Water quality of the Durance river at St Chamas - Hydro-electric power plant nutrients and suspended matter annual discharge into the Berre Lagoon

The Berre lagoon is a eutrophic ecosystem that receives freshwater and nutrients from two rivers and from the Durance river via Saint Chamas hydro-electric power plant (SC). Integrating hourly variations, daily sampling enables to calculate a representative annual nutrients flux: SC brings 1085 tons of Total N (93% are equally NO3 and DON) and 30 tons of Total P (80% is particulate P) from October 2008 to November 2009. Then the data set was resampled by randomly extraction of weekly, biweekly and monthly data to calculate annual nutrients flux. The frequency of water quality surveys required to obtain a Total N annual flux with close to 25% precision is one per month. Maximum precision on Total P annual flux ranges between -30% and +60% from a weekly sampling. Global nutrients discharges are lower than those estimated 2 decades ago. In 2006, SC brought 50% and 14% of allochthonous annual discharge of Total N and Total P respectively. Atmospheric and non-point sources and bioavailability of dissolved and particulate organic matter need to be assessed.