Temporal and spatial characteristics of chemical oxygen demand in Tokyo Bay |
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Authors: | Midori Kawabe Masaki Kawabe |
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Institution: | (1) Tokyo University of Fisheries, Konan 4-5-7, Minato-ku, 108 Tokyo, Japan;(2) Ocean Research Institute, University of Tokyo, Minami-dai 1-15-1, Nakano-ku, 164 Tokyo, Japan |
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Abstract: | Chemical oxygen demand (COD) at the sea surface in Tokyo Bay was examined using monthly data during 1980–89. The long-term
mean and the annual-cycle amplitude of COD are largest in the northwestern region, decrease southward, and are smallest near
the entrance of the bay. Based on their spatial properties, Tokyo Bay was divided into northwest, northeast, southwest, and
southeast regions, named Regions 1, 2, 3, and 4, respectively. The time mean and the annual-cycle amplitude are large in Regions
1 and 2 but much less in Region 4, and are highly correlated in Region 1 + 2 + 4. The annual-cycle amplitude in Region 3 is
larger than that in Region 4, although the time mean is similar. The monthly long-term averages show a clear seasonal change
of COD, with a large increase from April to June, the maximum in June, and the minimum in December. After the maximum, COD
in Regions 1 and 3 (western side of the bay) decreases monotonically, while that in Regions 2 and 4 (eastern side) has a secondary
maximum in August. The phase of annual cycle lags southward from the head to the mouth of the bay with a maximum lag of about
one month. Anomalously large COD was observed in the western region of Tokyo Bay mostly in June, but never in the east and
from July to April. This is related to a high concentration of chlorophylla plus phaeo pigment and is likely caused by blooming of phytoplankton. Yearly mean COD was at a maximum in 1984 or 1985 and
decreased greatly after that. The annual frequency of the observed anomalous COD was large in 1981, 1983, and 1985, then decreased
abruptly, remaining small after 1985, possibly associated with low COD. |
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Keywords: | Organic contamination chemical oxygen demand COD seasonal variation spatial distribution interannual variation phytoplankton bloom chlorophylla Tokyo Bay |
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