Correction: Exploring climate change on Twitter using seven aspects: Stance, sentiment, aggressiveness, temperature, gender, topics, and disasters.

[This corrects the article DOI: 10.1371/journal.pone.0274213.].

Time series and regression methods for univariate environmental forecasting: An empirical evaluation.

One of the most common and valuable applications of science to the environment is to forecast the future, as it affects human lives in many aspects. However, it is not yet clear which methods -conventional time series or regression- deliver the highest performance in univariate time series forecasting. This study attempts to answer that question with a large-scale comparative evaluation that includes 68 environmental variables over three frequencies (hourly, daily, monthly), forecasted in one to twelve steps into the future, and evaluated over six statistical time series and fourteen regression methods. Results suggest that the strongest representatives of the time series methods (ARIMA, Theta) exhibit high accuracies, but certain regression methods (Huber, Extra Trees, Random Forest, Light Gradient Boosting Machines, Gradient Boosting Machines, Ridge, Bayesian Ridge) deliver even more promising results for all forecasting horizons. Finally, depending on the specific use case, the suitable method should be employed, as certain methods are more appropriate for different frequencies and some have an advantageous trade-off between computational time and performance.

Biotreatment efficiency, degradation mechanism and bacterial community structure in an immobilized cell bioreactor treating triclosan-rich wastewater.

Biotreatment of triclosan is mainly performed in conventional activated sludge systems, which, however, are not capable of completely removing this antibacterial agent. As a consequence, triclosan ends up in surface and groundwater, constituting an environmental threat, due to its toxicity to aquatic life. However, little is known regarding the diversity and mechanism of action of microbiota capable of degrading triclosan. In this work, an immobilized cell bioreactor was setup to treat triclosan-rich wastewater. Bioreactor operation resulted in high triclosan removal efficiency, even greater than 99.5%. Nitrogen assimilation was mainly occurred in immobilized biomass, although nitrification was inhibited. Based on Illumina sequencing, Bradyrhizobiaceae, followed by Ferruginibacter, Thermomonas, Lysobacter and Gordonia, were the dominant genera in the bioreactor, representing 38.40 ± 0.62% of the total reads. However, a broad number of taxa (15 genera), mainly members of Xanthomonadaceae, Bradyrhizobiaceae and Chitinophagaceae, showed relative abundances between 1% and 3%. Liquid Chromatography coupled to Quadrupole Time-Of-Flight Mass Spectrometry (LC-QTOF-MS) resulted in the identification of catabolic routes of triclosan in the immobilized cell bioreactor. Seven intermediates of triclosan were detected, with 2,4-dichlorophenol, 4-chlorocatechol and 2-chlorohydroquinone being the key breakdown products of triclosan. Thus, the immobilized cell bioreactor accommodated a diverse bacterial community capable of degrading triclosan.

Exploring climate change on Twitter using seven aspects: Stance, sentiment, aggressiveness, temperature, gender, topics, and disasters.

How do climate change deniers differ from believers? Is there any correlation between human sentiment and deviations from historic temperature? We answer nine such questions using 13 years of Twitter data and 15 million tweets. Seven aspects are explored, namely, user gender, climate change stance and sentiment, aggressiveness, deviations from historic temperature, topics discussed, and environmental disaster events. We found that: a) climate change deniers use the term global warming much often than believers and use aggressive language, while believers tweet more about taking actions to fight the phenomenon, b) deniers are more present in the American Region, South Africa, Japan, and Eastern China and less present in Europe, India, and Central Africa, c) people connect much more the warm temperatures with man-made climate change than cold temperatures, d) the same regions that had more climate change deniers also tweet with negative sentiment, e) a positive correlation is observed between human sentiment and deviations from historic temperature; when the deviation is between -1.143°C and +2.401°C, people tweet the most positive, f) there exist 90% correlation between sentiment and stance, and -94% correlation between sentiment and aggressiveness, g) no clear patterns are observed to correlate sentiment and stance with disaster events based on total deaths, number of affected, and damage costs, h) topics discussed on Twitter indicate that climate change is a politicized issue and people are expressing their concerns especially when witnessing extreme weather; the global stance could be considered optimistic, as there are many discussions that point out the importance of human intervention to fight climate change and actions are being taken through events to raise the awareness of this phenomenon.

Ecological risk assessment of heavy metals in the sediments of a Mediterranean lagoon complex.

This study examines the heavy metal contamination in the surface sediments of six coastal lagoons in Northern Greece (Nestos River and Vistonikos complexes) in relation to particle size distribution, organic carbon, total phosphorus and total Kjeldahl nitrogen. Furthermore, the contamination degrees and the ecological risks were assessed using different indicators. The study of heavy metals in lagoon's sediments is important in evaluating natural contamination against anthropogenic impact, and consequently, providing knowledge that could lead to management measures to reduce heavy metal environmental risks. Lafri Lagoon is characterized by the highest metal levels in all elements, while Agiasma and Porto Lagos by the lowest. Comparison of metal (As, Cd, Cr, Cu, Mn, Pb, Zn and Ni) levels with Sediment Quality Guidelines showed that As and Cr were found above the toxic effect threshold values. Potential toxicity (RI) seems influenced mostly by As and Cd. CD and PLI values classified the lagoons under study as "very highly contaminated" and "polluted", respectively.

Effect of Chlorination on Microbiological Quality of Effluent of a Full-Scale Wastewater Treatment Plant.

The evaluation of effluent wastewater quality mainly relies on the assessment of conventional bacterial indicators, such as fecal coliforms and enterococci; however, little is known about opportunistic pathogens, which can resist chlorination and may be transmitted in aquatic environments. In contrast to conventional microbiological methods, high-throughput molecular techniques can provide an accurate evaluation of effluent quality, although a limited number of studies have been performed in this direction. In this work, high-throughput amplicon sequencing was employed to assess the effectiveness of chlorination as a disinfection method for secondary effluents. Common inhabitants of the intestinal tract, such as Bacteroides, Arcobacter and Clostridium, and activated sludge denitrifiers capable of forming biofilms, such as Acidovorax, Pseudomonas and Thauera, were identified in the chlorinated effluent. Chloroflexi with dechlorination capability and the bacteria involved in enhanced biological phosphorus removal, i.e., Candidatus Accumulibacter and Candidatus Competibacter, were also found to resist chlorination. No detection of Escherichia indicates the lack of fecal coliform contamination. Mycobacterium spp. were absent in the chlorinated effluent, whereas toxin-producing cyanobacteria of the genera Anabaena and Microcystis were identified in low abundances. Chlorination significantly affected the filamentous bacteria Nocardioides and Gordonia, whereas Zoogloea proliferated in the disinfected effluent. Moreover, perchlorate/chlorate- and organochlorine-reducing bacteria resisted chlorination.

Seagrass and hydrographic data for the Mediterranean Sea.

The dataset includes 1,771 locations of major seagrass families (Cymodoceaceae, Zosteraceae, Posidoniaceae, Hydrocharitaceae, Ruppiaceae), which are further divided into the species they include, as well as 1,284 locations of seagrass absence (algorithmically produced), in the Mediterranean Sea. For each location, 217 biological, chemical, physics, and human related parameters are available, which were merged from other publicly available data sources. As the most comprehensive dataset for seagrass in the Mediterranean to date, it is suitable for data analysis and machine learning. For more insight, please see "Seagrass Detection in the Mediterranean: A Supervised Learning Approach" (Effrosynidis et al., 2018). The dataset is available on Mendeley Data (Effrosynidis, 2019).

Quality Indicators and Possible Ecological Risks of Heavy Metals in the Sediments of three Semi-closed East Mediterranean Gulfs.

Pollution with copper (Cu), lead (Pb), zinc (Zn), chromium (Cr), and nickel (Ni) heavy metals of the surface sediments collected from three semi-closed East Mediterranean Gulfs, namely Kavala, Strymonikos, and Ierissos Gulfs, North Aegean Sea, Greece, was investigated to evaluate potential benthic ecological risks. The mean concentrations of the studied metals decrease according to the order: Zn > Pb > Cr > Ni > Cu (176.50, 166.23, 127.41, 43.12, and 33.64 mg kg-1 dry weight). Quality indicators and possible ecological risks for metals in surface sediments were evaluated at 60 sampling sites of these three gulfs using the contamination factor (CF), the contamination degree (CD), the pollution load index (PLI), the geoaccumulation index (Igeo), the potential risk factor (PRFi), and the potential ecological risk index (PERI). Based on Igeo, the Ierissos Gulf sampling sites IER 2, 3, 7, and 9 exhibit moderate Pb pollution, whereas the sampling sites IER 6 and 8 show moderate to strong and strong Pb pollution, respectively. Based on the PRFi and PERI, the studied heavy metals did not pose any significant environmental risks for most of the investigated sites except IER 6 and 8 sampling sites, which may pose considerable environmental risk for Pb. To evaluate potential sources for each metal, multivariate techniques including hierarchical cluster analysis and ANOVA were used.

Suspended particulate matter estimates using optical and acoustic sensors: application in Nestos River plume (Thracian Sea, North Aegean Sea).

The present study investigates the use of combined methods of optical and acoustic sensors, in collaboration with direct in situ measurements, for the calibration and validation of a model transforming acoustic backscatter intensity series into suspended particulate matter (SPM) concentration datasets. The model follows previously elaborated techniques, placing particular attention to the parameterization of the acoustic absorption index as a function of water physical properties. Results were obtained from the annual deployment (during 2007-2008) of an upward-facing acoustic Doppler current profiler (ADCP) (307 kHz), equipped with a Wave Array, and an optical backscatter sensor (OBS), at the bottom of Thassos Passage near Nestos River plume (Thracian Sea, Northern Greece). The OBS was calibrated through linear regression, using 2007 and 2012 field sampling data, exhibiting an error of 13-14 % due to chlorophyll presence. The ADCP signal was calibrated through simultaneous measurements of backscatter intensity and turbidity profiles. Harmonic analysis on the model-produced SPM concentrations explained the tidal influence on their variability, especially during the summer. Empirical orthogonal functions analysis revealed the impact of waves and wave-induced currents on SPM variability. Finally, Nestos River sediment load was found uncorrelated to the SPM change in Thassos Passage, due to the dispersal and sediment deposition near the river mouth.

Water quantity and quality assessment of lower Nestos river, Greece.

Monitoring quantity and quality data of a 3-yr (2006-2009) survey in the lower reach of Nestos river are presented. For the purposes of this study, monitoring was taking place at six sites along the river course. Discharge measurements were made at four stations. Physicochemical parameters (i.e., electrical conductivity, pH, dissolved oxygen and water temperature) were measured in situ while water quality samples were collected on a bi-weekly basis at all six stations along the river. Water samples for chemical analyses were collected for the determination of total phosphorus, orthophosphate, nitrite and nitrate nitrogen, ammonia, biochemical oxygen demand (BOD), chemical oxygen demand (COD), chlorophyll-a, TSS, alkalinity, sulfuric and chloride anions, major cations (Na(+), K(+), Mg(+), Ca(+)) and metals. Two autographic telemetric stations also provided continuous stage and water quality data at two of the sites. ANOVA and t-test statistical analysis were used for the interpretation of the collected data. Nutrient concentrations were found within acceptable limits, while bicarbonates were the dominant ions. No significant seasonal and spatial variations were observed, suggesting little impact from human activities on the part of river basin under investigation.

Quantification of water, salt and nutrient exchange processes at the mouth of a Mediterranean coastal lagoon.

Vassova lagoon is a typical Mediterranean (small, shallow, micro-tidal, well-mixed) coastal lagoon, receiving limited seasonal freshwater inflows from direct precipitation and underground seepage. An intensive study was carried out in order to quantify the mechanisms responsible for the intra-tidal and residual transport of water, salt, nutrients and chlorophyll at the mouth of this lagoon and to assess the lagoon's flushing behavior. Results indicated that although the system is micro-tidal, tidal effects appeared to be the dominant factor for the longitudinal distribution of physical and chemical parameters, while the associated residual flow is also important and serves as a baseline measure of overall circulation. However, analysis of the net longitudinal currents and fluxes of water, salt and nutrients revealed the importance of non-tidal effects (wind effect and precipitation incidents) in the mean tidal transport. It is shown that the Eulerian residual currents transported water and its properties inwards under southern winds, while a seaward transport was induced during precipitation incidents and northern winds. The Stokes drift effect was found an order of magnitude lower than the Eulerian current, directed towards the lagoon, proving the partially-progressive nature of the tide. Nutrients and chlorophyll-alpha loads are exported from the lagoon to the open sea during the ebb phase of the autumn and winter tidal cycles, associated with the inflow of nutrient-rich freshwater, seeped through the surrounding drainage canal. The reverse transport occurs in spring and early summer, when nutrients enter the lagoon during the flood tidal phase, from the nutrient-rich upper layer of the stratified adjacent sea. Application of a tidal prism model shows that Vassova lagoon has a mean flushing time of 7.5 days, ranging between 4 to 18 days, affected inversely by the tidal oscillation.

Sediment and suspended matter lead contamination in the gulf of Kavala, Greece.

Sediment and suspended particulate matter samples from 24 stations in the Gulf of Kavala have been examined for lead contamination. Grain size analysis and organic matter content were also performed. Total -- anthropogenic sediment lead concentrations and enrichment factors at stations close to harbors and chemical industries were found higher (up to 209-135 micro g/g and 4.12 respectively), in relation to concentrations from the rest of the coastal zone. In the above areas, increased suspended particulate lead in the bottom of the water column was also recorded (up to 109 micro g/g). Total sediment lead concentrations composed of high natural Pb background increased with decreasing grain size, suggesting their association with the fine fractions of the sediments (31.1-66.0% mud presence) and the organic matter content (6-9% higher values). Overall, higher total lead concentrations in the sediments, determined by this work, appear to be significantly different from those reported for the Gulf of Kavala in previous studies and similar to those detected in other highly contaminated eastern Mediterranean coastal areas.