Hydrochemical and isotopes studies in a hypersaline wetland to define the hydrogeological conceptual model: Fuente de Piedra Lake (Malaga, Spain).

The Fuente de Piedra lake is a hypersaline wetland of great extension (13.5km2) and rich in aquatic birds and other species. It became therefore the third Spanish wetland to be included in the Ramsar convention and has been a "nature reserve" since 1984. The lake has an endorheic basin (150km2) with variable-density flows dominated by complex hydrogeological conditions. The traditional conceptualization of endorheic basins in semiarid climates considered that the brine in this hydric system was exclusively of evaporative origin and was placed only in the lake and its surrounding discharge area in the basin. Previous geophysical and hydrochemical studies identified different types of waters and brines. In this work, natural tracers (Cl-, Br-, Na+, Mg2+) and environmental isotopes (18O, 2H, 14C, 13C and 3H) were employed to a) discriminate different types of brines according to their degree of evaporation and genesis, and b) to estimate residence times of brine waters and identify recharge areas of the different flow subsystems. A conceptual model of the hydrogeological system of the lake basin and its links to a regional karst system is proposed.

Sensitivity analysis of a sediment dynamics model applied in a Mediterranean river basin: global change and management implications.

Climate change and land-use change are major factors influencing sediment dynamics. Models can be used to better understand sediment production and retention by the landscape, although their interpretation is limited by large uncertainties, including model parameter uncertainties. The uncertainties related to parameter selection may be significant and need to be quantified to improve model interpretation for watershed management. In this study, we performed a sensitivity analysis of the InVEST (Integrated Valuation of Environmental Services and Tradeoffs) sediment retention model in order to determine which model parameters had the greatest influence on model outputs, and therefore require special attention during calibration. The estimation of the sediment loads in this model is based on the Universal Soil Loss Equation (USLE). The sensitivity analysis was performed in the Llobregat basin (NE Iberian Peninsula) for exported and retained sediment, which support two different ecosystem service benefits (avoided reservoir sedimentation and improved water quality). Our analysis identified the model parameters related to the natural environment as the most influential for sediment export and retention. Accordingly, small changes in variables such as the magnitude and frequency of extreme rainfall events could cause major changes in sediment dynamics, demonstrating the sensitivity of these dynamics to climate change in Mediterranean basins. Parameters directly related to human activities and decisions (such as cover management factor, C) were also influential, especially for sediment exported. The importance of these human-related parameters in the sediment export process suggests that mitigation measures have the potential to at least partially ameliorate climate-change driven changes in sediment exportation.

Analysis of the QUESTOR water quality model using a Fourier amplitude sensitivity test (FAST) for two UK rivers.

This paper presents the sensitivity analysis of a well-known in-stream water quality model, QUESTOR (QUality Evaluation and Simulation TOol for River systems) as applied to two rivers of contrasting land-use in the northeast of England: the 'rural' Ouse and the 'urban' Aire. The analysis employed a version of the Fourier Amplitude Sensitivity Test (FAST) that quantifies the contribution of changes in individual parameters and combination of parameters to the variance of the model output (here the Nash-Sutcliffe) in an efficient way. The quantification of the sensitivity of the model output to the parameters led to the identification of the most influential parameters. Differences between the Aire and the Ouse were found, reflecting their different water quality regime. Results highlighted the importance of interactions between two, or more, parameters on the model output. It led to question the one-at-a-time calibration method currently applied with QUESTOR and underlined the importance of including interactions between parameters in sensitivity analyses. Comparison of the relative influence of parameters versus input data showed contrasting results. In the urban system, the inputs from discharges (sewage treatment works and industrial effluents) were highly influential on model outputs and generally more important than the model parameters. For the rural river, the tributary discharges were most influential, but only at a similar or a lower level than the model parameters.