Fine scale mapping of fractional tree canopy cover to support river basin management

Management of water, regionally, nationally and globally will continue to be a priority and complex undertaking. In riverine systems, biotic components like flora and fauna play critical roles in filtering water so it is available for human use and consumption. Preservation of ecosystems and associated ecosystem functions is therefore vital. In highly regulated large river basins, natural ecosystems are often supported through provision of environmental flows. Flow delivery, however, should be underpinned by rigorous monitoring to identify and prioritise biotic water requirements. Currently, large-scale monitoring solutions are scaled from remote sensing data via measurement of field evapotranspiration for woody tree vegetation species. However, as there is generally a mismatch between field data collection area and remote sensing pixel size, new methods are required to proportion tree evapotranspiration based on tree fractional canopy area per pixel. We present a novel method to derive tree fractional canopy cover (FTCC) at 20 m resolution in semi-arid and arid floodplain areas. The method employs LiDAR as a canopy area field measurement proxy (10 m resolution). We used Sentinel-1 and Sentinel-2 (radar and multispectral imagery) in a Random Forest analysis, undertaken to develop a predictive FTCC model trained using LiDAR for two regions in the Murray–Darling Basin. A predictor model combining the results of both regions was able to explain between 71%–85% of FTCC variation when compared to LiDAR FTCC when output in 10% increments. Development of this method underpins the advancement of woody vegetation monitoring to inform environmental flow management in the Murray–Darling Basin. The method and fine scale outputs will also be of value to other catchment management concerns such as altered catchment water yields related to bushfires and as such has application to water management worldwide.     

δ53Cr values of catchment runoff exhibit seasonality regardless of bedrock Cr concentrations: Role of periodically changing chromium export fluxes

One pre-requisite for the construction of a global chromium isotope mass balance is detailed understanding of Cr isotope systematics in the critical zone where redox-processes can modify the isotope signature of geogenic Cr input into the hydrosphere. A Cr isotope inventory of bedrock, soil, and runoff was performed in a Central European headwater catchment underlain by amphibolite, situated in the vicinity of two previously studied catchments underlain by different bedrock types (serpentinite and leucogranite). Fresh bedrock in the amphibolite catchment NAZ contained ~300 mg/kg Cr, serpentinite at PLB contained ~800 mg/kg Cr, and leucogranite at LYS contained ~2 mg/kg Cr. Monthly hydrochemical monitoring at all three sites revealed higher Cr(VI) export fluxes in winter than in summer. NAZ was characterized by a distinct seasonality in the δ⁵³Cr values, with minima during winter/spring snowmelts (−0.35‰) and maxima during dry summers (0.40‰). Similar seasonality in δ⁵³Cr values had been reported from PLB and LYS. Bedrock at all three sites had similar Cr isotope composition close to −0.10‰, a value indistinguishable from the δ⁵³Cr value of bulk silicate Earth (BSE). Positive mean δ⁵³Cr value of NAZ runoff indicated Cr-isotope fractionations during weathering of geogenic Cr(III), combined with adsorption of the resulting Cr(VI) on soil particles during pedogenesis. However, the mass-weighted mean δ⁵³Cr of NAZ runoff was lower (−0.08‰), indistinguishable from the Cr isotope signature of bedrock. The same pattern of lower mass-weighted mean δ⁵³Cr values of runoff, compared to arithmetic mean δ⁵³Cr values of runoff, were observed also at PLB and LYS. We suggest that elevated Cr runoff fluxes in winter remove some of the residual isotopically light Cr that accumulated in the soil during summer. Seasonality in runoff δ⁵³Cr values appears to be a relatively widespread phenomenon, de-coupled from Cr availability for chemical weathering.     

Rapid simulation of multiple radially growing hydraulic fractures using an energy‐based approach

The goal of hydraulic fracturing stimulation of horizontal wells is typically to generate uniform, simultaneously growing hydraulic fractures from 3 to 6 initiation/entry sites that are spaced within a certain interval of the wellbore comprising a so‐called stage. Because of the stress interaction among growing hydraulic fractures, however, it is hard to attain simultaneous growth of all hydraulic fractures. While models have been proven useful for devising mitigation strategies of these so‐called stress‐shadow effects, the required simulations are so computationally expensive that optimization is possible only in the simplest cases. Here, we present an approximate (energy‐based) model capable of running an entire simulation in 1–2s, which is about one million times faster than the benchmark model. The approach is built on asymptotic solutions to approximate growth of radial hydraulic fractures, a far field approximation for the stress shadow interactions among growing hydraulic fractures, and coupling the effect of the stress shadow to fracture growth via a global energy balance equation. We show very close agreement in predictions of the lengths of each fracture in the array between the approximate model and the benchmark model, thus verifying that the new approximate model is useful for optimization of hydraulic fracture design. Copyright © 2015 John Wiley & Sons, Ltd.     

Prediction of rock alteration patterns: A potential tool in mineral exploration

Hydrothermal alteration of a quartz‐K‐feldspar rock is simulated numerically by coupling fluid flow and chemical reactions. Introduction of CO₂ gas generates an acidic fluid and produces secondary quartz, muscovite and/or pyrophyllite at constant temperature and pressure of 300°C and 200 MPa. The precipitation and/or dissolution of the secondary minerals is controlled by either mass‐action relations or rate laws. In our simulations the mass of the primary elements are conserved and the mass‐balance equations are solved sequentially using an implicit scheme in a finite‐element code. The pore‐fluid velocity is assumed to be constant. The change of rock volume due to the dissolution or precipitation of the minerals, which is directly related to their molar volume, is taken into account. Feedback into the rock porosity and the reaction rates is included in the model. The model produces zones of pyrophyllite quartz and muscovite due to the dissolution of K‐feldspar. Our model simulates, in a simplified way, the acid‐induced alteration assemblages observed in various guises in many significant mineral deposits. The particular aluminosilicate minerals produced in these experiments are associated with the gold deposits of the Witwatersrand Basin.     

Estimation of instantaneous peak flows from maximum mean daily flows using the HBV hydrological model

The record length and quality of instantaneous peak flows (IPFs) have a great influence on flood design, but these high resolution flow data are not always available. The primary aim of this study is to compare different strategies to derive frequency distributions of IPFs using the Hydrologiska Byråns Vattenbalansavdelning (HBV) hydrologic model. The model is operated on a daily and an hourly time step for 18 catchments in the Aller‐Leine basin, Germany. Subsequently, general extreme value (GEV) distributions are fitted to the simulated annual series of daily and hourly extreme flows. The resulting maximum mean daily flow (MDF) quantiles from daily simulations are transferred into IPF quantiles using a multiple regression model, which enables a direct comparison with the simulated hourly quantiles. As long climate records with a high temporal resolution are not available, the hourly simulations require a disaggregation of the daily rainfall. Additionally, two calibrations strategies are applied: (1) a calibration on flow statistics; (2) a calibration on hydrographs. The results show that: (1) the multiple regression model is capable of predicting IPFs with the simulated MDFs; (2) both daily simulations with post‐correction of flows and hourly simulations with pre‐processing of precipitation enable a reasonable estimation of IPFs; (3) the best results are achieved using disaggregated rainfall for hourly modelling with calibration on flow statistics; and (4) if the IPF observations are not sufficient for model calibration on flow statistics, the transfer of MDFs via multiple regressions is a good alternative for estimating IPFs. Copyright © 2015 John Wiley & Sons, Ltd.     

Variable water‐saturated areas and streamflow generation in the small Ringelbach catchment (Vosges Mountains,France): the master recession curve as an equilibrium curve for interactions between atmosphere,surface and ground waters

In the small Ringelbach research catchment, where studies on the water cycle components in a granitic mountainous environment have been conducted since 1976, the water‐saturated areas that are hydraulically connected to the outlet play a major role in the streamflow generation, as it is here that complex interactions between atmosphere, surface and ground waters take place. During baseflow recession periods, which may last several months between two groundwater recharge events, the atmospheric inputs of water and energy on these contributing areas only explain the streamflow fluctuations observed around the master recession curve, which defines the groundwater contribution: fluctuating above it in the case of precipitation input on these areas, below it in the case of evaporation output from these areas. Streamflow may therefore largely deviate from the master recession curve in the case of long, hot, dry spells. Detailed mapping has shown that their variable extent is well related to baseflow by a loglinear curve. On the other hand, a synthetic master recession curve, well fitted by a second‐order hyperbolic function, has been obtained from numerous pure recession periods. Both based on these two curves, a simple procedure and a simple model have been used to (i) validate the hypothesis that the connected saturated areas are the only permanent variable contributing areas and (ii) simulate the daily streamflow volumes over long baseflow recession periods by a water balance of the aquifer below these areas only. The storm runoff ratio for small to moderate rainfall events is indeed corresponding to the catchment saturated fraction at that time. The volume of daily streamflow oscillations is indeed corresponding to the evaporation at the potential rate from the saturated areas only. In both cases, streamflow naturally tends towards the master recession curve after the end of any atmospheric perturbation. Introducing these findings into TOPMODEL led to significantly improved simulation results during baseflow recession periods. The master recession curve may therefore be considered as a dynamic equilibrium curve. Together with the relationship between saturated extent and baseflow, it provides the main characteristics necessary to understand and model the interactions at this complex interface and the resulting daily streamflow variations during baseflow recession periods in this type of catchment. Copyright © 2016 John Wiley & Sons, Ltd.     

Effect of bedrock flow on catchment rainfall‐runoff characteristics and the water balance in forested catchments in Tanzawa Mountains,Japan

In this paper, we examined the role of bedrock groundwater discharge and recharge on the water balance and runoff characteristics in forested headwater catchments. Using rigorous observations of catchment precipitation, discharge and streamwater chemistry, we quantified net bedrock flow rates and contributions to streamwater runoff and the water balance in three forested catchments (second‐order to third‐order catchments) underlain by uniform bedrock in Japan. We found that annual rainfall in 2010 was 3130 mm. In the same period, annual discharge in the three catchments varied from 1800 to 3900 mm/year. Annual net bedrock flow rates estimated by the chloride mass balance method at each catchment ranged from ?1600 to 700 mm/year. The net bedrock flow rates were substantially different in the second‐order and third‐order catchments. During baseflow, discharge from the three catchments was significantly different; conversely, peak flows during large storm events and direct runoff ratios were not significantly different. These results suggest that differences in baseflow discharge rates, which are affected by bedrock flow and intercatchment groundwater transfer, result in the differences in water balance among the catchments. This study also suggests that in these second‐order to third‐order catchments, the drainage area during baseflow varies because of differences between the bedrock drainage area and surface drainage area, but that the effective drainage area during storm flow approaches the surface drainage area. Copyright © 2012 John Wiley & Sons, Ltd.     

地壳均衡理论及其在构造地貌研究中的应用

地壳均衡是地球科学的一个基本概念,其理论基础为“轻地壳（密度较小）漂浮在重地幔（较稠密）之上”。均衡理论（如冲压假说、弹性板理论等）和模型（如Airy模型、Pratt模型及弹性板模型等）的产生及发展对研究岩石圈流变学性质、圈层相互作用及造山作用等地球动力学过程有着重要意义。本文总结了相关均衡理论、模型及计算方法,并结合其在不同空间尺度构造地貌现象研究中的运用,包括：① 冰川均衡调整研究中不同模型的优化及其对全球海平面变化的指示意义、② 阐明海山洋岛发育过程及其制约因素、③ 利用弹性板模型重建山脉隆升和盆地挠曲沉降史并进一步探讨二者之间的相互作用、④ 通过研究变形湖滨线有效地约束地球的相关物理参数、⑤ 建立河流三角洲发育特征模型并服务于现代社会经济、⑥ 揭示水库蓄水导致的地壳挠曲变形与浅部地质灾害发育的关系及 ⑦ 同震滑坡对局部地貌改造的影响,讨论并展望了未来地壳均衡在构造地貌学领域的发展方向,即结合高精度大地测量技术与地质年代学方法,定量地解决构造地貌研究中的关键问题,更全面、系统地了解地表过程、地球深部过程与动力学和地球圈层之间的相互作用。     

‘It׳s part of me’; understanding the values,images and principles of coastal users and their influence on the social acceptability of MPAs

Improving the social acceptability or ‘social licence’ of Marine Protected Areas (MPAs) is a key challenge facing countries all around the world. As the world moves slowly towards the establishment of a global network of MPAs, it is increasingly apparent that a greater understanding of social responses to MPAs is required, given they are often met with resistance from local communities. A series of in-depth, semi structured interviews were conducted across coastal users in New South Wales, Australia, including surfers, recreational fishers, professional fishers, spearfishers, walkers, divers, snorkellers, kayakers and other community members. The research identified the values, images and principles at work amongst coastal users to determine the dominant ‘cultural models’ within the community and how these models influenced attitudes towards MPAs. This research indicates that traditional consultation models may not be sufficient to address the full spectrum of community needs, and in fact suggests the need to re-conceive the make -up of ‘the community’ itself. In the context of MPA planning ‘the community’ is not an amalgamation of a range of homogenous stakeholder groups but instead a diverse and complex mix of identities and value systems which are not confined to particular interest groups. Incorporating consideration of the diverse range of values, images and principles found within and across stakeholder groups will require new and innovative approaches to participation and management.     

Making modelling count - increasing the contribution of shelf-seas community and ecosystem models to policy development and management

Marine legislation is becoming more complex and marine ecosystem-based management is specified in national and regional legislative frameworks. Shelf-seas community and ecosystem models (hereafter termed ecosystem models) are central to the delivery of ecosystem-based management, but there is limited uptake and use of model products by decision makers in Europe and the UK in comparison with other countries. In this study, the challenges to the uptake and use of ecosystem models in support of marine environmental management are assessed using the UK capability as an example. The UK has a broad capability in marine ecosystem modelling, with at least 14 different models that support management, but few examples exist of ecosystem modelling that underpin policy or management decisions. To improve understanding of policy and management issues that can be addressed using ecosystem models, a workshop was convened that brought together advisors, assessors, biologists, social scientists, economists, modellers, statisticians, policy makers, and funders. Some policy requirements were identified that can be addressed without further model development including: attribution of environmental change to underlying drivers, integration of models and observations to develop more efficient monitoring programmes, assessment of indicator performance for different management goals, and the costs and benefit of legislation. Multi-model ensembles are being developed in cases where many models exist, but model structures are very diverse making a standardised approach of combining outputs a significant challenge, and there is a need for new methodologies for describing, analysing, and visualising uncertainties. A stronger link to social and economic systems is needed to increase the range of policy-related questions that can be addressed. It is also important to improve communication between policy and modelling communities so that there is a shared understanding of the strengths and limitations of ecosystem models.