Water residence time affecting phytoplankton blooms: study case in Ibitinga Reservoir (São Paulo, Brazil) using Landsat/TM images

Abstract

Satellite images are an effective tool for the detection of phytoplankton blooms, since they cause striking changes in water color. Bloom intensity can be expressed in terms of chlorophyll-a concentration. Previous studies suggest the use of Landsat TM4/TM3 reflectance ratio to retrieve surface chlorophyll-a concentration from aquatic systems. In this study we assumed that a remote sensing trophic state index can be applied to investigate how changes in HRT along the hydrologic year affect the spatial distribution of the phytoplankton blooms at Ibitinga's reservoir surface. For that, we formulated two objectives: (1) apply a semi-empirical model which uses this reflectance ratio to map chlorophyll-a concentration at Ibitinga reservoir along the 2005 hydrologic year and (2) assess how changes in hydraulic residence time (HRT) affect the spatial distribution of phytoplankton blooms at Ibitinga Reservoir. The study site was chosen because previous studies reported seasonal changes in the reservoir limnology which might be related to the reservoir seasonality and hydrodynamics. Six Landsat/TM images were acquired over Ibitinga reservoir during 2005 and water flow measurements provided by the Brazilian Electric System National Operator -ONS were used to compute the reservoir´s residence time, which varied from 5.37 to 52.39 days during 2005. The HRT in the date of image acquisition was then compared to the distribution of chlorophyll-a in the reservoir. The results showed that the HRT increasing implies the increasing of the reservoir surface occupied by phytoplankton blooms.Keywords: Landsat TM4/TM3 band ratios, chlorophyll-a, phytoplankton bloom, hydraulic residence time.Efeito de variações no tempo de residência hidráulica sobre a ocorrência de florações de fitoplâncton: estudo de caso no Reservatório de Ibitinga (SP) com o uso de imagens Landsat/TM ResumoAs imagens de satélite são frequentemente usadas para a identificação de florações de fitoplâncton porque sua presença causa mudanças significativas na cor da água. A abundância das florações pode ser quantificada por medidas de concentração de clorofila-a. Diversos estudos sugerem o uso da razão de reflectância das bandas TM4/TM3 Landsat, para determinar as concentrações de clorofila-a em sistemas aquáticos. Este trabalho tem como objetivos: (1) Palavras-chave: razões entre bandas TM4/TM3, clorofila-a, florações de fitoplancton, residência hidráulica.

The influence of environmental variables in the reproductive performance of Macrobrachium amazonicum (Heller, 1862) (Caridea: Palaemonidae) females in a continental population

“…This was already proposed for caridean shrimps, in which female overall investment (reproductive output) and investment per offspring (egg size) are not linked, because overall investment is set by conditions experienced by the female, while investment per offspring is related to conditions awaiting newly hatched larvae (Mashiko 1990, Clarke 1993, Hancock 1998. The Ibitinga reservoir is considered a eutrophic system, so high chlorophyll-a concentrations are expected independently of bloom events (Londe et al 2016). This could explain the absence of increment in egg volume during seasons in the present study, because feeding conditions (plankton) awaiting newly hatched larvae were abundant throughout the year in the studied site.…”

Freshwater mollusks from three reservoirs of Piauí, northeastern Brazil

“…Santos & Eskinazi-Sant'Anna (2010) attempted to explain the relatively low variety observed in semiarid tropical regions, attributing to prolonged dry periods a condition that selects to snail's community. Considering this assertion, in case of intermittent rivers dammed, the time of water residence is a factor that can play an important role in this phenomenon because drives the stratification processes and nutrient availability, causing considerably changes in water properties (Straškraba 1999, Londe et al 2016. Bennion et al (2005) described that retention periods longer than 30 days are very sensitive to enrichment, making the water more susceptible to eutrophication.…”

Hybrid Chlorophyll-a Algorithm for Assessing Trophic States of a Tropical Brazilian Reservoir Based on MSI/Sentinel-2 Data

“…These results corroborate the previous study of Luzia [57], who classified the reservoir as hypertrophic in the rainy season of January 2006 and as eutrophic in the dry season of June 2005. It is worth mentioning that previous studies at Ibitinga reservoir [17,58,60] were based on a single chl-a concentration algorithm for the entire reservoir. The algorithm was calibrated and validated using data acquired in only one survey campaign.…”

“…Chl-a concentration variation (mg/m 3 ) It is worth mentioning that previous studies at Ibitinga reservoir [17,58,60] were based on a single chl-a concentration algorithm for the entire reservoir. The algorithm was calibrated and validated using data acquired in only one survey campaign.…”

“…P1 and P2 stations (blue and red circles, respectively) were collected one day before Sentinel-2 overpass, and P6 station (orange circle) was collected an hour before the satellite overpass. Beyond the temporal gap between matchups, these errors could also be related to algal bloom hydrodynamic in the reservoir [60].…”