An Atlas Displaying Some Older Water Quality Data for Comparisons with Recent Data

Abstract

This Atlas portrays the 'trophic status' of Lake Erie, mostly for the early years of monthly monitoring from 1966 to 1986 by ships and staff of Canada's Environment and Fisheries Departments from their Burlington laboratory called the Canada Centre for Inland Waters. The structure or distribution of water temperature is thoroughly displayed, because of its importance in relation to water quality and especially the water-masses of well-mixed character. Secchi transparency was quite variable and had a broad minimum, that is, maximum turbidity, in the 1970's decade. Data for chlorophyll a in the Central Basin during July and August indicated declining valued to 1986, the last year considered. That trend is probably a response to reduced external loading of phosphorus from urban and agricultural areas, which was the goal of the 1972 Great Lakes Water Quality Agreement between the United States and Canada. The author's diagrams of distributions of dissolved oxygen show trends in the vulnerable Central and Eastern hypolimnions. A recovery of dissolved oxygen by 1984 is not revealed. Particulate organic carbon, particulate nitrogen, and particulate phosphorus all declined (up to 1984), confirming the observed changes in the chlorophyll a data. The measurements of 'total phosphorus' in the water samples showed no change in the mid-summer values up to 1984. The early work by Dr. Julian Williams of the National Water Research Institute, on apatite and related minerals in Lake Erie sediments, could perhaps be extended to the water column. Mineral equilibria could be stabilizing the phosphorus concentrations in some fractions.