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The transport and cycling of nutrients through the various pools in water, soil and sediment is controlling the long term and short term productivity of water bodies. An understanding of the size of these pools and the fluxes between them is essential for the assessment of the usefulness of management measures resulting in reduced external input and the anticipated resilience of the system towards changes in trophic character. Large pools, such as phosphorus in surficial sediments and nitrate in groundwater have a potential for prolonged stimulation of productivity. Diffuse sources, fluxes towards sinks, competition between biota and adsorbents for sparse nutrients, feedback mechanisms, non-linearities and shifts among prevailing processes are discussed.

Gross primary production, community respiration and reaeration coefficient were determined during an annual cycle on the Viroin River (South Belgium), based on the daily variations of dissolved oxygen concentration. Reaeration coefficient remains remarkably constant (0.26 h−1) during the year in spite of discharge variations. The autotrophic community is dominated by ‘Ranunculus fluitans’. Primary production parallels the variations of total solar radiations. It ranges from 0 in winter to 8 g O2 m−2 d−1 in summer. In spring and summer, respiration variations parallel those of primary production (average value: 10 g O2 m−2 d−1); in the dry autumn, decomposition of dying macrophytes considerably enhances the community respiration (15 g O2 m−2 d−1). A P/R diagram is used to characterize the trophic state of the Viroin., info:eu-repo/semantics/published