António Chambel

Influence of different land uses on groundwater quality in southern Portugal

In Alentejo region, southern Portugal, differences in groundwater samples from six groundwater bodies covered with different land uses were analysed based on the monitoring plan of the Alqueva multi-purpose project, created in the sequence of the construction of the Alqueva Dam on the Guadiana River, in South Portugal. For most of the groundwater bodies there is a statistical significant difference between magnesium, sulphate, chloride, and phosphate. All of these ions are strongly correlated with land use management. Groundwater, where land is covered by olive groves, has high levels of electric conductivity, calcium, potassium, sulphate, and phosphate. Dry land crops are correlated with calcium, magnesium, chloride and consequently, electric conductivity, phosphates and sulphate. Vineyards are strongly correlated with high sulphate and phosphate levels. This study clearly shows that different land uses within a certain groundwater body influence the water quality in a different way. Therefore, an appropriate soil management should be adjusted to each situation, taking into account the aquifer matrix and the overlying soil.

The Influence of Urbanisation on Groundwater Recharge and Discharge in the City of Évora, South Portugal

Urbanisation has had a major impact on groundwater beneath Evora, an ancient city in the south of Portugal. Land use change, notably the growth of impermeable surfaces, has led to a reduction in groundwater recharge. As the city has grown, impacts have increased. Understanding changes to the water balance are the first step in rationalising the use of groundwater. Currently groundwater is used largely for gardening and farming. In the oldest part of the city, within the city walls, groundwater is little used, while outside the city walls, groundwater usage is high. This study shows how the municipality can take advantage of groundwater to irrigate the majority of the public gardens instead of relying on filtered water from the Monte Novo Dam. This approach would also help solve the problem of pollution that occurs due to losses from the city’s sewage system.

HYDROCHEMICAL QUALITY OF GROUNDWATER IN URBAN AREAS OF SOUTH PORTUGAL

This investigation of urban groundwater problems in the city of Evora is one of the first in Portugal, its main objective being to develop a hydrochemical knowledge of the city’s groundwater. Thirteen water points, represented by 7 large diameter wells and 6 deep wells, were selected for sampling. The major ions were analysed, as well as temperature, EC, pH and total hardness. The results show that most of the waters are HCO3-Mg-Ca-Na type, but some of the samples are Cl in type and one is clearly Cl-Na in type. The EC varies between 230 and 2500 μS/cm. The nitrate content varies between 0.5 and 310 mg/L, but over 50 % of the samples exceed the 25 mg/L maximum recommended by Portuguese Law. The absolute permitted maximum of 50 mg/L is also exceeded in 30 % of the samples. When compared with water quality elsewhere in Alentejo, the results are clearly high in terms of EC, nitrates and chlorides. The high content of nitrates and chlorides may be an indication of urban contamination.