Natural attenuation of nutrients in a mediterranean drainage canal†‡ Fotini E. Stamati, * Nikolaos Chalkias, Daniel Moraetis and Nikolaos P. Nikolaidis Received 1st July 2009, Accepted 7th August 2009 First published as an Advance Article on the web 9th December 2009 DOI: 10.1039/b913083g This research is aimed at elucidating the removal mechanisms of nutrients due to natural attenuation in drainage canals in Evrotas River delta in Greece. We investigated nutrients fluxes in groundwater, sediments, and reeds (Phragmites Australis and Arundo Donax) of the drainage canal. Groundwater fluxes indicated that the rate of mineralization was 37.6 mg N/m 2 day. The accumulation of toxic ammonia was prevented through the nitrification process (26.6 mg N m 2 day 1 ). The decrease of NO 3 –N flux in groundwater in the riparian zone was calculated to be 56.1 mg N m 2 day 1 (20.48 g N m 2 year 1 ). Phosphate was adsorbed to sediments and its load to the drainage canal was minimized. Harvesting of above ground reed biomass in mid June, when maximum standing stock of nutrients was attained for both plants, would remove 2.73 g P m 2 and 11.2 g N m 2 . All the phosphorous (1.39 g P/m 2 year 1 ) and 76.5% of the nitrate nitrogen (14.64 g N m 2 year 1 ) entering the drainage canal was taken up by plants. Drainage canal management is suggested as an efficient low cost–high gain agri- environmental measure, which is easy to be adapted by farmers, to reduce diffuse nutrient pollution. 1. Introduction Nitrogen (N) and Phosphorous (P) inputs are essential for increasing agricultural production and maintaining the economic viability of farming systems worldwide. Increases in worldwide use of N fertilizers combined with average N use efficiencies of 50% have contributed to the eutrophication of surface and coastal waters. Fertilized farmland is frequently the main non- point source of nitrogen and phosphorous excess input to surface and groundwater ecosystems. 6 A number of approaches have been identified to reduce nutrient (especially nitrate) losses to surface waters including controlled drainage, diverting or directing drainage discharge through natural or constructed wetlands, bioreactors (zones that surround or border the drain pipes) and in-stream denitrification. 21,32,4,7,8,25,14 Agricultural drainage canals have been used in poorly drained agricultural landscapes for the regulation of water retention to allow crop production and to mitigate pollution (nutrients, pesticides and herbicides) as well as for erosion prevention. Drainage canals provide habitat for both aquatic and terrestrial biota and operate as a nutrient pool due to the decomposition of organic matter (lacking otherwise in dry and intensively managed agricultural areas). Drainage canals, usually situated in river deltas, are areas of accumulation for organic debris (sediment deposition) and growth of macrophytes, such as Phragmites australis (common reeds) and Arundo donax (giant reeds). Such areas have suitable anaerobic conditions and electron donors for denitrification. 15 In addition, plants (like reeds) can also promote phosphorous adsorption onto the sand and prevent ammonia accumulation by the release of oxygen from their roots. The removal of N in riparian wetlands, zones, strips and drainage canals is mainly attributed to denitrification. Therefore, drainage canals are likely to act both as narrow buffers in filtering runoff waters and as phosphorous pools during the dormant stage. Although ditch performance has been shown to be highly variable, 19 no holistic studies are available on the functioning of small field drains, with or without permanent water. 14 Plant N and P uptake is often considered less important compared to mitigation of nutrients in riparian buffers due to denitrification and phosphate adsorption in sediments. Most of the nutrients taken up by vegetation are released back into the water once the vegetation Department of Environmental Engineering, Technical University of Crete (TUC), University Campus, 73100 Chania, Crete, Greece. E-mail: fotini.stamati@enveng.tuc.gr; nikos_env@yahoo.com; moraetis@mred. tuc.gr; nikolaos.nikolaidis@enveng.tuc.gr; Fax: +30 28210 37847; Tel: +30 28210 37831 † Part of a themed issue dealing with water and water related issues. ‡ Electronic supplementary information (ESI) available: Fig. S1–S5 and Tables S1–S6. See DOI: 10.1039/b913083g Environmental impact In this work, the efficiency of natural attenuation of nutrients (i.e. denitrification and adsorption of phosphates) and phytor- emediation (P.australis and A.donax nutrient uptake and harvesting the above-ground biomass) was assessed in a Mediterranean drainage canal. Drainage canal management was suggested as an efficient low cost–high gain agri-environmental measure, which can be easily adapted by farmers, to reduce diffuse nutrient pollution. This work aimed at improving our understanding of the biogeochemical cycles of nutrients in the drainage canal ecosystem and supporting the design and implementation of watershed water quality protection technologies, based on natural attenuation mechanisms. 164 | J. Environ. Monit., 2010, 12, 164–171 This journal is ª The Royal Society of Chemistry 2010 PAPER www.rsc.org/jem | Journal of Environmental Monitoring