The influence of human activity in the Arctic on climate and climate impacts

Human activities in the Arctic are often mentioned as recipients of climate-change impacts. In this paper we consider the more complicated but more likely possibility that human activities themselves can interact with climate or environmental change in ways that either mitigate or exacerbate the human impacts. Although human activities in the Arctic are generally assumed to be modest, our analysis suggests that those activities may have larger influences on the arctic system than previously thought. Moreover, human influences could increase substantially in the near future. First, we illustrate how past human activities in the Arctic have combined with climatic variations to alter biophysical systems upon which fisheries and livestock depend. Second, we describe how current and future human activities could precipitate or affect the timing of major transitions in the arctic system. Past and future analyses both point to ways in which human activities in the Arctic can substantially influence the trajectory of arctic system change.     

Effects of temperature-dependent material properties and radioactive heat production on simple basin subsidence models

The effects of applying laboratory-derived material parameters to simple thermal basin subsidence models are examined. The temperature-dependent properties of thermal conductivity, specific heat and the coefficient of thermal expansion are considered, as well as conductivity contrasts between the crust and mantle and lithosphere-scale radiogenic heat production. The effects of conductivity and radioactivity are complementary, and can be predicted from the way in which they influence the initial and final steady-state geothermal gradient. A convex-up initial gradient, such as is generated by the conductivity and radioactivity functions and is also assumed to be the case based on independent evidence, will lead to more initial subsidence than in a simple constant-parameter model. The final subsidence will also be greater in the modified model, due to the fact that the stretching event will result in a lithospheric column which is intrinsically cooler than in the pre-deformation case. Because the coefficient of thermal expansion rises with increasing temperature, including its temperature dependence will result in a model with substantially less initial subsidence than one with a constant value. When these parameters are combined into a single model, the initial subsidence is approximately 15–20% less than in the constant-parameter model if radioactivity is not included, and 10% less if it is, while the final subsidence is about 5% greater without radioactivity and 7–9% greater with radioactivity included. Depending on the magnitude of extension, these effects can translate into differences of tens to hundreds of meters when compared to the constant-parameter model.     

Variation in biogeochemical parameters across intertidal seagrass meadows in the central Great Barrier Reef region

This survey provides baseline information on sediment characteristics, porewater, adsorbed and plant tissue nutrients from intertidal coastal seagrass meadows in the central region of the Great Barrier Reef World Heritage Area. Data collected from 11 locations, representative of intertidal coastal seagrass beds across the region, indicated that the chemical environment was typical of other tropical intertidal areas. Results using two different extraction methods highlight the need for caution when choosing an adsorbed phosphate extraction technique, as sediment type affects the analytical outcome. Comparison with published values indicates that the range of nutrient parameters measured is equivalent to those measured across tropical systems globally. However, the nutrient values in seagrass leaves and their molar ratios for Halophila ovalis and Halodule uninervis were much higher than the values from the literature from this and other regions, obtained using the same techniques, suggesting that these species act as nutrient sponges, in contrast with Zostera capricorni. The limited historical data from this region suggest that the nitrogen and phosphorus content of seagrass leaves has increased since the 1970s concomitant with changing land use practice.     

Setting nutrient thresholds to support an ecological assessment based on nutrient enrichment, potential primary production and undesirable disturbance

The EU Water Framework Directive recognises that ecological status is supported by the prevailing physico-chemical conditions in each water body. This paper describes an approach to providing guidance on setting thresholds for nutrients taking account of the biological response to nutrient enrichment evident in different types of water. Indices of pressure, state and impact are used to achieve a robust nutrient (nitrogen) threshold by considering each individual index relative to a defined standard, scale or threshold. These indices include winter nitrogen concentrations relative to a predetermined reference value; the potential of the waterbody to support phytoplankton growth (estimated as primary production); and detection of an undesirable disturbance (measured as dissolved oxygen). Proposed reference values are based on a combination of historical records, offshore (limited human influence) nutrient concentrations, literature values and modelled data. Statistical confidence is based on a number of attributes, including distance of confidence limits away from a reference threshold and how well the model is populated with real data. This evidence based approach ensures that nutrient thresholds are based on knowledge of real and measurable biological responses in transitional and coastal waters.     

Spatial interaction between collapsed pipes and landslides in hilly regions with loess‐derived soils

While most studies focus on the effect of soil pipes on hillslope stability, this present study investigates the impact of landsliding on pipe development. It is hypothesized that poorly drained active and dormant landslides change the hillslope hydrology through (i) surface flow obstruction, by changing topography, as well as (ii) subsurface flow obstruction by tilting less‐permeable clay‐rich substrates. Hence, new preferential flow paths are created at reverse slopes within the landslide zone and at the boundary of the landslide, enhancing pipe formation. This study aims at a better understanding of the interaction between collapsed pipe (CP) occurrence and landslide (LS) occurrence in the Flemish Ardennes (Belgium) by comparing their respective spatial patterns. At least 24.5% of the 139 sites with CP were related to the occurrence of an observed LS. Poorly drained LS may create favourable conditions for pipe development. Outside LS, natural and anthropogenic (e.g. broken field drains, road drainage) causes may result in concentrated subsurface flow, resulting in pipe development. No evidence was found that pipe development enhanced LS, probably because the subsurface drainage discharge generated upslope of the LS is too low. Even when pipes become blocked, it is more likely that new pipes develop and new collapses occur than they trigger or reactivate LS. A conceptual model is presented summarizing all elements that influence piping erosion in the Flemish Ardennes, including the role of LS. Copyright © 2012 John Wiley & Sons, Ltd.     

Historical trends in Florida temperature and precipitation

Because of its low topographic relief, unique hydrology, and the large interannual variability of precipitation, Florida is especially vulnerable to climate change. In this paper, we investigate a comprehensive collection of climate metrics to study historical trends in both averages and extremes of precipitation and temperature in the state. The data investigated consist of long‐term records (1892–2008) of precipitation and raw (unadjusted) temperature at 32 stations distributed throughout the state. To evaluate trends in climate metrics, we use an iterative pre‐whitening method, which aims to separate positive autocorrelation from trend present in time series. Results show a general decrease in wet season precipitation, most evident for the month of May and possibly tied to a delayed onset of the wet season. In contrast, there seems to be an increase in the number of wet days during the dry season, especially during November through January. We found that the number of dog days (above 26.7 °C) during the year and during the wet season has increased at many locations. For the post‐1950 period, a widespread decrease in the daily temperature range (DTR) is observed mainly because of increased daily minimum temperature (Tmin). Although we did not attempt to formally attribute these trends to natural versus anthropogenic causes, we find that the urban heat island effect is at least partially responsible for the increase in Tmin and its corresponding decrease in DTR at urbanized stations compared with nearby rural stations. In the future, a formal trend attribution study should be conducted for the region. Copyright © 2012 John Wiley & Sons, Ltd.     

Evidence for repeated re‐activation of old landslides under forest

Local reactivations of landslides in forests are rarely reported in landslide catalogues. The occurrence of hillslope sections with fresh morphological landslide features in forested old, deep‐seated landslides, however, suggests that landslide reactivations are not restricted to residential areas. In this study, a dendrogeomorphological analysis of beech stands was used to investigate the periods of reactivation of a deep‐seated rotational slide in the Koppenberg forest (Flemish Ardennes, Belgium). The relation to rainfall and the correspondence to landslide reactivations reported in a nearby built‐up area were also analysed. A dendrometrical study preceding the dendrochronological analysis proved that, compared with the nearby reference site, trees on the Koppenberg forest landslide site were significantly more inclined and showed more knees, indicating that the landslide site has not stabilized yet. As the sampled trees are younger than the landslide, dendrochronology did not allow determination of the year in which the landslide was initiated, but analysis of two different tree ring width parameters (i.e. ring eccentricity and growth change) calculated for trees sampled on the Koppenberg landslide and the reference site proved to be of great help in determining the temporal sequence of landslide reactivation. During the past 80 years, several periods indicative of local reactivations (i.e. 1943–1945, 1949–1952, 1967–1970, 1972–1977, 1979–1981, 1988–1997) were found within the investigated landslide, but delineation of the spatial extent of the reactivations during these indicative periods was not straightforward. These periods generally correspond to years with above‐average rainfall. Finally, the fact that at least 34% of the years indicative of reactivation of the Koppenberg forest landslide correspond to a year in which a landslide reactivation was reported in the Flemish Ardennes suggests that in built‐up areas, apart from anthropogenic interventions, natural triggering factors remain very important. Copyright © 2009 John Wiley & Sons, Ltd.     

Micellar-Enhanced Ultrafiltration and Air Stripping for Surfactant-Contaminant Separation and Surfactant Reuse

Micellar-enhanced ultrafiltration (MELT) and air stripping were evaluated for surfactant-contaminant separation and surfactant recovery. Two linear alkyl diphenyloxide disulfonate (DPDS) surfactants were evaluated with the contaminants naphthalene and trichloroethylene. A separation model developed from micellar partitioning principles showed a good correlation to batch MEUF studies, whereas flux analysis highlighted concentration polarization effects in relation to hydrophobe length. MEUF effectively concentrated the surfactant-contaminant system (93 to 99 percent retention); however, this did not result in surfactant-contaminant separation. Batch and continuous flow air stripping models were developed based upon air/water ratio, surfactant concentration, and Micellar partitioning; model predictions were validated by experimental data. Sensitivity analyses illustrated the decline in contaminant-surfactant separation with increasing surfactant concentration (e.g., TCE removal efficiency declines from 83 percent to 37 percent as C-16 DPDS concentration increases from 0 to 55 mM). This effect is greater for more hydrophobic contaminants (naphthalene vs. TCE) and surfactants with greater solubilization potential (C16-DPDS vs. C-12 DPDS). The resulting design equations can account for this effect and thus properly size air strippers to achieve the desired removal efficiency in the presence of surfactant micelles. Proper selection and design of surfactant-contaminant separation and surfactant recovery systems are integral to optimizing surfactant-enhanced subsurface remediation.     

岩背斑岩锡矿特征和成因

冉背斑岩锡矿为Ｓｎ－Ｆ型，不同于玻利维亚斑岩锡矿（Ｓｎ－Ｂ型）。含矿的火山－侵入杂岩属陆壳重熔型（Ｓ型）。矿体赋存于流纹斑岩和花岗斑岩的内外接触带，物质成分较为复杂；围岩蚀变的分带现象较明显，自内向外依次为黄英岩化带、绿泥石化带和绢云母化带。根据同位素资料，成矿热液以岩浆水为主，成矿物质主要来自岩浆。成矿作用在时间、空间和物质来源上与岩浆活动有着密切的成因联系。