Carmen Hernández-Crespo

Measurement of Acid Volatile Sulphide and Simultaneously Extracted Metals in Sediment from Lake Albufera (Valencia, Spain)

Lake Albufera (Valencia, Spain) is part of a legally protected wetland of international importance. However, it has deteriorated as a result of urban, industrial, and farming pollution. It is highly eutrophic, and its sediment contains persistent pollutants, such as heavy metals. In anoxic sediments, sulphides represent an important binding phase for heavy metals. In this study, acid volatile sulphide (AVS) and simultaneously extracted metals (SEM) were analyzed in surface sediment extracted from Lake Albufera; organic matter and total metals were also analyzed. Twelve sites were sampled in each of three sampling campaigns conducted in March and September 2007 and September 2008. The results revealed elevated organic matter contents varying between 6.9 and 16.7%. The concentrations of AVS in the lake were high, ranging from 8.5 to 48.5 μmol/g; the lowest concentrations were found in the central sites. The AVS results displayed significant differences between the samples from the winter and summer of 2007 (p < 0.05) but not between the two summer samples. The results obtained for SEM varied from 1.4 to 4.8 μmol/g. The difference SEM-AVS was less than zero for all sampling locations and campaigns, indicating the existence of a sulphide pool able to bind metals.

Characterization of wash-off from urban impervious surfaces and SuDS design criteria for source control under semi-arid conditions

Knowledge about pollutant wash-off from urban impervious surfaces is a key feature for developing effective management strategies. Accordingly, further information is required about urban areas under semi-arid climate conditions at the sub-catchment scale. This is important for designing source control systems for pollution. In this study, a characterization of pollutant wash-off has been performed over sixteen months, at the sub-catchment scale for urban roads as impervious surfaces. The study was conducted in Valencia, Spain, a city with a Mediterranean climate. The results show high event mean concentrations for suspended solids (98mg/l), organic matter (142mgCOD/l, 25mgBOD5/l), nutrients (3.7mgTN/l, 0.4mgTP/l), and metals (0.23, 0.32, 0.62 and 0.17mg/l for Cu, Ni, Pb, and Zn, respectively). The results of the runoff characterization highlight the need to control this pollution at its source, separately from wastewater because of their different characteristics. The wash-off, defined in terms of mobilized mass (g/m2) fits well with both process-based and statistical models, with the runoff volume and rainfall depth being the main explanatory variables. Based on these results and using information collected from hydrographs and pollutographs, an approach for sizing sustainable urban drainage systems (SuDS), focusing on water quality and quantity variables, has been proposed. By setting a concentration-based target (TSS discharged to receiving waters <35mg/l), the results indicate that for a SuDS type detention basin (DB), an off-line configuration performs better than an on-line configuration. The resulting design criterion, expressed as SuDS volume per unit catchment area, assuming a DB type SuDS, varies between 7 and 10l/m2.

Nitrogen in Infiltrated Water from Pervious Pavements Under Different Rainfall Regimes and Pollution Build-up Levels

Sustainable urban drainage systems (SUDS) are a nature based solution for best management of rainwater in urban areas. Pervious pavements are one of the SUDS typologies. This study evaluates the water quality filtered by a type of pervious pavement and the influence of the rainfall regime (Atlantic and Mediterranean) and the pollution build-up degree. Total nitrogen (TN) infiltrate concentrations have increased over the study due to the increasing of sediment build-up levels on the pavement surface, with maximum concentrations between 2.7 and 5.0 mg N/l depending on the rainfall regime and the pavement configuration; temperature also influences significantly the leachability of nitrogen. In fact, linear regression models for TN as dependent variable and accumulated mass and temperature have been obtained with a high goodness-of-fit. TN leached over the study represents between 22% and 31% of the total nitrogen present in the sediments accumulated on the pavement surface so the total load is much lower than what would have occurred in an impervious pavement under the same build-up conditions.