Ecosystem carbon (C) balance is hypothesised to be sensitive to the mycorrhizal strategies that plants use to acquire nutrients. To test this idea, we coupled an optimality-based plant nitrogen (N) acquisition model with a microbe-focused soil organic matter (SOM) model. The model accurately predicted rhizosphere processes and C-N dynamics across a gradient of stands varying in their relative abundance of arbuscular mycorrhizal (AM) and ectomycorrhizal (ECM) trees. When mycorrhizal dominance was switched - ECM trees dominating plots previously occupied by AM trees, and vice versa - legacy effects were apparent, with consequences for both C and N stocks in soil. Under elevated productivity, ECM trees enhanced decomposition more than AM trees via microbial priming of unprotected SOM. Collectively, our results show that ecosystem responses to global change may hinge on the balance between rhizosphere priming and SOM protection, and highlight the importance of dynamically linking plants and microbes in terrestrial biosphere models.

Abstract:A progressive perceptual understanding approach was used to identify a model structure able to represent the non-linear behaviour of the hydrological cycle in a small intermittent Mediterranean stream. The initial lumped model structure consisting of a series of four connected water tanks (LU3) progressed to a model with five tanks (LU4), and finally to a semidistributed model structure (SD4) in which spatial variability of the evapotranspiration according to the vegetation cover and to the local aspect was considered. In the final model structure, which gave the best fit (Nash-Sutcliffe efficiency index D 0Ð78), an additional tank representing the riparian zone was included (SD4-R). Results showed that the abrupt changes of the riparian water table during summer and the formation of a perched water table during the transition from dry to wet conditions were the main mechanisms leading to the non-linear hydrological behaviour. The transpiration process from the saturated zone and the spatial variability of evapotranspiration resulted in key factors successfully representing the annual water balance. The spatial and temporal validations carried out for each of the four model structures considered in this study supported the hypothesis adopted during the calibration process.

Large portions of Earth's terrestrial surface are arid or semiarid. As in these regions the hydrological cycle and the vegetation dynamics are tightly interconnected, a coupled modelling of these two systems is needed to fully reproduce the ecosystem behaviour and to predict possible responses to climate change. In this paper, the performance of two parsimonious dynamic EVI is reported in literature to be highly correlated with leaf area index so it is compared with modelled LAI mod (r WUE-model =0.45; r LUE-model =0.57). In contrast, NDVI appears highly linked to soil moisture, through the control exerted by this variable on chlorophyll production, and is therefore used to analyze LAI* mod , models' output corrected by plant water-stress (r WUE-model =0.62; r LUE-model =0.59).MODIS LAI and ET are found to be unrealistic in the studied area. The performance of both models in this semiarid region is found to be reasonable.However, the LUE-model presents the advantages of a better performance, the possibility to be used in a wider range of climates and to have been extensively tested in literature.

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SUMMARY IN ENGLISHThis Master Thesis, firstly, gives a general overview of occurrence of emerging pollutants in river water. A deeper study has been made for the emerging contaminant diclofenac and its behaviour, from consumption to natural degradation and effects. In order to predict the fate of diclofenac in a real catchment area main characteristics of Llobregat River Basin in Spain have been described. Data gathering, about the pharmaceutical diclofenac and hydrologic aspects of the catchment, were one of the most laborious works, as it is explained along the thesis. GREAT-ER has been the chosen model to simulate diclofenac occurrence in Llobregat River. Since its use is very limited worldwide, a full explanation about GREAT-ER geo-referenced aquatic exposure assessment model is included in this report: program methodology, main concepts, input files and simulation approach. Simulation approach involved defining different scenarios and a calibration process which is specified in this paper. The results of this process and the derivate discussion mainly conclude in the future possible viability of the model. This Master Thesis is addressed to researchers involved in water risk assessment as well as to people who work with water modelling systems. However, it is also intended to reach people interested in learning about emerging contaminants, its effects and a methodology to combat them: modelling. SUMMARY IN SWEDISHDetta examensarbete ger först en generell översikt av gifter i vattendrag som ökar i förekomst. En djupare undersökning är gjord för den ökande föroreningen diclofenac, och dess påverkan från konsumtion till nedbrytning i naturen. För att förutse vägen för diclofenac i ett verkligt upptagningsområde har huvudegenskaperna från upptagningsområdet Llobregat i Spanien beskrivits. Informationsinsamling av läkemedels-diclofenac och hydrologiska data från upptagningsområdet har varit bland de mer arbetskärvande uppgifterna, vilket förklaras i arbetet. GREAT-ER har används som modell för att simulera förekomsten av diclofenac i vattnet i Llobregat-floden. Eftersom modellens användning är mycket begränsad världen över finns en fullständig beskrivning av GREAT-ER georefereras vattenlevande exponeringsbedömning modell i rapporten, med huvudbegrepp, in-filer och simuleringsmetod. Simuleringsmetoden berör fastställande av olika scenarion och kalibreringsprocessen som användes i arbetet. Resultaten av denna process och följande diskussion fastställer främst framtida möjligheter för modellen. Detta examensarbete är riktat till forskare inom riskbedömning för vattenflöden och personer som arbetar inom modellering av vattensystem. Det är även tänkt att nå personer intresserade av att lära sig om dessa gifter som ökar i förekomst, med dess påverkan och metoder för att bekämpa dem. SUMMARY IN SPANISHEste Proyecto Final de Carrera, en primer lugar, ofrece una visión general de los contaminantes emergentes en aguas de ríos y el conflicto que supone. Además, se profundiza en el conocimiento del comportamiento del cont...

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Abstract:Mediterranean catchments are characterized by strong nonlinearities in their hydrological behaviour. Properly simulating those nonlinearities still represents a great challenge and, at the same time, an important issue in order to improve our knowledge of their hydrological behaviour. The main aim of this work is find out diverse modelling approaches to reproduce the observed nonlinear hydrological behaviour in a small Mediterranean catchment, Can Vila (Vallcebre, NE Spain). To this end, three hydrological models were considered: two lumped models called LU3 and LU4 of increasing complexity, and a distributed model called TETIS. The structures of these different models were used as hypotheses, which could explain and reproduce the observed nonlinear behaviour at the outlet. Four analyses were carried out: (i) goodness-of-fit criteria analysis, (ii) residual errors analysis, (iii) sensitivity analysis and (iv) multicriteria analysis based on the concept of Pareto Optimal. These analyses showed the higher capability and robustness of the distributed model to reproduce the observed complex hydrological behaviour in this catchment.

Abstract. The aim of this work was to couple a nitrogen (N) sub-model to already existent hydrological lumped (LU4-N) and semi-distributed (LU4-R-N and SD4-R-N) conceptual models, to improve our understanding of the factors and processes controlling nitrogen cycling and losses in Mediterranean catchments. The N model adopted provides a simplified conceptualization of the soil nitrogen cycle considering mineralization, nitrification, immobilization, denitrification, plant uptake, and ammonium adsorption/desorption. It also includes nitrification and denitrification in the shallow perched aquifer. We included a soil moisture threshold for all the considered soil biological processes. The results suggested that all the nitrogen processes were highly influenced by the rain episodes and that soil microbial processes occurred in pulses stimulated by soil moisture increasing after rain. Our simulation highlighted the riparian zone as a possible source of nitrate, especially after the summer drought period, but it can also act as an important sink of nitrate due to denitrification, in particular during the wettest period of the year. The riparian zone was a key element to simulate the catchment nitrate behaviour. The lumped LU4-N model (which does not include the riparian zone) could not be validated, while both the semi-distributed LU4-R-N and SD4-R-N model (which include the riparian zone) gave satisfactory results for the calibration process and acceptable results for the temporal validation process.