Abstract
Cyanobacteria blooms in lakes and reservoirs currently threaten water security and affect the ecosystem services provided by these freshwater ecosystems, such as drinking water and recreational use. Climate change is expected to further exacerbate the situation in the future because of higher temperatures, extended droughts and nutrient enrichment, due to urbanisation and intensified agriculture. Nutrients are considered critical for the deterioration of water quality in lakes and reservoirs and responsible for the widespread increase in cyanobacterial blooms. We model the response of cyanobacteria abundance to variations in lake Total Phosphorus (TP) and Total Nitrogen (TN) concentrations, using a data set from 822 Northern European lakes. We divide lakes in ten groups based on their physico-chemical characteristics, following a modified lake typology defined for the Water Framework Directive (WFD). This classification is used in a Bayesian hierarchical linear model which employs a probabilistic approach, transforming uncertainty into probability thresholds. The hierarchical model is used to calculate probabilities of cyanobacterial concentrations exceeding risk levels for human health associated with the use of lakes for recreational activities, as defined by the World Health Organization (WHO). Different TN and TP concentration combinations result in variable probabilities to exceed pre-set thresholds. Our objective is to support lake managers in estimating acceptable nutrient concentrations and allow them to identify actions that would achieve compliance of cyanobacterial abundance risk levels with a given confidence level.
Highlights
Freshwater is inextricably linked to human well-being and socio-economic development, while this dependence is a key condition for the sustainable management of freshwater resources
No clear pattern can be detected between the relationship of Cyanobacteria Biomass (CBB) and nutrients, even though higher mean Total Nitrogen (TN) and Total Phosphorus (TP) values result in higher CBB values for the most part
Enabling lake managers to define combinations of TP and TN concentrations that will result in exceedance risk levels for pre-defined thresholds appropriate for each ecosystem can lead to optimal monitoring schemes and can minimize uncertainty associated with each lake ecosystem
Summary
Freshwater is inextricably linked to human well-being and socio-economic development, while this dependence is a key condition for the sustainable management of freshwater resources. Water quality generally suffers from continuous degradation in many regions, and as a result, freshwater ecosystems often become inhospitable habitats for living organisms (UNEP, 2016). This trend is expected to worsen in the near future and generations are likely to face significant adverse impacts on water quan-. Since 2000, the European Water Framework Directive (WFD) has transformed water management in Europe, by bringing aquatic ecology to the forefront of decisions (Hering et al, 2010). The only common biological indicator of lake quality assessment and management was Chlorophyl-a (Chl-a), but following the implementation of the WFD, cyanobacteria abundance has become an additional indicator required for assessment of ecological status for European lakes (Birk et al, 2012)
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