154Operation of constructed wetlands is based on adetailed understanding of ecohydrological proces-ses in different types of natural wetland systems.In the purification of sewage/water, both abioticand biotic processes are involved. By employingevolutionary established regulation processes (see„green feedback concept”, Zalewski et al., 2003)it is possible to optimize these systems. For plan-ning high efficiency or long-term use of wetlands,these systems need additional management suchas plant harvesting, fishing, and sediment remo-val.WHEN TO APPLY CONSTRUCTED WETLANDSConstructed wetland can be applied to:treatment of sewage from small settlements;treatment of municipal and industrial sewage;storm water treatment (Fig. 10.1);purification of outflow from a sewage treat-ment plant for stabilization, reduction of nu-trients, reduction of microbial and other pa-thogens;treatment of surface runoff from arable land(Fig. 10.2); andfor use as a clean-up process in closed wa-ter cycles for industry or for water reuse.The key challenge for the ecohydrology conceptis converting potential threats, e.g., water pollu-tants, into opportunities such as energy sources.This new challenge of sustainable development canbe achieved by combining water purification sys-tems with the production of biomass in construc-ted wetlands, which can be utilized as bioenergyfor local communities and provide them with eco-nomic profits (Box 2.8).WHAT ARE THE ADVANTAGES OF USINGCONSTRUCTED WETLANDS?they utilize solar energy driven purificationprocesses;the establishment of a constructed wetlandis rather simple compared to building a se-wage treatment plant (there is no need forspecific building equipment);if available land is not a limitation, the longe-vity of large systems is calculated to be 50 -100 years; 10.A. CONSTRUCTED WETLANDS: HOW TO COMBINE SEWAGETREATMENT WITH PHYTOTECHNOLOGYproperly designed, they are self-sustainingsystems;because constructed wetlands are very pro-ductive systems, it is possible to combinewetlands with economic profits for local com-munities using proper phytotechnologies (fastgowning plants: willows, reeds, or other na-tive species for a region); andcombining constructed wetlands with spe-cific phytotechnologies, like phytoextractionor rizodegradation, can solve specific waterpollution problems such as heavy metals andorganic compounds.WHAT PROBLEMS CAN BE SOLVEDBY CONSTRUCTED WETLANDS?The following processes take part in constructedwetlands and solve respective environmental pro-blems (see Guidelines Chapter 5):denitrification whereby nitrate is denitrifiedunder anaerobic conditions in a wetland andorganic matter accumulated in the wetlandprovides a carbon source for microorgani-sms converting nitrate to gaseous nitrogen -oxygen conditions can be regulated by wa-ter flow rates;adsorption of ammonium and metal ions byclay minerals - the adsorption process canbe regulated by addition of various mineralsduring the filter design,adsorption of metal ions, pesticides, and pho-sphorus compounds by organic matter, andManagement: Land-Water InteractionFig. 10.1Constructed wetland for storm waterKarls-Einbau Project Company(photo: EKON Polska Biologia Inzynieryjna Sp. z o.o.)VwerySmatrBook03.p65 2004-06-17, 17:37154155the complexing of metal ions by humic acidsand other organic polymers, which signifi-cantly reduces the toxicity of these ions -stimulation of humus-forming processes;decomposition of biodegradable organic mat-ter, either aerobically or anaerobically, bymicroorganisms in the transition zone - cre-ation of proper microhabitats;removal of pathogens that are out-compe-ted by natural microorganisms within thetransition zone; UV radiation plays an im-portant role;uptake of heavy metals and other toxic sub-stances by macrophytes to varying degreesof efficiency; proper selection of plants andregulation of oxygen conditions using the wa-ter regime;decomposition of toxic organic compoundsthrough anaerobic processes in wetlands,which depends upon the biodegradability ofthe compounds and their retention time ina wetland;for regions with eutrophication problems, theuse of additional materials with high concentra-tions of magnesium, calcium, iron, and/or alumi-num, increases phosphorus sorption; andenhancement of sedimentation of TSS in we-tlands for storm water treatment by usinga sequence of different plants.HOW TO DESIGN A WETLANDPreliminary criteriaTo optimize the efficiency of a constructed we-tland, all possible potential processes should becarefully quantified at the design stage.The following aspects should be taken into ac-count: region, climate, key contaminants, mainpurpose, health aspects (e.g., pathogens, malaria).Examples of typical constructed wetlands are demon-strated in Box 10.1. In order to enhance the efficiencyManagement: Land-Water InteractionFig. 10.2Constructed wetland for surface runofffrom arable land, Japan(photo: V. Santiago-Fandino)VwerySmatrBook03.p65 2004-06-17, 17:37155156of purification, newly constructed systems compriseof sequential systems, with several - sometimes morethen 5 - stages of purification. For example, in a typi-cal system the following stages can be applied:horizontal subsurface flow;vertical flow; andstabilization pond(s).The combination of various wetland systems in-creases the efficiency of BOD and nutrient remo-val, even up to more than 90%.The preliminary criteria to be considered in or-der to construct a properly planned wetland sho-uld include:type of outflow to be controlled, e.g., needfor preliminary treatment or use of a multi-functional system combining different typesof constructions;hydrogeological characteristics of a site;surrounding landscapes provide the con-ditions for one of the following wetland types:overland flow;surface flow;subsurface flow; andponds.available space and the price of land;possible additional economic profits for lo-cal communities;the cost decrease for treating sewage.Plants to be used in wetlandsUse of native species is recommended in wetlands.For this purpose, recognition of vegetation communi-ties in natural wetlands and land/water ecotones isrecommended. The following plant types can be used:emergent species: cattails, bulrushes, reeds,rushes, papyrus, sedges, manna grass and wil-lows;submerged species: coontail or horn wart,redhead grass, widgeon grass, wild celery,Elodea, and water milfoil; andfloating plants: duckweed, water meal, bogmats and water hyacinth.Specific criteriaThe following