Nutrient mass balances at watershed scales
Increased reactive N input by human activities and widespread simplification of land use mosaic in watersheds have resulted in the gradual saturation of terrestrial areas N buffering capacity and augmented N loads towards surface and ground waters, with implication in term of eutrophication and toxicity. Rivers are particularly vulnerable because they link terrestrial and coastal ecosystems, aggregating stressors occurring at the landscape scale. Human-driven alterations such as channelization, impoundment, water withdrawals, reduction of riparian vegetation and wetlands have enhanced soil erosion and runoff processes, affected the biogeochemistry of riparian and in-stream zones and reduced the efficiency in N loads mitigation. Open questions about the fate of N surplus in impacted watersheds concern where and for how long does the excess N accumulate, and what processes and transformations does it undergo.
The Po River catchment is the largest hydrographic system in Italy (~71 000 km2, about one quarter of the whole national territory) and a strategic area for the Italian economy (intensive agriculture and farming activities, industry, and human settlement), accounting for about 40% of the country’s Gross Domestic Product. Here, nitrate contamination of surface and groundwater has relevant implications for environmental policies. The debate is focused on identifying the main N sources, with conflicting issues between diffuse (agriculture and livestock) and point ones (wastewater treatment plants).
The Po River catchment is the largest hydrographic system in Italy (~71 000 km2, about one quarter of the whole national territory) and a strategic area for the Italian economy (intensive agriculture and farming activities, industry, and human settlement), accounting for about 40% of the country’s Gross Domestic Product. Here, nitrate contamination of surface and groundwater has relevant implications for environmental policies. The debate is focused on identifying the main N sources, with conflicting issues between diffuse (agriculture and livestock) and point ones (wastewater treatment plants).
Nitrogen sources, sinks, major transformations and relation between land uses and nitrate pollution were assessed at the watershed scale of four tributaries of the Po River (Oglio, Mincio, Po di Volano and Parma). These catchments represent the typical study cases of lowland human exploitation, even if with different livestock pressure, crop production and population densities. N loads exported at river outlet are in the medium-high range measured for European watersheds, but these basins maintain the capacity to metabolize, even if partially, N loads. The development of the secondary drainage network dates back hundreds year ago and this “artificial” system is at present strongly integrated in the watershed dynamics and hosts relevant ecosystem services. Due to its capillary development and high denitrification rates, it has a large potential to remove nitrogen.
References:
Castaldelli G., Soana E., Racchetti E., Pierobon E., Mastrocicco M., Tesini E., Fano A.E., Bartoli M. Nitrogen budget in a lowland coastal area within the Po River Basin (Northern Italy): multiple evidences of equilibrium between sources and internal sinks. Environmental Management (2013) 52:567–580.
Bartoli M., Racchetti E., Delconte C.A., Sacchi E., Soana E., Laini A., Longhi D., Viaroli P. 2012. Nitrogen balance and fate in a heavily impacted watershed (Oglio River, Northern Italy): in quest of the missing sources and sinks. Biogeosciences 9, 361–373.
Soana E., Racchetti E., Laini A., Bartoli M., Viaroli P. 2011. Soil budget, net export and potential sinks of nitrogen in the lower Oglio River watershed (northern Italy). CLEAN – Soil, Air, Water 39, 956–965.
Soana E., Racchetti E., Pinardi M., Bartoli M., Viaroli P. 2010. Nitrogen mass balances and aquatic denitrification relevance: a watershed scale study for lower Oglio and Mincio Rivers. EURAC-Book 57, 103–112, Proceedings of the XIX SItE (Italian Society of Ecology) Congress (in Italian).
Soana E., Racchetti E., Romani F., Longhi D., Gardi C., Bartoli M. 2010. Nitrogen loading and associated environmental risk in the lower Oglio River basin (Northern Italy). Biologia Ambientale 24, 87–96, Proceedings of the XVIII SItE (Italian Society of Ecology) Congress (in Italian).
Castaldelli G., Soana E., Racchetti E., Pierobon E., Mastrocicco M., Tesini E., Fano A.E., Bartoli M. Nitrogen budget in a lowland coastal area within the Po River Basin (Northern Italy): multiple evidences of equilibrium between sources and internal sinks. Environmental Management (2013) 52:567–580.
Bartoli M., Racchetti E., Delconte C.A., Sacchi E., Soana E., Laini A., Longhi D., Viaroli P. 2012. Nitrogen balance and fate in a heavily impacted watershed (Oglio River, Northern Italy): in quest of the missing sources and sinks. Biogeosciences 9, 361–373.
Soana E., Racchetti E., Laini A., Bartoli M., Viaroli P. 2011. Soil budget, net export and potential sinks of nitrogen in the lower Oglio River watershed (northern Italy). CLEAN – Soil, Air, Water 39, 956–965.
Soana E., Racchetti E., Pinardi M., Bartoli M., Viaroli P. 2010. Nitrogen mass balances and aquatic denitrification relevance: a watershed scale study for lower Oglio and Mincio Rivers. EURAC-Book 57, 103–112, Proceedings of the XIX SItE (Italian Society of Ecology) Congress (in Italian).
Soana E., Racchetti E., Romani F., Longhi D., Gardi C., Bartoli M. 2010. Nitrogen loading and associated environmental risk in the lower Oglio River basin (Northern Italy). Biologia Ambientale 24, 87–96, Proceedings of the XVIII SItE (Italian Society of Ecology) Congress (in Italian).