The ecological competition and grazing reverse the effects of sulfamethoxazole on plankton: a case study on characterizing community-level effect

Potential geographical distribution of harmful algal blooms caused by the toxic dinoflagellate Karenia mikimotoi in the China Sea

The fish-killing dinoflagellate Karenia mikimotoi frequently blooms in China and poses a threat to food safety and human health. To better understand harmful algal blooms (HABs) caused by K. mikimotoi and predict the risk of HABs under climate change, the combined effect of nitrate and norfloxacin (NOR) on the growth of K. mikimotoi was tested. A growth model was used to test the effects of nutrients and pollutants on the carrying capacity of the unicellular algae. The carrying capacity increased with increasing concentrations of nitrate and NOR, reaching a maximum at 62.2 μmol L-1 of nitrate and 9.03 mg L-1 of NOR. The calculated carrying capacity of K. mikimotoi in the China Sea showed a declining trend from nearshore to offshore, with a value >30 × 106 cells L-1 in the estuary of the Changjiang River and Hangzhou Bay. The HAB index proposed in this study as a measurement of HAB risk was constructed using the carrying capacity and relative abundance from the MaxEnt (maximum entropy) model. The index showed that HABs caused by K. mikimotoi consecutively occurred in Zhejiang and Fujian coastal waters and predicted that they will continue until 2100, regardless of the greenhouse gas emission scenario. The center of the integrated area moved northward, with a range of 120-900 km. The HAB index integrates the characteristics of the carrying capacity and suitability of habitats, and expresses the information contained in the intensive and extensive variables that affect HAB occurrence. This index is a promising predictor of HAB risk in coastal waters.

Effect of Different Influent Conditions on Biomass Production and Nutrient Removal by Aeration Microalgae Membrane Bioreactor (ICFB-MMBR) System for Mariculture Wastewater Treatment

The nutrient removal and biomass production of the internal circulating fluidized bed microalgae membrane bioreactor (ICFB-MMBR) was studied under different cultivation modes, influent TOC, influent pH, and influent N/P. Platymonas helgolandica tsingtaoensis was used as the biological source. The growth of P. helgolandica tsingtaoensis and the removal efficiency of pollutants in the mixotrophy culture mode were improved compared with other culture modes. With the increased influent TOC, the average growth rate of P. helgolandica tsingtaoensis increased, and ammonia nitrogen and total phosphorus removal rate were improved. The P. helgolandica tsingtaoensis growth rate and nutrient removal efficiencies at the influent pH of 8 were the best among the different influent pH values. As the influent N/P ratio increased from 5 to 20, the P. helgolandica tsingtaoensis growth rate and pollutant removal rate increased gradually. When the influent N/P ratio was higher than 20, the P. helgolandica tsingtaoensis growth rate and pollutant removal rate tended to be stable and did not significantly change with the increase of influent N/P ratio. At the proper influent conditions, the high P. helgolandica tsingtaoensis biomass and nutrient removal efficiency could be obtained in the microalgae membrane bioreactor, which could provide a theoretical basis for the application of the system for wastewater treatment.

Wheat and ryegrass biomass ashes as effective sorbents for metallic and organic pollutants from contaminated water in lab-engineered cartridge filtration system

Three plant biomasses (miscanthus, ryegrass and wheat) have been considered for the preparation of five different sorbents evaluated for their potential to sorb cadmium and lead and four emergent organic compounds (diclofenac, sulfamethoxazole, 17α-ethynylestradiol and triclosan) from artificially contaminated water. Lab-created cartridges were filled with each sorbent and all experiments were systematically compared to activated charcoal Norit®. Results from activated charcoal, wheat straw and acidified wheat straw were supported by the Langmuir and Freundlich models. Wheat straw ashes were an excellent metal extractor that exceeded the potential of well-known activated charcoal. Acidified sorbents (wheat and ryegrass) were very effective in eliminating the selected emerging organic contaminants displaying equipotent or superior activity compared to activated charcoal. These results open the way for further in natura studies by proposing new biosource materials as new effective tools in the fight against water pollution.

A light-limited growth model considering the nutrient effect for improved understanding and prevention of macroalgae bloom

A useful growth process model for Ulva prolifera with light limitation considering the nutrient effect was proposed to better understand the development of macroalgae bloom. The interrelationship between light and nutrient limitation was demonstrated to obtain the mechanism. As a case study, thresholds of light and nutrients for different stages of Ulva prolifera growth were estimated using the proposed model. Limits of light intensity, nitrate, and phosphate concentration on the initial growth were found to be 40.0 W m^-2, 6.5 μmol L^-1, and 0.27 μmol L^-1, respectively. The minimal light intensity for initial growth was found to increase monotonously with decrease in the nutrient concentration. It was also observed that the minimal light intensity for growth increases as the density of Ulva prolifera increases and the nutrient concentration decreases. Similarly, the minimal nutrient concentration for initial growth increases monotonously with decrease in the light intensity. In addition, the minimal nutrient concentration for growth increases with increase in the density of Ulva prolifera and decrease in the light intensity. It was demonstrated that the phosphate limitation on the initial growth of Ulva prolifera seedling can occur in most coastal waters of the southern Yellow Sea and a tendency of approaching the phosphate limitation on the growth of the floating thalli of Ulva prolifera exists. Evidence was provided to support the argument that the macroalgae thalli from aquaculture rafts, rather than that from seedlings or spores, can contribute to the original biomass of the floating green Ulva prolifera in the southern Yellow Sea. The model presented in this study can provide new insights into the interrelationship between the light and nutrient limitation, as well as into the growth mechanism of floating seaweeds. It can also provide a more accurate prediction of seaweed growth in light- and nutrient-limited environments.

A toxic effect at molecular level can be expressed at community level: A case study on toxic hierarchy

This study demonstrated hierarchical toxicity and addressed the relevance and differences of toxic effects at the molecular, individual, population, and community levels. Superoxide dismutase (SOD) activity, photosynthetic oxygen production, filtration rate, life span and densities of Platymonas helgolandica var. tsingtaoensis, Isochrysis galbana, and Brachionus plicatilis in single-species tests and customized community tests were examined in response to a concentration gradient of aniline ranging from 0 to 50.0 mg L^-1. The SOD activity was the most sensitive endpoint with the fastest response to aniline according to the calculated no-detection of toxic effect concentration (NDEC) and the EC₅₀. The individual- and population-level endpoints, showing a lower response to aniline, could be constructed from the SOD activity in a stepwise manner. A multi-scale hierarchical model with endpoints at 4 levels was used to characterize toxic effects, at the scales of time and size. Linkage of SOD activity to toxic effects at a community level was established level by level to express the change in the customized community with the concentration of aniline. The calculated threshold concentration of aniline for the customized community was nearly equal to the minimum NDEC, demonstrating as great an impact on interactions by the toxic effect at subpopulation-level as that at the community level. However, we identified a trend of higher sensitivities of measured endpoints at sub-population level, decreasing sensitivity at higher levels but a great variety of sensitivities at community level. Although the characteristics of toxic effects are different at different levels, the structure and process of endpoints at adjacent levels are related to and interact with each other. The resulted indirect effects, together with direct effect, determine the toxic effect at every levels of biological complexity. The toxic effects at adjacent levels should be studied at the same time to better understand the ecological risk of contaminants.