Assessing land use and land cover change in Los Molinos reservoir watershed and the effect on the reservoir water quality

Abstract

Understanding and modelling land use and land cover (LULC) change have become one of the major subjects of interest for environmental management due to the negative effects that human activities generate on the normal functioning and dynamics of freshwater resources. Remote sensing and geographic information systems (GIS) are essential tools for assessing the drivers that cause LULC change and its relationship with lake and reservoir water quality. The objective of this study was to assess the spatial and temporal dynamics of LULC change in the watershed of Los Molinos reservoir (Argentina), and to investigate its relationship with the reservoir's water quality. Four Landsat imagery was used to analyse the LULC change in the studied watershed and in different buffer zones from 1990 to 2020. Further, the Normalized Difference Vegetation Index (NDVI) derived from a MODIS time-series dataset (2001–2020) was used to explain the effects of LULC change on the status of the reservoir. Results showed that the most significant LULC change started two decades ago and it has intensified during the last ten years. This change is related to the intensification of agriculture activities, and to the increasing conversion into urban areas, mainly on the shores of Los Molinos reservoir. During the period 2010–2020, urbanization located in the 1 km buffer zone defined from the shore of the reservoir increased at an annual rate of 18.02%. The degradation trend of LULC in Los Molinos watershed significantly contributed to the degradation of water quality of the reservoir. This was corroborated by analysing the MODIS NDVI time-series, which showed that since 2014 the NDVI trend-line presented an increasing behaviour and extreme values of NDVI, related to algal blooms, were more frequently observed.