243 



The biocihemicial oxygen demand (BOD) is the standard test for 

 this component. It is an index of the availability of organic matter 

 for biological food and the amount of oxygen utilized by organisms 

 in the metabolism of this food. BOD is generally expressed as milli- 

 grams per liter of 5-day BOD at 68° F. While natural waters have 

 values around 1, untreated domestic sewage may average around 300. 



The flow of oxygen resources in an estuary is analogous to the flow 

 of money in a bank if the estuarine system is viewed as a dissolved 

 oxygen bank. There is a certain amount of oxygen in the system just 

 as there are certain assets in a bank ; the oxygen is invested in support- 

 ing and renewing the biota, while the bank assets are invested to earn 

 money. There is a constant flow of oxygen into and out of the estuarine 

 system, both to and from the atmosphere and the ocean. In the bank 

 there is a cash flow to and from the depositors. Large waste discharges 

 may exert an abnormal demand on the oxygen resources such as an 

 emi3ezzler exerts on the cash resources of a bank. If enough dissolved 

 oxygen is utilized in stabilizing wastes the system goes bankrupt. 



The amount of organic wastes that can be assimilated in the estuarine 

 system without stressing the biota is dependent on the oxygen balance 

 or the flow of oxygen in the system. The rate of oxygen renewal is de- 

 pendent on the tidal driving force causing new oceanic water to flood 

 into the system, the fresh water inflow, the wind, the surface area, and 

 the amount of turbulence generated by the fresh-oceanic water mixing. 

 The more turbulent the system the greater opportunity for atmos- 

 pheric exchange with the attendant ability to assimilate more waste 

 (fig. IV.5.3). Severely depressed dissolved oxygen levels, which result 

 from an excess of oxygen-consuming organic wastes, affect many cate- 

 gories of beneficial uses. With aquatic habitat damage, pollution- 

 tolerant plants and animals replace the more sensitive types. Desirable 

 game and food fish may be completely eliminated; areas of low dis- 

 solved oxygen may block the passage of anadromous fish, thereby 

 aifecting the reproduction cycle. If oxygen is totally depleted, noxious 

 odors may develop, completely eliminating such uses as boating, swim- 

 ming, and esthetic appreciation. 



The level of dissolved oxygen in the water is one direct index of the 

 healthiness of the system. High levels generally indicate a healthy 

 system which will support a diverse biota and multiple use. The lower 

 the concentration of dissolved oxygen becomes, the sicker the system 

 is, and the less desirable it is for habitat or use. 



FLESH-TAINTING SUBSTANCES 



Another class of materials, primarily organic, which can have con- 

 siderable impact on the estuarine ecosystem, are the flesh-tainting sub- 

 stances. Generally these materials are contained in industrial waste 

 effluents and they result in offensive tastes, odors, and colors of fish and 

 shellfish. The most common culprits are the oils or petroleum products. 

 These materials in slight amounts will impart an oil or kerosene flavor 

 to a wide variety of fish and shellfish, including mullet, mackerel, 

 oysters, clams, and mussels (fig. IV.5.4) . 



Another source of tainting substances directly related to organic 

 waste discharges can develop when some areas receiving waters 



