No abstract

In order to implement spatial fisheries management in the Arabian Gulf, a better understanding of the distribution of fish in relation to benthic habitats is required. To facilitate this, hydroacoustic fish surveys were conducted over oyster bed/reef ("shallow") and surrounding soft sediment ("deep") habitats in the offshore central Gulf, within Qatari waters. Transects at 'shallow' sites had significantly higher mean fish density and biomass. Mean target strength of individual fish was also significantly higher at 'shallow' sites. Fish positions in the water column were examined and overall there was a closer association with the seabed at the 'shallow' sites. Larger fish were found significantly closer to the seabed than smaller fish across all sites, but more so at 'shallow' sites than at 'deep' sites. Acoustic return from the seabed was extracted to provide information on the habitat type both using 'Sonar5' and 'Visual Habitat' software. The different site categories ('shallow' vs 'deep') were significantly different for all the measures of acoustic habitat. Fish density was significantly related to 'Visual Habitat' data, more so than depth alone. Our results show that fish distribution in the offshore Gulf is associated with complex, shallow oyster bed/reef habitats, and this is particularly the case for larger demersal fish that are commercially 2 exploited. The ability to characterise benthic habitats from acoustic fish survey data shows promise, with important time saving implications for the monitoring of marine environments and developing a spatial approach to fisheries management. This may include the identification of habitats with a relatively high density of larger fish for inclusion in candidate marine protected areas.

In Tunisia, water used for irrigation is often saline, increasing the risk of salinization for soils and crops. In this study, an experiment was conducted on a tomato crop cultivated on a silty-clay soil irrigated with three different water qualities: 0, 3.5, and 7 dS·m−1. Experimental data were then used to calibrate and validate the Hydrus-1D model, which simulates water flow and salt transfer in soils. The successfully-calibrated and validated model was then used to study the combined effects of the soil osmotic and soil matrix potentials on root water uptake. The values of the root mean square error (RMSE), the coefficient of determination (CD), the modeling efficiency (EF), and the coefficient of residual mass (CRM) were close to their optimal values for both soil water content and soil electrical conductivity profiles, indicating the reliability of the model to reproduce water and salt dynamics. Relative yields (Yr), indirectly estimated using actual and potential root water uptake (transpiration), indicated that the multiplicative stress response model (using the S-shape model) satisfactorily simulates measured yields and reproduces the effects of irrigation with saline waters on crop yields. An alternative scenario using a reduction of water requirements by 50% was investigated to assess an irrigation method with considerable water savings. As the results show that relative yields, Yr, were only slightly reduced, the crop water requirements estimated by CROPWAT 8.0 must have been overestimated. The variation of the soil salinity in the root zone highlighted a high salinization risk in the short-term when water of 7 dS·m−1 is used for irrigation.

We analysed the hydrological behaviour of a wadi basin in Egypt, whose channel was modified into levelled terraces for cultivation. A yearly data set was used, consisting of weather data, distributed water content measurements in the terraces of the wadi channel, and run-off discharges at the wadi outlet. A modelling approach combining a run-off model and an agro-hydrological model was tested to simulate, respectively, the water stored in the wadi stream bed after a single rainfall event and the depletion of the stored water by evapotranspiration in the period between two subsequent rainfall events. Calibration and validation of the run-off model were based on both basin outlet run-off and distributed water storage measurements. High Nash-Sutcliffe efficiencies were obtained for both distributed channel water storage and outlet discharges, showing the importance of having available distributed storage measurements, besides basin outlet discharges, to obtain more robust model predictions. The soil-plant-atmosphere model was not calibrated as the parameters for the hydraulic properties, all coming from direct measurements, proved to describe effectively the distributed water storages measured in the terraces during the monitoring campaign. It was observed that the terraces (about 100,000 m 3 ) may store up to 50,000 m 3 of water. By considering that in the soil considered, the water content at the wilting point is about 5% and that in July, the soil profile is still able to retain about 40% of the initial volume, most of the water stored may be used by crops for the whole spring-summer period.