1 In Situ and Satellite Observation of CDOM and 2 Chlorophyll - a Dynamics in Small Water Surface 3 Reservoirs in the Brazilian Semiarid Region 4

We analyzed Chlorophyll-a and CDOM dynamics from field measurements and 17 assessed the potential of multispectral satellite data for retrieving water-quality parameters in 18 three small surface reservoirs in the Brazilian semiarid region. More specifically, this work 19 comprises i) analysis of Chl-a and trophic dynamics; ii) characterization of CDOM; iii) estimation 20 of Chl-a and CDOM from OLI/Landsat-8 and RapidEye imagery. The monitoring lasted 20 months 21 within a multi-year drought, which contributed to water-quality deterioration. Chl-a and trophic 22 state analysis showed a highly eutrophic status for the perennial reservoir during the entire study 23 period, while the non-perennial reservoirs ranged from oligotrophic to eutrophic, with changes 24 associated with the first events of the rainy season. CDOM characterization suggests that the 25 perennial reservoir is mostly influenced by autochthonous sources, while allochthonous sources 26 dominate the non-perennial ones. Spectral-group classification assigned the perennial as 27 CDOM-moderate and highly eutrophic reservoir, whereas the non-perennial ones were assigned 28 as CDOM-rich and oligotrophic-dystrophic reservoirs. The remote sensing initiative was partially 29 successful: the Chl-a was best modelled using RapidEye for the perennial; whereas CDOM 30 performed best with Landsat-8 for non-perennial reservoirs. This investigation showed potential 31 for retrieving water quality parameters in dry areas with small reservoirs. 32