High‐frequency logging technologies reveal state‐dependent hyporheic process dynamics: implications for hydroecological studies     

I. A. Malcolm  C. Soulsby  A. F. Youngson 《水文研究》2006,20(3):615-622

This paper presents a novel method for assessing hyporheic water quality dynamics using advances in sensor technology. High‐resolution (15 min) dissolved oxygen (DO) and hydraulic head data were combined to assess groundwater–surface water (GW–SW) interactions in the hyporheic zone. DO concentrations varied at fine temporal and spatial scales, depending on the relative contributions of GW and SW. The effect of sample frequency on observed patterns of variability was assessed with reference to studies of the ecology of salmon spawning habitat. Conventional approaches fail to capture the full range of temporal variability in hyporheic water quality and demonstrate the need to reassess the interpretations of previous studies of the hyporheic zone. © Crown Copyright 2006. Reproduced with the permission of Her Majesty's Stationery Office. Published by John Wiley & Sons, Ltd.  相似文献   

Lyman-break galaxies at z∼ 5 – I. First significant stellar mass assembly in galaxies that are not simply z∼ 3 LBGs at higher redshift     

Aprajita Verma  Matthew D. Lehnert †  Natascha M. Förster Schreiber  Malcolm N. Bremer  Laura Douglas 《Monthly notices of the Royal Astronomical Society》2007,377(3):1024-1042

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Importance of oceanic resolution and mean state on the extra-tropical response to El Niño in a matrix of coupled models     

Andrew Dawson  Adrian J. Matthews  David P. Stevens  Malcolm J. Roberts  Pier Luigi Vidale 《Climate Dynamics》2013,41(5-6):1439-1452

The extra-tropical response to El Niño in configurations of a coupled model with increased horizontal resolution in the oceanic component is shown to be more realistic than in configurations with a low resolution oceanic component. This general conclusion is independent of the atmospheric resolution. Resolving small-scale processes in the ocean produces a more realistic oceanic mean state, with a reduced cold tongue bias, which in turn allows the atmospheric model component to be forced more realistically. A realistic atmospheric basic state is critical in order to represent Rossby wave propagation in response to El Niño, and hence the extra-tropical response to El Niño. Through the use of high and low resolution configurations of the forced atmospheric-only model component we show that, in isolation, atmospheric resolution does not significantly affect the simulation of the extra-tropical response to El Niño. It is demonstrated, through perturbations to the SST forcing of the atmospheric model component, that biases in the climatological SST field typical of coupled model configurations with low oceanic resolution can account for the erroneous atmospheric basic state seen in these coupled model configurations. These results highlight the importance of resolving small-scale oceanic processes in producing a realistic large-scale mean climate in coupled models, and suggest that it might may be possible to “squeeze out” valuable extra performance from coupled models through increases to oceanic resolution alone.  相似文献   

The global distribution of seamounts based on 30 arc seconds bathymetry data     

Chris Yesson  Malcolm R. ClarkMichelle L. Taylor  Alex D. Rogers 《Deep Sea Research Part I: Oceanographic Research Papers》2011,58(4):442-453

Seamounts and knolls are ‘undersea mountains’, the former rising more than 1000 m from the seafloor. These features provide important habitats for aquatic predators, demersal deep-sea fish and benthic invertebrates. However most seamounts have not been surveyed and their numbers and locations are not well known. Previous efforts to locate and quantify seamounts have used relatively coarse bathymetry grids. Here we use global bathymetric data at 30 arc-sec resolution to identify seamounts and knolls. We identify 33,452 seamounts and 138,412 knolls, representing the largest global set of identified seamounts and knolls to date. We compare estimated seamount numbers, locations, and depths with validation sets of seamount data from New Zealand and Azores. This comparison indicates the method we apply finds 94% of seamounts, but may overestimate seamount numbers along ridges and in areas where faulting and seafloor spreading creates highly complex topography. The seamounts and knolls identified herein are significantly geographically biased towards areas surveyed with ship-based soundings. As only 6.5% of the ocean floor has been surveyed with soundings it is likely that new seamounts will be uncovered as surveying improves. Seamount habitats constitute approximately 4.7% of the ocean floor, whilst knolls cover 16.3%. Regional distribution of these features is examined, and we find a disproportionate number of productive knolls, with a summit depth of <1.5 km, located in the Southern Ocean. Less than 2% of seamounts are within marine protected areas and the majority of these are located within exclusive economic zones with few on the High Seas. The database of seamounts and knolls resulting from this study will be a useful resource for researchers and conservation planners.  相似文献   

Editorial     

Malcolm G. Anderson  Des E. Walling 《水文研究》1993,7(1):i-i

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The gold-in-calcrete anomaly at the ET gold prospect,Gawler Craton,South Australia     

Mel Lintern  Malcolm Sheard  Nicky Buller 《Applied Geochemistry》2011,26(12):2027-2043

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Is Ocean Acidification an Open-Ocean Syndrome? Understanding Anthropogenic Impacts on Seawater pH   总被引：2，自引：0，他引：2  

Carlos M. Duarte  Iris E. Hendriks  Tommy S. Moore  Ylva S. Olsen  Alexandra Steckbauer  Laura Ramajo  Jacob Carstensen  Julie A. Trotter  Malcolm McCulloch 《Estuaries and Coasts》2013,36(2):221-236

Ocean acidification due to anthropogenic CO₂ emissions is a dominant driver of long-term changes in pH in the open ocean, raising concern for the future of calcifying organisms, many of which are present in coastal habitats. However, changes in pH in coastal ecosystems result from a multitude of drivers, including impacts from watershed processes, nutrient inputs, and changes in ecosystem structure and metabolism. Interaction between ocean acidification due to anthropogenic CO₂ emissions and the dynamic regional to local drivers of coastal ecosystems have resulted in complex regulation of pH in coastal waters. Changes in the watershed can, for example, lead to changes in alkalinity and CO₂ fluxes that, together with metabolic processes and oceanic dynamics, yield high-magnitude decadal changes of up to 0.5 units in coastal pH. Metabolism results in strong diel to seasonal fluctuations in pH, with characteristic ranges of 0.3 pH units, with metabolically intense habitats exceeding this range on a daily basis. The intense variability and multiple, complex controls on pH implies that the concept of ocean acidification due to anthropogenic CO₂ emissions cannot be transposed to coastal ecosystems directly. Furthermore, in coastal ecosystems, the detection of trends towards acidification is not trivial and the attribution of these changes to anthropogenic CO₂ emissions is even more problematic. Coastal ecosystems may show acidification or basification, depending on the balance between the invasion of coastal waters by anthropogenic CO₂, watershed export of alkalinity, organic matter and CO₂, and changes in the balance between primary production, respiration and calcification rates in response to changes in nutrient inputs and losses of ecosystem components. Hence, we contend that ocean acidification from anthropogenic CO₂ is largely an open-ocean syndrome and that a concept of anthropogenic impacts on marine pH, which is applicable across the entire ocean, from coastal to open-ocean environments, provides a superior framework to consider the multiple components of the anthropogenic perturbation of marine pH trajectories. The concept of anthropogenic impacts on seawater pH acknowledges that a regional focus is necessary to predict future trajectories in the pH of coastal waters and points at opportunities to manage these trajectories locally to conserve coastal organisms vulnerable to ocean acidification.  相似文献   

Five millennia of paleotemperature from tree-rings in the Great Basin,USA     

Matthew W. Salzer  Andrew G. Bunn  Nicholas E. Graham  Malcolm K. Hughes 《Climate Dynamics》2014,42(5-6):1517-1526

The instrumental temperature record is of insufficient length to fully express the natural variability of past temperature. High elevation tree-ring widths from Great Basin bristlecone pine (Pinus longaeva) are a particularly useful proxy to infer temperatures prior to the instrumental record in that the tree-rings are annually dated and extend for millennia. From ring-width measurements integrated with past treeline elevation data we infer decadal- to millennial-scale temperature variability over the past 4,500 years for the Great Basin, USA. We find that twentieth century treeline advances are greater than in at least 4,000 years. There is also evidence for substantial volcanic forcing of climate in the preindustrial record and considerable covariation between high elevation tree-ring widths and temperature estimates from an atmosphere–ocean general circulation model over much of the last millennium. A long-term temperature decline of ~?1.1 °C since the mid-Holocene underlies substantial volcanic forcing of climate in the preindustrial record.  相似文献   

A deterministic river temperature model to prioritize management of riparian woodlands to reduce summer maximum river temperatures     

Faye L. Jackson  David M. Hannah  Valerie Ouellet  Iain A. Malcolm 《水文研究》2021,35(8):e14314

Increasing river temperatures are a threat to cold water species including ecologically and economically important freshwater fish, such as Atlantic salmon. In 2018, ca. 70% of Scottish rivers experienced temperatures which cause thermal stress in juvenile salmon, a situation expected to become increasingly common under climate change. Management of riparian woodlands is proven to protect cold water habitats. However, creation of new riparian woodlands can be costly and logistically challenging. It is therefore important that planting can be prioritized to areas where it is most needed and can be most effective in reducing river temperatures. The effects of riparian woodland on channel shading depend on complex interactions between channel width, orientation, aspect, gradient, tree height and solar geometry. Subsequent effects on river temperature are influenced by water volume and residence time. This study developed a deterministic river temperature model, driven by energy gains from solar radiation that are modified by water volume and residence time. The resulting output is a planting prioritization metric that compares potential warming between scenarios with and without riparian woodland. The prioritization metric has a reach scale spatial resolution, but can be mapped at large spatial scales using information obtained from a digital river network. The results indicate that water volume and residence time, as represented by river order, are a dominant control on the effectiveness of riparian woodland in reducing river temperature. Ignoring these effects could result in a sub-optimal prioritization process and inappropriate resource allocation. Within river order, effectiveness of riparian shading depends on interactions between channel and landscape characteristics. Given the complexity and interacting nature of controls, the use of simple universal planting criteria is not appropriate. Instead, managers should be provided with maps that translate complex models into readily useable tools to prioritize riparian tree planting to mitigate the impacts of high river temperatures.  相似文献   

Assessing the potential of drone‐based thermal infrared imagery for quantifying river temperature heterogeneity     

Stephen J. Dugdale  Christa A. Kelleher  Iain A. Malcolm  Samuel Caldwell  David M. Hannah 《水文研究》2019,33(7):1152-1163

Climate change is altering river temperature regimes, modifying the dynamics of temperature‐sensitive fishes. The ability to map river temperature is therefore important for understanding the impacts of future warming. Thermal infrared (TIR) remote sensing has proven effective for river temperature mapping, but TIR surveys of rivers remain expensive. Recent drone‐based TIR systems present a potential solution to this problem. However, information regarding the utility of these miniaturised systems for surveying rivers is limited. Here, we present the results of several drone‐based TIR surveys conducted with a view to understanding their suitability for characterising river temperature heterogeneity. We find that drone‐based TIR data are able to clearly reveal the location and extent of discrete thermal inputs to rivers, but thermal imagery suffers from temperature drift‐induced bias, which prevents the extraction of accurate temperature data. Statistical analysis of the causes of this drift reveals that drone flight characteristics and environmental conditions at the time of acquisition explain ~66% of the variance in TIR sensor drift. These results shed important light on the factors influencing drone‐based TIR data quality and suggest that further technological development is required to enable the extraction of robust river temperature data. Nonetheless, this technology represents a promising approach for augmenting in situ sensor capabilities and improved quantification of advective inputs to rivers at intermediate spatial scales between point measurements and “conventional” airborne or satellite remote sensing.  相似文献