Lay summary
The natural cycles of nitrogen and phosphorus have been severely disturbed in many rivers and lakes worldwide. Pressure on these aquatic systems will increase in the coming decades due to growing urbanization. In Africa, Asia and South America there is a lack of baseline data in order to analyze how aquatic systems respond to changing conditions. The goal of this proposal is to assemble an integrated system of field instruments for the analysis of nutrients (nitrate, ammonium, and phosphate), chlorophyll, and other key parameters in-situ, at high-frequency, and with low detection limits. In conventional field campaigns samples for nutrient analysis have to be transported to a laboratory for individual analysis. At the core of the new analytical instrument is an automated chemical analysis module capable of generating nutrient concentration data at the point of measurement with a frequency of up to one sample per second. The instrument will have profiling capabilities with a depth range up to 200 meters. The nutrient module will work together with a conductivity-temperature-depth (CTD) profiler with additional sensors. The instrument will have high-resolution sampling capabilities for individual analysis of trace components, microorganisms and for isotopic analysis. The equipment will be tested and optimized in Switzerland for profiling studies in lakes and reservoirs. For the analysis of biogeochemical nutrient fluxes in river systems the module will be used together with an acoustic doppler current profiler (ADCP) which provides runoff data. In this configuration a large-scale field campaign is planned for the Zambezi River in the framework of an interdisciplinary project on integrated water resource management.