Large‐scale solar development in desert ecosystems has the potential to generate electricity thereby reducing atmospheric CO2. Deserts are targeted as a vast “opportunity” for prioritizing ground-mounted utility-scale renewable energy (³ 1 MW) sitings. However, these ecosystems are large repositories of belowground C storage in the form of soil CaCO3 and stable organic carbon from long-lived, deep-rooted vegetation. In the California desert, water isotope ratios show that between 64% and 87% of the water for microphyll woodland species is groundwater. These plants support roots and associated microbes deep into the soil profile. Calcium carbonate crystals form, dissolve, and re-form deep in soil along mycorrhizal fungal hyphae. Along with endangered species mortality and blockage of dispersal corridors, conversion of microphyll woodlands to solar deployments could impact desert ecology. Unintentional destruction of terrestrial vegetation through uninformed siting of renewable energy installations could be counter-productive if those C sinks become C sources.
Current practices include stripping the vegetation and leveling the soil surface, as well as maintaining a soil surface devoid of vegetation. Both inorganic (CaCO3) and organic carbon are exposed and fragmented upon disturbance. Chemical equilibrium would suggest that little CO2 should escape as CaCO3 rapidly binds in the presence of water. But disequilibrium occurs in the presence of radiation and from the dispersion of Ca as well as the lowered concentration of CO2 in atmosphere (400ppm) as opposed to the rhizosphere (2,000 to 10,000ppm). Our goal was to assess carbon dynamics in desert ecosystems.
Isotopic ratios of carbon and oxygen were measured to assess dynamics of inorganic soil carbonates. Stable isotope ratios showed that in the surface layers of soil, caliche is dynamic as fractionation and exchange of C and O with the modern atmosphere is occurring. In laboratory studies, small amounts of inorganic carbon are lost from CaCO3 with intermittent saturation. Up to 5% of the C can be lost annually.
Using sensors and flux towers, flux rates of carbon between soil and atmosphere of desert ecosystems were measured. Using CO2 concentration and flux data, caliche formation and weathering were modeled. We found that carbon is being cycled in complex ways including between organic and inorganic forms in desert shrublands, and that carbon will be lost from areas stripped of vegetation.
Protecting native microphyll woodlands and other vegetation types that have deep roots is important to sequestering carbon and protecting buried inorganic soil carbon stocks.