J. Virgílio Cruz

Chemistry of waters from Furnas volcano, São Miguel, Azores: fluxes of volcanic carbon dioxide and leached material

Abstract The well-constrained hydrology of the Furnas caldera permits the quantification of the precipitation, evapotranspiration, runoff and the groundwater discharge out of the volcanic structure. Chemical composition of the discharge in Furnas has been stable for at least a century. A hydrogeochemical survey and discharge measurement of the springs and runoff in Furnas allow estimates of chemical fluxes from the volcanic structure. A tectonically controlled lineament of high carbon dioxide flux has been identified across the caldera floor. Three water types are encountered in Furnas: hydrothermal, carbonated and cold waters. The hydrothermal waters originate from shallow aquifers which derive their heat from local intrusions at shallow depth (100–200 m) at about 160°C. The carbonated waters, some of which are steam heated by discharge from underlying thermal aquifers occurs above the carbon dioxide anomaly across the caldera floor. Extensive leaching, in some cases stoichiometric, of glassy volcanic rocks by these mildly acid carbonated waters supplies most of the dissolved solids in Furnas waters. Chemical flux estimates for the volcano show that carbon dioxide (9358 tons/yr), leached silica (3994 tons/yr) and leached sodium (2628 tons/yr) are the dominating mobile components of the system.

Major ion chemistry of groundwater from perched-water bodies of the Azores (Portugal) volcanic archipelago

A dataset of major ion composition of 246 samples from cold-water springs discharging from perched-water bodies at volcanic islands (Azores archipelago, Portugal) reveal waters with low mineralization, which evolve due to two main geochemical processes: (1) seawater spraying and (2) dissolution of primary minerals of volcanic rocks. As a result, water facies range from Na–Cl to Na–HCO3 type waters. The relationship between alkali, alkali–earth metals and HCO3− shows differences between waters discharging from perched-water bodies in basaltic rocks comparing to more evolved rocks of trachytic nature. The use of principal component analysis shows that water-rock interaction is limited, which is compatible with the geochemical observations and with the hydrogeological environment.

Sete Cidades and Furnas lake eutrophication (São Miguel, Azores): analysis of long-term monitoring data and remediation measures.

Eutrophication of lakes in the Azores archipelago (Portugal) has been described since the 80s, and due to water quality deterioration several remediation methodologies were applied. Long-term monitoring data on water quality from Sete Cidades and Furnas lakes (São Miguel island) were analyzed in order to address that the success of the ongoing policy reverses their eutrophic status. Sete Cidades lake (4.46 km2), made by two branches (so-called Green and Blue lakes), has a water volume equal to 58×10(6) m3 and a depth in the range between 24 and 28.5m. Furnas lake (1.87 km2) has a volume equal to 14×10(6) m3 and a maximum depth of 15m. In Sete Cidades lake mean water temperature and pH range respectively between 13.4°C to 17.7°C and 7.04 to 8.06. Instead, mean temperature in Lake Furnas ranges between 16.6°C and 17.2°C, with a pH between 7.36 and 7.84. Mean water conductivity shows that both lakes correspond to very diluted waters, with values between 98.1 and 136.5 μS/cm. Water chemistry is influenced by the monomictic character of the lakes, as anoxic environment in the hypolimnion due to O2 consumption during the summer, when stratification prevents mixing along the water column, explains sharp increase in TP, TN, N-ammoniacal, Mn and Fe. Major-ion content is rather constant along time, with some seasonal fluctuations, despite a decrease in SO4 observed in Sete Cidades lake which is suggested to be a result of runoff diversion, a result also shown by the decrease of the molal ratio TN/TP in both studied lakes. Nevertheless, the application of the trophic state index (TSITP) does not suggest an improvement in what concerns trophic status, which is explained by the internal P-loading, a source that have to be managed by environmental authorities in the near future in order to revert eutrophication.

Implementation of the Water Framework Directive in an Outermost EU Region: The Case of Azores Archipelago

The Azores Water Plan (AWP) came to force in year 2003 in order to provide a coherent set of measures to protect and enhance water resources in the archipelago. The AWP was developed according to EU Water Framework Directive (WFD) and a close relationship can be found between goals on both documents. The evaluation of results associated to AWP implementation, made possible through a consultation procedure described in the present paper, provides an indirect assessment of the implementation of the WFD in an EU outermost region such as the Azores. The analysis suggests that major constrains to the full implementation of the AWP and WFD are associated with administrative arrangements, reflected in a lack of coordination, as well as adequate funding and cost recovery and strategies for public participation and information provision. Instead, water quality monitoring is already fully operational showing a strong relationship between science and water policy.