Effects of Land Use on Microbial Indices in Tantalite Mine Soils, Western Rwanda

Abstract

Rare metal mining in western Rwanda created massive degraded mine wastelands. Some of them were restored by afforestation with pine and eucalyptus forests while others have been cultivated alongside arable lands, owing to limited land availability. We assessed the effects of these land uses on microbial biomass and activity (basal C and net N mineralization) in a laboratory experiment with fresh soils (0–20 cm) of an unmined native forest, two tantalite mine soils (Technosols) afforested with pine and eucalyptus forests, an arable soil, and two cultivated Technosols. Afforestation increased soil organic C (SOC) and total N in pine and eucalyptus Technosols, reaching 34–40% and 28–30%, respectively, of that in the native forest. The tree species differed significantly in microbial activity and biomass, exhibiting a trajectory towards recovery depicted in lower metabolic quotient. Basal respiration of pine Technosol and native forest soil were similar, while that of eucalyptus Technosol was 11 and 14% less compared to its forest counterparts. Conversely, net N mineralization in pine and eucalyptus Technosols were 40 and 65% of that in native forest soil, respectively. Soil microbial biomass C in pine and eucalyptus Technosols were 33 and 48% of that in native forest soil. Furthermore, a decreased SOC availability to soil microorganisms at low soil pH promoted fungal ergosterol as an indicator for saprotrophic fungi. The arable soil and cultivated Technosols did not differ significantly in SOC, N, microbial biomass, and activity. The soil biological quality was constrained by soil acidity, dithionite‐extractable Al, and low P availability. Copyright © 2016 John Wiley & Sons, Ltd.

The Role of Soil pH in Plant Nutrition and Soil Remediation

“…is is controlled by soil pH [28]. Soil pH as a driving force for microbial ecophysical indices stems from its influence on the microbial community together with the maintenance demands of the community [28] and was among the predictors of the metabolic quotient [29,30]. e metabolic quotient was found to be two-and-a-half times higher in low pH soils compared to neutral pH soils [28].…”

Chemical and mineralogical properties of post-mining sites in two gold mining concessions in Ghana

“…These corroborate those reported by Tetteh and Dedzoe (2004) in mine soils of Bogoso and by Boateng et al (2012) in mine soils of Obuasi. Relatively high pH values have been found in mine soils in Rwanda (Neina et al, 2017) and in eastern Ohio (Shrestha and Lal, 2011) compared to their unmined counterparts. This could be due to the homogenisation of top-and subsoils during stockpiling.…”

“…The mine sites normally are re-vegetated as part of the reclamation process generally are done with and without amendments depending on the chemical and mineralogical properties of the mine soils. For instance, the mine soils are characterised by low soil organic carbon (SOC), total nitrogen contents (Shrestha and Lal, 2007;Neina et al, 2017), because of significant amounts of rock fragments from blasted rocks. Additionally, the impact of heavy duty vehicles may result in high bulk density and could influence soil structure.…”

“…These conditions require proper management to avoid "pollution havens" that lead to permanent environmental damage (Cohen, 1996;Tienhaara, 2006). Previous research revealed that reclamation may create pre-mine soil conditions with time (Barnhisel and Gray, 2000;Shrestha and Lal, 2006), especially after proper re-vegetation (Biemelt et al, 2005;Neina et al, 2017) because reclaimed mine soils have been identified to have high potentials to sequester SOC and improve soil conditions (Shrestha and Lal, 2006). However, this mostly depends on specific post-mining management practices employed and the target end land uses.…”

Can a Blend of Amendments Be an Important Component of a Rehabilitation Strategy for Surface Coal Mined Soils?

“…Mining of coal is responsible for massive amounts of land degradation through the removal of large quantities of topsoil and subsoil [1]. Such processes have been shown to negatively impact the physical [2] and chemical [3] properties of soils, and henceforth the plant production potential of soils after land reclamation [4]. Soil physical properties affect plant growth in two major ways: Compaction and consequently soil water availability.…”