Accumulation in Svalbard glaciers deduced from ice cores with nuclear tests and Chernobyl reference layers

Mean net annual balance and the related spatio-temporal variations have been determined on the basis of well-dated artificial layers in shallow ice cores (Chernobyl, 1986, and atmospheric thermonuclear tests, mainly in 1961-62 in Novaya Zemlya). Seventy ice cores from 13 Svalbard glaciers have been analysed. On each glacier, in its accumulation area and at the highest elevation, one ice core was recovered down to about 40 m and sampled for radioactivity measurements to determine the 1986 and 1962-63 layer (1954 was the initial date of the nuclear tests). For each glacier, at least five complementary ice cores from the accumulation area were analysed to determine the Chernobyl reference layer. Six ice cores exhibit both the Chernobyl and nuclear tests layers and are of special interest in this study.
This work provides new data on the deposition rates of natural and artificial radioisotopes. Using ice cores samples from the Arctic glaciers, even with superimposed ice accumulation, it is possible to distinguish between the Chernobyl and the nuclear tests fallouts. This work also shows that the mean annual net balance did not significantly change for at least five ice core locations in the Svalbard glaciers for the two periods extending from 1963 to 1986 to the recent date of drilling.     

Short-term impact of reservoir cleaning on the microhabitat use of three non-salmonid fishes in a piedmont river in south west France

As with many rivers of the Pyrenees Mountains, reservoirs on the River Ariège (SW Francc) are used for hydroelectricity generation, irrigation and to maintain summer flows in the River Garonne. Two river reservoirs on the River Ariège were simultaneously emptied in April 1991 to remove accumulated sediment. Fish and ten environmental variables were sampled using Point Abundance Sampling by electrofishing before (February 1991) and one year later (February 1992) at three study sites downstream of the dams. We examined the short-term impact of reservoir cleaning on the relative abundance, habitat availability and habitat use of three species of small fish: minnow Phoxinus phoxinus (L.), gudgeon Gobio gobio (L.) and stone loach Barbatula barbatula (L.).¶After the reservoir cleaning, areas covered by gravel, sand and mud increased significantly as the result of the sediment release. The three species did not react in the same manner to these environmental changes. Stone loach appeared to be the most sensitive species, with its relative abundance decreasing at all sites. Conversely, minnow seemed to be the most resistant species and as such is a leading pioneer species for colonizing new or impacted stretches of rivers channels. Finally, the number of gudgeon decreased particularly at the most downstream site where large deposits of mud were recorded.     

Flood forecasting based on an artificial neural network scheme

Natural Hazards - Nowadays, floods have become the widest global environmental and economic hazard in many countries, causing huge loss of lives and materials damages. It is, therefore, necessary...     

Controls on debris-flow initiation on burned and unburned hillslopes during an exceptional rainstorm in southern New Mexico,USA

AbstractUsing observations from 688 debris flows, we analyse the hydrologic and landscape characteristics that influenced debris-flow initiation mechanisms and locations in a watershed that had been partially burned by the 2012 Whitewater-Baldy Complex Fire in the Gila Mountains, southern New Mexico. Debris flows can initiate due to different processes. Slopes can fail as discrete landslides and then become fluidized and move downstream as debris flows (landslide initiated) or progressive bulking of sediment from a distributed area can become channelized and concentrated as it moves downslope (runoff generated). In this study, we have an unusual opportunity to investigate both types of debris-flow initiation mechanisms in our observations of debris flows, triggered by an exceptional rainstorm in the autumn of 2013. Additionally, we compare our observations with those of a dataset of 1138 debris flows in the Colorado Front Range, triggered during the same weather system. We found that runoff-generated debris flows dominated in burn areas, and runoff required to start these flows could be well characterized by the Shields stress. Landslide-initiated debris flows were dominant in unburned areas. Debris-flow densities were tied to total rainfall and precipitation intensities. Like the observations in the Colorado Front Range, debris-flow initiation locations were found primarily in areas of relatively sparse vegetation on south-facing slopes between 25 and 40°, and with upslope contributing areas less than 1000 m². In terms of preferential locations for debris-flow initiations, 2013 vegetation coverage, approximated by Green–Red Vegetation Index metrics, proved to be more influential than the 2012 burn-severity designation. The uniformity of observations between our study area and those in the Colorado Front Range indicate that the underlying hydrologic and landscape patterns of the debris-flow initiation locations documented in these studies could be applicable to the wider southwest and Rocky Mountain regions. © 2019 John Wiley & Sons, Ltd.     

Impact of reach geometry on stream channel sensitivity to extreme floods

Predicting spatial and temporal variations in bank erosion due to extreme floods presents a long‐standing challenge in geomorphology. We develop two methodologies for rapid, regional‐scale assessments of stream reaches susceptible to channel widening. The first proposes that channel widening occurs when unit stream power exceeds a critical threshold (300 W/m²). The second is motivated by the observation that widening often occurs at channel bends. We introduce a new metric, the bend stress parameter, which is proportional to the centripetal force exerted on a concave bank. We propose that high centripetal forces generate locally high bank shear forces and enhance channel bank erosion. We test both metrics using the geomorphic signature of Tropical Storm Irene (2011) on the White and the Saxtons Rivers, Vermont. Specifically, we test if reaches where significant channel widening occurred during Irene required one or both metrics to exceed threshold values. We observe two distinct styles of channel widening. Where unit stream power and bend stress parameter are high, widening is usually due to bank retreat. Elsewhere widening is usually due to the stripping of the upstream end of mid‐channel islands. Excluding widening associated with the stripping of the heads of mid‐channel islands, almost all the widening (> 98%) occurred along reaches identified as susceptible to widening. The combined metrics identify up to one‐quarter of the reaches lacking susceptibility to channel widening. Copyright © 2014 John Wiley & Sons, Ltd.     

Two acoustic surveys of pelagic fish in Hawke Bay,New Zealand, 1980

The design and execution of two acoustic surveys of Hawke Bay in February and September/October 1980 are described. Though the resulting acoustic data were, for technical reasons, of limited value, they illustrate the information which may be drawn from acoustic surveys. Fish distributions may be rapidly mapped, not only by area, but throughout most of the water column and over time. Qualitative observations on fish distribution may be quantified. The estimation of variance in acoustic surveys is discussed in detail with particular emphasis on the problems of systematic surveys. The role of replicate observations is stressed. Coefficients of variation for relative fish density estimates from the two surveys probably lie between 5 and 30%.     

Dissolved oxygen as an indicator of bioavailable dissolved organic carbon in groundwater

Concentrations of dissolved oxygen (DO) plotted vs. dissolved organic carbon (DOC) in groundwater samples taken from a coastal plain aquifer of South Carolina (SC) showed a statistically significant hyperbolic relationship. In contrast, DO-DOC plots of groundwater samples taken from the eastern San Joaquin Valley of California (CA) showed a random scatter. It was hypothesized that differences in the bioavailability of naturally occurring DOC might contribute to these observations. This hypothesis was examined by comparing nine different biochemical indicators of DOC bioavailability in groundwater sampled from these two systems. Concentrations of DOC, total hydrolysable neutral sugars (THNS), total hydrolysable amino acids (THAA), mole% glycine of THAA, initial bacterial cell counts, bacterial growth rates, and carbon dioxide production/consumption were greater in SC samples relative to CA samples. In contrast, the mole% glucose of THNS and the aromaticity (SUVA(254)) of DOC was greater in CA samples. Each of these indicator parameters were observed to change with depth in the SC system in a manner consistent with active biodegradation. These results are uniformly consistent with the hypothesis that the bioavailability of DOC is greater in SC relative to CA groundwater samples. This, in turn, suggests that the presence/absence of a hyperbolic DO-DOC relationship may be a qualitative indicator of relative DOC bioavailability in groundwater systems.     

Whitefish wars: Pangasius, politics and consumer confusion in Europe

Rapid growth in production of the farmed Vietnamese whitefish pangasius and its trade with the European Union has provoked criticism of the fish's environmental, social and safety credentials by actors including WWF and Members of the European Parliament and associated negative media coverage. This paper reviews the range of claims communicated about pangasius (identified as a form of mass mediated risk governance), in light of scientific evidence and analysis of data from the EU's Rapid Alert System for Food and Feeds food safety notification system for imported seafood. This analysis shows pangasius to be generally safe, environmentally benign and beneficial for actors along the international value chains that characterise the trade. The case is made that increasingly politicised debates in Europe around risk and uncertainty are potentially counterproductive for EU seafood security and European aquaculture industry, and that the trade in pangasius can contribute to sustainable seafood consumption in a number of ways. Transparent evidence-based assessment and systems for communicating complex issues of risk for products such as pangasius are required in order to support continuance of fair and mutually beneficial trade.