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Description
Microbial-Induced Calcite Precipitation (MICP) is a biogeochemical process that induces the formation of carbonate minerals. Via urea hydrolysis, soil microorganisms are stimulated through supplying urea, calcium, and simple carbon nutrients. Calcium chloride (CaCl$_2$) is typically used as a source for calcium, but basic silicate rocks and other materials have been investigated as alternatives. Weathering of calcium-rich silicate rocks (e.g., basalt and dolerite) releases calcium, magnesium, and iron, process associated with sequestration of atmospheric CO$_2$ and formation of paedogenic carbonates. Soil CO$_2$ emissions associated with MICP have been reported using both sources of calcium. Because MICP involves the inorganic carbon and nitrogen cycles, other greenhouse gas fluxes, particularly N$_2$O, could potentially occur. We present an investigation of soil-atmosphere CO$_2$, N$_2$O and CH$_2$ fluxes of a MICP treated quartz-sand in a soil column set up using CaCl$_2$ or dolerite fines applied on the soil surface as sources for calcium. Low and high concentrations of urea-calcium were studied to cover soil inputs used in agricultural and engineering applications, respectively. Greenhouse gas fluxes were monitored with a PICARRO instrument over 11 days following end of MICP treatment. In addition, soil inorganic and organic carbon and their isotopic composition were determined by isotope-ratio mass spectrometry. Soil-solution was analysed for pH, total nitrogen, organic carbon, ammonium, and nitrates to monitor urea hydrolysis and nitrification processes. Results indicated urea hydrolysis, soil carbonation, CO$_2$ emissions occurred with either source of calcium, while nitrates were detected at lower concentrations than the pristine soil. Compared to treatment with CaCl$_2$, dolerite fines induced an earlier urea hydrolysis, higher consumption of organic carbon and nitrogen, higher CO$_2$ emissions, and a lower precipitation of carbonates within soil. Interestingly, N$_2$O emissions were only detected with dolerite. The results of this study highlight that weathering of dolerite fines on soil is likely to induce a faster and diverse microbial response to nutrient application, resulting in higher short term greenhouse gas emissions.
