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  • 1
    Electronic Resource
    Electronic Resource
    Stochastic modelling of nutrient loading and lake ecosystem response in relation to submerged macrophytes and benthivorous fish (2003)
    Oxford, UK : Blackwell Science Ltd
    Freshwater biology 48 (2003), S. 0 
    Details
    ISSN: 1365-2427
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: SUMMARY 1. The strong stabilising effect of increased submerged macrophytes (charophytes) and benthivorous fish reduction on the clear water state was shown for shallow Lake Veluwe and Lake Wolderwijd.2. The first two links in the chain of relationships from external phosphorus (P) loading to in-lake total-P concentrations to chlorophyll a concentrations to water transparency, showed a significant correlation with the areal fraction of coverage with charophytes. Higher coverages lead to (i) lower ratios of the in-lake total-P concentration compared with the volume weighted average concentration in the inlet water, indicating a higher retention of P in the presence of charophytes (ii) lower chlorophyll a to total-P ratios, indicating a positive effect of charophytes on top-down control of algae, and (iii) higher water transparency because of lower algal turbidity. Transparency further improved as a result of benthivorous fish reduction and a significant positive correlation between non-algal turbidity and benthivorous fish biomass.3. A model was developed taking into account the inherent variability in precipitation and uncertainties in the empirical relationships determining phosphorus export from stream catchments and other sources and eutrophication variables in the receiving lakes. The model was used to compute (i) probability distributions for in-lake total-P, chlorophyll a and Secchi Disc transparency in relation to the coverage with charophytes and benthivorous fish biomass, and (ii) exceedence probabilities with respect to critical values for in-lake total-P and water transparency for several management scenarios.4. The effects of an expected rise in external nutrient loading on the in-lake total-P and chlorophyll a concentrations and on water transparency can be compensated for by two proposed control measures: (i) extended treatment at a waste water treatment plant directly discharging into Lake Veluwe, and (ii) diverting the outlet of a stream draining a catchment with high fertilisation. The minimal internal charophyte coverage needed to sufficiently stabilise the clear water state and to meet with the objective of a summer mean water transparency of at least 1 m was estimated at well over 30% of the lake area, while the benthivorous fish stock should be maintained at the present level of c. 20 kg ha−1.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-2427.2003.01029.x
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  • 2
    Electronic Resource
    Electronic Resource
    Relationships between eutrophication variables: from nutrient loading to transparency (1999)
    Springer
    Hydrobiologia 408-409 (1999), S. 375-387 
    Details
    ISSN: 1573-5117
    Keywords: eutrophication ; multi-lake studies ; phosphorus ; nitrogen ; chlorophyll-a ; transparency ; zooplankton ; macrophytes
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Monitoring data obtained from 231 freshwater lakes and ponds in the Netherlands, covering the period 1980–1996, were used to analyse the relationships between (a) transparency and chlorophyll-a, and the effect of system characteristics on this relationship, (b) chlorophyll-aand nutrient concentrations, and the effect of biological variables and (c) nutrient concentrations and nutrient loading. (a) Chlorophyll-aimposes a maximum on water transparency, but deviations from this maximum can be large. Reducing chlorophyll-a, therefore, does not guarantee a sufficient improvement of transparency. Soil type and the average depth of a lake were shown to influence the relationship between chlorophyll-aand transparency. (b) The maximum ratios of both chlorophyll-a: total-P and chlorophyll-a: total-N were higher in systems dominated by filamentous cyanobacteria than in systems dominated by other algae, indicating the efficiency of the former group with respect to nutrients. In systems with an areal coverage with submersed macrophytes above 5%, concentrations of chlorophyll-aand nutrients were lower than in systems with lower coverages. The ratios between chlorophyll-aand nutrients were lower at coverages larger than 10%. This indicates both bottom-up and top-down control of algae by macrophytes. Grazing pressure by zooplankton was also found to lower the chlorophyll-a: nutrient ratios. (c) System specific linear relationships were found between the average concentrations of total-P and total-N in the incoming water and the summer mean concentration in the lake. This allows the assessment of admissible loads for individual lakes, with narrower confidence limits compared to traditional relationships based on combined data from many lakes. From the analysis, it is concluded that the chain of relationships from nutrient loading to transparency is complex, and depends on biological variables as well as system characteristics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1017090931476
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  • 3
    Electronic Resource
    Electronic Resource
    Multi-lake studies in The Netherlands: trends in eutrophication (1999)
    Springer
    Hydrobiologia 408-409 (1999), S. 359-365 
    Details
    ISSN: 1573-5117
    Keywords: eutrophication ; trends ; lakes ; phosphorus ; nitrogen ; chlorophyll-a ; transparency
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The relation between (inter)national programs aiming at nutrient load reduction and changes in eutrophication has been studied for 231 Dutch lakes over the period 1980–1996. Trends in total-phosphorus (P) and total-nitrogen (N) were negative, as determined by analysis of both individual lakes and the complete data set. The relative trends in the nutrient concentrations as well as in the N/P ratio correspond with the significantly reduced P emission and the limited reduction of N emission in The Netherlands since the beginning of the 1980s. Negative trends in chlorophyll-aand positive trends in Secchi-disc transparency may be partly explained by reduced nutrient concentrations. Perspectives for the nearby future are discussed. Lake characteristics had only a minor impact on the trends. The improvement of the water quality was found for all subsets of average depth, surface area, hydraulic retention time and soil type. Furthermore, the effect of restoration measures and meteorological conditions on the trends were studied. Biomanipulation resulted in an additional improvement of several water quality variables compared to lakes that were only subject to (inter)national programs on nutrient load reduction. Specific measures resulting in additional P load reduction resulted only in lowered P concentrations. Severe winters resulted in lower chlorophyll-aconcentrations in the following summer and dry conditions in spring were favourable for all eutrophication variables in the following summer.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1017086830568
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    Paper (German National Licenses)
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  • 4
    Electronic Resource
    Electronic Resource
    Kinetics of luxury uptake of phosphate by algae-dominated benthic communities (1994)
    Springer
    Hydrobiologia 275-276 (1994), S. 349-358 
    Details
    ISSN: 1573-5117
    Keywords: benthic algae ; phosphate ; luxury uptake ; eutrophication ; intracellular P
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The uptake of phosphate by benthic communities, dominated by living algae, previously exposed to different levels of external nutrient loading, exhibited first-order kinetics with respect to the intracellular P-deficit. This deficit is the difference between the maximum and the actual intracellular P-concentration. The maximum storage capacity of P per unit of dry weight was positively correlated to the level of external nutrient loading, whereas the phosphate uptake rate constant was negatively correlated. The observed internal P concentrations in the benthic layer of test ditches over a period of two and a half years, indicated a slight decrease towards a minimum value in a ditch with a low external P-input. In a medium loaded ditch the internal P-concentration did not change significantly. In a high loaded ditch increasing internal P-concentrations over time were observed, towards P-saturation of the benthic community.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00026725
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