David Brito

From eutrophic to mesotrophic: modelling watershed management scenarios to change the trophic status of a reservoir.

Management decisions related with water quality in lakes and reservoirs require a combined land-water processes study approach. This study reports on an integrated watershed-reservoir modeling methodology: the Soil and Water Assessment Tool (SWAT) model to estimate the nutrient input loads from the watershed, used afterwards as boundary conditions to the reservoir model, CE-QUAL-W2. The integrated modeling system was applied to the Torrão reservoir and drainage basin. The objective of the study was to quantify the total maximum input load that allows the reservoir to be classified as mesotrophic. Torrão reservoir is located in the Tâmega River, one of the most important tributaries of the Douro River in Portugal. The watershed is characterized by a variety of land uses and urban areas, accounting for a total Waste Water Treatment Plants (WWTP) discharge of ~100,000 p.e. According to the criteria defined by the National Water Institute (based on the WWTP Directive), the Torrão reservoir is classified as eutrophic. Model estimates show that a 10% reduction in nutrient loads will suffice to change the state to mesotrophic, and should target primarily WWTP effluents, but also act on diffuse sources. The method applied in this study should provide a basis for water environmental management decision-making.

Development of class pedotransfer functions for integrating water retention properties into Portuguese soil maps

Hydrological modellers have recently been challenged to improve watershed models by better integrating soil information into model applications. Reliable soil hydraulic information is thus necessary for better describing the water balance components at the catchment scale. Frequently, that information does not exist. This study presents a set of class-pedotransfer functions (PTFs) for estimating the water retention properties of Portuguese soils. The class-PTFs were established from a dataset containing 697 soil horizons/layers, by averaging values of total porosity and volumetric water contents at –0.25, –1, –3.2, –6.3, –10, –33, –100, –250, and –1500 kPa matric potentials after grouping data by soil texture class, soil horizon, and bulk density. Fitted retention curves using the van Genuchten model were also obtained for every class-PTF. The root mean square error varied between 0.039 and 0.057 cm3/cm3, with smaller values found when using the 12 texture classes of the International Soil Science Society (ISSS) system rather than the five texture classes of FAO, and when bulk density was also considered. The class-PTFs were then integrated into Portuguese soil maps and its usage was demonstrated by deriving maps of available water capacity to be used for modelling the water balance in a small catchment area with the SWAT model. The model successfully simulated the reservoir inflow when using the derived maps, but the results did not vary much whether using coarser or finer description of the catchment soils. Nonetheless, the class-PTFs contributed to a better soil characterisation than when using coarse-scaled information. The approach followed here was simple, inexpensive, and feasible for modellers with few resources but interested in considering the spatial variability of soil retention properties at large scales and in advancing hydrologic modelling in Portugal.

Modeling flood dynamics in a temporary river draining to an eutrophic reservoir in southeast Portugal

Abstract Enxoé is a small temporary river with a flushy regime, which flash floods carry significant loads to the reservoir. As a result, the reservoir, which supplies 25,000 inhabitants, exhibits a high trophic state and cyanobacteria blooms since its construction in 1998, with water abstractions requiring extensive treatment. This study aimed to understand the contribution of flash floods to the Enxoé’s reservoir high trophic state using a modeling approach. This was the first time the river was monitored and that a modeling study was carried out. The MOHID-Land model was implemented to assess the water path in the catchment, and was integrated with field data to compute river loads. Results confirmed the importance of flash events. During flash floods, water properties were determined by soil surface and river bottom wash out, and depended mostly on the flush sequence and intensity. Model simulations showed that soil surface permeability reduction was an important factor regulating surface runoff while soil moisture was low. The first flood after the dry period contributed to 2% of the yearly discharge, 3% of yearly N load, and 7% of the yearly P loads. Winter floods contribution differed, producing 10% of both yearly discharge and loads. However, concentration of particulate matter and organic compounds in the first flood were one order of magnitude higher than in winter floods. This was due to river bottom resuspension and erosion of riparian areas, representative dynamics of a flushy regime. During subsequent winter floods, nutrient concentrations tended to remain constant as the watershed surface and respective soils were washed. Further work should link a watershed model to a reservoir model to depict the flood impact in the reservoir, and test management strategies to reduce the reservoir trophic state.

Modeling water quality in reservoirs used for angling competition: Can groundbait contribute to eutrophication?

Abstract Inland recreational fishing is a popular leisure activity in Portugal, which has close to 219,000 anglers. This study aimed to determine if the groundbait used to attract fish to the area in angling competitions contributes to eutrophication of reservoirs. We conducted a quantitative and qualitative assessment of commercial groundbait to examine the relationship between eutrophication and groundbaiting in angling competitions performed in Maranhão Reservoir, one of the most important southern Portugal angling reservoirs. Simulations using the CE-QUAL-W2 model were performed from January 2001 to February 2007 considering the number of anglers present in angling competitions and the chemical characteristics of commercial groundbait. The results indicated that the use of 5–10 kg of groundbait per angler (3–20 tons of groundbait per year) did not alter the ecological functioning of Maranhão Reservoir; however, higher angling pressures may lead to a significant increase in nutrient concentrations and consequent increases in primary production in the waterbody. Based on these concerns, we combined modeling with simulations to evaluate the environmental effects of groundbaiting in recreational angling and its relation to reservoir eutrophication. This study represents a contribution to more practical and holistic management of recreational fisheries.

Modelling trace metal transfer in large rivers under dynamic hydrology: a coupled hydrodynamic and chemical equilibrium model

Trace metals (TMs) in rivers experience a complex chemistry that affects their partitioning between the dissolved and particulate fractions. Predictive modelling of this partitioning is challenging, particularly under variable hydrodynamic conditions in rivers. This paper presents a coupled hydrodynamic–geochemical model for trace metal dynamics in rivers, to highlight key parameters and set a basis for developing simplified models. A coupled model based on the hydrodynamic model MOHID and the chemical speciation model WHAM was applied to the middle part of the Garonne River (SW-France). The predictions of the coupled model are compared to those of a fixed Kd partitioning model. The model accurately simulates trace metal behaviour under varying hydrological conditions. The importance of the riverbed geomorphology and the diurnal variations in pH on TM concentrations in the water column are underlined. The sensitivity analysis ranked all physico-chemical parameters according to their influence on TM behaviour.

Coupling watersheds, estuaries and regional ocean through numerical modelling for Western Iberia: a novel methodology

An original methodology for integrating the water cycle from the rain water to the open ocean by numerical models was set up using an offline coupling technique. The different components of the water continuum, including watersheds, estuaries and ocean, for Western Iberia were reproduced using numerical components of the MOHID Water Modelling System (http://www.mohid.com). This set of models, when combined through this novel methodology, is able to fill information gaps, and to include, in a realistic mode, the fresh water inputs in terms of volume and composition, into a regional ocean model. The designed methodology is illustrated using the Tagus River, estuary and its region of fresh water influence as case study, and its performance is evaluated by means of river flow and salinity observations.

AUTOMATED SYSTEM FOR NEAR-REAL TIME PREDICTION OF OIL SPILLS FROM EU SATELLITE-BASED DETECTION SERVICE

ABSTRACT 2017-244: The state-of-the-art in both operational oceanography, remote sensing, and computational capacity, enables now the possibility of developing near-real time, holistic automated se...