Long-term dynamics of watershed leaching and lake sediment sequestration of rare earth elements following deglaciation of two mountain watersheds.

0459979 - BC 2017 RIV NL eng J - Journal Article
Norton, S. A. - Pierret, M.C. - Kopáček, Jiří - Handley, M.J. - Perry, R.H.
Long-term dynamics of watershed leaching and lake sediment sequestration of rare earth elements following deglaciation of two mountain watersheds.
Journal of Paleolimnology. Roč. 55, č. 3 (2016), s. 209-222. ISSN 0921-2728. E-ISSN 1573-0417
Institutional support: RVO:60077344
Keywords : rare earth elements * aluminum * phosphorus * lake sediment * weathering
Subject RIV: DJ - Water Pollution ; Quality
Impact factor: 2.017, year: 2016

Sediment cores from Sargent Mountain Pond (SMP), Maine, USA and Plešné Lake (PL), Czech Republic, record the entire post-glacial terrestrial vegetation and chemical dynamics of the watershed and lake from 16,600 and 14,600 Cal Yr BP, respectively, to the present. Total rare earth element (REE) concentrations and fluxes to the sediment declined from deglaciation until forest developed prior to the Younger Dryas (YD) (12,600–11,600 Cal Yr BP) at SMP, and immediately after the YD at PL, peaked in value just after the YD, and then declined to the present. Before the YD, REE concentrations were dominated by detrital, soluble apatite. Weathering of apatite contributed the phosphorus (P) sequestered in the lake sediment. After the YD, REE concentrations and fluxes behave coherently with NaOH-extractable aluminum (Al) and P after forestation in each catchment. Concentrations of extractable REEs, P, and Al peak after the YD and decline coherently to the present. After afforestation and development of organic-rich forest soils, concentrations of dissolved organic carbon (DOC) in soil water and runoff increased. Concurrently, the weathering of apatite released phosphate and Ca to runoff, raising pH about 8. The soil DOC complexed with and mobilized Al and REEs, which were transported to the lakes in runoff. There, photooxidation of the Al–DOC and REE–DOC complexes caused release of ionic, inorganic Al and REEs, precipitation of Al hydroxide in the higher-pH environment, adsorption of REEs and phosphate by the Al hydroxide, and irreversible sedimentation. REE concentrations and fluxes declined from the YD to the present because the apatite was progressively depleted in the soil by weathering, while REEs were increasingly retained by secondary Al and Fe hydroxides in the soil.
Permanent Link: http://hdl.handle.net/11104/0260146