RETENTION AND RELEASE OF S FROM A FRESH-WATER WETLAND

A freshwater wetland at the Experimental Lakes Area in northwestern Ontario stored most of the SO//4**2** minus received annually from precipitation, runoff and experimental additions. The S budget was determined for a small fen spray irrigated with H//2SO//4 and HNO//3. Annual S retention was greatest during the first year of experimental addition of H//2SO//4 (73% of input in 1983). Retention was lowest (22%) in 1984, a year of lower than average precipitation, with a long hot summer. During years with hot, dry summers, SO//4**2** minus was produced from the reoxidation of reduced S compounds in the peat and released to surface waters. The autumn SO//4**2** minus pulse was accompanied by the release of Ca and Mg but was not accompanied by a H** plus release as has been detected in eastern Ontario and southern Norway, areas which receive more acidic precipitation.