Wetland and landscape indices for assessing the condition of semiarid Mediterranean saline wetlands under agricultural hydrological pressures

During last decades semiarid Mediterranean saline wetlands have undergone several hydrological and biological changes as a consequence of increased water inputs from agricultural areas. Specific indices are needed in order to assess the condition of these unique ecosystems in relation to major hydrological disturbances at watershed level. Through the long-term study of selected plant taxa in a set of representative wetlands in Murcia province (SE Spain), together with the characterization of their watershed agricultural land uses, plant indicators of wetland condition were sought and then combined into a wetland condition index. Percentages of land cover classes of interest were weighted taking into account land cover arrangement and receiving wetland size. Characteristic perennial plant taxa were sampled in 1989 and 2008 and significant taxa frequency changes at each wetland site were determined. Regression analysis was used to relate wetland plant taxa frequency and watershed condition during the study period. Limonium spp., Arthrocnemum glaucum, Phragmites australis, Tamarix canariensis and Atriplex halimus showed significant relationships with watershed condition. Indicator taxa were thus identified and their frequencies were combined into an integrated index of wetland condition, which showed a robust relationship with watershed hydrological condition.