Aquatic pollution caused by mercury, lead, and cadmium affects cell growth and pigment content of marine microalga, Nannochloropsis oculata

The present study investigated the acute (72 h) and sub-acute (14 days) toxicity of mercury, lead, and cadmium to the green microalga, Nannochloropsis oculata. The acute toxicity testing was conducted according to the modified OECD guideline (No. 201). The 72-h IC50 values of Hg, Pb, and Cd exposed to N. oculata were 0.87, 1.81, and 4.97 mg/L, respectively. These results showed that mercury is about twice as toxic as lead and about 5.7 times more toxic than cadmium to this marine microalga. Lead is about 2.7 times more toxic than cadmium. The chlorophyll a content of the microalga decreased in the 10th and 14th days of the sub-acute toxicity test. Although the carotenoid content increased following exposure to the low levels of tested heavy metals (which may show the protective role of carotenoids against oxidative stress), with increased exposure time the total carotenoid reduced compared to control. A regular monitoring program to examine the level of metals in the aquatic ecosystem for protecting microalgae should be implemented.

Impact of eelgrass bed recovery and expansion on phytoplankton growth through nutrient competition

Eelgrass beds are highly productive and support diverse faunal assemblages; they also take in nutrients from the water and prevent excessive phytoplankton growth in eutrophic coastal waters through the reduction of available nutrients. Despite its importance, the global distribution of eelgrass has declined worldwide. In eutrophic areas with high chlorophyll a (Chl.a) concentrations, natural recovery of eelgrass beds after eutrophication is possible. To facilitate this, sufficient water clarity can be reached after a large enough decrease in phytoplankton concentration. In this study, we proposed a novel indicator for the maximum possible Secchi depth (MPSD), defined as the Secchi depth when the Chl.a concentration is equal to a reference Chl.a concentration. We applied the MPSD to evaluate water clarity improvements through the reduction of terrigenous anthropogenic nutrient loading. We found that phytoplankton did not control water clarity in the study area, which was instead controlled by background factors. Therefore, improvements in water clarity would not be expected after reducing terrigenous anthropogenic nutrient loading. The habitat of Zostera marina is determined by light availability, so we investigated a potential area with ≥20% surface irradiance and Z. marina existed in 27% of it (100 of 373 ha). The maximum further recovery of eelgrass by Secchi depth improvements to the MPSD was estimated at 36 ha. The impact of eelgrass recovery and expansion on phytoplankton growth from May to September was evaluated by a mathematical model under two scenarios: the current eelgrass distribution (100 ha) and potential maximum eelgrass distribution (373 ha). A Chl.a decrease of 1.0-3.0 μg l^-1 from 4.0 to 7.0 μg l^-1 was achieved in an area from May to July, and the improvement decreased with time. These evaluation methods and findings could help us gain a better understanding of the nutrient management in seagrass-vegetated semi-enclosed seas subjected to anthropogenic nutrient input.

Characterizing spatial distribution of chlorophyll a in the Southern Ocean on a circumpolar cruise in summer

The spatial variation of chlorophyll a in the Southern Ocean (SO) was of great significance. Sea surface chlorophyll a concentrations was measured by Ferry Box monitoring system on the Chinese polar research vessel Xue Long, which circumnavigated the Antarctic continent in a clockwise direction during the austral summer 2013-2014 (November 2013-April 2014). The concentrations of chlorophyll a indicated a relatively uniform distribution of 0.049-11.647 mg m^-3 (mean 0. 869 mg m^-3, n = 152,751). The highest chlorophyll a concentrations (mean 1.847 mg m^-3) was found in the Ross sea (RS). In addition, six high-chlorophyll a hot spots were recognized. Analysis revealed that phytoplankton bloom could be controlled by multiple factors in different regions, and the chlorophyll a bloom is attributed to the combined effect of surface and subsurface processes such as, continental shelf, sea ice melting, Circumpolar Deep Water (CDW) upwelling, suitabletemperature, and nutrient injection from subsurface to the surface. The topographic effects, sea ice melting and CDW upwelling may play a major role in controlling primary productivity in the SO. Among of all, CDW upwelling may be the most important role improving primary productivity. This study presented the phytoplankton distribution patterns and the relation with potential growth-controlling factors in the SO, which will provide more insight in the mechanisms that control global warming to reduce global CO₂ the atmosphere into the ocean interior.

The role of carbonic anhydrase α-CA4 in the adaptive reactions of photosynthetic apparatus: the study with α-CA4 knockout plants

The role of α-carbonic anhydrase 4 (α-CA4) in photosynthetic machinery functioning in thylakoid membranes was studied, using Arabidopsis thaliana wild type plants (WT) and the plants with knockout of At4g20990 gene encoding α-CA4 (αCA4-mut) grown both in low light (LL, 80 μmol quanta m^-2 s^-1) or in high light (HL, 400 μmol quanta m^-2 s^-1). It was found that a content of PsbS protein, one of determinants of non-photochemical quenching of chlorophyll fluorescence, increased in mutants by 30% and 100% compared with WT plants in LL and in HL, respectively. Violaxanthin cycle pigments content and violaxanthin deepoxidase activity in HL were also higher in αCA4-mut than in WT plants. The content of PSII core protein, D1, when adapting to HL, decreased in WT plants and remained unchanged in mutants. This indicates, that the decrease in the content of Lhcb1 and Lhcb2 proteins in HL (Rudenko et al. Protoplasma 55(1):69-78, 2018) in WT plants resulted from decrease of both Photosystem II (PSII) complex content and content of these proteins in this complex, whereas in αCA4-mut plants from the latter process only. The absence of α-CA4 did not affect the rate of electron transport through Photosystem I (PSI) in thylakoids of mutant vs. WT, but led to 50-80% increase in the rate of electron transport from H₂O to Q_A, evidencing the location of α-CA4 close to PSII. The latter difference may raise the question about its causal connection with the difference in the D1 protein content change during adapting to increased illumination in the presence and the absence of α-CA4.

Towards the comprehensive water quality control in Lake Taihu: Correlating chlorphyll a and water quality parameters with generalized additive model

In this study, the generalized additive model (GAM) was used to analyze seasonal monitoring data from Lake Taihu, collected from 2010 to 2014, with the aim to explore the correlation between chlorophyll a (Chla) and other water quality parameters. The selected optimal multivariable GAM could effectively explain the concentration variation of Chla occurring during each season, and the interpretation degree followed the order: summer > autumn > spring > winter. The fitting results indicated that the concentration variation of Chla could reflect that of biochemical oxygen demand and chemical oxygen demand in all seasons. In addition, the total phosphorus showed strong ability to explain the concentration change of Chla in spring and summer, as the growth of algae would be affected when the concentration of phosphorus shifted high or low. Nitrogen showed strong ability to explain the variations in Chla concentration in autumn. The conclusions of the optimal multivariable GAM could provide decision basis for the eutrophication control. In other words, the prevention of eutrophication outbreaks could be carried out via the targeted control of key water pollutants. According to these results, the concentration of Chla was higher in northern and western lake during summer and autumn, the management should focus on nutrient input of adjacent rivers.

Effects of benthivorous fish disturbance on chlorophyll a contents in water and the growth of two submersed macrophytes with different growth forms under two light regimes

Low underwater light availability and benthivorous fish-mediated disturbance are two important factors that influence the growth of submersed macrophytes. However, the combined effects of these factors remain unclear. To determine the combined effects of low light and fish-mediated disturbance on the growth of two submersed macrophytes with contrasting growth forms, i.e., Vallisneria natans and Hydrilla verticillata, we conducted an outdoor mesocosm experiment with a two-by-two factorial design. The experiment involved two fish-mediated disturbance levels (0 and 1 Misgurnus anguillicaudatus) crossed with two levels of light intensity (ambient light and a low-light environment created by culturing the macrophytes under a shelter). The results showed that the chlorophyll a (chl a) concentration in the overlying water showed no difference among treatments for each macrophyte species. The fish-mediated disturbance significantly decreased the relative growth rate (RGR) of both species in the low-light environment but showed no effects in the ambient light environment. Low light availability and/or fish-mediated disturbance led to increased plant heights of both species compared with the heights under the ambient light regime. Low light availability combined with fish-mediated disturbance significantly reduced the ramet number and soluble carbohydrate (SC) content of both species; however, the free amino acid (FAA) content was not affected. Compared to V. natans, H. verticillata exhibited a high RGR and high ramet numbers in a low-light environment combined with fish-mediated disturbance. Our results indicated that the adaptability of H. verticillata is better than that of V. natans in turbid, shallow and hydrostatic water. Fish-mediated disturbance can negatively influence submersed macrophyte recovery in lakes when light is not abundant.

Nutrient over-enrichment and light limitation of seagrass communities in the Indian River Lagoon, an urbanized subtropical estuary

Historically, extensive seagrass meadows were common throughout the Indian River Lagoon (IRL) in east-central Florida, USA. Between 2011 and 2017, widespread catastrophic seagrass losses (~95%) occurred in the IRL following unprecedented harmful algal blooms (HABs), including persistent brown tides (Aureoumbra lagunensis). Little is known about how dissolved nutrients and chlorophyll a are related to light limitation or how biochemical factors, such as the elemental composition (C:N:P) and stable isotope signatures (δ¹³C, δ¹⁵N), of seagrasses within the IRL relate to coverage. Accordingly, we conducted a survey from 2013 to 2015 at 20 sites to better understand these relationships. Results showed a negative correlation between DIN and salinity, indicating freshwater inputs as a DIN source. Seawater N:P ratios and chlorophyll a concentrations were higher in the urbanized, poorly-flushed northern IRL segments. K_d values were higher in the wet season and often exceeded seagrass light requirements (0.8 m^-1) for restoration, demonstrating light limitation. Species distribution varied by location. Halodule wrightii was ubiquitous, whereas Syringodium filiforme was not found in the northernmost segments. Thalassia testudinum was only present in the two southernmost segments that had the lowest TDN and highest light availability (K_d). Blade %N and %P also frequently exceeded critical values of 1.8% and 0.2%, respectively, especially in the northern segments. Further, δ¹⁵N was positively correlated with ammonium, suggesting wastewater as a major N source. The δ¹³C values indicated a trend of increasing light limitation from south to north, which helps explain the recent catastrophic loss of seagrasses in the northern IRL. Overall, elemental composition reflected high N-availability and seagrass species distributions were relatable to spatial trends in N and light limitation. For effective restoration, resource managers must reduce N-loading to the IRL to diminish HABs and increase light availability. Regular biochemical monitoring of seagrass tissue should also be implemented during restoration efforts.

Photosynthetic pigments in acid mine drainage: Seasonal patterns and associations with stressful abiotic characteristics

Acid mine drainage represents an extreme type of water pollution. The environments develop especial hydrochemical and ecological characteristics, such as high concentrations of acidity and low biodiversity, with dominance of acidophilic organisms. Ecological criteria are assuming increasing relevance for assessing water quality, including in acid mine drainage-affected systems. Photosynthetic pigments, like chlorophyll, could be considered in this context as they are generally used to estimate phytoplankton biomass. The present work was focused on acid mine drainage and their relationships with chlorophyll a. It was developed in the historic mine of São Domingos (Iberian Pyrite Belt, SW Europe). The methodological approach comprised two sampling campaigns (October and February) to represent seasonal behaviour. The diversity of hydrological conditions was also considered through sampling sites established in the pit lake, acidic lagoons and affected stream. Hydrochemistry and chlorophyll a were analysed. The obtained results revealed very low pH values, with a minimum of 2.1. In general, hydrochemistry indicates higher concentrations of pollutants in summer. One of the sampling point, located in an acidic lagoon, stood out by highest concentrations, presenting maximum of sulfate (6564 mg/L), As (6.26 mg/L), and metals like Al (675 mg/L), Cd (1,30 mg/L), Zn (199 mg/L). These highest concentrations coincided with the maximum concentration of chlorophyll a (113 μg/L). The results suggested that the more contaminated the environment, more chlorophyll a was produced. Factor analyses emphasised the relationships between acid drainage properties and the photosynthetic activity, indicating a strong pH dependency of chlorophyll a production.

The implications of Simpson's paradox for cross-scale inference among lakes

Using cross-sectional data for making ecological inference started as a practical means of pooling data to enable meaningful empirical model development. For example, limnologists routinely use sample averages from numerous individual lakes to examine patterns across lakes. The basic assumption behind the use of cross-lake data is often that responses within and across lakes are identical. As data from multiple study units across a wide spatiotemporal scale are increasingly accessible for researchers, an assessment of this assumption is now feasible. In this study, we demonstrate that this assumption is usually unjustified, due largely to a statistical phenomenon known as the Simpson's paradox. Through comparisons of a commonly used empirical model of the effect of nutrients on algal growth developed using several data sets, we discuss the cognitive importance of distinguishing factors affecting lake eutrophication operating at different spatial and temporal scales. Our study proposes the use of the Bayesian hierarchical modeling approach to properly structure the data analysis when data from multiple lakes are employed.

The Effect of Goldfish (Carassius auratus) on Water Quality in Horse Stock Tanks

Goldfish (Carassius auratus) have been reported as a method to keep water tanks clean; however, little information exists on this approach. The objectives were to evaluate the efficacy of goldfish on maintaining water quality in tanks and to evaluate the frequency that this method is used. The first objective was completed during June through October 2017 in St. Paul, MN, using plastic and metal 379 L stock tanks, each with and without goldfish in a drylot that housed six adult horses. The stocking rate was 5 goldfish per tank. Daily readings of total dissolved solids (TDS) and water turbidity (NTU), and weekly samples to measure chlorophyll a were taken. At the end of each 28-day period, tanks were cleaned and rotated. Plastic tanks had lower TDS than metal tanks (P < .001); however, metal tanks had lower NTU and chlorophyll a (P ≤ .008). Adding goldfish resulted in lower TDS (P < .001); however, there was no effect on NTU or chlorophyll a (P ≥ .097). No parameters had an impact on horse preference (P ≥ .108). The second objective was completed using an online survey that was open from October 31 until December 15, 2018. Of the 672 completed surveys, 56% had not tried using goldfish in water tanks, 26% had utilized goldfish in the past, and 18% currently used goldfish. The inclusion of goldfish in water tanks did not affect all water quality parameters; however, 44% of survey respondents had tried, or were currently using, this management method.

Effect of microplastics exposure on the photosynthesis system of freshwater algae

Microplastics are widely distributed in freshwater environments. At present, most of the studies on the toxicity of microplastics are concentrated on aquatic feeding animals, but relatively few have addressed freshwater algae. This study investigated the effect of microplastics (polypropylene (PP) and polyvinyl chloride (PVC)) exposure on the photosynthetic system of freshwater algae over the logarithmic growth period. The results showed that both PVC and PP had a negative effect on chlorophyll a concentrations of Chlorella (C.) pyrenoidosa and Microcystis (M.) flos-aquae; among them, when the concentration of PVC exceeded 250 mg/L, compared with the control group, the chlorophyll a content of C. pyrenoidosa was reduced by 55.23%. For photosynthetic activity, higher concentrations of PVC and PP can induce lower values of F_v/F_m, F_v/F₀, and F_v'/F_m', suggesting a larger impact in algae. However, algae were able to adjust, with increased values of F_v/F_m, F_v/F₀, and F_v'/F_m'. This dose-negative effect phenomenon also exists in the study of the rapid light-response curves. In addition, comparing the two microplastics, we could see that PVC greatly inhibits the photosynthesis system of freshwater algae. Our study confirmed that microplastics can affect algae growth under certain concentrations, which provides evidence for understanding the risks of microplastics.

Biotoxicity of water-soluble species in PM2.5 using Chlorella

China has been faced with severe haze pollution, which is hazardous to human health. Among the air pollutants, PM_2.5 (particles with an aerodynamic diameter ≤ 2.5 μm) is the most dangerous because of its toxicity and impact on human health and ecosystems. However, there has been limited research on PM_2.5 particle toxicity. In the present study, we collected daily PM_2.5 samples from January 1 to March 31, 2018 and selected samples to extract water-soluble species, including SO₄^2-, NO₃^-, WSOC, and NH₄⁺. These samples represented clean, good, slight, moderate, and heavy pollution days. After extraction using an ultrasonic method, PM_2.5 solutions were obtained. We used Chlorella as the test algae and studied the content of chlorophyll a, as well as the variation in fluorescence when they were placed into the PM_2.5 extraction solution, and their submicroscopic structure was analyzed using transmission electron microscopy (TEM). The results showed that when the air quality was relatively clean and good (PM_2.5 concentration ≤ 75 μg m^-3), the PM_2.5 extraction solutions had no inhibiting effects on Chlorella, whereas when the air quality was polluted (PM_2.5 concentration > 75 μg m^-3) and heavily polluted (PM_2.5 concentration > 150 μg m^-3), with increasing PM_2.5 concentrations and exposure time, the chlorophyll a content in Chlorella decreased. Moreover, the maximum photochemical quantum yield (F_v/F_m) of Chlorella obviously decreased, indicating chlorophyll inhibition during polluted days with increasing PM_2.5 concentrations. The effects on the chlorophyll fluorescence parameters were also obvious, leading to an increase of energy dissipated per unit reaction center (DI_o/RC), suggesting that Chlorella could survive when exposed to PM_2.5 solutions, whereas the physiological activities were significantly inhibited. The TEM analysis showed that there were few effects on Chlorella cell microstructure during clean days, whereas plasmolysis occurred during light- and medium-polluted days. With increasing pollution levels, plasmolysis became more and more apparent, until the organelles inside the cells were thoroughly destroyed and most of the parts could not be recognized.

Nanoparticle-mediated Impact on Growth and Fatty Acid Methyl Ester Composition in the Cyanobacterium Fremyella diplosiphon

Insufficient light supply is a major limitation in cultivation of cyanobacteria for scaled up biofuel production and other biotechnological applications, which has driven interest in nanoparticle-mediated enhancement of cellular light capture. In the present study, Fremyella diplosiphon wild type (Fd33) and halotolerant (HSF33-2) strains were grown in solution with 20, 100, and 200 nm-diameter gold nanoparticles (AuNPs) to determine their impact on biomass accumulation, pigmentation, and fatty acid methyl ester (FAME) production. Results revealed a significant increase in growth of Fd33 (0.244 ± 0.006) and HSF33-2 (0.112 ± 0.003) when treated with 200 nm AuNPs. In addition, we observed a significant increase in chlorophyll a accumulation in 200 nm AuNP-treated Fd33 (25.7%) and HSF33-2 (36.3%) indicating that NPs enhanced photosynthetic pigmentation. We did not observe any alteration in FAME composition and biodiesel properties of transesterified F. diplosiphon lipids among all AuNP treatments. Interactions between F. diplosiphon and AuNPs were visualized using scanning electron microscopy. Energy dispersive X-ray spectroscopy confirmed the presence of AuNPs outside cells with aggregation in high cell density locales. Our findings indicate that nanotechnological approaches could significantly enhance growth of the organism with no negative effect on FAME-derived biodiesel properties, thus augmenting F. diplosiphon as a potential biofuel agent.

Excitation energy transfer in the far-red absorbing violaxanthin/vaucheriaxanthin chlorophyll a complex from the eustigmatophyte alga FP5

This work highlights spectroscopic investigations on a new representative of photosynthetic antenna complexes in the LHC family, a putative violaxanthin/vaucheriaxanthin chlorophyll a (VCP) antenna complex from a freshwater Eustigmatophyte alga FP5. A representative VCP-like complex, named as VCP-B3 was studied with both static and time-resolved spectroscopies with the aim of obtaining a deeper understanding of excitation energy migration within the pigment array of the complex. Compared to other VCP representatives, the absorption spectrum of the VCP-B3 is strongly altered in the range of the chlorophyll a Q_y band, and is substantially red-shifted with the longest wavelength absorption band at 707 nm at 77 K. VCP-B3 shows a moderate xanthophyll-to-chlorophyll a efficiency of excitation energy transfer in the 50-60% range, 20-30% lower from comparable VCP complexes from other organisms. Transient absorption studies accompanied by detailed data fitting and simulations support the idea that the xanthophylls that occupy the central part of the complex, complementary to luteins in the LHCII, are violaxanthins. Target analysis suggests that the primary route of xanthophyll-to-chlorophyll a energy transfer occurs via the xanthophyll S₁ state.

Hydrodynamic Modeling Coupled with Long-term Field Data Provide Evidence for Suppression of Phytoplankton by Invasive Clams and Freshwater Exports in the San Francisco Estuary

The San Francisco Estuary (California, USA) had abundant pelagic fish in the late 1960s, but has few pelagic fish today. A primary cause for this decline in fish is thought to be a trophic cascade, triggered by declining phytoplankton. Here, we describe the changes in pelagic community structure of the San Francisco Estuary. Then, we examine whether changes in hydrodynamics due to freshwater exports, which increased exponentially beginning in 1967, in addition to the 1986 invasion by the clam Potamocorbula amurensis, explain the phytoplankton loss. Hydrodynamic variables were reconstructed back to 1956 using statistical models fit to, and cross-validated against, output from a hydrodynamic model. Then, we regressed mean summer/fall chlorophyll a-the season with the largest phytoplankton decline-against the reconstructed hydrodynamic variables and the presence/absence of P. amurensis for 1969-2014. The regression model, which explained 78% of the interannual variation in chlorophyll a, was then used to quantify the influence of P. amurensis and exports on chlorophyll a. Based on monitoring data, chlorophyll a declined 22-fold from 1969-2014, zooplankton declined 32-fold from 1972-2014, and pelagic fish declined 92-fold from 1968-2014. Averaged over 1990-2014, the chlorophyll a model ascribed an 88% decline in chlorophyll a to P. amurensis, a 74% decline to exports (at minimum), and a 97% decline to the combined influence of P. amurensis and exports (at minimum). Thus, the decline in pelagic productivity in the San Francisco Estuary has occurred largely due to the combined impacts of the P. amurensis invasion and increased freshwater exports.

Assessment of lake eutrophication recovery: the filtering trajectory method (FTM) and its application to Dianchi Lake, China

Lake ecosystems follow convoluted trajectories impacted by climate change and human stress. In this study, we developed the filtering trajectory method (FTM), a mathematical model, to establish the empirical relationships between chlorophyll a (CHLa) and nutrient concentrations in eutrophic Dianchi Lake, China. FTM can identify cause-effect relationships over time in apparently stochastic data, and a filtering trajectory diagram is used to describe the driving forces of the complex trajectories of individual lake ecosystems. Our analysis showed that the nutrient concentrations of overlying water in Dianchi Lake have decreased to the levels recorded in the late 1980s and early 1990s, but CHLa has not declined synchronously. The ecosystem trajectories revealed the ups and downs of complex processes, which can be divided into four stages: (1) pollution stage (1988-1999): a macrophyte-to-phytoplankton transition occurred with an increase in nutrient inputs and a rise in temperature; (2) initial restoration stage (2000-2006): the response of CHLa to the nutrient load reduction presented an apparent time lag, or hysteresis effect; (3) recurrence stage (2007-2011): excessive water consumption and continuous drought in the watershed resulted in an increasing trend in CHLa, TP and TN; and (4) re-restoration stage (2012-2016): the implementation of a water-replenishment project resulted in a declining trend. Our approach can greatly improve our understanding of how lakes respond to broad changes in environmental conditions (e.g. climate warming) and improve water quality via targeted nutrient management, from "static" to "dynamic management" and from "One Standard for One Lake" to "Multiple Standards for One Lake".

Teleconnection between phytoplankton dynamics in north temperate lakes and global climatic oscillation by time-frequency analysis

We are still facing the knowledge gap of how the water-quality extremes (i.e. phytoplankton blooms), their causes, severity or occurrence could be directly related to the climatic oscillation. Considering that the climatic and phytoplankton concentration time series are highly non-stationary, we applied the advanced time-frequency analysis - Ensemble Empirical Mode Decomposition (EEMD), Hilbert-Huang Spectrum (HHS) and Wavelet Analysis (WA) - to examine the variability of long term phytoplankton dynamics from 1986 to 2014 in five North Temperate Lakes (NTLs). These analysis techniques isolated five separate time series for the surface Chlorophyll a concentrations (CHL) of the five NTLs and a time series for the global climate oscillation (denoted by multivariate ENSO index, MEI), and showed that these time series generally operated at similar time scales. The long-term residual trends of decreasing were found in three lakes (i.e., BM, SP and TR lakes), which are the same to global climate dynamics (MEI). The wavelet analysis reveals strong coherency between MEI and CHL data sets for all lakes, with a periodicity of 64-months. Intuitive associations between the CHL and MEI data set showed that two types of ENSO (El Nino and La Nina) differ in their influences to CHL. Potential mechanisms relating the phytoplankton dynamics in NTLs to climatic oscillation (ENSO) were also discussed.

Associating the spatial properties of a watershed with downstream Chl-a concentration using spatial analysis and generalized additive models

We examined the relationship between downstream algal growth potential and the spatial environmental factors of both upland areas and stream buffer zones using spatial analysis and generalized additive models (GAMs). The models employed site-representative concentrations of chlorophyll a (Chl-a) from a total of 688 national water quality monitoring stations and the spatial factors of the corresponding 688 watersheds. The spatial environmental factors included topography, climate, land use class, soil type, and proximity of the monitoring station to the weir downstream and wastewater treatment plants (WWTPs). The explanatory power (adjusted R² or R_adj²) of the models was used to compare different spatial influential scales defined by stream buffers and upstream circular buffers. The spatial environmental factors of the entire watershed area better explained the inter-station variation in Chl-a than did those of the stream buffer and/or upstream circular buffer areas. However, the spatial environmental factors of watershed areas more than 25 km upstream circular buffer zones had only minor influence on the explainability of the models with regards to the inter-station variation in Chl-a levels. Generally, land use patterns were more strongly related to the inter-station Chl-a variation than were point sources of pollutants such as WWTPs. The two most influencing land uses on the inter-station Chl-a variation were urban and agricultural land uses, with varying relative contributions depending on the spatial influential scale: In general relative contribution of urban land use was larger at a larger spatial influential scale while that of agricultural land use showed an opposite trend. In addition, the proximity to the weir downstream explained high Chl-a concentrations in the stream water. Relative importance and causal effects of the spatial environmental variables to instream Chl-a were established based on this national scale correlative analysis, leading to decision-making with the goal of controlling instream algal growth.

Total phosphorus-precipitation and Chlorophyll a-phosphorus relationships of lakes and reservoirs mediated by soil iron at regional scale

Phosphorus is a critical element determining trophic status and Chlorophyll a (Chl a) level in natural lakes and reservoirs, and total phosphorus (TP) concentrations can be predicted from data on phosphorus loading, hydraulic flushing rate and sedimentation. Due to their interactions with phosphorus, iron (hydr) oxides in suspended particles, originally derived from watershed soil, can strongly influence the phosphorus sedimentation and phosphorus bioavailability in water columns. Thus, the TP-precipitation relationship and the response of Chl a to TP are likely associated with watersheds soil iron. To test this assumption, we built hierarchical linear models for summer observation of natural lakes and reservoirs across a large geographic gradient. The intercepts and slopes of TP-precipitation relationships are higher in natural lakes than those in reservoirs, and these model coefficients exhibit latitudinal variations that are explained by the natural soil iron gradient. Soil iron, operating at a regional level, significantly mediates the effect of precipitation on TP concentration in both natural lakes and reservoirs, and drives the latitudinal variation in the Chl a-TP relationships for reservoirs. Our results imply that the increase in extreme precipitation events anticipated under future climate conditions may substantially mitigate eutrophication in tropical and subtropical reservoirs, but may worsen conditions in temperate lakes.

Effect of oil spill stress on fatty acid stable carbon isotope composition of Ulva pertusa

Petroleum is one of the most important pollutants in the marine ecosystem, and oil spills have a long-term effect on the marine environment. After an oil spill, petroleum continues to diffuse, flowing to the intertidal zone where it accumulates. Ulva pertusa is the main macroalgae species in the intertidal zone of the ocean, and petroleum is toxic to marine macroalgae. Fatty acids, which are involved in various physiological activities, including metabolism, are indispensable substances in organisms. Thus, an organism's fatty acid composition reflects its physiological state. Because fatty acids are carbon-rich compounds, their stable carbon isotope composition can be measured to assess the state of the organism. In this study, the effects of the water accommodated fraction (WAF) of different concentrations of 180# fuel oil and 0# diesel oil on the chlorophyll a and fatty acid carbon stable isotope composition (δ¹³C_FAs) of U. pertusa were assessed. The fatty acid carbon stable isotope value varied among the different petroleum treatments, and high WAF concentrations significantly inhibited the synthesis of unsaturated fatty acids. Thus, exposure to petroleum products affected the synthesis of fatty acids in U. pertusa and also caused carbon stable isotope fractionation during the fatty acid synthesis process. The results indicate that the saturated fatty acid δ¹³C_16:0 and the unsaturated fatty acid δ¹³C_18:1 can be used as biomarkers to evaluate the degree of petroleum-induced stress in U. pertusa and that carbon stable isotope analysis of U. pertusa can be used as an environmental risk assessment tool in the intertidal zone.

Different approaches and limitations for testing phytoplankton viability in natural assemblies and treated ballast water

Shipping is recognised as an unintentional efficient pathway for spreading non-native species, harmful organisms and pathogens. In 2004, a unique IMO Convention was adopted to control and minimize this transfer in ship's ballast water. This Convention entered into force on 8th September 2017. However, unlikely the majority of IMO Conventions, the Ballast Water Management Convention requires ships to comply with biological standards (e.g. concentration of organisms per unit of volume in ballast water discharges). This study aimed to apply different techniques developed to measure concentrations of viable phytoplankton in natural and treated ballast water samples and compare them with the established flow cytometry method and vital staining microscopy. Samples were collected in the English Channel over one year and on-board during ballast water shipboard efficacy tests. Natural abundance of live phytoplankton varied from 23% to 89% of the total, while for cells larger than 10 μm (a size defined by the BWM Convention) the percentage varied from 3% to 60%. An overall good correlation was seen between the measurements taken with the two fluorometers and in comparison with the flow cytometry analysis, as found in previous studies. Analysis of treated ballast water samples showed a large variation in the number of viable cells, however indicating a low level of risk on all occasions for regulatory purposes. One of the key aspects to bear in mind when sampling and analysing for compliance is to be aware of the limitations of each technique.

Effects of carotenoids on the absorption and fluorescence spectral properties and fluorescence quenching of Chlorophyll a

Fluorescence and absorption characteristics of Chlorophyll a (Chl-a) were modulated by the carotenoids (Cars) with different numbers of conjugated carbon‑carbon double bonds in solutions. The Chl-a absorption appears the redshift phenomenon with the effective conjugated of Cars increasing. The absorption of Chl-a and Cars are linearly dependent on intrinsic factors, namely effective conjugate length and functional groups, and on environmental factors, such as the polarizability of the solvent. Cars can be able to quench the Chl-a fluorescence by producing the non-emitting exciplex intermediate. The effective conjugated length of Cars is one of the reasons that effect the fluorescence quenching of Chl-a. According to the Stern-Volmer plots, the Chl-a fluorescence quenching should be predominantly dynamic rather than static.

Estimation of the water quality of a large urbanized river as defined by the European WFD: what is the optimal sampling frequency?

Assessment of the quality of freshwater bodies is essential to determine the impact of human activities on water resources. The water quality status is estimated by comparing indicators with standard thresholds. Indicators are usually statistical criteria that are calculated on discrete measurements of water quality variables. If the time step of the measured time series is not sufficient to fully capture the variable's variability, the deduced indicator may not reflect the system's functioning. The goal of the present work is to assess, through a hydro-biogeochemical modeling approach, the optimal sampling frequency for an accurate estimation of 6 water quality indicators defined by the European Water Framework Directive (WFD) in a large human-impacted river, which receives large urban effluents (the Seine River across the Paris urban area). The optimal frequency depends on the sampling location and on the monitored variable. For fast varying compounds that originate from urban effluents, such as PO[Formula: see text], NH[Formula: see text] and NO[Formula: see text], a sampling time step of one week or less is necessary. To be able to reflect the highly transient character of bloom events, chl a concentrations also require a short monitoring time step. On the contrary, for variables that exert high seasonal variability, as NO[Formula: see text] and O ₂, monthly sampling can be sufficient for an accurate estimation of WFD indicators in locations far enough from major effluents. Integrative water quality variables, such as O ₂, can be highly sensitive to hydrological conditions. It would therefore be relevant to assess the quality of water bodies at a seasonal scale rather than at annual or pluri-annual scales. This study points out the possibility to develop smarter monitoring systems by coupling both time adaptative automated monitoring networks and modeling tools used as spatio-temporal interpolators.

Effects of malathion and nitrate exposure on the zooplankton community in experimental mesocosms

Surface waters are likely to be contaminated by both pesticides and fertilizers. Such contamination can result in changes in community composition if there is differential toxicity to individual taxa. We conducted a fully factorial mesocosm experiment that examined the single and interactive effects of environmentally realistic concentrations of nitrate and malathion on zooplankton communities and phytoplankton productivity. Malathion significantly decreased the abundance of total zooplankton, cyclopoid copepods, copepod nauplii, and Ceriodaphnia, and increased the abundance of rotifers. Nitrate addition generally had no effect on zooplankton; however, Ceriodaphnia abundance was higher in control mesocosms than in nitrate-treated mesocosms. There was only one significant interaction between malathion and nitrate treatments: For Ceriodaphnia, the no malathion, no nitrate mesocosms had much higher abundances than all other combinations of treatments. Without nitrate addition, chl a levels were uniformly low across all malathion treatments, whereas in the presence of nitrate, there were differences among the malathion treatments. In conclusion, our results demonstrate that malathion contamination of aquatic ecosystems can result in changes in the abundance and composition of zooplankton communities. In contrast, nitrate contamination appeared to have much less potential impact on zooplankton communities, either on its own or in interaction with malathion. Our results reinforce the notion that the effects of contaminants on aquatic ecosystems can be complex and further research examining the single and interactive effects of chemical stressors is needed to more fully understand their effects.

Optical properties and composition changes in chromophoric dissolved organic matter along trophic gradients: Implications for monitoring and assessing lake eutrophication

Chromophoric dissolved organic matter (CDOM) is an important optically active substance in aquatic environments and plays a key role in light attenuation and in the carbon, nitrogen and phosphorus biogeochemical cycles. Although the optical properties, abundance, sources, cycles, compositions and remote sensing estimations of CDOM have been widely reported in different aquatic environments, little is known about the optical properties and composition changes in CDOM along trophic gradients. Therefore, we collected 821 samples from 22 lakes along a trophic gradient (oligotrophic to eutrophic) in China from 2004 to 2015 and determined the CDOM spectral absorption and nutrient concentrations. The total nitrogen (TN), total phosphorus (TP), and chlorophyll a (Chla) concentrations and the Secchi disk depth (SDD) ranged from 0.02 to 24.75 mg/L, 0.002-3.471 mg/L, 0.03-882.66 μg/L, and 0.05-17.30 m, respectively. The trophic state index (TSI) ranged from 1.55 to 98.91 and covered different trophic states, from oligotrophic to hyper-eutrophic. The CDOM absorption coefficient at 254 nm (a(254)) ranged from 1.68 to 92.65 m^-1. Additionally, the CDOM sources and composition parameters, including the spectral slope and relative molecular size value, exhibited a substantial variability from the oligotrophic level to other trophic levels. The natural logarithm value of the CDOM absorption, lna(254), is highly linearly correlated with the TSI (r² = 0.92, p < .001, n = 821). Oligotrophic lakes are distinguished by a(254)<4 m^-1, and mesotrophic and eutrophic lakes are classified as 4 ≤ a(254)≤10 and a(254)>10 m^-1, respectively. The results suggested that the CDOM absorption coefficient a(254) might be a more sensitive single indicator of the trophic state than TN, TP, Chla and SDD. Therefore, we proposed a CDOM absorption coefficient and determined the threshold for defining the trophic state of a lake. Several advantages of measuring and estimating CDOM, including rapid experimental measurements, potential in situ optical sensor measurements and large-spatial-scale remote sensing estimations, make it superior to traditional TSI techniques for the rapid monitoring and assessment of lake trophic states.

Imaging linear and circular polarization features in leaves with complete Mueller matrix polarimetry

Spectropolarimetry of intact plant leaves allows to probe the molecular architecture of vegetation photosynthesis in a non-invasive and non-destructive way and, as such, can offer a wealth of physiological information. In addition to the molecular signals due to the photosynthetic machinery, the cell structure and its arrangement within a leaf can create and modify polarization signals. Using Mueller matrix polarimetry with rotating retarder modulation, we have visualized spatial variations in polarization in transmission around the chlorophyll a absorbance band from 650 nm to 710 nm. We show linear and circular polarization measurements of maple leaves and cultivated maize leaves and discuss the corresponding Mueller matrices and the Mueller matrix decompositions, which show distinct features in diattenuation, polarizance, retardance and depolarization. Importantly, while normal leaf tissue shows a typical split signal with both a negative and a positive peak in the induced fractional circular polarization and circular dichroism, the signals close to the veins only display a negative band. The results are similar to the negative band as reported earlier for single macrodomains. We discuss the possible role of the chloroplast orientation around the veins as a cause of this phenomenon. Systematic artefacts are ruled out as three independent measurements by different instruments gave similar results. These results provide better insight into circular polarization measurements on whole leaves and options for vegetation remote sensing using circular polarization.

The advective origin of an under-ice spring bloom in the Arctic Ocean using multiple observational platforms

Under-ice blooms of phytoplankton in the Chukchi Sea have been observed, with strong implications for our understanding of the production regimes in the Arctic Ocean. Using a combination of satellite remote sensing of phytoplankton biomass, in situ observations under sea ice from an autonomous underwater vehicle (AUV), and in vivo photophysiology, we examined the composition, magnitude and origin of a bloom detected beneath the sea ice Northwest of Svalbard (Southern Yermak Plateau) in May 2010. In situ concentration of up to 20 mg chlorophyll a [Chl a] m⁻³, were dominated by the northern planktonic spring species of diatoms, Thalassiosira nordenskioeldii, T. antarctica var. borealis, Chaetoceros socialisspecies complex and Fragilariopsis oceanica. These species were also found south of the marginal ice zone (MIZ). Cells in the water column under the sea ice were typically high-light acclimated, with a mean light saturation index (E_k) of 138 μmol photons m⁻² s⁻¹ and a ratio between photoprotective carotenoids (PPC) and Chl a (w:w) of 0.2. Remotely sensed data of [Chl a] showed a 32,000 km² bloom developing south of the MIZ. In effect, our data suggest that the observed under-ice bloom was in fact a bloom developed in open waters south of the ice edge, and that a combination of northward-flowing water masses and southward drifting sea ice effectively positioned the bloom under the sea ice. This have implications for our general understanding of under-ice blooms, suggesting that their origin and connection with open water may be different in different regions of the Arctic.

Spatiotemporal evolution of the chlorophyll a trend in the North Atlantic Ocean

Analyses of the chlorophyll a concentration (chla) from satellite ocean color products have suggested the decadal-scale variability of chla linked to the climate change. The decadal-scale variability in chla is both spatially and temporally non-uniform. We need to understand the spatiotemporal evolution of chla in decadal or multi-decadal timescales to better evaluate its linkage to climate variability. Here, the spatiotemporal evolution of the chla trend in the North Atlantic Ocean for the period 1997-2016 is analyzed using the multidimensional ensemble empirical mode decomposition method. We find that this variable trend signal of chla shows a dipole pattern between the subpolar gyre and along the Gulf Stream path, and propagation along the opposite direction of the North Atlantic Current. This propagation signal has an overlapping variability of approximately twenty years. Our findings suggest that the spatiotemporal evolution of chla during the two most recent decades is part of the multidecadal variations and possibly regulated by the changes of Atlantic Meridional Overturning Circulation, whereas the mechanisms of such evolution patterns still need to be explored.

Phytoplankton can bypass nutrient reductions in eutrophic coastal water bodies

The EU-water framework directive aims at nutrient reductions, since anthropogenically induced eutrophication is a major threat for coastal waters. However, phytoplankton biomass in southern Baltic Sea coastal water bodies (CWB) remains high and the underlying mechanisms are not well understood. Therefore, a CWB data set was analysed regarding changes in phytoplankton biomass and nutrient concentration of nitrogen (N) and phosphorus (P) from 2000 to 2014. It was expected to find imbalances between produced phytoplankton biomass and total nutrient concentrations. Inner CWB were cyanobacteria-dominated and showed up to five times higher chlorophyll a-concentrations compared to outer CWB with similar total phosphorus-concentrations. Phytoplankton tended to be P-limited during spring and N-limited during summer. Phytoplankton biomass and nutrient concentrations were even higher during very humid years, which indicated a close coupling of the CWB with their catchment areas. This study suggests that re-mesotrophication efforts need to consider the importance of changed phytoplankton composition and nutrient availabilities.

A new tool for direct non-invasive evaluation of chlorophyll a content from diffuse reflectance measurements

Chlorophyll is a key biochemical component that is responsible for photosynthesis and is an indicator of plant health. The effect of stressors can be determined by measuring the amount of chlorophyll a, which is the most abundant chlorophyll, in vegetation in general. Nowadays, invasive methods and vegetation indices are used for establishing chlorophyll amount or an approximation to this value, respectively. This paper demonstrates that H-point curve isolation method (HPCIM) is useful for isolating the signal of chlorophyll a from non-invasive diffuse reflectance measurements of leaves. Spinach plants have been chosen as an example. For applying the HPCIM only the registers of both, a standard and the sample are needed. The results obtained by HPCIM and the invasive method were statistically similar for spinach leaves: 144±6mg/m² (n=5) and 155±40mg/m² (n=5), respectively. However, more precise values were achieved with the HPCIM, which also involved minimal experimental effort. The HPCIM method was applied to spinach plants stressed by the action of several pesticides and water scarcity, showing a decrease of chlorophyll a content with time, which is related with a loss of health. The results obtained were compared with those achieved by two different reflectance vegetation indices (Macc01 and NDVI). Although NDVI and HPCIM gave similar footprints for the plants tested, vegetation indices fail in the estimation of real content of the chlorophyll a. The HPCIM could contribute to improve the knowledge of the chlorophyll a content of vegetation like health indicator, by applying it to a much employed non-invasive technique such as diffuse reflectance, which can be used in place or in remote sensing mode.

Chlorophyll a in cyclodextrin supramolecular complexes as a natural photosensitizer for photodynamic therapy (PDT) applications

Chlorophyll a (Chl a), an amphipathic porphyrin, was employed as natural photosensitizer for photodynamic therapy applications. Due to its lacking solubility in water and high tendency to aggregate, Chl a was included into different modified cyclodextrins (CDs) to form stable water-soluble supramolecular complexes. To achieve this aim, 2-Hydroxypropyl-β-cyclodextrin (2-HP-β-CD), 2-Hydroxypropyl-γ-cyclodextrin (2-HP-γ-CD), Heptakis(2,6-di-o-methyl)-β-cyclodextrin (DIMEB) and Heptakis(2,3,6-tri-o-methyl)-β-cyclodextrin (TRIMEB) were used. The chemical physical properties of Chl a/CD complexes in cellular medium were studied by means of UV-Vis absorption spectroscopy. Results demonstrated the good aptitude of 2-HP-γ-CD, and more particularly of 2-HP-β-CD, to solubilize the Chl a in cell culture medium in monomeric and photoactive form. Then, Chl a/2-HP-β-CD and Chl a/2-HP-γ-CD complexes were evaluated in vitro on human colorectal adenocarcinoma HT-29 cell line, and cytotoxicity and intracellular localization were respectively assessed. Further tests, such as phototoxicity, ROS generation, intracellular localization and mechanism of cell death were then focused exclusively on Chl a/2-HP-β-CD system. This complex exhibited no dark toxicity and a high phototoxicity toward HT-29 cells inducing cell death via necrotic mechanism. Therefore, it is possible to affirm that Chl a/2-HP-β-CD supramolecular complex could be a promising and potential formulation for applications in photodynamic therapy.

Analysis on biomass and productivity of epilithic algae and their relations to environmental factors in the Gufu River basin, Three Gorges Reservoir area, China

The main purpose of this study conducted from August 2010 was to find biomass and productivity of epilithic algae and their relations to environmental factors and try to explore the restrictive factors affecting the growth of algae in the Gufu River, the one of the branches of Xiangxi River located in the Three Gorges Reservoir of the Yangtze River, Hubei Province, Central China. An improved method of in situ primary productivity measurement was utilized to estimate the primary production of the epilithic algae. It was shown that in rivers, lakes, and reservoirs, algae are the main primary producers and have a central role in the ecosystem. Chlorophyll a concentration and ash-free dry mass (AFDM) were estimated for epilithic algae of the Gufu River basin in Three Gorges Reservoir area. Environmental factors in the Gufu River ecosystem highlighted differences in periphyton chlorophyll a ranging from 1.49 mg m^-2 (origin) to 69.58 mg m^-2 (terminal point). The minimum and maximum gross primary productivity of epilithic algae were 96.12 and 1439.89 mg C m^-2 day^-1, respectively. The mean net primary productivity was 290.24 mg C m^-2 day^-1. The mean autotrophic index (AFDM:chlorophyll a) was 407.40. The net primary productivity, community respiration ratio (P/R ratio) ranged from 0.98 to 9.25 with a mean of 2.76, showed that autotrophic productivity was dominant in the river. Relationship between physicochemical characteristics and biomass was discussed through cluster and stepwise regression analysis which indicated that altitude, total nitrogen (TN), NO₃^--N, and NH₄⁺-N were significant environmental factors affecting the biomass of epilithic algae. However, a negative logarithmic relationship between altitude and the chlorophyll a of epilithic algae was high. The results also highlighted the importance of epilithic algae in maintaining the Gufu River basin ecosystems health.

Chlorophyll a with a farnesyl tail in thermophilic cyanobacteria

Photosystem II (PSII) of oxygenic photosynthetic organisms normally contains exclusively chlorophyll a (Chl a) as its major light-harvesting pigment. Chl a canonically consists of the chlorin headgroup with a 20-carbon, 4-isoprene unit, phytyl tail. We have examined the 1.9 Å crystal structure of PSII from thermophilic cyanobacteria reported by Shen and coworkers in 2012 (PDB accession of 3ARC/3WU2). A newly refined electron density map from this structure, presented here, reveals that some assignments of the cofactors may be different from those modeled in the 3ARC/3WU2 structure, including a specific Chl a that appears to have a truncated tail by one isoprene unit. We provide experimental evidence using high-performance liquid chromatography and mass spectrometry for a small population of Chl a esterified to a 15-carbon farnesyl tail in PSII of thermophilic cyanobacteria.

Chlorophyll a with a farnesyl tail in thermophilic cyanobacteria

Photosystem II (PSII) of oxygenic photosynthetic organisms normally contains exclusively chlorophyll a (Chl a) as its major light-harvesting pigment. Chl a canonically consists of the chlorin headgroup with a 20-carbon, 4-isoprene unit, phytyl tail. We have examined the 1.9 Å crystal structure of PSII from thermophilic cyanobacteria reported by Shen and coworkers in 2012 (PDB accession of 3ARC/3WU2). A newly refined electron density map from this structure, presented here, reveals that some assignments of the cofactors may be different from those modeled in the 3ARC/3WU2 structure, including a specific Chl a that appears to have a truncated tail by one isoprene unit. We provide experimental evidence using high-performance liquid chromatography and mass spectrometry for a small population of Chl a esterified to a 15-carbon farnesyl tail in PSII of thermophilic cyanobacteria.

In situ spectral response of the Arabian Gulf and Sea of Oman coastal waters to bio-optical properties

Mapping of Chlorophyll-a (Chl-a) over the coastal waters of the Arabian Gulf and the Sea of Oman using the satellite-based observations, such as MODIS (Moderate Resolution Imaging Spectro-radiometer), has shown inferior performance (Chl-a overestimation) than that of deep waters. Studies in the region have shown that this poor performance is due to three reasons: (i) water turbidity (sediments re-suspension), and the presence of colored dissolved organic matter (CDOM), (ii) bottom reflectance and (iii) incapability of the existing atmospheric correction models to reduce the effect of the aerosols from the water leaving radiance. Therefore, this work focuses on investigating the sensitivity of the in situ spectral signatures of these coastal waters to the algal (chlorophyll: Chl-a), non-algal (sediments and CDOM) and the bottom reflectance properties, in absence of contributions from the atmosphere. Consequently, the collected in situ spectral signatures will improve our understanding of Arabian Gulf and Sea of Oman water properties. For this purpose, comprehensive field measurements were carried out between 2013 and 2016, over Abu-Dhabi (Arabian Gulf) and Fujairah (Sea of Oman) where unique water quality data were collected. Based on the in situ water spectral analysis, the bottom reflectance (water depth<20m) are found to degrade the performance of the conventional ocean color algorithms more than the sediment-laden waters where these waters increase the R_rsat the blue and red ranges. The increasing presence of CDOM markedly decreases the R_rsin the blue range, which is conflicting with the effect of Chl-a. Given the inadequate performance of the widely used ocean-color algorithms (OC3: ocean color 3, OC2: ocean color 2) in retrieving Chl-a in these very shallow coastal waters, therefore, a new algorithm is proposed here based on a 3-bands ratio approach using [R_rs (656) ^-1-R_rs (506) ^-1]×R_rs (661). The selected optimum bands (656nm, 506nm, and 661nm) from this approach can be used to retrieve the Chl-a more accurately in these coastal Case II (turbid) waters which are close to the bands of the current missions such as Sentinel-3 OLCI (Ocean and Land Colour Instrument), MODIS, VIIRS (Visible Infrared Imaging Radiometer Suite) and LandSat 8. However, more uniformly distributed data over the Arabian Gulf is required to have a highly accurate regional model for Chl-a retrieval.

An assessment of direct and indirect effects of two herbicides on aquatic communities

Herbicides are often detected in watersheds at concentrations that are toxic to phytoplankton, potentially causing indirect effects on higher trophic organisms. The long-term effects of 5 applications over 30 d of binary mixtures of the herbicides diuron and hexazinone were assessed at "low" and "high" concentrations typically found in the environment, using mesocosms. Sixteen of 95 phytoplankton taxa, 3 of 18 zooplankton taxa, and 6 of 14 macroinvertebrate taxa responded negatively to contaminant exposures. Herbicide applications altered the phytoplankton community structure. Relative abundance of Cyanophyceae decreased following 5 applications from 52.1% in the control to 37.3% in the low treatment and to 25.9% in the high treatment, while Chlorophyceae increased to 50.6% in the low treatment and to 61.7% in the high treatment compared with the control (39.7%). Chlorophyceae had the greatest number of affected species (8), whereas 1 species within the Cyanophyceae was negatively affected on more than 1 sampling day. Further, chlorophyll a was reduced on 4 and 5 d out of the 8 total sampling days in the low and high treatments, respectively, compared with the control. These results highlight that integrating multiple taxa and contaminants with long-term exposures in ecological risk assessments of herbicides can facilitate the ability to make predictive and mechanistic generalizations about the role of herbicides in shaping patterns of species abundance in natural systems. Environ Toxicol Chem 2017;36:2234-2244. © 2017 SETAC.

Coastal and inland water monitoring using a portable hyperspectral laser fluorometer

The potential for a ship-mounted laser fluorometer to provide rapid, non-intrusively measurements in both coastal and lake conditions are investigated. The instrument consists of a high pulse repetition frequency (10-kHz) microchip laser for fluorescence excitation, a broadband hyperspectral micro spectrometer for spectral detection, and a confocal reflective fluorescent probe for signal collection; it weighs only about 1.7kg. Chlorophyll a (chl-a) and colored dissolved organic matter (CDOM) measured by the new instrument were observed to agree well with those measured by traditional time-consuming laboratory methods in Hangzhou Bay seawater and Qiandao Lake inland water. Subsequently, laser fluorescence distribution and characteristics of chl-a and CDOM in these regions were analyzed, which will improve our understanding of biogeochemical processes in these optically complex aquatic systems. The portable system is promising for water environment monitoring, especially in coastal and inland water.

Challenges for the WFD second management cycle after the implementation of a regional multi-municipality sanitation system in a coastal lagoon (Ria de Aveiro, Portugal)

In the scope of the first WDF management cycle, a multi-municipality sanitation system with secondary treatment was implemented in 2005 in Ria de Aveiro coastal lagoon, with the treated effluent discharging into the Atlantic Ocean through a submarine outfall. The lagoon water chemical status was evaluated regarding dissolved inorganic nutrients and chlorophyll a before and after 2005. The S. Jacinto outfall has effectively reduced the point source nutrient loads (ammonium and phosphate) into Ria de Aveiro, representing a step forward for the implementation of the WFD, through eutrophication abatement. However, the lagoon remains exposed to non-point nitrogen sources, as a consequence of the current land use and water management, which in a scenario of winter extreme precipitation events, nutrients increase through surface run-off. Besides, in a combined scenario of low freshwater input into the lagoon and favourable oceanic condition, nutrients enter through Ria outer boundary coming from the S. Jacinto outfall. Thus, changes in the system hydrodynamics in the context of global change might pose new challenges regarding the WFD second management cycle involving the second river basin management plan and the first flood risk management plan, foreseeing the 'Good' ecological status in all Ria's Water Bodies.

Effect of florfenicol and thiamphenicol exposure on the photosynthesis and antioxidant system of Microcystis flos-aquae

Florfenicol (FF) and thiamphenicol (TAP) are two typical pharmaceuticals used widely as therapeutica antibiotic agents in aquaculture. However, little is known about the potential adverse effects of these two antibiotics on non-target organisms in the aquatic ecosystem. In this study we investigated the effects of FF and TAP on photosynthesis and the antioxidant system of the cyanobacteria Microcystis flos-aquae. Over a concentration range of 0.001-1μg/L, the results showed that both FF and TAP significantly increased the chlorophyll a content of M. flos-aquae, while the superoxide dismutase (SOD) activity, catalase (CAT) activity and the levels of malondialdehyde (MDA) changed slightly. In contrast, the chlorophyll a content of M. flos-aqua was significantly inhibited (p<0.01) at high concentrations (>1μg/L) of FF and TAP, reaching a 46% inhibition level at 50μg/L FF and 56% inhibition at 100μg/L TAP. At the same time, the activities of SOD and CAT along with MDA content also increased significantly (p<0.01), indicating that the high concentrations of both FF and TAP led to oxidative stress in the algae. In addition, the M. flos-aquae fluorescence parameters (Fv/Fm, Fv/Fo, alpha, ETRmax and Ik) increased with increasing concentration of both FF and TAP, which may be the result of the increasing photoprotection capacity.

Long-term changes in nutrients, chlorophyll a and their relationships in a semi-enclosed eutrophic ecosystem, Bohai Bay, China

As the representative semi-enclosed bay of China, Bohai Bay has experienced severe eutrophication in recent decades. Monitoring data from 1995 to 2013 were analysed by generalized additive models (GAMs) to explore the temporal variations in nutrients concentrations, nutrient ratios, chlorophyll a (Chl a) concentrations and the responses of Chl a to the changes in nutrients in the spring and summer. The results showed that dissolved inorganic nitrogen (DIN) decreased from 1995 to 2000 but increased after 2000 in both the spring and summer, and soluble reactive phosphorus (SRP) decreased while the molar nitrogen/phosphorus (N/P) ratios (DIN to SRP) increased over the last two decades. Generally, P-limited phytoplankton growth was observed in the spring and summer and DIN was identified as the main pollutant constituent in Bohai Bay. Furthermore, negative correlations were found between DIN and Chl a in summer in Bohai Bay.

Significant seasonal variations of microbial community in an acid mine drainage lake in Anhui Province, China

Acid mine drainage (AMD),characterized by strong acidity and high metal concentrations, generates from the oxidative dissolution of metal sulfides, and acidophiles can accelerate the process significantly. Despite extensive research in microbial diversity and community composition, little is known about seasonal variations of microbial community structure (especially micro eukaryotes) in response to environmental conditions in AMD ecosystem. To this end, AMD samples were collected from Nanshan AMD lake, Anhui Province, China, over a full seasonal cycle from 2013 to 2014, and water chemistry and microbial composition were studied. pH of lake water was stable (∼3.0) across the sampling period, while the concentrations of ions varied dramatically. The highest metal concentrations in the lake were found for Mg and Al, not commonly found Fe. Unexpectedly, ultrahigh concentration of chlorophyll a was measured in the extremely acidic lake, reaching 226.43-280.95 μg/L in winter, even higher than those in most eutrophic freshwater lakes. Both prokaryotic and eukaryotic communities showed a strong seasonal variation. Among the prokaryotes, "Ferrovum", a chemolithotrophic iron-oxidizing bacterium was predominant in most sampling seasons, although it was a minor member prior to September, 2012. Fe²⁺ was the initial geochemical factor that drove the variation of the prokaryotic community. The eukaryotic community was simple but varied more drastically than the prokaryotic community. Photoautotrophic algae (primary producers) formed a food web with protozoa or flagellate (top consumers) across all four seasons, and temperature appeared to be responsible for the observed seasonal variation. Ochromonas and Chlamydomonas (responsible for high algal bloom in winter) occurred in autumn/summer and winter/spring seasons, respectively, because of their distinct growth temperatures. The closest phylogenetic relationship between Chlamydomonas species in the lake and those in Arctic and Alpine suggested that the native Chlamydomonas species may have been both acidophilic and psychrophilic after a long acclimation time in this extreme environment.

Chemical composition and biomass of Coscinodiscus asteromphalus in Jiaozhou Bay, China

The large diatom Coscinodiscus asteromphalus was separated from seawater in Jiaozhou Bay using a repeated precipitation method and then its chemical compositions of carbon (C), nitrogen (N), phosphorus (P), and silicon (Si) combined with chlorophyll a (Chl a) were examined for the first time for a natural population in this study. Results show that the contents of carbon, nitrogen, phosphorus, silicon, and Chl a in C. asteromphalus cells were 35,610.5, 9374.2, 352.4, 1105.5, and 1767.0 pg/cell, respectively, and the corresponding molar ratios of C/N, N/P, Si/P, and Si/N in C. asteromphalus cells were 4.5, 66.0, 2.7, and 0.07, respectively, which are different from the Redfield ratio. Additionally, their C/Chl a mass ratio was 23.2. High N/P ratio and low Si/P and Si/N ratios in C. asteromphalus cells were consistent with those in particulates of any size and seawater in the bay, reflecting an ecological response of phytoplankton to the nutrient structure of seawater, suggesting Si limitation to phytoplankton growth. The fact that C. asteromphalus spread all over the bay mainly in summer and autumn and the fact that Chl a content in C. asteromphalus cells could account for a maximum percentage of 78% of those in the water column suggest that the contribution of C. asteromphalus to phytoplankton biomass was significant in Jiaozhou Bay.

Copepod grazing and their impact on phytoplankton standing stock and production in a tropical coastal water during the different seasons

The grazing rate of copepods on the total and size-fractionated phytoplankton biomass in a coastal environment (off Kochi, southwest coast of India) were measured during pre-monsoon (PRM), peak southwest monsoon (PKSWM), late southwest monsoon (LSWM) and post-southwest monsoon (PSWM). The phytoplankton standing stock (chlorophyll a-Chl. a) and growth rate (GR) were less during the PRM (Chl. a 0.58 mg m^-3; GR 0.23 ± 0.02) and PSWM (Chl. a 0.89 mg m^-3; GR 0.30 ± 0.05) compared to PKSWM (Chl. a 6.67 mg m^-3; GR 0.43 ± 0.02) and LSWM (Chl. a 4.09 mg m^-3; GR 0.40 ± 0.04). The microplankton contribution to the total Chl. a was significant during the PKSWM (41.83%) and LSWM (45.72%). Copepod density was lesser during the PRM (1354 No m^-3) and PSWM (1606 No m^-3) than during PKSWM and LSWM (4571 and 3432 No m^-3, respectively). Seasonal changes in phytoplankton biomass, phytoplankton size structure, and copepod community were closely related to the hydrographical transformations in the study domain. Dominant calanoid copepods in the study region ingested 8.4 to 14.2% of their daily ration from phytoplankton during the PRM and PSWM, which increased to >50% during the PKSWM and LSWM. The cyclopoid Oithona similis was abundant during the PKSWM, ingesting only 21% of their daily ration from phytoplankton. Temporal variation in the phytoplankton biomass and copepod species composition caused differences in community level top-down control. The copepod community ingestion on phytoplankton was high during the LSWM (18,583 μg C m^-3d^-1), followed by PKSWM (9050 μg C m^-3d^-1), PSWM (1813 μg C m^-3d^-1), and PRM (946 μg C m^-3d^-1). During the low Chl. a period (PRM and PSWM), dominant calanoid copepods showed a positive selectivity for the micro- and nano-phytoplankton size fractions, whereas during the high Chl. a period (PKSWM and LSWM), they showed a positive selection for nano-phytoplankton fractions. Irrespective of the seasons, dominant calanoid copepods showed a negative selection of pico-phytoplankton fraction. The cyclopoid O. similis and Poecilostomatoid Corycaeus danae showed a positive selection of nano- and pico-phytoplankton fractions rather than micro-fraction. The grazing pressure of copepod community ingestion on micro-fraction was less (0.56% of the phytoplankton biomass and 1.06% of the phytoplankton production) during the PKSWM. This study provides, for the first time, clear findings on the seasonal variation in the top-down control of phytoplankton by copepods in a tropical coastal water ecosystem and discusses its implications on phytoplankton blooming, plankton food web, and biogeochemistry.

Do Varying Aquatic Plant Species Affect Phytoplankton and Crustacean Responses to a Nitrogen-Permethrin Mixture?

Hydraulically connected wetland microcosms vegetated with either Typha latifolia or Myriophyllum aquaticum were amended with an NH₄NO₃ and permethrin mixture to assess the effectiveness of both plant species in mitigating effects of the pollutant mixture on phytoplankton (as chlorophyll a) and Hyalella azteca. Phytoplankton grew in response to increased NH₄NO₃ in the presence of all plant species, but was unaffected by exposure to permethrin. H. azteca responses occurred rapidly (0.17 days), was mitigated within 1-2 days, and aqueous toxicity was unaffected by plant species type. A toxic unit model approach ascertained primary toxicity was permethrin with minimal additional toxicity from NH₄NO₃. Varying aquatic plant species had only modest influences on phytoplankton responses and no observable influence on animal responses during nitrogen-permethrin mixture exposures. As a result, both T. latifolia and M. aquaticum can be used as part of an effective agricultural best-management practice system for mitigating pollutant impacts of agricultural run-off.

Spatial and temporal distributions of Secchi depths and chlorophyll a concentrations in the Suo Nada of the Seto Inland Sea, Japan, exposed to anthropogenic nutrient loading

Thirty years of monitoring data were used to elucidate the spatial and temporal distributions of Secchi depths in the Suo Nada (Suo Sea) and to evaluate how chlorophyll a concentration and reductions of nutrient loading from the watershed affected those distributions. Secchi depths throughout the Suo Nada were positively correlated with water depths. The spatial and temporal variations of Secchi depths could be explained by variations of phytoplankton biomass in areas where the water depth exceeded 20m, but in areas shallower than 10m, other factors affecting light attenuation beside phytoplankton, which include suspended particulate matter and chromophoric dissolved organic matter, obscured relationships between phytoplankton biomass and Secchi depths. Phosphorus limited phytoplankton biomass in the Suo Nada. The main source of allochthonous phosphorus from the 1980s to the 1990s was the watershed. Because of significant reductions of nutrient loading from the watershed, the Pacific Ocean will most likely be the principal source of allochthonous phosphorus after around 2000, except in areas shallower than 10m.

Abnormally high phytoplankton biomass near the lagoon mouth in the Huangyan Atoll, South China Sea

Nutrient concentration and phytoplankton biomass were investigated in Huangyan Atoll in May 2015. The concentrations of nutrients were very low, and dissolved inorganic nitrogen was composed mainly of ammonia. Nitrogen likely was the primary limiting factor for phytoplankton growth. The spatial variation of phytoplankton biomass was significant among the lagoon, reef flats, and outer reef slopes. Extremely high chlorophyll a concentration and micro-phytoplankton abundance were found in the region near the lagoon mouth. This high phytoplankton biomass might be due to nutrient input from fishing vessels and phytoplankton aggregation driven by the southwestern wind. Our results indicate that phytoplankton biomass could be a reliable indicator of habitat differences in this coral reef ecosystem, and micro-phytoplankton seems to be more sensitive to nutrient input than pico-phytoplankton.

Evaluation of antidesmone alkaloid as a photosynthesis inhibitor

Antidesmone, isolated from Waltheria brachypetala Turcz., owns special structural features as two α,β-unsaturated carbonyl groups and a side alkyl chain that can compete with the quinones involved in the pool of plastoquinones at photosystem II (PSII). In this work, we showed that the alkaloid is an inhibitor of Hill reaction and its target was located at the acceptor side of PSII. Studies of chlorophyll (Chl) a fluorescence showed a J-band that indicates direct action of antidesmone in accumulation of Q_A^- (reduced plastoquinone A) due to the electron transport blocked at the Q_B (plastoquinone B) level similar to DCMU. In vivo assays indicated that antidesmone is a selective post-emergent herbicide probe at 300μM by reducing the biomass production of Physalis ixacarpa plants. Furthermore, antidesmone also behaves as pre-emergent herbicide due to inhibit Physalis ixacarpa plant growth about 60%. Antidesmone, a natural product containing a 4(1H)-pyridones scaffold, will serve as a valuable tool in further development of a new class of herbicides.

Hoarding and horizontal transfer led to an expanded gene and intron repertoire in the plastid genome of the diatom, Toxarium undulatum (Bacillariophyta)

Although the plastid genomes of diatoms maintain a conserved architecture and core gene set, considerable variation about this core theme exists and can be traced to several different processes. Gene duplication, pseudogenization, and loss, as well as intracellular transfer of genes to the nuclear genome, have all contributed to variation in gene content among diatom species. In addition, some noncoding sequences have highly restricted phylogenetic distributions that suggest a recent foreign origin. We sequenced the plastid genome of the marine diatom, Toxarium undulatum, and found that the genome contains three genes (chlB, chlL, and chlN) involved in light-independent chlorophyll a biosynthesis that were not previously known from diatoms. Phylogenetic and syntenic data suggest that these genes were differentially retained in this one lineage as they were repeatedly lost from most other diatoms. Unique among diatoms and other heterokont algae sequenced so far, the genome also contains a large group II intron within an otherwise intact psaA gene. Although the intron is most similar to one in the plastid-encoded psaA gene of some green algae, high sequence divergence between the diatom and green algal introns rules out recent shared ancestry. We conclude that the psaA intron was likely introduced into the plastid genome of T. undulatum, or some earlier ancestor, by horizontal transfer from an unknown donor. This genome further highlights the myriad processes driving variation in gene and intron content in the plastid genomes of diatoms, one of the world's foremost primary producers.

Genome-wide association mapping of soybean chlorophyll traits based on canopy spectral reflectance and leaf extracts

BACKGROUND

Chlorophyll is a major component of chloroplasts and a better understanding of the genetic basis of chlorophyll in soybean [Glycine max (L.) Merr.] might contribute to improving photosynthetic capacity and yield in regions with adverse environmental conditions. A collection of 332 diverse soybean genotypes were grown in 2 years (2009 and 2010) and chlorophyll a (eChl_A), chlorophyll b (eChl_B), and total chlorophyll (eChl_T) content as well as chlorophyll a/b ratio (eChl_R) in leaf tissues were determined by extraction and spectrometric determination. Total chlorophyll was also derived from canopy spectral reflectance measurements using a model of wavelet transformed spectra (tChl_T) as well as with a spectral reflectance index (iChl_T).

RESULTS

A genome-wide associating mapping approach was employed using 31,253 single nucleotide polymorphisms (SNPs) to identify loci associated with the extract based eChl_A, eChl_B, eChl_R and eChl_T measurements and the two canopy spectral reflectance-based methods (tChl_T and iChl_T). A total of 23 (14 loci), 15 (7 loci) and 14 SNPs (10 loci) showed significant association with eChl_A, eChl_B and eChl_R respectively. A total of 52 unique SNPs were significantly associated with total chlorophyll content based on at least one of the three approaches (eChl_T, tChl_T and iChl_T) and likely tagged 27 putative loci for total chlorophyll content, four of which were indicated by all three approaches.

CONCLUSIONS

Results presented here show that markers for chlorophyll traits can be identified in soybean using both extract-based and canopy spectral reflectance-based phenotypes, and confirm that high-throughput phenotyping-amenable canopy spectral reflectance measurements can be used for association mapping.

Recent evolution of the physical-chemical characteristics of a Site of National Interest-the Mar Piccolo of Taranto (Ionian Sea)-and changes over the last 20 years

The Mar Piccolo of Taranto, classified as a 'Site of National Interest' (SIN), is a semi-enclosed basin divided into two inlets with lagoon features and sea influences, seriously affected by anthropic activities. In the framework of the RITMARE project, a study has been carried out to evaluate the functionality of this ecosystem. As part of this work, measurements of the water abiotic parameters were performed in order to assess the physical-chemical features of this area after the activation, in the last decade, of treatment plants for various urban and industrial dumping. Seawater intrusions and continental inputs, as well as several submarine freshwater springs, clearly affect physical-chemical characteristics of the water column in the two inlets. This finding suggests that small-scale patterns in water circulation have the potential to influence the chemical properties of the seawater. The comparison with a 20-year dataset reveals a drastic decrease in nutrient concentrations after the year 2000, validating the functionality of the treatment plants. The reduction of nutrient inputs into the basin (up to -90 % in the first inlet characterized by lower hydraulic residence time) has changed the biogeochemical characteristics of the Mar Piccolo from being relatively eutrophic to moderately oligotrophic.