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We analyzed a 9-yr record of ocean color data from the Sea-viewing Wide Field-of-view Sensor (SeaWiFS) together with a 4-yr record of satellite-derived sea surface temperature (SST) measurements to investigate potential mechanisms influencing nearshore phytoplankton variability in the Southern California Bight. We also compared in situ physicochemical conditions at four shoreline stations during a year with an extensive nearshore dinoflagellate red tide (2005) to those of the following year when there was no extended red tide (2006). SeaWiFS data indicated that in spring, chlorophyll a (Chl a) and nitrate (NO3-) were inversely correlated to SSTs, consistent with an upwelling-dominated system, but in summer Chl a and NO3- were unrelated to SST. Summer dissolved inorganic nitrogen concentrations were not well correlated between alongshore sampling stations, but showed a significant effect of tide stage (low vs. high). Mean summer nearshore Chl a was positively, linearly related to rainfall in the previous winter. The relationship between summer Chl a and winter precipitation could be due either to direct freshwater inputs during the winter rainy season or to delayed input via groundwater discharge. A first-order analysis of nutrient delivery from both surface runoff and groundwater discharge showed that they could sustain summer blooms of up to 7540 and 1700 km², respectively-areas on the order of the study site. However, precipitation-induced physical changes to the nearshore water column cannot be conclusively ruled out as a potential causative mechanism. [ABSTRACT FROM AUTHOR]

Abstract: Internal waves have been implicated in the cross-shore transport of scalars such as larvae, nutrients, and pollutants at locations around the world. The present study combines physical measurements with a comprehensive set of surf zone water quality measurements to evaluate the possible impact of cross-shore internal wave transport on surf zone water quality during two study periods. An array of oceanographic moorings was deployed in the summer of 2005 and 2006 at 10–20m depth offshore of the beach to observe internal waves. Concurrently, surf zone water quality was assessed twice daily at night at an adjacent station (Huntington State Beach) by measuring concentration of phosphate, dissolved inorganic nitrogen (DIN), silicate, chlorophyll a, fecal indicator bacteria (FIB), and the human-specific fecal DNA marker in Bacteroidales. The baroclinic component accounted for about 30% of the total variance in water column velocity, indicating the importance of density-driven flow during the summer when the water column was stratified. Arrival of cold subthermocline water in the very nearshore (within 1km of the surf zone) was characterized by strong baroclinic onshore flow near the bottom of the water column. The near bottom, baroclinic, cross-shore current was significantly lag-correlated with the near bottom temperature data along a cross-shore transect towards shore, demonstrating shoreward transport of cold subthermocline water. Wavelet analysis of temperature data showed that non-stationary temperature fluctuations were correlated with buoyancy frequency and the near bottom cross-shore baroclinic current. During periods of large temperature fluctuations, the majority of the variance was within the semi-diurnal band; however, the diurnal and high frequency bands also contained a substantial fraction of total variance. The bottom cross-shore baroclinic current was proposed as a proxy for shoreward transport potential by internal waves and was positively correlated with phosphate concentration in both years, silicate in 2005, and fecal indicator bacteria measurements in 2006. The results suggest internal waves are an important transport mechanism of nutrient-rich subthermocline water to the very nearshore in the Southern California Bight, and may facilitate the transport of FIB into the surf zone or enhance persistence of land-derived FIB. [Copyright &y& Elsevier]

Despite being important etiological agents of waterborne illness, the sources, transport and decay of human viruses in recreational waters are not well understood. This study examines enterovirus and adenovirus concentrations in coastal water samples collected from four beaches impacted by microbial pollution: (1) Malibu Lagoon, Malibu; (2) Tijuana River, Imperial Beach; (3) Baja Malibu, Baja California; and (4) Punta Bandera, Baja California. Water samples were concentrated using a flocculation-based skim milk method and dead-end membrane filtration (MF). Viruses were enumerated using cell culture infectivity assays and reverse transcription quantitative polymerase chain reaction (RT-QPCR). Across concentration and quantification methods, enteroviruses were detected more often than adenoviruses. For both viruses, MF followed by (RT)QPCR yielded higher concentrations than skim milk flocculation followed by (RT)QPCR or cell culture assays. Samples concentrated by skim milk flocculation and enumerated by (RT)QPCR agreed more closely with concentrations enumerated by cell culture assays than MF followed by (RT)QPCR. The detection of viruses by MF and (RT)QPCR was positively correlated with the presence of infectious viruses. Further research is needed to determine if detection of viruses by rapid methods such as (RT)QPCR can be a useful water quality monitoring tool to assess health risks in recreational waters.