An expanded surface-water palaeotemperature inference model for use with fossil midges from eastern Canada

Using an expanded surface sample data set, representing lakes distributed across a transect from southernmost Canada to the Canadian High Arctic, a revised midge-palaeotemperature inference model was developed for eastern Canada. Modelling trials with weighted averaging (with classical and inverse deshrinking; with and without tolerance downweighting) and weighted averaging partial least squares (WA-PLS) regression, with and without square-root transformation of the species data, were used to identify the best model. Comparison of measured and predicted temperatures revealed that a 2 component WA-PLS model for square-root transformed percentage species data provided the model with the highest explained variance (r =0.88) and the lowest error estimate (RMSEP _jack =2.26 °C). Comparison of temperature inferences based on the new and old models indicates that the original model may have seriously under-estimated the magnitude of late-glacial temperature oscillations in Atlantic Canada. The new inferences suggest that summer surface water temperatures in Splan Pond, New Brunswick were approximately 10 to 12 °C immediately following deglaciation and during the Younger Dryas. During the Allerod and early Holocene, surface water temperatures of 20 to 24 °C were attained. The new model thus provides the basis for more accurate palaeotemperature reconstructions throughout easternmost Canada.     

Compartmentalisation and groundwater–surface water interactions in a prospective shale gas basin: Assessment using variance analysis and multivariate statistics on water quality data

An environmental concern with hydraulic fracturing for shale gas is the risk of groundwater and surface water contamination. Assessing this risk partly involves the identification and understanding of groundwater–surface water interactions because potentially contaminating fluids could move from one water body to the other along hydraulic pathways. In this study, we use water quality data from a prospective shale gas basin to determine: if surface water sampling could identify groundwater compartmentalisation by low-permeability faults; and if surface waters interact with groundwater in underlying bedrock formations, thereby indicating hydraulic pathways. Variance analysis showed that bedrock geology was a significant factor influencing surface water quality, indicating regional-scale groundwater–surface water interactions despite the presence of an overlying region-wide layer of superficial deposits averaging 30–40 m thickness. We propose that surface waters interact with a weathered bedrock layer through the complex distribution of glaciofluvial sands and gravels. Principal component analysis showed that surface water compositions were constrained within groundwater end-member compositions. Surface water quality data showed no relationship with groundwater compartmentalisation known to be caused by a major basin fault. Therefore, there was no chemical evidence to suggest that deeper groundwater in this particular area of the prospective basin was reaching the surface in response to compartmentalisation. Consequently, in this case compartmentalisation does not appear to increase the risk of fracking-related contaminants reaching surface waters, although this may differ under different hydrogeological scenarios.     

Time series analysis of the world's longest fluvial nitrate record: evidence for changing states of catchment saturation

Processes that drive the occurrence of nitrate concentrations in surface waters are known to operate over many decades longer than the available observations. This study considers the world's longest water quality record of nitrate concentrations in the River Thames (1868–2009) in order to understand whether the nature of the time series has changed with time and such external drivers as climate change and land use of hydrology. The study considers the linear trend, the seasonality, the memory and the impulsivity relative to river flow of the time series for moving windows of 6 years in length. The study can show that:

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Exploring for heavy minerals on Cape York Peninsula,Queensland, Australia

This paper describes the results of a preliminary study of the heavy mineral (HM) potential of the northwest coast of Cape York Peninsula in far north Queensland that was funded by the Queensland Government's Future Resources Program Industry Priorities Initiative. The study found that the northwest coast may have the potential to host world-class HM deposits. All the essential ingredients in a HM mineral system are present: fertile source rocks, effective transport mechanisms and abundant potential trap sites, particularly along the well-preserved Pleistocene coast.

The source rocks are Proterozoic metamorphic and Paleozoic granitic rocks of the Coen Inlier and Mesozoic sedimentary rocks of the Laura and Carpentaria basins, all of which crop out along the spine of the Peninsula. These rocks were exposed in the early Cenozoic and were vigorously eroded by seasonally active rivers throughout the Quaternary. Most of these rivers are currently carrying HM, and the zircon content in river sediments in the region is comparatively high. It is speculated that in the late Pleistocene HM delivered by rivers to the northwest coast were transported predominantly in a southwesterly direction, and trapped in the swash zone of prograding beaches. It is further speculated that at this time the coastline was deeply embayed with cliffs and headlands formed in bauxite, and that structural trap sites formed on the northeastern side of prominent headlands.

Pleistocene coastal sediments were partially reworked by Holocene coastal processes, and HM liberated by these processes may have been captured by prograding Holocene beach ridges. These Holocene beach ridges are not as extensive as the Pleistocene beach ridges but are more prominent, partly because they are less well vegetated. The Holocene coastline was probably more regular than the Pleistocene coastline, with fewer headlands to create structural traps. The modern coastline is relatively starved of river sediment because the Holocene and Pleistocene coastal sediments act as barriers to river flow.

It is recommended that ongoing exploration for HM in the region should focus on potential trap sites on the Pleistocene coast and that two sites, Vrilya Point and Jackson River, where structural traps may have been formed by coastal promontories, should be priority targets. It is also noted that if the exploration of Cape York Peninsula for HM deposits is to be effective, further research needs to be carried out into the geomorphological evolution of the west coast and, in particular, the role of cyclones in forming HM deposits in tropical climates.     

The fluvial flux of particulate organic matter from the UK: the emission factor of soil erosion

Soil erosion has been identified as a potential global carbon sink since eroded organic matter is replaced at source and eroded material is readily buried. However, this argument has relied on poor estimates of the total fate of in‐transit particulates and could erroneously imply soil erosion could be encouraged to generate carbon stores. These previous estimates have not considered that organic matter can also be released to the atmosphere as a range of greenhouse gases, not only carbon dioxide (CO₂), but also the more powerful greenhouse gases methane (CH₄) and nitrous oxide (N₂O). As soil carbon lost by erosion is only replaced by uptake of CO₂, this could represent a considerable imbalance in greenhouse gas warming potential, even if it is not significant in terms of overall carbon flux. This work therefore considers the flux of particulate organic matter through UK rivers with respect to both carbon fluxes and greenhouse gas emissions. The results show that, although emissions to the atmosphere are dominated by CO₂, there are also considerable fluxes of CH₄ and N₂O. The results suggest that soil erosion is a net source of greenhouse gases with median emission factors of 5.5, 4.4 and 0.3 tonnes CO_2eq/yr for one tonne of fluvial carbon, gross carbon erosion and gross soil erosion, respectively. This study concludes that gross soil erosion would therefore only be a net sink of both carbon and greenhouse gases if all the following criteria are met: the gross soil erosion rate were very low (<91 tonnes/km²/yr); the eroded carbon were completely replaced by new soil organic matter; and if less than half of the gross erosion made it into the stream network. By establishing the emission factor for soil erosion, it becomes possible to properly account for the benefits of good soil management in minimizing losses of greenhouse gases to the atmosphere as a by‐product of soil erosion. Copyright © 2015 John Wiley & Sons, Ltd.     

Carbon fluxes from eroding peatlands – the carbon benefit of revegetation following wildfire

Peatlands are among the largest long‐term soil carbon stores, but their degradation can lead to significant carbon losses. This study considers the carbon budget of peat‐covered sites after restoration, following degradation by past wildfires. The study measured the carbon budget of eight sites: four restored‐revegetated sites, two unrestored bare soil control sites, and two intact vegetated controls over two years (2006–2008). The study considered the following flux pathways: dissolved organic carbon (DOC); particulate organic carbon (POC); dissolved carbon dioxide (CO₂); primary productivity; net ecosystem respiration, and methane (CH₄). The study shows that unrestored, bare peat sites can have significant carbon losses as high as 522 ± 3 tonnes C/km²/yr. Most sites showed improved carbon budgets (decreased source and/or increased sink of carbon) after restoration; this improvement was mainly in the form of a reduction in the size of the net carbon source, but for one restored site the measured carbon budget after four years of restoration was greater than observed for vegetated controls. The carbon sequestration benefit of peatland restoration would range between 122 and 833 tonnes C/km²/yr. Copyright © 2011 John Wiley & Sons, Ltd.     

The effect of burning and sheep grazing on soil water composition in a blanket bog: evidence for soil structural changes?

This study considers the impact of managed rotational burning of vegetation and sheep grazing upon the composition of soil waters within an upland peat soil. The study has considered soil water compositions from a complete factorial design of treatment plots where three different burning treatments were considered in replication with grazing and no grazing. All plots were sampled across a complete year with three dipwells in each plot. The study included aluminium (Al), iron, calcium, sodium (Na), magnesium (Mg), potassium, sulphate, chloride (Cl^?), bromide, fluoride, phosphate (PO )and nitrate; and in order to clarify the nature of the results, the pH, conductivity and dissolved organic carbon were also considered, but the major results for these are reported elsewhere. The study finds: (1) Ca, Na, Mg and PO concentrations are significantly lower on all burnt plots, with only Al concentration being significantly higher on burnt plots. (2) Only Cl^? showed any significant changes (a decrease) with the presence of sheep grazing, and then only when plots were also burnt. (3) A principal component analysis shows that the composition of most soil waters can be described by rainwater and soil water components, but in unburnt plots a base‐rich, high ionic strength water is sometimes present. The study suggests that burning, but not grazing, caused significant changes in soil water composition leading to increased interaction between incoming rainwaters and the peat soil but led to loss of interaction with deeper waters. However, no evidence was found for structural change in the soils even after long term (50 years) grazing and burning management. Copyright © 2007 John Wiley & Sons, Ltd.     

Settlement and sustainability in the Polish Sudetes

The paper summarises the history of human settlement in the Sudetes from the Bronze Age. A more intensive stage was reached in the Middle Ages when settlers from the west established new villages deep in the mountain valleys. By the beginning of the 20th century the Sudetes were already overpopulated but after a near-complete ethnic replacement from a German to a Polish population in 1945–8, population continued to grow until the 1980s. However, the economic system was hardly sustainable by this time. There were many polluting industries in the region and massive transboundary pollution from adjacent areas of Czechoslovakia and Germany had a devastating effect on the forests. Moreover, subsidised state agriculture placed heavy pressure on vulnerable mountain grazings. Since 1989 there has been a process of deindustrialisation in the Sudetes and surrounding areas and, with the disappearance of the state farms and the reduction in subsidies, agriculture is now better adjusted to the natural potential and is complemented by a promising start with agrotourism. The population of the region is growing relatively slowly (0.8% per annum 1956–1999), with the rural areas now in decline. A sustainable future for the region is now a possibility, but while there is a consensus for continued environmental reconstruction, supported by alternative economies, this will have to be carefully managed in the years ahead when EU accession may bring heavier development pressures than those evident at the moment. This revised version was published online in July 2006 with corrections to the Cover Date.     

Detection and identification of north–south trending magnetic structures near the magnetic equator

Long, structurally undeformed north–south trending structures show no magnetic anomaly at the magnetic equator, except at the north and south truncations of the structure. However, folding, faulting, differential erosion or other structural deformation can produce detectable magnetic anomalies in a generally north–south trending equatorial structure. Spatial variation in magnetic susceptibility or remanent magnetization can also produce anomalies in equatorial north–south structures. These anomaly patterns are often more complicated than patterns produced by similar structures at high latitudes, but interpretational insight can be gained through numerical modelling of common structures. Reduction-to-pole and analytic signal filters can aid in interpretation of equatorial anomalies, but these must be applied carefully because of instabilities deriving from filter design and noise amplification.