地球化学

The importance of an ecosystem model as a tool to analyse ocean biogeochemical data has recently been increasing. That is because an ecosystem model can be used as a tool (1) to test hypotheses to explain observational data at hand, (2) to combine the generally scarce ocean observations into a more coherent picture and (3) to indirectly obtain some information about immeasurable process by a data-assimilative approach. In this review, we first show the basic model equations to construct a relatively simple ecosystem model. Then, we introduce some researches which use the above usefulness of an ecosystem model when analyzing ocean biogeochemical observational data. After that, we also briefly review the present large-scale biogeochemical circulation models because our ultimate aim in the ocean biogeochemistry is to clarify the dynamics of bioelements in the whole ocean. Finally, we show the other ways of using an ecosystem model, such as one including bioelement isotopes and biogenic gases.

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Relatively high levels of Hg were found in the bodies of low tropic animals inhabiting Yambaru area when compared with unpolluted ecosystems. Especially, large centipede species which are the strong carnivore of invertebrates accumulated Hg with high concentration due to their high tropic in food web. In the same way, some species of raptors and carnivorous snake inhabiting forest accumulated Hg in their bodies. These facts supported that biomagnification of Hg exists in the ecosystem of Yambaru area. Interestingly, rare animals in the Yambaru area such as Anderson's crocodile newt as amphibians, Okinawa woodpecker, Ryukyu robin, and Okinawa rail as birds accumulated Hg with higher levels when compared with other animals niching at the same tropic levels. From analysis of inter-elemental relationships using concentration data of 25 trace elements in the animal bodies collected from Yambaru area, three toxic elements (lead, cadmium, and silver), five essential elements (selenium, chromium, vanadium, nickel, and cobalt), and one trace element (strontium) were correlated with Hg in the various animal groups such as invertebrate, amphibians, reptilian, omnivorous birds, carnivorous birds, omnivorous mammals, and carnivorous mammals.

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