Changes of Technosol properties and vegetation structure along a chronosequence of dredged sediment deposition in areas with alluvial gold mining in Colombia

Abstract

PurposeAlluvial gold mining leaves a vast amount of dredged sediment that covers the natural soil, destroys riparian ecosystems, and impacts riverbeds and valleys. In Colombia, more than 80,000 ha are covered by dredged sediment. Technosols developed from such deposits undergo strong transformations during the early stages of formation due to the diverse nature of the constituents. The aims of this study are (i) to investigate changes in soil morphological and physicochemical properties at early stages of pedogenesis, (ii) to estimate the variability of size structure distribution of the new plant cover as affected by the time period since establishment and deposit type, and (iii) to determine which soil parameters correlate best with the size structure distribution of vegetation.Materials and methodsSoil characterization through morphological and physicochemical analysis was conducted on Technosols developed from gravel and sandy deposits of different ages (0–12 years). A vegetation survey was conducted to measure tree dimensions and identify the most common species. Data were analyzed using non-parametric tests to avoid the loss of information due to data smoothing.Results and discussionThe studied Technosols are subject to processes similar to those occurring in natural parent materials such as mineral transformations, changes in redox conditions, organic matter accumulation in the topsoil, and a rapid differentiation of horizons. However, the Technosols in our study sites show an unusually fast development not often observed in natural soils, with drastic changes observed at very early stages of formation. Gravel deposits offer more favorable conditions for plant growth, and marked changes in pedogenic processes can be observed compared with sandy deposits, which are reflected in changes of chemical properties.ConclusionsFactors such as the technology used for mining and the continuous deposition of dredged sediments in a cumulative way during the exploitation period, as well as the disturbances after deposition, result in a high diversity of constituents and high heterogeneity of dredged sediment deposits. Gravel and sand deposits, originated from the same sections of the river and after similar separation processes for ore extraction, undergo divergent pedogenic processes at different rates, which could be explained by a remarkable effect of particle size distribution. For vegetation establishment, the selection of tree species should be based on their capacity for nutrient pumping through deep rooting to sequester carbon and to adapt morphologically to heterogeneity in nutrient availability by growing roots in nutrient-rich zones.