SAND 



SILT CLAY 



SURFACE SEDIMENTS OF MUGU LAGOON (n=79). 

 MANY HABITATS ARE INCLUDED. ADAPTED 

 FROM WARME (1969B). 



SAND 



SILT 



CLAY 



SURFACE SEDIMENTS FROM TIJUANA ESTUARY 

 MARSH HABITATS: LOW=OPEN CIRCLES; 

 MIDDLE=HEXAGONS; HIGH=SOLID CIRCLES, AND 

 FROM LOS PENASQUITOS LAGOON: LOWER 

 MARSH=OPEN SQUARES; UPPER MARSH=OPEN 

 TRIANGLES. 



Figure 10. Soil texture data for two 

 tidal wetlands. Tijuana Estuary data 

 are from Zedler et al. (1980). 



were measured only in September or 

 February, very different results would be 

 obtained (c.f. Figure 11). Because 

 salinity is decreased only following 

 rainfall events, the best times to assess 

 salinity are at the end of the dry season 

 (to obtain maxima) and after each major 

 storm. Wet years should produce longer 

 periods of brackish soils, as well as 



greater leaching of salts. Hence species 

 relying on fresh water for seed 

 germination would have a higher 

 probability of population expansion during 

 such years, while populations might fail 

 during dry years. The higher a species 

 occurs in the intertidal zone, the more 

 unpredictable its soil salinity 

 environment will be. Again, if an annual 

 species occurs in the higher marsh 

 habitat, reproduction may not be assured 

 from year to year, and seeds would have to 

 remain viable for more than a year to 

 prevent extinction. 



Perhaps the instability of soil 

 salinity at middle and high elevations, 

 together with the requirement of fresh 

 water for seed germination (Waisel 1972), 

 explains why most marsh plants rely on 

 vegetative reproduction. Perhaps also the 

 variability of soil salinity explains why 

 the annual pickleweed ( Salicornia 

 bigelovii ) is widespread and successful at 

 Tijuana Estuary, while salt marsh bird's 

 beak ( Cordylanthus maritimus , ssp. 

 maritimus), an annual of high elevation, is 

 rare and patchy, both in space and time. 

 Clearly, there is need for a more detailed 

 examination of population changes with 

 soil salinity patterns. 



The extent to which physical factors 

 control the distributional limits of 

 perennial species is uncertain. 

 Laboratory tests of inundation and 

 salinity tolerance have been done only for 

 cordgrass ( Spartina foliosa ) and 

 pickleweed ( Salicornia virginica ) 

 utilizing San Francisco Bay populations 

 (Mahall and Park 1976a, b,c). Dominance of 

 low elevations by cordgrass is consistent 

 with Mahall and Park's finding that 

 cordgrass has greater inundation tolerance 

 than pickleweed. Likewise, the shift from 

 dominance by cordgrass to pickleweed and 

 other succulents could be explained by 

 their finding that pickleweed is more 

 tolerant of high salinity. Higher 

 salinities at about MHHW (mean higher high 

 water) could restrict the landward 

 extension of this species, at least during 

 dry years. However, it is more likely 

 that a combination of factors is involved. 



19 



