Damming leads to depletion of major elements in boreal river water, with potential effects on biological production in coastal marine areas (Humborg et al. 2002, Global Biogeochem. Cycles 16 in press), such as the Baltic Sea. Today, the causal mechanism to this element depeltion is unknown. The present project aims to estimate biological nutrient retention in a dammed river system (Luleälven) and an unregulated system (Torneälven). As to lenthic production, lake Torne träsk offers excellent opportunities to study the pelagic productivity regime of a pristine boreal aquatic system. Our field programme includes measurements of mictic conditions, nutrients (P, N, Si), dissolved and particulate constituents (major and minor elements), stabile isotopes (C, N, Sr, O), primary productivity, zooplankton abundance, and fish.