title: Dynamics of limnological parameters in reservoirs: A case study in South Brazil using remote sensing and meteorological data.
abstract: Reservoirs are important in Brazil for the production of hydroelectric power and human water consumption. The objective was to evaluate the variability of total suspended solids (TSS) and chlorophyll-a as well as the rainfall/temperature and land use impacts on these optically active constituents (OAC). The study area is the Passo Real reservoir in south Brazil. The methodology was divided in four steps. First, we used wavelet to detect anomalous periods of rainfall and temperature (2002-2014). Second, we carried out 12 field campaigns to obtain in situ measurements for limnological characterization (2009-2010). The third step was the analysis of Moderate Resolution Imaging Spectroradiometer (MODIS)/Terra and Aqua satellites data corrected and non-corrected for bidirectional effects. Finally, we evaluated potential drivers of OAC changes over time using cross-correlation analysis. The results showed a decrease in the TSS and chlorophyll-a concentrations from the upper to the lower streams of the reservoir. The exponential regression between the MODIS red reflectance and TSS had an adjusted r2of 0.63. It decreased to 0.53 for the relationship between the green reflectance and chlorophyll-a. MODIS data corrected for bidirectional effects provided better OAC estimates than non-corrected data. The validation of MODIS TSS and chlorophyll-a estimates using a separate set of measurements showed a RMSE of 2.98mg/l and 2.33μg/l, respectively. MODIS estimates indicated a gradual transition in OAC from the upper to the lower streams in agreement with the patterns observed using field limnological data. The analysis of land use (greenness) showed two well-defined crop cycles per year. The highest seasonal concentrations of TSS and chlorophyll-a were observed in December and the lowest concentrations in April. Despite the interrelationships between both factors, our cross-correlation analysis indicated that the great concentrations of TSS and chlorophyll-a were primarily controlled by rainfall and secondarily by land use.
authors.affiliation: Universidade Federal de Santa Maria (UFSM), Departamento de Engenharia Florestal, linha Sete de Setembro s/n, CESNORS/UFSM, 98400-000 Frederico Westphalen, RS, Brazil. Electronic address: breunig@ufsm.br.
authors.forename: Fábio Marcelo
authors.initials: FM
authors.lastname: Breunig
authors.affiliation: Universidade Federal de Santa Maria (UFSM), Departamento de Engenharia Florestal, linha Sete de Setembro s/n, CESNORS/UFSM, 98400-000 Frederico Westphalen, RS, Brazil.
authors.forename: Waterloo
authors.initials: W
authors.lastname: Pereira Filho
authors.affiliation: Divisão de Sensoriamento Remoto, Instituto Nacional de Pesquisas Espaciais (DSR-INPE), Caixa Postal 515, Av. dos Astronautas, 1758, Bairro Jardim da Granja, 12245-970 São José dos Campos, SP, Brazil.
authors.forename: Lênio Soares
authors.initials: LS
authors.lastname: Galvão
authors.affiliation: Universidade do Estado do Amazonas (UEA), Escola Normal Superior, Avenida Djalma Batista - 2470, Bairro Chapada, 69050-010 Manaus, AM, Brazil.
authors.forename: Flávio
authors.initials: F
authors.lastname: Wachholz
authors.affiliation: Centro Regional Sul de Pesquisas Espaciais, Instituto Nacional de Pesquisas Espaciais (CRS-INPE), Av. Roraima S/N, CEP:97105-970, Campus UFSM, Santa Maria, RS, Brazil.
authors.forename: Maria Angélica Gonçalves
authors.initials: MAG
authors.lastname: Cardoso
keywords: Chlorophyll; Greenness; Land use; MODIS; Rainfall; Total of suspended solids