Waterkwaliteitsonderzoek Reeuwijkse plassen. Studie naar de effecten van biomanipulatie in Klein Vogelenzang en P-fixatie in Groot Vogelenzang 1988-1992
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Series / Report no.
Open Access
Type
Report
Language
nl
Date
1997-10-31
Research Projects
Organizational Units
Journal Issue
Title
Waterkwaliteitsonderzoek Reeuwijkse plassen. Studie
naar de effecten van biomanipulatie in Klein Vogelenzang en P-fixatie in
Groot Vogelenzang 1988-1992
Translated Title
Water quality research Reeuwijk lakes. Study into
the effects of biomanipulation in Klein Vogelenzang and P-fixation in Groot
Vogelenzang 1988-1992
Published in
Abstract
Uit deze studie bleek dat biomanipulatie (ter
verbetering van de visstand) niet tot het gewenste effect heeft geleid;
door verlaging van de visstand nam het zooplankton wel toe, maar niet
voldoende om de algengroei binnen de perken te houden. De fosfaatfixatie
(ter vermindering van de fosfaatmobilisatie) gaf wel een afname van de
fosfaatmobilisatie en de fosfaatconcentratie te zien, maar deze verlaging
leidde niet tot minder algengroei. Aanbevolen wordt de mogelijkheid nader
te onderzoeken de bezinking van zwevend stof te bevorderen door het graven
van enige putten van 5-10 m in deze plassen, die gemiddeld 1.5 m diep zijn.
Aanbevolen wordt de permanente aanwas van de visstand door de
beroepsvisserij te laten reduceren. Nader onderzoek naar de effecten van
een combinatie van biomanipulatie en fosfaatfixatie door coagulatie met
ijzer is gewenst.
Restoration of the highly eutrophic Reeuwijk lakes (ca 700 ha) started in 1986 by reducing the external phosphorus loading. Reduction of the external phosphorus loading did not result in lower phosphorus concentrations in the lakes. In contrast, phosphorus and nitrogen increased in the lakes. Seasonal cycles point to a strong internal loading of nutrients. Phytoplankton biomass, measured as chlorophyll-a and seston increased. The number of blue-green algae increased especially in 1991 and 1992. Transparency in the lakes slightly decreased. As an additional measure to improve the quality of the lake water, the structure of the fish population in lake Klein Vogelenzang was altered in 1989 by removal of 50% of the bream-stock from the lake. The study shows that technical and biological factors can cause serious management problems for the implementation of biomanipulation in larger water bodies. Treatment of the sediments of lake Groot Vogelenzang with iron(III)chloride resulted in an immediate threefold decrease in the total phosphorus concentration in the lake. The improved water quality lasted only for a few months because of the short residence time of the lake. Treatment of lake sediments with iron is potentially an effective method to decrease internal phosphorus loading, but the durability of this method still needs to be proven.
Restoration of the highly eutrophic Reeuwijk lakes (ca 700 ha) started in 1986 by reducing the external phosphorus loading. Reduction of the external phosphorus loading did not result in lower phosphorus concentrations in the lakes. In contrast, phosphorus and nitrogen increased in the lakes. Seasonal cycles point to a strong internal loading of nutrients. Phytoplankton biomass, measured as chlorophyll-a and seston increased. The number of blue-green algae increased especially in 1991 and 1992. Transparency in the lakes slightly decreased. As an additional measure to improve the quality of the lake water, the structure of the fish population in lake Klein Vogelenzang was altered in 1989 by removal of 50% of the bream-stock from the lake. The study shows that technical and biological factors can cause serious management problems for the implementation of biomanipulation in larger water bodies. Treatment of the sediments of lake Groot Vogelenzang with iron(III)chloride resulted in an immediate threefold decrease in the total phosphorus concentration in the lake. The improved water quality lasted only for a few months because of the short residence time of the lake. Treatment of lake sediments with iron is potentially an effective method to decrease internal phosphorus loading, but the durability of this method still needs to be proven.
Description
available from Hoogheemraadschap van Rijnland, P.O. Box
156, 2300 AD Leiden, fax: 31-71-5123916
Publisher
Hoogheemraadschap van Rijnland
Leiden
Leiden
Sponsors
DGM