Abstract
Measurements of nutrient and suspended matter concentrations and loads entering and leaving the Castanhão reservoir during the rainy season were carried out to assess the influence of this large reservoir on land-sea fluvial transport in the ephemeral Jaguaribe river basin. Spatial variation indicated statistically significant attenuation of concentrations only for total phosphorous and suspended matter across the reservoir. Strong retention of nutrients and suspended matter loads by the reservoir was observed with average trapping efficiency of 89% for dissolved silicon, 98% of soluble reactive phosphorus, 71% for ammonium, 87% for total nitrogen, 98% for total phosphorus and 97% for suspended matter compared to the reservoir inflow. The dam operational procedure defined by the ephemeral conditions of the river reduced water releases compared to reservoir inflow and induced strong retention of nutrient and suspended matter loads within the reservoir when fluvial transfer occurs in this semiarid watershed.
Highlights
The influence of dams on land-sea river transport and the related effects on the coastal zones have been reported in many areas around the world adjacent to dammed drainage basins (Humborg et al, 1997; Gong et al, 2006; Schöne et al, 2006)
Alterations of nutrient fluxes by dams vary from small to strong retention capacity, the same reservoir which traps nutrients, seasonally can act as a source (Jossette et al, 1999; Friedl et al 2004); Teodoru and Wehrli, 2005; Cook et al, 2010). This variability occurs because nutrient loadings are dominated by flows and dam management imposed by various reservoir purposes determines specific inflow and outflow rates and the variability of nutrient loadings
With the flooding of the Castanhão reservoir, the discharge into the coast was further reduced to about 20 m3.s–1 (Campos et al, 1997)
Summary
The influence of dams on land-sea river transport and the related effects on the coastal zones have been reported in many areas around the world adjacent to dammed drainage basins (Humborg et al, 1997; Gong et al, 2006; Schöne et al, 2006). Alterations of nutrient fluxes by dams vary from small to strong retention capacity, the same reservoir which traps nutrients, seasonally can act as a source (Jossette et al, 1999; Friedl et al 2004); Teodoru and Wehrli, 2005; Cook et al, 2010). This variability occurs because nutrient loadings are dominated by flows and dam management imposed by various reservoir purposes determines specific inflow and outflow rates and the variability of nutrient loadings. More phytoplankton might reduce particulate and dissolved nutrient loads across the flooded river stretch by processes such as nutrient uptake followed by sedimentation and adsorption on suspended matter (Friedl and Wüest 2002); Harrison et al, 2009)
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