A philosophical basis for hydrological uncertainty

ABSTRACT

Uncertainty is an epistemological concept in the sense that any meaningful understanding of uncertainty requires a theory of knowledge. Therefore, uncertainty resulting from scientific endeavors can only be properly understood in the context of a well-defined philosophy of science. Our main message here is that much of the discussion about uncertainty in hydrology has lacked grounding in these foundational concepts, and has resulted in a controversy that is largely the product of logical errors rather than true (axiomatic) disagreement. As an example, we explore the current debate about the appropriate role of probability theory for hydrological uncertainty quantification. Our main messages are: (1) apparent (and/or claimed) limitations of probability theory are not actually consequences of that theory, but rather of deeper underlying epistemological (and ontological) issues; (2) questions about the appropriateness of probability theory are only meaningful if posed as questions about our preferred philosophy of science; and (3) questions about uncertainty may often be better posed as questions about available information and information use efficiency. Our purpose here is to discuss how hydrologists might ask more meaningful questions about uncertainty.     

复杂介质有限元法2.5维可控源音频大地电磁法数值模拟

利用有限元2.5维可控源音频大地电磁法（简称CSAMT）数值模拟方法,对100Ωm均匀半空间介质中有限长度的电偶极源产生的电场、磁场及视电阻率、相位特征进行了数值模拟,研究了场的空间变化规律. 在一个象限中,场的特征存在双叶现象,当收发距大于4个趋肤深度时,电阻率较接近介质真实的电阻率,这些结果为观测系统和收发距的选择提供了依据. 波数域场的特征表明,低波数对源的贡献占较大的比例. 有限元法2.5维CSAMT数值模拟的优势在于能较准确地获得复杂介质结构的波场特征. 本文结合直立异常体、倾斜异常体及断陷模型对CSAMT电阻率、相位剖面特征及频率曲线特征的可靠性进行了研究. 数值模拟结果直观地给出了异常体的剖面异常形态. 通过对比研究异常体的剖面异常形态和半空间场的特征进一步说明本文方法和软件在模拟复杂介质结构场特征时是可靠的. 这为认识观测数据,指导反演解释提供了较好的依据.     

The hydrochemistry of runoff from a ‘cold-based’ glacier in the High Arctic (Scott Turnerbreen,Svalbard)

There are still relatively few hydrochemical studies of glacial runoff and meltwater routing from the high latitudes, where non-temperate glacier ice is frequently encountered. Representative samples of glacier meltwater were obtained from Scott Turnerbreen, a ‘cold-based’ glacier at 78° N in the Norwegian high Arctic archipelago of Svalbard, during the 1993 melt season and analysed for major ion chemistry. Laboratory dissolution experiments were also conducted, using suspended sediment from the runoff. Significant concentrations of crustal weathering derived SO²⁻₄ are present in the runoff, which is characterized by high ratios of SO²⁻₄: (SO²⁻₄+HCO⁻₃) and high p(CO₂). Meltwater is not routed subglacially, but flows to the glacier terminus through subaerial, ice marginal channels, and partly flows through a proglacial icing, containing highly concentrated interstitial waters, immediately afront the terminus. The hydrochemistry of the runoff is controlled by: (1) seasonal variations in the input of solutes from snow- and icemelt; (2) proglacial solute acquisition from the icing; and (3) subaerial chemical weathering within saturated, ice-cored lateral moraine adjoining drainage channels at the glacier margins, sediment and concentrated pore water from which is entrained by flowing meltwater. Diurnal variations in solute concentration arise from the net effects of variable sediment pore water entrainment and dilution in the ice marginal streams. Explanation of the hydrochemistry of Scott Turnerbreen requires only one major subaerial flow path, the ice marginal channel system, in which seasonally varying inputs of concentrated snowmelt and dilute icemelt are modified by seepage or entrainment of concentrated pore waters from sediment in lateral moraine, and by concentrated interstitial waters from the proglacial icing, supplied by leaching, slow drainage at grain intersections or simple melting of the icing itself. The ice marginal channels are analogous neither to dilute supra/englacial nor to concentrated subglacial flow components. © 1998 John Wiley & Sons, Ltd.     

Land-use dominates climate controls on nitrogen and phosphorus export from managed and natural Nordic headwater catchments

Agricultural, forestry-impacted and natural catchments are all vectors of nutrient loading in the Nordic countries. Here, we present concentrations and fluxes of total nitrogen (totN) and phosphorus (totP) from 69 Nordic headwater catchments (Denmark: 12, Finland:18, Norway:17, Sweden:22) between 2000 and 2018. Catchments span the range of Nordic climatic and environmental conditions and include natural sites and sites impacted by agricultural and forest management. Concentrations and fluxes of totN and totP were highest in agricultural catchments, intermediate in forestry-impacted and lowest in natural catchments, and were positively related %agricultural land cover and summer temperature. Summer temperature may be a proxy for terrestrial productivity, while %agricultural land cover might be a proxy for catchment nutrient inputs. A regional trend analysis showed significant declines in N concentrations and export across agricultural (−15 μg totN L⁻¹ year⁻¹) and natural (−0.4 μg NO₃-N L⁻¹ year⁻¹) catchments, but individual sites displayed few long-term trends in concentrations (totN: 22%, totP: 25%) or export (totN: 6%, totP: 9%). Forestry-impacted sites had a significant decline in totP (−0.1 μg P L⁻¹ year⁻¹). A small but significant increase in totP fluxes (+0.4 kg P km⁻² year⁻¹) from agricultural catchments was found, and countries showed contrasting patterns. Trends in annual concentrations and fluxes of totP and totN could not be explained in a straightforward way by changes in runoff or climate. Explanations for the totN decline include national mitigation measures in agriculture international policy to reduced air pollution and, possibly, large-scale increases in forest growth. Mitigation to reduce phosphorus appears to be more challenging than for nitrogen. If the green shift entails intensification of agricultural and forest production, new challenges for protection of water quality will emerge possible exacerbated by climate change. Further analysis of headwater totN and totP export should include seasonal trends, aquatic nutrient species and a focus on catchment nutrient inputs.     

Contributions from glacially derived sediment to the global iron (oxyhydr)oxide cycle: Implications for iron delivery to the oceans

Estimates of glacial sediment delivery to the oceans have been derived from fluxes of meltwater runoff and iceberg calving, and their sediment loads. The combined total (2900 Tg yr⁻¹) of the suspended sediment load in meltwaters (1400 Tg yr⁻¹) and the sediment delivered by icebergs (1500 Tg yr⁻¹) are within the range of earlier estimates. High-resolution microscopic observations show that suspended sediments from glacial meltwaters, supraglacial, and proglacial sediments, and sediments in basal ice, from Arctic, Alpine, and Antarctic locations all contain iron (oxyhydr)oxide nanoparticles, which are poorly crystalline, typically ∼5 nm in diameter, and which occur as single grains or aggregates that may be isolated or attached to sediment grains. Nanoparticles with these characteristics are potentially bioavailable. A global model comparing the sources and sinks of iron present as (oxyhydr)oxides indicates that sediment delivered by icebergs is a significant source of iron to the open oceans, beyond the continental shelf. Iceberg delivery of sediment containing iron as (oxyhydr)oxides during the Last Glacial Maximum may have been sufficient to fertilise the increase in oceanic productivity required to drawdown atmospheric CO₂ to the levels observed in ice cores.     

西藏高原中、北部断裂构造特征:INDEPTH(Ⅲ)-MT观测提供的依据

根据1998年和1999年INDEPTH(Ⅲ)MT在西藏中、北部所完成的德庆-龙尾错(500线)和那曲-格尔木(600线)超宽频带大地电磁深探测剖面数据研究西藏高原中北部断裂构造特征,有助于推进印度板块与亚洲板块碰撞、俯冲构造模式的研究.研究结果表明,区内发育有F1～F10一系列深断裂.其中,F2向北倾斜是早期的主断裂,F1则是后期主逆冲断裂,它们共同构成空间结构复杂的嘉黎深断裂带.班公-怒江缝合带的主断裂系由略微向南陡倾的F3、F4和F5三组超壳深断裂构成;由于受后期构造运动强烈的改造,缝合带内发育多条延深不大的上地壳断层.唐古拉断裂带由F6、F7两组主断裂和一系列次级断裂构成;主断裂产状上陡、下缓,总体向南倾斜,向下延深达下地壳.而金沙江缝合带是由F8(金沙江断裂)和F9(可可西里断裂),以及它们之间存在的一系列上地壳次级断层共同组成的,是一组很宽的地块碰撞缝合带.F10即昆中断裂是产状陡立的超壳深断裂,是昆仑山断裂带的主体构造,它构成松潘-甘孜-可可西里地块的北部边界.从剖面电性结构特征分析,昆中断裂以南属于西藏高原主体;而以北地区是否还归属西藏高原?这有待更深入的讨论.值得特别关注的事实是,研究区内2组缝合带之下都存在向上地幔延伸的壳内高导体,它们可能反映区内壳幔热交换过程的痕迹.     

Hillslope scale surface runoff,sediment and nutrient losses associated with tramline wheelings

Research on arable sandy loam and silty clay loam soils on 4° slopes in England has shown that tramlines (i.e. the unseeded wheeling areas used to facilitate spraying operations in cereal crops) can represent the most important pathway for phosphorus and sediment loss from moderately sloping fields. Detailed monitoring over the October–March period in winters 2005–2006 and 2006–2007 included event‐based sampling of surface runoff, suspended and particulate sediment, and dissolved and particulate phosphorus from hillslope segments (each ～300–800 m²) established in a randomized block design with four replicates of each treatment at each of two sites on lighter and heavier soils. Experimental treatments assessed losses from the cropped area without tramlines, and from the uncropped tramline area, and were compared to losses from tramlines which had been disrupted once in the autumn with a shallow tine. On the lighter soil, the effects of removal or shallow incorporation of straw residues was also determined. Research on both sandy and silty clay loam soils across two winters showed that tramline wheelings represented the dominant pathway for surface runoff and transport of sediment, phosphorus and nitrogen from cereal crops on moderate slopes. Results indicated 5·5–15·8% of rainfall lost as runoff, and losses of 0·8–2·9 kg TP ha^?1 and 0·3–4·8 t ha^?1 sediment in tramline treatments, compared to only 0·2–1·7% rainfall lost as runoff, and losses of 0·0–0·2 kg TP ha^?1 and 0·003–0·3 t ha^?1 sediment from treatments without tramlines or those where tramlines had been disrupted. The novel shallow disruption of tramline wheelings using a tine once following the autumn spray operation consistently and dramatically reduced (p < 0·001) surface runoff and loads of sediment, total nitrogen and total phosphorus to levels similar to those measured in cropped areas between tramlines. Results suggest that options for managing tramline wheelings warrant further refinement and evaluation with a view to incorporating them into spatially‐targeted farm‐level management planning using national or catchment‐based agri‐environment policy instruments aimed at reducing diffuse pollution from land to surface water systems. Copyright © 2010 John Wiley & Sons, Ltd.     

An 11 000-year record of vegetation and environment from Lago di Martignano,Latium, Italy

A pollen diagram from Lago di Martignano, a maar lake in central Italy, provides an 11000-year record of vegetation and environment change. The earliest pollen spectra are dominated by Artemisia and Gramineae, representing late glacial steppe vegetation typical of the Mediterranean region. Broad-leaved forests were established by ca. 11 000 yr BP. Although Quercus initially dominated their canopy, a wide range of other mesophyllous trees were also present. Pollen values for sclerophyllous tree and shrub taxa characteristic of Mediterranean woodlands and scrub are initially low (<10%). After ca. 7000 yr BP, however, they begin to increase and rise to a peak of >40% of total land pollen at ca. 6700 yr BP, with Olea europaea the single most abundant taxon. Human influence upon the vegetation only becomes significant somewhat after this peak, with progressive clearance of woodland and expansion of herbaceous communities. Castanea sativa and luglans regia pollen is recorded consistently from the beginning of the rise in pollen values for taxa characteristic of Mediterranean scrub communities. Pollen values for arable crops increase progressively after ca. 5500 yr BP, following the peak pollen values for taxa characteristic of Mediterranean scrub vegetation. Late glacial and Holocene climate changes have been complex in this region, with the present character of the climate developing only during the last millennium. Rates of change of pollen spectra peak during this period.     

Direct effect of ice sheets on terrestrial bicarbonate, sulphate and base cation fluxes during the last glacial cycle: minimal impact on atmospheric CO2 concentrations

Chemical erosion in glacial environments is normally a consequence of chemical weathering reactions dominated by sulphide oxidation linked to carbonate dissolution and the carbonation of carbonates and silicates. Solute fluxes from small valley glaciers are usually a linear function of discharge. Representative glacial solute concentrations can be derived from the linear association of solute flux with discharge. These representative glacial concentrations of the major ions are 25% of those in global river water. A 3-D thermomechanically coupled model of the growth and decay of the Northern Hemisphere ice sheets was used to simulate glacial runoff at 100-year time steps during the last glacial cycle (130 ka to the present). The glacially derived fluxes of major cations, anions and Si over the glaciation were estimated from the product of the glacial runoff and the representative glacial concentration. A second estimate was obtained from the product of the glacial runoff and a realistic upper limit for glacial solute concentrations derived from theoretical considerations. The fluxes over the last glacial cycle are usually less than a few percent of current riverine solute fluxes to the oceans. The glacial fluxes were used to provide input to an oceanic carbon cycling model that also calculates changes in atmospheric CO₂. The potential change in atmospheric CO₂ concentrations over the last glacial cycle that arise from perturbations in glacial solute fluxes are insignificant, being <1 ppm.