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Freshwater discharge affects the biogeochemistry of river-influenced nearshore environments by contributing with carbon and nutrients. An increase in human activities in river basins may alter the natural riverine nutrients and carbon export to coastal ecosystems. Along a wide latitudinal range (32°55′S-40°10′S), this study explores the role of climate and land use in determining the nutrient and carbon concentrations in the river mouth and fluxes to adjacent coastal areas. Between winter 2011 and fall 2012, we collected monthly samples in five river mouths in central southern Chile and at rocky shore sites affected by river plumes. Basins were characterized by different land uses and meteorological conditions along this latitudinal range. Water samples were collected for pH measurements, nutrients, dissolved organic and inorganic carbon, particulate organic carbon, and isotopic signatures (δ 13 C). Our results show a north-south gradient in concentrations of nutrients and carbon. The highest concentrations were observed in the Maipo basin, which presents the highest percentage of urban-industrial activities. Nutrients and carbon contributions, in most cases, were lowest in the southern Valdivia basin, which has the least human intervention and a greater percentage of vegetation. The Biobío River had the highest nutrient and carbon fluxes, in most cases, due to its high river discharge. Our results show the influence of river plume effects on carbon and nitrogen concentrations in river-influenced rocky shore sites. Moreover, our study suggests that land use might influence some parameters of carbonate system in rivers and river-influenced rocky shore environments. River-influenced rocky shore environments may exhibit suppression in aragonite saturation state with implications for calcifiers inhabiting these marine environments.

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A combined data set, combining data from field campaigns and oceanographic cruises, was used to ascertain the influence of both river discharges and upwelling processes, covering spatial and temporal variation in dissolved inorganic carbon (DIC) and aragonite saturation state. This work was conducted in one of the most productive river-influenced upwelling areas in the South Pacific coasts (36°S). Additionally, further work was also conducted to ascertain the contribution of different DIC sources, influencing the dynamics of DIC along the land-ocean range. Six sampling campaigns were conducted across seven stations at the Biobío River basin, covering approximately 200 km. Three research cruises were undertaken simultaneously, covering the adjacent continental shelf, including 12 sampling stations for hydrographic measurements. Additionally, six stations were also sampled for chemical analyses, covering summer, winter, and spring conditions over 2010 and 2011. Our results evidenced that seaward extent of the river plume was more evident during the winter field campaign, when highest riverine DIC fluxes were observed. The carbonate system along the river-ocean continuum was very heterogeneous varying over spatial and temporal scales. High DIC and pCO 2 were observed in river areas with larger anthropogenic effects. CO 2 supersaturation at the river plume was observed during all campaigns due to the influence of low pH river waters in winter/spring and high-pCO 2 upwelling waters in summer. δ 13 C DIC evidenced that main DIC sources along the river and river plume corresponded to the respiration of terrestrial organic matter. We have linked this natural process to the carbonate saturation on the adjacent river-influenced coastal area, suggesting that Ω aragonite undersaturation in surface/subsurface waters is largely modulated by the influence of both river discharge and coastal upwelling events in this productive coastal area. Conditions of low Ω aragonite might impact negatively physiological traits for marine organisms, such as bivalves, gastropods, and crustaceans. Therefore, local populations from river-influenced sites could be inherently more tolerant to ocean acidification than organisms living in regions with lower Ω aragonite variability. VARGAS ET AL.

Porphyridium cruentum is a unicellular microalga that can synthesize and secrete to the culture medium-high amounts of polysaccharides. In this study, the immunomodulatory, cytotoxic effect and antioxidant activity of the sulfated polysaccharides (PcSPs) were determinate. The PcSPs were precipitated with 2% Cetylpyridinium bromide hydrate and ethanol and purified by dialysis. The extract was lyophilized for its characterization by Fourier transform-Infrared (FT-IR) spectroscopy and gas chromatography–mass spectrometry (GC-MS). The antioxidant activity of PcSPs were examined with assay 2,2′-azino-bis (3-ethylbenzothiazoline-6-sulfonic acid) and compared with that of the biomass, observing significant differences between the results obtained from the PcSPs and biomass. To determine their ability to induce cytokine production Tumor Necrosis Factor alpha (TNF-α) and interleukina-6 (IL-6), the immunomodulatory activity of the PcSPs has been evaluated. In the mouse macrophage cell line (RAW 264.7), PcSPs are potent inducers of IL-6 cytokines but mainly of TNF-α. The cytotoxic capacity of PcSPs was measured by the MTT colorimetric assay in colorectal carcinoma (HTC-116), human leukemia (U-937 and HL-60), breast cancer (MCF-7), lung cancer (NCI-H460) and human gingival fibroblasts (HGF-1) cell lines. The IC50 value of 2311.20 µg mL−1, 1676.74 µg mL−1, 1089.63 µg mL−1, 5498.14 µg mL−1 and 2861.49 µg mL−1 respectively in the tumor lines and 5022.55 µg mL−1 in gingival fibroblasts were obtained. Our study suggested that PcSPs from P. cruentum have a moderate immunomodulatory and cytotoxic effect. The results obtained indicate that the polysaccharides from P. cruentum are potent inducers of IL-6 cytokines and, most importantly, of TNF-α. PcSPs showed no evidence of antigenic activity or hypersensitivity when administered intraperitoneally in mice. Furthermore, the in vivo study revealed an improvement of local inflammatory response against stress in the peritoneum. These findings suggest that the PcSPs from P. cruentum might have potential as a valuable ingredient in nutraceutical products.