34 



loading has been implicated in local eelgrass declines because added 

 nutrients elevate the biomass of epiphytes on eelgrass and 

 phytoplankton, both of which decrease light availability, and ultimately 

 cause the death of eelgrass beds (Orth and Moore, 1983b; Sand-Jensen and 

 Borum, 1983). 



Most macrophyte seeds in marine and estuarine environments sink. 

 Davis (1985) examined the morphology, density, and settling velocities 

 of seeds produced by aquatic vegetation and concluded that most seeds 

 are deposited in or near the beds that produced them, even in moderate 

 currents. Because eelgrass seed coats are resistant to decay and remain 

 in the sediment even if a seed germinates, they are good indicators of 

 eelgrass abundance and distribution over many decades or centuries. 

 Eelgrass leaf and rhizome fragments are also present at considerable 

 depths in cores, but are less quantitative indicators of eelgrass 

 abundance. 



Cores can be dated by pollen profiles, radioisotopes, or by 

 remnants of human activity such as coal particles or other refuse 

 (Brush, 1984; Brush and Davis, 1984, Redfield, 1972). Changes in diatom 

 community, invertebrate abundance, and chemical composition not only 

 demonstrate changes in coastal ecosystems, but can also be used to date 

 core sections if some information is already available on historical 

 changes in the environment. Generally cores are meaningful only when 

 taken in depositional environments, remote from high current velocities, 

 wave action, dredging, or construction (Davis, 1984). 



When cores are not dated independently, a realistic range for 

 sedimentation rates for depositional environments can be approximated 



