|Trends in Marsdiep phytoplankton|
Cadée, G.C. (1992). Trends in Marsdiep phytoplankton, in: Dankers, N.M.J.A. et al. (Ed.) Present and Future Conservation of the Wadden Sea: Proceedings of the 7th International Wadden Sea Symposium, Ameland 1990. 20: pp. 143-149
In: Dankers, N.M.J.A. et al. (Ed.) (1992). Present and Future Conservation of the Wadden Sea: Proceedings of the 7th International Wadden Sea Symposium, Ameland 1990. NIOZ: Texel. VIII, 301 pp., more
|Also published as |
- Cadée, G.C. (1992). Trends in Marsdiep phytoplankton. Publ. Ser. Neth. Inst. Sea Res. 20: 143-149, more
Phytoplankton cell-counts indicate an almost continuous increase in non-diatom plankton since the early 1970s. Particularly Phaeocystis blooms increased in duration. Diatoms fluctuated more irregularly. Man-induced eutrophication -increase in phosphate and nitrogen, but not in silicate- can explain such trends. They are comparable to those round in Helgoland, but different from (climatic-induced) trends observed in the open North Sea during the Continuous Plankton Recorder survey. Such climatic effects are apparently overruled by eutrophication effects in coastal waters. Historical data on Phaeocystis for the Marsdiep area confirm the changes observed: they indicate blooming periods lasting some 50 days in 1897 and 1899, before eutrophication started. This blooming period has tripled in the late 1980s. Annual primary production was measured less regularly, but the first 14C production data were collected in 1963-1965. Primary production has remained c.150 g carbon (C) m-2 a-1 up to the early 1970s, but doubled in the early 1980s. A tentative estimate for 1990, based on data available up to September, gives a value or 250 g (C) m-2 a-1. Production in 1990 might be relatively low due to low freshwater (including nutrient) discharge from the IJsselmeer. Chlorophyll-a showed an increase parallel with the primary production increase in the late 1970s, but the annual variation is large. Comparison with the 1951-1953 data is hampered because of differences in the methods used.