Increase In Total Phosphorus Concentrations Research Articles

The Eutrophication of Lake Okeechobee

ABSTRACT Average annual total phosphorus concentrations in Lake Okeechobee increased from 0.049 mg/L in 1973 to 0.098 mg/L in 1984. The increases in total phosphorus concentrations were not correlated to external phosphorus inputs, but to changes in lake water levels. It is proposed that the flooding of marshes and exposed lake bottom primarily caused increased total phosphorus concentrations, but that the resuspension of bottom sediments by wind action may also be a major factor influencing in-lake total phosphorus concentrations. Reducing phosphorus inputs by 40 percent as proposed by the Lake Okeechobee Technical Advisory Committee (LOTAC) will not significantly improve water quality in Lake Okeechobee. Average total phosphorus concentrations will not decline significantly. Chlorophyll a concentrations and Secchi transparencies are not correlated to total phosphorus concentrations so massive expenditures of public funds to reduce nutrient inputs will not protect long-term water quality at Lake Okeechobee.

高度に汚染された溜池から得られた堆積物中の珪藻群集とその遷移

A recent sediment core was collected from a heavily polluted irrigation pond, “Niinomi-ike”. Vertical distribution of species composition of diatom assemblages was examined to evaluate their succession in relation to phosphorus concentration in the sediments. It was found that the species composition of planktonic and periphytic assemblages in the lower part of the core was replaced by different species in accordance with the increase in total-phosphorus concentration in the sediment. Thus in the planktonic assemblages, Cyclotella comta, C. stelligera, Melosira ambigua and M. distans were replaced by C. meneghiniana, C. pseudostelligera and M. granulate. In the periphytic assemblages, Achnanthes minutissima was also replaced by Navicula frugalis and Nitzschia palea. Additionally, there is the decrease in frustules of acidophilous taxa. The succession process observed in the planktonic assemblages was characterised by the replacement of the related species in the same genus. Based on the succession of diatom assemblages, it was concluded that this pond has changed from a eutrophic one to a hypereutrophic one, and the saprobity in the periphytic environment has changed from a oligo or β-mesosaprobic status to an α-mesosaprobic one.