Ecological value of macrophyte cover in creating habitat for microalgae (diatoms) and zooplankton (rotifers and crustaceans) in small field and forest water bodies

Single and combined effects of increased temperature and methylmercury on different stages of the marine rotifer Brachionus plicatilis

Rapid, anthropogenic activity-induced global warming is a severe problem that not only raises water temperatures but also shifts aquatic environments by increasing the bioavailability of heavy metals (HMs), with potentially complicated effects on aquatic organisms, including small aquatic invertebrates. For this paper, we investigated the combined effects of temperature (23 and 28 °C) and methylmercury (MeHg) by measuring physiological changes, bioaccumulation, oxidative stress, antioxidants, and the mitogen-activated protein kinase signaling pathway in the marine rotifer Brachionus plicatilis. High temperature and MeHg adversely affected the survival rate, lifespan, and population of rotifers, and bioaccumulation, oxidative stress, and biochemical reactions depended on the developmental stage, with neonates showing higher susceptibility than adults. These findings demonstrate that increased temperature enhances potentially toxic effects from MeHg, and susceptibility differs with the developmental stage. This study provides a comprehensive understanding of the combined effects of elevated temperature and MeHg on rotifers. ENVIRONMENTAL IMPLICATION: Methylmercury (MeHg) is a widespread and harmful heavy metal that can induce lethal effects on aquatic organisms in even trace amounts. The toxicity of metals can vary depending on various environmental conditions. In particular, rising temperatures are considered a major factor affecting bioavailability and toxicity by changing the sensitivity of organisms. However, there are few studies on the combinational effects of high temperatures and MeHg on aquatic animals, especially invertebrates. Our research would contribute to understanding the actual responses of aquatic organisms to complex aquatic environments.

Vertical optical complexity shaped by submerged macrophytes

The influence of macrophytes on the optical environment of the littoral zone was assessed by studying the effect of monospecific Potamogeton perfoliatus on the quantitative and qualitative properties of light and the response of plants to this altered environment. P. perfoliatus was shown to alter the optical environment and consequently its own architecture: in high-density pondweed patches, 67 percent of incident light was absorbed in the top 10 cm, while spectral properties of light was significantly altered. Leaf morphology and photophysiology adapted to these changes, with photosynthetically active biomass concentrated in the upper water layer and stem biomass increasing in the basal parts due to self-shading. This study highlights the importance of submerged macrophytes in shaping the optical environment and ecological dynamics of littoral zones. Not only do pondweed plants from different sites show very similar vertical patterns of morphological and physiological parameters, but they also contribute to similar vertical spatial variability in water optics, thus increasing habitat complexity. This added optical heterogeneity not only increases the diversity of the littoral zone, but also enriches the entire aquatic ecosystem of shallow lakes by providing additional optical ecological niches.

Physiological effects and molecular response in the marine rotifer Brachionus plicatilis after combined exposure to nanoplastics and copper

Because nanoplastics (NPs) can transport pollutants, the absorption of surrounding pollutants into NPs and their effects are important environmental issues. This study shows a combined effect of high concentrations of NPs and copper (Cu) in the marine rotifer Brachionus plicatilis. Co-exposure decreased the growth rate, reproduction, and lifespan. The highest level of NP ingestion was detected in the co-treated group, but the Cu concentration was higher in the Cu single-exposure group. ERK activation played a key role in the downstream cell signaling pathway activated by the interaction of NPs and Cu. The increased sensitivity of B. plicatilis to Cu could be due to the impairment of MXR function caused by a high concentration of NPs, which supports our in vivo experiment results. Our results show that exposure to NPs could induce the dysfunction of several critical molecular responses, weakening resistance to Cu and thereby increasing its physiological toxicity in B. plicatilis.

Paleo-diatom records reveal ecological change not detected using traditional measures of lake eutrophication

Lakes provide crucial ecosystem services and harbour unique and rich biodiversity, yet despite decades of research and management focus, cultural eutrophication remains a predominant threat to their health. Our ability to manage lake eutrophication is restricted by the lack of long-term monitoring records. To circumvent this, we developed a bio-indicator approach for inferring trophic level from lake diatom communities and applied this to sediment cores from two lakes experiencing eutrophication stress. Diatom indicators strongly predicted observed trophic levels, and when applied to sediment cores, diatom predicted trophic level reconstructions were consistent with monitoring data and land-use histories. However, there were significant recent shifts in diatom communities not captured by the diatom-based index or monitoring data, suggesting that conventional trophic level indices obscure important ecological change. New approaches, such as the one in this study, are critical to detect early changes in water quality and prevent the decline of lake ecosystems worldwide.

Diatom community composition on submerged macrophyte species from an Ontario (Canada) lake

The introduction of invasive macrophyte species can affect submerged macrophyte community composition and abundance, which in turn can alter the functions of lake ecosystems. Knowing when and how invasive macrophytes arrive and spread can help disentangle the effects of invasive species from other stressors on lake ecosystems. This requires a long-term (decades) perspective of macrophyte community composition, which is rarely available. An alternative is paleolimnological inferences of macrophyte community composition from fossil diatom assemblages, which requires knowledge of epiphytic diatom communities. Here, we investigated the epiphytic diatom community composition of three common submerged macrophyte species (Chara sp., Potamogeton robbinsii, and the invasive Myriophyllum spicatum) in a typical temperate, mixed forest lake, Chandos Lake, Ontario, Canada, to provide a basis for future paleolimnological research. Non-parametric, multivariate analysis of variance indicated a statistically significant difference in the epiphytic diatom communities of different macrophyte species, despite principal components analysis showing some overlap among the diatom communities. Diatom community composition of all macrophytes had abundant Achnanthidium minutissimum and Cocconeis placentula. Generalized linear models and univariate analysis of variance identified six diatoms (Encyonopsis microcephala, Epithemia turgida, Gomphonema parvulius, Navicula gerloffi, Rhopalodia gibba, and Rossithidium anastasiae) that were significantly different among macrophyte species. Although it remains uncertain whether these differences are sufficient to infer historical macrophyte community composition from epiphytic diatom fossil assemblages, our results indicate the potential of such an approach and offer suggestions for future research.

Chlorophytes response to habitat complexity and human disturbance in the catchment of small and shallow aquatic systems

Human-originated transformation in the catchment area may be reflected in the water quality and ecological state of the aquatic environment. Chlorophytes, the most common and diverse group of microalgae, may be a valuable tool for studies of small water bodies, ecosystems poorly recognized but extremely sensitive to the climate changes. Here we investigated the response of the chlorophytes to abiotic and biotic factors in different habitats and ponds' catchments. Chlorophytes demonstrated a prevalence towards a specific type of catchment area. Field ponds supported chlorophytes typical for nutrient-rich/high-organic and shallow well-mixed waters. Forest ponds supported high chlorophyte diversity. A high importance of desmids, tolerant to light deficiency, confirms their preferences towards lower pH and lower trophic state in the forest ponds. Habitat type strongly impacted the distribution of chlorophytes. Great abundance and fertile-water species were associated with the open water, whereas aquatic plants hosted relatively low chlorophyte abundance which is a derivate of the filtrators grazing as well as the nutrient uptake and shadowing by macrophytes. Macrophyte-dominated zones created favorable conditions for some periphytic desmids and filamentous chlorophytes, species preferring lower trophic state and co-occurring with zooplankton. We assume that cosmopolitan chlorophytes can be adapted for determination of the ecological value of small water bodies, including the level of habitat heterogeneity. But chlorophytes clearly react to the level of human impact in the ponds' catchment, both specific species and functional groups. Thus, we recommend them, particularly desmids, for water quality state assessment in ponds.

The influence of land use in the catchment area of small waterbodies on the quality of water and plant species composition

Land use significantly affects the function of waterbodies in landscape. Although there have been numerous studies on the influence of the catchment area on the trophic and ecological status of waterbodies, still is not reached an agreement on the width of the buffer zone that is necessary for effective protection of waterbodies. The aim of the study was to show whether small waterbodies are predominantly influenced by land use in the entire catchment area or only in the zone extending 100 or 200 m away from the shoreline. For two years the waters in six small waterbodies located in the Wielkopolska region (Poland) were analysed. The canonical correspondence analysis (CCA) showed that the influence of land use, especially agricultural land, was much greater within the zone extending 100 m from the shore line of the waterbodies than in the total catchment area. Therefore, it would be advisable to move the border of intensive farming areas beyond the entire 100-m-wide buffer zone, or at least to reduce the intensity of agriculture and to introduce diversified and perennial vegetation creating effective biogeochemical barriers.

Snail communities increase submerged macrophyte growth by grazing epiphytic algae and phytoplankton in a mesocosm experiment

The relationships between producers (e.g., macrophytes, phytoplankton and epiphytic algae) and snails play an important role in maintaining the function and stability of shallow ecosystems. Complex relationships exist among macrophytes, epiphytic algae, phytoplankton, and snails. We studied the effects of snail communities (consisting of Radix swinhoei, Hippeutis cantori, Bellamya aeruginosa, and Parafossarulus striatulus) on the biomass of phytoplankton and epiphytic algae as well as on the growth of three species of submerged macrophytes (Hydrilla verticillata, Vallisneria natans, and one exotic submerged plant, Elodea nuttallii) in a 90-day outdoor mesocosm experiment conducted on the shore of subtropical Lake Liangzihu, China. A structural equation model showed that the snail communities affected the submerged macrophytes by grazing phytoplankton and epiphytic algae (reduction in phytoplankton Chl-a and epiphytic algal abundance), enhancing the biomass of submerged macrophytes. Highly branched macrophytes with high surfaces and morphologies and many microhabitats supported the most snails and epiphytic algae (the biomass of the snail communities and epiphytic algae on H. verticillata was greater than that on V. natans), and snails preferred to feed on native plants. Competition drove the snails to change their grazing preferences to achieve coexistence.

Species diversity and community structure of crustacean zooplankton in the highland small waterbodies in Northwest Yunnan, China

Small waterbodies are a unique aquatic ecosystem with an increasing recognition for their important role in maintaining regional biodiversity and delivering ecosystem services. However, small waterbodies in Northwest Yunnan, one of the most concerned global biodiversity hot-spots, remain largely unknown. Here, we investigated the community structure of crustacean zooplankton and their relationships with limnological, morphometric and spatial variables in the highland small waterbodies in Northwest Yunnan in both the dry (October 2015) and rainy (June 2016) seasons. A total of 38 species of crustacean zooplankton were identified in our study, which is significantly higher than many other reported waterbodies in the Yunnan–Guizhou plateau as well as in the Yangtze River basin. This suggests that the highland small waterbodies are critical in maintaining regional zooplankton diversity in Northwest Yunnan. Meanwhile, we found limnological variables could explain most variation of crustacean zooplankton community, comparing to the morphometric and spatial variables in both the rainy and dry seasons. Our study revealed the diversity and community structure of crustacean zooplankton in the highland small waterbodies in Northwest Yunnan and highlighted the importance of small waterbodies in maintaining regional biodiversity.

Phytoplankton communities in temporary ponds under different climate scenarios

Temporary water bodies, especially vernal pools, are the most sensitive aquatic environments to climate change yet the least studied. Their functioning largely depends on their phytoplankton community structure. This study aimed to determine how temperature and photoperiod length (by simulating inundation in different parts of the year under five climate scenarios) affect the succession and structure of phytoplankton communities soon after inundation. Photoperiod was the most important factor affecting phytoplankton species richness, total abundance and the abundance of taxonomic groups in the course of succession. A long photoperiod (16 h) and a moderate temperature (16 °C) in vernal pool microcosms (late spring inundation after a warm snowless winter) were the most favourable conditions for phytoplankton growth (especially for the main taxonomic groups: chlorophytes and cryptophytes) and species richness. With short photoperiods (inundation in winter) and low temperatures, the communities transformed towards diatoms, euglenoids and cyanobacteria. In line with our predictions, a high temperature (25 °C) favoured a decline in phytoplankton species diversity. Our study shows that climate change will result in seasonal shifts in species abundance or even in their disappearance and, finally, in potential strong changes in the biodiversity and food webs of aquatic ecosystems in the future.

Ecotoxicity of pesticides and semiochemicals used for control and prevention of conifer bark beetle (Dendroctonus spp.) outbreaks

Application of pyrethroid pesticides and semiochemicals are two treatments used worldwide to control conifer bark beetles (Dendroctonus spp.); their residues can reach water reservoirs and water currents through run off and affect non-target organisms such as freshwater invertebrates. Therefore, we assessed the 48-h lethal toxicity, chronic toxicity (reproduction inhibition), and bioaccumulation of three pyrethroid pesticides (bifenthrin, cypermethrin, and deltamethrin) and two semiochemicals (verbenone and 3-methyl-2-cyclohexen-1-one) in two freshwater invertebrates: the cladoceran Alona guttata and the rotifer Lecane papuana. Bifenthrin was the most toxic of the five chemical compounds tested followed by deltamethrin and then cypermethrin, which was the least toxic pyrethroid for both species. Semiochemicals were far less toxic than pyrethroids and verbenone was most toxic than 3-methyl-2-cyclohexen-1-one for both species. For the rotifer Lecane papuana, the pyrethroid with the highest Bioconcentration Factor was bifenthrin, and for the semiochemicals it was 3-methyl-2-cyclohexen-1-one. For the cladoceran Alona guttata, the pyrethroid with the highest bioconcentration factor was cypermethrin and for the semiochemicals it was verbenone. The pyrethroid with highest body burdens both lethal and chronic was cypermethrin. Semiochemicals showed lethal and chronic body burdens 12-fold higher than pyrethroids and were therefore less toxic than pyrethroids. These results showed that the semiochemicals verbenone and 3-methyl-2-cyclohexen-1-one are a safe tool for the freshwater invertebrates tested when compared with pyrethroid pesticides. Cypermethrin was the least toxic of the pyrethroids tested and therefore could be considered as a good candidate to control outbreaks of the conifer bark beetle.

Effects of Water Quality Adjusted by Submerged Macrophytes on the Richness of the Epiphytic Algal Community

Submerged macrophytes and epiphytic algae play significant roles in the functioning of aquatic ecosystems. Submerged macrophytes can influence the epiphytic algal community by directly or indirectly modifying environmental conditions (nutrients, light, etc.). From December to June of the following year, we investigated the dynamics of the dominant winter species Potamogeton crispus, its epiphytic algae, and water quality parameters in the shallow Liangzi Lake in China. The richness of epiphytic algae had a trend similar to that of P. crispus coverage, which increased in the first four months and then decreased in the following three months. The structural equation model (SEM) showed that P. crispus affected the richness of epiphytic algae by reducing nutrient concentrations (reduction in total organic carbon, total nitrogen and chemical oxygen demand) and enhancing water transparency (reduction in turbidity and total suspend solids) to enhance the richness of epiphytic algae. The results indicated that high amounts of submerged macrophyte cover can increase the richness of the epiphytic algal community by changing water quality.

Cyanobacteria in small water bodies: The effect of habitat and catchment area conditions

Cyanobacteria are an important component of microalgae communities in aquatic ecosystems, however, their response to environmental factors in different habitats and catchment areas of small water bodies is still not well recognised. We examined ponds from two types of surroundings (field vs. forest) in order to find the best triggers for the distribution of cyanobacteria species, and analysed different habitats (open water and macrophyte-dominated zones) to find the habitat preferences of cyanobacteria species. Our results underline the important role of habitats in the determination of the abundance of cyanobacteria species in small water bodies. Cyanobacteria as a group preferred macrophyte-dominated sites with stable water column conditions, which to lesser extent were inhabited by representatives of other systematic groups of algae. The co-occurrence of many cyanobacteria species and zooplankton in the studied ponds may have indirectly resulted from biotic interactions in the food web. In the open water a positive relationship between zooplankton and cyanobacteria suggests stimulation of their development through the elimination of smaller edible taxa or by nutrient resupply through zooplankton excretion. The type of catchment area also impacted the cyanobacterial community. Field ponds with significantly higher values of pH and NO₃ were characterised by a higher abundance of cyanobacteria compared with ponds within the forest catchment. A positive relationship between pH and cyanobacteria indicates that they raise pH during photosynthesis. However, some species were negatively associated with water temperature and occurred exclusively only in forest ponds. The study revealed that cyanobacteria in small water bodies can be a valuable indicator of important ecosystem conditions. Despite the fact that their prevalence in agricultural ponds may confirm their potential as an indicator of pollution, their high diversity associated with macrophytes contributes to an increase of overall landscape biodiversity.