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Algal-available Phosphorus Entering the Gulf of Finland as Estimated by Algal Assays and Chemical Analyses

Ekholm, Petri, Rita, Hannu, Pitkänen, Heikki, Rantanen, Pirjo, Pekkarinen, Jouko, Münster, Uwe
Journal of environmental quality 2009 v.38 no.6 pp. 2322-2333
surface water, rivers, wastewater, phosphorus, bioavailability, eutrophication, algae and seaweeds, algal blooms, chemical composition, Phaeodactylum tricornutum, Selenastrum capricornutum, laboratory techniques, bioassays, accuracy, estimation, nutrient availability, effluents, Gulf of Finland
Algal-available phosphorus (P) in river water and wastewater entering the Gulf of Finland (a Baltic Sea sub-basin) was estimated by a fresh-water and a brackish-water modification of the dual-culture algal assay. The assay results were further related to those obtained by routine chemical analyses. According to the brackish-water assay, an average of 44% (range, 9–88%) of total phosphorus (TP) in water samples from the Neva, Kymijoki, and Narva rivers consisted of P, whereas the mean value given by the fresh-water assay was 22% (range, 0–48%). Bohlin, which was used as the test alga in the brackish-water assay, had higher phosphoesterase activity and P affinity than did Korschikov, which was used in the fresh-water assay. This difference may explain the higher values of P shown by the brackish-water assay. Of the analytical P forms, total dissolved P best approximated, yet underestimated, the P in river water samples. As for the biologically purified wastewaters of the city of St. Petersburg, both assays suggested that about 80% of TP (range, 59–103%) was available. That the assays gave similar results was probably due to the fact that most of the P in the wastewater samples was in the form of readily available dissolved reactive P. In untreated urban wastewaters, the mean proportion of P in TP was 46% (range, 19–76%). Although the true P may not be obtained by any assay, our findings corroborate the view that severe underestimation may occur if the test conditions are suboptimal for the release and uptake of P.