Rise of toxic cyanobacterial blooms is promoted by agricultural intensification in the basin of a large subtropical river of South America.

Toxic cyanobacterial blooms are globally increasing with negative effects on aquatic ecosystems, water use and human health. Blooms' main driving forces are eutrophication, dam construction, urban waste, replacement of natural vegetation with croplands and climate change and variability. The relative effects of each driver have not still been properly addressed, particularly in large river basins. Here, we performed a historical analysis of cyanobacterial abundance in a large and important ecosystem of South America (Uruguay river, ca 1900 km long, 365,000 km2 basin). We evaluated the interannual relationships between cyanobacterial abundance and land use change, river flow, urban sewage, temperature and precipitation from 1963 to the present. Our results indicated an exponential increase in cyanobacterial abundance during the last two decades, congruent with an increase in phosphorus concentration. A sharp shift in the cyanobacterial abundance rate of increase after the year 2000 was identified, resulting in abundance levels above public health alert since 2010. Path analyses showed a strong positive correlation between cyanobacteria and cropland area at the entire catchment level, while precipitation, temperature and water flow effects were negligible. Present results help to identify high nutrient input agricultural practices and nutrient enrichment as the main factors driving toxic bloom formation. These practices are already exerting severe effects on both aquatic ecosystems and human health and projections suggest these trends will be intensified in the future. To avoid further water degradation and health risk for future generations, a large-scale (transboundary) change in agricultural management towards agroecological practices will be required.

Las floraciones de cianobacterias tóxicas vienen aumentando drásticamente a nivel mundial con efectos negativos en los ecosistemas acuáticos, los usos del agua y la salud humana. Los principales mecanismos promotores de las floraciones son la eutrofización, la construcción de represas, la contaminación con residuos urbanos, la pérdida de vegetación natural y el cambio y la variabilidad climáticos. Los efectos relativos de cada determinante aún no se han abordado adecuadamente, particularmente en las grandes cuencas fluviales de América del Sur. En este trabajo, realizamos un análisis histórico de la abundancia de cianobacterias en un gran e importante ecosistema de América del Sur (el Río Uruguay, c.a. 1.900 km de largo, cuenca de 365.000 km2). Evaluamos las relaciones entre la abundancia de cianobacterias y el cambio en los usos del suelo, el caudal de los ríos, la contaminación urbana, la temperatura y la precipitación desde 1963 hasta el presente. Nuestros resultados evidencian un aumento exponencial en la abundancia de cianobacterias durante las últimas dos décadas, de forma congruente con el aumento en la concentración de fósforo en agua. Fue identificado además, un cambio brusco en la tasa de aumento de la abundancia de cianobacterias después del año 2000, lo que resultó en niveles de alerta por encima de riesgo para la salud pública desde 2010. Los análisis estadísticos indicaron una fuerte y positiva correlación entre las cianobacterias y el área de cultivo en la cuenca, mientras que la precipitación, la temperatura y el flujo de agua fueron insignificantes. Estos resultados contribuyen a identificar que las prácticas agrícolas con alto aporte de nutrientes y el enriquecimiento de nutrientes son los principales impulsores de la formación de floraciones tóxicas. Estas prácticas ya están teniendo graves efectos en los ecosistemas acuáticos y la salud humana y las proyecciones sugieren que se intensificarán en el futuro. Para evitar una mayor degradación de la calidad del agua y el incremento de los riesgos para la salud de las generaciones futuras, se requerirá un cambio a gran escala (transfronterizo) en la gestión agrícola hacia prácticas agroecológicas.

Trajectory, fate, and magnitude of continental microplastic loads to the inner shelf: A case study of the world's largest coastal shallow lagoon.

The Patos Lagoon estuary is a highly significant ecosystem where freshwater from a vast and densely populated area continuously flows into the Atlantic Ocean by coastal plumes, exporting not only freshwater but also sediment, nutrients, plastics, and other contaminants. In this work, numerical modeling tools together with field data were used to assess for the first time the capacity of the coastal plume to export microplastics (MPs) to the inner shelf under different hydrodynamic conditions. Two field surveys were conducted during plume events to quantify MP concentrations and validate the model approach. A bottom-up approach was employed to estimate the potential MP export from the estuary's domain to the Atlantic Ocean. MP concentration in surface plume waters ranged from 0.20 items m-3 to 1.37 items m-3, confirmed by FTIR as synthetic polymers in a 90 %, being Polypropylene (PP) and Polyethylene (PE) the most abundant in a 73 %. The accumulation pattern was observed on the plume's frontal system, consistent with simulation results. The estimated average MP potential export rate attained 9.0 million items day-1 during moderate plume events and 47.5 million items day-1 during high discharge plume events. Strong discharge events, coupled with intense northeast winds, facilitated rapid southwestward export of MPs. Conversely, moderate to weak discharge events retained MPs closer to the estuary's mouth, enabling either longer trajectories or earlier deposition. Significant MP accumulation hotspots were identified in the gyre between the jetties and Cassino beach, as well as in the saline front within the plume boundaries. These accumulation zones may function as reservoirs for MP particles, potentially posing threats to local ecosystems. Understanding these dynamics is crucial for ongoing monitoring efforts to assess potential harmful interactions over time.

Tracing last millennium cycles of Río de la Plata Plume Water input into the Southwestern Atlantic Ocean.

Recent studies established a strong connection between instrumental hydroclimatic changes in the Río de la Plata (RdlP) watershed and the influx of continental terrigenous material and productivity changes. This correspondence was further validated for the last millennium. Here, we identified centennial, multi-decadal, and interannual changes in diatom composition, as a proxy for La Plata Plume Water (PPW) discharge into the inner shelf. Core GeoB13813-4 diatom data were revisited, and grouped into freshwater, marine, and brackish categories for multivariate, timeseries, and correlation analyses. Such record exhibits a noteworthy resemblance to paleoclimatic and paleoceanographic variations throughout the past millennium. A Detrended Correspondence Analysis (DCA) on the dominant taxa, and Axis-1 revealed a salinity gradient over the past millennium. DCA1-scores exhibited significant correlation with reconstructions of El Niño Southern Oscillation (ENSO), the Pacific Decadal Oscillation (PDO), and the Atlantic Multidecadal Oscillation (AMO) over the same period. By plotting DCA1-scores, we inferred time intervals with varying levels of PPW influence. During ∼936-1500 CE, the PPW influence was weak, as the record was dominated by marine taxa, indicating lateral transport from the Brazilian upwelled water and a stronger influence of the Subtropical Shelf Water. After 1500 CE, a well-developed plume was inferred, with the highest influence occurring after 1800 CE, as evidenced by an increased presence of freshwater/brackish taxa. This increased PPW influence after 1500 CE can be attributed to the onset of more humid conditions and associated increased river discharge, particularly under El Niño conditions, with further ENSO intensification after 1800 CE. We identified significant centennial (250 years) and multidecadal cycles (25-50 years) in diatom community composition. These cycles are related to solar forcing, PDO, and AMO. During the 20th Century, cycles of 2 to 7 years were associated with interannual ENSO variability, while 40-year cycles were linked to AMO and PDO variability.

Salt marshes as the final watershed fate for meso- and microplastic contamination: A case study from Southern Brazil.

Plastics pose a major threat to aquatic ecosystems especially in smaller size fractions. Salt marshes play a crucial role in maintaining the coastal zone and aquatic food web, yet their contamination, including by plastic materials, is still poorly investigated. This work investigated meso- (MEP, 5-25 mm) and microplastic (MIP, 1 µm-5 mm) contamination of a salt marsh, which reached average levels of 279.63 ± 410.12 items kg-1, 366.92 ± 975.18 items kg-1, and 8.89 ± 8.75 items L-1 in surface sediment, sediment cores and water, respectively. Photomicrographs revealed a complex fouling community on plastics surface for both different salt marsh zones and plastic formats. Abundance of plastics in sediment was higher in the dryer, vegetated zones compared to flooded, unvegetated zones. This is consistent with the role of vegetation as a trap for solid litter and final fate of plastic deposition, but also with local hydrodynamics influencing deposition pattern. Plastics were detected up to 66 cm-depth, presenting higher levels at surface sediments. It was also possible to identify the main groups of microorganisms (1638 bacterial cells, 318 microalgae cells, and 20049.93 µm2 of filamentous fungi) composing the Plastisphere communities on all plastic items recorded in the different zones. These results are a pioneer contribution, highlighting that regional salt marshes participate in sequestration and longstanding accumulation of plastic particles in estuarine environments, before exportation to the ocean.

Trophic assessment in South American Atlantic coastal lagoons: Linking water, sediment and diatom indicators.

Within two coastal shallow lagoons, trophic state was assessed by integrating water and sediment chemical indicators such as the TRIX and the benthic biopolymeric carbon (BPC) trophic indicator, altogether with biological environmental indicators (diatom species characterization). Spatial and temporal behavior of TRIX and BPC indices suggest that water column trophic indicators reflect rather short-term variations in water quality changes, while benthic trophic indicators rather reflect consistent long-term trends which make them useful as enduring indicators of eutrophication. Canonical Correspondence Analysis (CCA) showed that both sediment and transitional water trophic state indices increased eutrophic conditions with a decreasing salinity and increasing total nutrients. Diatom species associated with elevated eutrophic condition such as Staurosirella martyi, Staurosira breviestriata, Amphora copulata, Amphora veneta, Nitzschia sp., and Bacillaria paradoxa, showed a positive correlation with both trophic indices. We highlight the need for considering sediment eutrophication indicators towards in monitoring programmes within shallow coastal lagoons.

Discriminating sources and preservation of organic matter in surface sediments from five Antarctic lakes in the Fildes Peninsula (King George Island) by lipid biomarkers and compound-specific isotopic analysis.

Lakes are important paleoenvironmental archives retaining abundant information due to their typical high sedimentation rates and susceptibility to environmental changes. Here, we scrutinize the organic matter (OM) composition, origin and preservation state in surface sediments from five lakes in a remote, warming-sensitive, and poorly explored region partially covered by the retreating Collins Glacier in King George Island (Antarctica), the Fildes Peninsula. Lipid biomarkers of terrestrial origin (i.e. high-molecular weight n-alkanes, n-alkanoic acids, and n-alkanols; ß-sitosterol, campesterol, and stigmasterol) were detected in the five Fildes Lakes, with the smallest basin (i.e., Meltwater) showing a particularly strong moss imprint. Aquatic source indicators such as low C/N and terrestrial over aquatic ratios (TAR), or less negative δ13C values were preferentially found in the mid-sized lakes (i.e., Drake and Ionospheric). Sedimentary carbon in the larger lakes (i.e., Uruguay and Kitezh) displayed a largely biogenic origin (i.e., values of carbon preference index, CPI, ≫1), whereas the three lakes close to Collins Glacier (i.e., Drake, Meltwater, and Ionospheric) showed certain contribution from petrogenic sources (CPI ~ 1). The results suggest that the geochemical signature of the surface sediments in the five Fildes lakes is determined by factors such as the distance to the retreating Collins Glacier, the proximity to the coast, or the lake depth. This study illustrates the forensic interest of combining lipid biomarkers, compound-specific isotopic analysis, and bulk geochemistry to reconstruct paleoenvironments and study climate-sensitive regions.

A multi-molecular marker assessment of organic pollution in shore sediments from the Río de la Plata Estuary, SW Atlantic.

Organic pollution was evaluated in surface sediments along the middle portion of the Río de la Plata Estuary, SW Atlantic. A multi-molecular marker approach was performed to identify major sources of organic compounds using diagnostic indices. The relative contribution of different sources of hydrocarbons was quantified by source apportionment employing Principal Component Analysis/Multiple Linear Regression (PCA/MLR) as chemometric technique. All molecular markers indicated high chronic organic pollution in the stations of Montevideo Bay. Main sources of aliphatic and polycyclic aromatic hydrocarbons were petroleum inputs and combustion, due to oil transport and refinement, harbour activities and vehicular emissions. Major sources of linear alkylbenzenes and steroids were industrial and domestic sewage. Although, significant anthropogenic inputs, a natural footprint of terrestrial higher plants contribution was recognized. Multi-molecular marker and comprehensive assessments can improve the establishment of more precise regulation actions to reduce pollution levels.

Apertura comercial y medio ambiente / Trade globalization and environment

Si bien hasta ahora el sistema de comercio se ha desarrollodo en forma independiente del sistema de protección ambiental, se están produciendo importantes esfuerzos para compatibilizar los objetivos de ambos. Estan comprometidas en esta tarea organizaciones internacionales globales, como la Organización Mundial del Comercio (OMC), instrumentos como el Tratado de Libre Comercio de América del Norte (TLCAN) y las convenciones internacionales sobre el medio ambiente que se han realizado en los últimos diez años. La relación entre comercio internacional y medio ambiente será uno de los ejes obligados de la política exportadora para los países latinoamericanos durante la presente década. En estos países se ha ido consolidando un modelo de desarrollo basado en el crecimiento de las exportaciones, por lo que sus economías se verán enfrentadas al desafío de cumplir con los estándares ambientales, por lo general más estrictos en los países compradores. En el contexto de la inserción de los países de América Latina en los mercados internacionales, el tema ambiental no ha sido, hasta ahora, tratado con la profundidad que se requiere. Esto se traduce en la escasez de estudios sobre las relaciones entre inserción global y medio ambiente, en una actitud pasiva a las exigencias externas y en la ausencia de un perfil ambiental congruente con el sistema natural, económico y social. El desarrollo de este último es indispensable para poder continuar con el proceso de inserción global, lo que implica reconocer tanto las realidades institucionales y legales del país, como el manejo y potencialidades de sus recursos naturales. Todo indica que la búsqueda de los consensos entre comercio y medio ambiente es la tendencia que predominará en la proxima década