Monitoring of nutrient concentration and primary and secondary productivity in coastal area of Miyagi Prefecture
Period and Interval2014/04/01 - 2015/03/31
Once a month
Research Area
Onagawa Bay and other coastal areas of Miyagi Prefecture
CategoryField survey
OverviewKey words: Onagawa Bay, Nutrients, phytoplankton, zooplankton, primary production, microbial loop
Research Point Table
| Point | | Name | 1 |
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| Coordinates | 38.44123,141.4586 |
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| Name | 12 |
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| Coordinates | 38.41193,141.48242 |
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| Name | 17 |
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| Coordinates | 38.43543,141.48842 |
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| Name | 3 |
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| Coordinates | 38.4295,141.4788 |
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| Name | 6 |
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| Coordinates | 38.4237,141.52158 |
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| Name | 8 |
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| Coordinates | 38.42397,141.56317 |
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| Name | 11 |
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| Coordinates | 38.40182,141.4749 |
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Results and Future PlanDIN (dissolved inorganic nitrogen) concentration in the surface layers (0-10 m) was low from April to August in the whole bay, especially low in April less than 2 micro mol/L. DIN increased to more than 2 micro mol/L from September to December in the surface layer. In the deeper layers, however, DIN less than 2 micro mol/L was found only in May. Surface phosphate concentration was low in July and August, especially in July when the concentration less than 0.1 micro mol/L was found at many station. In other months, however, higher values were observed. Phosphate concentration in deeper layers showed similar seasonal change. Surface Silicate was low in April-July. It was especially low in April, being less than 5 micro mol/L at every station. In September, it was also less than 5 micro mol/L at the innermost bay, aquaculture field, and mouth area of the bay. Such a low value was found only in May and July in the deeper layers.
Chlorophyll a concentration had a peak in April at every station. This was the spring bloom and occurred at the same time with the entrance of Oyashio water into the bay. Chlorophyll a concentration has a tendency to increase from 2012.
Primary production at the innermost bay ranged from 0.08 to 0.41 gC/m2/d from April to August 2014. Highest values were found in April and May, which is different from last year when the peak was in August. Total zooplankton abundance shows the tendency to increase from 2012 onward. In April 2014, the abundance is not so high, but the settling volume was highest exceeding 100 ml/m3 at several stations. It increased in May, with values higher than 100,000 ind./m3 at several stations. High values in abundance were found until July. In August-October, higher values were restricted to the inner half of the bay. It was very low in the whole bay in December.
