High Water Transparency Research Articles

Ecological impacts of freshwater algal blooms on water quality, plankton biodiversity, structure, and ecosystem functioning

Harmful algal blooms are among the emerging threats to freshwater biodiversity that need to be studied further in the Anthropocene. Here, we studied freshwater plankton communities in ten tropical reservoirs to record the impact of algal blooms, comprising different phytoplankton taxa, on water quality, plankton biodiversity, and ecosystem functioning. We compared water quality parameters (water transparency, mixing depth, pH, electrical conductivity, dissolved inorganic nitrogen, total dissolved phosphorus, total phosphorus, chlorophyll-a, and trophic state), plankton structure (composition and biomass), biodiversity (species richness, diversity, and evenness), and ecosystem functioning (phytoplankton:phosphorus and zooplankton:phytoplankton ratios as a metric of resource use efficiency) through univariate and multivariate analysis of variance, and generalized additive mixed models in five different bloom categories. Most of the bloom events were composed of Cyanobacteria, followed by Dinophyta and Chlorophyta. Mixed blooms were composed of Cyanobacteria plus Bacillariophyta, Chlorophyta, and/or Dinophyta, while non-bloom communities presented phytoplankton biomass below the threshold for bloom development (10 mg L−1, WHO alert level 2). Higher phytoplankton biomasses were recorded during Cyanobacteria blooms (15.87–273.82 mg L−1) followed by Dinophyta blooms (18.86–196.41 mg L−1). An intense deterioration of water quality, including higher pH, eutrophication, stratification, and lower water transparency, was verified during Cyanobacteria and mixed blooms, while Chlorophyta and Dinophyta blooms presented lower pH, eutrophication, stratification, and higher water transparency. All bloom categories significantly impacted phytoplankton and zooplankton structure, changing the composition and dominance patterns. Bloom intensity positively influenced phytoplankton resource use efficiency (R2 = 0.25; p < 0.001), while decreased zooplankton resource acquisition (R2 = 0.51; p < 0.001). Moreover, Cyanobacteria and Chlorophyta blooms negatively impacted zooplankton species richness, while Dinophyta blooms decreased phytoplankton richness. In general, Cyanobacteria blooms presented low water quality and major threats to plankton biodiversity, and ecosystem functioning. Moreover, we demonstrated that biodiversity losses decrease ecosystem functioning, with cascading effects on plankton dynamics.

&lt;p&gt;&lt;strong&gt;&lt;em&gt;Brachysira&lt;/em&gt;&lt;/strong&gt;&lt;strong&gt; &lt;em&gt;aristidesii&lt;/em&gt; &lt;em&gt;sp. nov.&lt;/em&gt; (Bacillariophyceae, Brachysiraceae): a new species from oligotrophic and mesotrophic tropical reservoirs in southeastern Brazil&lt;/strong&gt;&lt;/p&gt;

A new diatom species, Brachysira aristidesii sp. nov., is described from three oligotrophic and mesotrophic reservoirs in Piracicaba River basin, State of São Paulo, Brazil. Descriptions are based on light and scanning electron microscopy. The new species is mainly characterized by rhombic-lanceolate valves with strongly capitated ends, filiform and straight raphe, narrow and linear axial area, slightly radiate striae and transapically elongated areolae. It is compared to Brachysira microcephala, B. silvicola, B. vitrea, B. neoexilis and Nupela brachysiroides. Our findings suggest that Brachysira aristidesii is a species mainly associated to high water transparency, low to moderate conductivity, slightly acidic and low nutrient environments.

Kecenderungan Naiknya Suhu Permukaan Laut dan Resiliensi Karang Setelah Kejadian Pemutihan Karang 2010 dan 2016 di Taman Wisata Perairan (TWP) Pulau Pieh, Padang, Sumatra Barat

&lt;strong&gt;Trend of Sea Surface Temperature Increase and Coral Resilience After Bleaching Events of 2010 and 2016 in The Marine Tourism Park (TWP) of Pieh Island, Padang, West Sumatra&lt;/strong&gt;. The coral bleaching event has hit almost all of Indonesia's waters at least 4 times (in the last 34 years), which the last two events (2010 and 2016) have been discussed rather deeply. However, detailed studies in a specific location, such as in Marine Tourism Park (TWP) of Pieh Island, Padang waters, West Sumatra Province that influenced by the water mass of Indian Ocean have not yet been studied. The aim of this paper is to examine the trend of sea surface temperatures (SST)’s increase in the TWP of Pieh Island in 2010 and 2016 coral bleaching, and the coral resilience after the events. In this study, the long-term SST data acquired from the Aqua MODIS satellite images were used intensively. Results show that the highest mean monthly SST called MMM that corals can be tolerated in the TWP of Pieh is 29.6 &lt;sup&gt;o&lt;/sup&gt;C, higher than in all Indonesian waters (29.1 &lt;sup&gt;o&lt;/sup&gt;C).The differences between the anomaly SST and the normal SST (MMM) or called Hot Spot (HS) has exceeded the average MMM in the 2010 bleaching event around 0.4-0.5 &lt;sup&gt;o&lt;/sup&gt;C with its peak in April, and with alert-1 severity (Degree Heating Weeks (DHW) &amp;lt; 8 &lt;sup&gt;o&lt;/sup&gt;C-weeks; which means that the coral has partial bleaching with patchy pattern).In 2016, the HS increased by an average of 0.5 ~ 1.0 &lt;sup&gt;o&lt;/sup&gt;C with peaks in January-February and May-June and with the severity of Alert-2 (DHW ≥ 8 &lt;sup&gt;o&lt;/sup&gt;C-weeks, which means corals experienced severe bleaching, over wider areas, and some of corals are died). One year earlier (2015), higher HS with an average value of 0.3-0.8 &lt;sup&gt;o&lt;/sup&gt;C and DHW ~ 4 &lt;sup&gt;o&lt;/sup&gt;C-weeks were also observed. This indicates that coral bleaching events in the TWP of Pieh Island is repeated and occurs for long periods.The trend of increasing SST in this TWP is 0.23&lt;sup&gt;o&lt;/sup&gt;C/decade, lower than in the all Indonesian waters (0.36 &lt;sup&gt;o&lt;/sup&gt;C/decade). This trend shows that coral reefs in Indonesian waters including this TWP have a high resilience to recover themselves from bleaching, since the trend of increasing SST &amp;lt; 1.0 &lt;sup&gt;o&lt;/sup&gt;C/decade of the 11 coral resilience key factors, positive factors that support high coral resilience are low pollution/nutrients, low sedimentation (high water transparency), and low unfriendly of human activities, while the most negative one is the explosion of crown-of-thorns starfish, Acanthaster planci population as well as coral disease.

Zooplankton functional traits as a tool to assess latitudinal variation in the northern-southern temperate European regions during spring and autumn seasons

Abstract Zooplankton structure may serve as predictor of a multiplicity of environmental conditions, including long-scale distance between shallow water bodies. Two different categories of zooplankton indices (1/ biocoenotic indices, including dominating species; 2/ trait-based approaches, including ecological groups: littoral vs. pelagic community and functional feeding groups) were compared in small water bodies of two regions of Europe (1/ Northern water bodies (N-WB): Poland, and 2/ Southern water bodies (S-WB): Croatia). We hypothesized that latitudinal variation between these regions will result in distinguishing specific environmental factors that in turn affect the structure of zooplankton communities. In order to avoid weather extremes in both countries, we focused our research on less frequently investigated periods of the year; during the unvegetated and mild-temperature seasons (spring and autumn). Despite well pronounced differences in some abiotic characteristics of water between both regions (higher chlorophyll a and phosphorus contents in N-WB compared to better oxygenated waters and higher water transparency in S-WB) we observed rather uniform pattern with respect to zooplankton trait-based indices in N-WB and S-WB. This may have been caused by poor habitat heterogeneity due to macrophyte absence (spring) or decaying state (autumn) and poor food supply during the spring/autumn seasons. Planktonic and detrivorous rotifers (e.g. from genera Keratella and Brachionus) predominated in both countries. Ecological and trophic functional traits were mostly determined by the morphometric and trophic properties. Irrespective of latitudinal variation, water transparency emerged as a significant factor, negatively affecting zooplankton abundance, especially the dominating detrivorous rotifers, and positively littoral zooplankton. Moreover, an increase in water area, related to higher contents of nutrients and food resources, supported a higher abundance of the majority of zooplankton feeding guilds. Our results suggested that only at the level of taxa the distinctiveness between the two European regions, northern and southern, was clear. Apart from taxa dominating in both countries (Keratella cochlearis, Bosmina longirostris), Polyarthra spp. and Eudiaptomus gracilis dominated exclusively in Croatia and Cyclops sp. in Poland during the unvegetated and temperature-transitional seasons. This indicates that only the taxonomic approach, referring to certain dominating species, was a sensitive tool. Functional trait-based approaches, despite providing relevant information on the quality of aquatic ecosystems, are not sufficiently sensitive in identification of latitudinal variation of zooplankton in the spring/autumn season.

HOW LIMNOLOGICAL VARIABLES INFLUENCE THE OCCURRENCE AND ABUNDANCE OF A VISUAL PREDATOR IN AN INVADED RIVER-FLOODPLAIN SYSTEM

Environmental characteristics of an invaded environment can predict the invasion success of a species, depending on its habits and life strategies. Cichla kelberi is a visual and voracious predator introduced in the Upper Paraná River floodplain, an area that suffers with several upstream dams that caused many environmental changes over the years (e.g. increased water transparency). As this species is a pre-adapted species to environments that presents high water transparency, our main goal was to test the hypothesis that variables related to the underwater visibility would be important drivers of the successful invasion of C. kelberi in the Upper Paraná River floodplain. We predict that turbidity (proxy of water transparency) is one of the major limnological determinants of occurrence and abundance of C. kelberi. Individuals of the invasive species and seven limnological variables were sampled quarterly between February 2000 and November 2018. This long-term data is part of the sixth site of the Brazilian Long Term Ecological Program (PELD). We fitted two regression models to all occurrence and abundance data (response variables) against the limnological variables (explanatory variables). For occurrence data, we fitted a Generalized Linear Mixed Model and for abundance data, we fitted a Linear Mixed Effects Model. The occurrence data of C. kelberi showed that turbidity and dissolved oxygen were the variables that most influenced the presence of this species, negatively and positively, respectively. The abundance data showed that dissolved oxygen and concentration of chlorophyll-a were the ones that most influenced the abundance of this species, negatively and positively, respectively. Our findings showed that besides turbidity, other limnological variables were also determinants for the occurrence and abundance of C. kelberi . Therefore, our results provided important information about the main environmental drivers of the establishment process of C. kelberi in the Upper Paraná River floodplain.

COVID-19 lockdown measures reveal human impact on water transparency in the Venice Lagoon

The lagoon of Venice has always been affected by the regional geomorphological evolution, anthropogenic stressors and global changes. Different morphological settings and variable biogeophysical conditions characterize this continuously evolving system that rapidly responds to the anthropic impacts. When the lockdown measures were enforced in Italy to control the spread of the SARS-CoV-2 infection on March 10th 2020, the ordinary urban water traffic around Venice, one of the major pressures in the lagoon, came to a halt. This provided a unique opportunity to analyse the environmental effects of restrictions to mobility on water transparency. Pseudo true-colour composites Sentinel-2 satellite imagery proved useful for qualitative visual interpretation, showing the reduction of the vessel traffic and their wakes from the periods before and during the SARS-CoV-2 outbreak. A quantitative analysis of suspended matter patterns, based on satellite-derived turbidity, in the absence of traffic perturbations, allowed to focus on natural processes and the residual stress from human activities that continued throughout the lockdown. We conclude that the high water transparency can be considered as a transient condition determined by a combination of natural seasonal factors and the effects of COVID-19 restrictions.

Response of Zooplankton Indices to Anthropogenic Pressure in the Catchment of Field Ponds

As methods for assessing the environmental conditions in ponds are still not well developed, I studied zooplankton to identify a response of community indices to abiotic, biotic, and habitat type in two types of ponds differing in the level of human stress. Ponds of low human alterations (LowHI) harbored generally richer communities and a higher share littoral zooplankton, whose occurrence was associated with higher water transparency and complex macrophyte habitat, particularly the presence of hornworts and charoids. In high human-impact ponds (HighHI) planktonic communities prevailed. Their distribution was mainly related to the open water area and fish presence. Anthropogenic disturbance was also reflected in the frequency of rare species, which were associated with LowHI ponds. Higher diversity of zooplankton increased the chance for rare species to occur. Despite the fact that the majority of rare species are littoral-associated, they had no prevalence towards a certain ecological type of plants, which suggests that any kind of plant cover, even macrophytes typical for eutrophic waters (e.g., Ceratophyllum demersum) will create a valuable habitat for conservation purposes. Thus, it is postulated that a complex and dense cover of submerged macrophytes ought to be maintained in order to improve the ecological value of small water bodies.

Suppression of Phytoplankton Blooming in Water Bodies with the Use of Filtering Zooplankton in Flow-Through Ecosystems

The study has been focused on the population composition dynamics and trophic relationships of Simocephalus vetulus (O.F. Muller, 1776) in the absence of the food stress of ichthyofauna in flow-through ecosystems in Patriarshie Prudy pond. The role of S. vetulus species in the plant-eating zooplankton, the suppression of blooming, and the preservation of high water transparency have been assessed. The largest daily consumption of edible phytoplankton biomass by zooplankton under flowage has been shown to be 102.96 mg/L in late August at maximal biomass and dominating S. vetulus (up to 99.8% of the biomass of plant-eating zooplankton).

Measurement of temperature dependent absorption coefficient of water at 1064nm wavelength

Measurements of the water absorption coefficient at a laser wavelength of 1064 nm are reported as a function of water temperature. A low power laser beam was used as the probe. The measurement net procedure took into consideration the absorption of the cuvette, while it included detection of bubble formation on the walls of the measurement cuvette and in the water volume. The measurements indicate that the absorption coefficient of water slightly increases in the range of temperatures below 40 °C, reaches maximum and then significantly decreases in the range of temperatures 40 °C – 70 °C. The significant decrease of the temperature dependence of the absorption coefficient supports the supposition that a high transparency of water can be achieved.

Recovery of the Velky Bolevecky pond (Plzen, Czech Republic) via biomanipulation – Key study for management

Promotion of successful examples of biomanipulation and long-term monitoring is important for encouragement of similar activities, which are still relatively scarce. A project to improve water quality in the Velky Bolevecky pond (Plzeň, Czech Republic) began in 2006. The main activities in this project were: large scale fish reduction; stocking of predatory fish; usage of phosphorus binding coagulants; and reintroduction of macrophytes. During five years the impact of a eutrophic system with massive cyanobacterial blooms with low water transparency transformed into a clear water system with high water transparency and well developed macrophyte cover. All aspects relating to the ecological status of the water body such as total phosphorus concentration, chlorophyll-a concentration and cyanobacterial and other phytoplankton density improved significantly during or immediately after the project realization. For example, water transparency increased three fold. Zooplankton density also increased, however the difference was not significant. Oligotrophication of the system became evident also in the species composition of zooplankton and phytoplankton. Species adapted to nutrient reduction and macrophyte cover developed. Seven years after the project was over, the fish stock remained on the low densities naturally. A good ecological stage was achieved with low nutrient levels, high water transparency, very low densities of cyanobacteria and other phytoplankton together with a well-developed macrophyte cover. All of which has been maintained without any expensive impact. The highest expenditure is, paradoxically, due to macrophyte harvesting because their massive explosion in the pond is not in accordance with recreational and sporting utilization. It seems, that reduction of nutrient loading and switching of a formerly eutrophic system to an oligotrophic one is possible and sustainable over a relatively long time period in a shallow temperate pond. Subsequent good management of the system will, of course, be necessary.

Influence of environmental parameters on habitat preference of gelatinous zooplankton in various coastal ecosystems, the Straits of Malacca

This study examined spatial distribution patterns of gelatinous zooplankton in three coastal areas, namely Matang mangrove area (managed mangrove area, MMA), Kuala Selangor coastal waters (reclaimed mangrove area, RMA) and Port Dickson coastal waters (a resort area, PDC). In each area, non-gelatinous and gelatinous zooplankton samples were collected by horizontal tows of a plankton net (140μm mesh size) and a Bongo net (500μm mesh size). Various environmental parameters were measured in situ (temperature, dissolved oxygen, pH, turbidity) as well as analyzed in the laboratory (nutrients, chlorophyll-a , zooplankton). Nineteen hydromedusae, two siphonophore and two ctenophore species were recorded from three different areas. Matang mangrove (MMA) had the highest number of species (19 species), followed by RMA (13 species) and PDC (9 species). Gelatinous zooplankton density and biomass were significantly higher (p < 0.05) in MMA than the other areas. Different gelatinous zooplankton groups dominated in different areas with ctenophores as the most important group (Pukia sp. formed 79.0% of total gelatinous zooplankton) in MMA. The hydromedusae (55.0% was Eirene brevigona) was the most dominant group in RMA that had high total suspended solids, and siphonophores (58.0% was Lensia subtiloides) dominated PDC characterized by high water transparency. Biotic-environmental (BIO-ENV) analysis showed significant roles of turbidity, salinity, nutrients, chlorophyll-a and non-gelatinous zooplankton (p < 0.05) in the distribution of gelatinous zooplankton in these tropical coastal ecosystems. Two-way ANOSIM (analysis of similarities) showed that there were significant differences in gelatinous zooplankton amongst the three habitats. In terms of monsoonal seasons, the gelatinous zooplankton density showed significant differences (p < 0.05) between the southwest and northeast monsoons. This study illustrated that gelatinous zooplankton diversity and density varied with the degrees of habitat disturbance and seasonal changes, implying the potential impacts of anthropogenic activities and climate change on its community structure.

URRENT STATE OF THE ECOSYSTEM OF LAKE UROZERO, KARELIA, ASSESSED THROUGH PRIMARY PRODUCTION AND DESTRUCTION INDICATORS

Lake Urozero has the status of a regional-level state hydrological nature monument in the Republic of Karelia. Up until the mid-2000’s, the lake have been noted for very high water transparency and the ultra-oligotrophic state of the ecosystem. In 2018, the prima-ry production and destruction characteristics of the Urozero ecosystem were studied as integral indicators of the current state and direction of its functioning. Such assessments are necessitated by the modified climatic conditions in Karelia, which affect catchments. These changes result in enlarged flow of allochtonous organic matter to water bodies. The values of photosynthesis (average 22 μg C/l per day), chlorophyll a(average 1.6 μg/l), daily assimilation number (on average 21 μg C/μg Chl), P/B factor (average 1.2 days-1) and water transparency (average 9.8 m) were measured in May, July and September. These measurements confirm that the lake ecosystem has retained its ultra-oligotrophic state. In spring and summer, when solar radiation is excessive and water transparency is high, the vertical distribution of chlorophyll ashowed a pattern unusual for Karelia, with maximum values found at the depth of one transparency. The change in the values of or-ganic matter destruction down the water column corresponds to the vertical dynamics of chlorophyll a. This vertical distribution of the values of destruction, as well as the con-sistently high transparency of the lake water, indicates that allochtonous organic mat-ter does not affect the water ecosystem. The natural ecological state of Lake Urozero in the current circumstances of climate change in the catchment area and human pres-sure is retained owing to the absence of surface inflows and nature conservation mea-sures to counteract pollution.

Is there a zonation pattern in aquatic macrophytes communities in the aquatic environments of the Brazilian semiarid?

Communities of aquatic macrophytes are influenced by a series of biotic and abiotic factors that determine which species or life forms will colonize an aquatic environment. Different stretches may harbor a distinct macrophyte diversity within the same drainage basin in response to different local environmental conditions. Thus, we hypothesized a pattern of longitudinal zonation in macrophytes communities in the aquatic environments of the Brazilian semiarid. The study was carried out in the Apodi/Mossoro Hydrographic Basin, in the semiarid region of Rio Grande do Norte State in northeastern Brazil. Four sampling campaigns were carried out in quarterly intervals along 23 sampling sites distributed from the headwaters to the estuarine region. In each sampling station, the presence of macrophytes was recorded and water variables were measured; in addition, water samples were also collected for analyses and plant material was collected for identification. The macrophytes community as a whole did not show a well-established gradient, although some life forms could be related to specific patterns. Some species, such as Ceratophyllum submersum L., were restricted to environmental conditions of low nutrient levels and high water transparency, while others, such as Ipomoea fistulosa Choisy, were widely distributed. The zonation pattern of aquatic macrophytes was determined by different characteristics of the environment, which ranged from nutrient-rich waters to stretches with high salinity, evidencing the adaptations of each ecological group.

Assessment of trophic status of the northeastern Mediterranean coastal waters: eutrophication classification tools revisited.

The Eastern Mediterranean and its Cilician Basin offshore waters have oligotrophic features with low nutrient concentrations, low primary production, and high water transparency. However, the wide shelf area of the Cilician Basin is subject to contaminated river inflows with enhanced nutrient loads and direct discharges of urban wastewaters of southern Turkey, leading to develop local eutrophic/mesotrophic conditions in the inner sites of Mersin and Iskenderun Bays on the Cilician Basin. For the assessment of changing trophic status of the coastal and the bay water bodies under anthropogenic pressures since the 1980s, five extensive field studies were performed in summer and winter periods of 2014, 2015, and 2016. Physical and eutrophication-related biochemical parameters (salinity, temperature, Secchi Disk Depth, nutrients, dissolved oxygen, chlorophyll-a) were measured at 65 stations in different water bodies occupying the Northeastern (NE) Mediterranean coastal, offshore areas and bays. The collected data sets were used in scaling the trophic status of the visited water bodies of NE Mediterranean coastal, offshore areas and semi-enclosed bays, using novel classification tools of Trophic Index (TRIX), Eutrophication Index (E.I.), chl-a, and HELCOM Eutrophication Assessment Tool (HEAT), developed by different experts for highly productive seas. These tools, which can successfully classify highly productive coastal water masses under human pressures, and their sensitivities have been tested for scaling of the current trophic status of the NE Mediterranean coastal water bodies being subject to human pressures. The scaling results of classical TRIX, E.I., and chl-a indices in the NE Mediterranean water masses are not sensitive enough to differentiate mesotrophic and eutrophic water bodies because these indices principally assume to have higher concentrations of eutrophication-related parameters in the least effected (reference) water bodies. The HEAT tool, which uses a site-specific "reference value" for each eutrophication-indicator, has allowed us to produce more reliable and sensitive scaling of the current trophic status of the NE Mediterranean shelf areas, even though we used only the "reference values" derived from the composite data sets. The results of the indices were compared with the HEAT tool and the actual status was assessed from observations, indicating revision requirements of the multi-metric classification tools. For this goal, scales of natural (oligotrophic) and anthropogenic (eutrophic) levels of eutrophication indicators should be determined at a sub-basin scale using long-term site-specific observations in the NE Mediterranean. The revised scale ranges of TRIX for oligotrophic, mesotrophic, and eutrophic water bodies of Mersin Bay are in line with ranges of TRIX classification tool proposed for Aegean Sea waters, which can be used to assess trophic status of the entire Eastern Mediterranean and Aegean coastal seas (surface salinity > 37.5) having oligotrophic properties in the offshore waters.

Phytoplankton species interactions and invasion by Ceratium furcoides are influenced by extreme drought and water-hyacinth removal in a shallow tropical reservoir

This study explored the interactions of phytoplankton species during the invasion of Ceratium furcoides and the environmental variables that contributed to its establishment and ecological success in a shallow eutrophic reservoir (Garcas Reservoir, southeast Brazil), which has been monitored monthly for 20 years (1997–2017). The Ceratium furcoides invasion in September 2014 was preceded by disturbance events (macrophyte removal and a historical drought period), which disrupted the dominance of cyanobacteria by modifying resource availability (high water transparency and soluble reactive phosphorus concentrations) and recruiting other species. Ceratium blooms at the water surface were preceded by high abundance near the bottom, suggesting the importance of the propagule bank. However, the pattern of Ceratium-Microcystis coexistence that is usually recorded in temperate lakes was not observed. Instead, Ceratium replaced Cylindrospermopsis raciborskii in mixing periods with high light and nitrogen availabilities, significantly influencing the abundance of Trachelomonas spp. Flagellated forms became dominant in the Garcas Reservoir, due to the higher water transparency and relatively lower water-column stability, and alternative states between Ceratium-Trachelomonas in mixing periods and Microcystis-Cryptomonas in stratified periods have been repeated. Since then, cyanobacterial dominance ceased, and the “skillful” Ceratium apparently has come to stay, influencing interactions among phytoplankton species.

Controllable Synthesis of Gold Nanorod/Conducting Polymer Core/Shell Hybrids Toward in Vitro and in Vivo near-Infrared Photothermal Therapy.

Photothermal therapy (PTT) is a minimally invasive tumor treatment technology, and is regarded as a potential anticancer strategy because of its targeted destruction and low toxicity. Specifically, near-infrared light-induced PTT has attracted intriguing interest because of the high transparency of tissue, blood, and water. However, effective PTT generally requires the assistance of photothermal agents. Gold nanorods (GNRs) and conducting polymer are often used as photothermal materials because of their high absorption efficiency and photothermal conversion efficiency. Herein, we combined GNRs with poly( o-methoxyaniline) (POMA, a polyaniline derivative) to form GNRs/POMA core/shell hybrids through the surfactant-assisted chemical oxidative polymerization route and studied their photothermal conversion properties. The configuration of GNRs/POMA core/shell hybrids has been precisely controlled through adjusting the monomer concentration, and the relationship between morphology and absorption band of GNRs/POMA core/shell hybrids has been revealed. Finally, the in vitro and in vivo experiments were performed, and the results indicated that the GNRs/POMA core/shell hybrids with optimized absorbance at around 808 nm exhibited the best performance on photothermal therapy under 808 nm NIR laser irradiation.

Close Link Between Harmful Cyanobacterial Dominance and Associated Bacterioplankton in a Tropical Eutrophic Reservoir.

Cyanobacteria tend to become the dominant phytoplankton component in eutrophic freshwater environments during warmer seasons. However, general observations of cyanobacterial adaptive advantages in these circumstances are insufficient to explain the prevalence of one species over another in a bloom period, which may be related to particular strategies and interactions with other components of the plankton community. In this study, we present an integrative view of a mixed cyanobacterial bloom occurring during a warm, rainy period in a tropical hydropower reservoir. We used high-throughput sequencing to follow temporal shifts in the dominance of cyanobacterial genera and shifts in the associated heterotrophic bacteria community. The bloom occurred during late spring-summer and included two distinct periods. The first period corresponded to Microcystis aeruginosa complex (MAC) dominance with a contribution from Dolichospermum circinale; this pattern coincided with high water retention time and low transparency. The second period corresponded to Cylindrospermopsis raciborskii and Synechococcus spp. dominance, and the reservoir presented lower water retention time and higher water transparency. The major bacterial phyla were primarily Cyanobacteria and Proteobacteria, followed by Actinobacteria, Bacteroidetes, Verrucomicrobia, and Planctomycetes. Temporal shifts in the dominance of cyanobacterial genera were not only associated with physical features of the water but also with shifts in the associated heterotrophic bacteria. The MAC bloom was associated with a high abundance of Bacteroidetes, particularly Cytophagales. In the second bloom period, Planctomycetes increased in relative abundance, five Planctomycetes OTUs were positively correlated with Synechococcus or C. raciborskii OTUs. Our results suggest specific interactions of the main cyanobacterial genera with certain groups of the heterotrophic bacterial community. Thus, considering biotic interactions may lead to a better understanding of the shifts in cyanobacterial dominance.

Comparison of seasonal distribution patterns of Discostella stelligera and Lindavia bodanica in a boreal lake during two years with differing ice-off timing

Widespread changes in the relative abundances of Cyclotella sensu lato taxa have occurred in lakes of the Northern Hemisphere over the last ∼150 years, with these changes often attributed to climate-driven physical changes in lakes. While the links between Cyclotella ecology and lake thermal structure have been investigated extensively now, the role of the timing of ice-off in driving these diatom patterns remains unclear. We compared the seasonal distribution patterns of Cyclotella taxa in a boreal lake with high water transparency during two years with differing timing of ice-off. Vertical distributions of taxa in Jordan Pond (Maine, USA) were assessed every 5–24 days from early May to late October during an early ice-off year (19 March 2012) and a late ice-off year (29 April 2015). Seasonal succession patterns differed over the two years. During the early ice-off year, Lindavia bodanica cell densities were higher and peaked in the hypolimnion from July to October. The abundance of this taxon during the late ice-off year may have been negatively affected by fungal infection, which was visible with microscopic investigation. In contrast, Discostella stelligera cell densities were higher during the late ice-off year and peaked from May to August. This taxon was distributed uniformly in the water column throughout July, during phosphorus-limited conditions, and was then more abundant in the epilimnion during August, during nitrogen-limited conditions. Multiple linear regression models suggested that variation in D. stelligera cell densities was explained by year, number of days since ice-off and mixing depth (R2 = 0.55), while variation in L. bodanica cell densities was explained by year, number of days since ice-off, total phosphorus, dissolved oxygen, and Secchi disk depth (R2 = 0.16). Our results reveal variable seasonal distribution patterns of these two taxa over the two years and suggest that these patterns are the result of many drivers, some of which may be affected by ice-off timing.

Surfactants: a real threat to the aquatic geoecosystems of lobelia lakes

Abstract Lobelia lakes are valuable elements of the natural environment. They are characterised by low trophy, mainly in-forest location and a high transparency of water. However, similarly to other surface waters, they are subjected to increasing anthropogenic pressures, a good indicator of which is the level of surfactants, also called surface-active agents (SAAs). The aim of the study was to evaluate the intensity of anthropogenic pressures in 13 selected lobelia lakes and 14 streams in the catchments of these lakes in Northern Poland, based on SAA concentrations in the waters of these water bodies. We collected one water sample from each of these water bodies and determined the concentrations of cationic, anionic and non-ionic SAAs. We then compared the results with data concerning the ways in which these catchments and water bodies are used. While ionic (cationic and anionic) SAAs were found to be present in all the 27 samples (with concentrations ranging from 0.05 to 0.51 mg dm−3), non-ionic SAAs were identified in 17 of 27 samples (from 0.00 to 2.43 mg dm−3) with three samples largely exceeding the maximum concentration values reported by other authors. We concluded that SAAs are a real threat to the aquatic geoecosystems of lobelia lakes and that the pressures of tourism and leisure have the greatest impact.

A Satellite-Based Assessment of the Distribution and Biomass of Submerged Aquatic Vegetation in the Optically Shallow Basin of Lake Biwa

Assessing the abundance of submerged aquatic vegetation (SAV), particularly in shallow lakes, is essential for effective lake management activities. In the present study we applied satellite remote sensing (a Landsat-8 image) in order to evaluate the SAV coverage area and its biomass for the peak growth period, which is mainly in September or October (2013 to 2016), in the eutrophic and shallow south basin of Lake Biwa. We developed and validated a satellite-based water transparency retrieval algorithm based on the linear regression approach (R2 = 0.77) to determine the water clarity (2013–2016), which was later used for SAV classification and biomass estimation. For SAV classification, we used Spectral Mixture Analysis (SMA), a Spectral Angle Mapper (SAM), and a binary decision tree, giving an overall classification accuracy of 86.5% and SAV classification accuracy of 76.5% (SAV kappa coefficient 0.74), based on in situ measurements. For biomass estimation, a new Spectral Decomposition Algorithm was developed. The satellite-derived biomass (R2 = 0.79) for the SAV classified area gives an overall root-mean-square error (RMSE) of 0.26 kg Dry Weight (DW) m-2. The mapped SAV coverage area was 20% and 40% in 2013 and 2016, respectively. Estimated SAV biomass for the mapped area shows an increase in recent years, with values of 3390 t (tons, dry weight) in 2013 as compared to 4550 t in 2016. The maximum biomass density (4.89 kg DW m-2) was obtained for a year with high water transparency (September 2014). With the change in water clarity, a slow change in SAV growth was noted from 2013 to 2016. The study shows that water clarity is important for the SAV detection and biomass estimation using satellite remote sensing in shallow eutrophic lakes. The present study also demonstrates the successful application of the developed satellite-based approach for SAV biomass estimation in the shallow eutrophic lake, which can be tested in other lakes.