Proceedings of the Sixty-first Annual Meeting of the Northeastern ...

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WATER QUALITY AFFECTS DUE TO A CONTINUOUS LAKE WIDE MILFOIL
CANOPY IN A SHALLOW CT LAKE. G.W. Knoecklein, Northeast Aquatic Research,
Mansfield, CT.
ABSTRACT
Lake of Isles, an 88 acre lake with maximum depth of 10 feet in North
Stonington, CT., has a dense cover of hybrid variable leaved milfoil (Myriophyllum
heterophyllum x pinnatum). In water shallower than about 5 feet the milfoil reaches the
surface and produces aerial inflorescence. In water deeper than 5 feet the milfoil forms
a canopy between 1 and 3 feet below the surface. Typically, water above the canopy is
clear giving the impression that that the lake is nutrient poor. Water quality monitoring,
started in 2001, initially did not include bottom water samples collected below the
canopy. However, temperature and oxygen profile measurements showed that water
below the canopy became anoxic and that temperature gradients existed in the canopy
suggesting that that canopy prevented mixing of waters below the canopy.
Beginning in 2003 samples were collected from above, and below, the canopy
with testing including total phosphorus, total dissolved phosphorus, nitrate/nitrite,
ammonium, organic N, and total iron. Results revealed that P levels were generally 10 ppb, (maximum 39 ppb) below the canopy, and that total
nitrogen was