576 



greater. More data is needed in this area in order to make informed 

 decisions as to whether or not we can sacrifice large acreage of the 

 irregularly flooded marsh. One of the most active programs in these 

 areas has been ditching and draining for mosquito control. There is 

 considerable disagreement as to the impact and value of this kind 

 of activity; it can be argued that it is beneficial — while others feel 

 that it is detrimental. Probably a case can be made for both points. 



Bottom sedvtnent — vouter interface 



The bottom sediments represent an important element in the 

 balancing of the marine community and must be included in any con- 

 sideration of estuarine management. Disturbing these sediments by 

 dredging or by the working of bottom animals such as worm and 

 fish, can reintroduce materials which have become associated with the 

 bottom sediments into the water mass. Heavy metals, pesticides, herbi- 

 cides, nutrients, oil residues, and many industrial chemical mixtures 

 are examples of the kinds of materials which become incorporated 

 into the bottom. For example, lead is found present in almost all types 

 of deposits in amounts varying from 70 to 580 parts per million on 

 a dry mud basis. Most of this lead comes from atmospheric pollution 

 which has passed through the waters, precipitated, and adsorbed to 

 bottom sediments. The presence of high concentrations of copper vary- 

 ing from 209 to 600 parts per million on a dry mud basis are also 

 found. These are due to sewage effluents containing human excreta. 

 Nickel is present in amounts ranging from 290 to 1,300 parts per mil- 

 lion in muds which are polluted with industrial waste. Investigations 

 of conditions effecting the biological and chemical release of adsorbed 

 or precipitated nutrients and toxicants from marine benthic environ- 

 ments are essential. The bottom sediments also serve as a reservoir 

 into which these materials may be extracted from the water mass. 

 They can also serve as the reservoir of carbonate materials which help 

 to maintain the innate buffering system of marine waters. Thus, any 

 consideration of the estuarine ecosystem must include full understand- 

 ing of the relationship between the bottom sediments and the overly- 

 ing water mass. 



Air-water interface 



The fourth major interface, that of the water and the atmosphere, 

 frequently is ignored in investigations. These interfaces are charac- 

 terized by surface films which are areas of concentration not only of 

 surface active materials, but of bacteria and other micro-organisms as 

 well as inorganic particles of various kinds. These natural films should 

 be distinguished from layers of oil which are much thicker and possess 

 different properties. They occur on the sea surface around all islands 

 and along all continental shores and, hence, are characteristic of estu- 

 arine zones. They travel wdth the wind at speeds approaching the 

 wind speed and can rapidly concentrate materials along shore lines, 

 especially on a windward coast. These effects are very important in 

 case of associated radioactive pollution, as well as bacterial pollution. 

 Some of the surface active materials are of natural origin and are 

 greatly increased by agents that kill marine organisms. Other film- 

 forming materials result from oil spillage. The film, from whatever 

 source, changes the transfer rate of gas through the water surface, the 



