Table 3.65. Summary of discharge, loading rate, and eutrophic state of surface waters of Chenier Plain 

 Basins. 



Item 



Vermilion 



Mermentau 

 and Chenier 



Calcasieu 



Sabine 



East Bay 



Total discharge into 

 major water body 

 (m^/yearx 10^) 



15.89 



53.42 



49.75 



149.58 



5.22 



Total phosphorus 

 (g/yearx 10 ) 



3.86 



10.72 



12.96 



4.90 



0.42 



Loading rate 



(g/m^/year) 



0.24 



0.20 



0.26 



0.03 



0.08 



Eutrophication 

 sensitivity 



Excessive 



See Appendix 6.4 for sources and details. 



Borderline 



Excessive 



Permissible Permissible 



was the agricultural land. Not only does each water- 

 shed have a large proportion of its land tied up in agri- 

 culture, but the P coefficients are high because of soil 

 erosion and excess fertilizer runoff. Vermilion and 

 Calcasieu basins have high loading rates and danger- 

 ous stages of eutrophication could develop. Memientau 

 Basin is borderiine; P loads in Sabine and East Bay 

 basins appear to be in the permissible range. The 

 Vermilion Basin has a high rate because of the Ver- 

 milion River discharge volume. The loading rate of 

 the river suggests that dangerous eutrophic states could 

 develop, but when emptied into Vermilion Bay and 

 exchanged with West and East Cote Blanche bays, the 

 volume is probably diluted to the permissible range. 

 Measurements of P indicate a decreasing concentra- 

 tion as one progresses eastward. 



The Calcasieu Basin, on the other hand, has a 

 high loading rate (0.26) and is probably very prone to 

 eutrophication problems. The P loading is high because 

 of the high proportion of agricultural land in the up- 

 stream watershed. The low P load in the Sabine Basin 

 results from the relatively high discharge rate that ef- 

 fectively dilutes P. 



Brine. Salt is a naturally occurring material, but 

 in high concentrations it may become a toxin, rather 

 than a nutrient. Marine organisms are adapted to con- 

 centrations of about 36 %o, and estuarine organisms 

 are usually able to tolerate wide fluctuations in salt 

 concentration. However, sudden severe changes or ex- 

 treme concentrations can kill flora and fauna. Small 

 changes in the mean concentration result in shifts in 

 the dominant plant species. The greatest damage oc- 

 curs in fresh waters and fresh marshes where endemic 

 species usually have a low salt tolerance. 



The Gulf of Mexico provides the largest source of 

 salt on the Chenier Plain. Intrusion of this salt into 

 freshwater estuaries was discussed in part 3.3.8. In ad- 

 dition, release of large quantities of highly concen- 

 trated brines from industrial sites has severe local ef- 

 fects and perhaps long-term general effects. Major 

 sources of brine are oil wells and leachate from salt 



domes (particularly in the Calcasieu Basin). A 1956 

 survey conducted by the Louisiana Department of 

 Conservation reported that salt water composed al- 

 most 70% of the total liquids produced by oil and gas 

 wells. Brines which are separated and released at well- 

 sites, contained concentrations of dissolved constitu- 

 ents (table 3.66) that range from 20 %o to more 

 than 300 %o (Collins 1970). The average concentra- 

 tion is 110 °/oo (Lisa Levins, Pers. Comm., Energy 

 Resources Co., Cambridge, Massachusetts). 



As an oil field becomes older, its saltwater pro- 

 duction tends to increase. Not only is there a higher 

 concentration of salt in the water, but the ratio of 

 salts differs from that of sea water. Because of the 

 differences in major ions, brines are often far more 

 toxic than sea water. 



Whether an oil field brine will damage the marsh 

 environment depends in part upon the method of dis- 

 posal. The return of brine through injection into suit- 

 able subsurface formations below the lowest known 

 freshwater aquifer is the most satisfactory method of 

 disposal. In addition to subsurface injection, brine is 

 sometimes retained in pits. Large voumes are then re- 

 leased into surface waters. This is the most deleterious 

 disposal technique. 



Another significant source of brine is leachate 

 from salt domes. Some of the salt domes are leached 

 to create caverns for storing wastes and oU. For oil 

 storage, a large surface reservoir of brine must be kept 

 to pressurize the well (Gosselink et al. 1976), but 

 most of the leachate is disposed of permanently. Dis- 

 posal offshore in Gulf waters is projected for the ex- 

 tremely large volumes of brine anticipated for the 

 proposed Louisiana Offshore Oil Port storage caverns 

 (Gosselink et al. 1976) and the Hackberry dome Stra- 

 tegic Petroleum Reserves Program (NOAA 1977). In 

 the latter case, it was predicted that under normal 

 conditions, a brine diffuser located about 9.6 km (6 

 mi) off the Calcasieu Basin coast (at the basin/Gulf 

 boundary) would produce a salinity change at the 

 bottom of the water column greater than 1 °/oo over 



93 



