Survival of copepods passing through a nuclear power station on northeastern Long Island Sound, USA

Abstract

About 70% of the copepods entering the cooling water system of a nuclear power plant on northeastern Long Island Sound (USA) are not returned to the Sound in the effluent. Copepod mortalities are caused by the mechanical or hydraulic stresses of passage, although our experimental design could not determine whether heat or chlorination could cause mortality in the absence of mortality induced by hydraulic stress. After passing through the power plant, copepods sink rapidly (ca. 2.5 times faster than controls). This leads to an increase in concentrations of copepods suspended in the deep water (25 to 30 m) of the effluent pond. About half of the live copepods collected at the discharge and held in situ died within 3.5 days, and 70% died within 5 days, whereas only 10% of those from the intake died in 5 days. About 60% of the copepods observed suspended in deep water in the pond were dead. The copepod mortality caused by the power plant reflects the loss in secondary production occurring below about 270×10³ m² of sea surface in Long Island Sound annually. This loss represents a reduction of about 0.1% in the annual secondary production over a 333 km² area of Long Island Sound adjacent to the power plant. Highest losses occurred during the spring (April, 1.4×10⁶ g dry weight), the lowest in autumn (November, 45.8×10³ g). If the same copepod loss rate exists for all power plants in Long Island Sound, then secondary production in 1.69×10⁶ m², or 0.05% of the total copepod production may be lost annually. A comparison of the surface outflow from Long Island to Block Island Sound with the water entrained through Millstone Unit One, and the 70% copepod loss rate in the latter area, indicates that Unit One eliminates about 0.1 to 0.3% of the copepod production in eastern Long Island Sound. This calculation compares favorably with losses computed from production data.