the sediments will depend upon the amount of 

 exchangeable stable element in the sedinnent 

 and the rate of exchange of these elements be- 

 tween sediments and water. Studies of the 

 levels of three trace metals in sediments of 

 a relatively small estuary (Newport River 

 estuary) and complementary laboratory ex- 

 periments are now underway. 



The Newport River estuary is typical of the 

 "drowned-river" type estuary that occurs 

 along the Atlantic coast. A flat deltaic marsh 

 at the head of the estuary extends 3.2 km, 

 upstream. The river discharges into the es- 

 tuary through a narrow channel across the 

 delta. The shoreline of the estuary is very 

 irregular due to the many drowned tributaries 

 that border it. Most of the estuaryis shallow-- 

 less than a meter at low tide. Because of this 

 condition, wind and tidal action mix the water 

 and stratification is almost nil. Thus, tem- 

 perature and salinity differ little between the 

 surface and bottom water. 



Particle size of the bottom sediment grades 

 progressively from near-shore sandy facies 

 to clayey-silt facies in central areas. A few 

 shell fragments are found in the sediments 

 and only traces of foraminifera are present. 

 The sediment is well sorted because of con- 

 tinuous stirring by tidal currents. 



The trace element content of sediments in 

 this estuary depends upon the type of sediment 

 that is transported into the estuary and the 

 postdepositional changes or diagenesis of the 

 sediment. The rate of diagenetic change in 

 estuarine sediments depends upon the medium 

 of deposition and the type of sediment being 

 deposited. The top 2 or 3 cm. of marine and 

 estuarine sediments are of special interest, 

 since they contain the highest number of bac- 

 teria and benthic invertebrates. These organ- 

 isms affect the- rate of exchange of elements 

 between sediment and water. Also, ion ex- 

 change takes place among the sediment par- 

 ticles, interstitial water, and the overlying 

 water within this zone. Thus, the amount of zinc, 

 manganese, and iron in sedimentof the Newport 

 River estuary is influenced by factors such as 

 temperature, salinity, pH, and organic content of 

 interstitial and overlying water. To determine 

 the amounts of these trace metals which occur in 

 the sediment of this estuary and the effect of 

 certain environmental factors on these amounts, 

 we collected and examined monthly samples of 

 sediment from selected sites for zinc, iron, 

 and manganese for the past 18 months. 



We chose these three elements because each 

 has a relatively long-lived radioactive species 

 which may be present in fallout or in radio- 

 active effluents released from nuclear power 

 plants. This project was scheduled for conn- 

 pletion in September 1968, 



Methods 



Samples of sediment were collected monthly 

 during mean high water from three stations in 

 the Newport River estuary. One station is at 

 the head of the estuary where the salinity does 

 not exceed 1 p.p.t. (Tall Pine); one is within 

 the estuary where the salinity at high tide may 

 range from 5 to 25 p.p.t, (Cross Rock); and 

 one is in the lower portionof the estuary where 

 the salinity at high tide may range from 25 to 

 34 p.p,t, (Newport Bridge). Two distinct types 

 of sediment were sampled at each station. One 

 substation consisted of sandy sediment, and 

 the other of a clayey sediment. These types 

 were differentiated on the basis of particle 

 size analyses. Samples of sediment consisting 

 of 22.7 cm. 3 were collected from the surface 

 layers with a coring device. Depth of pene- 

 tration was 2 cm. Ten samples were col- 

 lected monthly from each substation, and each 

 sample was placed in a preweighed poly- 

 propylene container immediately upon collec- 

 tion. In addition, measurements of temperature, 

 salinity, and pH were made at each station. 



In the laboratory, the samples were dried at 

 90° C. for 24 hours after which 50 ml, of 0,1 N 

 HCl made with deionized water were added to 

 each sample. The samples were left standing 

 for 24 hours and then were ground with a pestle 

 and diluted to 100 ml, with 0.1 N HCl. Two hours 

 later they were filtered with Whatman No. 42 

 filter paper, rinsed previously with 0.1 N HCl, 

 The resulting filtrate was diluted to a volume 

 of 150 ml, with 0,1 N HCl, and concentrations 

 of iron, manganese, and zinc were determined 

 by atomic absorption spectrophotometry. 



Variation of Iron, Manganese, and Zinc in 

 Sediment 



The concentrations of iron, manganese, and 

 zinc in sediment collected from the Newport 

 River estuary varied with element and with 

 location (figs, 14, 15, and 16), These data con- 

 sist of samples collected from the clayey 

 sediments only. At all three stations, iron was 

 the most abundant element in the 0,1 N HCl 

 extracts, followed by manganese and then zinc. 

 The concentrations of all three elements are 

 higher at the Tall Pine station at the head of 

 the estuary, which is essentially fresh water 

 during all seasons of the year. Concentrations 

 of iron are three times greater at Tall Pine 

 than at either Cross Rock or Newport Bridge, 

 Concentrations of manganese and zinc are 

 twice as great at Tall Pine than at the other 

 two stations. This distribution of the trace 

 metals--lower levels in sediment from the 

 higher salinity water- -could be expected. The 

 higher the salinity of the overlying water, the 



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