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Pyrethroids are the active ingredients in most insecticides available to consumers for residential use in the United States. Yet despite their dominance in the marketplace, there has been no attempt to analyze for most of these compounds in watercourses draining residential areas. Roseville, California was selected as a typical suburban development, and several creeks that drain subdivisions of single-family homes were examined. Nearly all creek sediments collected caused toxicity in laboratory exposures to an aquatic species, the amphipod Hyalella azteca, and about half the samples caused nearly complete mortality. This same species was also found as a resident in the system, but its presence was limited to areas where residential influence was least. The pyrethroid bifenthrin is implicated as the primary cause of the toxicity, with additional contributions to toxicity from the pyrethroids cyfluthrin and cypermethrin. The dominant sources of these pyrethroids are structural pest control by professional applicators and/ or homeowner use of insecticides, particularly lawn care products. The suburbs of Roseville are unlikely to be unique, and similar sediment quality degradation is likely in other suburban areas, particularly in dry regions where landscape irrigation can dominate seasonal flow in some water bodies.

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Measurements of Secchi disk depth are correlated with beam transmittance (B) in turbid coastal water.Both k (the irradiance attenuation coefficient) and a! (the beam attenuante coefficient) can be estimated from the Secchi depth either on an empirical basis or by using the Duntley-Preisendorfer equation of contrast reduction, Such estimates possess relatively large standard errors of estimate.

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A b~ Three marine diatoms, Skeletonema costatum, Chaetoceros debilis, and Thalassiosira g r a~d a were grown under no limitation and a m m o n i u m or silicate limitation or starvation. Changes in cell m o r p h o l o g y were d o c u m e n t e d with p h o t o m i c r o g r a p h s of a m m o n i u m and s i l i c a t e-l i m i t e d and n o n-l i m i t e d cells, and c o r r e l a t e d with observed changes in chemical composition. Cultures grown under silicate starvation or limitation showed an increase in p a r t i c u l a t e carbon, nitrogen and phosphorus and c h l o r o p h y l l a per unit cell volume compared to n o n-l i m i t e d cells; p a r t i c u l a t e silica per cell v o l u m e decreased. Si-starved cells were d i f f e r e n t from S i-l i m i t e d cells in that the former c o n t a i n e d more p a r t i c u l a t e carbon and silica per cell volume. The most sensitive indicator of silicate limitation or s t a r v a t i o n was the ratio C:Si, being 3 to 5 times higher than the values for n o n-l i m i t e d cells.

A statewide investigation of urban creek sediment toxicity was conducted in California in recognition of increased incidences of toxicity linked to pyrethroid pesticides. The goals were to examine the spatial occurrence and magnitude of sediment toxicity in California urban creeks, and to examine the role of pyrethroids in toxic urban creek sediment samples. After a preliminary screening of 90 sites, 30 creeks were sampled in eight geographical regions. Sediment toxicity was assessed using 10 day bioassays with the resident amphipod Hyalella azteca. Bioassays were conducted at two test temperatures of 23 degrees C and at 15 degrees C to provide evidence of the cause of toxicity, and to more accurately reflect ambient environmental temperatures. Twenty-five of 30 samples were toxic when tested at 23 degrees C, and all 30 samples were toxic when tested at 15 degrees C. The magnitude of toxicity increased in samples tested at 15 degrees C suggesting the influence of pyrethroids, which are more toxic at colder temperatures. Pyrethroids were present in all sediment samples and were the only compounds detected at concentrations toxic to H. azteca. Bifenthrin was the pyrethroid of greatest toxicological concern, occurring in all 30 samples at concentrations up to 219 ng/g. Pyrethroid contamination of urban creeks was most severe in the Los Angeles, Central Valley, and San Diego regions, respectively. However, pyrethroids were also linked to urban creek aquatic toxicity in all regions sampled, including the less urbanized areas of the North Coast and Lake Tahoe.

Five red water dinoflagellate blooms took place in La Jolla Bay, California, between May 1964 and Deeember 1966. Predominant organisms were Gymnodinium spp. and Cochlodinium spp. (May 1964), Prorocentrum micans (April 1965) and Gonyaulax polyedra (June–July 1964, June—July 1965, and December 1966). Cell concentration and chlorophyll a content were measured during each bloom with values up to 20 × 106 cells/ liter and approximately 500 µg chlorophyll a/liter. During the day, the organisms appeared in discrete patches that apparently dispersed at night. Cell carbon and nitrogen content of the organisms often exceeded that available in surface waters or in the water column. Cells must be concentrated both vertically and horizontally to account for the numbers observed in patches during the day. Even in the densest patches the cells appeared to be physiologically active based upon measurements of photosynthetic rate, nitrate reductase activity, and observed motility. Decline of blooms was associated with increases in dissolved organic carbon, orthophosphate and monophosphate esters. The May 1964 bloom was decimated by grazing of Polykrikos sp., Noctiluca sp., and rotifers. A steep shallow thermocline was associated with the blooms.