Rare earth element and phosphorus mobility depend on adsorption to Al-, Fe-, and Mn-oxyhydroxides in a headwater stream in Vermont, USA

Abstract

We evaluated base cations, Al, Fe, Mn, REEs, DOC, anions, and P mobilization during three discharge events (E-1, E-2, E-3) at the headwater catchment W-9, Sleepers River, Vermont, USA. Peak discharge ranged from 3.696 (E-1) to 0.073 (E-3) mm h −1 . Eight samples from each event were speciated for total (unfiltered-acidified) and dissolved (0.45 µm filtered-acidified). During E-1, total Al, Fe, and Mn increased to maxima of 376 (1790X), 161 (194X), and 38 (45X) µmol L −1 , respectively. Concurrently, total La, Ce, Pr, and Nd increased to maxima of 87 (590X), 114 (671X), 15 (375X), and 53 (408X) nmol L −1 , respectively, greatly exceeding the dissolved fraction. Totals for Er > Yb > Tm > Lu reached comparable enrichments near or at maximum discharge. Discharge ranged from 0.41 to 0.94 mm h −1 during E-2, a snowmelt event. Total Al was comparatively stable; total Fe and Mn increased 15X and 79X, remaining less than total Al. Total La, Ce, Pr, and Nd peaked with total Fe and Mn. E-3, a late summer rain, resembled E-1 but had much lower maxima for all REEs, P, Al, Fe, and Mn. Particulate, total, and dissolved REEs and P correlated with DOC and with total Al, Fe, and Mn over all discharges, with molar Al > Fe > Mn (most samples) for E-1 and E-3. Maximum total and dissolved P declined from 15.4 and 0.89 (E-1) to 0.98 and 0.27 µmol L −1 (E-3), respectively. Particulate REEs correlated strongly (R 2 = 0.95–0.96) with Al, Fe, and Mn particulates eroded from the stream bed and continuously precipitated during and after high discharge of groundwater.