Ceratophyllum demersum hampers phytoplankton development in some small Norwegian lakes over a wide range of phosphorus concentrations and geographical latitude |
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Authors: | MARIT MJELDE,& BJØ RN FAAFENG |
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Affiliation: | Norwegian Institute for Water Research, P.O. Box 173, Kjelsås, 0411 Oslo, Norway |
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Abstract: | 1. Data on submerged and floating-leafed macrophytes, phytoplankton, nutrients (N, P) and calcium were collected from twenty-four small lakes ( 1 km2) over a wide range of latitudes in Norway. The majority of the investigated lakes were mesotrophic or eutrophic, and most of the lakes were markedly affected by diffuse and point-source runoff from agriculture. According to their macrophyte species composition, the majority of the lakes can be classified as Potamogeton lakes or Chara lakes, or a combination of these. 2. This study is consistent with the 'two alternative stable states' hypothesis. We observed clearwater lakes with dense macrophyte cover over a wider range of total P concentration than has been reported previously: from 30 to more than 700 mg P m–3. The clearwater state was only observed in lakes with mean depths of less than 1.9 m. 3. Most clear lakes with high cover of submerged vegetation showed indications of N limitation. 4. In this study nearly all the macrophyte-dominated lakes with P concentrations above 30 mg m–3 had dense stands of Ceratophyllum demersum (L.). This indicates that Ceratophyllum may also play an important role in stabilizing and maintaining a clearwater state at high P concentrations. |
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