Surface measurements of nutrients in the East Frisian Wadden Sea from 2019 to 2022

Phytoplankton biomass is increasing in the Wadden Sea since 2005, while nutrients concentrations are declining since 1995. A survey started in 2006 by the Lower Saxony Water Management, Coastal and Nature Protection Agency regularly monitors nutrient levels, including silicates, nitrate, and phosphate, and temperature and salinity in the East Frisian Wadden Sea. A total of 17 stations are sampled from a monthly to weekly frequency. Samples are taken at the surface with a bucket, and kept in 5L canisters with Lugol's iodine solution to be stored in the cold and dark until analysis. The analysis of samples followed the procedures for seawater analysis given by Grasshoff et al. 1983. Dissolved nutrients, such as orthophosphate, nitrate, nitrite and silicate, were measured photometrically. Total nitrogen and phosphorus concentration were estimated by digesting total nutrients using heat and pressure, or in microwave with peroxodisulfate. The pH, salinity, and temperature were measured using a multisensor. The data provides a detailed time series of physical and chemical properties in the East Frisian Wadden Sea surface waters from 2019 to 2022.