Coastal Power Plant Discharge Enhances Nitrogen Content of Kelp (Macrocystis pyrifera)

Abstract

Heated water from the San Onofre Nuclear Generating Station (SONGS) is discharged through a multiport diffuser system, which secondarily entrains about 10 times its volume of ambient water, principally from below the thermocline. On average, this rising and spreading plume should be enriched in inorganic nutrients, including nitrogen, compared to ambient surface waters. Effects from the plume on kelp were investigated by sampling kelp canopy tissues and analyzing for nitrogen content. In seven samplings from August 1991 to March 1994, the area of the San Onofre kelp bed (SOK) nearest the offshore diffuser consistently yielded higher than average nitrogen on a percent dry weight basis, and there was an overall pattern of decreasing enrichment with distance from the diffusers (X² probability < 0.005).

The presumed SONGS-induced nutrient upwelling is therefore considered to exist. The portions of SOK that benefit from the artificially upwelled nutrients would be more likely to survive a period of generally poor conditions such as an El Niño, and then serve as a source of spores for repopulating the kelp bed.