Ch. 6— Impacts and Mitigation • 131 



and methods used, and good project planning and 

 management, especially during the first two or three 

 growing seasons. However, even a properly devel- 

 oped wetland will require an extended period of 

 time for the functions of a natural wedand to evolve. 

 For example, hydrological values and the ability 

 of manmade wetlands to enhance sedimentation of 

 suspended material are achieved within a relative- 

 ly short time; wedand ability to assimilate nutrients 

 and toxic substances takes somewhat longer. The 

 diversity of a site and its ability to support more 

 wildlife also generally increase over time. However, 

 there is insufficient data at this time to say how long 

 it takes for all the biological functions of a natural 

 wetland to develop. 



WETLAND PRESERVATION VS. 

 RESTORATION OR CREATION 



Some States may call for protecting wetlands 

 equivalent in biological value to the wetlands filled 

 or diked. Others, such as Oregon, prescribe that 

 no net loss of existing wetland values should oc- 

 cur: "Oregon's mitigation requirement . . . is that 

 areas of similar biological potential must be created 

 or restored, not simply protected (25)." The mitiga- 

 tion goal is to replace lost wetlands with restored 

 or new wetlands similar in quantity and quality of 

 flora and fauna. Recently, the concept of "no net 

 loss" has been criticized. The skepticism arises from 

 a concern over whether new marsh creation really 

 compensates for losses of natural wetlands. Race 

 and Christie (42), for instance, write: 



A reevaluation of data from manmade marshes 

 is necessary before there can be a determination 

 of whether coastal salt marshes are truly being 

 replaced or expanses of marsh vegetation that per- 

 sist temporarily are merely being planned ... a 

 newly created marsh is not the functional equiva- 

 lent of a 1,000-year-old marsh. 



These authors warn that mitigation should not 

 be offered as justification for the development and 

 destruction of wetlands. The assumed ability to 

 "create" wetlands, they say, creates the percep- 

 tion that wetlands are a renewable resource, a 

 perception that could lead to more widespread de- 

 velopment. Regulators, they feel, should be "ju- 

 dicious" in allowing mitigation by marsh creation. 

 Race and Christie conclude that: 



Marsh creation in suitable situations can be an 

 effective tool to minimize onsite damage at post- 

 construction sites, to abate shoreline erosion, and 

 to return degraded wetlands to tidal influence by 

 means of restoration. However, because of the lim- 

 ited scientific evidence on the development and sta- 

 bilization of important biotic and physical charac- 

 teristics of manmade salt marshes, managers must 

 be cautious in the widespread adoption of marsh 

 creation as a mitigation strategy. 



OPPORTUNITIES FOR WETLAND 

 MITIGATION BANKING 



The Statewide Interpretive Guideline for Wet- 

 lands and Other Wet, Environmentally Sensitive 

 Habitat Areas, adopted pursuant to the California 

 Coastal Act, provides for the payment of a fee to 

 a public agency for purchase and restoration of a 

 degraded wetland to a productive value at least 

 equivalent to that of a wetland being filled. The 

 payment to a "mitigation bank" would be in lieu 

 of dedicating or restricting the use of a comparable 

 wedand provided direcdy by the permitholder (36). 

 This feature relieves the burden on landowners and 

 developers of searching out suitable mitigation sites. 

 It also promotes a cohesive rather than a 

 fragmented approach to wedand-impact mitigation, 

 with significant opportunity for economy of scale. 



A Federal wetland bank, as suggested by the 

 Corps, would operate as in California except that 

 creation of replacement wetlands would be empha- 

 sized (54). In fact, Congress has authorized use of 

 a wetland mitigation bank associated with the Ten- 

 sas project in Louisiana. 



Onsite Mitigation to Minimize 

 Impacts 



Site-Specific Requirements 



Many development activities produce primary, 

 secondary, and cumulative impacts in or adjacent 

 to wetlands that can be minimized feasibly when 

 ftdly understood. Thus, successful control of the pri- 

 mary impact, in turn, will reduce subsequent sec- 

 ondary and cumulative impacts. Further mitiga- 

 tion efforts may be necessary, however, where an 

 activity is known to produce significant indirect or 



