12 3 4 5 

 Height Class 



Figure 5.12. September height distribu- 

 tions for cordgrass over a three-year period. 

 Stem heights were pooled for ten 0.1 -m 2 

 quadrats x 4 stations. Height classes are 30- 

 cm intervals (approximately 1 -ft), i.e., 1 = 

 0-30 cm, 2 = 31-60 cm, 3 = 61-90, 4 = 

 91-120, 5 = 120-150 cm. The number of 

 stems was 406 in 1989, 446 in 1990, and 

 579 in 1991. 



Plants of the constructed marshes at both 

 the Chula Vista Wildlife Reserve and the 

 Sweetwater Marsh National Wildlife Reserve 

 have reduced stature because soil nitrogen 

 supplies are limiting (Langis et al. 1991, 

 Zedler 1991b). 



The importance of having many tall stems 

 (60-120 cm) has led to the recommendation 

 that cordgrass canopy architecture be a 

 primary criterion in judging habitat 

 suitability. Two San Diego Bay marshes that 

 were designed and constructed for clapper rail 

 nesting have not yet attracted the species. 

 Their canopies differ from those at Tijuana 

 Estuary in having fewer tall stems; densities, 

 on the other hand, are often similar or higher. 

 Thus, the data from Tijuana Estuary suggest 

 that densities alone are not the critical factor, 

 but rather the density of tall stems. These 

 reference data suggest minimum standards for 

 "suitable clapper rail habitat" in southern 

 California (Zedler, in review). 



Individual data sets have far less use in 

 marsh-to-marsh comparisons than long- 

 term records. The magnitude of year-to-year 

 variations within a marsh must be known in 

 order to determine if a man-made marsh is 

 truly different from natural ones. The 1989 

 and 1990 data at Tijuana Estuary were 

 critical to the comparison of constructed 

 marshes sampled in 1989 and 1990 (Zedler, 

 in review). Of further value is the fact that 

 the Tijuana Estuary monitoring program 

 provides information on a variety of factors 

 that elucidate cause-effect relationships. 

 Understanding the reasons for differences 

 between natural and constructed marsh 

 vegetation (e.g., nitrogen limitation) leads to 

 corrective measures (e.g., soil amendments). 

 Because there is a long-term monitoring 

 program, the Tijuana River National 

 Estuarine Research Reserve has unique value 

 as a reference site. 



5.8 RESPONSES OF FISHES AND BENTHOS 

 TO HYDROLOGIC DISTURBANCES 



Wastewater has flowed down the Tijuana 

 River in large volumes from 1986 through 

 1991. A peak discharge in winter 1986 was 



1 19 



