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Ecological state of selected urban streams in Coimbra, Portugal

2010Ecological state of selected urban streams in Coimbra, PortugalDEL ARCO OCHOA Ana Isabel (Spain)
Organisation:University of Coimbra, Coimbra (PT) - University of Georgia, Athens (USA)Supervisor :Manuel Graça & Verónica Ferreira
Summary: The growth of human population in the last decades has resulted in the development of metropolitan areas and land use changes that affect watersheds and theirs streams. This, added to the long history of human settlement in the city of Coimbra, Portugal, will likely lead to socio-economic and environmental changes compromising streams ecological integrity and water quality, and therefore their ecosystems services. These urban stream services have a double face: a more natural face related to providing, supporting and regulating services. and a more anthropogenic face related to cultural and aesthetic values.The pressures (eg. channelization, flow flashiness, absence of riparian vegetation) and symptoms (eg. elevated nutrient concentrations, altered channel morphology, increase of tolerant species) of urban streams are included under the concept of ‘urban stream syndrome’, which also affects urban streams in Coimbra, Portugal. The urban streams were assessed under the assumption that their ecological integrity and water quality would change predictably along an urbanization gradient. This study aims at: (a) assessing for the first time the ecological state of selected urban streams in Coimbra, Portugal, following the Water Framework Directive (WFD 60/EC/2000) guidelines, (b) determining if urban streams accomplish the WFD requirements of good water and ecological quality, and (c) identifying the main pressures affecting urban streams, necessary for potential future mitigation or restoration action. Two urban streams crossing the city of Coimbra (Coselhas stream named as Casa do Sal and a small tributary of Mondego named as Vale das Flores) and one stream crossing a suburban area (São Paulo de Frades stream named as Eiras) were selected. Urban, physical-chemical and biotic (structural and functional) aspect where considered. Percentage of Total Imperviousness Cover (% TIC) and percentage of Pervious Cover (%PC) were mapped and used as urban indicators. Environmental and mandatory physical-chemical variables by the WFD were assessed and analyzed by Principal Component Analysis (PCA). Benthic macroinvertebrates were used as structural indicators: the Iberian Biological Monitoring Working Party biotic index (IBMWP, modified), the Índice Português de Invertebrados Sul (IPtlS), a predictive macroinvertebrates community model (RIO), common biometrics, and, a PCA using macroinvertebraes communities were determined and analyzed. Breakdown rates of oak (Quercus robur L.) and alder (Alnus glutinosa (L.) Gaertner) leaves were used as functional indicators of ecological integrity. Water quality was apparently in a good state in the three streams. However, ecological integrity was impacted at structural and functional levels, both showing the same increasing degradation pattern that agrees with the TIC increasing gradient from Eiras (suburban area, 3% TIC), to Casa do Sal (19% TIC), to Vale das Flores (61% TIC). Brief conclusions are that chemical and physical measures of water quality and channel characteristics may not reflect with accuracy the ecological state of the streams as they only give information on what is occurring at the sampling moment. Contrary, structural and functional indicators integrated information on environmental factors over a longer period of time allowing perceiving changes in the system beyond those occurring at the sampling moment. PCA of physical-chemical and macroinvertebrate communities suggest that habitat modification and flashiness due to runoff may have stronger influence in communities’ structure than water quality. This study was a first step towards a deeper understanding of the many and diverse stressors affecting urban streams in Coimbra, which represents an important challenge for finding appropriate mitigation or restoration approaches in a novel and relevant topic as urban streams.