Stability of lysosomal and cell membranes in haemocytes of the common mussel (Mytilus edulis): effect of low temperatures.

Expanding industrial activities in the Arctic require an urgent assessment of the toxicity of chemicals at low temperatures. Organisms acclimatized to low temperature exhibit specific adaptations. For example, the amount of unsaturated lipids is increased to maintain the fluidity of the cell membranes. It has been hypothesized that such temperature-induced alterations in membrane lipid composition may affect the stability of lysosomal and cell membranes in the common mussel, Mytilus edulis, an organism exposed to seasonal temperature extremes. As mussels may be exposed to petroleum compounds along industrialized coastlines, we tested the combined effects of exposure to low temperature and the petroleum compound, phenanthrene, on haemocyte membrane stability. Test animals, acclimated to either 0 or 10 degrees C, were exposed to phenanthrene (0 = control or 500 micrograms l-1) and haemocytes were examined using the neutral red retention assay (lysosomal stability) and a fluorescence assay (cell membrane stability). At 0 degree C, lysosomal and cell membranes from uncontaminated mussels were destabilized compared with 10 degrees C (P = 0.0005). No significant effects (P > 0.05) of phenanthrene were detected at either temperature. Possible mechanisms underlying membrane destabilization include a weaker physical resistance of the membrane due to a higher amount of unsaturated lipids, a potentially higher level of reactive oxygen radicals at low temperature and the higher susceptibility of unsaturated lipids to oxidative stress. More work is required to better understand the consequences of this membrane destabilization at low temperature on the susceptibility of the organism to pollutants.     

Assessment of carbon in woody plants and soil across a vineyard-woodland landscape

Background

Quantification of ecosystem services, such as carbon (C) storage, can demonstrate the benefits of managing for both production and habitat conservation in agricultural landscapes. In this study, we evaluated C stocks and woody plant diversity across vineyard blocks and adjoining woodland ecosystems (wildlands) for an organic vineyard in northern California. Carbon was measured in soil from 44 one m deep pits, and in aboveground woody biomass from 93 vegetation plots. These data were combined with physical landscape variables to model C stocks using a geographic information system and multivariate linear regression.

Results

Field data showed wildlands to be heterogeneous in both C stocks and woody tree diversity, reflecting the mosaic of several different vegetation types, and storing on average 36.8 Mg C/ha in aboveground woody biomass and 89.3 Mg C/ha in soil. Not surprisingly, vineyard blocks showed less variation in above- and belowground C, with an average of 3.0 and 84.1 Mg C/ha, respectively.

Conclusions

This research demonstrates that vineyards managed with practices that conserve some fraction of adjoining wildlands yield benefits for increasing overall C stocks and species and habitat diversity in integrated agricultural landscapes. For such complex landscapes, high resolution spatial modeling is challenging and requires accurate characterization of the landscape by vegetation type, physical structure, sufficient sampling, and allometric equations that relate tree species to each landscape. Geographic information systems and remote sensing techniques are useful for integrating the above variables into an analysis platform to estimate C stocks in these working landscapes, thereby helping land managers qualify for greenhouse gas mitigation credits. Carbon policy in California, however, shows a lack of focus on C stocks compared to emissions, and on agriculture compared to other sectors. Correcting these policy shortcomings could create incentives for ecosystem service provision, including C storage, as well as encourage better farm stewardship and habitat conservation.

     

Environmental toxicology: population modeling of cod larvae shows high sensitivity to loss of zooplankton prey

Two factors determine whether pollution is likely to affect a population indirectly through loss of prey: firstly, the sensitivity of the prey to the pollutants, and secondly, the sensitivity of the predator population to loss of prey at the given life stage. We here apply a statistical recruitment model for Northeast Arctic cod to evaluate the sensitivity of cod cohorts to loss of zooplankton prey, for example following an oil spill. The calculations show that cod cohorts are highly sensitive to possible zooplankton biomass reductions in the distribution area of the cod larvae, and point to a need for more knowledge about oil-effects on zooplankton. Our study illustrates how knowledge about population dynamics may guide which indirect effects to consider in environmental impact studies.     

Terrestrial laser scanning soil surfaces: a field methodology to examine soil surface roughness and overland flow hydraulics

Conventional roughness–resistance relationships developed for pipe and open‐channel flows cannot accurately describe shallow overland flows over natural rough surfaces. This paper develops a new field methodology combining terrestrial laser scanning (TLS) and overland flow simulation to provide a high‐resolution dataset of surface roughness and overland flow hydraulics as simulated on natural bare soil surfaces. This method permits a close examination of the factors controlling flow velocity and a re‐evaluation of the relationship between surface roughness and flow resistance. The aggregate effect of flow dynamics, infiltration and depression storage on retarding the passage of water over a surface is important where runoff‐generating areas are distant from well‐defined channels. Experiments to separate these effects show that this ‘effective resistance’ is dominated by surface roughness. Eight measurements of surface roughness are found to be related to flow resistance: standard deviation of elevations, inundation ratio, pit density (measured both perpendicular and parallel to the flow direction), slope, median depth, skewness of the depth distribution and frontal area. Hillslope position is found to affect the significant roughness measures. In contrast, infiltration rate has little effect on the velocity of water fronts advancing over the soil surfaces examined here and the effect of depression storage is limited. Overland flow resistance is depth dependent where complex microtopographic structures are progressively inundated. Copyright © 2010 John Wiley & Sons, Ltd.     

Influence of water mixing on the inhibitory effect of UV radiation on primary and bacterial production in Mediterranean coastal water

The scaling of the solar ultraviolet radiation (UVR, 280–400 nm) effect on phyto- and bacterio-plankton at the ecosystem level is difficult since its estimate is often based on short-time incubation experiments performed at fixed depths, neglecting the previous days’ radiation history and the variable radiation caused by vertical mixing. To examine this issue, we measured primary (PP) and bacterial (BP) production in samples from coastal water in the Northwest Mediterranean Sea incubated at fixed depths or moving vertically within the water column (0–8 m) with a periodicity of 22 min, exposed to full sun, PAR or maintained in dark. Three experiments were carried out on consecutive days to measure day-to-day variations in planktonic response. In surface waters, PP was inhibited by ~32 to 42% by UVR, and BP was inhibited by ~50 to 70% by solar radiation (UVR + PAR). We observed a general decrease in the integrated inhibition of PP due to UVR for both fixed and moving incubations over the 3 days from ~27% of inhibition to non-significant inhibition. In contrast, large discrepancies were observed in the integrated inhibition of BP due to solar radiation (UVR + PAR) between fixed and moving incubations. Whereas both type of incubations gave similar estimation of solar radiation inhibition on day 1 (~25%), inhibition became much higher for fixed incubation compared to moving incubation on days 2 and 3. Differences in responses between days suggest that light history, spectral quality, photoadaptation or acclimation may be important factors in daily observed responses. Our results also underline, for the first time, the importance of the vertical mixing in the BP inhibition by solar radiation.     

Volcanic sands of Iceland ‐ Diverse origins of aeolian sand deposits revealed at Dyngjusandur and Lambahraun

The origin, formation and evolution of volcanic sands are less well known than the formation of the much more common quartz‐rich sand sheets. Combining active volcanism and a cold climate, Iceland is covered for about 21% of its surface by sandy areas. The sands were analyzed in detail at two sites and results reveal their diverse origins. The first site is Dyngjusandur, located north of Vatnajökull, and the second site is the Lambahraun area, located south of Langjökull. At both sites, the sand origin is determined from field observations (wind directions from ventifacts), chemical and mineralogical analyses of rocks and sands. At Dyngjusandur, the sand is dominated by glass grains, a situation typical of sand plains in Iceland. Hyaloclastite ridges presently buried beneath Vatnajökull are the dominant source of the sand, and only large size plagioclase crystals (0.5 cm) in sands seem to be derived from the lava flows. Hyaloclastite ridges were crushed by glaciers and mechanically eroded sediments were washed out by melt‐water onto flood plains. The sand chemical composition is spatially homogeneous and similar to the average composition of neighboring sub‐aerial lava flows, reflecting efficient mixing of distinct sources below the glacier. The presence of sand north of Dyngjujökull can be taken as a way to explore the average chemical composition of non‐exposed volcanic material beneath the glacier. In the case of Lambahraun, prevailing winds indicate several potential sources of sand at the north of the sand sheet. Comparison of chemical and mineralogical analyses of sands and rock samples helped to refine the exact origin. In contrast with the first site, the sand is dominated by crystals and is chemically consistent with a mixture of material derived from the lava flows of Eldborgir and Skersli shield volcanoes. Analysis of the contact between the lava flows and the glacier reveals that basaltic sand grains formed as the result of recent advances of the glacier abrading the rocks. The direct interaction of glacial and fluvio‐glacial activity with basaltic plains appears to be necessary to produce a large amount of sands in a relatively short period of time (<4000 years). This site appears to be an excellent natural laboratory for further studies concerning the sand evolution and physical sorting processes in basaltic material, which have important implications for understanding aeolian processes on Mars. Copyright © 2011 John Wiley & Sons, Ltd.     

A 500 yr speleothem-derived reconstruction of late autumn–winter precipitation, northeast Turkey

A verified instrumental calibration of annually resolved δ¹⁸O for a stalagmite from Gümü?hane in northeast Turkey is presented and cross-validated using a ‘leave-one-out’ technique. The amount of late autumn to winter precipitation is negatively correlated with stalagmite δ¹⁸O between AD 1938 and 2004. The observed relationship is extrapolated back to ~ AD 1500 leading to the first long winter precipitation reconstruction for this region. Modern day October to January precipitation is linked to pressure fields in Western Russia. Anomalously lower reconstructed rainfall is recorded in AD 1540–1560 at which time higher pressure over the Caspian Sea region is inferred.     

Meteorological effects on seasonal displacements of the ?knes rockslide, western Norway

In the alpine topography along one of the long fjords with steep and high mountain sides in western Norway the large ?knes rockslide area is defined by a distinct back scarp rising from 800 to 1,000 m a.s.l. In 2004, an extensive monitoring program started, including establishment of a meteorological station above the upper tension crack, 900 m a.s.l. This paper evaluates the significance of meteorological conditions affecting the displacements recorded by five extensometers and two laser sensors in the tension crack from November 2004 to August 2008. Meteorological factors of importance for the recorded activity in the tension crack are found to be melt water in spring and large temperature fluctuations around the freezing point in spring, autumn, and early winter. The records show less acceleration phases in the measured distance across the tension crack in the second half of the analyzed period even though annual displacements are increasing, indicating that other processes, like disintegration of irregularities along unfilled joints and disintegration of intact rock bridges in the sliding plane have become more important.     

Origin and evolution of Castalia Macula, an anomalous young depression on Europa

Europa's Castalia Macula region was comprehensively imaged by the Galileo spacecraft on several orbits, at both local and regional resolutions and with different illumination geometries. Using these datasets we have mapped and identified the different geological units within the Castalia area, and derived digital elevation models (DEMs) of the topography within most of the Castalia Macula region. Using these data sets in combination allows us to map the geology and topography of this area in greater detail than perhaps any other site on Europa. Castalia Macula consists of unusually dark and reddish material, most of which is confined to a broad topographic depression 350 m deep located between two large uplifted domes 900 and 750 m high, to the north and south, respectively. The preservation of topography at the bottom of Castalia Macula indicates that dark material initially filled the depression to a certain depth but was subsequently removed via drainage, resulting in a dark stain up to the original equipotential surface. Superposition and topographic relationships suggest that the Castalia Macula plains deposit formed prior to uplift of both domes, and at least two distinct episodes of chaos formation have occurred near and on top of the northern dome. It appears that Castalia Macula is comparatively young and was active relatively recently, therefore it could provide an ideal place to sample material that has recently been erupted from the subsurface, and may have been in communication with Europa's ocean. These factors combine to make Castalia Macula a very attractive site for a future Europa lander.