Aquatic Primary Production Research Articles

Natural and anthropogenically driven change of organic carbon burial rate in two alpine lakes from the southeastern margin of the Tibetan Plateau

The rate of organic carbon (OC) burial in lakes depends considerably on natural and anthropogenic factors. Delineating how and to what extent potential drivers shape a lake’s OC burial rate is crucial for anticipating OC sequestration under future environmental change scenarios. Alpine lakes provide valuable opportunities for studying the influence of climate warming and atmospheric nitrogen (N) deposition on OC burial in lakes, owing to the lack of human activities in their catchments; however, this aspect has not been sufficiently documented. Here, the OC burial rate was reconstructed in two alpine lakes (Heihai and Jiren) from the southeastern margin of the Tibetan Plateau over the past ∼ 160 years, and the associated drivers were identified by resolving the temporal trends in organic matter (OM) input from specific sources to lake sediments via paleolimnological methods. The results demonstrated a consistently low OC burial rate (6.21–10.86 g m−2 yr−1) in Lake Heihai. The low hydrogen index (HI), moderate Paq, and high long-chain n-alkane flux revealed that submerged macrophytes and terrestrial plants are major contributors to the sequestrated OC. The notable decrease in the OC burial rate after 1980 was hypothesized to be caused by regional climate warming during this period because a greater export of terrestrial materials under such a climate can inhibit light penetration, diminishing submerged macrophyte productivity and OM input. In contrast, the synchronous input of higher amounts of terrestrial plant OM was largely degraded owing to the increased water temperature and the intensification of water column stratification. In Lake Jiren, a notably high OC burial rate (13.82–46.75g m−2 yr−1) was observed. The high HI, Paq, and short-chain n-alkane flux showed that phytoplankton and submerged macrophytes were the major contributors to the sequestrated OC. The two-phase increase in the OC burial rate in this lake, including a slow increase after 1947 and a rapid increase after 1983, might have resulted from strengthening aquatic primary productivity and OM input, driven by anthropogenic intensification of nutrient emissions, especially reactive N, from highly urbanized areas and the subsequent long-term atmospheric transport and deposition of these materials over the lake basin. A comparative analysis of the results between the two lakes suggested that atmospheric N deposition has a stronger influence on the OC burial than climate warming. These drivers affect the OC burial rate by altering aquatic productivity rather than the terrestrial OM input. This study provides a basic for predicting future OC burial scenarios in warmer climates with more intense anthropogenic N emissions.

Terrestrial support of wetland food webs via a dissolved inorganic carbon pathway

AbstractStudies of terrestrial support of aquatic food webs have focused primarily on terrestrial organic matter (t‐OM) directly used by animal and microbial consumers. However, dissolved inorganic carbon (DIC) released from t‐OM might also support aquatic primary producers, a key resource for zooplankton and upper trophic levels. Using 2‐yr 13C measurements of algae, zooplankton, terrestrial detritus, sediments, dissolved and particulate organic matter from six seasonal wetlands, we found that in January when algal concentration was low, zooplankton used t‐OM directly or heterotrophic microbes that decompose t‐OM, but in March and May zooplankton was mainly supported by algae as their basal resources, and the algae used DIC derived from the mineralization and methanogenesis of t‐OM, suggesting the DIC pathway of terrestrial support of aquatic food webs. The decomposition of abundant t‐OM from both bed sediments and water column caused high concentrations of DIC. Despite uptake by algae, about half of DIC produced in January and March ended up as emissions to the atmosphere in the form of CO2. This finding revealed the dual roles of t‐OM in maintaining the productivity and stability of aquatic food webs and in contributing to global carbon emissions. This duality poses challenges for simultaneously mitigating carbon emissions and conserving biological communities in seasonal wetlands. Finally, wide seasonal differences in δ13C in DIC (−12.4‰ to 6.7‰) were observed, mainly driven by air–water CO2 exchange and photosynthesis, suggesting that 13C may be a powerful tool to investigate carbon cycling in shallow, temporary freshwater ecosystems that are widespread but understudied.

Multi-tracer evidence of hydrology and primary production controls on dissolved organic matter composition and stability in the semi-arid aquatic continuum

Autochthonous dissolved organic matter (Auto-DOM) produced by a biological carbon pump using dissolved inorganic carbon (DIC) from carbonate weathering plays an important role in carbon cycling within inland waters. However, little is known regarding how environmental conditions impact the composition and fate of organic matter, especially in surface waters of the semi-arid Loess Plateau, which is enriched in DIC by significant carbonate weathering. To obtain novel insight, we combined hydrochemistry, isotopic composition (δ2H, δ18O, and δ13CDIC), Rayleigh fractionation model, optical spectroscopy (absorbance and fluorescence), and Fourier transform ion cyclotron resonance mass spectrometry measurements to elucidate how primary production and hydrology impact the composition of DOM and the stability of the resulting Auto-DOM throughout the river–reservoir–wetland aquatic continuum of the Bahe River in the carbonate-mineral-rich semi-arid Loess Plateau where carbonate weathering is significant. The Rayleigh fractionation model results indicated that watershed DIC is primarily consumed through aquatic primary production rather than CO2 degassing. Further investigation revealed that primary production and evaporation co-occurred in this watershed. With the enrichment of the stable water isotope δ2H, the relative abundances of the allochthonous compounds decreased and the relative abundances of the autochthonous substances increased, suggesting that the terrestrial signal of riverine DOM decreased while autochthonous production increased along the flow pathway. In addition, associations between optical and molecular characteristics among DOM samples from different water bodies revealed that the stability ratio (Fmax(C2/(C2 + C4))) of Auto-DOM to the ratio of carboxylic-rich alicyclic molecules showed a consistent trend, suggesting that phytoplankton-derived and biomineralized C2 compounds are potentially recalcitrant DOM in inland waters. We conclude that hydrology and primary production affect the source, composition, and, potentially, the stability of DOM in DIC-enriched surface waters of the semi-arid Loess Plateau, which may lead to a more humic-like DOM composition in inland water and export this lower bioavailability DOC to the ocean in the long term.

Response of aquatic ammonia-oxidizing archaea to thermal stratification and nutrient levels since the Last Glacial Maximum in the deep lake Fuxian, southwestern China

Ammonia-oxidizing archaea (AOA) are the critical nitrifier in lake ecosystems and participate in the global nitrogen cycle. However, the response of aquatic AOA to long-term climate change remains unclear. Here, we obtained a continuous sediment record from a deep, oligotrophic lake (Lake Fuxian, China) and reconstructed changes in AOA productivity over the past 26 thousand years (cal ka BP) using a multi-proxy approach. AOA productivity (estimated using diagnostic archaeal lipids) was low during the Last Glacial Maximum (LGM) before peaking during the cold-dry Heinrich event 1 (H1, 17.7–15.9 cal ka BP). As the Indian Summer Monsoon (ISM) intensified and the climate became warmer and wetter, aquatic AOA productivity progressively declined. We show that a combination of factors modulates millennial-scale AOA productivity. In particular, low lake levels under cold-dry climate conditions strengthen lake mixing and nutrient upwelling, promoting AOA productivity; in contrast, high lake levels during warm-humid climate conditions weaken upwelling, resulting in reduced AOA blooms. Changes in terrestrial nutrient availability also exert a secondary control on aquatic primary production and by extension, AOA productivity. We also show that anthropogenic human activities can potentially alter AOA productivity levels due to climate and land-use change.

Impact of urban pollution on freshwater biofilms: Oxidative stress, photosynthesis and lipid responses

Urban ecosystems are subjected to multiple anthropogenic stresses, which impact aquatic communities. Artificial light at night (ALAN) for instance can significantly alter the composition of algal communities as well as the photosynthetic cycles of autotrophic organisms, possibly leading to cellular oxidative stress. The combined effects of ALAN and chemical contamination could increase oxidative impacts in aquatic primary producers, although such combined effects remain insufficiently explored. To address this knowledge gap, a one-month experimental approach was implemented under controlled conditions to elucidate effects of ALAN and dodecylbenzyldimethylammonium chloride (DDBAC) on aquatic biofilms. DDBAC is a biocide commonly used in virucidal products, and is found in urban aquatic ecosystems. The bioaccumulation of DDBAC in biofilms exposed or not to ALAN was analyzed. The responses of taxonomic composition, photosynthetic activity, and fatty acid composition of biofilms were examined. The results indicate that ALAN negatively affects photosynthetic yield and chlorophyll production of biofilms. Additionally, exposure to DDBAC at environmental concentrations induces lipid peroxidation, with an increase of oxylipins. This experimental study provides first insights on the consequences of ALAN and DDBAC for aquatic ecosystems. It also opens avenues for the identification of new biomarkers that could be used to monitor urban pollution impacts in natural environments.

Evaluation of acute toxicity of an emerging contaminant Oxybenzone on an ecologically important aquatic macrophyte Lemna minor

Oxybenzone is an ultraviolet filter frequently used in Personal Care Products, plastics, furniture, etc. and is listed as an Emerging Contaminant. This report studied the acute toxicity of Oxybenzone to Lemna minor after exposure to graded concentrations of Oxybenzone for 7 days. IC50 for growth was found to be 8.53 mg L−1. The hormesis effect was reported at lower concentrations, while growth and pigments reduced from 2.5 to 12.5 mg L-1 in a concentration-related manner. The impact of Oxybenzone on protein and antioxidant enzymes- Catalase and Guaiacol Peroxidase revealed less stress up to 2.5 mg L-1 than control, increasing further from 5 to 10 mg L-1. Enzyme activity decreased over-time but always remained higher than control over a period of 7 days. Thus, our findings reveal that indiscriminate discharge of Oxybenzone could be potentially toxic to the aquatic primary producers at higher concentrations, causing an ecological imbalance in aquatic ecosystems.

Microeukaryotic plankton evolutionary constraints in a subtropical river explained by environment and bacteria along differing taxonomic resolutions.

Microeukaryotic plankton communities are keystone components for keeping aquatic primary productivity. Currently, variations in microeukaryotic plankton diversity have often been explained by local ecological factors but not by evolutionary constraints. We used amplicon sequencing of 100 water samples across five years to investigate the ecological preferences of the microeukaryotic plankton community in a subtropical riverine ecosystem. We found that microeukaryotic plankton diversity was less associated with bacterial abundance (16S rRNA gene copy number) than bacterial diversity. Further, environmental effects exhibited a larger influence on microeukaryotic plankton community composition than bacterial community composition, especially at fine taxonomic levels. The evolutionary constraints of microeukaryotic plankton community increased with decreasing taxonomic resolution (from 97% to 91% similarity levels), but not significant change from 85% to 70% similarity levels. However, compared with the bacterial community, the evolutionary constraints were shown to be more affected by environmental variables. This study illustrated possible controlling environmental and bacterial drivers of microeukaryotic diversity and community assembly in a subtropical river, thereby indirectly reflecting on the quality status of the water environment by providing new clues on the microeukaryotic community assembly.

Impacts of climate warming and atmospheric deposition on recent shifts in chironomid communities in two alpine lakes, eastern China

Climate warming and atmospheric deposition are altering alpine lake ecosystems at unprecedented rates, whereas their direct and indirect effects on primary consumer communities are unclear. This study presents sedimentary multi-proxy records including chironomids, diatoms, elements and stable isotopes of carbon and nitrogen in 210Pb-dated cores from two alpine lakes located above the timberline in the Taibai Mountain, eastern China. Before ∼2000 CE, chironomid communities were co-dominated by Heterotrissocladius marcidus-type and Micropsectra atrofasciata-type in the two lakes. Thereafter, Tanytarsus glabrescens-type increased rapidly to be a dominant species. Redundancy analyses (RDAs) revealed that chironomid fauna shifts were significantly correlated with rising diatom concentrations in both lakes, declining Ti content in the upstream lake and δ13C depletion in the downstream lake. Although temperature, precipitation and δ15N were not significant explanatory variables in RDAs, climate warming and atmospheric deposition likely promoted terrestrial and aquatic primary production, indicated by synchronous increases in organic matter contents and diatom concentrations in the two sediment cores. Since diatoms contain essential polyunsaturated fatty acids that are essential for chironomids, rising diatom concentrations can promote food quantity and quality. In addition, increased primary production would create organic substrates for chironomid larvae. Recent shifts in chironomid fauna driven by indirect effects of global warming and atmospheric deposition might be a widespread phenomenon in alpine lakes, probably triggering regime shifts in headwater lake ecosystems.

Relationships of primary productivity with anuran abundance, richness, and community composition in tropical streams.

The relationship between primary productivity and diversity has been demonstrated across taxa and spatial scales, but for organisms with biphasic life cycles, little research has examined whether productivity of larval and adult environments influence each life stage independently, or whether productivity of one life stage's environment outweighs the influence of the other. Experimental work demonstrates that tadpoles of stream-breeding anurans can exhibit a top-down influence on aquatic primary productivity (APP), but few studies have sought evidence of a bottom-up influence of primary productivity on anuran abundance, species richness and community composition, as seen in other organisms. We examined aquatic and terrestrial primary productivity in two forest types in Borneo, along with amphibian abundance, species richness, and community composition at larval and adult stages, to determine whether there is evidence for a bottom-up influence of APP on tadpole abundance and species richness across streams, and the relative importance of aquatic and terrestrial primary productivity on larval and adult phases of anurans. We predicted that adult richness, abundance, and community composition would be influenced by terrestrial primary productivity, but that tadpole richness, abundance, and community composition would be influenced by APP. Contrary to expectations, we did not find evidence that primary productivity, or variation thereof, predicts anuran richness at larval or adult stages. Further, no measure of primary productivity or its variation was a significant predictor of adult abundance, or of adult or tadpole community composition. For tadpoles, we found that in areas with low terrestrial primary productivity, abundance was positively related to APP, but in areas with high terrestrial primary productivity, abundance was negatively related to APP, suggesting a bottom-up influence of primary productivity on abundance in secondary forest, and a top-down influence of tadpoles on primary productivity in primary forest. Additional data are needed to better understand the ecological interactions between terrestrial primary productivity, aquatic primary productivity, and tadpole abundance.

Interactions between temperature and nutrients determine the population dynamics of primary producers.

Global change is rapidly and fundamentally altering many of the processes regulating the flux of energy throughout ecosystems, and although researchers now understand the effect of temperature on key rates (such as aquatic primary productivity), the theoretical foundation needed to generate forecasts of biomass dynamics and extinction risk remains underdeveloped. We develop new theory that describes the interconnected effects of nutrients and temperature on phytoplankton populations and show that the thermal response of equilibrium biomass (i.e. carrying capacity) always peaks at a lower temperature than for productivity (i.e. growth rate). This mismatch is driven by differences in the thermal responses of growth, death, and per-capita impact on the nutrient pool, making our results highly general and applicable to widely used population models beyond phytoplankton. We further show that non-equilibrium dynamics depend on the pace of environmental change relative to underlying vital rates and that populations respond to variable environments differently at high versus low temperatures due to thermal asymmetries.

Recycling and deposition of inorganic carbon from calcium carbonate encrustations of charophytes

AbstractMany aquatic primary producers can use bicarbonates as a carbon source for photosynthesis. Charophytes of the two genera: Chara and Nitellopsis are quite efficient in this process. Some species of these macroalgae produce carbonate encrustations, mainly calcium carbonate, constituting up to 86% of the summer maximum dry weight of the standing crop. In this study, we analyzed the fate of inorganic carbon accumulated this way in Chara spp. and Nitellopsis obtusa from six Polish lakes located in two regions (warmer W Poland and cooler NE Poland). Our study distinguished two groups of charophyte species that differed in the way of CaCO3 release from their summer standing crops. On average, the corticate Chara rudis and C. tomentosa belonging to the first group were less efficient in depositing CaCO3 from summer to autumn than the less corticate C. contraria and ecorticate N. obtusa of the second group. The latter two species were more efficient in inorganic carbon burial in sediments. On the contrary, dissolution of encrustation was more typical of the first species group and was facilitated by decreasing the pH and saturation index of calcite in lake water. The final output of CaCO3 loss mainly resulted from combined species‐specific features, lake water properties and overwintering patterns. Our study revealed that inorganic carbon cycling through charophytes involves burial and dissolution and is more complex than previously thought.

High-throughput sequencing of Diatoms using V4 region of 18S rRNA gene in Bayug Island, Iligan City, Philippines

Abstract. Estor DEP, Tabugo SR. 2023. High-throughput sequencing of Diatoms using V4 region of 18S rRNA gene in Bayug Island, Iligan City, Philippines. Biodiversitas 24: 6343-6350. Diatoms are the main contributors to aquatic primary production and are the most dominant phytoplankton. Their adaptability and growth in diverse natural resources enable them to thrive in various climates and geographical areas, making them suitable for monitoring and biotechnology applications. This study aimed to analyze the diatom composition in two study sites: a mangrove area and the estuary in Bayug Island. The analysis was conducted using metabarcoding of the V4 region of the 18S rRNA gene, amplified and sequenced on the Illumina MiSeq platform. Four amplicon libraries were generated, representing the diatom composition at the two study sites. Data processing was performed using the Parallel-Meta-Suite software. Following quality control and processing, 20,433 amplicon sequence variants (ASVs) were obtained. Among these, the genera Navicula, Thalassiosira, Chaetoceros, Guinardia, Amphora, and Minidiscus were the most abundant ASVs. The assessment of diatom alpha diversity using the Shannon index indicated a higher diversity in the estuary site. Furthermore, the analysis done within the Parallel Meta Suite suggested that the presence of these specific diatom species can be linked to salinity levels, and may indicate environmental disturbances such as water pollution. The presence of these diatoms has the potential to be utilized in ecological treatments, disease prevention, biotechnology, and as nutrient indicators for other marine organisms. Physico-chemical parameters were recorded in the estuary area (S1), with the average water pH measuring around 7.6, salinity at approximately 36.6 ppt, and water temperature at 26.7?. In contrast, the measurements in the mangrove area (S2) revealed an average water temperature of 30?, salinity of around 35 ppt, and a water pH of 7.7. This research will serve as baseline data for diatom community in the area and a pioneering work on using NGS and eDNA for diatom study.

Micro- and nanoplastics interact with conventional pollutants on microalgae: Synthesis through meta-analysis

Micro- and nanoplastics (MNPs) have been found to occur intensively in aquatic environments, along with other conventional pollutants (Po) such as heavy metals, pesticides, pharmaceuticals, etc. However, our understanding of how MNPs and Po interact on aquatic primary producers is fragmented. We performed a quantitative meta-analysis based on 933 published experimental assessments from 44 studies to examine the coupled effects of MNPs and Po on microalgae. Although the results based on interaction type frequency (the proportion of each interaction type in all results) revealed dominantly additive interactions (56%) for overall physiological performance, an overall antagonistic effect was observed based on the mean interaction effect sizes. A higher proportion of antagonistic interaction type frequency was found in marine species compared to fresh species. The antagonistic effects were particularly significant for growth, oxidative responses, and photosynthesis, which could be attributed to the adsorption effect of MNPs on Po and thus the decreasing concentrations of pollutants in the medium. Larger-sized, negatively charged or uncharged and aged MNPs had higher proportions of antagonistic effects compared to smaller-sized, positively charged and virgin MNPs, due to their stronger adsorption capacity to Po. This study provides a comprehensive insight into the interactive effects of MNPs and Po on microalgae.

Linking prescribed fire, nutrient deposition and cyanobacteria dominance through pyroeutrophication in a subtropical lake ecosystem from the mid Holocene to present

Prescribed fire (Rx-fire) is a common management tool for many forested ecosystems and promotes tree and forest soil health. Although burned materials from Rx-fire areas can enter adjacent aquatic environments, very few studies have focused on the water quality impacts of increased nutrients on aquatic primary producer communities. Here, we applied paleolimnological techniques on a 170-cm sediment core collected from Ditch Pond, AL, USA, a subtropical lake system located in the Conecuh National Forest where Rx-fire has been the primary management tool for ∼90 years. Macroscopic charcoal, nutrients (C, N, P) and photosynthetic pigments were measured throughout the core which spans from the middle Holocene until modern day. Our research questions were: 1) What were the sedimentary nutrient and stoichiometric changes associated with the Rx-Fire period beginning in 1937 CE? and 2) Did these nutrient changes alter historic algae/cyanobacteria groups? Following the onset of Rx-fire, nutrients (C, N, P) increased in deposition in the lake with P showing the greatest proportional increase at over 300%, suggesting that P inputs from Rx-fire are a primary artifact of burning. Photosynthetic pigments showed that increases in nutrients from Rx-fire caused extensive increases in total primary producer abundance and cyanobacteria dominance, called pyroeutrophication. These data suggest a greater need to understand the implications of fire-associated nutrients on aquatic primary producers wherever fire (but especially Rx-fire) is occurring, as well as an increase in collaboration between forest and aquatic ecosystem managers.

Patterns and drivers for benthic algal biomass in sub-Arctic mountain ponds

This study investigated the spatial variation in total benthic algal biomass and within cyanobacteria, green algae, and diatoms in sub-Arctic ponds. Additionally to more widely used explanatory variables, snowmelt and ice duration were considered as their importance on algal communities is poorly understood. The data comprised algal biomasses from 45 sub-Arctic ponds in the Finnish Lapland. A generalized linear model and hierarchical partitioning were used to identify the significantly influential variables. Cyanobacteria were the most abundant algal group. Trace elements (e.g. Fe, Al, and Mn) were the most significant explanatory variable group in explaining algal biomasses. Macronutrients apart from K were found insignificant in all models. There were positive relationships between some algal biomasses indicating no strong competition between them. Snow and ice variables were found insignificant for all models, but they could have an important secondary role on algal communities. The results highlight the importance of trace elements in shaping algal biomasses in sub-Arctic ponds and thus their wider use in research can be advocated to better understand the productivity of nutrient poor and acidic waters in sub-Arctic regions. Focussing on benthic algal biomasses and the chemical composition of sub-Arctic freshwaters provides important information on the aquatic primary production.

Phosphorus deficiency induces sexual reproduction in the dinoflagellate Prorocentrum cordatum

Nitrogen (N) and phosphorus (P) are essential elements whose availability promotes successful growth of phytoplankton and governs aquatic primary productivity. In this study, we investigated the effect of N and/or P deficiency on the sexual reproduction of Prorocentrum cordatum, the dinoflagellate with the haplontic life cycle which causes harmful algal blooms worldwide. In P. cordatum cultures, N and the combined N and P deficiency led to the arrest of the cell cycle in the G0/G1 phases and attenuation of cell culture growth. We observed, that P, but not N deficiency triggered the transition in the life cycle of P. cordatum from vegetative to the sexual stage. This resulted in a sharp increase in percentage of cells with relative nuclear DNA content 2C (zygotes) and the appearance of cells with relative nuclear DNA content 4C (dividing zygotes). Subsequent supplementation with phosphate stimulated meiosis and led to a noticeable increase in the 4C cell number (dividing zygotes). Additionally, we performed transcriptomic data analysis and identified putative phosphate transporters and enzymes involved in the phosphate uptake and regulation of its metabolism by P. cordatum. These include high- and low-affinity inorganic phosphate transporters, atypical alkaline phosphatase, purple acid phosphatases and SPX domain-containing proteins.

A critical examination of the protection level for primary producers in the first tier of the aquatic risk assessment for plant protection products

BackgroundThe aim of environmental risk assessment (ERA) for pesticides is to protect ecosystems by ensuring that specific protection goals (SPGs) are met. The ERA follows a prospective tiered approach, starting with the most conservative and simple step in risk assessment (RA) (so-called tier 1) using the lowest available appropriate endpoint derived from ecotoxicological tests. In 2015, for the tier 1 RA of aquatic primary producers, the recommendation was changed from using the lowest of the 50% inhibition (EC50) values based on biomass (area under the curve—EbC50), increase in biomass (yield- EyC50) or growth rate (ErC50) to only using the growth rate inhibition endpoint (ErC50) because it is independent of the test design and thus more robust. This study examines the implications of this such on the level of conservatism provided by the tier 1 RA and evaluates whether it ensures a suitable minimum protection level.ResultsOur analysis shows that replacing the lowest endpoint with the growth rate inhibition endpoint while maintaining the assessment factor (AF) of 10 significantly reduces the conservatism in the tier 1 RA. Comparing protection levels achieved with different endpoints reveals that the current assessment is less protective. To maintain the previous level of protection, and since the protection goals have not changed, we recommend to multiply the default AF of 10 by an extra factor of minimum 2.4 in the tier 1 RA based on ErC50. Independently of the endpoint selected in tier 1 RA, several issues in the general RA of pesticides contribute to uncertainties when assessing the protection levels, e.g., lack of appropriate comparison of the higher tier experimental studies (i.e., best achievable approximation of field situation, so-called surrogate reference tier) with field conditions or the regulatory framework's failure to consider realistic conditions in agricultural landscapes with multiple stressors and pesticide mixtures.ConclusionsWe advise to consider adjusting the risk assessment in order to reach at least the previous protection level for aquatic primary producers. Indeed continuing using an endpoint with a higher value and without adjustment of the assessment factor is likely to jeopardize the need of halting biodiversity loss in surface waters.

Exposure pathways matter: Aquatic phototrophic communities respond differently to agricultural run‐off exposed via sediment or water

Abstract Small shallow ponds are widespread but understudied water bodies in agricultural landscapes. Agricultural run‐off (ARO) transports pesticides and nutrients into adjacent aquatic ecosystems where they occur dissolved in the water column or are bound to sediments. Consequently, aquatic communities are affected by ARO via different exposure pathways. We hypothesize that sediment‐bound ARO mainly affects submerged rooted macrophytes, while phytoplankton and periphyton are more prone to ARO in water. These primary producers compete for resources resulting in a regime shift between alternative stable states of macrophyte or phytoplankton dominance. We hypothesize that warming increases nutrient release from sediments and thereby facilitates the occurrence of phytoplankton dominance. Using a full‐factorial microcosm design, we exposed aquatic primary producers to either sediment or water application of a mixture of common pesticides (terbuthylazine, pirimicarb, tebuconazole and copper) and nitrate at two concentrations and two temperatures (22°C and 26°C) for 4 weeks. Initial and final concentrations of pesticides and nitrate, final biomass of macrophytes, periphyton and phytoplankton, pesticide accumulation in macrophytes and changes in carbon, nitrogen and phosphorus content and selected exoenzyme activities in the sediment were measured. We found lower final macrophyte biomass for both ARO treatments compared to controls, indicating a prevalence of negative effects by herbicides and competition for light with other phototrophs. In contrast, phytoplankton and periphyton biomass increased, but only when exposed to ARO via the water column, indicating a prevalence of positive effects by nutrient supply. Microbial carbon and nutrient cycling in sediments was not affected by ARO. Higher temperature mitigated ARO‐related effects on macrophytes under sediment exposure. Synthesis and application. ARO poses a strong risk of submerged macrophyte loss and establishment of turbid conditions with phytoplankton dominance in aquatic ecosystems. In conclusion, exposure pathways as well as indirect and interacting effects of multiple stressors need to be considered when designing appropriate mitigation measures. Under climate change, we suggest to prioritize local measures as buffer strips a reduced use of pesticides and fertilizers, and sediment removal as appropriate measures to protect these vulnerable but widespread aquatic systems, which are highly relevant for biodiversity in agricultural landscapes.

Tier-1 pesticide risk assessment for aquatic primary producers: A protectiveness check based on European Food Safety Authority endpoints.

Tier-1 pesticide risk assessment for aquatic primary producers: A protectiveness check based on European Food Safety Authority endpoints.

Growth inhibition, oxidative stress and characterisation of mortality in green algae under the influence of beta-blockers and non-steroidal anti-inflammatory drugs

Bisoprolol and ketoprofen are widely used pharmaceuticals in medical treatment hence these substances are occurring in wastewaters and in water environment. This research investigated the toxic effects of bisoprolol and ketoprofen on two microalgae taxa, Chlorella vulgaris and Desmodesmus armatus. The results showed that both drugs inhibited the growth of the species tested and induced a decrease in chlorophyll a content compared to controls. Ketoprofen turned out to be harmful to algae as the half maximal effective concentration (EC50) values (14 days) were 37.69 mg L−1 for C. vulgaris and 40.93 mg L−1 for D. armatus. On the other hand, for bisoprolol, the EC50 values were greater than the established NOEC, 100 mg L−1. Bisoprolol and ketoprofen induced oxidative stress in the tested microorganisms, as indicated by changes in the activities of antioxidant enzymes. Exposure to 100 mg L−1 of drugs significantly increased the activity of catalase, peroxidase and superoxide dismutase. Fluorescence microscopy showed that both medicaments changed the cells' morphology. There was atrophy of chlorophyll in the cells, moreover, dying multinuclear cells and cells without nuclei were observed. In addition, there were atrophic cells, namely cells that lacked nuclei and chlorophyll. Profile area analyses showed that bisoprolol and ketoprofen treated C. vulgaris cells were approximately 4 and 2 times greater compared to control ones. Our experimental findings highlight the ecotoxicological threats for aquatic primary producers from bisoprolol and ketoprofen and provide insight into the characteristics of their death.