a Succulent 



8 Succulent 



1977 



1978 



O 



MAY 



JUL SEP NOV 



JAN MAR 



1977 



1978 



1977 



1978 



Figure 4.8. Net flux of particulate (left) and dissolved (right) organic carbon in tidal waters of a) 

 the succulent-dominated and b) mixed cordgrass-succulent study sites of Winfield (1980). 

 Reprinted from Winfield (1980) with permission. 



because of enormous difficulties in sampling. 

 Since temporal variability in all of these 

 processes is high, it is unwise to set a 

 percentage for materials lost from the marsh 

 to adjacent tidal creeks. Suffice it to say that, 

 from these data, most of the marsh plant 

 production appears to be used within the 

 marsh. 



4.5.4 Temporal Variability in Filtering 

 Functions 



There is little information on year-to- 

 year differences in nutrient uptake rates, 

 sediment accretion, and peat formation. 

 Limited studies of peat accumulation (Scott 

 1976; Mudie and Byrne 1980) show that 

 marsh elevations have increased through 

 geologic time, and comparisons of elevations 

 before and after flooding (Zedler 1983b) 



document short-term accretion. Not much can 

 be said about the processes that reverse these 

 "filtering" functions either. No measure- 

 ments have been made of erosion, other than 

 what is obvious from aerial photos (Chapter 

 2). Overall, Tijuana Estuary is accumulating 

 sediments within the channels and losing area 

 due to shoreline retreat. The importance of 

 catastrophic sedimentation events makes 

 prediction difficult. 



A conceptual model was developed by 

 Zedler and Onuf (1984) to describe estuarine 

 filtering during the wet and dry seasons of 

 nonflood years and during flood years (Figure 

 4.11). Nonflood years are the most commonly 

 occurring condition. During these times, the 

 estuary is believed to be a sink for nutrients 

 and sediments coming from both the watershed 

 and the ocean. It is also a sink for salts that 

 are brought in by tides and accumulated 

 through evaporation. 



95 



