Long-term pollution by chlordecone of tropical volcanic soils in the French West Indies: New insights and improvement of previous predictions.

Chlordecone (CLD), was widely applied in banana fields in the French West Indies from 1972 to 1993. The WISORCH model was constructed to assess soil contamination by CLD and estimated that it lasts from 100 to 600 years, depending on leaching intensity and assuming no degradation. However, recent studies demonstrated that CLD is degraded in the environment, hence questioning the reliability of previous estimations. This paper shows how to improve the model and provides insights into the long-term dissipation of CLD. In-situ observations were made in nearly 2545 plots between 2001 and 2020, and 17 plots were sampled at two dates. Results of soil analyses showed an unexpected 4-fold decrease in CLD concentrations in the soil, in contrast to simulations made using the first version of WISORCH at the time. Neither erosion, nor CLD leaching explained these discrepancies. In a top-down modeling approach, these new observations of CLD concentrations led us to implement a new dissipation process in the WISORCH model that corresponds to a DT50 dissipation half-life of 5 years. The new version of the improved model allowed us to update the prediction of the persistence of soil pollution, with soil decontamination estimated for the 2070s. This development calls for re-evaluation of soil pollution status. Further validation of the new version of WISORCH is needed so it can contribute to crop management on contaminated soil.

Landscaping compromises for land degradation neutrality: The case of soil erosion in a Mediterranean agricultural landscape.

Soil erosion is the primary process driving land degradation. Using multiple scales of management to minimize soil erosion is crucial to achieve land degradation neutrality targets within the Sustainable Development Goals agenda. Land management (LM) influences both on-site and off-site erosion on the event-scale and over the long-term. However, each LM differs in effectiveness depending on the temporal scale considered. In order to understand how LM effects internal and external catchment dynamics, we apply LandSoil, a physically based landscape evolution model, to evaluate 7 LM scenarios over long- (30 years) and short-terms (event scale). LM scenarios included changes in land use and/or landscape structure. Under current LM, mean surface soil erosion was ∼0.69 ±â€¯39·10-3 m over 30 years. In contrast, a single extreme event (435 mm/24 h) in January resulted in ∼0.62 ±â€¯3·10-3 m loss and ∼0.04 ±â€¯2·10-3 m if it occurred in October. Heterogeneous patterns of erosion and deposition developed after 30 years, whereas extreme events dominantly showed soil loss and high catchment connectivity. Effectiveness of LM in erosion mitigation and sediment trapping differed according to temporal and spatial scales for each scenario. We concluded that multiple temporal and spatial scales must be incorporated in order to adaptively manage land degradation and meet neutrality targets.

Landscape evolution and agricultural land salinization in coastal area: A conceptual model.

Soil salinization is a major threat to agricultural lands. Among salt-affected lands, coastal areas could be considered as highly complex systems, where salinization degradation due to anthropogenic pressure and climate-induced changes could significantly alter system functioning. For such complex systems, conceptual models can be used as evaluation tools in a preliminary step to identify the main evolutionary processes responsible for soil and water salinization. This study aimed to propose a conceptual model for water fluxes in a coastal area affected by salinity, which can help to identify the relationships between agricultural landscape evolution and actual salinity. First, we conducted field investigations from 2012 to 2016, mainly based on both soil (EC1/5) and water (ECw) electrical conductivity survey. This allowed us to characterize spatial structures for EC1/5 and ECw and to identify the river as a preponderant factor in land salinization. Subsequently, we proposed and used a conceptual model for water fluxes and conducted a time analysis (1962-2012) for three of its main constitutive elements, namely climate, river, and land systems. When integrated within the conceptual model framework, it appeared that the evolution of all constitutive elements since 1962 was responsible for the disruption of system equilibrium, favoring overall salt accumulation in the soil root zone.

Soft water level sensors for characterizing the hydrological behaviour of agricultural catchments.

An innovative soft water level sensor is proposed to characterize the hydrological behaviour of agricultural catchments by measuring rainfall and stream flows. This sensor works as a capacitor coupled with a capacitance to frequency converter and measures water level at an adjustable time step acquisition. It was designed to be handy, minimally invasive and optimized in terms of energy consumption and low-cost fabrication so as to multiply its use on several catchments under natural conditions. It was used as a stage recorder to measure water level dynamics in a channel during a runoff event and as a rain gauge to measure rainfall amount and intensity. Based on the Manning equation, a method allowed estimation of water discharge with a given uncertainty and hence runoff volume at an event or annual scale. The sensor was tested under controlled conditions in the laboratory and under real conditions in the field. Comparisons of the sensor to reference devices (tipping bucket rain gauge, hydrostatic pressure transmitter limnimeter, Venturi channels…) showed accurate results: rainfall intensities and dynamic responses were accurately reproduced and discharges were estimated with an uncertainty usually acceptable in hydrology. Hence, it was used to monitor eleven small agricultural catchments located in the Mediterranean region. Both catchment reactivity and water budget have been calculated. Dynamic response of the catchments has been studied at the event scale through the rising time determination and at the annual scale by calculating the frequency of occurrence of runoff events. It provided significant insight into catchment hydrological behaviour which could be useful for agricultural management perspectives involving pollutant transport, flooding event and global water balance.