424 KESER, LARSON, VADAS, AND McCARTHY 



average temperatures (1.3°C at 0.15 m and 2.1°C at 3 m) than in 

 1972 to 1974. These were caused by increased exchange with the 

 colder waters when the causeway was removed. Temperatures at Bailey 

 Marsh declined significantly after relocation of the thermal discharge. 

 Surface and bottom temperatures were higher at Bailey Marsh (2.7°C 

 and 3.6° C, respectively) in spring and early summer (April— July) 

 than at Causeway Marsh during this post-stress phase. The differen- 

 tial was caused by increased insolation and heat conduction to the 

 water column from newly exposed mud flats (Dean and Officer, 

 1977). Average yearly temperatures were lower in Bailey Marsh, 

 however, because of the entrapment of freshwater and the presence 

 of ice. Turbidity decreased slightly after completion of the diffuser. 

 Incoming solar radiation patterns were similar throughout stress and 

 post-stress phases. 



Plant Density 



The density of Spartina at Causeway Marsh exhibited two 

 distinct peaks, one in late spring and one in early fall (Fig. 3). 

 Densities were highest from 1972 to 1974, averaging 704 and 1118 

 shoots/m^ in July and August, respectively (Vadas etal., 1976). 

 Mean densities from 1975 to 1977 averaged 434 and 686 shoots/m^ 

 in July and August, respectively. The decline in density during this 

 period was attributed to removal of the causeway, which allowed a 

 greater influx of colder and more saline water. 



At Bailey Marsh the late spring peak did not develop in 1974, 

 and its absence was attributed to the thermal discharge. This peak 

 was reestablished in 1976, however, 1 year after the discharge into 

 Bailey Cove was discontinued (Fig. 3). The density of Spartina in 

 July and August 1972 was 560 and 900 shoots/m' , respectively, 

 whereas in stressed years (1973 and 1974), densities in July and 

 August averaged 625 and 750 shoots/m^ , respectively. Average shoot 

 density for the marsh was lowest in 1975 but increased in 1976 and 

 1977 to 222 and 476 shoots/m^ for July and August, respectively. In 

 40% of the marsh, however, where healthy plants and rhizomes were 

 present, plant densities in poststressed years (1976, 1977) averaged 

 672 and 1188 shoots/m^ in July and August. These values were 

 higher than those in 1972 and higher than densities at Causeway 

 Marsh for the same periods. The plants at Bailey Marsh had thin 

 shoots and leaves, however, and were not as robust as those at 

 Causeway Marsh. These data suggest that recovery in the overall 

 marsh is sparse and that, where plants survived, they recovered only 

 partially. 



