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Emerging pollutants, such as pharmaceuticals and microplastics have become a pressing concern due to their widespread presence and potential impacts on ecological systems. To assess the ecosystem-level effects of these pollutants within a multi-stressor context, we simulated real-world conditions by exposing a near-natural multi-trophic aquatic food web to a gradient of environmentally relevant concentrations of fluoxetine and microplastics in large mesocosms over a period of more than three months. We measured the biomass and abundance of different trophic groups, as well as ecological functions such as nutrient availability and decomposition rate. To explore the mechanisms underlying potential community and ecosystem-level effects, we also performed behavioral assays focusing on locomotion parameters as a response variable in three species: Daphnia magna (zooplankton prey), Chaoborus flavicans larvae (invertebrate pelagic predator of zooplankton) and Asellus aquaticus (benthic macroinvertebrate), using water from the mesocosms. Our mesocosm results demonstrate that presence of microplastics governs the response in phytoplankton biomass, with a weak non-monotonic dose-response relationship due to the interaction between microplastics and fluoxetine. However, exposure to fluoxetine evoked a strong non-monotonic dose-response in zooplankton abundance and microbial decomposition rate of plant material. In the behavioral assays, the locomotion of zooplankton prey D. magna showed a similar non-monotonic response primarily induced by fluoxetine. Its predator C. flavicans, however, showed a significant non-monotonic response governed by both microplastics and fluoxetine. The behavior of the decomposer A. aquaticus significantly decreased at higher fluoxetine concentrations, potentially leading to reduced decomposition rates near the sediment. Our study demonstrates that effects observed upon short-term exposure result in more pronounced ecosystem-level effects following c

This White Paper has been prepared by the World Water Quality Alliance (WWQA) Ecosystems Workstream as a contribution to the work of the United Nations Environment Programme (UNEP) in their implementation of United Nations Environment Assembly (UNEA) Resolution 3/10 on "Addressing water pollution to protect and restore water-related ecosystems" (UNEP/EA.3/Res.10). The White Paper has been prepared following a peer review process and represents the views of the authors. The White Paper does not necessarily reflect the opinions or policies of contributing organisations.

Data of chemostats used in the following paper: Veraart, A. J., E. J. Faassen, V. Dakos, E. H. van Nes, M. Lürling, and M. Scheffer. 2012. Recovery rates reflect distance to a tipping point in a living system., Data of chemostats used in the following paper: Veraart, A. J., E. J. Faassen, V. Dakos, E. H. van Nes, M. Lürling, and M. Scheffer. 2012. Recovery rates reflect distance to a tipping point in a living system. Nature 481:357-359. doi:10.1038/nature10723

Blooms and scums of cyanobacteria led to prolonged swimming bans in Lake Rauwbraken (The Netherlands). We mitigated this nuisance by imposing phosphorus limitation on the lake. Our lake system analysis revealed that, over 40 years history, small dispersed sources built up a legacy phosphorus pool in the sediment and that the internal sediment release of phosphorus was the main phosphorus-source to the cyanobacteria (Chapter 2). The practically and economically most feasible approach was to reduce the internal phosphorus load by applying a solid phase phosphorus sorbent (SPS). We combined the flocculent poly aluminium chloride (PAC; Floc; Chapter 3) with the SPS lanthanum modified bentonite (Lock; Phoslock®; Chapter 3) as sinking weight to sink a present bloom, additional lanthanum modified bentonite was applied to the reduce internal phosphorus load. The treatment first stripped the water column of phosphorus using a flocculant (Floc) (Chapters 3, 4), shifting the lake from a (hyper) eutrophic state to a mesotrophic state. It also provided an instantaneous cure to the nuisance and lifted the imposed swimming ban (Chapter 4). Longer term, water quality remained good for more than a decade, but due to ongoing and increased external phosphorus loads, the lake is returning to a eutrophic state (Chapter 5). Directly after its application, the treatment caused a temporarily decrease in the Daphnia population in the lake (Chapter 4). Four years after the treatment Microcystis cells emerged from the lake sediment and produced a minor low-toxic scum. The event did not lead to a proliferation into a nuisance bloom (Chapter 5). Other than this mystery scum, the lake remained free of cyanobacterial nuisances. Directly after the application the Dutch maximum permissible filterable lanthanum concentration was exceeded for after 75 days (Chapter 6). Three years after the application, part of the LMB is relocated to the deeper part in the lake (Chapter 6). The lanthanum from the LM

Om blauwalgenoverlast te bestrijden is in een natuurplas bij Bergen op Zoom een pakketverbetermaatregelen uitgevoerd, na een watersysteemanalyse. Doel was: helder water met waterplanten.

Eutrophication and cyanobacterial blooms are increasing worldwide. Despite being studied for almost a century, mitigating eutrophication remains a challenge. Motivated by this challenge, we studied potential geo-engineering materials and in-site techniques to manage the eutrophication and cyanobacterial blooms in controlled experiments and a whole-ecosystem intervention. As phosphorus (P) control is essential to manage eutrophication, this thesis started evaluating natural and modified clays and soils for their capacity to adsorb P (chapter 2). We showed that four out of ten materials were able to adsorb P, and that P adsorption differed under varying abiotic conditions. The modified materials (lanthanum (La) modified bentonite, commercially called Phoslock® and Aluminium modified zeolite, commercially called Aqual-P®) were able to adsorb more P than the naturals ones such as Fe-rich soils The need to mitigate eutrophication in coastal areas prompted us to evaluate Phoslock® efficiency and behaviour in saline waters in chapter 3. Phoslock® was able to adsorb P in all salinities tested from brackish to seawater, whilst filterable La concentrations remained very low. We concluded that the use of Phoslock® on saline waters should be considered, yet, ecotoxicological studies must be performed before field applications in saline environments. Beside solid-phase P sorbents, flocculants have also been used in lake restoration. In this context, chitosan has been proposed as an “eco-friendly” flocculant as an alternative to metal based flocculant, such as polyaluminium chloride (PAC). In chapter 4, we tested the effect of chitosan on several cyanobacterial species and showed that chitosan may cause rapid cell lysis. In chapter 5, we looked closer into strain variation whilst also measuring cyanotoxin release. We showed that chitosan was able to cause cyanotoxins release. These effects were, however, strain dependent. Chitosan application might therefore cause toxin release i

Small lakes and ponds are common features in urban areas and they contribute to the quality of citizens’ life. A poor water quality, however, can easily give rise to nuisance. A major cause for a poor water quality is a high concentration of plant-nourishing nutrients, eutrophication. In (semi-)standing waters, eutrophication often results in a high biomass of blue-green algae (cyanobacteria), turbid water and the disappearance of submerged aquatic plants. The cyanobacterial blooms can be accompanied with fish kills due to anoxia, the development of unpleasant surface scums and malodors. As cyanobacteria can produce potent toxins, they impose a serious risk for citizens’ health, pets and wildlife. The cyanobacterial blooms hamper the anthropogenic use of the water and can have negative economic impacts. Water managers experience that the reduction of cyanobacterial nuisance is arduous. As long-term positive effects of management interventions are not often achieved, there is need for effective approaches. The objective of this study was to investigate the efficacy of promising methods to reduce cyanobacterial nuisance in city waters, targeting the clear water state and promoting the growth of aquatic plants. Various methods were tested, in the laboratory, in small and large compartments and were eventually applied in whole ponds and lakes. It is widely accepted that the reduction of nutrient inputs is essential for long-term positive effects. This study focused on the reduction of the input and the availability of the key-nutrient phosphorus. It was shown that cyanobacterial nuisance was wide spread in urban ponds and lakes in the Dutch province of North Brabant. The phosphorus inputs of four urban lakes in this province were addressed. The study lakes differed greatly in the phosphorus sources and loads, depending on site-specific characteristics. These differences affected the selection of measures. It was shown that in-lake measures were effective in realizing th, Deze studie had als doel te onderzoeken welke kansrijke aanpak effectief blauwalgenoverlast bestrijdt en de waterkwaliteit langdurig verbetert, met helder water en goede groeimogelijkheden voor waterplanten.

The amount of nano- and microplastic in the aquatic environment rises due to the industrial production of plastic and the degradation of plastic into smaller particles. Concerns have been raised about their incorporation into food webs. Little is known about the fate and effects of nanoplastic, especially for the freshwater environment. In this study, effects of nano-polystyrene (nano-PS) on the growth and photosynthesis of the green alga Scenedesmus obliquus and the growth, mortality, neonate production, and malformations of the zooplankter Daphnia magna were assessed. Nano-PS reduced population growth and reduced chlorophyll concentrations in the algae. Exposed Daphnia showed a reduced body size and severe alterations in reproduction. Numbers and body size of neonates were lower, while the number of neonate malformations among neonates rose to 68% of the individuals. These effects of nano-PS were observed between 0.22 and 103 mg nano-PS/L. Malformations occurred from 30 mg of nano-PS/L onward. Such plastic concentrations are much higher than presently reported for marine waters as well as freshwater, but may eventually occur in sediment pore waters. As far as we know, these results are the first to show that direct life history shifts in algae and Daphnia populations may occur as a result of exposure to nanoplastic.

We tested the hypothesis that ultrasound in controlling cyanobacteria and algal blooms is “environmental friendly” by exposing the non-target zooplankton grazer Daphnia magna to ultrasound produced by commercially available ultrasound transducers. In populations of 15 Daphnia (~2 mm body size) exposed in 800 mL of water to ultrasound supplied at 20 kHz, 28 kHz, 36 kHz or 44 kHz, all animals were killed between 10 min (44 kHz) and 135 min (20 kHz). Differently sized Daphnia (0.7–3.2 mm) were all killed between 4 and 30 min when exposed to 44 kHz. Increasing water volumes up to 3.2 L and thus lowering the ultrasound intensity did not markedly increase survival of Daphnia exposed to 44 kHz ultrasound. A tank experiment with six 85 L tanks containing a mixture of green algae, cyanobacteria and D. magna was performed to study the effect of ultrasound over a longer time period (25 d). In controls, when Daphnia flourished, algal biomass dropped and the water became clear. In contrast, in ultrasound treatments, Daphnia abundance was extremely low releasing phytoplankton from grazing control, which resulted in high phytoplankton biomass. Hence, we conclude that ultrasound from commercially available transducers sold to clear ponds, aquaria and small reservoirs, should not be considered environmentally friendly and cannot be viewed as efficient in controlling phytoplankton.

In April and May 2011, three dogs died and one dog became ill after swimming in Lake IJmeer (The Netherlands). At the time, the lake was infested with the benthic cyanobacterial species Phormidium. A Eurasian Coot (Fulica atra) and a Black-headed Gull (Chroicocephalus ridibundus) also died near Lake IJmeer in the same period. One of the dogs and both birds were subjected to a pathological investigation. Furthermore, the Phormidium mat; algal samples from the dikes; contents of the animals' digestive systems and organ tissues were analysed for the following cyanobacterial toxins: (homo)anatoxin-a; (7-deoxy-)cylindrospermopsin; saxitoxins and gonyautoxins by LC-MS/MS. Samples were also analysed for the nontoxic (homo)anatoxin-a metabolites dihydro(homo)anatoxin-a and epoxy( homo) anatoxin-a. The dog necropsy results indicated neurotoxicosis and its stomach contained Phormidium filaments. Anatoxin-a was detected in the Phormidium mat (272 mu g g(-1) dry weight, stdev 65, n = 3) and in the dog's stomach contents (9.5 mu g g(-1) dry weight, stdev 2.4, n = 3). Both samples also contained the anatoxin-a metabolite dihydroanatoxin-a, and a trace of homoanatoxin-a was detected in the Phormidium mat. The birds were in bad nutritive condition at the time of necropsy and their stomachs and intestines did not contain any cyanobacterial material. Furthermore, no cyanobacterial toxins were detected in their stomachs, intestines and organs and they both had lesions that are not associated with cyanobacterial intoxication. This is the first report of anatoxin-a and homoanatoxina occurrence in The Netherlands, these toxins have likely caused the deaths of three dogs. The birds probably died of other causes. Dutch recreational waters are at this moment only screened for pelagic cyanobacterial species, the current bathing water protocol therefore does not protect humans and animals from negative effects of blooms of benthic cyanobacteria.

In controlled experiments, the ability of ‘‘Effective Microorganisms (EM, in the form of mudballs or Bokashi-balls)’’ was tested for clearing waters from cyanobacteria. We found suspensions of EM-mudballs up to 1 g l-1 to be ineffective in reducing cyanobacterial growth. In all controls and EM-mudball treatments up to 1 g l-1 the cyanobacterial chlorophyll-a (Chl-a) concentrations increased within 4 weeks from&120 to 325–435 lg l-1. When pieces of EM-mudballs (42.5 g) were added to 25-l lake water with cyanobacteria, no decrease of cyanobacteria as compared to untreated controls was observed. In contrast, after 4 weeks cyanobacterial Chl-a concentrations were significantly higher in EM-mudball treatments (52 lg l-1) than in controls (20 lg l-1). Only when suspensions with extremely high EM-mudball concentrations were applied (i.e., 5 and 10 g l-1), exceeding the recommended concentrations by orders of magnitude, cyanobacterial growth was inhibited and a bloom forming concentration was reduced strongly. In these high dosing treatments, the oxygen concentration dropped initially to very low levels of 1.8 g l-1. This was most probably through forcing strong light limitation on the cyanobacteria caused by the high amount of clay and subsequent high turbidity of the water. Hence, this study yields no support for the hypothesis that EM is effective in preventing cyanobacterial proliferation or in terminating blooms. We consider EM products to be ineffective because they neither permanently bind nor remove phosphorus from eutroficated systems, they have no inhibiting effect on cyanobacteria, and they could even be an extra source of nutrients.

Filtrates from crushed Moringa oleifera seeds were tested for their effects on growth and Photosystem II efficiency of the common bloom-forming cyanobacterium Microcystis aeruginosa. M. aeruginosa populations exhibited good growth in controls and treatments with 4- and 8-mg crushed Moringa seeds per liter, having similar growth rates of 0.50 (±0.01) per day. In exposures of 20- to 160-mg crushed Moringa seeds L-1, growth rates were negative and on average -0.23 (±0.05) .day-1. Presumably, in the higher doses of 20- to 160-mg crushed seeds per liter, the cyanobacteria died, which was supported by a rapid drop in the Photosystem II efficiency (FPSII), while the FPSII was high and unaffected in 0, 4, and 8 mg L-1. High-density populations of M. aeruginosa (chlorophyll-a concentrations of ~270 µg L-1) were reduced to very low levels within 2 weeks of exposure to =80-mg crushed seeds per liter. At the highest dosage of 160 mg L-1, the FPSII dropped to zero rapidly and remained nil during the course of the experiment (14 days). Hence, under laboratory conditions, a complete wipeout of the bloom could be achieved. This is the first study that yielded evidence for cyanobactericidal activity of filtrate from crushed Moringa seeds, suggesting that Moringa seed extracts might have a potential as an effect-oriented measure lessening cyanobacterial nuisance.

The Dutch company WiseUse International BV has proposed using a so-called bio stimulator “PoCo” (Pollution Control) in ecological restoration of Lake Ypacarai (Paraguay). In this study results of laboratory assays are reported testing the performance of PoCo regarding the alleged enhanced mineralization of organic matter in the water phase and sediment, the inhibition of cyanobacterial growth (as a clear measure counter acting the symptoms of eutrophication) and effects on survival of the waterflea Daphnia.

Two-day life cycle tests with the rotifer Brachiomus calyciflorus were run to study the nutritional quality effects to rotifers of Scenedesmus pectinatus grown under non-limiting nitrogen limiting and phosphorus limiting conditions and the feedback of the rotifers oil the Food algae. Under nutrient-limited conditions of its algal food Brachionus production was depressed, animals produced fewer eggs and were smaller sized. Clearance rates of Brachionus offered non-nutrient-limited and nutrient-limited Food were similar. The number of cells per colony was similar for S. pectinatus Under nitrogen limited and phosphorus limited conditions both in the absence and presence of Brochionus. Cell volumes phosphorus limited S. pectinatus were larger than those of nitrogen limited cells. The most dramatic response of the food alga S. pectinatus was observed in non-nutrient-limited conditions: a strong, size enlargement occurred only in file presence of Brachionus. This was caused by a higher share of eight-celled colonies and larger individual Cell volumes in the Presence of rotifers than in their absence. S. pectinatus might gain an advantage of becoming larger in moving out of the feeding window of its enemy, but nutrient limited conditions might undermine the effectiveness of such reaction.

The green alga Chlainydomonas reinhardtii usually occurs in Cultures as single, biflagellated cells. However, C. reinhardtii is known for its ability to form gelatinous and palmelloid stages that arise as a result of an interaction with its environment. Exponentially growing unicellular C. reinhardtii formed palmelloid colonies rapidly within 25 h when Cultured together with their enemy the rotifer Brachionus calyciflorus. Consequences of palmelloid formation for population dynamics of both C. reinhardtii and B. calyciflorus were examined in continuous flow systems. Palmelloids were only formed in a one-stage system where B. calyciflorus grazers and C. reinhardtii prey were Cultured together. but not in a two-stage system in which mainly unicellular C. reinhardtii was pumped into a rotifer culture placed in darkness. The rotifer abundance was lower and the algal biomass higher in the one-stage system compared to the grazing unit of the two-stage system. Inasmuch as palmelloids seemed to give C. reinhardtii cells resistance to grazing, we suggest that at least one of the reasons why C. reinhardtii is capable of forming palmelloids is to cope with herbivory.

Organisms belonging to the green algal genera Desmodesmus and Scenedesmus are characterized by a high degree of flexibility allowing them to be true cosmopolitans and to withstand harsh conditions. The environmental conditions determine which phenotypes are being produced and one of the most dangerous situations for the algae is when the organisms are confronted with strong grazing pressure from numerous zooplankton organisms. An overview is given of several aspect of an induced defense in many non-spiny Scenedesmus and some spiny Desmodesmus that may form typical protective eight-celled colonies to avoid mortality from numerous grazers. The morphological response does seem to be linked with a herbivorous zooplankton chemical cue, rather than to a more general animal excretory product. The grazing activity of small sized grazers is reduced, but not of large Daphnia. However, arguments are given why grazing protection of colonial Scenedesmus is probably more efficient under natural than under carbon/light limited laboratory conditions. Finally, a life-history cycle of Desmodesmus and Scenedesmus is presented in which biological aspects such as the anti-grazer response and sexual reproduction are being included.