Abstract
In the Netherlands, legacies and diffuse nutrient pollution continue to fuel recurrent cyanobacterial blooms in mostly shallow and relatively small surface waters. A survey in peer-reviewed literature and Dutch grey-literature was performed to gain insight into the physical-, chemical- and biological in-lake interventions used to bring these waters towards their desired state. A critical overview is presented on efficacy of different measures to counteract cyanobacterial blooms directly via targeting the cyanobacteria or indirectly via reduction of nutrient availability. Many actions have no or limited effects on minimising cyanobacterial blooms (air-bubble- or oil screens, surface mixers, low-energy ultrasound, effective micro-organisms, fish introduction), while others are more effective, but may vary in longevity and costs (dams, excavation or dredging, hydrogen peroxide, phosphorus inactivation agents), meet legislation restrictions (copper-based algaecides, herbicides, dreissenids), or are not currently implemented (hypolimnetic withdrawal). The selection of promising interventions requires a proper diagnosis of each problem lake, based on water- and nutrient fluxes, the biology of the lake (plants, fish), the function of the lake and the characteristics of the method, such as efficacy, costs, safety and ease of implementation. In the Netherlands, ongoing diffuse loads and legacies necessitate repetitive in-lake interventions.
Highlights
Intensity, and duration of cyanobacterial blooms comes with nuisance, such as consequences for human- and environmental health effects; nasty odours, high water turbidity, fish kills, food web alterations and impairment of important ecosystem services, such as drinking water preparation, irrigation, recreation, aquaculture and fisheries (e.g. Pearl & Paul, 2012)
It has already been known for decades that over-fertilisation of surface water can lead to impaired water quality and cyanobacterial blooms (Edmondson et al, 1956; Parma, 1980), eutrophication is still the most important water quality issue worldwide (Smith & Schindler, 2009; Downing, 2014)
In 2016, the load of nutrients that leached from soil to surface waters was 44.6 million kg N (58% of total load) and 3.95 million kg P (62% of total load) (CBS, 2018)
Summary
Nutrient losses from inadequate wastewater treatment, soil erosion and intensified agricultural activities lead to ongoing eutrophication of inland waters with forecasted climate change to further exacerbate this over-fertilisation and its symptoms (Forsberg, 1998; Cordell et al, 2009; Jeppesen et al, 2009; Moss et al, 2011; Sinha et al, 2017; Beaulieu et al, 2019). Cyanobacterial blooms, as a key symptom of eutrophication in lakes, ponds and reservoirs (Smith et al, 1999), show a worldwide proliferation (Paerl & Huisman, 2008; O’Neil et al, 2012; Paerl & Paul, 2012; Huisman et al, 2018) Such increased incidence, intensity, and duration of cyanobacterial blooms comes with nuisance, such as consequences for human- and environmental health effects; nasty odours, high water turbidity, fish kills, food web alterations and impairment of important ecosystem services, such as drinking water preparation, irrigation, recreation, aquaculture and fisheries (e.g. Pearl & Paul, 2012). In 2016, the load of nutrients that leached from soil to surface waters was 44.6 million kg N (58% of total load) and 3.95 million kg P (62% of total load) (CBS, 2018) Such high diffuse sources imply that in the Netherlands, within-system interventions are inevitable to reach a water quality that meets societal demands for recreation or as set by legislation (e.g. WFD). Scientific testing of some end-of-pipe solutions revealed that they are not as effective as claimed (Lurling et al, 2016a), and an overview over several interventions
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