Citizen Science as an Innovative Approach to Analyze Spatial and Temporal Influences on Nitrate Pollution of Water Bodies: Results of a Participatory Research Project in Germany

Anthropogenic influences and the excessive input of reactive nitrogen compounds into the environment have already severely destabilized the natural nitrogen cycle. Especially in northwestern Germany, many water bodies are polluted by nitrate, inducing negative effects on the ecosystem and drinking water as well as possible risks to human health. In cooperation with almost 600 citizens and 200 students, this issue was addressed in a citizen science project carried out by the Universities of Osnabrück and Oldenburg, gathering 8754 nitrate measurements at 545 monitoring sites from September 2019 to March 2021. The data were used to evaluate the potential of citizen science for research on nitrogen pollution of water bodies. In a pre-investigation, we proved that nitrate test strips are suitable as a measurement method for the citizen science approach to provide an overview of nitrate pollution. We then analyzed whether the citizen science approach can be used to establish an area-wide representative measurement network, to what extent the data can be used for spatial and temporal analyses, and whether the data are consistent with the results of other monitoring initiatives. For this purpose, geoprocessing tools, such as spatial joins and heatmaps, were combined with descriptive statistics and nonparametric statistical tests. Although it was not possible to establish a representative monitoring network due to the uneven spatial distribution of monitoring sites, a large part of the intended area was covered by monitoring sites. Thus, the data provide a good overview of the nitrate pollution in the region and shed light on influencing factors. Spatial impacts, such as land cover and use and hydrogeological conditions, as well as seasonal impacts were statistically evidenced with the citizen science data. Furthermore, the consistency of the data with the measurement results of established measurement initiatives confirm the quality of the citizen science dataset. Accordingly, citizen science can be used to investigate spatial and temporal factors influencing nitrogen pollution, and thus contributes to water conservation research as an innovative approach.