May, 1945 



Bennett: Overfishing, Onized Lake 



377 



mately 8 feet. Although the drainage area 

 is small, the water level rarely fluctuates 

 more than 2 or 3 feet during the year. A 

 12-inch tile serves adequately as a spill- 

 way. 



The area immediately around the lake 

 is used extensively for picnics. Large oaks 

 are scattered over this area, and the shores 

 are well grassed except where heavily 

 shaded or worn by traffic. 



Aquatic plants are cattails, Typha lati- 

 foUa L. ; pickerelweed, Pontederia cor- 

 data L. ; arrowhead, Sagittaria spp. ; 



Table \. — Vertical series of temperatures 

 and oxygen samples from Onized Lake during 

 very hot weather, 10:00 a.m., August 29, 1938. 



American lotus, Nelunibo pentapetala 

 (Walt.) Fern.,* planted pond lilies of 

 unknown species; coontail, Ceratophylluiii 

 deinersum L. ; elodea or waterweed, Ana- 

 rharis canadensis (Michx.) Planch.; and 

 creeping water primrose, Jussiaea diffusa 

 Forsk. These plants have encroached upon 

 all of the limited shallow water area. 



In many respects, Onized Lake is typi- 

 cal of small deep ponds that are protected 

 from wind action. The waters of these 

 ponds become thermally stratified late in 

 spring and remain so until late fall. Suf- 

 ficient organic matter is present to pro- 

 duce a high oxygen demand, with the 

 result that throughout most of the sum- 

 mer little or no oxygen is present at depths 

 below 3 or 4 feet. 



A series of oxygen samples and temper- 



*Ndumbo lutea (Willd.) Pers. of some manuals. 



Table 2. — Mineral analysis of a sample of 

 water from Onized Lake, collected from the 

 lake surface near the dam on August 31, 1938. 

 Analysis made by J. B. Swartz of the State 

 Water Survey Division. 



Analysis 



Parts Per 

 Million 



Iron (total) Fe 0.6 



Silica SiOj 8.0 



Calcium Ca 18.0 



Magnesium Mg 11.2 



Ammonium NH4 1 .7 



Sodium and potassium. . Na, K 2.5 



Sulfate SO4 11.9 



Nitrate NO3 1.8 



Chloride CI 8.0 



Methyl orange alkalinity 76.0 



Total hardness 91.5 



atures was taken in Onized Lake, August 

 29, 1938, during a period of very hot 

 weather. These temperatures and oxygen 

 analyses, given in table 1, are probably 

 representative of extreme summer condi- 

 tions. 



Water samples showed little oxygen at 

 3 feet and none at a depth of 5 feet and 

 below. The surface water was warm (78 

 degrees F. ) but at 3 feet the temperature 

 had dropped almost 3 degrees F., and at 

 depths of 5 to 17 feet the samples taken 

 at 2-foot intervals showed drops of 1 

 degree to more than 4 degrees per inter- 

 val. Throughout the three greatest 

 depths, 17, 19 and 21 feet, the tempera- 

 ture changed very little. 



There is evidence that drainage from 

 the barn lot entering the main arm of the 

 lake adds materially to the fertility of the 

 water, but produces some conditions that 

 are undesirable from a recreational stand- 

 point. Heavy rains in late spring and 

 early summer are frequently followed by 

 a bloom of subsurface algae, or by the 

 appearance of numerous patches of float- 

 ing bluegreens ( Oscillatoria) . A large 

 yearly crop of bullfrog tadpoles, Rana 

 catesbeiana Shaw, is produced in the lake. 

 These die in large numbers during periods 

 of water bloom, presumably from eating 

 partially decayed bluegreen algae. The 

 appearance and odor, at these times, of 

 putrifying tadpoles and algae are obnox- 

 ious to the public. Efforts to control algae 

 by hauling out the floating mats and by 



