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Description
Buena Vista Lagoon is a closed lagoon situated in northern San Diego county. The lagoon is transversed by Interstate 5, railroad tracks and Route 101 and is bordered by Route 78 on the north. The lagoon is in a state reserve and therefore is considered to be relatively undisturbed. This study was part of acollaboration with Jeannie Chick to obtain sedimentation rates and a records of metal contamination through analysis of sediments from the lagoon. Three continuous core samples were taken from Buena Vista Lagoon in the fall of 1993. The first sample (core 1) was collected in an enclosed (salt pond) section on the north side of the lagoon. The second and third cores were taken from the approximate center of the eastern section of the lagoon bounded by Interstate 5 and Route 101. Only the first and third cores were analyzed for sedimentation rates. The sedimentation rates for cores 1 and 3 were determined by the use of 210Pb geochronology. 210Pb has a half-life of 22.3 years. By plotting the 210pb activity an a function of depth in the core, and using the half-life of the isotope, the sedimentation rate for the lower portion of core one was calculated to be 2.6 cm./yr. whereas the average sedimentation rate for core three was determined to be 3.2 cm./ yr. A total age in years of core 1 and specific year dates for different depths could not be calculated for the core because of a radical drop in 210pb activity in the top 10 cm. of the core. This anomaly (reverse slope of radioactive decay with depth) is most easily explained by the isolation of the small salt pond from the rest of the lagoon by cattail growth, thus changing the influx of 210:fb from the constant value assumed for all calculations. The 60 cm. length of core 3 was calculated to contain a record of the last 19 years (from 1993 to 1975) .. The 210pb plot versus depth for both cores exhibited considerable scatter. The major causes of the scatter are thought to be: (l)The varying and pulsating seasonal deposition of the sediment from winter rains combined with the fact that each sample depth' analyzed was less than one year, (2)the sporadic introduction of sea water into the lagoon, and (3)the small total volume of the lagoon. Using the high sedimentation rate calculated from core 3 the area of the lagoon bounded by Interstate 5 and Route 101 is projected to completely silt up in the next 30-40 years.
