

amplitude is about 1.1 m (3.6 ft) for most 

 monitoring stations and the average 

 amplitude of spring tides is generally 

 over 1.6 m (5.2 ft; USC&GS 1978). 



Extreme conditions are probably more 

 important to marsh organisms than annual 

 averages. Macdonald's (1977a) data on 

 maximum submergence and exposure times for 

 different elevations at Mission Bay Marsh 

 indicate the broad range of environmental 

 conditions found in the intertidal zone 

 (Figure 4). Additional patterns occur 

 during the year. Lowest low tides occur 

 during the daytime in fall to winter and 

 during nighttime in spring and summer. A 

 seasonal progression of tidal character- 

 istics can be seen by averaging the higher 

 high tides for each week of the year 

 (Figure 4). This analysis shows that 

 upper marsh habitats go for long periods 

 during spring without much tidal wetting. 

 For years of low spring rainfall, 

 desiccation of soils and vegetation, 

 especially soil algae, may be severe 

 (Zedler 1980). 



w 



o 

 w o 

 3 O 



o •-- 



Z 

 I— I 

 H 

 2 

 O 



u 



I salt marsh ]'W D 



_i I I I I 



7ft 6 5 4 3 2 

 ELEVATION ABOVE tlLLW 



Duration of maximum tidal exposure (E) 

 and submersion (S]^=Nov. 1964; S2=Jan. 

 1965) for Mission Bay Marsh. Adapted 

 from Macdonald (1977a). MHHW = mean 

 higher high water; MLHW = mean lower 

 high water; MLLW = mean lower low water. 



1.3 CLIMATE AND WEATHER 



The southern California climate is 



termed Mediterranean because of the warm, 



dry summers and cool, moist winters which 



are similar to Mediterranean countries. 



Frost is rare along the coastline. Annual 



o 

 daily temperatures average from 15 C 



(59°F) at Santa Barbara to 21°C (70°F) at 



San Diego, with winters about 5^0 (41°F) 



cooler than summer. Annual rainfall is 



quite low, averaging from 20 cm (8 in) at 



Chula Vista (near Tijuana Estuary) to 40 



cm (16 in) at Santa Barbara (near Goleta 



Slough) (Table 1). However, annual 



averages do not satisfactorily describe 



the conditions to which coastal wetlands 



are subjected. Rainfall is usually 



concentrated in the winter months, but the 



timing of storm events and the total 



winter rainfall are both highly variable 



(e.g. San Diego rainfall. Figure 5). Two 



years of similar rainfall can lead to 



drastically different conditions if 



precipitation occurs in one or two storm 



periods instead of being distributed over 



several months. 



Weekly mean high water predicted for 

 San Diego in 1977 (from Zedler 1980). 

 Data are in decimeters (dm) above mean 

 sea level (MSL) as well as feet above 

 mean lower low water (MLLW) . 



Figure A. Tidal characteristics in 

 southern California. 



