50 MARINE FISHERIES OF NORTH CAROLINA 



formed, has been the source of the dissolved salts characteristic of sea water. 

 Important minerals, such as the phosphates and nitrates, the scarcity of 

 which may limit production, are usually present in and added by the streams. 

 The quantity of any critical nutrient entering the North Carolina coastal 

 waters by this means is not known ^° and, if such data were available, they 

 would mean very little till additional studies revealed their ultimate fate and 

 use in the water in question. It is probable, for example, that many nutrients 

 adhere to the silt in the stream and settle out of circulation when salting 

 out ^^ and other sedimentation processes carry the silt to the bottom at the 

 river mouths. With erosion " as great as it is, heavy losses from this action 

 are to be expected. Erosion also leads to unchecked and highly varied run-off 

 conditions causing floods, sudden changes in salinity, and great variations in 

 nutrients contributed by river discharge. 



The Offshore Bar and Its Inlets 



As mentioned in the discussions of geography, an offshore bar interrupted 

 by a few narrow inlets extends the entire length of the North Carolina coast 

 (Figures i and 24). Ocracoke Island, a typical segment of this coastline is 

 described by Engels (1942) as follows: 



"Through the greater part of its length of 1 7 miles, Ocracoke is only about 

 )4 mile wide; near the southwest end it is at one point nearly two miles in 

 width, but for a considerable distance, toward Hatteras Inlet, barely 200 

 yards separate the sound from the sea. Much of the island is less than one 

 foot above sea level; little of it rises more than three feet above the sea. The 

 dunes scarcely exceed 20 feet in elevation — most of them are much lower; 

 they occur as scattered, isolated hills of sand, or as small clusters of hills, not 

 forming a continuous barrier to the encroachment of the sea." That such an 

 offshore bar persists is obviously due to the continuation of the dynamic 

 forces that built it, for in itself the loose shifting sand comprising this barrier 

 beach offers no stability. 



A wealth of information on the history of the inlets through the bar is 

 contained in the report issued by the North Carolina Fisheries Commission 

 Board in 1923. Appendix III of this report is a letter from S. T. Abert to the 



20. Studies to date have been planned primarily for industrial use of the water and have been 

 made at more or less upstream stations not applicable to the river mouths. For the latest such 

 records see Lamar (1947). 



21. Neutralization of electric charges on the silt particles by charges on the salt ions of the 

 sea water tends to destroy one of the major forces maintaining such material in suspension. As 

 a result a pronounced settling, or salting out as it is called, may take place where fresh and salt 

 water mix. 



22. Available data on the degree of erosion in North Carolina applies to upstream locaUties 

 and not to river mouths. A promising method for determining erosion is by comparing old 

 and recent surveys of bottom contours in the river mouths as has been done by Gottschalk (1*945) 

 in other areas. 



