In the central region of Chile, the Mega-Drought together with the demographic increase near the coast threatens groundwater availability and the hydrogeological functioning of coastal wetlands. To understand the hydric relationship between an aquifer and a wetland in a semi-arid coastal region of Central Chile (Valparaíso, Chile), as well as its geoenvironmental effects, four data collection campaigns were conducted in the wetland–estuary hydric system and surroundings, between 2021 and 2022, including physical, hydrochemical, and isotopic analyses in groundwater (n = 16 sites) and surface water (n = 8 sites). The results generated a conceptual model that indicates a hydraulic connection between the wetland and the aquifer, where the water use in one affects the availability in the other. With an average precipitation of 400 mm per year, the main recharge for both systems is rainwater. Three specific sources of pollution were identified from anthropic discharges that affect the water quality of the wetland and the estuary (flow from sanitary landfill, agricultural and livestock industry, and septic tank discharges in populated areas), exacerbated by the infiltration of seawater laterally and superficially through sandy sediments and the estuary, increasing salinity and electrical conductivity in the coastal zone (i.e., 3694 µS/cm). The Del Sauce subbasin faces strong hydric stress triggered by the poor conservation state of the riparian–coastal wetland and groundwater in the same area. This study provides a detailed understanding of hydrological interactions and serves as a model for understanding the possible effects on similar ecosystems, highlighting the need for integrated and appropriate environmental management.

The main objective of this work was to evaluate the water quality of the El Sauce estuary and its tributaries. The El Sauce estuary basin is located in the town of Laguna Verde, Valparaiso, Central Chile. Sampling took place in the summer season of 2013 and 2015, in 11 stations located along the basin, five of them distributed from its origin to its mouth in the sea and six located before entering its tributaries. Point and non-point sources downloaded in its course were identified. The direct discharge of water from a sewage treatment plant in the area of origin of the estuary, and in its middle zone the percolation of a municipal landfill, stand out for their volume. Its mouth is affected by non-point sources of domestic waters in the town of Laguna Verde. The results show that the estuary is a shallow water course, which quality Class 4 (poor) in most of its extension presents due to the content of organic matter, nutrients, chlorides, and fecal contamination, not complying with environmental regulations for any use. There is a lack of management and control plans in the use of this important resource. It has become a risk to the community, who use the water of the stream both to irrigate subsistence agriculture and for recreation with a direct contact at its mouth.

Coastal zones are ecosystems that are sensitive to climate change and anthropogenic pollution, resulting in a potential loss of biodiversity and ecosystem services through eutrophication and nutrient imbalances, among others. The coastal El Sauce catchment area, Central Chile, is under multiple anthropogenic pressures including wastewater treatment plant (WWTP) discharge, which its broad effect remains underexplored. In order to assess the impact of the WWTP on El Sauce stream, the benthic microbial communities and key functional groups variability (i.e., nitrifiers, methanogens and methanotrophs) were determined by 16S rDNA high-throughput sequencing and by functional genes quantification, respectively, during two contrasted seasons in three catchment areas (pre-, WWTP and post-discharge). The microbial communities’ structure profiles were associated with the water quality, nutrients, greenhouse gas (GHG) distribution, and the organic matter isotopic signatures in the sediments, for the first time, in this ecosystem. The results show that organic matter isotopic signatures using nitrogen and carbon (δ¹⁵N and δ¹³C) and the physicochemical conditions in El Sauce estuary changed from the pre- to WWTP discharge areas (i.e., a pH decrease of 0.5 units and an increase of 4–6 °C in the water temperature). The WWTP discharge area was characterized by a low nutrient concentration and significantly higher GHG distribution (>600 µM CO₂, >30,000 nM CH₄, and >3000 nM N₂O). In addition, the benthic microbial community structure shifted spatially and seasonally, including specific phyla known as sewage bioindicators, such as Firmicutes (Clostridiales order) and Bacteroidetes. In addition, other taxa were enriched or only retrieved in the sediments of the WWTP influenced area, e.g., Tenericutes, Lentisphaerae, Synergistetes, and LCP-89. Methanogens were more enriched near the WWTP discharge compared to those in the pre-discharge site in both seasons, while methanotrophs and ammonia oxidizers were unfavored only during winter. Our results indicate that the WWTP discharge impacts the biogeochemical conditions in El Sauce catchment area modifying the benthic microbial communities, including a decrease in the key functional groups able to mitigate CH₄ and regulate nutrients recycling in these aquatic ecosystems.

Carbon dioxide (CO₂) emissions due to human activities are responsible for approximately 80% of the drivers of global warming, resulting in a 1.1 °C increase above pre-industrial temperatures. This study quantified the CO₂ assimilation and productivity of the brown macroalgae Lessonia spicata in the central Pacific coast of Chile, across seasonal and daily cycles, under different environmental stressors, such as temperature and solar irradiance. Measurements were performed using an infra-red gas analysis (IRGA) instrument which had a chamber allowing for precise quantification of CO₂ concentrations; additional photophysiological and biochemical responses were also measured. CO₂ assimilation, along with the productivity and biosynthesis of proteins and lipids, increased during the spring, coinciding with moderate temperatures (~14 °C) and high photosynthetically active radiation (PAR). Furthermore, the increased production of photoprotective and antioxidant compounds, including phenolic compounds, and carotenoids, along with the enhancement of non-photochemical quenching (NPQ), contribute to the effective photoacclimation strategies of L. spicata. Principal component analysis (PCA) revealed seasonal associations between productivity, reactive oxygen species (ROSs), and biochemical indicators, particularly during the spring and summer. These associations, further supported by Pearson correlation analyses, suggest a high but seasonally constrained photoacclimation capacity. In contrast, the reduced productivity and photoprotection observed in the summer suggest increased physiological vulnerability to heat and light stress. Overall, our findings position L. spicata as a promising nature-based solution for climate change mitigation.

Este trabajo tuvo por objetivo principal evaluar la calidad del agua del estero El Sauce en toda su extensión y sus afluentes. La cuenca del estero El Sauce se ubica en la localidad de Laguna Verde, Valparaíso, Chile Central. La toma de muestras se realizó en la época estival de 2013 y 2015, en 11 estaciones ubicadas a lo largo de la cuenca, cinco de ellas distribuidas desde su origen hasta su desembocadura en el mar y seis ubicadas antes del ingreso en sus afluentes. Se identificaron fuentes puntuales y no puntuales descargadas en su curso. Destaca por su volumen, en la zona de origen del estero, la descarga directa de una planta de tratamiento de aguas servidas, y en su zona media el ingreso de percolados de un relleno sanitario municipal. En tanto, su desembocadura se ve afectada por fuentes no puntuales de aguas domésticas en la localidad de Laguna Verde. Los resultados muestran que el estero es un curso de agua somero, que en gran parte de su extensión presenta calidad Clase 4 (mala) debido al contenido de materia orgánica, nutrientes, cloruros y contaminación fecal, por lo cual incumple con la normativa ambiental para cualquier uso. Se observan falta de planes de manejo y de fiscalización en la utilización de este importante recurso, cuyo uso se ha convertido en un riesgo para la comunidad. Ésta utiliza el agua del estero para el riego de una agricultura de subsistencia y recreación con contacto directo en su desembocadura.