**5.3 Stormwater detention ponds (SDP)**

Detention ponds are open water bodies for the retention of stormwater runoff from urban, agricultural and other areas. The stormwater treatment facility must be flexible to manage high flow rates of the runoff followed by dry periods, and high pollutant concentrations in the first flush followed by diluted concentrations in the main flow. Stormwater detention ponds are diverse biological system with a high buffering capacity that enable water detention, minimize the hydraulic peaks and reduce the pollutant input in downstream facilities and/or receiving waters (Hvitved-Jacobsen et al., 1994). Detained and treated water can be used for different purposes or discharged to the environment. Different plant species can appear in detention ponds (usually colonized by natural way): at the shallower marginal areas emergent and in deeper parts floating and submerged species. The treatment processes in wet detention ponds are similar to those occurring in natural smaller lakes and pools: e.g. contaminant accretion in the bottom deposits via sedimentation, adsorption to colloidal and particulate matter, conversions and degradation of biodegradable compounds by microorganisms and uptake of contaminants by plants. Among those, the key mechanism for pollutants removal in detention ponds is sedimentation. Since the main removal mechanism in wet detention ponds is sedimentation, the wet detention ponds generally have high efficiency in particulate matter removal (Terzakis et al., 2008). Organic matter is subdued to microbial and macroinvertebrate decomposition and final transformation to inorganic matter in the sediment, where it is stored. Sediment accretion at the bottom of wet ponds might vary greatly according to inflow and catchment characteristics. Hvitved-Jacobsen et al. (1994) estimated that excavation and removal of the sediments from wet ponds would be needed every 25 years of the operational period.

Ecosystem Technologies and Ecoremediation for Water Protection, Treatment and Reuse 205

is to reduce the wastes' impacts on the environment through a closed hydrological and pollution cycle within a landfill site and the utilisation of leachate as a nutrient source. Leachate recycling belongs to a phytoremediation method where the assimilation of plant nutrients from leachate into biomass and faster waste decomposition by enabling leachate infiltration into the landfill body take place. Discharge of treated leachate to vegetation caps can provide an opportunity for closing the nutrient cycling loop and producing an effluent of a suitable quality. A controlled input of leachate results in a better provision of soil with nutrients and organic substances, improved growth of vegetation and intensified microbiological activity in soil. Today, the phytotechnology employing ligneous plants is used for the treatment of various forms of pollution. With a large water uptake from soil pores, plants take up also water pollutants and create a new capacity for water accumulation in soil. Poplars and willows are capable of taking up diverse pollutants and nutrients (nitrate, ammonium, phosphorus), metals, metalloids and petrochemical compounds (fuels, solvents), pesticides and soluble radionuclides (Zupančič et al., 2005). The methods applied for the treatment of leachate are vegetation barriers, filters, vegetation caps and short rotation coppices (SRC) with fast growing woody species. In addition to landfill sites, the planting of trees is used for the remediation of watercourse banks, abandoned and polluted industrial areas, at the margins of intensive agricultural areas and other polluted areas, as well as for the treatment of wastewater and sludge (Griessler Bulc & Zupančič Justin, 2007).

Natural watercourses have a great ability of water retention, a great diversity of habitats and biodiversity and high self-cleaning capacity. Regulations or canalizations of watercourses were common in the past but in some places sill appearing in the present with the main goal of flood protection and gaining space for agriculture and urbanization. Canalizations of watercourses do decreased flooding in a local scale but downstream floods were even more severe. Canalized watercourse has trapezium profile; river bed is straightened and often covered with stones or concrete. Habitats for different animal and plant species are destroyed, self-cleaning capacity is scarce and there is no water retention in the riverbed, banks and floodplains. In a canalized watercourse pollutants from surroundings can freely flow into the water. With revitalization of a watercourse ecological balance is restored using appropriate water management interventions. Revitalization of a watercourse enables restoration of habitats for aquatic plants and animals, increases water retention and self-cleaning capacity of a water body. The type of revitalization is chosen according to the scope of revitalization and space abilities in the environment. Where the space around watercourse is limited revitalizations can be implemented inside existing canal. With revitalization measures like stabilization of river banks with vegetation, construction of weirs, pools, rapids, water deflectors, buffer strips along the watercourse, purification beds, creation of meanders and floodplains, backwater etc. habitat and biotic diversity is improved, self-purification

Additional technologies can be integrated in ET systems in order to enhance the removal of target pollutants. Those technologies mainly target at different soluble pollutants like phosphorous, nitrogen, soluble heavy metals and specific micropollutants. Enhanced

capability and water retention are increased (Vrhovšek et al., 2008).

**5.7 Additional technologies for integration in ET systems** 

**5.6 Watercourse revitalization** 
