from this strategy. All tagged giant kokopu remained in stream reaches partially cleared of macrophytes, while in completely cleared reaches all individuals were displaced. These results demonstrate the threat current drain management practices pose to New Zealand native fish and highlight the value of trialling alternative methods of macrophyte removal.     

Evaluation of forest disturbance in south-west Zabaikalia （East Siberia）Evaluation of forest disturbance in south-west Zabaikalia （East Siberia）Evaluation of forest disturbance in south-west Zabaikalia （East Siberia）

The forest estate in south-west Zabaikalia, a territory included in the Lake Baikal catchment area, has been investigated. For this purpose we have used both data of our own studies and monitoring data of environmental protection bodies. It shows that in our study area, fires, fellings, entomo-parasites and air pollution are the major negative factors affecting the state of the forest. In the period from 2003 to 2008 fires were registered in the area of over 500 thousand ha, pest foci in the forests covering an area of over 330 thousand ha, where almost 5 million m3 wood was cut in an area of about 43 thousand ha. The total area of forests in our study affected by air pollution amounts to about 700 thousand ha. According to the results, forest pollution in the territory is concentrated in the vicinity of large-scale industrial complexes, for distances up to about 40 km. The total area of forests weakened by air pollution amounts to about 2 million ha.