5 6 RESULTS OF THE NEW ADAPTIVE 



MONITORING PROGRAM, 1989-1991 



The revised salt marsh monitoring 

 program began in September 1989. The four 

 lower-elevation stations are all located in 

 Oneonta Slough, coinciding with the 

 occurrence of cordgrass (Figure 5.11). The 

 upper- and middle-elevation stations are 

 more broadly spaced; one is near the mouth of 

 the estuary, and one is in the south arm. 

 There are no obvious differences in soil 

 salinity between the latter site and its Oneonta 

 Slough counterparts; however, the upper- 

 elevation vegetation has more salt grass 

 (Distichlis spicata) and less shore grass 

 (Monanthochloe littoralis), while the middle- 

 elevations are less diverse (only pickleweed 

 and alkali heath are present). 



5.6.1 Soil Salinities 



Marsh soils were relatively stable in 

 salinity between 1989 and 1991, three years 

 that had below-average annual rainfall 

 (Zedler et al. 1991). Despite the low annual 

 totals, growing conditions were quite 

 favorable in both 1990 and 1991. The 

 rainfall distribution appears to be far more 

 important than annual totals. In 1989, 

 rainfall was low overall, and the wet season 

 was essentially over by the end of March. In 

 1990, however, there was substantial rain in 

 January through June. And in 1991, there 

 were heavy rains in March. With long-term 

 data on soil salinity and vegetation during 

 years of low rainfall, it will be possible to 

 evaluate the effects of rainfall distribution. 



April soil salinities in 1990 and 1991 

 averaged lower than September salinities 

 (Table 5.5). Evaporation during the long dry 

 summer and transpiration during the growing 

 season act together to elevate soil salinity to 

 hypersaline conditions. In fall and winter, 

 high spring tides may reduce hypersaline 

 conditions somewhat, but rainfall probably 

 has the more important leaching effect. By 

 April, surface soils are usually near sea 

 water in salinity. Surface soil salinities (5 

 cm) were representative of those at greater 

 depth (25 cm) during the monitoring period. 



Table 5.5. Soil salinities for lower-, 

 middle-, and upper-elevation transects, at 5 

 and 25 cm depth. April data are from 1990- 

 91; September data are from 1989-91. 



April September 



Mean Range Mean Range 



The March 1991 rainfall totalled 7 inches 

 (17.7 cm) at Lindbergh Field, San Diego. 

 This was 4.4 times the average March rainfall 

 and 75% of the annual average. Soil salinities 

 were lowered by the event; for 23 of the 24 

 comparisons (12 transects, 2 depths), the 

 1991 April salinity means were lower than 

 those of 1990. 



5.6.2 Salt Marsh Vegetation 



Most of the vascular plants remained 

 similar in cover over the three-year period 

 (Table 5.6). The data provide a summary of 

 lower-, middle-, and upper-elevation species 

 composition, which can be used to set 

 objectives for restoration projects. 



The cordgrass canopy showed small but 

 significant changes over the 1989-91 

 sampling period. Densities increased overall, 

 from 101/m 2 in 1989, to 112/m 2 in 1990 

 and 145/m 2 in 1991. Total stem lengths 

 followed the same pattern, since the two 

 variables were almost perfectly correlated in 

 this data set (R 2 = 0.99, n = 12). 



1 1 7 



