1 14 
William F. Adams 
Possible Causes of Change 
Degraded water quality has been a persistent problem in Greenfield 
Lake in recent years, and its decline has been brought about primarily 
by the urbanization of the watershed. Elevated levels of nutrients, 
pesticides, and metals and the occurrences of algal blooms have been 
documented or suspected to have adverse effects on mollusks (Havlik 
1987, Havlik and Marking 1987) and have probably done so in the lake. 
Several fish kills that occurred in the lake during the study period were 
attributed by local authorities to low levels of dissolved oxygen resulting 
from excess nutrients. The copper-based algacides used to control 
Lyngbia may be adversely affecting the entire benthic macroinvertebrate 
community. Havlik and Marking (1987) report that copper sulfate is 
toxic to freshwater bivalves at concentrations of 2 to 18.7 mg/ liter in 
acute exposures and as low as 25 parts per billion in long-term exposures. 
Hanson and Stefan (1984) studied the effects of long-term copper 
sulfate application on lakes in Minnesota and found that the normal 
functioning of the ecosystems were severely disrupted. Long-term effects 
that were discovered included copper accumulation in lake sediments, 
changes in species composition from game fishes to rough fishes, 
disappearance of macrophytes, and severe reductions in benthic 
macroinvertebrates. 
The water quality of tributaries of Greenfield Lake may have 
changed over time, because of improved drainage in the upper portions 
of its basin and the removal of groundwater from the underlying aquifer 
by residential wells. Bartsch (1908) states that Greenfield Lake was 
spring fed at the time of his collection, but much of the present 
freshwater input comes from runoff. In addition, groundwater in the 
vicinity of the lake may be polluted. If so, it may take many years for 
pollutants entering the lake to be purged, even if similar pollutants from 
overland runoff are curbed. 
I suspect that the factor most damaging to the unionid populations 
has been winter-season partial drawdowns. They have a twofold purpose: 
to permit removal of nearshore trash and debris and to kill the exposed 
algae mats through cold temperatures and desiccation. These drawdowns 
have had, and continue to have, a profound effect on the mollusks of 
the lake ecosystem, because all mollusks occurring in this exposed area 
are subjected to desiccation and to nighttime temperatures that are 
frequently well below freezing. Anodonta cataracta killed by exposure 
were observed in several locations. Long (1983) noted significant mortality 
of A. cataracta, A. imbecillis, and Lampsilis radiata in a Maryland 
reservoir when summer water levels were drawn down rapidly. Samad 
and Stanley (1986) found that Elliptio complanata and L. radiata were 
