Institute for Hydrobiology, Dresden University of Technology, 01062 Dresden, Germany.
Water Res. 2011 Oct 15;45(16):4973-82. doi: 10.1016/j.watres.2011.06.043. Epub 2011 Jul 13.
In many lakes and reservoirs, problems caused by off-flavours are known to be particularly associated with the occurrence of planktonic and benthic cyanobacteria. Frequently observed objectionable taste and odorous products of cyanobacteria are geosmin and 2-methylisoborneol. Investigations focused on the littoral zone of Wahnbach Reservoir (Germany) revealed that benthic cyanobacteria were present in this oligotrophic drinking water reservoir. Benthic cyanobacteria were found in the depth horizon between 1.75 m and 11 m, particularly on south-exposed slopes. This spatial distribution indicates a possible key role of the underwater light climate. Moreover, cell-bound and dissolved geosmin were detected in corresponding littoral samples. Both fractions were subjected to spatial and primarily temporal variations with maximum concentrations at the end of summer. However, a substantial lowering of the water level caused a diminution of cyanobacterial growth. Due to the drawdown of the water level concentrations of cell-bound geosmin and pigments (as a proxy of cyanobacterial biomass) were remarkably reduced, and dissolved geosmin was never detected during this phase. Except for the influence of water level fluctuation no other abiotic variables had a significant influence on pigment and geosmin concentrations. From geosmin concentrations detected in the littoral zone, the probability of serious episodes of odour events in the raw water of the Wahnbach Reservoir was estimated. Hence, the probability that the raw water was affected by geosmin was minor, which was supported by routine flavour profiles. Nevertheless, the study shows that odorous episodes caused by benthic cyanobacteria are likely to develop even in an oligotrophic lake or reservoir when these cyanobacteria, and consequently odorous production, proliferate. In principle, such a proliferation cannot be excluded as nutrients are available from the sediment pore water, and underwater light at the sediment surface in the sub-littoral is sufficiently high due to very low phytoplankton-induced turbidity under oligotrophic conditions. Thus, management-induced fluctuations of the water level seem to be the main control variable to generate light conditions at the sediment surface fluctuating in a given depth horizon faster than cyanobacteria can develop there.
在许多湖泊和水库中，已知异味问题特别与浮游和底栖蓝藻的发生有关。经常观察到蓝藻产生的令人不快的味道和气味产物是土臭素和 2-甲基异莰醇。对 Wahnbach 水库（德国）滨水区的研究表明，底栖蓝藻存在于这个贫营养饮用水水库中。底栖蓝藻存在于 1.75 米至 11 米的水深层，特别是在朝南的斜坡上。这种空间分布表明水下光照条件可能起着关键作用。此外，在相应的滨岸样本中检测到细胞结合的土臭素和溶解土臭素。这两个部分都受到空间和主要时间变化的影响，最大浓度出现在夏末。然而，由于水位下降，蓝藻的生长减少了。由于水位下降，细胞结合的土臭素和色素（作为蓝藻生物量的替代品）的浓度显著降低，并且在此阶段从未检测到溶解土臭素。除了水位波动的影响外，没有其他非生物变量对色素和土臭素浓度有显著影响。根据在滨水区检测到的土臭素浓度，估计 Wahnbach 水库原水中发生严重异味事件的可能性。因此，原水受到土臭素影响的可能性较小，这也得到了常规风味分析的支持。然而，该研究表明，即使在贫营养的湖泊或水库中，当这些蓝藻（以及随之而来的臭味产生）增殖时，底栖蓝藻引起的异味事件也很可能发生。原则上，由于贫营养条件下浮游植物引起的浊度非常低，因此，从沉积物孔隙水中可以获得营养物质，并且在亚滨水区的沉积物表面的水下光足够高，因此不能排除这种增殖。因此，管理引起的水位波动似乎是主要的控制变量，可以使沉积物表面的光照条件在给定的水深层中更快地波动，而蓝藻无法在那里生长。
