2.0 THE ECOSYSTEM 



2o 1 How does the LIS ecosystem function? 



Long Island Sound is an estuary -- a semi-enclosed coastal body of 

 water with a free connection to the open sea and within which sea water is 

 measurably diluted with fresh water derived from land drainage. Long Island 

 Sound is a unique estuary in that it is open at both ends and subject to an 

 unusual source of fresh water input; most of the Sound's freshwater enters from 

 the eastern Connecticut rivers near the oceanic end of the Soundo 



Physically, the Sound is 113 miles long and 21 miles i-Tide at its 

 widest pointo It is fairly deep in comparison to other east coast estuaries, 

 averaging about 80 feet with depths up to 320 feeto Light rarely penetrates 

 below 30 feet, as opposed to 600 feet in the open oceanso Very little fresh 

 water enters the Sound from the Long Island side because of the small surface 

 drainage area and the generally southward flow of the island's ground watero 

 Most fresh water input, therefore, is from the mainland side, especially from 

 the Connecticut Rivero Salt water enters the Sound through tidal action at its 

 eastern and western ends, mostly at the former » 



Within the Sound, the circulation pattern is considerably influ- 

 enced by this tidal action and by the Sound's lateral boundaries. Other fac- 

 tors such as land drainage, meterological effects, and wind currents also 

 influence the circulation pattern. Water temperature varies between 32°F 

 and 90°F and salinity varies between 23°/00 and 31°/00 (parts per thousand), 

 except at river mouths where it is less. The Sound has been classified as a 

 moderately-stratified estuary in that ocean waters and fresh water do not mix 

 completely. The dense marine waters remain unmixed below the surface over a 

 large area of the eastern Sound. The lighter fresh water enters mostly in the 

 eastern end from the Connecticut rivers, remains near the surface, and is 

 flushed out to sea rather rapidly. However, sampling by the Connecticut Dept. 

 of Environmental Protection, Region V, demonstrated that the low salinity wedge 

 emerging at the Connecticut River estuary is rapidly mixed and cannot be de- 

 tected far offshore. 



It is believed that in the eastern part of the Sound the water 

 tends to flush out to sea the lighter suspended pollutants from inland sources 

 and brings up nutrient-rich waters from the bottom. This upwelling of richer 

 water at deeper levels contributes to high nutrient levels Cj,).-'- 

 (A more complete description of circulation patterns in the Sound is pub- 

 lished in another interim report. Sources and Movements of Water .) 



Biologically, Long Island Sound, like all estuaries, is a region 

 of transition. To survive and successfully reproduce in an estuary an organism 

 must be adaptable to a wider range of environmental fluctuations than those 

 encountered in a strictly marine or fresh water environment. A wide combination 

 of factors determines the distribution of estuarine organisms. This extreme 



HJnderlined numerals in parentheses are references in Appendix A. 



