Baltimore Ecosystem Study Cary Institute of Ecosystem Studies

2012 BES Annual Meeting Presentation and Poster Abstracts

Pilot testing of a Picarro water isotope analyzer
Welty, Claire
Co-Authors: Claire Welty, Julia Miller, Jon Duncan, Dakota Smith, Dan Bain, Matt Baker, Larry Band, Kenneth Belt, Peter Groffman, Sujay Kaushal, Michelle Lorah, Andrew Miller, Stuart Schwartz

Abstract: We received a NSF MRI grant in 2010 to purchase a Picarro water isotope analyzer (Model L2010-i) to enable determination of 18O/16O and 2H/1H ratios (δ18O, δ2H) in liquid water samples. As a pilot study, we analyzed two sets of 40 stream samples from Dead Run collected under high (March) and low (July) flow conditions in 2011 and 50 precipitation samples collected throughout 2011. From analysis of the precipitation samples, we calculated a Baltimore meteoric water line that was parallel to and shifted upward from the global meteoric water line, with a best fit of δ2H = 8.20 δ18O + 20.5. Some seasonality was exhibited with respect to isotopic composition of precipitation, with clustering of convective storms toward the less negative end of the data. Frontal storms occurred throughout the year and were variable with respect to isotopic content and direction of origin. Stream synoptic samples were collected in one day (after one week of no rain), by sampling tributaries at road crossings. The resulting spatial variability in isotopic content of stream samples was striking, with the summer synoptic having a greater spread of values. For the March synoptic, δ2H = 6.32 δ18O + 4.6; for the July synoptic, δ2H = 6.01 δ18O + 3.4. The slopes (~6) were similar for the two synoptics and lower than the Baltimore meteoric water line slope of 8.2. This reduced-slope effect has been documented by others and is attributed to evaporation. Analyses in the coming year will span a range of studies carried out by co-PIs.