Monitoring litter interception of rainfall using leaf wetness sensor under controlled and field conditions

Leaf litter interception of water is an integral component of the water budget for some vegetated ecosystems. However, loss of rainfall to litter receives considerably less attention than canopy interception due to lack of suitable sensors to measure changes in litter water content. In this study. a commercially available leaf wetness sensor was calibrated to the gravimetric water content of eastern redcedar (Juniperus virginiana) litter and used to estimate litter interception in a subhumid eastern redcedar woodland in north-central Oklahoma. Under controlled laboratory conditions, a strong positive correlation between the leaf wetness sensor output voltage (mV) and measured gravimetric litter water content (theta(g))( )was determined: theta(g) = (.0009 x mV(2)) (0.14 x mV) - 11.41 (R-2 = .94, p < .0001). This relationship was validated with field sampling and the output voltage (mV) accounted for 48% of the observed variance in the measured water content. The maximum and minimum interception storage capacity ranged between 1.16 and 12.04 and 1.12 and 9.62 mm, respectively. The maximum and minimum amount of intercepted rain was positively correlated to rainfall amount and intensity. The continuous field measurements demonstrated that eastern redcedar litter intercepted approximately 8% of the gross rainfall that fell between December 16, 2014 and May 31, 2015. Therefore, rainfall loss to litter can constitute a substantial component of the annual water budget. Long-term in situ measurement of litter interception loss is necessary to gain a better estimate of water availability for streamflow and recharge. This is critical to manage water resources in the south-central Great Plains, USA where grasslands are rapidly being transformed to woodland or woody dominated savanna.