Glomalin Production and Microbial Activity in Soils Impacted by Gypsum Mining in a Brazilian Semiarid Area

Problem statement: Mining activities involve the removal of the vegetal cover and the soil organic layer, causing a severe environmental impact. In Northeast Brazil, 40% of the world’s crude gypsum is found in a semiarid area, making this region responsible for 95% of the gypsum demand in the national market. Although economically important, this activity is harmful to the environment. Studies of soil microbiological and biochemical attributes can help in the identification of the limitations of impacted ecosystems, providing data to define strategies for sustainability of such environments. Approach: To evaluate and compare the biological state of preserved and mining degraded semiarid soils, a native preserved area and areas impacted by gypsum mining were selected at the Araripina Experimental Station, located in the semiarid region of Pernambuco State, Northeast Brazil. The four sampling areas included: (1) A native, preserved “caatinga” area with spine bearing trees and shrubs and some characteristic xerophytic plants (AN); (2) An area surrounding the mine, presenting the same type of vegetation although already degraded (AM); (3) A waste deposit area (AR); (4) Interface area between the waste deposit and a mining degraded area (AI). Samples were taken in each area (1000 m²) during two periods: wet (December/2003, Rainfall = 28.7 mm) and dry (September/2004, Rainfall = 1.3 mm). Results: Fluorescein diacetate hydrolysis values, microbial biomass C and basal respiration were higher in the preserved “caatinga” than in the impacted areas. The gypsum mining activity reduced the concentration of easily extractable glomalin in relation to the native “caatinga” area in both sampling periods. Higher deposits of total glomalin also occurred in the native area, however, mainly during the wet period. Conclusion: The mining activity produced a negative impact on the soil microbiota, reducing the total enzymatic activity. The microbial biomass was significantly lower in the waste deposit area than in the native and interface areas. The results indicated that the mining activity is harmful to the soil microbiota in this area and that glomalin can be a useful indicator of soil disturbance.