ORGANIC CONTENT OP LAKE WATER 
189 
lakes. The sample was taken just above the entrance of the stream into Lake 
Mendota, the upper lake of the series. 
The data of the table disclose no difference in the content of dissolved organic 
matter between hard-water lakes with large amounts of carbonates in solution and 
soft-water lakes with little mineral matter. Lake Wingra, with the highest dry 
residue, has also the second highest figure for organic carbon; while Bass Lake, whose 
organic carbon is nearly as great, has by far the smallest amount of dry residue. In 
Bass Lake the total carbon dioxide was 112.9 per cent of the weight of the dry residue, 
while the evolved carbon dioxide was only 2.51 per cent of the same weight. The 
five waters in the list (omitting Mendota) whose dry residue is smallest have an aver- 
age of 6.99 milligrams per liter of organic carbon; the nine others average 6.48 
milligrams. 
The nature of the drainage basin of the lakes and the resulting character of the 
inflowing water seem also to make no noteworthy differences. Turtle Lake has the 
greatest amount of organic carbon and its water is very high colored, derived through 
streams from the drainage of marshes. On the other hand, Bass Lake, a lakelet 
with no affluent and with very clear water, stands very high in organic carbon. The 
area and volume of Lake Michigan are so enormous in relation to its margin and the 
small amount of water brought in by affluents that its organic carbon must come 
almost entirely from its inner resources. The 14 observations on Lake Mendota 
show no clear relation between depth or season in the amount of organic carbon. 
The nitrogen-carbon ratio has a wide range in these observations. The mini- 
mum ratio is 1 to 27; the maximum 1 to 9.1; and the range is nearly as great in 
the series from Lake Mendota — minimum 1 to 20.6, maximum 1 to 9.1. If, how- 
ever, the observations are grouped and the mean nitrogen-carbon ratio is computed 
the results are singularly uniform. The computation may be made in two ways — 
the mean of the single ratios may be found, or the quantity of carbon and nitrogen 
in the observations may be added and the ratio of their sums computed. The result 
will differ somewhat according to the method employed. 
Table 3. — Nitrogen-carbon ratios 
Mean of ratios 
Mean of obser- 
vations 
N 
C 
N 
C 
Mendota, surface, 8 cases 
1 
15.4 
1 
14.9 
Mendota, bottom, 6 cases 
1 
14.9 
1 
14.5 
Mendota, all cases 
1 
15.2 
1 
14.8 
Other lakes, 14 cases 
1 
15.5 
1 
14.5 
All cases, 28 
1 
15.4 
1 
14.6 
The average yield from all observations, 28 in number from 13 different lakes 
and aggregating 3,495 liters of water, is as follows: 
Organic nitrogen 0.426 milligram per liter 
Organic carbon 6.230 milligrams per liter 
Ratio— N:C::1: 14.6 
44699—27 13 
