salt-marsh plant of the North Carolina coast. 

 For this analysis, the standing crop of needle 

 rush was divided into three categories--live, 

 dying, and dead. These categories averaged 

 344, 504, and 1,604 g./m.^ (dry weight), and 

 had turnover rates of 2.137, 1.485, and 0.458/ 

 year, respectively. The annual production of 

 organic matter by needle rush, 735 g./m. , 

 was slightly greater than that of cord grass, 

 another important salt-marsh species. 



The Biogeochemistry Program continued 

 work on the radioecology of fallout radioiso- 

 topes in the Trent and Neuse Rivers, N.C. 

 Cesiunn 137 and potassium 40 were analyzed in 

 a brackish- water clam, Rangia cuneata , and 

 in water samples from the Neuse es- 

 tuary. Although concentration factors 

 for both isotopes in the clam were inversely 

 related to the salinity of the water, actual 

 concentrations of cesium 137 in Rangia were 

 nearly independent of salinity. The cesium 

 concentration in the estuary varies directly 

 with the salinity. This observation contradicts 

 earlier predictions that cesium 137 might con- 

 stitute a greater threat to the more fluviatile 

 biota in an estuary. Our extensive collecting of 

 Rangia cuneata for the radioecological studies 

 also provided an opportunity to estimate the 

 growth rate of the clam. From length measure- 

 ments of over 6,000 clams in 12 samples over 

 a 20-month period, a hypothetical von 

 Bertalanffy growth curve was constructed. The 

 growth curve indicated that Rangia reaches a 

 40 n-im. length in about 4 years and approaches 

 a maximum length of about 76 mm. in 1 to 

 1 2 years. 



Other research in the program has been 

 directed toward the distribution and cycling of 

 trace elenaents in the estuarine environment. 

 During chemical analysis of mollusk shells. 

 Bureau scientists noted that sample dilution 

 did not give predictable changes in atomic 

 absorption by copper, manganese, and zinc. 

 This- nonlinear instrumental response was 

 traced to spectral interference by the very high 

 levels of calcium in the shells and to changes in 

 the viscosity of the samples, which affected 

 flow rates into the instrument. This analytical 

 problem was resolved satisfactorily by analyz- 

 ing shell samples at a standardized dilution, 

 that is, at a constant calcium concentration, 

 and by adding the same amount of calcium to 

 standard solutions of the metals. The Bio- 

 geochemistry Program also collaborated with 

 the Pollution Studies Program in the develop- 

 ment of instrumentation and techniques for 

 studying the exchange of trace elements be- 

 tween estuarine sediments and water. 



The Pollution Studies Program continued 

 field studies and laboratory experiments on the 

 cycling of elements and the flow of energy in 

 the estuarine environment. A field project has 

 been underway since October 1966 to measure 

 the seasonal variations of iron, manganese, 

 and zinc in surface sediments collected monthly 



from three stations in the Newport River, N.C. 

 estuary. The project is scheduled for com- 

 pletion in September 1968. In addition, samples 

 of estuarine water have been collected from 

 each station since November 1967 and are now 

 being analyzed for iron, manganese, and zinc. 

 In a separate study, seven species of marine 

 polychaetous worms are being collected semi- 

 monthly from two stations within the Newport 

 River estuary and from three stations in Bogue 

 Sound. Elemental analyses of concentrations of 

 iron, manganese, and zinc in these species 

 reveal a direct relation between concentrations 

 of iron and manganese and an inverse relation 

 between concentrations of iron and zinc. Feed- 

 ing habits appear to play an important role in 

 the partition of these elements. Also, geograph- 

 ical location significantly affected the levels of 

 zinc and manganese in several species. 



In the laboratory, a technique has been de- 

 veloped to measure the rate of exchange of 

 elements between water and sediment. Cores 

 of sediment collected from various locations 

 in the estuary are placed in 1-1. polyethylene 

 cylinders and covered with estuarine water. A 

 radioactive tracer (carrier-free) of a par- 

 ticular elennent is added to the water, and the 

 loss of this tracer from the water to the sedi- 

 ment is measured instantaneously and con- 

 tinuously with a single- channel analyzer con- 

 nected to a 2-inch sodium iodide crystal. At 

 equilibrium, i.e., when there is no further loss 

 of radioisotope from the water, the amount of 

 exchangeable element in the sediment can be 

 calculated. In another laboratory study, res- 

 piration measurements were made on five 

 species of estuarine fish to determine if the 

 relation between oxygen consumption and weight 

 can be described by a single equation. Results 

 of this study indicate that metabolism varies 

 with size of species, and therefore one equation 

 will not describe the relation between metabo- 

 lism and weight for all species offish. 



The Radiation Effects Program continued the 

 investigation of the effects of ionizing radia- 

 tion as altered by its interactions with salinity 

 and temperature. The interactions of chronic 

 irradiation, salinity, and tennperature upon the 

 growth of postlarval pinfish, Lagodon 

 rhomboides, were determined by using conn- 

 binations of three levels of radiation, three 

 salinities, and three temperatures. Nine dif- 

 ferent body characteristics were measured, 

 and statistically significant effects of the en- 

 vironmental factors on these characteristics 

 were described after 45 days. Radiation af- 

 fected two of the measured characteristics, 

 salinity affected five, and temperature affected 

 all nine characteristics. Interactions between 

 radiation and salinity caused changes in four 

 of the characteristics, and interactions of 

 radiation and temperature altered eight. Salin- 

 ity and temperature did not interact to alter the 

 growth of postlarval pinfish. The second-order 

 interaction among radiation, salinity, and 



