INFLUENCES OF DISCHARGE, pH, AND DOC ON RARE EARTH ELEMENT CONCENTRATIONS DURING RECOVERY FROM ACID RAIN AT THE BEAR BROOK WATERSHED IN MAINE (BBWM) USA
BBWM is a paired forested watershed experiment. One watershed (EB) has experienced a constant decline in atmospheric SO4 and NO3 deposition from 1987 to 2018, and is recovering from acid rain. Base cations in EB runoff declined faster than (SO4+NO3), causing further acidification (lower alkalinity and pH; higher Al+n) until 2005. Alkalinity and pH then increased slowly, as base cations reached a minimum about 2015 and then slowly increased. We sampled high discharge episodes in 2017 and 2018 from base flow through high discharge and the falling limb. Al and REEs were speciated in the field for total, dissolved, and organically-bound forms. We calculated particulate and ionic species. ?mol Al/L ? 103 times ?mol REEs/L; the five species of Al are generally in the same proportion as the REE species. Peak concentrations of Al and REEs co-occur at peak flow, corresponding to lower pH and higher DOC. The close correspondence between Al and REEs in acid soluble particulates suggests adsorption of REEs on precipitated Al(OH)3. ISCO samplers are unsuitable for such studies because of precipitation of Al(OH)3, caused by CO2 degassing in the vessels, and subsequent adsorption of REEs.
Stephen Norton (Primary Presenter/Author), University of Maine, Norton@maine.edu;
Ivan Fernandez (Co-Presenter/Co-Author), University of Maine, Ivanjf@Maine.edu;
Sarah Nelson (Co-Presenter/Co-Author), School of Forest Resources and Senator George J. Mitchell Center, University of Maine, Orono, ME, firstname.lastname@example.org;
Kaizad Patel (Co-Presenter/Co-Author), Pacific Northwest National Laboratory, Kaizad.Patel@Maine.edu;