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| Carl Sagan's COSMOS is one of the most influential science programs ever made.
Q. Does the moon have a dark side?
A. The moon does have a far side which is impossible to see from the earth, but it doesn't mean that it's always dark. Each side of the moon is dark for no longer than 15 days at a time.
Q. Where does sound come from?
A. The air is always filled with sound waves. All things give off vibrations, but some have a low frequency which most cannot hear. The reason: it may take 3 minutes to make a single vibration. They may be caused by earthquakes and storms.
Did You Know?
The microwave was invented after a researcher walked by a radar tube and a chocolate bar melted in his pocket.
Coke-a-Cola was originally green.
Rubberbands last longer when refrigerated.
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Waddenzee fresher than ever
by Netherlands Organization for
Scientific Research. Contact: Michel Philippens philippens@nwo.nl
The seawater in the Waddenzee is becoming fresher. More river water is reaching the Waddenzee via the outlet sluices of the IJsselmeer Dam. This is the conclusion of Dr. Hendrik van Aken from the Netherlands Institute for Sea Research. Along with the fresh water, more nitrate and phosphate are entering the Waddenzee.
During the past 140 years the average quantity of fresh water in the Waddenzee has doubled. This is due to a strong increase in the water supply from the IJsselmeer. The river IJssel in particular is transporting increasingly more water. Over the last 70 years the discharge from the IJssel has in fact doubled. This is due to human intervention in the course of the rivers Waal, Nederrijn and IJssel. One of the aims of this has been to improve the navigability of the IJssel.
Since the 1970s, the Netherlands Institute for Sea Research has not only measured the salinity, but also the water temperature, the quantity of plankton and the species composition of plankton. The measurements are carried out in the western part of the Waddenzee, in the Marsdiep. The KNMI [Netherlands Meteorological Institute] has carried out systematic measurements of the salinity there since 1861.
With the greater influx of river water the Waddenzee is also been supplied with more nutrients, in particular nitrate and phosphate. This is further increased by the fact that the rivers themselves contain more nutrients. Furthermore, the self-cleaning capacity of the IJsselmeer has decreased. In the 1950s about 70% of the nitrate compounds entering the lake were decomposed. Now this is scarcely 50%. The plankton in the IJsselmeer are no longer able to clean up the large quantities of nitrate. This is in part due to the fact that the volume of water in the IJsselmeer has decreased since the closing off of the Markermeer.
The measurements in the Marsdiep reveal that in particular the quantity of nitrate and to a lesser extent the quantity of phosphate have increased. The Netherlands Institute for Sea Research has also observed a shift in the species composition of the plankton. Species which thrive at high concentrations of nutrients are becoming more common. The algal bloom is also continuing to increase.
The lower salinity, however, scarcely affects the composition of the marine life in the Waddenzee. Species there are very tolerant for other salinities. This is hardly surprising because the salinity in the Waddenzee varies strongly per season.
Further information can be obtained from Dr. Hendrik van Aken, Netherlands Institute for Sea Research, tel 31-222-369-416, fax 31-222-319-674, e-mail aken@nioz.nl or from Dr. Wim van Raaphorst, tel 31-222-399-446, e-mail wimvr@nioz.nl. At the start of October a paper about this study will appear in a special edition of the journal ICES Marine Science Symposia, which is completely devoted to long-term changes in the sea.
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