Eindrapport waterkwaliteitsonderzoek Reeuwijkse plassen 1983-1992
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Type
Report
Language
nl
Date
1997-10-31
Research Projects
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Journal Issue
Title
Eindrapport waterkwaliteitsonderzoek Reeuwijkse
plassen 1983-1992
Translated Title
Final report on water quality research Reeuwijkse
Plassen 1983-1992
Published in
Abstract
Dit rapport beschrijft een studie naar de effecten van
eutrofieringsbestrijding in de Reeuwijkse plassen, Elfhoeven en Nieuwenbroek
(1983-1992), en een studie naar de effecten van biomanipulatie (ter
verbetering van de visstand) en P-fixatie (ter vermindering van de
fosfaatmobilisatie) in resp. de Reeuwijkse plassen, Klein- en Groot
Vogelenzang (1988-1992). Geconcludeerd wordt dat ondanks de sterk verlaagde
fosfaatconcentratie in het aangevoerde water van de Rijn en de ter plaatse
genomen maatregelen ter verlaging van de fosfaatconcentratie in de plassen,
zoals defosfatering van het effluent van de nabijgelegen awzi en riolering
van de bebouwing langs de plassen de overmatige algengroei in de plassen
niet is afgenomen. De fosfaatconcentratie in de plassen is niet afgenomen
en de hoeveelheid blauwwieren is, zowel relatief als absoluut, toegenomen.
Ook biomanipulatie heeft niet tot het gewenste effect geleid; door
verlaging van de visstand nam het zooplankton wel toe, maar niet voldoende
om de algengroei binnen de perken te houden. De fosfaatfixatie 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 phophorus loading. Two lakes, Lake Elfhoeven and Lake Nieuwenbroek , differing in phosphorus load and residence time were selected for monitoring water quality parameters before (1983-1985) and after (1986-1992) these restoration measures. Reduction of the external phosphorus loading did not result in lower phosphorus concentrations in both lakes. In contrast, phosphorus and nitrogen increased in lake Nieuwenbroek. Seasonal cycles point to a strong internal loading of nutrients. In both lakes phytoplankton biomass, measured as chlorophyll-a and seston increased. The number of blue-green algae increased in both lakes, but especially in Nieuwenbroek. 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 phophorus loading. Two lakes, Lake Elfhoeven and Lake Nieuwenbroek , differing in phosphorus load and residence time were selected for monitoring water quality parameters before (1983-1985) and after (1986-1992) these restoration measures. Reduction of the external phosphorus loading did not result in lower phosphorus concentrations in both lakes. In contrast, phosphorus and nitrogen increased in lake Nieuwenbroek. Seasonal cycles point to a strong internal loading of nutrients. In both lakes phytoplankton biomass, measured as chlorophyll-a and seston increased. The number of blue-green algae increased in both lakes, but especially in Nieuwenbroek. 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, the Netherlands, telefax:
31-71-5123916
Publisher
Hoogheemraadschap van Rijnland
Leiden
Leiden
Sponsors
DGM