Use of mercury (Hg) for gold-mining in French Guiana (up until 2006) as well as the presence of naturally high background levels in soils, has led to locally high concentrations in soils and sediments. The present study maps the levels of Hg concentrations in river sediments from five main rivers of French Guiana (Approuague River, Comté River, Mana River, Maroni River and Oyapock River) and their tributaries, covering more than 5 450 km of river with 1 211 sampling points. The maximum geological background Hg concentration, estimated from 241 non-gold-mined streams across French Guiana was 150 ng g-1. Significant differences were measured between the five main rivers as well as between all gold-mining and pristine areas, giving representative data of the Hg increase due to past gold-mining activities.These results give a unique large scale vision of Hg contamination in river sediments of French Guiana and provide fundamental data on Hg distribution in pristine and gold-mined areas.

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During May 1996 and April 1997, eight harlequin duck males were captured and fitted with satellite transmitters while migrating along the shores of Forillon National Park, Québec, Canada. Another 17 males were equipped with satellite transmitters in river systems of eastern Hudson Bay, Ungava Bay and northern Labrador in June 1997 and 1998. Our objectives were to determine relationships between breeding, moulting and wintering areas, and to determine whether distinct population segments existed among harlequin ducks in eastern North America. All birds tracked from Forillon migrated to Labrador. Moulting areas were identified for six birds. Forillon males were followed to the eastern North American major wintering site in Maine. Males captured in northern Québec and Labrador migrated to moult and winter in south‐western Greenland. Our data suggest the presence of two demographically distinct population segments in eastern North America, perhaps originating from the Pleistocene glacial refuge in western Greenland and south of the Laurentide ice sheet in eastern Canada or United States.

The loggerhead shrike (Lanius ludovicianus) is a grassland bird species whose preferred nesting habitat in eastern Canada is pastureland. This species has been extirpated from much of its historical range in this region, and breeding habitat loss is suspected to be an important cause of this decline. We evaluated the availability of suitable breeding habitats in Québec using satellite imagery. Because this species no longer breeds in Québec, we established habitat selection criteria from known nesting sites in the adjacent province of Ontario, from analysis of a Landsat-TM satellite image, and applied these criteria to Landsat-TM images covering southern Québec. We developed regional landscape criteria in 100 km 2 plots and patch indices criteria at the pasture level. Spatial analyses were conducted to characterize plots and pastures on the basis of pasture availability and spatial distribution. Pastures suitable for nesting loggerhead shrikes were those fulfilling patch criteria at the pasture level and located in plots fulfilling regional landscape criteria. Overall, 310 out of 1700 plots located in the historical breeding range of the loggerhead shrike in Québec fulfilled landscape criteria, supporting 3988 pastures that fulfilled patch criteria. More than 500 of these pastures were visited to validate their current status. The Outaouais region would be the most suitable region for nesting loggerhead shrikes in southern Québec, where suitable breeding habitat still remains because more than two-thirds of visited sites were still pastureland, hawthorns were well-distributed in the region, and pastureland fragmentation was lowest. We conclude that the availability of breeding habitat does not limit the establishment of a breeding population of loggerhead shrike in southern Québec, as we estimated that thousands of hectares of suitable habitat still remain in that province.

Abstract. To improve the understanding of soil gas emanations with the aim of groundwater prospecting in fractured substrates, radon anomalies were mapped in a tropical region (French Guyana) where the structural features of a potential gas source are masked owing to the thick regolith cover. Two anomalies were located. Two probes were then installed, one (B1) on the border of the north anomaly and the second (B2) at the center of the south anomaly, as well as a meteorological station, and monitoring was carried out for 6 months extending from the dry to the rainy season. Signal processing of radon signal-atmospheric pressure time series allowed us to determine the physical processes causing migration of the gases in the soil and the subsoil. The radon anomalies are very probably associated with the presence, in the hard rock substratum, of a permeable structure that permits the transit of "deep" origin gas to the surface. This transport by advection disturbs the radon diffusion profile from the first meters of soil into the atmosphere. The radon thus behaves as a marker of deeper gases percolating through the regolith cover. Indeed, in such a context with low-permeability weathered formations, because of its short half-life (3.8 days) the radon measured in the first decimeters of the soil displays an exclusively superficial origin. Hence the measurement of the radon content in soil, at an identical depth from one sampling site to another, helps locate the zones affected by advective gas transfers which explains why the radon anomalies in soil gases, identified at the scale of a hydrogeological prospecting site located in a hard rock context, usually coincide vertically in hydraulically active fracture zones. This fully justifies the use of this method to site water wells, provided some precautions are observed, particularly pertaining to the spatial and temporal variability of the signal associated with different types of soils and changes in the meteorological parameters and soil moisture contents. The methodology is simple since only robust equipment is required. The estimation of gas transport parameters also helped identify the extent of advection areas. During the dry season they are characterized by low gas velocity. These zones shrink with the early rains, and the advection area is confined vertically up the fault where a channeling effect occurs: Soil gas preferably follows the less constricted pores, and the increased pressure gradient offsets the decrease in permeability.