Restauration de zones humides de montagne : le rôle du régime hydrologique et de l'introduction de plantes après 15 ans dans le massif des Rocheuses au Colorado

International audienceTwelve wetland complexes were buried and/or drained by golf course and ski area development in the Colorado Rocky Mountains in the 1980s and early 1990s. We restored all or portions of each wetland, including fens, wet meadows and riparian areas, during 1997-2002. Intensive pre- and post-construction monitoring was used to develop restoration plans and evaluate their success. We revisited the sites to analyze long-term restoration processes in 2013-2016. Prior to construction the depth to the water table was measured weekly in monitoring wells installed through the fill, and into the wetland surfaces during and following restoration. Reference sites for each wetland type were used to characterize water table depth and vegetation for each wetland type. Restoration included removal of fill material and drains to create land surfaces with water table depth and dynamics similar to the reference areas for each wetland type. We planted each site with nursery grown sedges, willows and herbaceous dicots. Post restoration monitoring of water table depth, vegetation composition, sedge shoot density and willow growth was analyzed. The water table depth and dynamics of each restored wetland was similar to suitable reference sites on short and long time scales, indicating a stable hydrologic regime. Carex utriculata reached its maximum shoot density 4-5 years after planting indicating rapid growth and high production. Willow stems were still increasing in height 15 years after planting and basal stem density was also increasing. Most planted herbaceous dicots disappeared, indicating the difficulty of establishing them from plantings. Exotic (non-native) plants have invaded all three wetland types, with their highest cover in riparian areas. Critical factors that led to success were careful hydrological analysis of reference and restoration sites prior to earthwork, creating appropriate land/ground water interactions, and establishing clonal rhizomatous sedges and native willows

Carbon storage and long-term rate of accumulation in high-altitude Andean peatlands of Bolivia

(1) The high-altitude (4,500+ m) Andean mountain range of north-western Bolivia contains many peatlands. Despite heavy grazing pressure and potential damage from climate change, little is known about these peatlands. Our objective was to quantify carbon pools, basal ages and long-term peat accumulation rates in peatlands in two areas of the arid puna ecoregion of Bolivia: near the village of Manasaya in the Sajama National Park (Cordillera Occidentale), and in the Tuni Condoriri National Park (Cordillera Real). (2) We cored to 5 m depth in the Manasaya peatland, whose age at 5 m was ca. 3,675 yr. BP with a LARCA of 47 g m-2 yr-1. However, probing indicated that the maximum depth was 7–10 m with a total estimated (by extrapolation) carbon stock of 1,040 Mg ha-1. The Tuni peat body was 5.5 m thick and initiated ca. 2,560 cal. yr. BP. The peatland carbon stock was 572 Mg ha-1 with a long-term rate of carbon accumulation (LARCA) of 37 g m-2 yr-1. (3) Despite the dry environment of the Bolivian puna, the region contains numerous peatlands with high carbon stocks and rapid carbon accumulation rates. These peatlands are heavily used for llama and alpaca grazing

Dual in-aquifer and near surface processes drive arsenic mobilization in Cambodian groundwaters

Millions of people globally, and particularly in South and Southeast Asia, face chronic exposure to arsenic from reducing groundwater in which arsenic release is widely attributed to the reductive dissolution of arsenic-bearing iron minerals, driven by metal reducing bacteria using bioavailable organic matter as an electron donor. However, the nature of the organic matter implicated in arsenic mobilization, and the location within the subsurface where these processes occur, remains debated. In a high resolution study of a largely pristine, shallow aquifer in Kandal Province, Cambodia, we have used a complementary suite of geochemical tracers (including 14 C, 3 H, 3 He, 4 He, Ne, δ 18 O, δD, CFCs and SF 6 ) to study the evolution in arsenic-prone shallow reducing groundwaters along dominant flow paths. The observation of widespread apparent 3 H- 3 He ages of <55 years fundamentally challenges some previous models which concluded that groundwater residence times were on the order of hundreds of years. Surface-derived organic matter is transported to depths of >30 m, and the relationships between age-related tracers and arsenic suggest that this surface-derived organic matter is likely to contribute to in-aquifer arsenic mobilization. A strong relationship between 3 H- 3 He age and depth suggests the dominance of a vertical hydrological control with an overall vertical flow velocity of ~0.4 ± 0.1 m·yr −1 across the field area. A calculated overall groundwater arsenic accumulation rate of ~0.08 ± 0.03 μM·yr −1 is broadly comparable to previous estimates from other researchers for similar reducing aquifers in Bangladesh. Although apparent arsenic groundwater accumulation rates varied significantly with site (e.g. between sand versus clay dominated sequences), rates are generally highest near the surface, perhaps reflecting the proximity to the redox cline and/or depth-dependent characteristics of the OM pool, and confounded by localized processes such as continued in-aquifer mobilization, sorption/desorption, and methanogenesis