Carla Vanesa Spetter

Context: Land-based activities within a river basin alter nutrient and particle transport, affecting estuarine water quality and ecological health. Aim: To assess spatial and seasonal dynamics of nutrients, particulate materials, and physicochemical parameters in Sauce Chico River (SCR), Napostá Grande Stream (NGS) and inner Bahía Blanca Estuary (BBE, Argentina) from autumn 2017 to summer 2018. Methods: We analysed 14 sites located in freshwater bodies and within the estuary. Flows, pH, temperature, salinity, turbidity, ammonium (NH4⁺), chlorophyll a (Chl-a), phaeopigments (Phaeo), particulate organic carbon (POC) and suspended particulate matter (SPM) were determined. Key results: Average flow rates reflected rainfall patterns. SCR acts as the primary driver of physical sedimentation, transporting significantly more SPM (3492 Mg year−1) than NGS. NGS exerted a stronger chemical influence, with sewage discharges triggering critical NH4+ spikes. Wide POC:Chl-a ratio range in BBE (94–595) and winter POC peaks from the NGS indicate seasonal shifts between terrestrial inputs and estuarine productivity. Conclusions: BBE is subjected to dual, tributary-specific stressors – sediment loads from the SCR and nutrient pollution specially from the NGS. Implications: Protecting of vulnerable ecosystems, as BBE, requires distinct, integrated watershed management strategies tailored to the unique anthropogenic pressures of each tributary.

Estuaries are dynamic systems where physical forcing rapidly reorganizes suspended particulate matter and the trophic environment available to consumers. We performed high-frequency sampling across a full semidiurnal tidal cycle in the mesotidal Bahía Blanca Estuary (SW Atlantic, Argentina) during autumn 2024, under pre-bloom, low-chlorophyll conditions. We quantified dissolved inorganic nutrients, chlorophyll-a, nano- and microplankton, mesozooplankton, size-fractionated seston fatty acids, and anthropogenic microparticles to evaluate how tidal forcing modulates seston origin, fatty-acid-based nutritional quality, and particulate redistribution at sub-tidal timescales. No polyunsaturated fatty acids were detected, and variability in seston fatty acid composition was primarily associated with tidal transport rather than changes in phytoplankton biomass or community structure. Flood and high tide were associated with signatures indicative of more pelagic-derived organic matter, whereas ebb and low tide showed increased contributions of bacterially associated fatty acids and benthic-derived particulate material. Coherent patterns across chlorophyll-a, plankton compartments, and fatty acid indices support a tidally driven nutritional shuttle that synchronizes seston origin and composition over hourly timescales, even in the absence of active blooms. Anthropogenic microparticles exhibited marked short-term variability, indicating that tidal forcing structures both biogenic and non-biogenic components of suspended particulate matter in shallow, turbid estuaries. Together, these findings demonstrate that short-term tidal forcing can rapidly restructure the trophic environment of shallow, turbid estuaries during low-productivity periods.

The Patagonian Shelf is recognized for its high potential for carbon uptake, driven by intense biological productivity. While net CO2 uptake persists much of the year, the mechanisms shaping sea-air CO2 fluxes (FCO2) under low-productivity conditions remain unclear. We examined surface FCO2 during autumn 2022 on the northern Patagonian Shelf, influenced by the Brazil and Malvinas Currents, where submesoscale activity generates patchy flux regimes. Even under low productivity, chlorophyll-a (Chl-a) was the strongest predictor of seawater pCO2 and modulated FCO2: high Chl-a areas acted as CO2 sinks, whereas low-Chl-a regions were near equilibrium or sources. Bloom phenology explained coherent patterns, with sinks associated with off-season peaks and sources with late-stage declines. Strongest uptake occurred in a retention zone offshore the upwelling front, where Malvinas Current circulation concentrated pigmented cells. Conversely, adjacent upwelling areas with stronger advection promoted outgassing of aged, carbon-rich waters that offset biological uptake, underscoring the dual role of upwelling. Planktonic assemblages also modulated carbon cycling: Prochlorococcus dominated oligotrophic Brazil Current waters with low Chl-a, depleted microbes, and reduced fluorescent dissolved organic matter (DOM), reflecting limited sequestration and persistent outgassing. Conversely, Synechococcus, picoeukaryotes, and heterotrophic bacteria co-occurred in sink regions, where DOM showed signatures of recent production. On the shelf, abundant bacteria and viruses were linked to humic-like refractory DOM, suggesting microbial reworking as a pathway for long-term storage. These findings demonstrate that while temperature set the FCO2 landscape at the Brazil-Malvinas confluence, while physical transport, bloom dynamics, and microbial transformations interact to produce heterogeneous CO2 source-sink patterns.

The Patagonian Shelf is recognized for its high potential for carbon uptake, largely driven by intense biological productivity. While net CO2 uptake persists much of the year, the mechanisms shaping sea–air CO2 fluxes (FCO2) in the low-productivity season remain unclear. We examined surface FCO2 during autumn 2022 on the northern Patagonian Shelf, influenced by the Brazil and Malvinas Currents, where submesoscale activity generates patchy flux regimes. Even under low productivity (mean surface chlorophyll-a (Chl-a) 1.1 mg m⁻³), Chl-a was the strongest predictor: high Chl-a areas acted as CO2 sinks, whereas low-Chl-a regions were near equilibrium or acted as net sources. Bloom phenology explained coherent patterns, with sinks associated with off-season peaks and sources to late-stage declines. Strongest uptake occurred in a retention zone offshore the upwelling front, where Malvinas Current circulation concentrated pigmented cells. Conversely, adjacent upwelling areas with stronger advection promoted outgassing of aged, carbon-rich waters that offset biological uptake, underscoring the dual role of upwelling. Planktonic assemblages also modulated carbon cycling: Prochlorococcus dominated oligotrophic Brazil Current waters with low Chl-a, depleted microbes, and reduced fluorescent dissolved organic matter (DOM), reflecting limited sequestration and persistent outgassing. Conversely, Synechococcus, picoeukaryotes, and heterotrophic bacteria co-occurred in sink regions, where DOM showed signatures of recent production. On the shelf, abundant bacteria and viruses were linked to humic-like refractory DOM, suggesting microbial reworking as a pathway for long-term storage. These findings demonstrate how physical transport, bloom dynamics, and microbial transformations interact to produce heterogeneous CO2 source–sink patterns in the Brazil/Malvinas confluence.

Spetter, C.V.; Fernández, E.M.; Speake, M.A.; Abasto, B.; Carbone, M.E.; Garzón Cardona, J.E.; Fernández Severini, M.D., and Martinez, A.M., 2023. Indirect effects on tourism and water quality along the Argentinian Atlantic Coast during COVID-19 pandemic scenarios. Journal of Coastal Research, 39(5), 970–983. Charlotte (North Carolina), ISSN 0749-0208. The coronavirus 2019 (COVID-19) pandemic forced governments to make drastic decisions, mainly about isolation and social distance. In 2020, the lockdown in Argentina lasted 37 days in the entire national territory and up to 280 days in some jurisdictions. The tourism activity at the beginning of the summer season raised questions regarding the influx of tourists and the impact of new security measures on the environment. In this work, different probable scenarios are discussed, including a pandemic expected before the summer season, what eventually happened, and how it could have impacted tourism and the water quality of the Argentine Atlantic Coast. A survey was carried out via Google during October–November 2020. The data (2017–2021) on tourist influx statistics for eight coastal destinations were analyzed. A literature review (2020–2022) was carried out, and the probable loads of nutrients, organic compounds, emergent contaminants, and other solid wastes (such as plastics) were evaluated. The results showed that the neutral scenario was the predominant one. Despite the decrease in the arrival of tourists to the Argentine Atlantic coastal destinations studied, there was a disposition of the population to travel and a strong preference for sun-and-beach tourism compared to other tourist modalities. In a pandemic scenario, the concern in coastal management is centered on the need to adapt wastewater treatment plants in coastal tourist areas to minimize the impact of liquid effluents as well as the proper management of urban solid waste. In addition, a set of potentially useful strategies for global environmental sustainability is proposed.

Estuarine sediments play a key role in the processes of nutrient remineralization; among them, phosphorus (P) is an essential element for life. In this work, we evaluated the levels of P in sediments of the surface layer (S: 0-5mm depth) and sub-surface layer (SS: 5-10mm depth) of the low supratidal plain of Puerto Rosales (middle zone of the Bahía Blanca estuary, Argentina). This is also the first study of P speciation in this area. In order to assess the relationship among physico-chemical parameters and the different fractions of P analyzed, we determined granulometric composition, percentage of moisture and organic matter, pH, Eh and temperature in the sediments. The results showed high levels of total P (up to 1.055 mg P g-1 dw) and there were no significant differences between layers, reflecting the ability of these sediments to retain native and / or anthropogenic P. In general, P tended to remain as P linked to phosphate minerals of Ca and as refractory or residual P (40% and 35%, and 20% and 31% in S and SS, respectively). The granulometric composition of the sediment would favor the retention of P while the flood would be affecting it, especially in the fraction corresponding to the labile o adsorbed P (11% and 23% for S and SS, respectively). In both layers, the variability observed in the proportions of P-Fe and the moderately labile P seems to be related to the dissolution of PO43- and its diffusion towards the water column through porewater.

Los humedales costeros conforman uno de los ecosistemas más productivos del mundo, brindando diversos servicios ambientales tales como la regulación hídrica, climática, provisión de alimentos, recreación y disfrute espiritual, entre muchos otros. No obstante ello, los rápidos procesos de modificación antropogénica que enfrentan en la actualidad han logrado alterar dramáticamente su biocapacidad y resiliencia. La disponibilidad de información completa y actualizada resulta de vital importancia para la planificación y la gestión estratégica de las áreas litorales. Por ello, en el presente estudio se analiza el sistema socio-ecológico del estuario de Bahía Blanca (SSE-BB) bajo un enfoque integral. El método empleado se basó en el marco conceptual de la Evaluación de Ecosistemas del Milenio (EM), diseñado por la Organización de Naciones Unidas. Los resultados obtenidos permiten afirmar que las presiones más importantes que recibe el SSE-BB son la concentración de infraestructura en el borde costero, el dragado y relleno artificial de los humedales, la contaminación ambiental y la invasión de especies exóticas. Las consecuencias directas sobre el bienestar de la población local están signadas por la disminución de los alimentos provenientes de la pesca, la pérdida de valores asociados a la herencia cultural y de recursos turísticos de primer orden, problemas de salud derivados de la calidad del aire y conflictos entre usuarios de recursos, como es el caso de los pescadores artesanales y las empresas industriales. Se espera que el diagnóstico operativo realizado facilite la adecuada comprensión de los problemas actuales del área de estudio y fomente la búsqueda de soluciones integrales.