CoFish: co-designing citizen science between fishers and scientists to monitor the phosphorus distribution across two lake Geneva basins.

backgroundEutrophication, followed by re-oligotrophication during lake restoration, in many perialpine lakes has caused changes to the biodiversity and functioning of freshwater ecosystems. In Lake Geneva, total phosphorus (TP) concentration has reduced since the 1970-80s and the yearly average is now close to the upper value of the target range of 10-15 µg/L. For over 60 years the lake has been monitored at SHL2, the central, deepest point in the Eastern basin, complemented by data from GE3 in the Western basin. Selection of these reference points was based on a lake-wide TP analysis in the 1950s. Lake Geneva is a popular fishing destination for anglers and over 100 commercial fishers, who have expressed concerns that further TP reductions could damage the sustainability of their livelihoods. They have called for a re-evaluation of the historical sampling points to determine whether SHL2 and GE3 can still be considered representative for lake nutrient concentrations.

resultsWe present the scientific and societal impacts of CoFish, a co-designed research project between scientists and fishers of Lake Geneva. To reassess the spatial variability of TP, we collected integrated water samples across the lake, using stoppered hosepipes as a collection instrument. In this article, we present four key messages: i) there was spatial variation in phosphorus levels, and in most cases the two long-term monitoring stations fall within an acceptable range of variability; ii) the concentrations of phosphorus are generally low, at levels that could impact plankton development; iii) citizen science complemented long-term monitoring for a more spatially extensive dataset; iv) the co-design process resulted in community empowerment and a willingness to further collaborate.

conclusionsThe management implications of this work are that using a single reference sampling point to represent the lake basin is practical but not straightforward. In the discussion we advocate for a re-evaluation of the TP targets, given radical changes in the lake's physical structure and food web. We further highlight the important role of engaging fishers in citizen science, which in CoFish resulted in bridging existing gaps between lake management, science and fisheries, providing a broader basis for lake conservation.