Interstitial water metabolite chemistry in a marine mine tailings deposit, Rupert Inlet, B.C.

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Abstract
The distributions of PO43-, NH4+, SO42-, titration alkalinity, Ca2+ and pH in interstitial waters collected from mine tailings and natural sediments in Rupert and Holberg inlets (Vancouver Island, British Columbia) are discussed. In natural sediments, NH4+, PO43- and titration alkalinity increase with depth, and SO42- decreases, following established patterns for coastal sediments. In rapidly accumulating tailings, no dissolved PO43- enrichment is observed despite significant SO42- reduction. This PO43- depletion is accompanied by a Ca enrichment and a relatively high pH, which is probably due to the addition of lime to the tailings during milling. Solubility considerations suggest that the PO43- distributions in both tailings and natural deposits are controlled by equilibrium with respect to carbonate fluorapatite. Lime addition appears to increase the supersaturation of the pore water with respect to carbonate fluorapatite, resulting in consumption by the tailings. The tailings thus inhibit benthic PO43- regeneration, which is important in the P budget of some coastal waters. Such inhibition is not important in Rupert Inlet due to a short water residence time, but it could be significant in poorly mixed or stratified water bodies including lakes and some fjords.