A multi-isotope approach （Pb, S, N, O and Sr） to estimate the impact of long distance air pollution

The impact of air pollution is a substantial European and global problem which has been observed even in the most remote areas of our planet. Not only surface water, but also groundwater resources are partly endangered by dry and wet deposition from the air. Karst and other sensitive aquifers contribute up to 90 % to the total drinking water supply in some European regions. However, they are more vulnerable to contamination than other aquifers due to short transfer times from recharge to source. Therefore, the main objective of this paper is to show possibilities to quantify the impact of air pollution on sensitive water resources （e.g. karst）, to develop an innovative surveillance tool based on isotopes and meteorological considerations. Comparisons of lead isotope measurements in precipitation, spring waters, soil profiles and dolomite bedrock in a relatively pristine and remote area at the front-range of the Northern Calcareous Alps in Austria with literature data indicate that radiogenic Australian gasoline-lead still dominates with 60%-80% the composition of the trace lead in the spring waters. In addition to the lead leached from the dolomite bedrock a third source contributes about 5%-10%. This second long distance Pb-contribution may originate from coal burning and/or Ag-Pb-ore smelting in central Europe in the past. The monthly precipitation （May and September 2005） samples show ^18O-rich sulphate ions, whereas the soil sulphates change in the direction to lower ^18O- and higher ^34S values with depth. The spring waters and bedrock dolomites show relatively low delta ^34S values （4‰-9 ‰）. Assuming the precipitation samples and the dolomite bed rocks are end-members the contribution of atmospheric sulphate can estimated to be 20% in the spring waters and between 10% to 45% in the soil samples. The ^87Sr/^86Sr-isotope results in the precipitation （0.7092） support at least a more radiogeradiogenic, far transported source in addition to a possible recycling of local dolomite and limestone （0.7080-0.7083） dust.     

Reviewing pre-TRANSALP DSS models

The interpretation of DSS (deep seismic soundings) profiles in Central and Eastern Alps is recalled in the paper and the models of the lower crust and Moho proposed several years ago are compared to the results of the TRANSALP seismic reflection profile. This evaluation highlights a good agreement as far as the geometry of the deep crustal structure is concerned. Therefore, the reliability of the interpretative models, previously exclusively based on DSS profiles, becomes improved. The deep structure beneath the whole Alpine range is examined reconsidering the map of the Moho boundary and the structural model already proposed for the central-eastern sector. Five main interpretative transects are put side by side, starting from the Western Alps and moving eastwards to the Swiss–Lombardian Central Alps (“European Geotraverse”), to the cross section from southern Bavaria to the Euganei Hills, to the TRANSALP profile, and finally to the easternmost profile available so far (southern Bavaria–Trieste). The comparison outlines lateral variations of the deep crustal structure as well as a sharp contrast between the Adria and the European lower crust and Moho. The transition from the Adria plate to the Dinaric domain remains, up to now, undefined.     

Fine sediment delivery and transfer in lowland catchments: modelling suspended sediment concentrations in response to hydrological forcing

Fine sediment delivery to and storage in stream channel reaches can disrupt aquatic habitats, impact river hydromorphology, and transfer adsorbed nutrients and pollutants from catchment slopes to the fluvial system. This paper presents a modelling tool for simulating the time‐dependent response of the fine sediment system in catchments, using an integrated approach that incorporates both land phase and in‐stream processes of sediment generation, storage and transfer. The performance of the model is demonstrated by applying it to simulate in‐stream suspended sediment concentrations in two lowland catchments in southern England, the Enborne and the Lambourn, which exhibit contrasting hydrological and sediment responses due to differences in substrate permeability. The sediment model performs well in the Enborne catchment, where direct runoff events are frequent and peak suspended sediment concentrations can exceed 600 mg l^?1. The general trends in the in‐stream concentrations in the Lambourn catchment are also reproduced by the model, although the observed concentrations are low (rarely exceeding 50 mg l^?1) and the background variability in the concentrations is not fully characterized by the model. Direct runoff events are rare in this highly permeable catchment, resulting in a weak coupling between the sediment delivery system and the catchment hydrology. The generic performance of the model is also assessed using a generalized sensitivity analysis based on the parameter bounds identified in the catchment applications. Results indicate that the hydrological parameters contributing to the sediment response include those controlling (1) the partitioning of runoff between surface and soil zone flows and (2) the fractional loss of direct runoff volume prior to channel delivery. The principal sediment processes controlling model behaviour in the simulations are the transport capacity of direct runoff and the in‐stream generation, storage and release of the fine sediment fraction. The in‐stream processes appear to be important in maintaining the suspended sediment concentrations during low flows in the River Enborne and throughout much of the year in the River Lambourn. Copyright © 2007 John Wiley & Sons, Ltd.     

高寒沙区生物土壤结皮覆盖区凝结水组分分析

凝结水作为干旱半干旱地区重要的组分,对生物土壤结皮具有重要的生态学作用。为阐明高寒沙区青海共和盆地生物土壤结皮表层5 cm凝结水水汽来源,利用2017年5—9月自制微渗仪对土壤表层5 cm不同类型生物土壤结皮(苔藓结皮、藻类结皮、物理结皮)和流沙凝结水进行了观测。结果表明:高寒沙区凝结水量随结皮发育程度变化呈增加趋势,表现为:苔藓结皮>藻类结皮>物理结皮>流沙;生物土壤结皮覆盖区凝结水量显著大于流沙凝结水量,即生物土壤结皮有利于凝结水的产生;凝结水主要由吸湿水和大气水汽凝结水与土壤凝结水两部分组成;观测期间,不同类型结皮日土壤凝结水量无显著性差异;吸湿水量和大气水汽凝结水总量显著高于土壤凝结水量(P<0. 05);随时间的变化,吸湿水和大气水汽凝结水与土壤凝结水对凝结水的贡献率呈波动性变化;吸湿水和大气水汽凝结水贡献率主要集中在65%～80%,土壤凝结水贡献率主要集中在20%～35%。     

麻多高寒湿地冻结过程中土壤热通量变化特征分析

准确量化高寒湿地下垫面冻结过程中土壤热通量的变化特征,对认识高寒湿地—大气间水热交换过程有重要的科学意义。本文利用中国科学院麻多气候与环境综合观测站2014年5月至2015年5月的观测资料,分析了下垫面冻结过程中土壤热通量变化特征,探讨了冻结潜热对土壤热通量的贡献。基于温度积分计算土壤热通量的算法,指出在计算冻结过程中的土壤热通量时,需要同时考虑土壤热通量板以上的土壤热贮存及热通量板以上的冻结潜热。研究表明:（1）冻结锋面形成后,锋面所在深度土壤体积含水量迅速降低,锋面以下土壤热通量接近于零,土壤液态水开始冻结,冻结潜热向上穿过热通量板所在土壤层;降水下渗土壤后冻结所释放的潜热能使次日凌晨5 cm深度土壤热通量接近于零。（2）季节性冻结期,凌晨气温较高时穿过5 cm土壤层的向上土壤热通量很小,可能是由表层土壤发生了日冻融循环所致。土壤水释放的冻结潜热使土壤温度波动减弱并维持在冰点附近。高寒湿地下垫面仅在很浅的表层发生日冻融循环,无法通过5 cm土壤温度资料判断下垫面循环出现日期。（3）加入冻结潜热项,土壤热通量的计算值与实测值之间的均方根误差将会从11.5 W m-2下降到6.2 W m-2。以上研究结果对认识寒区陆面过程有重要的贡献。     

唐古拉山冬克玛底冰川流域河水总溶解固体和悬移质的变化特征

通过2013年6-9月对唐古拉山冬克玛底冰川流域河水的逐日定时样品采集,并结合流域水文与气象资料,对径流的总溶解固体（TDS）和悬移质的变化特征进行分析。结果表明：2013年消融期的平均气温为3.7℃,消融期降水量为546 mm,7月和8月两个月径流量占消融期总径流量的63%。消融期逐日的TDS变化范围为31~140 mg·L^-1,平均值为60 mg·L^-1,TDS随径流变化显著,表现为消融强烈时（7-8月） TDS浓度较低,消融初期（6月）和末期（9月）时TDS浓度较高;径流中TDS与悬移质浓度（SSC）变化表现出相反变化趋势,即消融强烈时悬移质浓度较高,而消融初期与末期悬移质浓度较低,消融期平均悬移质浓度为122.8 mg·L^-1,流量-SSC时序关系表现为以顺时针滞后事件为主。2013年冬克玛底冰川流域消融期的化学侵蚀总量和物理侵蚀总量分别为2.214×10³ t和6.722×10³ t,化学侵蚀与物理侵蚀率的比值为0.33。     

北疆地区的水化学组成特征及其影响因素

流域尺度上的水化学组成特征和来源会受到何种因素的影响和限制,是研究区乃至全球环境变化的焦点问题,需要综合考虑不同地表要素和环境下的天然水体来揭示其答案。本文选择北疆地区的三大水系（伊犁水系、准噶尔水系、额尔齐斯水系）开展水化学组成研究,以期认识中亚造山带中部干旱环境下典型水系的水化学组成特征、成因及其影响因素。本研究利用已采集的北疆三大水系天然水样品及其水化学组成分析数据,同时系统收集了北疆及其周边地区文献资料,并与其他中纬度地区和国际典型气候带地区进行了综合对比。综合数据分析结果表明,北疆水系的河流溶解性固体总浓度（TDS值）普遍高于中国季风区和湿润地区河流,也高于世界平均水平;水体的主要阴阳离子分别以Ca²⁺和HCO₃^-占主导地位;主量离子间相对浓度与中国东部季风区河流类似,也与世界大部分以碳酸盐岩风化为主导的河流相似。岩石风化作用在水化学成因上对北疆大部分地区都占据主导地位;进一步定量的结果发现,不同来源对天然水溶质贡献量大小的顺序为：蒸发岩溶解>碳酸盐岩风化>硅酸盐岩风化>大气降水,证明了蒸发岩溶解和碳酸盐岩风化的主导地位。对比硅酸盐岩风化与碳酸盐岩风化,北疆水系的中低地形区硅酸盐岩影响更大,海拔较高的山地地区则碳酸盐岩影响更大。区域降水、水热组合、径流、岩性等因素都对水化学过程产生重要的影响,但与温度的关系不明显,与流域物理侵蚀过程及其季节变化等的关系尚不明确,需要开展进一步的研究工作。     

Initial hydro‐geomorphic development and rill network evolution in an artificial catchment

The formation of erosion rills and gullies is a critical step in land surface development, but possibilities to study initial unaffected surface development under natural conditions and with well‐defined initial and boundary conditions are rare. The objective of this study was to characterize rill network development from ’point zero’ in the artificially‐created catchment ‘Hühnerwasser’. To ensure unaffected development, the study was largely restricted to the analysis of remotely‐sensed data. We analyzed a series of photogrammetry‐based digital elevation models (DEMs) for 10 points in time, over a period of five years and beginning with the initial state. The evolving erosion rill network was quantitatively described based on mapping from aerial photographs. DEMs and rill network maps were combined to specifically analyze the development of morphometry for different parts of the network and to characterize energy dissipation and connectivity. The restriction to remote‐sensing data did not allow for analyzing specific processes governing rill network development, nevertheless, two major development phases could be characterized. We observed a phase of growth of the rill network along with variations in drainage patterns during the first two years of development and a subsequent phase of reduction of its area along with comparably stable patterns. Region‐specific analysis of morphometry indicates that, besides effects of changing sediment characteristics and vegetation cover development, locally evolving hydro‐geomorphic feedback cycles influenced this development. Results show an increasing similarity of overall statistical characteristics (e.g. drainage density) for two parts of the catchment, but a persistent influence of initial conditions on specific rill geometry. The observed development towards higher orderliness and increased connectivity is consistent with experiments and concepts on drainage network evolution across scales; however, we did not observe major influences of rill piracy and cross grading or a reduction of energy dissipation with network development. Copyright © 2013 John Wiley & Sons, Ltd.     

Model structure and uncertainty for stochastic non-point source modelling applications

Abstract

The uncertainty associated with a rainfall–runoff and non-point source loading (NPS) model can be attributed to both the parameterization and model structure. An interesting implication of the areal nature of NPS models is the direct relationship between model structure (i.e. sub-watershed size) and sample size for the parameterization of spatial data. The approach of this research is to find structural limitations in scale for the use of the conceptual NPS model, then examine the scales at which suitable stochastic depictions of key parameter sets can be generated. The overlapping regions are optimal (and possibly the only suitable regions) for conducting meaningful stochastic analysis with a given NPS model. Previous work has sought to find optimal scales for deterministic analysis (where, in fact, calibration can be adjusted to compensate for sub-optimal scale selection); however, analysis of stochastic suitability and uncertainty associated with both the conceptual model and the parameter set, as presented here, is novel; as is the strategy of delineating a watershed based on the uncertainty distribution. The results of this paper demonstrate a narrow range of acceptable model structure for stochastic analysis in the chosen NPS model. In the case examined, the uncertainties associated with parameterization and parameter sensitivity are shown to be outweighed in significance by those resulting from structural and conceptual decisions.

Citation Parker, G. T. Rennie, C. D. & Droste, R. L. (2011) Model structure and uncertainty for stochastic non-point source modelling applications. Hydrol. Sci. J. 56(5), 870–882.