Vol. 15—1961 - NorthEastern Weed Science Society

52e.
There is a constant reinfection that occurs annually. The seedlings
throughout the sun:mer and early fall are carried by the prevailing wind - at
Lake Mohawkfrom southwest to northeast. Any protruding land acts as a
seed trap. Areas that lie in the wind shadow of the prevailing wind currents
hold their seedlings. It is more difficult to control seed dispersal
where the prevailing wind is contrary to the 'Water flow. These conditions
prevail at Upper Mohawk and nearby Lake Hopatcong. In view of the general
movement of seedlings we have put one cove at the northwestern end of the lake
under special observation. This area is nine acres. Due to its location and
width of opening to the main lake (200 yards) this area has a lesser chance
for reinfection. In 1950 every square foot was covered with Potamogeton
crispus and was unusable for recreational purposes. In 1900 this area is
usable at all times and an annoying insect problem has been reduced because
of the high degree of weed control. For three years we have double treated
this area in the manner described with the hope of exhausting the seeds stored
in the bottom. In 1960this area had a very light growth and was treated but
once.
Although sodium. arsenite controls our main problem, its use creates an
obnoxious by-product. The disintegration of the dead weeds sharply raises
the bacteria, which in turn are finally reduced to fertiliZing elements that
support a heavy growth of algae. We rake out as much of the dead weeds as
we can through nine beaches and have persuaded many property owners to do
likewise. As Lake Mohawk is man-made the lake bottom .... ras formerly farm land
and pasture land and carried with it all the nutrients kindred to farming
and cattle grazing. We are on a migratory flight line for birds and their
fertilizing droppings. Property owners keep their lawns well fertilized and
every rain storm washes in more nutrients J organic and inorganic. The evidence
of persistent foam indicates that detergents are carrying organic
nitrogeneous compounds into the lake. The cumulative effect fram these
sources and others of nutrient material contribute heavily toward the continued
support of weed and algae growth.
In consideration of these factors of lake fertility we altered our algae
control program in 1956. We try to run off by natural means 88 much alga
laden water as possible. To maintain a constant run off we control our spillway
outlet by the use of six 2 x 6" boards laid flat one on the other, as opposed
to 'the eustomary gate used in small lakes. As the lake level drops,
the top board is removed, thereby assuring a two-inch flow of outgoing water
off' the top level of the lake where the blue green algae thrives, such as
Anabaena and MY!=rocystis. In this manner we are able to flush off large
quantities of algae and their resultant nutrients. \olhen there is a sharp
differential between the daytime atmospheric temperature and cooler air at
night, a thermal inversion occurs. The cooler water on top" due to its increased,
density, segregates temporarily a greater amount of algae in the top
water. This is run off' if the wind is favora.ble. '-Thenthe lake water reaches
thermal equilibrium later in the day, the board is replaced to save water.
By means of' a top water control we are also abl.e to fl.ush off IDaIl¥Potamogeton
see