Water Resources Professional Project Reports

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Technical Report

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Soils play an essential role in ecosystem health as they are the medium for terrestrial and aquatic life. Soils can be drastically altered by wildfire as seen in the Jemez River watershed following the 2011 Las Conchas fire which burned over 31,800 acres. The aim of this research is twofold: 1) to characterize the effects of fire on the cation and anion composition in soil by burn severity following the 2011 Las Conchas wildfire and 2) to assess the leaching capacity of nitrate (NO3-), phosphate (PO43-), sulfate (SO42-), aluminum (Al3+), calcium (Ca2+), iron (Fe2+), potassium (K+), and magnesium (Mg2+) from soils. The pH, % organic matter (OM), and anion and cation rom 32 soil samples collected at the Valles Caldera National Preserve from four burn categories: high, moderate, low and unburned in December 2016 and April 2017. The pH was highest in the moderate burn severity category and statistically different between the moderate/low burn severity categories. The % OM was higher in burned soils than unburned soils and statistically different between the moderate/unburned soils. Principal component analysis showed a clear separation between the chemical composition of soils collected in December and those collected in April; the analysis also showed that sites within the unburned/low severity categories were more homogenous than those from the high/moderate, high/low or moderate/low categories. Sulfate was the only anion that did not differ significantly by season. Three of eight ions, NO3-, Ca2+ and Fe2+, were statistically different between burn severity categories. The leaching of these eight ions in 10 mmol Na2CO3 resulted in higher concentrations in solution over 0 and 30-minutes for every ion except Mg2+ (concentrations for Mg2+ were below detection for ICP-OES). All three anions either adsorbed back onto the soil surface or were removed from solution after 1 hour. The results suggest that post-fire recovery of soils may differ among burn severity category but the burned soils following the Las Conchas fire as indicated by the measurements used are at least as fertile as the unburned areas examined.

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soils, ecosystem health, jemez river, las conchas, las conchas fire

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