Nutrients and not temperature are the key drivers for cyanobacterial biomass in the Americas.

Cyanobacterial blooms imperil the use of freshwater around the globe and present challenges for water management. Studies have suggested that blooms are trigged by high temperatures and nutrient concentrations. While the roles of nitrogen and phosphorus have long been debated, cyanobacterial dominance in phytoplankton has widely been associated with climate warming. However, studies at large geographical scales, covering diverse climate regions and lake depths, are still needed to clarify the drivers of cyanobacterial success. Here, we analyzed data from 464 lakes covering a 14,000 km north-south gradient in the Americas and three lake depth categories. We show that there were no clear trends in cyanobacterial biomass (as biovolume) along latitude or climate gradients, with the exception of lower biomass in polar climates. Phosphorus was the primary resource explaining cyanobacterial biomass in the Americas, while nitrogen was also significant but particularly relevant in very shallow lakes (< 3 m depth). Despite the assessed climatic gradient water temperature was only weakly related to cyanobacterial biomass, suggesting it is overemphasized in current discussions. Depth was critical for predicting cyanobacterial biomass, and shallow lakes proved more vulnerable to eutrophication. Among other variables analyzed, only pH was significantly related to cyanobacteria biomass, likely due to a biologically mediated positive feedback under high nutrient conditions. Solutions toward managing harmful cyanobacteria should thus consider lake morphometric characteristics and emphasize nutrient control, independently of temperature gradients, since local factors are more critical - and more amenable to controls - than global external forces.

Baseline assessment of the hydrological network and land use in riparian buffers of Pampean streams of Uruguay.

The integrated assessment of stream networks and terrestrial land use contributes a critical foundation for understanding and mitigating potential impacts on stream ecology. Riparian zone delineation and management is a key component for regulating water quality, particularly in agricultural watersheds. We present a national assessment of riparian zone land uses according to stream order for the entire hydrological network in the Uruguayan landscape in Southeastern South America. We classified over 82,500 km of streams and rivers in Uruguay into seven Strahler order classes and delineated riparian buffers of 100 and 500 m, depending on stream order, covering a total of 13% of the terrestrial land area in Uruguay. Natural vegetation cover in riparian zones averaged 77% among basins, whereby natural grassland dominated first and second order stream buffers at 58% and 49%, respectively. This highlighted the importance of grasslands in headwater regions of the country. Riparian forests formed corridors along larger streams, representing a mere 9% of buffers in first order streams but reaching 46% of buffers of 6th order streams. Among the six major basins of Uruguay, we found differences in the relative importance of riparian forests and crop cover in headwater stream riparian zones, as well as differences in relative crop cover within riparian zones. Results show that streams in subtropical grassland landscapes originate in open grassland environments, which has major implications for thermal regimes, carbon inputs, and stream biodiversity. Riparian buffer management should consider geographic differences among different basins and ecoregions within Uruguay.

Nuisance phytoplankton transport is enhanced by high flow in the main river for drinking water in Uruguay.

Eutrophication, climate change, and river flow fragmentation are the main cause of nuisance algal blooms worldwide. This study evaluated the conditions that trigger the growth and occurrence of nuisance phytoplankton in the Santa Lucía River, a subtropical floodplain lotic system that supplies drinking water to 60% of the population of Uruguay. The main variables that explained phytoplankton biovolume were extracted from generalized linear models (GLM). The potential impact of nuisance organism advection on water utility was estimated by the phytoplankton biovolume transport (BVTR, m3 day-1), an indicator of biomass load. Santa Lucía River had a wide flow range (0.7×105-1438×105 m3 day-1) and eutrophic conditions (median, TP: 0.139 mg L-1; TN: 0.589 mg L-1). GLMs indicated that phytoplankton biomass increased with temperature and soluble reactive phosphorus. Contrary to expectations, the presence of cyanobacteria was positively associated with periods of high flow that result in high cyanobacterial biovolume transport, with a probability of 3.35 times higher when flow increased by one standard deviation. The cyanobacterial biovolume transported (max: 9.5 m3 day-1) suggests that biomass was subsidized by allochthonous inocula. Biovolume from other nuisance groups (diatoms, cryptophytes, and euglenophytes) was positively associated with low-flow conditions and high nutrient concentrations in the main river channel, thereby indicating that these conditions boost eukaryote blooms. The evaluation of BVTR allows a better understanding of the dynamics of fluvial phytoplankton and can help to anticipate scenarios of nuisance species transport.

Assessing the origin of a massive cyanobacterial bloom in the Río de la Plata (2019): Towards an early warning system.

The Río de la Plata estuary drains the second largest river basin of South America. The occurrence of frequent cyanobacterial blooms of the Microcystis and Dolichospermum complex in the Uruguayan coast are associated with high flows of Uruguay River due to rainy years. In summer 2019, a massive cyanobacterial bloom reached up to the Uruguayan Atlantic coast. This study seeks to unveil the origin and the environmental conditions that favored the occurrence of the last cyanobacterial bloom in the Río de la Plata, and to contribute with the development of an early warning system of cyanobacterial scum on Montevideo beaches. A complementary approach was applied with Sentinel-2 imagery, environmental data of monitoring programs of Salto Grande Reservoir and Montevideo beaches, hydro-meteorological information, and hydroelectric dam operation. Images were analyzed with the Normalized Difference Chlorophyll Index (NDCI), which allowed evaluating several water bodies within the same ranges. Positive anomalous rainfall increased river flows, particularly that of Uruguay and Negro rivers, which caused the opening of the dam spillways. NDCI maps showed that areas with high values (NDCI>0.06) in Salto Grande reservoir kept a similar surface area before and after the prolonged overflow period (8.7-7.8 km2, before and after). In the Río Negro reservoirs, however, NDCI>0.06 coverage remarkably changed (62.5 km2, Palmar reservoir), with a subsequent 56-fold reduction in the post-discharge of surface water. Twenty days after opening the spillways, Montevideo beaches were closed to swimming and the NDCI>0.06 surface reached 51.7 km2 in the Río de la Plata coast. The dynamics of NDCI areas, the downstream bloom discharge, and the predicted Río de la Plata residual currents, suggest that the cyanobacterial bloom originated in the Negro River (Palmar reservoir). This bloom event was one of the worst that occurred in the Río de la Plata in last 20 years, circulated along the Uruguayan sub-corridor to the Atlantic coast along 690 km from its origin, and lasted three months on Montevideo coast. This is the first study that addresses the impact of cyanobacterial blooms from the Negro River reservoirs on the Río de la Plata estuary. Therefore, the Negro River basin is where the main efforts should be directed to mitigate massive cyanobacterial blooms.

Temperature and precipitation shape the distribution of harmful cyanobacteria in subtropical lotic and lentic ecosystems.

Cyanobacterial blooms are expected to become more frequent in freshwaters globally due to eutrophication and climate change effects. However, our knowledge about cyanobacterial biogeography in the subtropics, particularly in lotic ecosystems, is still very limited and the relationship of blooms to temperature and precipitation remains unclear. We took advantage of a comprehensive database of field data compiled over several years (1997 to 2015) to compare cyanobacteria biomass and distribution between lentic and lotic subtropical freshwaters (36 ecosystems, 30°-35°S) and to investigate the role of water temperature and precipitation as significant predictors in eutrophic ecosystems. A filamentous Nostocales, Dolichospermum (Anabaena), was the most widely distributed and frequent genus in the region of the study, followed by the colonial Microcystis, supporting observations of a global latitudinal pattern. Similar total cyanobacteria biovolumes (TCB) were found in lentic and lotic ecosystems, but the proportion of Dolichospermum was higher in lotic ecosystems. Using generalized linear models (GLMs), we found that temperature and rainfall explained 27% of the variation in TCB in lotic ecosystems, while temperature explained 19 and 28% of Dolichospermum and Microcystis biovolume, respectively. In lentic ecosystems, accumulated rainfall explained 34% of the variation of Microcystis biovolume while temperature explained 64%. Our results imply that the increase in extreme meteorological events and temperature predicted by climate models will promote increasingly severe cyanobacterial blooms in eutrophic subtropical freshwaters. Our analysis provides new information about the occurrence of bloom-forming cyanobacteria for southeastern South America and thus fills an important knowledge gap for subtropical freshwaters.

Magnetic resonance imaging in the pre-operative evaluation of obstructive epiphora: true-FISP and VIBE vs gadolinium.

PURPOSE: To assess unenhanced magnetic resonance imaging (MRI) in the preoperative evaluation of obstructive epiphora in patients undergoing dacryocystorhinostomy (DCR) and in particular, to evaluate the efficacy of this technique in the detection of the exact level of obstruction occurring in the naso-lachrymal duct (NLD). The correct identification and characterization of the NLD and its obstructions lead to a more effective surgery, preventing recurrent dacryocystitis after the surgical treatment. METHODS: From January 2009 to December 2014, 127 obstructive epiphoras were diagnosed and treated in 127 patients (35 M, 92 F; mean age 60.7 ± 7.48 years, range 42-75 years) with endoscopic DCR, in a IRB-approved protocol. To precisely define the morphology of the NLD and the site of obstruction, some of these patients (67/127) underwent unenhanced 1.5-T MR with TrueFISP and VIBE sequences, while the remaining (60/127) underwent Gadolinium-enhanced 1.5-T MR. Afterwards, surgery checked the real site of obstruction in both groups of patients (enhanced and unenhanced MR), with surgical outcomes matched with previous MR reports. RESULTS: In all cases, unenhanced MRI was able to detect the exact site of obstruction along the NLD, allowing a correct planning of surgical endoscopic procedures. On the contrary, enhanced MRI wrongly diagnosed six patients with proximal stenosis (6/60, 10.0%) as intermediate NLD obstruction. Unenhanced MRI was found to be more accurate than enhanced MRI with a statistical significant difference (p value = 0.0256) and obviously cheaper and easier to perform. All imaging reports were verified with surgery. The correct identification of the level of obstruction allowed successful surgery in around 73% (93/127) of patients, who had no recurrence during 6-month follow-up. CONCLUSION: In patients with epiphora, unenhanced MR showed to be highly reliable and even more effective than enhanced MR in the preoperative characterization of NLD stenosis, with no need of performing complex, time-wasting and expensive procedures for the administration of topical contrast media.

Peptidomic approach based on combined capillary isoelectric focusing and mass spectrometry for the characterization of the plasmin primary products from bovine and water buffalo beta-casein.

The main peptides produced by hydrolysis of water buffalo beta-casein with plasmin were characterized by capillary electrophoresis and mass spectrometry and compared with their bovine homologous. A novel breakdown product arising from the hydrolysis of water buffalo beta-casein, originated by the presence of a plasmin-sensitive Lys bond at position 68 was identified, which was not present in bovine beta-casein. On the basis of this evidence, an improved procedure for the detection and the differentiation of the products of plasmin hydrolysis of bovine and water buffalo beta-casein by capillary isoelectric focusing was set-up. In the experimental conditions, the gamma-casein from the two species was efficiently separated. Comparison of the capillary electropherograms with those obtained by ultra-thin-layer isoelectric focusing, the reference method for routine analysis of plasmin digests of casein, suggests that capillary electrophoresis isoelectric focusing may constitute a successful alternative to the traditional slab gel electrophoresis analysis of plasmin digests of casein either for basic structural studies or for applications in the quality assessment of dairy products.