Seasonal patterns in nutrient bioavailability in boreal headwater streams

Changes in nutrient bioavailability due to increased loading of dissolved organic matter (DOM) may impact boreal freshwaters. Yet, the relative carbon (C), nitrogen (N), and phosphorus (P) associated with terrestrial DOM remains poorly understood. We applied short-term bioassays natural bacterial inocula determine seasonal variation bioavailable pools from four headwater streams northern Sweden. Experiments were designed exhaust nutrients by inducing limiting conditions when all required resources except for targeted (C, N, or P) are provided excess. hypothesized that supply different would reflect variations demand, hydrology, temperature. The delivery DOM-associated were, on average, 2%, 11%, 38% total C, P, respectively, emphasizing relatively low C these DOM-rich waters. Bioavailable N : P ratios peaked autumn sites, lower values winter spring. Both terms (% total) absolute concentrations, pattern was characterized systematically high period. Furthermore, links between temperature hydrology varied across time periods, elements. Thus, elevated concentrations suggest potential leaf fall, as well late season storms rewet dry soils, serve considerable sources aquatic ecosystems.