HIGH TOTAL ORGANIC SOIL CARBON (TOSC), LOW DISSOLVED ORGANIC CARBON (DOC) AND BLACK CARBON (BC) HORIZONS, SAN JUAN MOUNTAINS, COLORADO: IMPLICATIONS FOR ENHANCED NATURAL TERRESTRIAL CARBON SEQUESTRATION (NTS) LAND USE MANAGEMENT AND RECLAMATION PROTOCOLS

The need to reduce CO₂ levels has stimulated studies to better understand and quantify potential carbon sinks. Soils represent a significant natural terrestrial sink needed to mitigate rising atmospheric CO₂. To examine NTS, TOSC stability and the potential for DOC as a climate change proxy, soil cores and water samples from high plains to alpine sites in non-wetland environments were analyzed.

Forest soils derived from intermediate to mafic volcanic bedrock that exhibit BC horizons have the highest TOSC (34.15 wt %), C: N (43) and arylsulfatase enzyme activities (EA) >278 µg p-nitrophenol/g/h). Monzonite, shale and gneiss terrain has intermediate TOSC. Unreclaimed mine sites have the lowest TOSC (0.01 wt %), C: N (0 – 6.5) and EA (0 - 41). In mineralized areas, naturally reclaimed and undisturbed soils derived from propylitized volcanic rock also exhibit high TOSC (13.5 - 25.6 wt %), C: N and EA. This is consistent with earlier studies in which propylitic bedrock was found to have a high, natural acid neutralizing capacity (ANC) as characterized by calcite-chlorite-epidote. Charcoal radiocarbon dates collected from paleo-burn horizons indicate an old and, if undisturbed, stable carbon pool (500 -5,440 yr B.P.). Peak runoff and low-flow samples from surface waters at monitored sites were analyzed for DOC. In general, DOC flux in undisturbed and natural reclaimed areas is low (ave.0.9 mg/L) –indicating that C is not readily released.

The resulting high NTS potential is attributed to: host-rock weathering nutrients, contaminant neutralization, formation of secondary mineral carbonates, formation of soil aggregates, high specific surface area and adsorption enhancing Ca-Mg-Fe clays that stabilize C and N, and BC horizons, which support soil development and cation exchange. The data suggest TOSC and DOC correlate with soil properties, bedrock geology and alteration type. Data from recovering burn areas and natural reclamation sites indicate biogeomimicry practices correlated with bedrock and site specific soil amendments including ANC rock and biochar can support ecosystem services such as soil productivity, moisture retention and erosion mitigation. Enhancing the NTS potential of soils may be a cost-effective strategy to help draw down atmospheric CO₂ and restore forests, watersheds and disturbed lands.