246 



there may be increases in the general productivity of the entire ecosys- 

 tem, or there may be no changes at all if one necessary factor is missing. 

 When there is excessive growth with associated changes in distribu- 

 tion patterns and predator-prey relationships, some organisms may 

 reach a state of "nuisance growths." This condition is defined as a 

 density of growth that interferes with a desirable water use or the 

 growth and reproduction of organisms desirable to man. Examples 

 of these situations are : (1) excessive drifting plant growths that make 

 bathing beaches unattractive, produce unpleasant odors, foul the bot- 

 toms of boats, and spoil the esthetic appearance, and (2) dense popula- 

 tions of rooted aquatics which interfere with the movement and re- 

 production of fish (fig. IV.5.5) . 



In any case it must be stressed that some other environmental condi- 

 tion, and not nutrients alone, maj^ be the controlling factor in such 

 growths. The estuarine ecosystem is highly complex ; its composition 

 is dependent on a large number of variables, many of which are as yet 

 not understood. 



PATHOGENIC ORGANISMS 



One unfavorable consequence of municipal and some industrial 

 wastes is the contamination of the receiving environment with bac- 

 teria, viruses, and other pathogens with public health significance. 

 The organisms, especially those from the intestines of warmblooded 

 animals, frequently persist for sufficient periods of time and distance 

 to pose a threat to the health and well-being of unsuspecting water 

 users. Secondary channels of exposure to these organisms exist through 

 the contamination of shellfish which can be harvested for food. 



Multiple use of any estuarine zone requires careful consideration of 

 the potential for contact with disease-producing agents. The problem 

 of finding pathogenic organisms in water is difficult. The methods 

 available for determining the numbers of these micro-organisms in 

 sewage and receiving water are not practical for routine use; nor is 

 it possible to decide which organisms should be included in the testing 

 procedures. 



Evaluation of the micro-organism density in water receiving waste 

 discharges is based on the test for the total number of viable coliform 

 bacteria present. This test procedure may be further extended to differ- 

 entiate between the total numbers and those of probable fecal origin. 

 The coliform bacteria in this instance are used strictly as indicator 

 organisms. Although the coliform organism has been associated with 

 infant diarrhea, it is generally considered as nonpathogenic in water. 

 The organism is present in fecal material in large numbers, is highly 

 viable in water, and is relatively easy to identify. The use of an indi- 

 cator organism is justified on the premise that, if coliforms of fecal 

 origin are present, other pathogens of fecal origin probably are present 

 also. 



Although most human enteric pathogens do not survive for extended 

 periods outside the host's body, evidence indicates that they may re- 

 main sufficiently viable in all types of aquatic environment to reinfect 

 healthy individuals. Although considerable investigative work has been 

 done on fresh water and on oceanic water, many questions are yet to 

 be answered where the two meet in the estuarine zone. 



