Bureau Waardenburg
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4101 CK Culemborg
the Netherlands
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Zevenhuizerplas onderwatervegetatie inventariseren
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Diving for stoneworts in Zevenhuizerplas

The Zevenhuizerplas is a deep lake near to Rotterdam that was created through gravel extraction in 1978. Historically, the lake is known for the stoneworts (Characeae) that grow there and for the birds that feed off of these plants. Over the past ten year, the lake has become shallower and has been joined to a new gravel extraction. In 2010, Bureau Waardenburg surveyd the vegetation in both the old and the new parts of the lake. Our qualified professional divers made descriptions of the underwater vegetation along the contours of the lake. The old lake was surveys along the same transects that were surveyed following the shallowing of the lake in 2002. The transects of the new lake were surveyed for the first time. 

The results revealed that the vegetation cover was similar, and in places had increased slightly, compared to the 2002 survey. Vegetation cover in shallow areas (0-2.5m) was between 20-40 percent. The amounts of stoneworts, Ranunculus circinatus and small pondweed had increased, while western waterweed and Myriophyllum spicatum had declined. The vegetation had partly recovered following the shallowing work in 2002. Furthermore, there was no deterioration in water quality and the complete disappearance of stoneworts has not occurred.

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