Vol. 16—1962 - NorthEastern Weed Science Society

more than 2 feet. ExceptionalUdes several feet ~yond the normal ran~
occasionally occur.
'
Nosingle creek in the lower Potomachad suffIciently extensive mil.
foil beds to accommodateall ofth~ replicated plots and provide adequate
buffer zones betweenthem. Tbethree creeks selected were as nearly alike
as possible but had slight differences in salinity-and in other characteristics
of minor importance. Since it was moredesirable to replicate
measurementsof the differences in 'mortality betw~n groups of animals etposed
to zero, 30and f:IJLbs, AFJAof 2,4-D than tOrepl1cate identical!
treatments, a complete series of the three treatmen~swas placed in each
creek. Hence, plot numbersfor one each of thethfee treatments were
chosen separately and at randomfor the individual' .creeks. The site of· 1
the 120 Ibs. AEtAtreatment and'of a control were¢rawnfrom plots near J
the mouthof \'lhite NeckCreek. Plots for each typ~f of treatment in the i
low salinity habitat of DundeeCreekalso were chal$enat random. "
WATERTElJ,FERATURE ANDSALINITY
Collection of certain envlronmentaldata begaa·in early spring when
the plot sites were se~ected. ~ing the period o~test-animal exposure,
the salinity of the MarylandPotomactributariesu~ually varied between
7 and 9 parts per thoulland, whllethat of plots in]he upper portionot
the LowerMachodocwas ap~roximatelY two parts lo~r. salinity in Dundee
Creek remainedwell under 1 ppt or essentially tr~~h. ThePotomacvalues
were about twoppt below the seasonal normal tpr that area.
j' .
Water temperatures rose irregularly during the study period and generally
were below seasonal normal. At the time of.herbicide application
in the MarylandPotomactributaries (May29-June I), water temperatures
ranged between18.5° and 21.5° C. , During the preceding week, they ran
from one to twodegrees higher. Whenthe Machodoc:plotswere treated on
June 7, water temperatures were unrecorded'at the time of application but
were ranging in the low to mid.twenties as determined from parallel data.
During the subsequent period of observation, water temperatures ranging
up to 27.5° were recorded in the Potomacplots.
In DundeeCreek the water temperature was l6.~o C whenherbicide was'
applied on May20 at 5:30 A.M. Higher temperature~ had occurred at this
location a tew days earlier and on'May21 the tem~ature was 18.5°. No
further temperature readings"were taken in the'to%\cological study plots'
at this location. "
HOLDING QFExpERIMENTAL ANIMALS
In each treatment plot, cages of experi~ental animals were placed
near the center, about 10 ft. outside the plot boundaryand at a point
about 200 ft. outside the plot. Oncontrol plots, animals were held near
the center. Limitations of time and personnel did not permit replication
of cages at each holding site.
4.51