The Hydrological Base Network at SMHI

Stream water is assessed in two programs in which SMHI conducts most river discharge observations. It has 155 discharge stations in northern Sweden that belong to the Base Hydrological Network (Fig. 5, Table 6, #3.1). SMHI reports daily discharges in 46 rivers north of 60°N to BALTEX (Table 6, #3.2). The size distribution of the catchments is characterized as minimum 30 km2, median 6 400 km2 and maximum 33 930 km2, and the relative area of lakes as minimum 3%, median 6.4%, and maximum 21%. SLU is in charge of the water quality and SFB of the test fishing program. In the River Mouth Survey the goal is to estimate the element discharge from Sweden to the sea. Monthly sampling is conducted in 23 rivers and the samples are analyzed for pH, conductivity, NH4, NO2, NO2+NO3, Kjeldahl-N, Tot-N, Tot-P, PO4, TOC, Si, absorbance (on filtered and nonfiltered samples), KMnO4, Fe, Mn, alkalinity, Ca, Mg, Na, K, SO4, Cl, F, Cu, Zn, Cd, Pb, Cr, Ni, Co, Ni, V, As, Al, Hg. The primary goal of the Trend Streams program is to build time series to detect eventual environmental changes. The streams are of quite different sizes, with drainage basins from 1 to 10 000 km2. For water chemistry 37 streams are sampled monthly and the samples analyzed as for the River Mouth Survey. Out of the 37 streams 27 are selected for yearly sampling of bottom fauna and benthic diatoms, and in turn electrical test fishing is performed once per year in 16 of these.