Influence of the use and the land cover of the catchment in the water quality of the semiarid tropical reservoirs

Abstract

The aim of this study was to evaluate some parameters of water quality of semiarid reservoirs under different uses and occupation of the catchment’s soil. For this, the reservoirs Acauã and Boqueirão, belonging to the Paraíba do Norte river watershed and Middle and Upper course sub catchments, respectively, were studied. For this, water samples were collected in August, September and October 2016. From these samples, total and dissolved phosphorus, nitrate, nitrite, ammonia, chlorophyll, dissolved and suspended solids were analyzed. In addition, images of the Landsat 8 satellite were acquired for the calculation of the Normalized Difference Vegetation Index (NDVI), and for the supervised classification of the use and occupation of the sub catchments. Thus, it was observed that, in general, the Acauã reservoir presented values of phosphorus and nitrogen and solids larger than the Boqueirão reservoir, due to the greater urban area, even though it had a smaller total area of the basin. Both reservoirs presented low vegetation rates and high areas of sparse vegetation and exposed soil, increasing the propensity to soil erosion and the transport of nutrients from the basin to the reservoirs, making water quality worse or impossible.

Removal efficiency of phosphorus, cyanobacteria and cyanotoxins by the “flock & sink” mitigation technique in semi-arid eutrophic waters

“…This reservoir is part of the Paraíba river basin and has an average total volume of 253,000,000 m 3 . This shallow system with a mean area of 2300 m 2 and maximum depth of 58 m has experienced an intense eutrophication process since its inception and presents perennial blooms of potentially toxic cyanobacteria (Cavalcante et al, 2017). The reservoir can be considered hypereutrophic with high mean concentrations of TP (945 ± 21 mg PL À1 ) and chlorophylla (133 ± 4 mg L À1 ), with the dominance of the species Planktothrix agardhii and Cylindrospermopsis raciborskii.…”

Changes in Selected Water Quality Parameters in the Utrata River as a Function of Catchment Area Land Use

“…The contamination of the waters of the Utrata River with nitrate nitrogen in urban and agricultural areas exceeded the limit values specified in the Regulation of the Minister of Maritime Economy and Inland Navigation throughout the entire year (Figure 4). The mean concentration of nitrogen from nitrates in the waters of the Utrata River was 2.76 mg N-NO 3 /dm 3 and significantly exceeded the permissible values for water quality classes I and II, which are <1.1 and <2 mg N-NO 3 /dm 3 , respectively. The lowest mean concentration of nitrated nitrogen in river waters was recorded in the summer, in the upper course of the river in grasslands (measurement points 1-10) and averaged 1.32 N-NO 3 /dm 3 , while the highest (5.13 N-NO 3 /dm 3 ) was recorded in the winter, in agricultural areas.…”

“…The conversion of natural areas for agricultural or urban use increases the generation and transfer of pollutants into flowing waters and water bodies. The main pollutants are organic matter and nutrients from agricultural fields or sewage treatment plants, as well as toxic substances, such as heavy metals and hydrocarbons, generated as a result of intensifying urbanisation processes [3,4]. Another very important cause of pollution in agro-urban rivers is a combination of pollution from untreated sewage and surface run-off from agricultural land.…”

Identificação de conflitos de uso e cobertura da terra na área de proteção ambiental – APA do lago de sobradinho, Bahia

“…Segundo Cardoso et al (2006), áreas com declividade superior a 20º apresentam escoamento superficial rápido na maioria dos solos, o que pode causar sérios problemas de erosão. A cobertura vegetal nessas áreas minimiza os efeitos erosivos e a lixiviação nos solos, contribuindo também para regularização do fluxo hídrico, redução do assoreamento dos cursos d'água e reservatórios, e trazendo também benefícios para a fauna (Costa et al, 1996;Cavalcante et al, 2017).…”