Alistair Borthwick

Recent changes of water discharge and sediment load in the Yellow River basin, China

The Yellow River basin contributes approximately 6% of the sediment load from all river systems globally, and the annual runoff directly supports 12% of the Chinese population. As a result, describing and understanding recent variations of water discharge and sediment load under global change scenarios are of considerable importance. The present study considers the annual hydrologic series of the water discharge and sediment load of the Yellow River basin obtained from 15 gauging stations (10 mainstream, 5 tributaries). The Mann-Kendall test method was adopted to detect both gradual and abrupt change of hydrological series since the 1950s. With the exception of the area draining to the Upper Tangnaihai station, results indicate that both water discharge and sediment load have decreased significantly (p<0.05). The declining trend is greater with distance downstream, and drainage area has a significant positive effect on the rate of decline. It is suggested that the abrupt change of the water discharge from the late 1980s to the early 1990s arose from human extraction, and that the abrupt change in sediment load was linked to disturbance from reservoir construction.

Adsorption mechanisms of thallium(I) and thallium(III) by titanate nanotubes: Ion-exchange and co-precipitation

Hydrothermally-synthesized titanate nanotubes (TNTs) are found to be excellent at adsorption of highly toxic thallium ions. Uptake of both thallium ions is very fast in the first 10 min. The adsorption isotherm of Tl(I) follows the Langmuir model with maximum adsorption capacity of 709.2 mg g(-1). Ion-exchange between Tl(+) and Na(+) in the interlayers of TNTs is the primary mechanism for Tl(I) adsorption. Excess Tl(+) undergoes further exchange with H(+). The adsorption mechanism is different for Tl(III), and involves either ion-exchange with Na(+) at low Tl(III) concentration or co-precipitation in the form of Tl(OH)3 with TNTs at high Tl(III) concentration. XPS analysis indicates that the ion-exchange process does not change the basic skeleton [TiO6] of TNTs, whereas Tl(OH)3 precipitation increases the percentage composition of O within the surface hydroxyl groups. XRD analysis also confirms the formation of Tl(OH)3 on TNTs at high initial concentration of Tl(III). Coexisting Na(+) and Ca(2+) hardly inhibit adsorption, indicating good selectivity for thallium by TNTs. Furthermore, TNTs can be reused efficiently after HNO3 desorption and NaOH regeneration, making TNTs a promising material to remove thallium from wastewaters. This study also confirms that co-precipitation is another important adsorption mechanism for easily hydrolytic metals by TNTs.

Simultaneous removal of Cr(VI) and 4-chlorophenol through photocatalysis by a novel anatase/titanate nanosheet composite: Synergetic promotion effect and autosynchronous doping.

Clean-up of wastewaters with coexisting heavy metals and organic contaminants is a huge issue worldwide. In this study, a novel anatase/titanate nanosheet composite material (labeled as TNS) synthesized through a one-step hydrothermal reaction was demonstrated to achieve the goal of simultaneous removal of Cr(VI) and 4-cholophenol (4-CP) from water. TEM and XRD analyses indicated the TNS was a nano-composite of anatase and titanate, with anatase acting as the primary photocatalysis center and titanate as the main adsorption site. Enhanced photocatalytic removal of co-existent Cr(VI) and 4-CP was observed in binary systems, with apparent rate constants (k1) for photocatalytic reactions of Cr(VI) and 4-CP about 3.1 and 2.6 times of that for single systems. In addition, over 99% of Cr(VI) and 4-CP was removed within 120min through photocatalysis by TNS at pH 7 in the binary system. Mechanisms for enhanced photocatalytic efficiency in the binary system are identified as: (1) a synergetic effect on the photo-reduction of Cr(VI) and photo-oxidation of 4-CP due to efficient separation of electron-hole pairs, and (2) autosynchronous doping because of reduced Cr(III) adsorption onto TNS. Furthermore, TNS could be efficiently reused after a simple acid-base treatment.

Marine Renewable Energy Seascape

ABSTRACT Energy production based on fossil fuel reserves is largely responsible for carbon emissions, and hence global warming. The planet needs concerted action to reduce fossil fuel usage and to implement carbon mitigation measures. Ocean energy has huge potential, but there are major interdisciplinary problems to be overcome regarding technology, cost reduction, investment, environmental impact, governance, and so forth. This article briefly reviews ocean energy production from offshore wind, tidal stream, ocean current, tidal range, wave, thermal, salinity gradients, and biomass sources. Future areas of research and development are outlined that could make exploitation of the marine renewable energy (MRE) seascape a viable proposition; these areas include energy storage, advanced materials, robotics, and informatics. The article concludes with a sustainability perspective on the MRE seascape encompassing ethics, legislation, the regulatory environment, governance and consenting, economic, social, and environmental constraints. A new generation of engineers is needed with the ingenuity and spirit of adventure to meet the global challenge posed by MRE.

Lateral transport of soil carbon and land−atmosphere CO2 flux induced by water erosion in China

Significance The role of soil erosion as a net sink or source of atmospheric CO2 remains highly debated. This work quantifies national-scale land−atmosphere CO2 fluxes induced by soil erosion. Severe water erosion in China has caused displacement of 180 ± 80 Mt C⋅y-1 of soil organic carbon during the last two decades, and the consequent land−atmosphere CO2 flux from water erosion is a net CO2 sink of 45 ± 25 Mt C⋅y-1, equivalent to 8–37% of the terrestrial carbon sink previously assessed in China. This closes an important gap concerning large-scale estimation of lateral and vertical CO2 fluxes from water erosion and highlights the importance of reducing uncertainty in assessing terrestrial carbon balance. Soil erosion by water impacts soil organic carbon stocks and alters CO2 fluxes exchanged with the atmosphere. The role of erosion as a net sink or source of atmospheric CO2 remains highly debated, and little information is available at scales larger than small catchments or regions. This study attempts to quantify the lateral transport of soil carbon and consequent land−atmosphere CO2 fluxes at the scale of China, where severe erosion has occurred for several decades. Based on the distribution of soil erosion rates derived from detailed national surveys and soil carbon inventories, here we show that water erosion in China displaced 180 ± 80 Mt C⋅y−1 of soil organic carbon during the last two decades, and this resulted a net land sink for atmospheric CO2 of 45 ± 25 Mt C⋅y−1, equivalent to 8–37% of the terrestrial carbon sink previously assessed in China. Interestingly, the “hotspots,” largely distributed in mountainous regions in the most intensive sink areas (>40 g C⋅m−2⋅y−1), occupy only 1.5% of the total area suffering water erosion, but contribute 19.3% to the national erosion-induced CO2 sink. The erosion-induced CO2 sink underwent a remarkable reduction of about 16% from the middle 1990s to the early 2010s, due to diminishing erosion after the implementation of large-scale soil conservation programs. These findings demonstrate the necessity of including erosion-induced CO2 in the terrestrial budget, hence reducing the level of uncertainty.

Microbial reduction and precipitation of vanadium (V) in groundwater by immobilized mixed anaerobic culture

Vanadium is an important contaminant impacted by natural and industrial activities. Vanadium (V) reduction efficiency as high as 87.0% was achieved by employing immobilized mixed anaerobic sludge as inoculated seed within 12h operation, while V(IV) was the main reduction product which precipitated instantly. Increasing initial V(V) concentration resulted in the decrease of V(V) removal efficiency, while this index increased first and then decreased with the increase of initial COD concentration, pH and conductivity. High-throughput 16S rRNA gene pyrosequencing analysis indicated the decreased microbial diversity. V(V) reduction was realized through dissimilatory reduction process by significantly enhanced Lactococcus and Enterobacter with oxidation of lactic and acetic acids from fermentative microorganisms such as the enriched Paludibacter and the newly appeared Acetobacterium, Oscillibacter. This study is helpful to detect new functional species for V(V) reduction and constitutes a step ahead in developing in situ bioremediations of vanadium contamination.

An electrical analogy for the Pentland Firth tidal stream power resource

Several locations in the Pentland Firth, UK, have been earmarked for the deployment of separate farms of tidal turbines. However, recent numerical modelling suggests that these farms will be inter-dependent and that they must work together to optimize their collective performance. To explain this inter-dependence, in this paper we develop an electrical circuit analogy to describe flow through the Pentland Firth, in which parallel connections in the circuit represent different sub-channels formed by the islands of Swona, Stroma and the Pentland Skerries. The analogy is introduced in stages, beginning with turbines placed in a single channel, then turbines placed in a sub-channel connected in parallel to another sub-channel, and finally more complicated arrangements, in which turbines are installed both in parallel and in series within a multiply connected channel. The analogy leads to a general formula to predict the tidal power potential of turbines placed in a sub-channel connected in parallel to another sub-channel, and a predictive model for more complicated multiply connected channel arrangements. Power estimates made using the formula and predictive model (which may be applied using only measurements of the undisturbed natural tidal hydrodynamics) are shown to agree well with numerical model predictions for the Pentland Firth, providing useful insight into how to best develop the resource.

Life cycle assessment of the environmental performance of conventional and organic methods of open field pepper cultivation system

PurposeAs the scale of the organic cultivation sector keeps increasing, there is growing demand for reliable data on organic agriculture and its effect on the environment. Conventional agriculture uses chemical fertilizers and pesticides, whilst organic cultivation mainly relies on crop rotation and organic fertilizers. The aim of this work is to quantify and compare the environmental sustainability of typical conventional and organic pepper cultivation systems.MethodsTwo open field pepper cultivations, both located in the Anthemountas basin, Northern Greece, are selected as case studies. Life cycle assessment (LCA) is used to quantify the overall environmental footprint and identify particular environmental weaknesses (i.e. unsustainable practices) of each cultivation system. Results are analysed at both midpoint and endpoint levels in order to obtain a comprehensive overview of thexa0environmental sustainability of each system. Attributional LCA (ALCA) is employed to identify emissions associated with the life cycles of the two systems. Results are presented for problem-oriented (midpoint) and damage-oriented (endpoint) approaches, using ReCiPe impact assessment.Results and discussionAt midpoint level, conventional cultivation exhibits about threefold higher environmental impact on freshwater eutrophication, than organic cultivation. This arises from the extensive use of nitrogen and phosphorus-based fertilizers, with consequent direct emissions to the environment. The remaining impact categories are mainly affected by irrigation, with associated indirect emissions linked to electricity production. At endpoint level, the main hotspots identified for conventional cultivation are irrigation and fertilizing, due to intensive use of chemical fertilizers and (to a lesser degree) pesticides. For organic pepper cultivation, the main environmental hotspots are irrigation, machinery use, and manure loading and spreading processes. Of these, the highest score for irrigation derives from the heavy electricity consumption required for groundwater pumping associated with the fossil-fuel-dependent Greek electricity mix.ConclusionsOrganic and conventional cultivation systems have similar total environmental impacts per unit of product, with organic cultivation achieving lower environmental impacts in ‘freshwater eutrophication’, ‘climate change’, ‘terrestrial acidification’ and ‘marine eutrophication’ categories. Conventional cultivation has a significantly greater effect on the freshwater eutrophication impact category, due to phosphate emissions arising from application of chemical fertilizers.

Tidal stream power in the Pentland Firth – long-term variability, multiple constituents and capacity factor

The Pentland Firth, Scotland, is one of the World’s prime locations for the eventual installation of large farms of tidal stream turbines. This paper seeks to improve the upper bound estimate of available power output obtained by Adcock et al. (2013) who used a depth-integrated numerical model of the region containing the Pentland Firth with the outer boundary forced solely by M2 and S2 tidal constituents. Herein, the analysis is extended to include six additional tidal constituents and the model run for 11.5 years, more than half of the 18.6-year lunar nodal cycle, to allow variations over this to be analysed. The consequent increase in available power is estimated, and the variation in power output over an 11-year period is examined. Although further power could theoretically be extracted from the additional six tidal constituents, this would require the tidal turbine farm to have such a low capacity factor that it would probably be economically unfeasible.

A Hybrid Wavelet de-noising and Rank-Set Pair Analysis approach for forecasting hydro-meteorological time series

Abstract Accurate, fast forecasting of hydro‐meteorological time series is presently a major challenge in drought and flood mitigation. This paper proposes a hybrid approach, wavelet de‐noising (WD) and Rank‐Set Pair Analysis (RSPA), that takes full advantage of a combination of the two approaches to improve forecasts of hydro‐meteorological time series. WD allows decomposition and reconstruction of a time series by the wavelet transform, and hence separation of the noise from the original series. RSPA, a more reliable and efficient version of Set Pair Analysis, is integrated with WD to form the hybrid WD‐RSPA approach. Two types of hydro‐meteorological data sets with different characteristics and different levels of human influences at some representative stations are used to illustrate the WD‐RSPA approach. The approach is also compared to three other generic methods: the conventional Auto Regressive Integrated Moving Average (ARIMA) method, Artificial Neural Networks (ANNs) (BP‐error Back Propagation, MLP‐Multilayer Perceptron and RBF‐Radial Basis Function), and RSPA alone. Nine error metrics are used to evaluate the model performance. Compared to three other generic methods, the results generated by WD‐REPA model presented invariably smaller error measures which means the forecasting capability of the WD‐REPA model is better than other models. The results show that WD‐RSPA is accurate, feasible, and effective. In particular, WD‐RSPA is found to be the best among the various generic methods compared in this paper, even when the extreme events are included within a time series. HighlightsA new hybrid approach is proposed to improve forecasts of hydro‐meteorological time series.Rank‐Set Pair Analysis combined with wavelet de‐noising markedly improves forecasting accuracy.The performance of the proposed approach proves best among its present competitors even when the extreme value occurs.