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Here, we demonstrate how a combination of three multivariate statistic techniques can identify key environmental factors affecting the seasonal and spatial variability of chlorophyll-a (Chl-a) in a productive tropical estuarine-lagoon system. Remote estimation of Chl-a was carried out using a NIR-Red model based on MODIS bands, which is highly consistent with the in situ measurement of Chl-a with root mean square error (RMSE) of 15.24 mg m−3 and 13.43 mg m−3 for two independent datasets used for the model’s calibration and validation, respectively. Our findings suggest that the river discharges and hydraulic residence time of the lagoons promote a stronger effect on the spatial variability of Chl-a in the coastal lagoons, while wind, solar radiation and temperature have a secondary importance. The results also indicate a slight seasonal variability of Chl-a in Mundaú lagoon, which are different the from Manguaba lagoon. The multivariate approach was able to fully understand the relative importance of key environmental factors on the spatiotemporal variability of Chl-a of the aquatic ecosystem, providing a powerful tool for reducing dimensionality and analyzing large amounts of satellite-derived Chl-a data.

Reservoirs are considered transition systems between rivers and lakes with particular features due to its morphology and watershed inflows. Studies about aquatic metabolism in subtropical aquatic ecosystems, particularly in reservoirs, have been based on direct measurements and statistical relationships in specific gauge stations of the system rather than on analytical models, which are capable of representing the metabolic processes at different temporal and spatial scales. This paper aimed to evaluate the temporal variability of metabolism in a subtropical reservoir, named Faxinal reservoir, located in Caxias do Sul, Rio Grande do Sul state, Brazil, by using an ecological model (IPH-ECO) which was coupled with a hydrological model (IPH-II) to estimate inflows and nutrient loadings from the watershed. After model calibration, metabolic daily rates of gross primary production (GPP) and respiration (R) were estimated over a 1-year period (from November 2011 to December 2012), considering a process-based algorithm based on dissolved-oxygen budget implemented in the IPH-ECO model. Faxinal reservoir were net heterotrophic 97% of the simulation period. The temporal variability of GPP and R followed the general pattern of phytoplankton biomass in reservoir, which was more related to autochthonous factors such as water residence time, light availability, nutrient concentration and zooplankton grazing. Only during heavy rainfall period, increasing the terrestrial exports, the concentration of phosphorus was higher leading to an increase of chlorophyll-a concentration and hence metabolic rates of GPP and R. Therefore, considering the long dry period during the simulation, the aquatic metabolism of Faxinal reservoir is more influenced by the internal dynamic of the aquatic ecosystem than the watershed inputs. RESUMO A morfologia e o aporte da bacia hidrográfica fazem dos reservatórios um sistema de transição entre rios e lagos com características particulares em termos hidrodinâmicos e de metabolismo. Estudos sobre o metabolismo em ecossistemas aquáticos subtropicais, particularmente em reservatórios, têm se baseado mais em medições diretas e pontuais e em relações estatísticas que em modelos analíticos capazes de representar os processos envolvidos em diferentes escalas espaço-temporais. O objetivo deste trabalho foi avaliar a variabilidade temporal do metabolismo de um reservatório subtropical na cidade de Caxias do Sul/RS através do modelo ecológico IPH-ECO, o qual foi acoplado ao modelo hidrológico IPH-II para estimar as contribuições da bacia hidrográfica. Após a calibração dos modelos, foram calculadas as taxas metabólicas de produção primária (GPP) e respiração (R) para o período de nov/2011 a dez/2012 através dos processos que compõem o balanço de oxigênio no modelo IPH-ECO. O reservatório apresentou um metabolismo autotrófico em 97% do período de simulação. As variações temporais de GPP e R acompanharam o padrão de variação da comunidade fitoplanctônica, sendo esta variação mais associada a fatores autóctones, tais como tempo de residência, disponibilidade de luz na água, concentração de nutrientes e predação por herbívoros. No período de chuva, foi observado um maior aporte de fósforo da bacia hidrográfica que provocou um aumento da concentração de clorofila-a e, consequentemente, das taxas de GPP e R. Considerando o período simulado, o metabolismo do reservatório respondeu mais em função da dinâmica interna do sistema do que ao aporte da bacia hidrográfica.

Resumo As alterações de temperatura da água e a dinâmica de estratificação térmica de um ecossistema aquático influenciam diretamente os processos físicos, químicos e biológicos. Devido às perturbações em que esses ambientes estão expostos, tais como mudanças climáticas e usos múltiplos da água, os estudos por meio de modelagem são importantes para suportar tomadas de decisão emergenciais e planejamentos futuros. Neste contexto, este trabalho teve como objetivo principal avaliar o comportamento térmico do reservatório de São Pedro utilizado para abastecimento de água, localizado no município de Juiz de Fora, MG, por meio da modelagem matemática com o modelo IPH-ECO para avaliar a temperatura superficial da água, com base em dados meteorológicos e hidrológicos, representando as forçantes e as condições de contorno, respectivamente. A modelagem do regime térmico mostrou correspondência significativa entre os valores simulados e observados, caracterizando o reservatório como um ambiente homogêneo. As simulações indicaram que a contribuição dos afluentes determina o padrão de distribuição espaço-temporal da temperatura da água no reservatório, limitando ou regularizando a sua variabilidade da temperatura. Abstract Water temperature changes and the dynamics of thermal stratification of an aquatic ecosystem directly influence physical, chemical and biological processes. Due to disturbances in these environments, such as climate change and multiple water uses, studies which employ modeling are important to support emergency decision-making and future planning. In this context, this study evaluated the thermal behavior of the water supply reservoir of São Pedro, located in the city of Juiz de Fora, MG, using mathematical modeling with the IPH-ECO model to evaluate the surface temperature of water, based on meteorological and hydrological data representing the forcing and boundary conditions, respectively. The modeling of the thermal system showed a significant correlation between predicted and observed values, characterizing the reservoir as a homogeneous environment. The simulations indicated that the tributary contribution determines the pattern of spatio-temporal distribution of water temperature in the reservoir, limiting or regulating the variability of its temperature.

Water resource management involves analyzing the different economic-social scenarios and environmental development. A shallow aquatic ecosystem such as wetlands or lakes can become eutrophic due affluent conditions, as well as physical, chemical and biological elements. Primary production responds to nutrient availability, suggesting that alterations at the top of the food-web can influence the highest trophic levels. Eutrophication is correlated with the variation in the composition of the phytoplankton population, which can be characterized as a strong biological indicator of the trophic level of those ecosystems. Aiming to evaluate the potential of eutrophication in shallow aquatic ecosystems a model was developed to represent the main abiotic and biotic processes of these systems. The considered model is comprised of three modules: (a) hydrodynamic; (b) nutrient transport and (c) biological which deals with phytoplankton productivity. This paper presents the sensitivity analysis of the biological parameters model, parameter calibration of the hydrodynamic model and eutrophication simulation of the Taim Hydrologic System (SHT-Sistema Hidrologico do Taim), whose aim is to identify regions with a high eutrophication potential. The sensitivity analysis of the biological parameters has shown that the chlorophyll a concentration is most sensitive to changes in the parameters involving water temperature effect and the losses due to respiration and grazing. The eutrophication simulations have shown that the shallow regions present the most favorable conditions for eutrophication, while in the deep region (pelagic region) and in the wetland region where solar radiation is decreased due to the aquatic macrophyte barrier found there, productivity is lower. Key-words: calibration, sensitivity analysis , phytoplank