MOBILITY OF HEAVY METALS AND THE INFLUENCE ON SOIL MICROBIOLOGICAL CONSTITUENTS IN RESPONSE TO CLIMATE CHANGE

Climate change is the forethought of modern Geoscience. The impacts may induce substantial change of the abiotic and biotic systems we observe in near-surface soil geology. A major contributor of these impacts comes from heavy metal sources including disposal of mine tailings, disposal of high metal wastes, and land application of pesticides. Heavy metals that enter soil may linger for years depending on several factors. A factor is the pattern of wetting and drying of the soil due to rainfall events and their alternating dry periods. Due to climate change, we are seeing changes in precipitation patterns with high-volume storms and alternating periods of drought.

Movement of metals in soils is dominated by the colloidal fraction of the soil. This research aims to better understand: 1) How heavy metals migrate in response to precipitation cycles, 2) The effect of the charge of the heavy metals on their migration impact regarding depths reached, and 3) The impact on soil microbial diversity and inhibition.

The experimental design of the study is focusing on the metals lead, in its divalent form (Pb²⁺), and chromium, in the form of chromate (CrO4 ^2-). These metals are toxic or carcinogenic and represent environmental threats. The experimental unit is based on soil cores, where each replicate receives artificial precipitation events. These events are simulated with premeasured amounts of water, then distributed with pipettes. The initial exposure of the cores to the metal reagents follows an identical method. The cores are to be subdivided after all precipitation events have been completed. This will allow an analysis to determine the depth of the metals.

Once complete, a microbiological survey of each set of replications and their subsets will be exposed to one last simulated precipitation event to expose bacterial populations. A Flow Cam will be used to determine counts and diversity of the microbial constituents. The microbes will represent soil health, as such organisms provide the building blocks for primary producers to cultivate themselves. Some aspects include those that are classified as nitrifying and denitrifying bacteria. Other examples include elemental cycles and bacteria that may even be metal reducing. This study will provide a crucial and holistic perspective of soil health.