The depth and number of ruts created by marsh vehicles are dependent upon 

 the total number of trips and the degree to which vehicles retrace exist- 

 ing tracks. In areas that are submerged continuously (or nearly so), the 

 depressions are less likely to significantly alter water movement pat- 

 terns. In such regions, confinement of marsh vehicle traffic to a narrow 

 corridor may be wise. However, in areas of higher elevation, deep ruts 

 resulting from retraced trails will form depressions for the movement of 

 water and, if deep enough, may result in standing bodies of water during 

 wet seasons. The orientation and depth of the depressions determine 

 whether they (1) remain for long periods of time and (2) alter the water 

 regime of a given area of land by increasing or decreasing the average 

 depth of water. Areas dominated by maiden cane or other shallow-water 

 species may be replaced by stands of rushes, sedges, canes, or other 

 deepwater emergent species. 



The depressions allow a faster runoff of surface and standing water in 

 localized areas, but this drying effect on adjacent regions is usually 

 small. Although the total areas affected by buggy tracks during canal 

 excavation is site specific, it is usually small when compared to the 

 total area of undisturbed marsh. Because both of the major vegetation 

 types support the same consumers, no significant faunal changes would be 

 expected unless the depressions caused drainage of large areas. 



The long-term effects on suspended sediments and nutrients are insigni- 

 ficant in this turbid, nutrient-rich system. If vehicle tracks occur in 

 areas of the marsh where isolated ponds exist, intramarsh circulation 

 could be affected. Depressions could connect individual water bodies and 

 increase the intermixing of their contents. In extreme cases, depres- 

 sions may be deep enough and aligned such that they become permanent 

 branches of the existing dendritic drainage patterns. Waterfowl and 

 wading bird use would be expected to increase in these new depressions 

 with standing water. At the ecosystem level, however, the increase is 

 insignificant. 



Increases in suspended sediments associated with excavation are transient 

 and affect a relatively small area, especially if temporary plugs are 

 placed at the mouth of the canal. Long-term effects are results of 

 erosion of canal banks and spoil deposits; erosion of the former is 

 proportional to the river discharge and the speed and amount of boat 

 traffic. Erosion of spoil deposits will proceed until they become 

 vegetated by pioneering plant groups. This ecesis usually occurs within 

 two years. Increases in suspended sediments associated with marsh buggy 

 traffic also have short-term and long-term components; effects of in- 

 creased turbidity from all sources are usually negligible when compared 

 to the existing suspended sediment load of the riverine discharge. 



The canal creates a large route for increased inundation by adjacent 

 fresh waters. These waters are brackish only during periods of low 

 discharge and/or hurricanes. The pattern and height of spoil placement 

 are the most important factors that determine whether this new standi ng- 



274 



