In temporary (or intermittent) rivers the first storm event after a dry period is responsible for... more In temporary (or intermittent) rivers the first storm event after a dry period is responsible for transferring large amounts of sediment and nutrients into water reservoirs, thereby justifying close monitoring. The objective of this study was to analyse the contribution of storm events to sediment and nutrient transport in the Enxoé temporary river (southern Portugal) using detailed monitoring collected during three hydrological years (September, 2010 to August, 2013), and identify possible sediment and nutrient source areas based on the interpretation of hysteresis in the concentration-discharge relationship. The Enxoé River was monitored for suspended sediment concentration (SSC), total phosphorus (TP), particulate phosphorus (PP), soluble reactive phosphorus (SRP), and nitrate (NO 3 −). An empirical model was used to describe changes in solute concentrations, and the magnitude and rotational patterns of the hysteretic loops. Twenty-one storm events were registered. SSC, TP, PP, SRP, and NO 3 − concentrations varied between 1.6 and 3790.1, 0.05-11.4, 0-7.6, 0-0.67, and 0-27.84 mg l −1 , respectively. The highest SSC, TP, and PP concentrations were registered during the first storm event after an extended drought period. Annual sediment yields (13-480 kg ha −1 y −1) and nitrate (4.4-45.5 kg ha −1 y −1) were relatively low, while phosphorus losses (0.04-0.96 kg ha −1 y −1) reached relatively high values during humid years. Sediment and phosphorus transport was influenced by the stream transport capacity and particle availability, whereas nitrate loads were influenced by rainfall, soil hydraulic characteristics, and land management. This work highlights the main processes involved in sediment and nutrients loads in a temporary river during storm events, with a quantification of the relevant elements.
The Enxoé reservoir in southern Portugal has been exhibiting the highest trophic state in the cou... more The Enxoé reservoir in southern Portugal has been exhibiting the highest trophic state in the country since its early years of operation. The problem has attracted water managers’ and researchers’ attention as the reservoir is the water supply for two municipalities. Extensive research was thus conducted over the last few years, including field monitoring and modelling at the plot, catchment, and reservoir scales. This study now frames all partial findings within the Driver-Pressure-State-Impact-Response (DPSIR) framework to better understand the eutrophication process in the Enxoé reservoir. Agriculture and grazing were found to have a reduced role in the eutrophication of the reservoir, with annual sediment and nutrient loads being comparably smaller or similar to those reported for other Mediterranean catchments. Flash floods were the main mechanism for transporting particle elements to the reservoir, being in some cases able to carry up three times the average annual load. Howev...
The temporal variability of particulate (POC) and dissolved (DOC) organic carbon concentrations w... more The temporal variability of particulate (POC) and dissolved (DOC) organic carbon concentrations was analyzed in the Enxoé temporary river, southern Portugal, between September, 2010 and August, 2013. The overall aim was to study the variability of those elements during storm events, and determine their origin and the main transfer mechanisms to the river. Twenty-one flood events were observed. An empirical model was used to describe changes in solute concentrations, and the magnitude and rotational patterns of the hysteretic loops during flood events. POC and DOC concentrations varied between 0.49-88.93 and 0.25-25.75 mg L-1 , respectively. POC and DOC annual yields varied between 0.06-2.15 and 0.03-1.47 t km-2 , respectively. Flood events had greater effect in POC than in DOC variability. POC had mostly a terrestrial origin, with exports being related to soil erosion and runoff. POC revealed a flushing behavior during the entire monitored period, and clockwise or anticlockwise trajectory loops whenever the predominant origin of the exports was in river bed deposits or arable lands, respectively. DOC had also a terrestrial origin, but it revealed a contrasting dilution behavior and, in general, anticlockwise hysteresis loops. DOC showed a delay in the arrival of solutes to the river, consistent with mass flow through subsurface flow. DOC exports were thus associated with soil weathering and crop mineralization. This work highlights the main processes involved in POC and DOC loads in a temporary river during flood events, with a precise quantification of those elements.
The Enxoé reservoir has been exhibiting frequent high chlorophyll-a concentrations (reaching a ge... more The Enxoé reservoir has been exhibiting frequent high chlorophyll-a concentrations (reaching a geometric mean six times the national limit for eutrophication of 10 μg L−1) since 2000, and represents the reservoir with the highest eutrophic state in Portugal. Toxic algal blooms have also been observed, which pose serious challenges to water managers, as the reservoir is used for potable water production. In an effort to contribute to the reduction of the reservoir trophic state, the watershed inputs (monthly flows, sediment, nitrogen (N) and phosphorus (P) loads) were characterized with the Soil Water Assessment Tool (SWAT). Field data were collected in the ungauged watershed during 2010 and 2011. Model results were then used to characterize the long-term watershed dynamics in terms of water and nutrients. SWAT estimates of the simulated flow, and the sediment and nutrient loads were in good agreement with field data (R2 between 0.42–0.78; Nash-Sutcliffe efficiencies between 0.19–0.7...
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Papers by Maria Branco