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Ecological risk assessment of chemicals focuses on the response of different taxa in isolation not taking ecological and evolutionary interplay in communities into account. Its consideration would, however, allow for an improved assessment by testing for implications within and across trophic levels and changes in the phenotypic and genotypic diversity within populations. We present a simple experimental system that can be used to evaluate the ecological and evolutionary responses to chemical exposure at microbial community levels. We exposed a microbial model system of the ciliate Tetrahymena thermophila (predator) and the bacterium Pseudomonas fluorescens (prey) to iron released from Magnetic Particles (MP-Fedis), which are Phosphorus (P) adsorbents used in lake restoration. Our results show that while the responses of predator single population size differed across concentrations of MP-Fedis and the responses of prey from communities differed also across concentration of MP-Fedis, the community responses (species ratio) were similar for the different MP-Fedis concentrations. Looking further at an evolutionary change in the bacterial preys' defence, we found that MP-Fedis drove different patterns and dynamics of defence evolution. Overall, our study shows how similar community dynamics mask changes at evolutionary levels that would be overlooked in the design of current risk assessment protocols where evolutionary approaches are not considered.

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This study assessed the convenience of using magnetic particles (MPs) to reduce phosphorus (P) concentration in treated wastewater. The working hypothesis is that MP addition increases P removal in artificial wastewater treatment ponds. Water samples were collected at the inlet and outlet of a semi-natural pond receiving secondary municipal effluent that is discharged in a Ramsar site (Fuente de Piedra, Málaga, Spain). Then, laboratory batch experiments were run to (i) assess the effect of adding MPs on the chemical composition of treated wastewater, (ii) identify the number of adsorption cycles (by reusing MPs) which are able to trap a high percentage of P (>50%) and (iii) select the optimum ratio between MP mass and initial dissolved inorganic P (DIP) concentration. The results show the suitability of using MPs to remove P in treated wastewater due to both their high equilibrium adsorption capacity (q) and P removal efficiency. Lastly, considering its practical and economical relevance, based on the advantages (P removal efficiency) and disadvantages (economic price), the optimum dose of MPs (0.16 g MP mg-1 P) to achieve a high P removal efficiency (>50%) was identified.

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Inactivation by adding different phosphorus (P) adsorbents is one of the most frequently used methods for combating inland water eutrophication. The aim of this work was to assess the toxic effects of novel P adsorbents (magnetic particles, MPs) on the phytoplankton community. An outdoor microcosm experiment, containing lake water and surface sediment from a hypertrophic Mediterranean lake, was carried out following a factorial design (n = 5) with three different treatments: control (C), where no MPs were added; Treatment-Water (T-W) and Treatment-Sediment (T-S). In T-W and T-S treatments, MPs were added on the surface water layer and on the sediment, respectively, to obtain a final concentration of 1.4 g MP L-1. This concentration was based on both the sedimentary mobile P concentration of the study site and the maximum P adsorption capacity of the MPs, obtained from the literature. After 24 h of contact time, the MPs were removed using a magnetic rake. Physicochemical measurements and biological samples were taken after 24 h of exposure to the MPs and at different time points after such exposure (day 2, 7, 21, 35 and 70). Changes in phytoplankton community such as abundance (biovolume and Chla), species composition and taxonomic groups were assessed, as well as changes in the Shannon-Wiener diversity index. Additionally, the eutrophic metric Algae Group Index (AGI), one of the metrics proposed in the Water Framework Directive, was also calculated. Our results indicate that there is no strong evidence to infer that MPs caused an effect on the phytoplankton community, since no significant differences (GLM test; p > 0.05) were found between controls and treatments in any of the studied variables (phytoplankton taxonomic groups, AGI, Chla concentration, biovolume, diversity and community responses). Accordingly, MPs did not cause any toxic effects on the phytoplankton community of the lake, encouraging the use of MPs in a future whole-lake restoration strategy. However, if the final goal of the restoration plan is to combat nuisance cyanobacteria blooms, higher initial MPs doses or repeated MPs applications are required to achieve a reduction in P concentrations below biological thresholds in order to prevent algal blooms.

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Aquatic population responses to chemical exposure may be exacerbated by intraspecific competition pressures, being also shaped by habitat heterogeneity. Magnetic particles (MPs) have been recently proposed as promising phosphorus (P) adsorbents for lake restoration. This study focuses on assessing the effects of MPs on the abundance of the crustacean Daphnia magna under different levels of both intraspecific competition pressure and habitat heterogeneity. The experimental design consisted of two experiments (in homogeneous and heterogeneous habitats) done in glass jars with four concentrations of MPs: controls of 0g MPsL-1, and treatments of 1, 1.5 and 2g MPsL-1. In addition, competition treatments were established by using different population densities, and hence, no competition (C), low (L) and high (H) competition pressures were simulated. The experiments lasted for 7 days, with a 4-day pre-exposure period, in which competition was all allowed to take place, and a 3-day post-exposure period. Twenty-four hours after adding MPs, the MPs were removed by applying a magnetic separation technique. The results showed that competition pressures occurred and significantly reduced population abundances during the pre-exposure period. During the post-exposure period, the combined effects of competition and MPs were detected in both homogeneous (Ho-) and heterogeneous (He-) habitat experiments, showing a significantly drastic reduction in abundances. In fact, the lethal concentration for 50% of the population (LC50 -24h) was 0 and 0.16g MPsL-1 in the Ho- and He-experiments respectively, indicating that the addition and especially the removal of MPs cause extreme mortality. These results indicated that even though competition plays a role in shaping populations, its influence was down-weighted by the stronger pressures of MPs. In addition, as no significant differences between homogeneous and heterogeneous habitats were found, we may state that the refuge offered was not protective enough to avoid the effects of MPs. In conclusion, the removal of the MPs causes drastic effects on D. magna abundances despite the concentration of MPs, competition or habitat structure. Finally, considering the validated high efficiency of MPs for P removal, and in the context of a future whole-lake application, it is essential to restrict the use of MPs to the moments when D. magna is absent in the study site. Further research on the effects of MP removal on other organisms is required before implementing the addition of MPs as a restoration tool.

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Sediment desiccation is expected to drastically affect nutrient cycling in Mediterranean wetlands as global climate change models predict that many areas will become significantly drier than they currently are. In this study, we selected two Mediterranean wetlands that clearly differ in their water chemical composition (Honda and Hituelo wetlands) in order to determine the impact of sediment desiccation on phosphate (PO4(3-)) adsorption and desorption properties. A decrease in PO4(3-) sorption properties was observed in transects from the littoral zone to dry land in both lakes concomitantly with a reduction in organic matter content, revealing a critical role of organic matter for sequestering P in the lake sediment. Our experiments designed to determine if drying events would lead to an enhanced P release upon re-wetting have shown that, simulating natural conditions of re-flooding (that is without adding sodium azide), PO4(3-) concentrations were notably higher in the overlying water than those initially measured in the lake water. These results highlight the impact of drying sediment and the subsequent re-wetting on increasing P concentrations in lake water and accordingly, affecting to lake trophic state. Finally, we aimed on determining the overall effect of biotic versus abiotic activity on P release patterns observed upon re-wetting. Our results have evidenced that while in Honda, biotic processes upon re-wetting are crucial for increasing P retention in the sediment; P exchange across sediment and water upon dry sediment re-wetting is basically mediated by abiotic processes in Hituelo.

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Innovative approaches are of outstanding importance to devise technologies for dealing with eutrophication of inland waters. This study provides a quantitative estimate showing the convenience of using magnetic nano- and micronsized particles as phosphate absorbents and their later removal from solution by high gradient magnetic separation. Two different materials are investigated (iron and magnetite) having a controlled shape and size well in the colloidal domain. Magnetite particles adsorb more phosphate (empirical saturation constant=27.15 mg P g(-1) Fe) than iron particles (empirical saturation constant=18.83 mg P g(-1) Fe) as a consequence of the different particle size (average values for particle diameters of 90.6+/-1.2 and 805+/-10 nm for magnetite and for iron, respectively). A protocol is established for the successful reutilization of these magnetic particles by repeated washing with NaOH and therefore, optimizing the economic cost of this technology. Magnetic particles are also surface treated with amino silane groups (APTS) to counteract magnetic and van der Waals attractive interactions and promote kinetic stability. APTS-coated iron particles experience a notable increase in phosphate maximum adsorption capacity which could be explained by a remarkable increase in electrophoretic mobility. We propose the use of APTS-coated iron particles which are less-expensive and easy to obtain as a promising technique for lake restoration.

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Electron transport system (ETS) activity of sediments as an indication of microbial metabolic activity was examined in two adjacent Mediterranean wetlands (southern Spain). We determined the spatio-temporal variation in ETS, and we explored the potential biological [organic matter (OM), chlorophyll a (Chl a), aerobic and anaerobic bacteria] drivers of sediment ETS activity. ETS activity was notably higher in the eutrophic Lake Nueva (34.91 microl O(2) g(-1) D.W. h(-1)) than in the hypertrophic Lake Honda (24.99 microl O(2) g(-1) D.W. h(-1)). Strong spatial differences were observed in ETS in both study sites. Highest ETS values were achieved at the surface sediment at the deepest sampling station in each lake and a notable reduction in ETS with sediment depth was observed. By using linear regression and multiple regression analysis, OM was identified as the best predictor of ETS in Lake Honda while Chl a was the best predictor in Lake Nueva. The strong influence of OM supply on ETS activity in sediment from Lake Honda was the consequence of the labile nature of sedimentary OM, while a more refractory OM (with a higher contribution of vascular plants) comprised most of the sedimentary OM from Lake Nueva. By contrast, a large contribution of phytobenthos (supported by a higher lake water transparency) to ETS has been recognized in sediments from Lake Nueva. In summary, the results of this study revealed that the relative importance of planktonic primary producers (phytoplankton), benthic algae and vascular plants in the study sites could explain the differences observed in the intensity of sediment ETS as well as in their drivers.

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Lake restoration by in-lake precipitation of PO4(3-) with Al(OH)3 is commonly used but there is currently no good guidelines for calculating doses (amounts and application) that can ensure long lasting effects. We studied the effect of aging of Al(OH)3 on PO4(3-) adsorption and desorption properties with and without PO4(3-) in solution and found that Al(OH)3 aged without PO4(3-) lost 75% of the maximum adsorption capacity in 90 days after which no further changes occurred. Al(OH)3 aged in presence of PO4(3-) maintained the adsorption capacity through 6 months and even increased it for PO4(3-) concentrations < 150 microM. On this basis, we suggest that repeated dosing of smaller Al-aliquots may be more efficient than adding a single big dose. Also, Al should be added at the time when PO4(3-) availability in the lake is highest. At laboratory conditions we obtained molar P:Al binding ratios of 0.12-0.19 at PO4(3-) concentrations similar to those in eutrophic lake sediments, but when examining Al(OH)3 aged in situ in two lake sediments lower ratios (approximately 0.1) were found. We suggest that total Al-dosage should be calculated relative to the pool of potential mobile P in the lake with a molar ratio not less than 10 Al: 1 P.

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