Fayetteville green lake, new york. ii. precipitation and sedimentation of calcite in a meromictic lake with laminated sediments1

TLDR: The activities of calcium and carbonate in Fayetteville Green Lake were estimated from detailed seasonal measurements of pH, calcium, and titration alkalinity as discussed by the authors, which was confirmed by collection of crystals in the water column by filtration, identification by X-ray diffraction, and quantitative measurement by a gas chromatographic technique.

Abstract: The activities of calcium and carbonate in Fayetteville Green Lake were estimated from detailed seasonal measurements of pH, calcium, and titration alkalinity. By comparison of observed ion activity products (IAP) for Ca2+ and CO32− with the calcite equilibrium activity product (Kcq), the water column was found to be supersaturated throughout the year. In the surface waters of the mixolimnion, the ratio IAP: Keq increased from 2 to 4 in winter to 6 to 8 during late May through October. Precipitation of calcite was confirmed by collection of crystals in the water column by filtration, identification by X-ray diffraction, and quantitative measurement by a gas chromatographic technique. Maximal crystal loads of 35 g CaCO3 m−2 in the water column occurred in June and July (1965–1967), while calcite loads in fall, winter, and early spring were reduced by an order of magnitude. From isopleths of suspended calcite, settling rates of 2–4 in day−1 were estimated for spring, which was close to values predicted from Stokes’ Law. About 90% of the total sedimentation occurred from June through October, and 80% of this mass was calcite. The laminae occurring in monimolimnetic sediments were regarded as annual couplets resulting from seasonal sedimentation of calcite, with deposition of organic matter throughout the year. The sedimentation rate derived from sediment trap data was 300 g dry matter m−2 yr−1. From the chemical composition of these samples, sedimentation rates were derived for CaCO3, acid insoluble organic carbon, acid insoluble nitrogen, and total nitrogen, sulfur, phosphorus, silicon, and iron.