Control measures

in water-body management

Cyanobacterial proliferation is most effectively controlled by measures in the catchment. Internal control measures such as the management of the water body often have a minor prospect of success, if at the same time the nutrient load from the catchment area is not sufficiently reduced to values that make cyanobacterial bloom development unlikely. However, in-water body measures may be useful to enhance water body reactions to reduced nutrient loads, or in cases where the nutrient concentration remains just too high.

Also, in some situation, external loads cannot be sufficiently reduced to control cyanobacteria. While biological measures such as manipulating fish stocks [1] and the planting of reed-belts [2] have not proven effective in such settings, controlling physical factors such as light penetration by vertical mixing (to improve conditions for the growth of other phytoplankton that outcompete cyanobacteria) has worked because these act independently of nutrient availability.

A prerequisite for the choice of appropriate measures is an estimation of their influence on the nutrient budget and/or food web of the water body. The control of cyanobacteria by internal measures is very difficult and requires expertise in limnology and plankton ecology to plan and implement, and also to accompany the initial investigations and subsequent monitoring. Therefore, management measures in a water body are not inexpensive. Even if such expertise is available, uncertainties in the prediction of successful management outcomes can be much higher than with control measures in the catchment area, the water offtake or in water treatment.

Examples of measures in the water body and their operational monitoring can be found here

Examples of measures	Examples of (operational) monitoring
Artificial mixing to suppress buoyancy-regulating cyanobacteria such as Microcystis, Anabaena and Aphanizomenon.	Review plans for this measure esp. with respect to clarifying prospects of success; monitoring if aerators are in operation as planned, e.g. by visual inspection, records of pump operation, depth profiles of continuously or periodically (e.g. weekly) measured water temperature.
Measures to control internal loading with phosphorus stored in the sediments (if this is the major P-source), e.g. by sediment capping or sediment oxidation.	Review plans for this measure esp. with respect to prospects of success, feasibility and necessity (with sufficient reduction of the P-load and water exchange rate also P from the sediment will be removed, though this may require several years).
Manipulation of the food web (i.e. biomanipulation, [1]) by adding or removing fish, especially predators. Attention: Prospects of success rather low in water bodies with total phosphorus (TP) > 50- 100 µg/L.	Review plans for this measure esp. with respect to clarifying prospects of success; regular determination of fish population sizes.
Planting and maintenance of aquatic macrophytes and reed belts [2]. Attention: Prospects of success rather low in water bodies with low share of shallow shorelines and TP > 50- 100 µg/L.	Review plans for this measure esp. with respect to clarifying prospects of success; regular mapping of reed growth.

The management of a water-body leading to a change in biomass and productivity usually affects a number of different stakeholders, e.g. angling and water sports. Success in implementation is therefore more likely if the different stakeholders collaborate in defining, developing and implementing the control measures in the given system.

[1]

Food chain manipulation by adding or removing fish, especially predators of phytoplankton-grazers,

[2]

Planting reeds and other macrophytes has often proven unsuccessful, with rapid die-off, in very eutrophic water-bodies,