Diego Bay, creation of channel and 

 intertidal marsh by removing sandy beach 

 material is planned for a 0.7-ha (1.7-ac) 

 area near Coronado Cays. 



Concerns which should be addressed in 

 developing guidelines for dredging 

 include: 



» It is desirable to salvage 

 resources that are removed during the 

 dredging process whenever possible. 

 For example, eelgrass and marsh 

 vegetation should be saved for future 

 replanting or transplantation to 

 other areas which would be enhanced 

 by such vegetation. 



• Disturbances to fish and bird 

 life could be minimized by timing the 

 dredging to avoid their reproductive 

 periods. Late summer appears to be 

 the least disruptive time for these 

 species. 



• Habitats designed to support 

 intertidal marsh vegetation should be 

 gently sloped (see the example of a 

 natural profile in Figure 16, which 

 averages 0.7J, or 0.8 m rise in 115 

 m) . Marsh vegetation can be expected 

 to grow from about 2 dm above mean 

 sea level to extreme high water (cf. 

 Figure 9) . 



• Habitats designed to support 

 selected fish species should take 

 into account their usual habitat 

 features, especially bottom sediment 

 types and current speeds. 



Vehicle And Other Trampling Problems 



The accessibility of upper marsh and 

 transitional areas to vehicle and foot 

 traffic subject them to denudation (Figure 

 30) and other abuses to the point where 

 species become threatened by extinction 

 (e.g. the salt marsh bird's beak). The 

 corresponding popular view of marshlands 

 as wastelands has likewise had a negative 

 impact, as marsh habitats have been used 



as dumping grounds for refuse. It is a 

 rare wetland that escapes deposition of a 

 used couch, shopping cart, mattress, or 

 garden trimmings. 



In many cases, a single vehicle pass 

 can have a lasting effect on marsh 

 vegetation. When soils are wet, tires 

 readily cut through root systems and bury 

 plants in mud. The resulting ruts impede 

 drainage when they are made across the 

 slope, and accelerate drainage when they 

 proceed downslope. Because marsh plants 

 are sensitive to changes in elevation of 

 as little as 10 cm, and because changes in 

 drainage alter both soil moisture and 

 salinity, such off-road vehicle use can 

 cause dramatic changes in species 

 composition. In addition to denudation 

 and rut formation, off-road vehicles pose 

 a noise problem. 



Less damaging to the marsh, but still 

 a potential cause for concern, is foot 

 traffic. Effects of trampling pickleweed 

 ( Salicornia virginica ) were studied by 

 Mclntyre (1977) in the San Diego River 

 marsh. Both timing and intensity of 

 trampling were investigated experimentally 

 in winter, spring and summer of 1976. The 

 soil and vegetation were both extremely 

 sensitive to trampling, even in the least 

 severe treatments. Soils became compacted 

 and drainage was altered. Heavy trampling 

 in winter decreased soil moisture, while 

 trampling in summer led to higher soil 

 moisture as the depressed topography 

 trapped tidal water. Damage to vegetation 

 tended to be greatest during the spring 

 trampling experiments, which coincided 

 with the period of greatest growth. 



In developing recommendations for 

 control of visitor usage of marsh 

 habitats, it is important to recognize 

 that there is an immediate impact to 

 animals through noise and visual 

 disturbance, and a lasting impact to soils 

 and vegetation. Since off-road vehicles 

 and dumping activities are detrimental, 



» All wheeled vehicles should be 

 excluded from coastal marshes. Since 

 visitors on foot can derive 



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