Diel changes in aquatic biogeochemistry of a pristine stream receiving untreated urban sewage at Brazilian rainforest.

Freshwater bodies experience diel variations in aquatic chemistry, driven by natural processes. However, changes in land use, like urbanization, can modify the natural dynamics of such systems. This article describes changes in biogeochemistry of a pristine stream after receiving untreated sewage of an urban nucleus. Water samples were collected and field parameters measured, during low flow period. Temperature, pH, dissolved oxygen, electric conductivity, turbidity, total suspended solids, silicate, N-NO3, N-NO2, N-NH4, dissolved and particulate organic nitrogen, PO4, and dissolved and particulate organic phosphorus were measured hourly during a diel cycle. Upstream hydrochemistry resembles pristine watersheds in tropical rainforest, and results are restricted to a narrow range of values during the entire sampling period. Conversely, values downstream varied widely and, for some analytes, presented differences between day and night. Dissolved oxygen and electric conductivity showed the effect of the urban pulse, varying according to the routine of the population. Other field parameters did no presents a pattern that could distinguish up- and downstream stations. All the nutrients, but silicate, increased in concentration downstream. Particulate organic phosphorus, N-NO2, and N-NH4 were the nutrients that highlight the magnitude of the changes driven by urban effluents. These three nutrient species, and dissolved organic phosphorus, revealed a remarkably pattern that reflects the routine of the urban population, with low concentrations at night and a progressive increase starting at the early morning.

Natural and anthropic processes controlling groundwater hydrogeochemistry in a tourist destination in northeastern Brazil.

The objective of this study was to analyze spatial-seasonal changes to identify the natural and anthropic processes that control groundwater hydrogeochemistry in urban aquifers in municipality of Lençóis (Bahia). Tourism is the main activity of this municipality, which is an important tourist destination in northeastern Brazil and which maintains its tourism infrastructure by using groundwater. Two field campaigns were conducted (dry and rainy seasons) in order to collect groundwater samples extracted from 15 tubular wells distributed over the urban area of the municipality. The Piper diagram, multivariate statistical analyses, and artificial neural networks indicated that there are two types of water (Na-Cl and Na-[Formula: see text]-), which were divided into five different clusters. Seasonal variation was observed to significantly alter groundwater hydrogeochemistry. According to the Gibbs diagram, groundwater within the urban area of Lençóis belonged to the rainfall dominance, demonstrating low water-rock interaction. Hydrogeochemical modeling results suggested hydrolysis as the main natural factors controlling process. However, mineral dissolution also occurred in one of the clusters. Human-originated trace contamination by nitrate, chloride, and sulfate occurred in a zone of the urban area. This contamination was observed regardless of climate seasonality, indicating that the main controlling process for groundwater hydrochemistry in this region is wastewater mobilization (indirect artificial recharge).