Decision support tool

Control measures

in catchment management

Especially in the catchment, very efficient and sustainable measures can be implemented to control cyanotoxin risks. As the high nutrient loading of water bodies is the primary cause of cyanobacterial proliferation and thus potential cyanotoxin build-up, measures in the catchment should primarily aim to reduce the nutrient input into the water body. The premise for the selection of appropriate measures is an estimate of nutrient load from the catchment from different sources (Background information: catchment and water body).

Examples of possible measures in the catchment and their operational monitoring can be found here for

Water management

Examples of measures Examples of (operational) monitoring
Land use plans to minimize nutrient loading via erosion, seepage and tributaries, e.g. by requiring forest cover for designated areas and/or buffer strips with shrub vegetation along shorelines. Review of the plans by the competent authority and periodic site inspections to monitor their implementation: do forest lands and buffer strips still exist? Are they intact and managed in a way to prevent erosion?
Water management plans that optimise the balance between stakeholder interests and water-body protection, ensuring sufficiently high minimal flows to avoid conditions conducive for cyanobacterial growth (exchange of water body volume once in 30 days giving a sufficiently high inflow). Review of the plans by the competent authority and periodic inspection of discharge data to monitor if the targets are met.
Drinking-water protection zones in vulnerable catchment areas with restrictions of uses. Site inspection and inspection to monitor compliance.
Permits for eutrophication-related activities (esp. in agriculture) including management plans (e.g. maximum density of livestock for pasture, fertilisation plans for fields, wastewater treatment for large stables, etc.). Review of the plans by the competent authority and periodic (site) inspection to monitor compliance (e.g. by controlling the farm records about use of fertilizers).
Discharge permits for waste water from wastewater treatment plants, industry and factories with definition of maximum nutrient concentrations. Review of the plans by the competent authority and periodic (site) inspection of plants and facilities.

Diffuse sources

Examples of measures Examples of (operational) monitoring
Restrictions on agricultural activity in vulnerable catchments, e.g. fertiliser and manure application, livestock density. Periodische Ortsbegehung/Periodic (site) inspection to monitor compliance by visual inspection and by controlling farm records about use of fertilizers and manure (amount and time) and livestock density, sampling and analysis of nutrient residues in the soil.
Gentle soil tillage methods to minimise erosion. Periodic inspection of cultivated areas before and after tillage.
Winter crop cover to reduce erosion. Periodic inspection of the areas in winter.
Pasture fences around reservoirs and vulnerable tributary areas to keep out farm animals (to reduce erosion and nutrient input due to faeces). Periodic (site) inspection to control the integrity of fences.

Point sources

Examples of measures Examples of (operational) monitoring
Discharge permits for waste water from wastewater treatment plants, industry and factories with definition of maximum permitted nutrient concentrations. Review of plans by the competent authority and periodic (site) inspections of the plants for controlling nutrient reduction.
Design of wastewater treatment plants to meet loading targets for phosphorus (and nitrogen). Review of plans to ensure necessary capacity to accommodate nutrient loads for the respective water body; periodic inspection of the plants and maintenance plans.
Design of surface runoff collection or auxiliary (debris) dams prior to reservoirs to avoid pulse nutrient loading during precipitation events. Review of plans to ensure the necessary capacity to meet nutrient loads for the respective water body; periodic inspection of the buildings and maintenance plans.
Design and construction of sewers for wastewater and surface water to minimise overflow into reservoir tributaries. Review of plans to ensure the necessary capacity to meet nutrient loads for the respective water body; periodic inspection of the buildings and maintenance plans.
Operation of nutrient elimination in wastewater treatment plants to meet targets for effluent concentrations. Unannounced inspection including sampling of discharges and analyses of nutrients in waste water.

This is not a comprehensive catalogue of strategies; instead, they are examples of possible options and should trigger the selection and development of your own measures: you and your team should decide whether these (or other) measures and operational monitoring are suitable for your system. For the “catchment” issue, the necessary specific knowledge is probably the modeling of nutrient loads (limnology, hydrology).

Catchment management usually involves a number of different stakeholders. Success in implementation therefore is more likely if they collaborate in developing and defining the control measures to be implemented in the given system.