Grant: Strategic Projects - Group

We are proposing a whole-lake sodium sulfate addition to a fishless, remote lake in the Experimental Lakes Area in Northwestern Ontario - artificially eutrophic Lake 227 which has received only phosphorus since 1990 to study several major questions related to eutrophication management, mercury bioaccumulation and road salt impacts. We hypothesize that varying sulfate levels in eutrophic lakes across Canada accounts for much of the chemical and biological variation in lake responses. The experiment will examine (1) the extent to which sulfate regulates internal phosphorus and iron loading from lake sediments which in turn, (2) control formation of nuisance cyanobacteria blooms, and (3) the extent to which sulfate regulates methylmercury formation rates. (4) This experiment requires a sodium chloride (i.e., road salt) control and thus one experiment will investigate four environmental problems. Our goal is to manipulate internal loading of iron and phosphorus from bottom sediments by adding sodium sulfate to increase microbial sulfide production rates in its anaerobic sediments. The rationale for this intervention is based on our current understanding of how a lake's internal nutrient dynamics are affected under under low and high sulfate levels. We argue that adding high levels of sulfate will (i) increase internal phosphorus loading, (ii) reduce internal loading of ferrous iron, (iii) decrease the relative abundance of the cyanobacteria which normally reach 100% by mid June, to a very low level by starving them of ferrous iron at high sulfate levels - in spite of increased whole-lake P levels, (iv) decrease cyanotoxin levels and cyanobacterial nitrogen fixation and hence decrease biologically available nitrogen in the lake. (v) We also hypothesize that high levels of sulfate addition will increase formation of methylmercury (a toxic form of mercury) and affect the potential for mercury bioaccumulation. The study builds on an earlier study on Lake 227 which showed that cyanobacterial bloom formation could be prevented by suppressing access to ferrous