of suspended sediments, dissolved nutrients, water turbidity, and bio- 

 logical oxygen demand at the construction site. Subsequent weathering 

 and erosion of barren spoil deposits and routine maintenance traffic 

 through the access canals sustain these alterations for longer periods, 

 but at reduced levels. Construction-associated increases are typically 

 short term and usually confined to the site area. Neither short-term nor 

 long-term increases are significant when compared to the existing sedi- 

 ment load of the riverine discharge. 



Although care is exercised at the production complex to avoid release of 

 toxic substances into the marsh, small-scale discharges of oil, gas, 

 gasoline, assorted treatment chemicals, and brine inevitably occur in 

 spite of the preventive and maintenance procedures insituted. Ecological 

 alterations associated with large spills, discharges, and associated 

 cleanup procedures are treated as a separate section. Toxicity of petro- 

 chemical hydrocarbons is a function of the quantity released, distillate 

 fraction(s) discharged, and susceptibility of the biota to those frac- 

 tions. The constant low-level release of toxic petrochemicals over long 

 periods and their subsequent effects upon delta marsh dynamics are poorly 

 understood and cannot be satisfactorily evaluated. Effects of occa- 

 sional, low-level discharges are probably never felt much beyond the 

 immediate site as certain microbial elements of the marsh muds can 

 readily absorb and decompose small quantities. Movements of large 

 volumes of water through this marsh system can effectively flush such 

 pollutants from the site. 



Brine may be introduced into the marsh unintentionally as a result of 

 leakage from flowlines or storage facilities. Although plants and 

 animals of the salt marsh can withstand salinities of up to 40 ppt, 

 freshwater species are intolerant of saline conditions. Introduction of 

 brine of high or even moderate salt concentration (and unnatural ion 

 distribution) stresses fresh marsh species to a point where survivial is 

 not possible. Larval and juvenile stages of aquatic vertebrates, and most 

 aquatic invertebrate forms, are particularly affected by saline water 

 influx. Death or stunted growth may occur. Much of the impact of brine 

 effluent depends upon duration of discharge, quantity released, brine 

 concentration, brine temperature, and dilution factors. Though some 

 species may be able to tolerate moderate salinities, tolerance does not 

 last long under such stressed conditions. The salinity tolerances of 

 most species is decreased with increased brine temperatures. In situa- 

 tions where chronic low-concentration discharge is prevalent, fresh marsh 

 species may be replaced by more tolerant brackish marsh flora. Such 

 changes, however, would most likely occur only in localized areas. 



Routine maintenance operations require regular visits to the complex, and 

 activities may disturb sensitive wildlife concentrations, causing behav- 

 ioral changes. If equipment monitoring, maintenance, and repair requires 

 the use of boats, water turbidity increases within the access canal due 

 to resuspension of bottom sediments and erosion of canal banks. The 

 extent of this increase depends upon the erosion of canal banks. The 

 extent of this increase depends upon the frequency of boat passage, boat 



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