Assessment of constructed wetlands in arid regions with special regard to ecology and multifunctionability

CWs have been studied under various aspects. Mostly, two aspects have been considered: The purification of CWs (Kadlec et al., 2010, Moreno et al., 2007, Vymazal, 2007) and the ecosystem services (Andersen et al., 2003, Balcombe et al., 2005a+b, Hansson et al., 2005). FWS CWs are built mainly because of both treat water or attract wildlife. But until now it is not fully understood whether CWs are capable of both simultaneously. One advantage among others is their great potential of being integrated into existing landscapes. Wetlands serve as food sources and provide niches for organisms and therefore play a vital role in many landscapes. Their ecosystem services can ultimately affect whole landscapes (Hansson et al., 2005). To date the knowledge about the multifunctionality of FWS CWs is limited. It is still not fully understood whether wetlands can mimic natural conditions, serve as habitats for a wide range of animals and at the same time treat water. Additionally, the hydrologic impacts of FWS CWs on the water budget of whole catchments are completely understudied. Two FWS CWs, built in 2000 along the New River in the Imperial Valley, were investigated under the aspects of purification and multifunctionality. Their purpose is to treat water degraded by non-point source pollution. Additionally, they serve as habitats and attract wildlife, especially birds. The Imperial Valley in Southern California is one of the agricultural hotspots in the United States. The Salton Sea is California’s biggest inland waterbody. It is under concern because the rivers which are discharging into the lake are degraded because of non-point source pollution. Additionally, the arid climate in this part of the world contributes to the effects of pollution by great evaporation rates. Contrary, the Salton Sea is recognized as a water body with great ecological importance because of its location along the Pacific Flyway of migratory birds. Therefore, this waterbody is unique in the Western United States. An ecohydrological approach was chosen to address the effects mentioned and to answer the question of multifunctionality. This thesis provides a systemic insight of FWS CWs in arid regions altered by agriculture. The questions that are going to be answered are (1) which processes or parameters delineate purification?, (2) what is the wetland’s influence on the landscape hydrologically and ecologically?, and (3) what is the meaning of a high biodiversity in an arid region that is additionally degraded by agriculture? Thus, answering these questions will enable to evaluate whether FWS CWs in arid regions are beneficial from an ecohydrological point of view. To my knowledge, this is the first approach that combines biological, chemical, and hydrological parameters in a region affected by agriculture and aridity. The combination of the different research aspects revealed the following: (1) Considering various mechanisms within FWS CWs leads to a more dimensional assessment of FWS CWs because (2) the water losses are high but (3) the purification is quantifiable and moreover (4) the FWS CWs do play a role as an alternative to the Salton Sea being a refuge for birds.