Time series of nitrate, ammonium and phosphorus in low-salinity estuarine waters and streams along the coast of Gipuzkoa (Basque Country, Bay of Biscay).
Description
Data are provided on molar concentration of nitrate, ammonium and total dissolved phosphorus (sum of organic and inorganic forms), together with salinity, for six estuaries in the south-east corner of the Bay of Biscay. These are the mesotidal estuaries of the Deba, Urola, Oria, Urumea, Oiartzun and Bidasoa rivers. In addition, the dataset includes the Endara stream, a tributary of the Bidasoa, and five other small rivers that also flow into the Basque coast: the Mijoa, Narrondo, Igara, Añorga and Molinao streams. The frequency of the nutrient data is approximately eight times per year for most of these systems, although the Oiartzun estuary and some of the streams present a smaller amount of data. The data were gathered from the water quality control network of the Gipuzkoa Provincial Council (GPC), which started in 1986. The GPC network stablished 5−9 sampling stations along the longitudinal axe of the estuaries, from head to mouth, and one station in each of the streams. Samplings took place mostly during the morning and the tidal state was not considered to choose the dates. The water samples were collected just below the surface using a clean bucket and immediately, their salinity was measured by field sensors. In the laboratory, from 2011 on, nitrate was determined by ion chromatography with chemical suppression followed by conductivity detector; ammonium by indophenol blue colorimetry; and phosphorus by inductively coupled plasma mass spectrometry (ICP−MS) after filtration (0.45 µm) and nitric acid acidification. This dataset mainly represents low salinity waters (≤1 PSU) because the analytical methods were not optimised for other matrices and, in the laboratory, the samples whose conductivity was higher than 1500 µS/cm were generally rejected. Therefore, the tidal state and the river runoff at the time of sampling largely influenced which estuarine stations were to be analysed for nutrients. The instrumentation and the detection limits varied little during long time periods (>10 years), both in the field and in the laboratory. We want to thank the staff of the GPC for their assistance with the field work and the Fraisoro Agro‑environmental Laboratory for performing the chemical analyses. The data processing was carried out by AZTI and funded by the GPC and by the Horizon Europe GES4SEAS project (grant agreement no. 101059877; www.ges4seas.eu).