alterations, but at reduced levels. Construction-associated in- i 

 creases are typically short term and are usually confined to the J 

 site area, especially if the surrounding marsh is densely vegetated 

 with few or no open-water bodies. Open-water bodies or channels may 

 facilitate extension of these effects over wider marsh areas, depend- 

 ing on local currents and flow velocities, but the affected areas 

 are still small relative to the whole ecosystem. 



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 proce- 

 dures instituted. Ecological alterations associated with large 

 spills, discharges, and associated cleanup procedures are treated as 

 a separate section. Toxicity of petrochemical hydrocarbons is a 

 function of the quantity released, distillate fraction(s) 

 discharged, and susceptibility of the biota to those fractions. The 

 constant low-level release of toxic materials over long periods and 

 their subsequent effects upon brackish marsh dynamics are less well 

 understood and cannot be satisfactorily evaluated. Effects of 

 occasional low-level discharges are probably never felt much beyond 

 the imn.ediate site, as certain microbial elements of the marsh muds 

 can readily absorb and decompose small quantities. 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, brackish 

 species are unable to tolerate such high salt concentrations. 

 Introduction of brine of high salt content and unnatural ion distri- 

 bution stresses even salt marsh species to a point where survival is 

 not possible. Marsh species are more capable of coping with gradual 

 rather than sudden increases in salinity. Larval and juvenile 

 stages of a species are particularly affected by high salinities, 

 and stunted growth may occur. Plants may have very low germination 

 rates. Much of the impact of brine effluent depends upon duration 

 of discharge, quantity released, brine concentration, and brine 

 temperature. Though some species are able to tolerate very high 

 salinities, tolerance does not last long under such stressed condi- 

 tions. The salinity tolerances of most species is driven down with 

 increased brine temperatures. 



Routine maintenance operations require regular visits to the 

 complex. If access is accomplished over leveed roads, temporary 

 increases of dust and noise result. Vehicular activity may disturb 

 sensitive wildlife concentrations, causing behavioral 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 frequency of boat passage, 

 boat size and speed, and canal dimensions. Continued high turbidity 

 levels may inhibit phytoplankton productivity levels and stress 

 local benthic populations. 



230 



