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Abstract:A study of the hydrologic effects of catchment change from pasture to plantation was carried out in Gatum, south-western Victoria, Australia. This study describes the hydrologic characteristics of two adjacent catchments: one with 97% grassland and the other one with 62% Eucalyptus globulus plantations. Streamflow from both catchments was intermittent during the 20-month study period. Monthly streamflow was always greater in the pasture-dominated catchment compared with the plantation catchment because of lower evapotranspiration in the pasture-based catchment. This difference in streamflow was also observed even during summer 2010/2011 when precipitation was 74% above average summer rainfall. Streamflow peaks in the plantation-based catchment were smaller than in the pasture-dominated system. Flow duration curves show differences between the pasture and plantation-dominated catchments and affect both high-flow and low-flow periods. Groundwater levels fell (up to 4.4 m) in the plantation catchment during the study period but rose (up to 3.2 m) in the pasture catchment. Higher evapotranspiration in the plantation catchment resulted in falling groundwater levels and greater disconnection of the groundwater system from the stream, resulting in lower baseflow contribution to streamflow. Salt export from each catchment increases with increasing flow and is higher at the pasture catchment, mainly because of the higher flow. Reduced salt loading to streams due to tree planting is generally considered environmentally beneficial in saline areas of south-eastern Australia, but this benefit is offset by reduced total streamflow.

The 500,000 inhabitants of Mayo Tsanaga River Basin are vulnerable to a "silent" fluorosis from groundwater consumption. For the first time, the groundwater is investigated for the purpose of identifying the provenance of fluoride and estimating an optimal dose of fluoride in the study area. Based on the fluoride content of groundwater, fluorine and major oxides abundances in rocks from the study area, mean annual atmospheric temperature, and on-site diagnosis of fluorosis in children, the following results and conclusions are obtained: Fluoride concentration in groundwater ranges from 0.19 to 15.2 mg/l. Samples with fluoride content of <1.5 mg/l show Ca-HCO(3) signatures, while those with fluoride >1.5 mg/l show a tendency towards Na-HCO(3) type. Fluor-apatite and micas in the granites were identified as the main provenance of fluoride in the groundwater through water-rock interactions in an alkaline medium. The optimal fluoride dose in drinking water of the study area should be 0.7 mg/l, and could be adjusted downward to a level of 0.6 mg/l due to the high consumption rate of groundwater, especially during drier periods.

Stable isotopes and geochemical studies have been applied in the investigation of groundwater resources in Sokoto Basin, northwestern Nigeria. Generally, the characteristic hydrochemical classification in the study area is calcium-alkali-bicarbonate. Surface waters are characterized by alkali-calcium-bicarbonate while groundwater is of Ca-Mg-HCO 3. The plot of δ 18 O versus δ 2 H shows that five isotopic groups can be distinguished. Group I-III is of groundwater origin while group IV and V represent surface water. A combination of the hydrochemical and isotope data (14 C, 13 C and 3 H) reveals the Sokoto basin aquifers generally contains good quality groundwater of Holocene age (100 to 10,000 years BP).

This study uses a multidisciplinary approach to simulate the spatial and temporal patterns of hydrodynamics and water quality in a thermally stratified reservoir in the southern side of the Mediterranean Sea in response to water withdrawal elevation using the 2D water quality and laterally averaged hydrodynamic model CE-QUAL-W2. The withdrawal elevation controls largely the transfer of heat and constituents in the dam in particular during thermal stratification. Fifteen scenarios of withdrawal elevation are possible. To identify the most effective scenarios, a hierarchical clustering technique was performed and only four scenarios were clustered. Deep withdrawals deepen the hypoxia, increase the thickness of the metalimnion, and weaken the stratification stability, which facilitate the vertical transfer of heat and dissolved oxygen mainly. Surface withdrawals, however, shrink the metalimnion and tend to strengthen the stratification, resulting in less transfer of matter from the epilimnion to the hypolimnion. Most of the bottom sediment is overlaid by the hypolimnion. The oxygen depletes significantly and waters become anoxic at a few meters depth. For all scenarios, the reservoir experiences a summer hypolimnetic anoxia, which lasts from 42 to 80 days and seems to decrease as withdrawal elevation increases. At the end of stratification, waters below the withdrawal elevation showed a noticeable release of iron, nutrients, and suspended sediments that increases with depth and near-bottom turbulence. Attention should be drawn to shallower withdrawals because they accumulate nutrients and silts continuously in the reservoir, which may deteriorate water quality. Based on these results, a withdrawal elevation rule is presented. This rule may be adjusted to optimize water withdrawal elevation for dams in the region with similar geometry.