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Increasing interest in restoring wetlands within a multipurpose approach is observed in degraded lands submitted to intensive human uses. This study evaluates the effectiveness of constructed and natural wetlands in removing nutrients from agricultural wastewater and their potential contribution to landscape heterogeneity in semiarid Monegros area, NE Spain. To achieve the first aim, wetland plots of differing sizes (50, 200, 800m(2)) were constructed upon fields abandoned four years earlier. Water has been sampled at the inflow and outflow of the plots for two years. Results show a 24-43% rate of total nitrogen removal and no clear trend for phosphorus in constructed wetlands. Slight effectiveness improvements took place in the second working year and in large-size plots. For the second goal, a number of catchments with wetlands that originated as a consequence of irrigation were selected. These wetlands do not contribute significantly to improving the landscape diversity of agricultural catchments. Based on this experimental work, it is estimated that it should be necessary to restore wetlands in 3.25 and 5.60% of total watershed areas to remove most nitrogen from wastewater. Their restoration should be implemented also with the objective of increasing the landscape diversity of zones extensively transformed and homogenized by agricultural practices. (C) 2006 Elsevier B.V. All rights reserved.