Leaf litter water content and soil surface CO2 fluxes in a deciduous forest

Abstract

This study has examined the ability of a commercial, miniature soil moisture probe to measure water content within the leaf litter layer found on the floor below a deciduous forest site in Oak Ridge, eastern Tennessee. With its small size and high moisture sensitivity, this probe provides a potential opportunity for monitoring the water content beneath complex vegetation systems within the soil–air interface normally characterized by a large spatial variability and small magnitude of energy, water and carbon fluxes. With its low-cost and low-power, many of these probes can be easily deployed at a much lower cost than the single traditional soil moisture probe that is usually used for monitoring local-site soil moisture and is unsuitable for litter wetness. Miniature probe measurements of litter moisture were compared with gravimetric measurements from litter sample baskets positioned across the forest floor and the change in the magnitude of the probe output correlated linearly to the water content of the litter. Gravimetric measurements of the litter water content ranged from 1 to 3 g (H2O) g−1 (litter dry weight), and hourly values varied with precipitation, radiation, and wind speed. Measurements of the litter and soil water content were incorporated into empirical models adopted from the literature for estimating the litter and soil components of the CO2 flux. The comparison between the modeled and the measured hourly CO2 flux on the forest floor produced root means square differences (RMSD) of about 1.11 and 1.32 umol m−2 s−1 for estimates with and without litter layer, respectively, and about 25% of the forest floor CO2 flux was due to direct contributions from the litter layer. The results of the study indicate that the probes performed well in a complex forest environment and can be used to help evaluate the water, energy and CO2 fluxes on the soil surface inside a variety of vegetation stands.