Effects of the Invasive Freshwater Mussel Limnoperna fortunei on Sediment Properties and Accumulation Rates

Since its introduction into South America around 1990, the freshwater bivalve Limnoperna fortunei (the golden mussel) has spread rapidly and is now a dominant component of the benthic and periphytic fauna in many rivers, lakes, and reservoirs. Sizable impacts of this nonindigenous species on nutrient recycling, plankton abundance and composition, and trophic relationships with fishes have been reported, but its effects on the sediments have received little attention. In this work, we use eighteen 20-L flow-through experimental units with and without mussels where changes in the mass and characteristics of the sediments accumulated throughout a yearly cycle in monthly, biannual, and annual intervals are analyzed. Experimental units with mussels yielded almost 2 times more sediments than units without mussels and contained significantly higher loads of organic matter and total N. Total P was not affected by the presence of mussels. Sediments accumulated in the biannual and annual experimental units agreed well with the yields of the monthly units, but the vertical stratification of organic matter, N, and P was unpatterned. Seasonal changes in the volume of total sediments, biodeposits, and their organic matter and N contents were positively associated with ambient water temperature and with intermediate (~150–250 NTU, nephelometric turbidity units) turbidity. Our results suggest that ecosystem-wide modifications in the living conditions of the benthic epifaunal and infaunal organisms in waterbodies invaded by the mussel are likely significant, although variable locally, regionally, and across taxa.Fil: Tokumon, Romina Andrea. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Museo Argentino de Ciencias Naturales “Bernardino Rivadavia”; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Ecología, Genética y Evolución de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Ecología, Genética y Evolución de Buenos Aires; ArgentinaFil: Boltovskoy, Demetrio. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Ecología, Genética y Evolución de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Ecología, Genética y Evolución de Buenos Aires; ArgentinaFil: Cataldo, Daniel Hugo. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Museo Argentino de Ciencias Naturales “Bernardino Rivadavia”; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Ecología, Genética y Evolución de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Ecología, Genética y Evolución de Buenos Aires; Argentin

The atomic gas of star-forming galaxies at z∼\sim0.05 as revealed by the Five-hundred-meter Aperture Spherical Radio Telescope

We report new HI observations of four z$\sim$0.05 star-forming galaxies undertaken during the commissioning phase of the Five-hundred-meter Aperture Spherical Radio Telescope (FAST). FAST is the largest single-dish telescope with a 500 meter aperture and a 19-Beam receiver. Exploiting the unprecedented sensitivity provided by FAST, we aim to study the atomic gas, via the HI 21cm emission line, in low-$z$ star-forming galaxies taken from the Valpara\'iso ALMA/APEX Line Emission Survey (VALES) project. Together with previous ALMA CO($J=1-0$) observations, the HI data provides crucial information to measure the gas mass and dynamics. As a pilot HI survey, we targeted four local star-forming galaxies at $z\sim0.05$. In particular, one of them has already been detected in HI by the Arecibo Legacy Fast ALFA survey (ALFALFA), allowing a careful comparison. We use an ON-OFF observing approach that allowed us to reach an rms of 0.7mJy/beam at a 1.7km/s velocity resolution within only 20 minutes ON-target integration time. We demonstrate the great capabilities of the FAST 19-beam receiver for pushing the detectability of the HI emission line of extra-galactic sources. The HI emission line detected by FAST shows good consistency with the previous ALFALFA results. Our observations are put in context with previous multi-wavelength data to reveal the physical properties of these low-$z$ galaxies. We find that the CO($J=1-0$) and HI emission line profiles are similar. The dynamical mass estimated from the HI data is an order of magnitude higher than the baryon mass and the dynamical mass derived from the CO observations, implying that the mass probed by dynamics of HI is dominated by the dark matter halo. In one case, a target shows an excess of CO($J=1-0$) in the line centre, which can be explained by an enhanced CO($J=1-0$) emission induced by a nuclear starburst showing high velocity dispersion.Comment: 5 pages, 3 figures, 2 appendix, A&A Letter accepte

Multiple flares and asymmetric broad emission lines in a recurring changing-look active galactic nucleus

\ua9 The Authors 2025. We report a case of a changing-look (CL) active galactic nucleus (AGN) at a redshift of z = 0.337, identified as J075947.73+112507.3 (hereafter J0759), which exhibits recurring changing-look (RCL) phenomena accompanied by extreme asymmetry in the broad emission-line profiles. J0759 was discovered through the CL-AGN project conducted with the Dark Energy Spectroscopic Instrument. The most recent CL event was confirmed with new spectroscopic observations obtained using the Big Telescope Alt-azimuthal. Variability trends observed in the optical and mid-infrared light curves reveal multiple flares, indicating four to six potential CL events over time. We decomposed the asymmetric broad Hα emission line into two components, which persist in both high and low states. The RCL events in J0759 are inconsistent with the obscuration model and are more likely driven by variations in the accretion rate. However, the physical mechanism underlying such rapid accretion-rate changes remains unclear