1st Annual Meeting of the Society of Wetland Scientists – Europe

“Integrating our approaches to Wetland Science”

Bangor, Wales, UK.

January 5th- January 7th 2006.

TROPHIC WEBS FROM DISCHARGES: NATURE ENHANCEMENT THROUGH THE WATERHARMONICA CONCEPT

Lluís Sala¹, Theo Claassen², Ruud Kampf³, Jordi Sala⁴, Dani Boix⁴, Harm van der Geest⁵

3 Vrije Universiteit Amsterdam and Waterboard Hollands Noorderkwartier, The Netherlands

Wastewater treatment has improved surface water quality enormously during the last decades reducing the impact of discharges on the different water bodies. But the impact of the treated wastewater on the aquatic ecosystems is still noticeable, especially in places where dilution flows are low, such as in Mediterranean streams but also in small streams and canals in northern Europe.

In order to overcome this problem and to help comply with the European Water Framework Directive (EWFD), the Waterharmonica (www.waterharmonica.nl) concept has been developed in Netherlands and it is currently expanding throughout practitioners from all over Europe. This concept consists on reducing the discharges into water bodies by turning the pollutants into resources and using them to create biomass. The original idea came after the observation that the use of constructed wetlands for effluent polishing produced trophic webs similar to those in natural wetlands, something that gave an additional value to these constructed wetlands themselves and also to the natural habitats of the surroundings, including the discharge point.

The Waterharmonica concept is a very useful instrument to close the gap between tap and source, enabling water reuse programmes in a more natural framework and enhancing levels of biodiversity with re-naturalizing what once were effluents. It has also proved very useful in bringing people from different disciplines (engineering, ecology) together, and to understand each others’ goals and needs for better overall solutions.

A new use of the Waterharmonica concept has recently come from experiences in Costa Brava, Spain, where water reuse and nutrient recycling have protected local water sources and helped restore macroinvertebrate abundance in coastal temporary streams. Some full-scale experiences and some possibilities for future research, such as removal or pathogenic microorganisms and micropollutants, or assessment of their ecological quality will be described.

1. Vrije Universiteit Amsterdam and Waterboard Hollands Noorderkwartier, The Netherlands

A massive growth of Daphnia (mainly Daphnia magna, Strauss) has been observed to occur in the 4.400 m³ pond of the Everstekoog constructed wetland (Island of Texel, The Netherlands) that receives high quality effluent from a very low loaded activated sludge plant. This phenomena has been studied extensively on laboratory, mesocosms and semi-technical scale since 1998, leading to the development of the “Grickleback process”. The experiments showed that Daphnia in ponds are very effective in diminishing the number of coliform bacteria within a hydraulic retention time of as low as 4 days, but only in a plug flow regime of ponds in series. Sludge particles appear to be the main food source for Daphnia in the first ponds. Contrary to the expectations the ponds stay clear with low algae numbers, because of the indistinctive feeding behaviour of the Daphnia.

A newly developed digital Daphnia counting method provides not only quick and cheap counts but also produces data on their size distribution within the population, giving a good insight of the population dynamics. Especially when following daphnid populations over time this gives much more insight in the dynamics than abundance only. Even in winter time, with temperatures well under 10 °C, neonates were born throughout most of the winter 2004/2005.

Filtration by Daphnia could be a good alternative for technical filtration processes, like sand filtration or membrane filtration. In 2005, research on processes to fulfil the new foreseen standards of the European Water Frame Work Directive has started on the Horstermeer WWTP, near Amsterdam. This research is aimed at demonstrating whether natural processes like Daphnia ponds and constructed wetland systems can convert treated effluent in to a “usable surface water” such as more complex, technical processes do. Plans for 2006 include monitoring/research programmes for the ecological treatment in the first “Grickleback” constructed wetland system in Grou (Wetterskip Fryslân) and the development of an ecological filter to convert effluent of the upgraded Ootmarsum WWTP, of the waterboard Regge en Dinkel (both Interreg Urban Water Cycle projects). Above this preparations are being made for the use of ponds on the Empuriabrava WWTP of the Consorci de la Costa Brava in Spain be used for comparable experiments in 2006.