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Papers by Steven Vermij
SIL Proceedings, 1922-2010, 1984
Archiv Fur Hydrobiologie, 1992
Aquatic Sciences, 1990
We compare results of a new model for predicting the short term inter annual changes in chlorophy... more We compare results of a new model for predicting the short term inter annual changes in chlorophylla (chl-a) in lakes after reductions in total phosphorus (TP) to predictions made by least squares regression models. In the new method, slopes ofchl-a/TP graphs (both axes in mg• m-3) are depicted in frequency diagrams and used to extract information on the expected, short term chl-a/TP response. The short term response for nine shallow (< 10 m deep) and nutrient rich lakes to changes in TP was found to be: Chl-a = 0.49-TP + 17.3, and for nine deep, P-limited lakes: Chl-a = 0.08 • TP + 3.5. If the TP-reduction is known to be greater than 10 mg • m-3, the expected slope increases to 0.58 for shallow lakes and to 0.26 for deep lakes. The slope, 0.58, is 8 % lower than the slope for the long term response calculated by regression for the shallow lakes. For deep lakes the slope, 0.26, is 2 to 3 times higher than that calculated by regression, indicating that reductions in TP for deep lakes give greater effects than least squares regression equations suggest. We have also calculated the reduction in TP which will give about 80 % probability that a reduction in chl-a will be observed next year. For shallow, P-limited lakes this reduction is about 30 mg" m-3 (5% of average initial in-lake TP concentration), and for deep lakes about 14mg.m-3 (35% of average initial in-lake TP concentration).
Journal of the American Water Resources Association, 1980
A one-dimensional model for heat and oxygen transport is frequently used for the estimation of pr... more A one-dimensional model for heat and oxygen transport is frequently used for the estimation of primary productivity. Such a model employs free oxygen and temperature measurements at discrete time and depth intervals. In this method the eddy diffusion coefficients of heat and oxygen are assumed to be interchangeable. This method was applied to hourly data for 24-hour periods in a small temperature stratified lake. Primary productivity was simultaneously measured with the light and dark bottle method. The application of the free oxygen method resulted in unrealistic estimates of productivity. Some consideration is given to the origin of the failure in the application of this method.
Internationale Revue der gesamten Hydrobiologie und Hydrographie, 1985
Hydrobiologia, 1992
Total phosphorus and chlorophyll decreased significantly after reduction of the external phosphor... more Total phosphorus and chlorophyll decreased significantly after reduction of the external phosphorus loading and the start of flushing Veluwemeer with polder water in 1979. Flushing of Veluwemeer has had a large impact on nutrient dynamics. Especially in the first winter, dilution was the main cause of changes in water quality. On a longer term the increase of the inactivation of phosphorus in sediments is important. Oscillatoria agardhii has been brought to the margins of its habitat. Three successive cold winters were an additional causal factor in the disappearance of Oscillatoria agardhii and the dominance of diatoms and green algae from 1985 onwards. Due to higher detritus and inorganic suspended matter concentrations transparency increased less than expected. Since 1985 chlorophyll only contributes for a small percentage to the transparency. In the present situation further improvement of the water quality of Veluwemeer is questionable, as the phosphorus concentration in the lake and the polder water is almost the same. Therefore it is recommanded to shift flushing operations, at least in the winter period, from Veluwemeer towards Wolderwijd.
SIL Proceedings, 1922-2010, 1984
Archiv Fur Hydrobiologie, 1992
Aquatic Sciences, 1990
We compare results of a new model for predicting the short term inter annual changes in chlorophy... more We compare results of a new model for predicting the short term inter annual changes in chlorophylla (chl-a) in lakes after reductions in total phosphorus (TP) to predictions made by least squares regression models. In the new method, slopes ofchl-a/TP graphs (both axes in mg• m-3) are depicted in frequency diagrams and used to extract information on the expected, short term chl-a/TP response. The short term response for nine shallow (< 10 m deep) and nutrient rich lakes to changes in TP was found to be: Chl-a = 0.49-TP + 17.3, and for nine deep, P-limited lakes: Chl-a = 0.08 • TP + 3.5. If the TP-reduction is known to be greater than 10 mg • m-3, the expected slope increases to 0.58 for shallow lakes and to 0.26 for deep lakes. The slope, 0.58, is 8 % lower than the slope for the long term response calculated by regression for the shallow lakes. For deep lakes the slope, 0.26, is 2 to 3 times higher than that calculated by regression, indicating that reductions in TP for deep lakes give greater effects than least squares regression equations suggest. We have also calculated the reduction in TP which will give about 80 % probability that a reduction in chl-a will be observed next year. For shallow, P-limited lakes this reduction is about 30 mg" m-3 (5% of average initial in-lake TP concentration), and for deep lakes about 14mg.m-3 (35% of average initial in-lake TP concentration).
Journal of the American Water Resources Association, 1980
A one-dimensional model for heat and oxygen transport is frequently used for the estimation of pr... more A one-dimensional model for heat and oxygen transport is frequently used for the estimation of primary productivity. Such a model employs free oxygen and temperature measurements at discrete time and depth intervals. In this method the eddy diffusion coefficients of heat and oxygen are assumed to be interchangeable. This method was applied to hourly data for 24-hour periods in a small temperature stratified lake. Primary productivity was simultaneously measured with the light and dark bottle method. The application of the free oxygen method resulted in unrealistic estimates of productivity. Some consideration is given to the origin of the failure in the application of this method.
Internationale Revue der gesamten Hydrobiologie und Hydrographie, 1985
Hydrobiologia, 1992
Total phosphorus and chlorophyll decreased significantly after reduction of the external phosphor... more Total phosphorus and chlorophyll decreased significantly after reduction of the external phosphorus loading and the start of flushing Veluwemeer with polder water in 1979. Flushing of Veluwemeer has had a large impact on nutrient dynamics. Especially in the first winter, dilution was the main cause of changes in water quality. On a longer term the increase of the inactivation of phosphorus in sediments is important. Oscillatoria agardhii has been brought to the margins of its habitat. Three successive cold winters were an additional causal factor in the disappearance of Oscillatoria agardhii and the dominance of diatoms and green algae from 1985 onwards. Due to higher detritus and inorganic suspended matter concentrations transparency increased less than expected. Since 1985 chlorophyll only contributes for a small percentage to the transparency. In the present situation further improvement of the water quality of Veluwemeer is questionable, as the phosphorus concentration in the lake and the polder water is almost the same. Therefore it is recommanded to shift flushing operations, at least in the winter period, from Veluwemeer towards Wolderwijd.