The impact of atmospheric deposition on the aquatic ecosystem with special emphasis on lake productivity, Newfoundland, Canada

Abstract

To document and analyze the ecosystem response to acidification and possible concurrent heavy metal enrichment process, a detailed paleoecological study was conducted in Lake 817, a small, and sensitive, second order lake, in insular Newfoundland. The inferred pH history of the lake was recreated using the region-specific equation relating fossil diatom taxa to pH. The profile demonstrated a fairly stable pH history over the bottom 22 cm of the sediment core with an appreciable pH decline in the upper 5 cm. The decrease of inferred pH began in the 1930's (ca. 1931 to 1944) and the lowest inferred pH value (5.3) was observed in the surface stratum. The decreasing pH trend (0.4 unit; 5.7 to 5.3) between ca. 1931 and 1985 correlated well with changes in sediment chemistry. Major elements (P, Mg, Ca, Na, and K) showed significant decrease in deposition primarily in the upper 3 cm level (ca. 1944). The profiles of selected metals (Fe, Mn, Cr, Cu, Zn, Pb, Co, Hg, As, and Ni) indicated that the deposition of these elements increased noticeably, primarily in the upper 3 cm level. The enrichment of Pb began earlier, about 50 years ago (1931 to 1944). The stratigraphy of fossil pigments (chlorophyll derivatives and total carotenoids) demonstrated a general trend of increasing accumulation upwards in the core while the only significant decrease in pigments was observed in the recent strata (ca. between 1957 to 1985). The most dramatic decrease of primary production occurred during ca. 1957 to 1974 period and this phenomenon was associated with increased levels of heavy metals. It seems that primary production in oligotrophic, acidifying lakes in Newfoundland is controlled more by nutrients loading and the possible toxicological effects of heavy metals, than directly by water acidity.