Phosphorus and potentially toxic elements in stream waters, sediments, mine tailings, and pines across Lake Anna watershed, VA, USA, and biochar-lime remediation

TL;DR

This study examines pollution in Lake Anna's watershed, focusing on toxic elements and phosphorus, and evaluates remediation using biochar and lime.

Contribution

The study identifies mine tailings as a major source of pollution and evaluates biochar-lime remediation effectiveness for reducing metal leaching.

Findings

Phosphorus export in suspended sediment was higher than dissolved P, but most P was not retained in Lake Anna.

Contrary Creek subwatershed had ecologically hazardous concentrations of Cr, Cu, Pb, and Zn.

Biochar and lime reduced Pb and Zn leaching but were ineffective for As and Cu.

Abstract

Lake Anna is an important ecological and recreational body of water in Virginia but struggles with stream water and sediment quality impairments due to historical and modern anthropogenic activities. The overarching goal was to quantify potentially toxic elements (PTEs) (As, Cr, Cu, Pb, Ni, and Zn) and P pollution across nine subwatersheds and the outflow of Lake Anna to evaluate the role of exposed mine tailings, agriculture, and physicochemical properties on sourcing and transport. Phosphorus enrichment in stream waters and sediments was associated with DOM and Fe, but not agricultural land cover. Suspended sediment total annual P export (191 Mg/year) was greater than dissolved P export (0.7 Mg/year), but < 56% of the P was retained within Lake Anna. Stream water, suspended sediment, and bottom sediment Cr, Cu, Pb, and Zn concentrations at Contrary Creek subwatershed (CC) exceeded ecologically hazardous concentrations and was a major PTE source for the reservoir. Comparing total annual exports, Lake Anna was a net accumulator of PTEs and P. Exposed mine tailings at CC had ecologically hazardous concentrations of As, Pb, and Cu, but pine tree needle PTEs were not elevated, demonstrating limited bioavailability. Lastly, our column experiment using exposed mine tailings found an application rate of 9.2 tonnes/ha of lime and biochar could decrease the leaching of Pb and Zn and increase leachate pH but could not significantly reduce As or Cu. Additional research of subsurface transport pathways and mobility of legacy sediments is warranted to immobilize PTE transport.

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