Stone runs in the Falkland Islands: Periglacial or tropical?

“Stone runs” is the Falklands vernacular term for openwork boulder accumulations, which include extensive blockstreams like the famous Darwin “stone-river” and associated features such as stone stripes. Since the early 20th century, they have been interpreted as the product of a suite of periglacial processes, including frost-wedging, gelifluction, frost heave, frost-sorting and snowmelt runoff. Following a literature review, the results of recent field investigations of the valley-floor blockstreams of East Falkland are presented. Access to the internal structure of these forms provides evidence for the existence of a three-fold profile, with clear vertical size gradation presenting striking similarities with an inverted weathering profile. Micromorphological analyses, SEM, XRD, thin sections and grain-size analyses lead to the hypothesis of an alternative model of stone run formation. It is suggested that the material forming the stone run profile lato sensu (including the superficial pavement) is not of periglacial origin, but derives directly from the stripping and accumulation downslope of a regolith, possibly Tertiary in age and formed under subtropical or temperate conditions. The valley-floor stone runs should, therefore, be considered as complex polygenetic landforms that may have formed according to a six-stage scenario, including in situ chemical weathering, regolith stripping by mass movements, soil formation, further regolith stripping, downslope accumulation and matrix washing-out (all phases possibly achieved by the Early Quaternary). Periglacial reworking of the stone run material would have operated at a “final” stage, i.e. during Quaternary cold stages, with boulder bioweathering and limonite-staining operating during the temperate intervals including the present one. The suggested antiquity of the Falklands blockstreams is in accordance with Caine's pioneer interpretation of Tasmania blockfields and with recent analyses and cosmogenic datings of blockfields from Scandinavia and North America.     

Assessing temporary carbon sequestration and storage projects through land use, land-use change and forestry: comparison of dynamic life cycle assessment with ton-year approaches

In order to properly assess the climate impact of temporary carbon sequestration and storage projects through land-use, land-use change and forestry (LULUCF), it is important to consider their temporal aspect. Dynamic life cycle assessment (dynamic LCA) was developed to account for time while assessing the potential impact of life cycle greenhouse gases (GHG) emissions. In this paper, the dynamic LCA approach is applied to a temporary carbon sequestration project through afforestation, and the results are compared with those of the two principal ton-year approaches: the Moura-Costa and the Lashof methods. The dynamic LCA covers different scenarios, which are distinguished by the assumptions regarding what happens at the end of the sequestration period. In order to ascertain the degree of compensation of an emission through a LULUCF project, the ratio of the cumulative impact of the project to the cumulative impact of a baseline GHG emission is calculated over time. This ratio tends to 1 when assuming that, after the end of the sequestration project period, the forest is maintained indefinitely. Conversely, the ratio tends to much lower values in scenarios where part of the carbon is released back to the atmosphere due to e.g. fire or forest exploitation. The comparison of dynamic LCA with the ton-year approaches shows that it is a more flexible approach as it allows the consideration of every life cycle stage of the project and it gives decision makers the opportunity to test the sensitivity of the results to the choice of different time horizons.     

Estimating species diversity: Comparison of two algorithms

Two approaches to estimating the number of species in a lithologic unit are compared. An empirical model of the sampling process, which involves fitting the equation of a rectangular hyperbola to the data from a collector's curve, is compared with a logarithmic model derived from a statistical theory of sampling. The two approaches give equally accurate estimates of species richness when organisms are randomly dispersed but the logarithmic model generally requires more sampling than the hyperbolic model.     

A gap in the North American Central Plains conductivity anomaly

The palaeotectonic models of the North American continent have been deeply influenced by the concept of a North American Central Plains conductivity anomaly (NACPCA) which was postulated as a result of large area, wide-spaced, array studies, using the Magnetic Deep Sounding (MDS) method.

A recent closely spaced magnetotelluric (MT) survey across this proposed anomaly near the Canadian-U.S. boundary by Jones and Savage (1986) failed to detect the NACPCA at the location suggested by the MDS. However, this survey did verify a conductivity anomaly discovered by Rankin and Kao (1979) and a new anomaly 75 km east of NACPCA. Our present study verifies this latter anomaly and quantitative results are presented. The striking isotropy in apparent resistivity does not prevent the interpretation of anomalous resistivity distributions. This is discussed in the text.

The failure of the MDS array studies to detect our anomaly is readily explainable by the wide station spacing; however, the failure of the MT survey to detect the NACPCA leads us to the conclusion that it may not be a continuous feature.     

Spartina anglica eradication experiment and in situ monitoring assess structuring strength of habitat complexity on marine macrofauna at high tidal level

The cordgrass Spartina anglica is an introduced species that tends to invade sheltered sand and mudflats, at the upper low marsh level. In Arcachon Bay, a lagoon in South West of France, the cordgrass can also replace Zostera noltii beds. The consequence of cordgrass presence on macrobenthic fauna was estimated and compared to adjacent habitats (bare sands, Z. noltii sea grass beds) during one year. The communities of the three habitats were characterised by low species richness, low abundance and biomass (when Hydrobia ulvae, 90% of abundance, is not considered) and high seasonal stability. The infaunal assemblages were particularly homogeneous between habitats without any characteristic species.Cordgrass eradication experiments were performed and zoobenthic recolonisation was observed the following year. Modifications in benthic fauna were observed on epifauna only.These results highlight the limited structuring effect of habitat heterogeneity at high tidal levels and in soft-bottom sediments where desiccation becomes the dominant factor determining infauna community structure.     

Multi-method investigation of mass transfer mechanisms in a retrogressive clayey landslide (Harmalière,French Alps)

Landslides - The mass transfer mechanisms in landslides are complex to monitor because of their suddenness and spatial coverage. The active clayey Harmalière landslide, located 30 km south of...     

Effectiveness of land management measures to reduce coastal georisks, eastern Québec, Canada

Erosion and flooding are geohazards that pose a significant problem in eastern Québec, as they do throughout the world. To manage such risks, zoning to set limits on new construction projects is generally the first adaptation solution introduced in an area. However, very few studies have evaluated the effectiveness of zoning in terms of risk reduction. Offered here is a retrospective approach to evaluate the evolution of settlement in coastal areas before and during the progressive implementation of zoning laws and regulations in the Percé region of eastern Québec, Canada. It was possible to evaluate the evolution of the built environment and coastal hazards by using 6 series of aerial photographs (1934-2001) and archived processed in a GIS. The results show a significant change in coastal land use. At first land use was consistent with a fishery-based economy, and later with an economy based on the tourism industry. Such a transformation in human activity leads to changes in the typology of the built environment, and consequently to an increase in the value of buildings at risk. Due to widespread ignorance respecting the intensity of hazards and the rhythm of coastal evolution, a lack of understanding and acceptance of land management regulations, an excessive level of confidence respecting anti-erosion protective structures and conscious risk taking by property owners seeking to take advantage of the coast’s attractiveness among others for tourism purposes, the implementation of land use planning and development laws and regulations in the 1980s was not able to limit the number of buildings at risk in the coastal zone. In fact, a 133% increase in buildings at risk was observed between 1980 and 2001. Only one quarter of this increase can be attributed to the coastline’s movement caused by erosion, whereas 74% of the buildings newly at risk were new, built in a zone where building was prohibited. Poorly adapted measures that limited risks over an insufficient period were also observed. Such observations reveal a problem of governance respecting the management and prevention of natural coastal hazards. While it may be useful to redefine measures for the zoning of coastal risks with precision and based on criteria that take into account the dynamics of coastal hazards, zoning on its own is no guarantee of risk reduction. Such zoning measures must be developed and applied along with a strategy for communicating hazards and risk to all actors in the coastal zone. Due to the complexity of the problems involved, reinforcing adaptive capacities of coastal communities with respect to coastal hazards requires a process whose efficiency is ensured by close collaboration among the various actors (scientists, managers, levels of government, the general public).     

Long-term fish and macro-crustacean community variation in a Mediterranean lagoon

The fish and macro-crustacean community of the Vaccarès lagoon (Rhône River delta, South France) was sampled monthly from 1993 to 2002. The lagoon salinity shifted from 15 in 1993 to 5 in 1994–1997 and went back to 15 in 1999–2002. Connections with the sea also varied during the study period with larger openings in 1996–1997. During the study period, the community changed to revert in 2002 to a state similar to 1993. These changes consisted of a sequence of increased and decreased patterns of freshwater species and some marine species. Typical lagoon species tended to resist to salinity changes. Freshwater species colonised the lagoon when the salinity was low. Marine species may have varied both in relation to connections with the sea and to indirect effects of freshwater outflow. This study shows that community changes following environmental variations can be delayed in time, and emphasises the need for long-term studies.