gent aquatic plants if the nutrient content of the water and sediments are 

 high. Beds of Sphaerotilus indicate a significant increase in carbona- 

 ceaous materials in the water. Furthermore, such studies are able to deter- 

 mine shifts in the diversity of habitats or physical changes in the river 

 channel. This information is not determined by monitoring with substrates, 

 for by the use of substrates one simply determines facts concerning the 

 organisms, but not the condition of the area in which they live. 



Another difference is that when one sends a team of scientists into a 

 body of water one determines facts concerning many different groups of 

 organisms. This is extremely important if one wants to determine subtle 

 changes. Often an ecological change that has nothing to do with pollution 

 will affect a single group of organisms, but it is extremely rare that an 

 ecological change will affect many groups of organisms such as the algae; 

 invertebrates such as molluscs and worms; insects; and fish. This 

 methodology was first developed by my staff at the Academy of Natural 

 Sciences in 1948. Therefore, the more lines of evidence from different 

 kinds of organisms that one has the more sure one is of his diagnosis of 

 conditions. Such studies are particularly valuable when one is concerned 

 with small sublethal effects which are important to detect before they 

 become problems. Wth the possible problems in our country due to increases 

 in chlorinated hydrocarbons, heavy metals, and radioactivity, this type of 

 thorough examination of conditions in monitoring becomes more important. 

 Of course, this type of monitoring is intermittent, and it is more expen- 

 sive, and therefore between studies things may occur that one does not 

 realize. For this reason it is best to combine a continuous monitoring 

 system with this more thorough, intermittent system. I often compare these 

 types of studies to medical treatment. If one wants to know if something 

 is wrong a simple procedure can be used such as examining the condition of 

 a single group of organisms. This compares with taking one's temperature 

 or doing a cardiogram. But if one wants to understand trends or causes of 

 change a thorough study of aquatic areas or a detailed physical examination 

 of an individual is needed. 



As noted above, the kinds of changes which one observes are first the 

 changes in relative sizes of populations of species. If we find that those 

 species that are tolerant to a given type of pollution are becoming more 

 common, then one strongly suspects that it is present. For example, in a 

 stream in eastern United States if one finds a shift from mayflies and 

 stoneflies and certain species of caddisflies being \jery common to a great 

 increase in chironomids, dragonflies, Physa snails, the limpid, Ferrissia , 

 and tubificid worms, we know that the nutrient load of the river has in- 

 creased. Furthermore, if we find that only organisms such as the flatworm 

 Dugesia tigrina , Ferrissia tarda , Physa heterostropha , and tubificid worms 

 are present we know that the degradation is caused by increased nutrients 

 and resultant increase in bacteria, and probably no toxicity. However, if 

 we find and increase in certain of the chironomids and of certain dragonfly 

 larvae without an increase in the above mentioned species, we can infer 

 that the organic load may occasionally have low levels of toxicity present 

 (Patrick observations). 



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