Li 111 



Imperial 

 Beach 



Figure 5.11. Sampling stations for the 

 revised salt marsh monitoring program. 

 Cordgrass is now monitored annually at the 

 four northernmost stations (Peninsula. 

 Original, E-W Channel, and Tributary). Mid- 

 elevation and upper-elevation transects were 

 placed at the Peninsula, Original, Near Mouth 

 and Old River stations. Each station includes 

 one or more transects of 20-m length. There 

 are 4 transects for each of the habitats 

 (lower, mid- and upper intertidal elevation). 



from the ocean inlet. The south arm of 

 Tijuana Estuary is included in comparisons of 

 middle and upper elevation transects. Since 

 cordgrass is restricted to the northern arm, 

 all four lower-marsh transects are located 

 along Oneonta Slough. 



At each site, a 20-m transect is located 

 along the elevation contour. Cover of each 

 species is recorded to the nearest 10 cm, 

 within 1-m intervals. Bare space is recorded 

 separately. At 2-m intervals (n = 10) 

 within the lower marsh, a circular quadrat 

 (0.10 m 2 ) is used to select cordgrass stems 

 for height measurements. At 10-m intervals 

 (i.e., 3 per transect), soil salinity is 

 measured at 10 and 30 cm depth. Soils in the 

 lower and middle transects are generally 

 moist enough to express soil water onto the 

 refractometer. Drier soil samples at the 

 upper transects are collected, returned to the 

 laboratory, and mixed with deionized water to 

 form a uniform soil paste before expressing 

 the filtrate onto the refractometer. The upper 

 marsh data are thus representative of soil 

 salinities that follow rainfall, while the lower 

 and middle marsh data represent ambient 

 conditions. 



The above sampling program began in 

 1989 and, as of this 1991 writing, has 

 characterized the marsh soils and vegetation 

 during a period of relatively similar 

 environmental conditions. Sewage flows from 

 Mexico, which averaged up to 13 MGD from 

 1986 on, were terminated in early October 

 1991. The three-year data base is thus a 

 detailed summary of conditions with sewage 

 inflows and before tidal restoration. 



The 215 stations will be sampled at 5- 

 year intervals, with the next effort to occur 

 in 1993. Cover estimates will be omitted for 

 this broad survey, as will measurements of 

 cordgrass height. Species composition will be 

 reexamined by sampling for occurrence. Soil 

 salinities will be subsampled (e.g., every 5th 

 station) to increase efficiency. In the event of 

 an environmental catastrophe (flood, inlet 

 closure, etc.), more frequent resampling 

 would be in order (pending funding). 



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