New Mexico Geological Society Annual Spring Meeting — Abstracts

The Southern Sacramento Mountains, located in southeastern New Mexico serves as a recharge area for adjacent regional aquifers. Out of concern about the region’s future groundwater and surface water supplies, water resource managers are interested in potentially increasing groundwater levels and stream discharges by thinning trees in mountain watersheds. The Sacramento Mountain Watershed Study (SMWS) is focused on assessing the effects of tree-thinning on the local hydrologic system in the Sacramento Mountains. A watershed-scale water balance will be evaluated before and after thinning. The SMWS field area is 3 L Canyon, a small watershed located in the southern Sacramento Mountains. The forest in 3 L Canyon is mixed conifer, with Douglas fir being the primary species. An important parameter affecting input to the water balance is the amount of rainfall lost to tree canopy interception, which can be upwards of 40% in a mixed conifer forest. Throughfall was measured in 3 L Canyon from September 2008 to December 2010 as part of the baseline data before thinning, and interception loss was determined using the volume balance method.

Gross rainfall and other meteorological data were collected at the highest elevation in the watershed. Throughfall was measured at two locations near the ridgetop. The two throughfall collectors were located under visibly different densities of tree canopy. Direct leaf area index (LAI) measurements were made at each throughfall measurement point using an optical plant canopy analyzer (LI-COR LAI-2000). Averaged over the period from May until September, interception loss was generally greater at the throughfall collector with higher LAI and denser canopy than at the throughfall collector with smaller LAI and less dense canopy. However, for shorter timescales (monthly and per-event), the observed interception loss was not always greater at the throughfall collector with higher LAI. This could be due to spatial variability, which gets averaged out when looking at longer timescales. The ultimate goal of this research is to correlate throughfall to LAI and other spatial data, including satellite imagery, to create throughfall maps for the 3 L Canyon watershed that will be used to estimate rainfall inputs to the watershed-scale water balance.