Excerpt from Sacramento River Water Pollution Survey: Appendix D: Public Health AspectsIt is necessary to examine all aspects of water quality to gain a clear understanding of past and present characteristics of a stream. Chemical and physical measurements provide data on water conditions at a particular moment. On the other hand, biological observations reflect conditions that have existed for some time previously. A study of bio logical characteristics and the ecological relationships of plants and animals in a stream may therefore provide the best overall picture of past and. Present water quality conditions in that stream.About the PublisherForgotten Books publishes hundreds of thousands of rare and classic books. Find more at www.forgottenbooks.comThis book is a reproduction of an important historical work. Forgotten Books uses state-of-the-art technology to digitally reconstruct the work, preserving the original format whilst repairing imperfections present in the aged copy. In rare cases, an imperfection in the original, such as a blemish or missing page, may be replicated in our edition. We do, however, repair the vast majority of imperfections successfully, any imperfections that remain are intentionally left to preserve the state of such historical works.