Variation of stream temperature among mesoscale habitats within stream reaches: southern Appalachians

Stream mesoscale habitats have systematic topographic relationships to hyporheic flow patterns, which may create predictable temperature variation between mesoscale habitat types. We investigated whether systematic differences in temperature metrics occurred between mesoscale habitats within reaches of small streams tributary to the upper Little Tennessee River, southern Appalachians. Surface water temperature was recorded over three or four mid‐summer days in four mesoscale habitat types: riffle, main riffle, pool and alcove in 44 stream segments (sites). Temperature metrics were calculated for each mesoscale habitat relative to the mean value of the metric over the stream: Δ maximum temperature, Δ average maximum temperature and Δ maximum daily variation and also for each site: standard deviation of the maximum temperature and average diurnal variation (ADV). Sites were categorized as fully or partially forested. Pool tailouts had statistically significantly lower Δ maximum temperature and Δ average maximum temperature than riffle tailouts in partially forested sites, although differences were small. This was the opposite of what was expected in the presence of hyporheic exchange, indicating hyporheic exchange is not a dominant driver of mesoscale habitat temperatures at these sites. Temperature differences between mesoscale habitat units were small and unlikely to have ecological significance. We also evaluated relationships between stream temperature and riparian condition, watershed % impervious surfaces, watershed % non‐forested and elevation. ADV and standard deviation of the maximum temperature were significantly higher in partially forested sites, indicating that partially forested sites have greater temperature ranges and spatial variation of maximum temperatures. ADV decreased with elevation and increased with % impervious surfaces. Copyright © 2013 John Wiley & Sons, Ltd.     

Assessing the potential impact of climate change on the UK’s electricity network

We investigate how weather affects the UK’s electricity network, by examining past data of weather-related faults on the transmission and distribution networks. By formalising the current relationship between weather-related faults and weather, we use climate projections from a regional climate model (RCM) to quantitatively assess how the frequency of these faults may change in the future. This study found that the incidences of both lightning and solar heat faults are projected to increase in the future. There is evidence that the conditions that cause flooding faults may increase in the future, but a reduction cannot be ruled out. Due to the uncertainty associated with future wind projections, there is no clear signal associated with the future frequency of wind and gale faults, however snow, sleet and blizzard faults are projected to decrease due to a reduction in the number of snow days.     

State in formation: the Ghetto State as typified in the West Bank and Gaza Strip

State formation is a complex process. Using the notion of the ghetto state, the case of the West Bank and Gaza Strip are analyzed. State formation processes among the Palestinians are shown to be a direct reaction to the processes of political and military control put into operation by Israel since 1967. The continued administrative and political separation of the West Bank and Gaza from the dominant Israeli territory enable the Palestinians to formulate their own independent national identity. This includes the establishment of economic, cultural and local political organizations, providing the foundations for future statehood. Such organizational capability is indicative of the wide range of non-violent forms of power which, in many cases, are more effective than direct acts of violence against Israel. The Intifada — or popular uprising — which has been in operation since 1987 has enforced these processes of statehood formation, through its combination of both violent and non-violent forms of power.     

AN L6 CHONDRITE FOUND NEAR PARACHILNA,SOUTH AUSTRALIA*

An 8.82 kg stony meteorite found on Motpena Station, 31°6' S, 138° 16' E, near Parachilna, South Australia, is shown to be a somewhat weathered L6 (olivine-hypersthene) chondrite. This is listed in The Meteoritical Bulletin, No. 53, June 1975 as MOTPENA, Synonym, Parachilna.     

Origin and age of The Hillocks and implications for post‐glacial landscape development in the upper Lake Wakatipu catchment,New Zealand

Ambiguous landscape histories can arise from equivocal or incomplete geomorphological, sedimentological or geochronological evidence. In this study, we apply quantitative analyses to robustly assess the origin and age of a field of rounded mounds, known as ‘The Hillocks’. Using clast analysis, the sediment is shown to be consistent with a landslide origin but inconsistent with other glacial sediments in the region. Cosmogenic ¹⁰Be exposure age dating suggests The Hillocks formed ~8 ka. Ground‐penetrating radar reveals that the deposit rests upon deltaic foreset beds; combined with topographical data, we calculate a deposit volume of ~15–27 M m³, consistent with the estimated volume of the proposed source area. Overall, our data support a rock avalanche origin, indicating that by 8 ka the valley was ice‐free at The Hillocks’ location, and the level of Lake Wakatipu was lower than 340 m asl by this time. The Dart River delta shoreline was situated somewhere between The Hillocks and the present day shoreline at that time, and has prograded at a maximum average rate of 1 m a^?1 since ~8 ka. These findings are significant given the lack of landforms by which to constrain glacial or post‐glacial landscape histories in this region of New Zealand. Copyright © 2019 John Wiley & Sons, Ltd.     

Clearcutting and pine planting effects on nutrient concentrations and export in two mixed use headwater streams: Upper Coastal Plain,Southeastern USA

Timber harvest temporarily increases water yield; however, relationships between hydrologic and nutrient chemistry changes have not been consistent. This study quantified the effects of forest harvesting and site preparation without fertilization and with modern best management practices on nutrient concentrations and yields in small headwater streams of the Southeastern Coastal Plain. We monitored two watershed pairs for 2 years prior to and 1 year following timber harvest and for 2 more years following site preparation and planting. Treatment watersheds were clearcut, and downstream portions of streamside management zones were thinned in Fall 2003. Site preparation (herbicide application and burning) and planting followed a year later. All operations followed 1999 Georgia forestry best management practices. Previously published research revealed a large increase in water yield following harvest. Nutrient concentrations varied significantly within and between monitoring periods, even in reference watersheds. Silvicultural activities had no discernible effect on phosphorus and ammonium concentrations; however, statistically significant increases in nitrate/nitrite (67–340 µg L⁻¹) and total nitrogen concentrations (100–400 µg L⁻¹) in treatment watersheds followed stand re‐establishment. Nutrient yields increased after timber harvest largely as a result of increased water yields, although increased nutrient yields were small relative to inter‐annual and inter‐watershed variability and variability. Annual water yield largely explained the variability in annual nitrogen and phosphorus export from reference and treatment streams (r² values from 0.65 to 0.98). High NO_x concentrations coming from an upstream agricultural area decreased 1600–1800 µg L⁻¹ over several hundred metres in the treatment streams by dilution, uptake or denitrification. Copyright © 2013 John Wiley & Sons, Ltd.     

Large ice‐contact slope movements: glacial buttressing,deformation and erosion

Glaciers and slope movements may act simultaneously to erode and modify glaciated slopes. Undercutting by glaciers can destabilize slopes but the extent to which slope failure may progress prior to subsequent glacier withdrawal has not hitherto been considered. The traditional view has been that the buttressing effect of ice prevents slope movement. The problem with this view is that ice is one‐third the density of rock and flows under low applied stress. Consequently, failed slopes may move into the glacier if they exert a stress in excess of the resistance provided by the glacier. Slope movement rate depends on ice rheology and other factors influencing driving and resisting stresses. Simple viscous equations are used to investigate these variables. The equations predict that small (<125 000 m³) ice‐contact rockslides can deform ice at several mm/year, increasing to several m/year for very large (>10⁸ m³) rockslides. To test these estimates, field evidence is presented of slope movements in glaciated valleys of New Zealand; narrowing or squeezing of glaciers adjacent to unstable rock slopes is demonstrated and considered to be the result of slope movement. For one site, geomorphic mapping and slope movement monitoring data show that movement rates are of similar order of magnitude to those predicted by the viscous equations; closer agreement could be achieved with the application of modelling techniques that can more realistically model the complex slope geometries and stability factors encountered, or by obtaining additional empirical data to calibrate the models. This research implies that, while the concept of glacial debuttressing – the reduction of slope support from withdrawal of glaciers – is valid, complete debuttressing is not a prerequisite for the movement of ice‐contact rock slopes. These slope movements may contribute to the erosional processes of glaciers and the evolution of glaciated slopes in a previously unrecognized way. Copyright © 2012 John Wiley & Sons, Ltd.     

The effect of glaciation on the intensity of seismic ground motion

Seismicity is known to contribute to landscape denudation through its role in earthquake‐triggered slope failure; but little is known about how the intensity of seismic ground motions, and therefore triggering of slope failures, may change through time. Topography influences the intensity of seismic shaking – generally steep slopes amplify shaking more than flatter slopes – and because glacial erosion typically steepens and enlarges slopes, glaciation may increase the intensity of seismic shaking of some landforms. However, the effect of this may be limited until after glaciers retreat because valley ice or ice‐caps may damp seismic ground motions. Two‐dimensional numerical models (FLAC 6.0) were used to explore how edifice shape, rock stiffness and various levels of ice inundation affect edifice shaking intensity. The modelling confirmed that earthquake shaking is enhanced with steeper topography and at ridge crests but it showed for the first time that total inundation by ice may reduce shaking intensity at hill crests to about 20–50% of that experienced when no ice is present. The effect is diminished to about 80–95% if glacier ice level reduces to half of the mountain slope height. In general, ice cover reduced shaking most for the steepest‐sided edifices, for wave frequencies higher than 3 Hz, and when ice was thickest and the rock had shear stiffness well in excess of the stiffness of ice. If rock stiffness is low and shear‐wave velocity is similar to that of ice, the presence of ice may amplify the shaking of rock protruding above the ice surface. The modelling supports the idea that topographic amplification of earthquake shaking increases as a result of glacial erosion and deglaciation. It is possible that the effect of this is sufficient to have influenced the distribution of post‐glacial slope failures in glaciated seismically active areas. Copyright © 2012 John Wiley & Sons, Ltd.     

Availability of soil and sediment phosphorus to a planktonic alga

Chlorophyll production by Chlorella vulgaris Beij. var. vulgaris was used to estimate alga‐available phosphorus in clays, soils, and lake sediments suspended in water at concentrations appropriate to lake inflows during floods (100–500 g/m³). Chlorella apparently used 24–81% of 0.5M H2SO4 extractable phosphorus in clays from topsoils, about 25% from lake sediments, and 0.3–1.0% from, subsoils low in phosphorus and with high phosphorus retention.

The presence of suspended soil material did not reduce the availability to Chlorella of inorganic phosphorus added to the cultures. Increasing the Chlorella population by adding inorganic phosphorus resulted in an apparent increase in availability of phosphorus from the soil, possibly as a result of enzymic mineralisation of organic soil phosphorus. The amount of available phosphorus in lake sediments was not a reliable guide to the trophic condition, of the lake.

Suspended material from sediments, soils, and especially clay eroded from fertilised topsoils may provide phosphorus for algal growth in lakes. If allophanic clays are applied to lakes to sorb phosphorus and hence control eutrophication, the particles must settle out before planktonic algae in the photic zone can use the adsorbed phosphorus.