Vol. 15—1961 - NorthEastern Weed Science Society

542.
The dissolved oxygen content refleoted in general the seasonal
trend of temperature, both in the control and experimental plots.
The control was consistently the lowest, ranging from 5.5 ppm on
June 8, to a low of 4.0 ppm on July 20, and returning to 7.5 ppm
on September 15. Within the experimental plots the same trend
was apParent, but the variation ocourred over a wider range.
On June 8 a reading of 8.0 ppm was oommon, deoreasing to
4.0-6.0 ppm by July 20, and returning to 8.0 ppm by september 15.
There appeared to be no correlation of dissolved oxygen oontent
with different concentrations of weedioide in the plots.
The pH readings, although reflecting slightly a seasonal
change were remarkably constant. In both oontrol and experimental
plots the readings usually fell between 7.2-7.6. Only
during late July when temperatures were high and 02 ppm low did
the pH fall to 7.0 in the control and two of the experimental
plots. No correlation of pH with different conoentrations of
the weedicide can be established.
The plankton identified can be conveniently grouped With
the same divisions as in previous years: Myxophyoeaei
Chlorophyceae (including desmids and diatoms); Protozoa;
Rotifera; Annelida; Crustacea (Copepoda, Cladocera, Ostraooda,
and Amphipoda); Insecta (larvae or nymphs of Mayflies, Damselflies,
Dragonflies, and Diptera); Gastropoda; and Arachnida
(many mites). Again as last year, there were So commonly ocourring
species large enough to be identified by the low power
of the oompound microscope, and many additional tiny forms.
The constant ooourrenoe of the same organisms over and over
again was monotonous to identify. Out of the 27 hauls made,
three forms, Arcella, Microasterias and Ceratium ocourred every
time. Many other forms oocurred 25 out of 27 times. No
acourate quantitative studies were attempted beoause of the
difficulties of preoise collecting. However, any qualitative
seasonal variation was refleoted by control and experimental
plots alike.
Within the first 2 days following application of the
granUles, however, the plankton population of all experimental
plots appeared to be "siok
ll • While it is very diffioult to
desoribe this condition, espeoially since there was no quantitative
data as proof, the general description is as follows:
In all plots, but especially at concentrations of 2.6 ppm and
3.6 ppm, there was a decrease in the phyto plankters, namely
the green filamentous and coccus forms and the blue green
filamentous. In the large finger boWls, there were fewer
lively active crustacean forms, which were usually very
abundant and easily seen. In general, a little of everything
survived, but the representation 1n abundanoe was poor. Many
plankters from the experimental plots died in the finger bowls
after two or three hours, while those in the control survived
as usual until the following day. It should be mentioned that