Evening star. [volume] (Washington, D.C.) 1854-1972, 1931-01-17
Current of BrookEet. Near
Cabin John Measured in
Test by U. S. Expert.
U. S. DATA MAY HELP
SOLVE CROP PROBLEMS
Puzzle Of Returning Flow With
Changing Leaves Traced by
Weather Observers.
BY THOMAS r. HENRY.
pluttnns for water.

Trees are gluttons for water.
Thirty-two of them, ranging In d.
ameter from to 80 inches, "dranB"
nearly tons in SO hours, according
to measurements by DR.. Harry B.
Humphrey of the Department OF Agri-
culture.
The measurements were made at the
height of the recent drought on the
discharge rate Of a brooklet flowing
into Cabin John Greek near DR.. Hum
phrey's home. He noted that the water
in this little stream, which was fed by
springs and flowed approximately 200
yards through q ravine into a reser-
voir, was much greater at night than
during the day. In the evening 1t
would be entirely dry, while the next
morning 1t would be diScharging into
the reservoir from to quarts q
minute. The stream was so shaded
by low vegetation that the water loss
through evaporation was negligible.
There would be no rain during the
night. The source Of the water In
obviously was not due to increased ac-
tivity of the feeding springs at night.
Trees Thirst in Daytime.
But in the ravine along the course Of
the little brook he counted the 80 trees,
all Of which required water. During
the day when the sun was shining
these trees were active, and their meta
bolic processes required lots Of water.
At night they were asleep" Their
living requirements were at a minimum.
And the rise and fall of the stream
discharge correspondent approximately
to this waking and sleeping Of the
vegetation. The warmer the day the
more water they required, and conSe-
quently the less water in the stream,
which was their only source Of supply.
DR.. Humphrey has reported to the
Weather Bureau observations over %
days, during which there was no rain.
At noon one day he found the stream
discharging quarts a minute. Four
hours later this had been cut in half,
the afternoon being hot and sunny
and the vital processes Of the trees
proceeding at rapid rate. On cloudy
days the differences were not so marked.
The measurements conducted over
the 26-hour period started at z pm,
when no water was flowing into the
reservoir. Two hours later a trickle
was observable, and this gradually in
creased during the night to a maximum
of nearly quarts a minute, which
was flowing at am. the next day.
During this period the temperature,
the trees, had fallen from 10 to So.
This flow continued until about 10 am,
when the vegetation began making an
increasing pull" so that by 3 pm. the
stream was dry. There was no water
until after sunset that evening. But
this night was warmer than the night
before, so the trees were more active,
and the water did not reach quite as
high q level
Winter Sleep Begun.
Then came the first heavy frosts, the
leaves which are the breathing organs
of the tree fell, and the trees went to
sleep for the Winter. The brooklet
began discharging approximately 6
quarts a minute into the reservoir and
this did not vary appreciably night or
day. DR.. Humphrey calculated that
this was the amount which the springs
and underground when they were ac-
tive had minimum requirement of
about l quart per minute merely to
keep breathing and this was all that
they took from the stream during the
night. During the 36-hour period the
total discharge would have been IL, $50
quarts. Actually only $685. quarts went
into the reservoir. The thirst Of the
trees accounted for the rest.
WIFI IIl6 COIuLuB Oh CO1Q WcdLIlGI, d.
though there was no rain, the level
Of Cabin John Greek rose more than
6 inches, Dr.. Humphrey found, and
this could not be accounted for by any
increased supply of underground water.
Similar observations were made on
nearby streams by Weather Bureau OBJ
servers, the return of normal flow CO.
NEEDING almost exactly with the color
ing Of the leaves. This had proved a
great puzzle to Virginia farmers who
suddenly found it possible to water their
cattle again from the pasture brooks,
although there had been no actual in
crease in the water supply. There Is
no reason to believe, say Weather
Bureau experts, that the same phe-
nomenon observed in the hill country
Of Virginia does not take place every
where.
May Further Studies.
DR.. Humphreys observations, the ex-
pertS say, may have an important bear
ing on further studies of the disposition
of ground waters which become de-
pleted rapidly in periods of extended
drought through the drain upon them
by vegetation. They lead to the hope
that during the Winter when the trees
are quiescent there can be considerable
recovery to At the soil for the Spring
crops, even without much rainfall. The
thirst" and capacity of the trees APP
pear from the measurements consider
ably greater than hitherto had been
believed.