MEASURING PRIMARY PRODUCTIVITY IN ESTUARIES 



MICROSCOPIC 

 PLANTS 



MACROSCOPIC 

 AQUATIC PLANTS 



SALT MARSH 

 PHANEROGAMS 



HARVESTING MARSH GRASS 

 TO MEASURE ITS ANNUAL 

 PRODUCTION 



PLACING BELL JARS TO MEASURE 

 THE PRODUCTION OF ATTACHED 

 ALGAE 



MEASURING PHYTOPLANKTON PRODUCTION 



Figure 11. — The amount of energy flow through an ecosystem depends on the sunlight energy fixed by photosynthesis in 

 producer organisms; all other organisms ultimately depend on this source for food. In the estuarine environment, pri- 

 mary producers can be separated into three broad categories — microscopic floating plants (phytoplankton), rooted 

 plants (marsh grass), and macroscopic "attached" plants (benthic algae). Investigators are measuring the amount of 

 energy (carbon) fixed by these primary producers by: measuring the uptake of radioactive carbon by phytoplankton; 

 harvesting marsh grass and measuring its annual growth; and measuring rates of photosynthesis of algae attached 

 to bottom sediments by isolating sediment, algae, and water with a bell jar. Changes in dissolved oxygen in the water 

 enclosed by the bell indicate rates of photosynthesis. 



Research at the laboratory is separated 

 into four programs --three concerned with 

 cycling of nutrient elements and their radio- 

 nuclides, and one with the effects of radiation 

 on marine organisms, 



Estuarine Ecology 



The Estuarine Ecology Program investi- 

 gates the biological productivity of estuaries. 

 The ultimate aim of this research is predic- 

 tion of the fate of radionuclides introduced into 

 the estuarine environment --especially their 

 accumulation by organisms consumed by 

 humans. Accuracy in estimating this accumula- 

 tion in edible species requires, however, 

 knowledge of the pathways and mechanisms of 

 accumulation for the entire ecosystem. Shallow 

 estuaries are different from--and in some 

 ways more complex than--the open sea, be- 

 cause of the ea^e with which materials may 

 move between the water and the sediment, and 



the presence of food chains based on primary 

 producers other than phytoplankton. Work is 

 being done on the rate of primary production 

 by phytoplankton, attached algae, and higher 

 plants, and on transfer of this production to 

 other trophic levels, because the flow of 

 energy influences the cycle of materials and 

 thus the movement of radionuclides. 



Biogeochemistry 



The rapid accumulation of certain radio- 

 nuclides by estuarine organisms reflects the 

 metabolism of trace elements. Complete under- 

 standing of the cycling of radionuclides in the 

 estuary requires knowledge of the elemental 

 composition of estuarine organisms; the trans - 

 port processes operating in the organism to 

 incorporate the elements; and the physiological 

 disposition, i.e., the metabolism, of the ele- 

 ments. 



11 



