Watersheds in Kamchatka's volcanic areas are of interest because they are enriched with nutrients (N, P, Si) and trace elements that cause microalgae blooms, contribute significantly to food chains, and thus impact coastal marine ecosystems as a whole. The Nalychevo River is one of the largest rivers in the Avachinsky Gulf drainage basin. However, due to the inaccessibility of this area, expeditionary research on the Nalychevo River is limited. Our goal is a comprehensive study of the Nalychevo River and the coastal waters of Avachinsky Gulf. A new complex of data on bio-hydrochemical characteristics was obtained from the middle basin of the Nalychevo River to the deep-water part of Avachinsky Gulf and the adjacent waters of the Pacific Ocean. It is observed that the phytoplankton “bloom” with a chlorophyll “a” concentration of up to 40 μg/l in the area of the Nalychevo River plume is caused by the intensive influx of nutrients and microelements with river runoff during the spring-summer flood and the development of maximum water stratification. Variability of DIN/DIP ratios in Avachinsky Gulf due to fluxes of nutrients from volcanic catchments is considered to be the main cause of the occurrence of “red tides” in the summer-autumn period.

Kamchatka Peninsula, Volcanic Catchment, DIN/DIP-ratios, Phytoplankton Blooms, Coastal Ecosystem Health