rainfall and runoff are rare. The smaller 

 lagoons are most likely to close. The 

 enclosed lagoon water may become brackish, 

 (<30 ppt) if rainfall or runoff 

 accumulates, or hypersaline (>40 ppt), if 

 evaporation exceeds freshwater input. The 

 changes following closure have no doubt 

 been modified by man. Urban and 

 agricultural runoff, a result of 

 irrigation by imported water, has the 

 potential of reducing salinities, while 

 upstream dams may have the opposite 

 effect. Hence, the present salinity 

 status of enclosed coastal lagoons may be 

 very different from early historic and 

 prehistoric systems. Whether man has 

 substantially increased the range of 

 salinities in enclosed lagoons or not, it 

 is safe to say that such wetlands endure a 

 much broader range of salinities than 

 tidally flushed systems. 



In addition to salinity, other 

 physical and chemical features change 

 following lagoon closure, including 

 elevated temperatures and decreased 

 oxygen. The surrounding marsh will be 

 most influenced by the depth of the 

 enclosed water and its salinity. Closure 

 followed by runoff accumulation may 

 subject the marsh to a long period of 

 inundation by brackish water (Macdonald 

 1971). But if the closure is followed by 

 a period of low runoff, the marsh will 

 experienfie extended drought conditions. 

 Observations at Los Penasquitos Lagoon 

 (Chapter 2 and Zedler et al. 1980) 

 document some of the consequences of 

 lagoon closure on marsh vegetation. 



these wetlands are compared to coastal 

 marshes elsewhere in the United States. 

 The soils have an extremely broad range of 

 salinities, and long periods of 

 hypersalinity occur. Unfortunately, no 

 widespread system for recording marsh soil 

 salinities has been developed. The 

 generalization that southern California 

 wetlands are usually hypersaline is based 

 on detailed, long-term observation of 

 Tijuana Estuary and scattered information 

 from other wetlands (Table 3). However, 

 the conclusion is consistent with records 

 of water salinities within lagoons, which 

 are more readily available, and with 

 predictions based on the previous 

 information about tidal circulation and 

 climatic conditions because most of the 

 soil water derives from tidal sea water 

 and because evaporation usually exceeds 

 precipitation, salts accumulate in the 

 soils. 



The specific annual and long-term 

 patterns are less easily predicted. 

 Measurements of soil salinity in the lower 

 marsh of Tijuana Estuary, where cordgrass 

 ( Spartina foliosa ) is the dominant, record 

 how variable the salt conditions are for 

 the upper 10 cm of substrate (Figure 6). 

 Salinities decreased slightly following 

 the winter rains of 1979, dropped 

 dramatically following the extensive 

 flooding of 1980, but remained hypersaline 

 throughout the dry year of 1981. The 

 rapid return to hypersaline conditions in 

 1979 and 1980 occurred because of the 

 predominating influence of tides in this 

 low marsh habitat. 



Biological changes within the lagoon 

 water also occur and make the enclosed 

 lagoon esthetically unappealing. Floating 

 algal mats flourish, then die, decay and 

 emit offensive odors. _Mosquitos and 

 midges reach pest densities. Hence, 

 various measures to reopen lagoons have 

 been attempted (see Chapter 6). 



1.5 INTERTIDAL SOIL SALINITY 



Two characteristics of southern 

 California marsh soils stand out when 



Lagoon closure can result in large 

 changes in soil salinity, as the impounded 

 water either accelerates or prevents the 

 leaching of salts. Closure followed by 

 the accumulation of runoff or urban 

 effluent can result in a brackish water 

 lagoon. For example, Buena Vista Lagoon 

 (Figure 7) received fresh water throughout 

 Carpelan's (1969) study. Water levels 

 were maintained by a weir, and the 

 lagoon's meter-deep water was consistently 

 under 5 ppt in 1958-59. San Elijo Lagoon 

 and San Dieguito Lagoon were also closed 

 to tidal flow, but freshwater input was 



10 



