416 NATIONAL OCEANOGRAPHIC PROGRAM—1965 
plentiful at depths less than 40 fathoms. Various gastropods~-Lymnea, 
Valvata, Amnicola, Goniobasis--are important in shallow areas. Trichoptera 
larvae and especially the ephemeropteran, Hexagenia, are abundant in some 
areas. 
A major weakness in Great Lakes research has been the lack of long- 
term studies. Our solution to this lack is to take information from general 
surveys and specific studies, such as the synoptic surveys of western Lake 
Erie, and attempt to divide the Great Lakes into ecological zones. Once 
we have established an “ecological zone," we establish one or more "index 
stations." Intensive sampling of most aspects of the environment is done 
at these stations at least three times each year. Present sampling includes: 
net and nannoplankton, bottom fauna, temperatures, analyses for Ca, K, Mg, 
Na, Cl, SO}, Si0s, dissolved oxygen, alkalinity, pH, and P, water movements, 
turbidity, transparency, trawling, and pill netting. Three "index stations" 
have been established in the Apostle Islands rejion of Lake Superior and 
seven in western Lake Erie. 
Comparison of data compiled during the past 60 years with those from 
more recent studies demonstrates that major changes have occurred in some 
of the lakes, particularly in the benthic and fish faunas of Lake Erie. May- 
fly nymphs are 10 percent or less of their former abundance, while a marked 
increase has occurred in the numbers of oligochaetes and midge larvae. Blue 
pike and cisco, which formerly dominated the commercial catch, have almost 
disappeared from the fishery. 
The bacterial load in the western basin of Lake Erie increased three- 
fold between 1913 and 1948. Concentrations of various major ions have in- 
creased since 1907. Recent analyses show increases of from 1 to 10 ppm in 
calcium, magnesium, sodium plus potassiun, ond sulfate over earlicr values, 
The average chloride concentration was around 10 ppm or less in 1930. Today 
the average chloride concentration is around 25 ppm. Present mean annual 
water temperatures are approximately 2° F. warmer than those for the 1918- 
1928 period. Very low dissolved oxygen concentrations have been observed 
in Lake Erie in recent years, although low concentrations have been reported 
several times since 1930. Nevertheless, the severity of oxygen depletion 
is greater at present. Synoptic surveys made of dissolved oxygen concen- 
trations in 1959 and 1960, showed that bottom waters over an area of 1,400 
square miles had concentrations less than 1 ppm. The nitrogen and phosphorus 
content of the water has shown a marked increase. The exact degree of 
increase is uncertain, since data from previous years are conflicting. 
Last year, laboratory and field measurements were made of the oxygen 
demand of the water and sediments, and of the organic content of the sedi- 
ments in Lake Erie. A very rapid uptake of dissolved oxygen occurs in less . 
than 5 minutes, when a small amount of bottom sediment is mixed with 
oxygenated water. This immediate demand is probably chemical whereas a sub- 
sequent, continued gradual uptake of oxygen is probably biolo;ical. The 
biological oxygen demand of the hypoiimetic waters was not great enourh 
to account for the low dissolved oxy;en concentrations observed in the lake. 
