EFFECTS OF PH AND SELECTED METALS ON GROWTH OF THE FILAMENTOUS GREEN-ALGA MOUGEOTIA UNDER ACIDIC CONDITIONS

When acid precipitation impacts freshwater systems, littoral blooms of the filamentous green alga Mougeotia (Zygnematales, Charophyceae) fre quently develop. Field observations of its development in Little Rock Lake, an experimentally acidified seepage lake in north-central Wiscon sin, indicated that the species of Mougeotia present there may have an optimum pH for growth of similar to 5.2. Because a number of metals i ncrease in concentration in acidified waters, we also proposed that th is species of Mougeotia may be particularly tolerant of metals. To tes t these hypotheses, we grew Mougeotia from Little Rock Lake in culture at eight levels of pH (3 through 10) and measured net photosynthesis and respiration at each level. We also grew this isolate over a range of Zn concentrations from 10 to 2,400 mu g liter(-1) and Al concentrat ions from 10 to 3,600 mu g liter(-1). Little Rock Lake Mougeotia grew over a broad range of pH levels from 3 to 9 with an optimum at 8, in c ontrast to our expectation. Mougeotia, however, was tolerant to levels of Zn and Al considerably higher than the elevated levels to which it had been exposed in the acidified basin of the lake. Mougeotia may gr ow luxuriously in acidified waters because of an efficient uptake of C O2 and dissolved organic C and a lack of grazing pressure.