Teses

• Flávio Wachholz: Influência da bacia hidrográfica e características espaço-temporais de variáveis limnológicas sobre reservatórios no Rio Jacuí – RS
• ABSTRACT:
• The building of a dam is an anthropic intervention in the drainage system that changes the natural water flow. This work has characterized and analyzed the limnological and spectral structure on a spatial and temporal scale of the freshwater reservoirs Hidropower Plants (HPP) Passo Real and Dona Francisca of the river Jacuí – RS and, the relationship with the hydrographic basins that make up on the Alto Jacuí. The relationship with the hydrographic basins that make they up on the Alto Jacuí. The hypothesis was that the optical proprieties varies on the spatial and temporal scale as a function of the own reservoir proprieties as well of the hydrographic basins. The methodological procedures were: 1) limnological data acquisition (Secchi transparency, temperature, total of suspended solids – TSS, dissolved organic carbon and chlorophyll a) and field spectroradiometry (hyperspectral data) of the period from February 2009 to March 2010; 2) data base elaboration with the hydrographic basin elements (geosystem and social-economic system) and the limnological variables at the spatial and temporal perspective; 3) identification of the fragility areas of the hydrographic basin and the reservoir characteristics that affect the water quality; 4) relation analysis between the spectral and the limnological data to verify the potential of these to reservoir monitoring. The results showed that Passo Real reservoir hydrographic basin, with a hilly relief, has land use predominance of agriculture, especially for crops such as soybean in the summer and wheat at the winter season. The Dona Francisca reservoir, which is in the basis of the sequence of reservoirs, receives the tributary named Jacuizinho, has a relief characterized by hills and land use with predominance of forest and open fields. In both reservoirs the water temperature is bellow to 20 ºC in the winter season. Further, the greatest thermic amplitude of water was verified always in the Passo Real reservoir. The transparency, TSS and chlorophyll a values were related to a normal rain occurrence (February to July 2009 and February to Mach 2010) and to the winter rainy season (August 2009 to January 2010). Concentration of TSS was higher in the rainy season, therefore the water transparency decreased in this season. The pulse of material provided by the hydrographic basin in the rainy season created favorable conditions to the algae development, especially in the Passo Real reservoir, which showed a eutrophic to hyper-eutrophic state. The higher concentration of TSS and chlorophyll a in the Passo Real reservoir in relation to the Dona Francisca reservoir is related to several factors: larger water retention time, which is more similar to a lake even in the rainy season; higher water temperature; presence of several aquatic compartments; more wind access, which re-suspend sediment and moves part of the nutrients; and the mainly factor is related to the agricultural land use in the hydrographic basin. The dissolved organic carbon showed low concentrations along all period. The correlation between the limnological data and field spectral data presented significant correlation for the red and near infrared wavelengths, allowing the derivations of regression equations (e.g. water transparency: y = 1.0094*(752/697 nm) – 0.5747, R²=0.97). The hypothesis was confirmed for the Alto Jacuí reservoir, where a higher material input from the hydrographic basin was verified and the longer water residence time in the Passo Real reservoir lead to siltation and to an excessive development of algae.

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• Rosana Corazza: Algae blooms identification in the guaíba lake with the use of satellite images and field spectroradiometry. 
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Abstract:

The eutrophication of freshwater ecosystems is a slow and natural process, but that has intensified greatly because of the influence of human activity. One of the consequences of artificial eutrophication are increasingly frequent and intense algae blooms. Some genera groups of algae, and cyanobacteria can produce toxins that pose a risk to humans and aquatic biota and therefore blooms deserve special attention. The Guaiba Lake is an important water body in the State of Rio Grande do Sul and the main source of Porto Alegre city. Its basin covers about 30% of the state area and major rivers – Jacuí, Caí, Sinos and Gravataí – drain areas of intense agricultural and industrial use. In the Guaiba Lake, blooms have been frequent, especially in the last decade and represent a serious environmental challenge. In this context, the objective of this study was to evaluate the potential for identification of episodes of algal bloom in the Guaiba Lake from the integration of radiometric data in situ simultaneously acquired with limnology data (chlorophyll-a, suspended solids total, water transparency, etc.) and satellite images. To obtain the reflectance spectra a portable spectroradiometer FieldSpec® HandHeld was used, with a collection of 16 sampling points defined a priori. The fieldwork took place in March 2012, May 2013 and April 2014. The spectra were correlated with limnological variables obtained simultaneously. For the spatio-temporal analysis of the blooms 10 images produced by Landsat satellites 5 and 7 (TM and ETM+ sensors) were selected and provided by United States Geological Survey (USGS), adjusted for the effects of the atmosphere and converted to surface reflectance. These images were produced in the months of summer and fall, between the years 2005 and 2012, and coincided with the dates of the blooms identified by the Municipal Department of Water and Sewerage (DMAE) in the city of Porto Alegre. Three processing routines were applied to images: 1) Normalized Difference Vegetation Index (NDVI); 2) Linear Spectral Mixture Model (LSMM) and 3) the Analysis by Principal Component (ACP). During the collection of spectra in the field no bloom was identified, but even so it was possible to identificaty reflectance standards in different areas and climatic conditions in the Lake as well as the influence of chlorophyll-a and suspended solids in the spectral response of the water. The main results of the satellite images processing were: a) the NDVI is suitable for mapping the scope and intensity of blooms and results greater than -0.2 indicate flowering areas; b) the LSMM presented limitations for mapping the blooms related to the difficulty of obtaining good reference spectra directly on the images but allowed the evaluation of spatial variations of water features; c) the technique of ACP increased correlations of image data with Chl-a and cyanobacteria compared to NDVI, and non-supervised classification of the principal component identified in the flowering cluster areas as well as areas where other components were at play. Factors that contributed to the establishment of blooms in the lake were slower rate of water flow, the less depth of the water column, lower wind speed and lower levels of rainfall, combined with the greater availability of light and nutrient supply. It was concluded that the techniques used were suitable for mapping blooms and the analysis using data from different natures can improve existing methodologies and open new possibilities for identification and monitoring of algae.

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