Another encouraging sign has been the resurgence of many 
native SAV species, as well as the exotic species hydrilla, in 
the tidal fresh water portions of the Potomac River, where lush 
stands were reported to occur in the early 1900s. Whether or 
not this vegetation persists today and is indicative of a 
renewal of favorable growing conditions, remains for future 
surveys to document. 
Hydrilla is a species with an extremely rapid growth rate 
and can rapidly colonize new areas as well as out-compete other 
species. While hydrilla is generally considered a nuisance 
species in many areas of the United States, its role in the 
ecology of the Potomac River is largely unknown and remains to 
be demonstrated. 
The causes for the most recent SAV decline are several. 
Although herbicides were initially indicated because of the 
large quantities being used by farmers, research showed that 
levels of herbicide found in the water were significantly below 
the levels needed to suppress the SAV growth. 
Both field observations and controlled experiments have 
suggested that the major factors are nutrient enrichment and 
increased turbidity. Areas of the greatest SAV decline occurred 
in those areas where nutrient enrichment has been the greatest. 
Nutrients stimulate phytoplankton growth and epiphyte growth 
on the plant surface? this along with the increased turbidity 
have reduced the light available for plant photosynthesis. 
The biological factors such as the reduction of periphyton 
grazing community, or swan and ray activity may be locally 
important, but probably play a secondary role in the overall SAV 
decline of the Bay. 
Although there has been no accurate documentation of the 
decline's impact, some direct and indirect evidence indicates 
that the effects on water quality and secondary production may 
be considerable. Several waterfowl species that eat SAV have 
declined. Some shoreline areas once protected by the baffling 
effects of the plants are now having increased problems with 
erosion. Because SAV supports very dense populations of 
invertebrates, the decline has virtually eliminated the habitats 
for many species and has had an effect on the overall production 
in these areas. 
The two major issues presently facing SAV communities today 
are, one, how best can we conserve and manage the remaining beds 
of SAV in the Bay? And two, what can be done to restore SAV 
communities to areas that once contained these lush stands that 
are now devoid of vegetation? 
61 
