No abstract

Urban lakes and ponds (L&Ps) provide numerous ecological and social services for local populations living in urban areas. Their monitoring and management are mostly based on water quality and ecological indicators and poorly consider public preferences and expectancies related to these artificial ecosystems. Even fewer studies bring together expert indicators and public expectations to inform management objectives for urban lakes. Based on an interdisciplinary study, this paper compares an expert assessment of the ecological quality of three urban L&Ps located in the Ile-de-France area with the public perception of these lakes. This approach permits us to explore the compatibilities and incongruences between the various ways in which scientists, managers and urban users assess urban L&P quality. Based on these data, we discuss how it could be possible to define management objectives that integrate quality indicators and expect these objectives to be used in a territorial approach that might allow to obtain a better adequacy between social users' expectations and the ecological status of these L&Ps.

The Rambla de Algeciras lake in Murcia is a reservoir for drinking water and contributes to the reduction of flooding. With a semi-arid climate and a very friable nature of the geological formations at the lakeshore level, the emergence and development of bank gullies is favored and poses a problem of silting of the dam. A study was conducted on these lakeshores to estimate the sediment input from the bank gullies. In 2018, three gullies of different types were the subject of three UAV photography missions to model in high resolution their low topographic change, using the SfM-MVS photogrammetry method. The combination of two configurations of nadir and oblique photography allowed us to obtain a complete high-resolution modeling of complex bank gullies with overhangs, as it was the case in site 3. To study annual lakeshore variability and sediment dynamics we used LiDAR data from the PNOA project taken in 2009 and 2016. For a better error analysis of UAV photogrammetry data we compared spatially variable and uniform uncertainty models, while taking into account the different sources of error. For LiDAR data, on the other hand, we used a spatially uniform error model. Depending on the geomorphology of the gullies and the configuration of the data capture, we chose the most appropriate method to detect geomorphological changes on the surfaces of the bank gullies. At site 3 the gully topography is complex, so we performed a 3D distance calculation between point clouds using the M3C2 algorithm to estimate the sediment budget. On sites 1 and 2 we used the DoD technique to estimate the sediment budget as it was the case for the LiDAR data. The results of the LiDAR and UAV data reveal significant lakeshore erosion activity by bank gullies since the annual inflow from the banks is estimated at 39 T/ha/year.

The abundance and properties of small standing water bodies (SSWB) is globally not well known for their ecological importance is undervalued and their detection suffers from technical limitations. In the current study, we used a combination of GIS-based methods (satellite, orthophoto, ground validation) to evaluate regional estimates of standing water body (SWB) inventories in two geographically different parts of Europe – France, and Estonia. In our study the SWBs surface area threshold limit was 0.00001 km2, exceeding the limits of previous studies (>0.002 km2). The total number of SWBs in Estonia is 111 552 (2.5 per km2) and in France 598 371 (1.1 per km2). Our estimates show that the median size of SWBs in Estonia and France is 0.0003 km2 and 0.0007 km2 respectively, meaning that most of the SSWBs are not included in the global inventories, and their number is therefore underestimated. SSWBs (area below 0.01 km2) form a significant share of the total shoreline length of SWBs, 70.3% in Estonia and 58.8% in France. As nearshore areas are often very productive with diverse habitats, the SSWBs hold a crucial role in maintaining biodiversity. Our results provide quantitative evidence that SSWBs are vital and abundant landscape elements, freshwater resources, and habitats that should not be ignored in global inventories.