A Proposed Biological Measure
of Stream Conditions
Ruth Patrick, Curator of Limnology
The Academy of Natural Sciences of Philadelphia
Philadelphia, Pennsylvania
In the spring of 1948 the Sanitary Water Board of the Common¬
wealth of Pennsylvania asked the Academy of Natural Sciences of
Philadelphia to conduct a biological survey of the streams of the Cones-
toga Basin. The purpose of this survey was to see if the organisms
living in a stream could serve as indicators of stream conditions, par¬
ticularly as related to sanitary and industrial wastes.
For this purpose the Conestoga Basin was chosen. It is particu¬
larly well suited for such a project because it consists of small as well
as intermediate-size streams. Therefore in most cases the stream could
be waded and the bottom conditions carefully studied. As the shallow
water forms are the most important food sources in the biodynamic
cycle of a stream whether it is large or small, it was believed that
streams of this type would be the best ones on which to first conduct
the studies. The conclusions reached from these studies will be further
tested on large rivers. This stream basin also afforded conditions repre¬
senting different degrees of pollution, since both industrial and sanitary
wastes enter into the streams of the system at various points. On the
other hand, certain streams, except for farmhouse wastes, were free
of sanitary and industrial pollution.
The Conestoga Basin, which has an area of 474.8 square miles, is
in Lancaster County, Pennsylvania. Its bedrock is composed of lime¬
stone and shale. The gradients of the streams near their headwaters
are relatively steep, but soon flatten out. Occasionally there are sudden
drops. The topography of the land is rolling. Lancaster County is
intensively farmed, so that the stream margins are largely bordered by
pastures and cultivated fields. Because of erosion of the clay soils, the
larger streams of the system are usually turbid, and the waters are of
a eutrophic type.
In the planning of this biological survey the major consideration
was the biodynamic cycle of the stream, which normally results in a
balance of plant and animal life.   Brinley (1943) has recognized that
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