PLANKTON OF LAKE MONONA 123 



maximum difference appears in October when the amount in Lake 

 Monona is two and a half times as large as that of Lake Mendota. (See 

 table 26.) 



The second part of table 37 shows the quantity of dry organic matter 

 in the total plankton per unit of area of Lake Monona when the entire 

 body of water is taken into account. The mean depth of the lake is 

 8.43 meters. As noted in the discussion of the results on Lake Mendota 

 (p. 102), the amount of material attributed to areas shallower than the 

 mean depth is larger than is actually present there, and that assigned 

 to areas that are deeper than the mean is too small when computations 

 are made on this basis. On the other hand, such results give some idea 

 of the general abundance of the plankton material when the whole lake 

 is taken into account, and for this reason they are well worth con- 

 sidering. 



Taking the entire body of water into account, the amount of dry or- 

 ganic matter in the total plankton of Lake Monona varied from a 

 minimum of 124 kilograms per hectare (111 pounds per acre) in July 

 to a maximum of 478 kilograms per hectare (426 pounds per acre) 

 in October. The minimum of Lake Monona is below that of Lake Men- 

 dota (table 26), but the maximum of the former lake is more than one 

 and a half times as large as that of the latter. 



The average amount for the whole of Lake Monona is a little more 

 than 40.0 per cent of the quantity noted for the deep water in the first 

 part of table 37 ; this is due to the fact that the mean depth of the whole 

 lake is only slightly more than 40.0 per cent of the mean depth of the 

 area bounded by the 20 meter contour line. In Mendota the mean 

 depth of the entire lake is about 55.0 per cent of the mean depth within 

 the 20 meter contour line, so that the average quantity of organic mat- 

 ter in the total plankton when the whole body of water is taken into 

 account is about 55.0 per cent of the amount found in the deep water. 



It should be noted that the results given for Lake Monona in table 

 37 are stated in terms of dry organic matter ; the weight of the living 

 organic matter would be about ten times as large as these amounts. 

 Thus, within the 20 meter contour line, the live weight of the organic 

 matter in the total plankton would range from a minimum of 3,100 

 kilograms per hectare of surface (2,760 pounds per acre) in July to a 

 maximum of 11,920 kilograms per hectare (10,630 pounds per acre) in 

 October. When the whole body of water is taken into account, the 

 amounts vary from 1,240 kilograms per hectare (1,110 pounds per acre) 

 in July to 4,780 kilograms per hectare (4,260 pounds per acre) in 

 October. To obtain the total live weight of these organisms, it would 

 be necessary to add to these amounts from 10 per cent to perhaps 15 

 per cent of the dry weight of the organic matter for the inorganic mat- 

 ter or ash that they contain. 



