176 Theories and Techniques of Management 



which began to die in a small area of shallow water at the upper end of 

 the pond and spread until all of the vegetation had died and disintegrated, 

 and an algal bloom of Aphanizomenon flos-aquae had developed. A second 

 example of vegetation die-offs occurred in Ridge Lake ( Illinois ) in 1946 

 when Mr. W. W. Fleming was studying plant-invertebrate relationships 

 in dense stands of the pond weeds, P. joliosus, P. nodosiis, P. pectinatus, 

 Najas flexilis, and Elodea canadensis. ^^ In 1948, this die-oflF began about 

 July 8 and gradually eliminated the rooted vegetation until on July 23 

 nothing but open water could be found at his selected sampling stations 

 which were previously in dense stands of rooted pond weeds. 



This die-off at Ridge Lake has occurred during most summers since 

 1946; usually when the last of the early summer vegetation is dying, a 

 new second crop is developing in areas where the old crop died first. By 

 early September, there is almost a complete replacement of vegetation 

 in areas where it was present before the die-off, but the stand is some- 

 what less dense than it was in the original stand that grew in late spring 

 and early summer. It seems possible that this die-off is caused by some 

 disease or parasite, but no causative organism has been isolated. 



Role of Aquatic Vegetation in Management 



Originally, aquatic biologists held the belief that beds of higher aquatic 

 plants were an essential part of the aquatic environment, presumably be- 

 cause they were almost always present in lakes and ponds. This concept 

 was entirely discarded by Swingle and Smith ^^^ who recommended the 

 use of inorganic fertilizers in ponds to stimulate the growth of "blooms" 

 of phytoplankton to shade rooted aquatics and thereby cause them to die. 

 These investigators demonstrated that the phytoplankton blooms stimu- 

 lated a higher production of zooplankton which, in turn, raised the level 

 of food for such omnivorous feeders as bluegills, and thereby increased 

 the total fish production. 



At present, excessive amounts of either rooted aquatic vegetation or 

 algae are considered undesirable in ponds and lakes used for fishing, 

 boating, and bathing. Where there is no history of intentional fertilization, 

 excessive vegetation may be indicative of mild or severe organic pollution 

 from barn lots or septic tanks. One of the drawbacks to locating housing 

 developments around small artificial lakes is that such developments often 

 are not connected with sewage disposal systems; rather, each house is 

 supplied with its own septic tank and tile field. If the house is close enough 

 to the lake to benefit aesthetically from it, the tile field must of necessity 

 be laid in land sloping toward the lake. Eventually effluents from these 

 tile fields enter the lake and, because they carry phosphates and nitrates, 

 they act as fertilizers which stimulate aquatic vegetation and create 

 nuisance problems. Prospective home owners who contemplate the pur- 



