Chemical effects of spring and summer alum additions to a small,Northwestern Ontario Lake

Aluminum was added as aluminum sulfate (alum) to Lake 114, a small, shallow lake of the Experimental Lakes Area, northwestern Ontario, in spring and summer point-source additions. Aluminum and H⁺ gradients were established during the additions, with high Al and low pH (about 1000 μg L^?1 Al, pH 4.7) near the alum sources, and background conditions (< 50 μg L^?1 Al, pH 5.7) further from the sources. Approximately 80% of the added Al was lost from the water column in two weeks. Phosphorus concentrations remained unchanged during the additions, whereas lake alkalinity decreased and sulfate increased close to the sources. Dissolved organic carbon (DOC) concentrations decreased slightly (from 540 μM L^?1 to about 500 μM L^?1) near the alum source during the summer addition.