Chemico-mineralogical changes of ultramafic topsoil during stockpiling: implications for post-mining restoration

International audienceLateritic topsoils, which are usually removed and stored apart before mining operations take place, play an essential role in the success of post-mining restoration. They contain elements to recover chemical (organic matter, nutrients) and biological (seed and bud banks, microorganisms) fertility of the soil. Conserving topsoil fertility during storage time is essential for a successful use of topsoil during restoration. In this study, different chemico-mineralogical properties of a lateritic topsoil from the Goro nickel mine (New Caledonia) were monitored from its original in situ emplacement on the soil profile, immediately after its stockpiling and after 24 months of storage. Our analyses show that topsoil experienced noticeable changes immediately after storage, mostly produced by mixing of different soil profiles. Cation Exchange Capacities and concentrations of most elements did not vary even after 24 months of storage. However, a slight reduction of Ni, Cr, K, Na and of the C:N ratio, and an increase of Ca have been observed. Stockpiling has not affected negatively the chemical fertility of the topsoil, although biological parameters should be considered to have a complete view of stockpiling sustainability

Structural development of vegetation on rehabilitated North Stradbroke Island: Above/belowground feedback may facilitate alternative ecological outcomes

Introduction: This study depicts broad-scale revegetation patterns following sand mining on North Stradbroke Island, south-eastern Queensland, Australia. Methods: Based on an ecological timeline spanning 4-20 years post-rehabilitation, the structure of these ecosystems (n = 146) was assessed by distinguishing between periods of 'older' (pre-1995) and 'younger' (post-1995) rehabilitation practices. Results: The general rehabilitation outlook appeared promising, whereby an adequate forest composition and suitable levels of native biodiversity (consisting of mixed-eucalypt communities) were achieved across the majority of rehabilitated sites over a relatively short time. Still, older sites (n = 36) appeared to deviate relative to natural analogues as indicated by their lack of under-storey heath and simplified canopy composition now characterised by mono-dominant black sheoak (Allocasuarina littoralis) reaching up to 60% of the total tree density. These changes coincided with lower soil fertility parameters (e.g., total carbon, total nitrogen, and nutrient holding capacity) leading us to believe that altered growth conditions associated with the initial mining disturbance could have facilitated an opportunistic colonisation by this species. Once established, it is suspected that the black sheoak's above/belowground ecological behaviour (i.e., relating to its leaf-litter allelopathy and potential for soil-nitrogen fixation) further exacerbated its mono-dominant distribution by inhibiting the development of other native species. Conclusions: Although rehabilitation techniques on-site have undergone refinements to improve site management, our findings support that putative changes in edaphic conditions in combination with the competitive characteristics of some plant species can facilitate conditions leading to alternative ecological outcomes among rehabilitated ecosystems. Based on these outcomes, future studies would benefit from in depth spatio-temporal analyses to verify these mechanisms at finer investigative scales

Common surgical procedures in pilonidal sinus disease: A meta-analysis, merged data analysis, and comprehensive study on recurrence

Abstract We systematically searched available databases. We reviewed 6,143 studies published from 1833 to 2017. Reports in English, French, German, Italian, and Spanish were considered, as were publications in other languages if definitive treatment and recurrence at specific follow-up times were described in an English abstract. We assessed data in the manner of a meta-analysis of RCTs; further we assessed non-RCTs in the manner of a merged data analysis. In the RCT analysis including 11,730 patients, Limberg & Dufourmentel operations were associated with low recurrence of 0.6% (95%CI 0.3–0.9%) 12 months and 1.8% (95%CI 1.1–2.4%) respectively 24 months postoperatively. Analysing 89,583 patients from RCTs and non-RCTs, the Karydakis & Bascom approaches were associated with recurrence of only 0.2% (95%CI 0.1–0.3%) 12 months and 0.6% (95%CI 0.5–0.8%) 24 months postoperatively. Primary midline closure exhibited long-term recurrence up to 67.9% (95%CI 53.3–82.4%) 240 months post-surgery. For most procedures, only a few RCTs without long term follow up data exist, but substitute data from numerous non-RCTs are available. Recurrence in PSD is highly dependent on surgical procedure and by follow-up time; both must be considered when drawing conclusions regarding the efficacy of a procedure