BUFFERING CAPACITY AND PHYTOREMEDIATION POTENTIAL OF DRAINAGE CANALS AS A LOW COST AGRI-ENVIRONMENTAL MEASURE

Drainage canals are areas of accumulation of organic debris due to erosion and growth of plants such as Phragmites australis. Denitrification is one of the main biological processes responsible for the buffering capacity against diffuse nitrate pollution due to anaerobic conditions and suitable electron donors. In addition, nitrates and phosphates decrease due to plant uptake. It has been shown in the literature that plants like reeds uptake P throughout the year and then (March – April) release it back in the aquatic environment and their roots. This work aims to estimate the efficiency of drainage canal’s sediments to reduce nitrate pollution from ground water as well as the timing of the cutting of the reeds that will maximize the removal of phosphates by plant uptake but also keep the N/P ratio high enough to avoid toxic algal blooms. The drainage canal is located in Evrotas River Basin, Greece and drains fields of orange groves. To monitor the 3-dimensional variability of hydrology and chemistry of surface and ground water in the drainage canal, eleven multi-level (3, 4 and 5 m) wells were installed. The probes and the drainage canal water were sampled every 2 months (based on the velocity of movement of contaminants) and analyzed for inorganic nitrogen species, phosphates, phenols, dissolved organic carbon (DOC) and nitrogen (DON) and chemical oxygen demand (COD). Plant (reed) samples were collected on a monthly basis to determine the uptake rates by the plants. Laboratory studies on sediment samples from the bottom and the bank of the drainage canal were conducted to study the predominant processes in the N and P cycles