Locally tuned model to map the chlorophyll-a and the trophic state in Porto Primavera reservoir using MODIS/Terra images

Abstract

In this work we hypothesized that the damming of a rural River for hydropower generation, altering the water retention time should increase the chlorophyll-a (Chl-a) concentration, consequently changing the trophic status. To test this hypothesis, we selected the Porto Primavera (PP) reservoir, which the construction of the dam began in 1998, as study area. Two field-works were conducted in order to obtain water quality and optical data. These field data were used to adjust and validate a statistical-based model. The adjusted model was applied to a time-series of MODIS/Terra images from 2000 to 2015 to obtain the spatial and temporal Chl-a concentration and consequently the trophic status classification. The results showed the following pattern: lower concentration occurred during the dry season and the highest during wet season. The Chl-a time series analysis showed a small tendency in Chl-a concentration to increase over time, but the trophic status has not changed over these 15 years. Our hypothesis can be accepted for the Chl-a concentration but not for the trophic status change. We believe that our findings can improve our knowledge about the water quality dynamics in PP reservoir and can help in future modeling approaches.