CNR-IRSA activities related to INHABIT

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Biogeochemical processes

The term “nutrient retention” refers to all the processes by which nutrients are removed from the water column, but also stored and transformed. It is an important functional property of the aquatic  ecosystem able to affect  the biogeochemical cycles of elements. Within the ecosystems rates and reactions of biogeochemical processes vary in space and time to produce both “hot spots” and “hot moments” of elemental cycling.  Biogeochemical hot spots are areas that show disproportionately high reaction rates relative to the surrounding area; hot moments are short periods of time that show disproportionately high reaction rates (McClain, 2003). These function areas occur at different scales, from the microhabitats within a river reach to the hydrographic  network of a river catchment. Examples of these functional units are the microbial communities developing on cobbles and, at basin level, the riparian areas.
Many studies have identified vegetation uptake and microbial denitrification as the primary mechanisms responsible for nitrogen removal in riparian areas. Denitrification is a microbial process involving the stepwise  reduction of nitrate ending with the release of  gaseous nitrogen to  the atmosphere.  Denitrification represents a true systems of nitrogen removal, since nitrogen is lost from ecosystems. The importance of vegetation on denitrification is indirect, in that vegetation supplies energy to bacteria through litter decay and root exudates. Of crucial importance on both processes is the water regime. The interaction of water regime on vegetation is such that the primary productivity of the riparian zone is higher than the neighboring terrestrial system. The water regime affects denitrification  in two ways: i) the flooding of this zone supplies sediments rich of carbon, so when saturated they become an ideal environment for denitrification, ii) the saturation of the soil leads to anaerobic conditions essential for denitrification process if nitrate is available. So, on annual scale the removal efficiency of riparian strips will result from the combination of all the factors indicated (uptake, availability of C, saturation, etc.) and will therefore be restricted spatially  (extension of the vegetation zone), and temporally  (the absence of one of the factors in a particular season). For example, in temperate regions, the uptake by the vegetation will take place in the summer. In the same period, characterized by high temperatures and low rainfall, the denitrification will reach a minimum because the soils are well aerated and dry. During dormancy, when, in many regions of  North Europe the leaching of nitrate is greater, the best conditions for the onset of the process of denitrification occur (ie, waterlogged soil and availability of organic matter and nitrate). Thus, the coupling of these two processes will ensure, on an annual basis, a stable reduction efficiency of the nitrogen load from cultivated fields to aquatic ecosystems.


Publications:

  • BALESTRINI R, ARESE C, DELCONTE C.A, LOTTI A, SALERNO F (2011). Nitrogen removal in subsurface water by narrow buffer strips in the intensive farming landscape of the Po River watershed, Italy. ECOLOGICAL ENGINEERING, vol. 37, p. 148-15.
  • BALESTRINI R, ARESE C, DELCONTE C (2008). Lacustrine wetland in an agricultural catchment: Nitrogen removal and related biogeochemical processes. HYDROLOGY AND EARTH SYSTEM SCIENCES, vol. 12, p. 539-550.
  • BALESTRINI R, ARESE C, DELCONTE C (2006). Nitrogen removal in a freshwater riparian wetland: an example from italian lowland spring. VERHANDLUNGEN - INTERNATIONALE VEREINIGUNG FUR THEORETISCHE UND ANGEWANDTE LIMNOLOGIE, vol. 29/5, p. 2217-2220.
  • BALESTRINI R, ARESE C, DELCONTE C (2004). Funzionalita’ degli ecosistemi acquatici: il ruolo delle fasce riparie nella dinamica dei nutrienti. Quaderno IRSA 121. QUADERNI IRSA DEL CNR, vol. 121, p. 1-140