Abstract
ABSTRACTThis research is focused on the application of water indexes derived from historical Landsat image series to quantify the impact caused by anthropic activities on wetlands. This work is focused specifically on the Bajo Sinú Wetlands Complex (BSWC) located on the northern Colombian Caribbean Coast. We modelled the spatio-temporal dynamics of the BSWC in three specific periods (1991, 2003 and 2015) and during two seasons: dry and wet. We used data from Landsat 4 Thematic Mapper (TM), Landsat 7 Enhanced Thematic Mapper Plus (ETM) and Landsat 8 Operational Land Imager (OLI) and Thermal Infrared Sensor (TIRS) (Oli-Tirs) images, based on which we evaluated seven different water indexes in order to select the one which best describes changes in the BSWC.The modelling consisted of the identification of spatio-temporal changes over the BSWC caused by two main pressure factors: (1) anthropic activity in the Sinú River Watershed, which is the main water source of the BSWC and (2) the launch of the Urrá Hydroelectric Dam Project located in the upper basin of the Sinú River in 2000.The most suitable water index was found to be the Normalized Difference Water Index (NDWI), based on which we acquired water index images and digital classifications. Reliability of these products was rated in terms of the Overall Classification Accuracy values above 87% and a Kappa index between 0.75 and 0.86.We found that over the 25 year study period, the maximum water storage capacity decreased by 56.2%, the number of the waterbodies reduced by 24.7%, and the average size of the waterbodies decreased by 41%. All the results indicate a deterioration of the water storage capacity in the BSWC.
Highlights
The selection of indexes in this study was carried out employing a qualitative method, we can affirm that this selection is consistent with the results found by Rokni et al (2014), who compared a group of six indexes to calculate the surface of the Urmia Lake in Iran and found that the indexes that had the lowest absolute error values were the Normalized Difference Water Index (NDWI) and NDVI, whereas the NDMI and WRI indexes showed the highest error values
The results of this research, in addition to those reported by Corporación Autónoma Regional de los Valles del Sinú y del San Jorge; CVS (2008) and Ambiotec Ltda (1998) suggest that the tendency towards reduction of the Bajo Sinú Wetlands Complex (BSWC) began before the launch of the Urrá Hydroelectric Dam, resulting from changes in land use
We cannot ignore the hydrological and ecological impacts on the BSWC caused by Urrá, it is necessary to understand that the recovery and conservation of these wetland ecosystems are directly associated with limiting agricultural and cattle ranching activities
Summary
Wetlands are considered the most valuable landscape elements in the context of providing ecosystem services (Costanza et al 2014) as they offer habitat to a large number of animal and plant species (Mitsch and Gosselink 2007), improve the quality of water (Sabater et al 2003; Verhoeven et al 2006), mitigate damages caused by storms and floods, favour the recovery of aquifers (Gosselink and Turner 1978); (MEA 2005); (Keddy and Fraser 2000); (De Groot et al 2006), allow for carbon dioxide capture (Hernandez et al 2015); (Villa and Mitsch 2015); (Estrada et al 2015), and play a key role in climate change mitigation (Fisher and Turner 2008); (Watanabe and Ortega 2011); (Mitsch et al 2013) Despite their importance, wetlands are among the most degraded ecosystems in the world (Finlayson et al 2013).
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