Stream water quality is controlled by the interaction of natural and anthropogenic factors over a range of temporal and spatial scales. Among these anthropogenic factors, land cover changes at catchment scale can affect stream water quality. This work aims to evaluate the influence of land use and seasonality on stream water quality in a representative tropical headwater catchment named as Córrego Água Limpa (Sao Paulo, Brasil), which is highly influenced by intensive agricultural activities and urban areas. Two systematic sampling approach campaigns were implemented with six sampling points along the stream of the headwater catchment to evaluate water quality during the rainy and dry seasons. Three replicates were collected at each sampling point in 2011. Electrical conductivity, nitrates, nitrites, sodium superoxide, Chemical Oxygen Demand (DQO), colour, turbidity, suspended solids, soluble solids and total solids were measured. Water quality parameters differed among sampling points, being lower at the headwater sampling point (0m above sea level), and then progressively higher until the last downstream sampling point (2500m above sea level). For the dry season, the mean discharge was 39.5ls⁻¹ (from April to September) whereas 113.0ls⁻¹ were averaged during the rainy season (from October to March). In addition, significant temporal and spatial differences were observed (P<0.05) for the fourteen parameters during the rainy and dry period. The study enhance significant relationships among land use and water quality and its temporal effect, showing seasonal differences between the land use and water quality connection, highlighting the importance of multiple spatial and temporal scales for understanding the impacts of human activities on catchment ecosystem services.

La participacion directa o indirecta de los nitritos y nitratos en la biosintesis de nitrosaminas, productos de conocido poder cancerigeno, nos ha inducido a comprobar de que modo afecta la coccion en el contenido de nitratos, atendiendo al tiempo de ebullicion. Asi pues, hemos querido comprobar tambien la posible correlacion existente entre el contenido de las sales nitrogenadas en el producto cocido y en el agua de coccion, de 50 muestras correspondientes a cinco productos horticolas (zanahorias, judias verdes, nabos, acelgas y espinacas). Los nitratos han sido cuantificados basandonos en la NORMA AFNOR NF 04-410 (metodo espectrofotometrico); los resultados se expresan en forma de nitrato potasico.

Over the past decades, fractured and karst groundwater systems have been studied intensively due to their high vulnerability to nitrate (NO₃⁻) contamination, yet nitrogen (N) turnover processes within the recharge area are still poorly understood. This study investigated the role of the karstified recharge area in NO₃⁻ transfer and turnover by combining isotopic analysis of NO₃⁻ and nitrite (NO₂⁻) with time series data of hydraulic heads and specific electrical conductivity from groundwater monitoring wells and a karstic spring in Germany. A large spatial variability of groundwater NO₃⁻ concentrations (0.1–0.8 mM) was observed, which cannot be explained solely by agricultural land use. Natural-abundance N and O isotope measurements of NO₃⁻ (δ¹⁵N and δ¹⁸O) confirm that NO₃⁻ derives mainly from manure or fertilizer applications. Fractional N elimination by denitrification is indicated by relatively high δ¹⁵N- and δ¹⁸O-NO₃⁻ values, elevated NO₂⁻ concentrations (0.05–0.14 mM), and δ¹⁵N-NO₂⁻ values that were systematically lower than the corresponding values of δ¹⁵N-NO₃⁻. Hydraulic and chemical response patterns of groundwater wells suggest that rain events result in the displacement of water from transient storage compartments such as the epikarst or the fissure network of the phreatic zone. Although O₂ levels of the investigated groundwaters were close to saturation, local denitrification might be promoted in microoxic or anoxic niches formed in the ferrous iron-bearing carbonate rock formations. The results revealed that (temporarily) saturated fissure networks in the phreatic zone and the epikarst may play an important role in N turnover during the recharge of fractured aquifers.