THE ORIGINS OF FOOD RESOURCES ASSIMILATED BY FOULING ORGANISMS IN SEAWATER COOLING SYSTEMS OF POWER STATIONS: A STABLE ISOTOPIC ANALYSIS

Abstract

 We examined the orignins and nutritional value of suspended particulate organic matter (POM) in seawater, which are the potential food source for fouling organisms, in seawater cooling systems of six power stations located in the norseastern Japan. We sampled POM and fouling organisms, and analyzed them for C and N stable isotope ratios (δ¹³C, δ¹⁵N) and the ratio of C/N. As a result, the chemical properties of POM varied between the power stations. POM from the three stations on the Japan Sea coast was considered to have relatively higher contents of POM originating from terrestrial plant and/or riverine producers. POM from the other three stations on the Pacific Ocean coast likely had higher contents of marine phytoplanktons. The POM concentration was generally positively related to dissolved inorganic nitrogen in the seawaters, suggesting that the reduction of anthropogenic nitrogen can potentially be an effective tactics to mitigate the biofoulings in the cooling systems. Furthermore, δ¹³C and δ¹⁵N of the fouling organisms were markedly higher compared with those of POM. This suggests that the fouling organisms selectively assimilated the marine phytoplankton fraction of the bulk POM. Therefore, when the food supply for the fouling ornigsms is evaluated based on bulk POM, that is potentially overestimated. To properly predict effects of nutrient/POM reductions on the production of fouling organisms, further studies are necessaly to accumulate field data and develop reliable, quantitative models describing relationships for POM vs. nutrients as well as fouling organisms vs. POM.