Impact assessment of local land use on ecological water quality of the Guayas river basin (Ecuador)

Extensive anthropogenic activities including land conversion have been taking place in the Guayas river basin (Ecuador) due to increasing population growth. Land use changes are considered one of the key sources affecting the ecological water quality of the Guayas river basin. Therefore, we investigated the effect of land use on the ecological water quality both within direct vicinity and within a distance of 200 m from the sampling sites. We investigated which of three land use assessment methods (i.e. data retrieved from field protocols, from aerial pictures (Google maps) and from GIS data) is most suitable to quantify the impact of local land use on the ecological water quality and which key environmental variables influence the ecological water quality. To do so, we collected data on macroinvertebrates and environmental variables from 120 sampling sites throughout the river basin during an integrated sampling campaign. The Biological Monitoring Working Party adapted for Colombia (BMWP-Col) was calculated and used to assess the ecological water quality status of the river basin, based on macroinvertebrates. The relation between the BMWP-Col, local land use and other environmental variables was investigated using generalized linear models (GLMs) and sensitivity analyses. Based on multi-model comparison, the ecological water quality was best associated with the land use close to the sampling sites (field protocol, R2 = 0.93, p < 0.05). Models involving land use assessed using aerial pictures, field protocols and GIS data were associated mainly with hydromorphological variables. However, the models incorporating land use evaluated on a larger spatial scale (i.e. Google maps and GIS maps) were also associated with physical-chemical variables. Although, the land use assessment based on aerial pictures using Google maps” had the best outcome, a combined approach using field observation and aerial pictures can provide comprehensive land use data to the water management and provides the most complete information to define local land use of the sampling sites.