Nitrates directive restriction: To change or not to change in terms of climate change, that is the question

The positive effect of nitrogen fertilization in agriculture inevitably increases residual nitrogen losses. Water pollution led to legal restrictions of some farm practices within the framework of the Nitrates Directive of the EU. Nevertheless, even several decades later, the situation has not improved significantly. We present a possible science-based explanation of such a state and provide it to farmers and government as a support for environmental management settings. This study aimed to compare an established approach to implementing the Nitrates Directive, specifically the climate-based zoning of nitrogen fertilization restrictions using data from the mid-20th century. We evaluated this approach by juxtaposing the initial climate data with more recent data spanning from 1991 to 2020. Subsequently, we examined this zoning framework from the perspective of the non-vegetative period, characterized by temperatures below 5 °C, which is widely acknowledged as a critical threshold for nitrogen intake by plants. We found out that i) the employed climate-born zoning does not correspond to recent climate data; ii) nonvegetation period is longer than nitrogen fertilization restrictions. Therefore, despite a noteworthy 22 day reduction in the nonvegetation period from 1961/1962 to 2019/2020, we cast doubt on the notion that the period limiting nitrogen fertilizer application should also be shortened, while admitting that there are other abiotic and biotic factors affecting nitrogen behaviour within the ecosystem.

Groundwater Governance in the Azores Archipelago (Portugal): Valuing and Protecting a Strategic Resource in Small Islands

Studies on groundwater governance status at EU national and river basin district levels are rare, hindering lessons learned at each administrative scale to be shared. Groundwater is a common-pool resource of strategic significance in the Azores archipelago (Portugal), thus calling for sustainable development. Groundwater governance emerged in the last decades as a path to sustainable resources management, and the present paper characterizes the current status of governance in the Azores, where management is pursued according to a vertically-integrated system. A survey made among 43 specialists showed that despite the instrumental role of groundwater for water supply there is a need to increase awareness on groundwater valuing and protection. The application of benchmark criteria to evaluate the groundwater governance state-of-art shows that technical capacities are diminishing governance effectiveness due to the lack of quantitative data, and further enforcing of the groundwater legal framework to the specificities of the Azores is needed. The empowerment of the government agency being responsible for the groundwater management is also envisaged. The failure to account for the economic dimension of the groundwater governance, the insufficient development of cross-sectorial approaches, and the unsuccessful public participation are other weaknesses on the groundwater governance in the Azores.

Natural background groundwater composition in the Azores archipelago (Portugal): a hydrogeochemical study and threshold value determination

Groundwater discharges were sampled in selected springs from São Miguel (Furnas and Fogo trachytic central volcanoes) and Santa Maria islands (Azores, Portugal), in order to characterize natural background levels (NBLs) and proceed to the determination of threshold values (TVs). Besides being a key issue in order to fully assess the anthropogenic pressures, NBLs are also instrumental to derive TVs, therefore complying with requirements from the European Union Groundwater Directive. The composition of groundwater corresponds mainly to low mineralized Na-HCO3 to Na-Cl water types, the latter dominant in Santa Maria island, with a decreasing order of Na>Ca>Mg>K and Cl>HCO3>SO4>NO3 for cations and anion respectively. The majority of the samples are slightly acid to slightly alkaline (pH range of 5.45-7.43), and the electrical conductivity range between 180 and 1458 μS/cm. Groundwater composition is controlled by two major drivers, addition of sea salts and dissolution of silicate minerals. Results shown that TVs established along the present study are in general in the lower rank when compared to the range of values proposed by the several EU member states, with the main exception of NO3, reflecting the impact of agriculture activities over water quality in the Azores, and lower than the national ones. The comparison between the estimated NBL and TV with values derived with another dataset from the Azores, usually higher, depicts the effect of a larger and diverse number of groundwater sources over calculations. On the other hand, all samples which show a contribution from volcanic/hydrothermal systems were excluded from the dataset, which explains why the derived NBLs and TVs are lower comparing to other active volcanic areas, which is also a conservative approach on a subject that has regulatory implications.

Spring geochemistry in an active volcanic environment (São Miguel, Azores): source and fluxes of inorganic solutes

Mineral waters were monthly sampled in selected springs from Furnas and Fogo trachytic central volcanoes (São Miguel, Azores, Portugal). Water temperatures between 15.1 °C and 90.2 °C, characterize poorly mineralized waters of Na-HCO₃ and Na-HCO₃-Cl types. According to the spring location, two watersheds were selected in each volcano to evaluate solute fluxes and chemical weathering rates (Fogo volcano: Ribeira Grande river - RRG; Furnas volcano: Ribeira Quente river - RRQ). Na, Mg, K and Ca fluxes in groundwater represented 43%, 60%, 46% and 57% of the total (subsurface plus surface fluxes) in RRG, and respectively 43%, 53%, 46% and 49% in RRQ. Average HCO₃ flux is ten times higher in RRQ (130.1 × 10(6) mol/yr) compared to RRG (13.8 × 10(6) mol/yr), reflecting the volcano degassing and the lower ratio between groundwater and river water fluxes. Based on these values, total CO₂-consumption by weathering ranged from 1.5 × 10(6)mol/km(2)/yr (RRG) to 4 × 10(6)mol/km(2)/yr (RRQ). TDS load varied between 3772 t/yr (RRG) and 15388 t/yr (RRQ), and the ratio between values in groundwater and in surface water is respectively equal to 0.72 and 2.04. The associated chemical weathering rates in groundwater were 206 t/km(2)/yr (RRG) and 399 t/km(2)/yr (RRQ). Coupled to river water, these values indicate that total chemical weathering rates are respectively equal to 493 t/km(2)/yr and 594 t/km(2)/yr. A similar approach developed for the entire archipelago showed that the chemical weathering rates due to groundwater are in the range from 33 to 321 t/km(2)/yr, being partially controlled by the age of the islands. Results of the present study point out to the need to consider groundwater solute fluxes due to weathering when establishing geochemical budgets.

Fluvial geochemistry in São Miguel Island (Azores, Portugal): source and fluxes of inorganic solutes in an active volcanic environment

River water chemistry in two of the major rivers in São Miguel Island (Azores archipelago, Portugal) has been characterized monthly between June 2010 and October 2011 in order to estimate the main geochemical processes that explain water composition and to estimate solute fluxes and the thermal water input to rivers. Both rivers (Ribeira Grande - RRG, and Ribeira Quente - RRQ) drain active trachytic central volcanoes. The number of sampling stations is seven in RRG and six in RRQ. Rivers are mainly slightly acid to basic in nature (pH in the range 5.41-8.70 in RRG and 5.90-8.10 in RRQ) and from the Na-HCO3 and Na-HCO3-Cl water types. In both cases water temperature increases towards the river mouth and median values are slightly higher in Ribeira Quente (15.5-22.4°C) comparing to Ribeira Grande river (15.2-19.7°C). Electrical conductivity suggests poorly mineralized waters (139-456 μS/cm in RRG and 209-402 μS/cm in RRQ, and values increase downstream. Higher solute fluxes are associated to HCO3 and Na, and the total CO2 flux is equal to 3647 t/yr in RRQ and 7546 t/yr in RRG. Mixture with thermal water discharges also influences river water chemistry and in RRQ the contribution to the annual average discharge rate was estimated in 2.96×10(6)m(3)/yr (12.8% of overall discharge rate in the watershed). In RRG thermal water discharges were estimated in 2.4×10(6)m(3)/yr (14.9% of the discharge rate). The minimum total CO2-consumption associated with low-temperature weathering is equal to 0.58×10(6)mol/km(2)/yr in Ribeira Quente river and equal to 0.78×10(6)mol/km(2)/yr in Ribeira Grande river.