BIOGEOCHEMISTRY OF ORNITHOGENIC GEOSYSTEMS OF THE NORTHWESTERN PACIFIC (CASE STUDY OF THE TOPORKOV AND STARICHKOV ISLANDS)

The paper focuses on the biogeochemical diversity and heterogeneity of ornithogenic geosystems formed by large colonies of sea birds. The objects of the study were two islands in the Northwest Pacific with centuries-old bird bazaars of about 100,000 birds, i. e. Toporkov Island in the Commander Archipelago and Starichkov Island near the southeast coast of Kamchatka. To identify their biogeochemical heterogeneity, special schemes reflecting the catenary structure of the islands, the neighborhood and diversity of elementary geochemical landscapes of different types and genera, the variability of herbaceous phytomass depending on the species composition of phytocenoses, the bird population and the degree of its influence were compiled. The fractional structure of phytomass and the stocks of chemical elements in it showing various modifications of elementary landscapes under the ornithogenic pressures were used as informative indicators. It was found that the biogeochemical heterogeneity of the islands is initially preconditioned by the history of their evolution and the differentiating influence of abiotic factors on the structure of catenas, which were subsequently overlaid by the influence of birds. It is shown that specific impact of the bird population results in the multidirectional transformation of the species composition of phytocenoses, which is modified by the bird numbers and the inflow of their metabolites into the soil, increasing the heterogeneity of resulting biogeochemical fields. The ornithophile species change the activity of autotrophic biogenesis, the capacity of phytobarriers and the accumulation of biogenic elements (P, Zn, B) on them depending on the phylogenetic specialization of plants and the fractional structure of herbaceous phytomass. It was revealed that the number of elementary geochemical landscapes could differ almost twice within the same area of islands. The increase in biogeochemical heterogeneity is promoted by increasing absolute height of the island, the complexity of the structure of catenas, and formation of new types of landscapes with different resistance to ornithogenic effects. Local contrasts in phytomass reserves and chemical element accumulation at the intra-landscape level may differ by an order of magnitude. This determines the specificity of ornithogenic geosystems, where birds are the leading factor of structural and functional organization.