Inter-annual variability on the water quality in the Lower São Francisco River (NE-Brazil)

Abstract

Aim This study characterized the water quality in the lower São Francisco River (NE-Brazil).This research represents the first work to be carried out in the lower sector of the São Francisco river aiming to quantify and compare limnological variables, during three different years (2001, 2004 and 2007). Methods Water samples were collected in a transversal section of the river at monthly intervals period on surface layer. Temperature, conductivity, pH, and dissolved oxygen were obtained using a multiparameter probe YSI-6600. The dissolved inorganic nutrients (ammonium, nitrite, nitrate, dissolved phosphorus and silicates), chlorophyll-a and total suspended sediment (TSS) were also determined. Results The three hydrological years showed differences in precipitation rates and discharge conditions. The year 2001 had precipitation rates below the historical series of rainfall. The mean annual water temperature showed negligible differences among the three years. Dissolved inorganic nutrient concentrations were highest in 2004, with ammonia and nitrate differing statistically between the years (p<0.05); the later showed the largest concentration of dissolved inorganic nitrogen. Chlorophyll-a showed a slight difference among years. Conclusions Precipitation intensity has a direct impact on the São Francisco River discharge, but the geographical distribution of the precipitation is also a determinant factor for alterations of the chemical and physical characteristics of the water that reaches the lower sector of the São Francisco River.

Circulation and salt balance in the São Francisco river Estuary (NE/Brazil)

“…The estuarine channel up to the premises of the freshwater end at the town of Piaçabuçu, 15 km upstream from the mouth, has an area of 19.23 km 2 , a mean depth of 3 m and a maximum depth of 12 m at low tide conditions (MEDEIROS et al, 2016;KNOPPERS et al, 2005). The near to constant river flow after 1994 dampened the migration of the estuarine mixing zone, which is now generally set along the river mouth shoals.…”

“…Some of these physical characteristics have undergone substantial human modification (KNOPPERS et al, 2005;MEDEIROS et al, 2011). The impacts associated with human modification reflect different types of construction used, for example, for industrial, agricultural, commercial, and residential activities (MEDEIROS et al, 2016). Such human modification of estuarine environments has resulted in dramatic modification of downstream river flow, with man-made structures (e.g., dams) being responsible for reducing the annual discharge by 30% from about 1/3 of 137 rivers throughout the world (MILLIMAN et al, 2008).…”

Expedition on the Lower São Francisco: An X-ray of fisheries and agriculture, pollution, silting and saline intrusion

“…Associated with this issue, the lower purifying capacity of the river resulting from lower flows over longer periods contributes significantly to the maintenance of pollutants at concentrations harmful to the biota, consumption, and irrigation of crops (MEDEIROS et al, 2016). The São Francisco river flow was drastically reduced in recent years from 1,300 m³/s in 2012 to 550 m³/s in 2017 (resolution ANA n o 1,291/2017), as an immediate effect the increase of salinity was detected at the mouth of the São Francisco.…”

“…There are several consequences of this reduction to the Lower São Francisco, because the advance of the saline wedge on the river has brought significant impacts on ecosystems and the local population, with probable increase of the concentration of pollutants, harmful interference in economic activities such as fishing and rice-growing, and may make it impossible to use the waters for human supply purposes. Possibly, the effects of the salinization are promoting changes in the local biota, with increased competition between species, dwindling fishing stocks and the disappearance of some species of fish and crustaceans (SOARES et al, 2011;MEDEIROS et al, 2016;SOARES, 2017;BARBOSA et al, 2018).…”

Limnologia Aplicada à Análise de Água em Duas Nascentes do Povoado Baixa da Areia, Alagoas (Limnology applied to analysis of water in two springs of the Baixa da Areia Village, Alagoas)

“…No que concerne à qualidade das águas, a Limnologia enquanto ciência caracteriza-se pelo estudo análitico de parâmetros físicos, químicos e microbiológicos, que pode ser oriundo de interferências de ordem natural, do próprio ecossistema, ou de ordem antrópica, advindas das atividades de uso e ocupação do solo, exercidas pela ação do homem no meio ambiente (Medeiros et al, 2016). Paralelo a isso, Abreu e Cunha (2017) ressaltam que a qualidade da água apresenta variações espaço-temporais significativas, relacionandas à dinâmica dos parâmetros físicos (sólidos suspensos, turbidez, sólidos totais, etc.…”