How can top-down and bottom-up manipulation be used to mitigate eutrophication? Mesocosm experiment driven modeling zooplankton seasonal dynamic approach in the trophic cascade.

Eutrophication leads to algae blooms and reduces the transparency of water bodies, which seriously affects water quality and ecosystem equilibrium, especially in shallow water body ecosystems (SWE). Controlling foodwebs by manipulating fish and macrophytes provides a feasible method to mitigate the effects of eutrophication. The response of zooplankton as the primary consumer to biomanipulation is mostly conceptualized and lacks detailed observation. Mesocosm experiments that altered the biomass of planktivorous fish and macrophytes were set up and their boundary conditions were extended into a series of scenarios for modeling biomanipulation. Thus, this study utilizes a one-dimensional lake ecosystem model Water Ecosystems Tool (WET) which considered each zooplankton group: rotifers, cladocerans, and copepods, to predict the seasonal dynamic effects of biomanipulation on zooplankton in SWE, and the model results are analyzed in comparison with the mesocosm results. Observed data from mesocosm experiments set up in a temperate pond, including water temperature, dissolved oxygen (DO), total nitrogen (TN), total phosphorus (TP), chlorophyll a (Chl a), macrophytes, zooplankton, and fish, were used to calibrate and validate the models. The modeled results showed that in spring and summer zooplanktivorous fish removal would increase all three categories of zooplankton and consequently cause a decrease of phytoplankton, whilst an increase in fish biomass would increase phytoplankton, and concomitantly water turbidity. However, in autumn, rotifers and phytoplankton increased in response to fish removal, but cladocerans and copepods decreased, 27% and 41%, respectively. Across all three vegetated seasons, increasing the biomass of macrophytes revealed a similar pattern: all three categories of zooplankton increased and phytoplankton subsequently decreased. Our study proposes a "fish-zooplankton-macrophyte-phytoplankton" trophic cascade and quantitatively predicts the dynamics of each zooplankton group under biomanipulation through this pathway, and provides support for establishing macrophyte beds and removing zooplanktivorous fish (in spring and summer) as an effective approach to mitigate eutrophication.

Impact of biotic interactions on the survival of emerging pathogen Acinetobacter baumannii in aquatic media.

Acinetobacter baumannii is an opportunistic pathogen causing infections in immunocompromised patients. Recent studies recorded its persistence in a variety of abiotic conditions, but data regarding the biotic interactions with other microorganisms are limited. The aim was to assess the interaction of clinically relevant A. baumannii with common faecal bacteria Escherichia coli and Enterococcus faecium. Additionally, the interaction with a bdelloid rotifer Adineta vaga as a potential agent for biological control of A. baumannii was examined. Experiments were conducted in nutrient-poor spring water (SW) and nutrient-rich diluted nutrient broth (DNB) at 22 °C. A. baumannii coexisted with E. coli and E. faecium in both media, suggesting the absence of inter-bacterial competition in long-term survival. No difference in the survival of pandrug-resistant, extensively drug-resistant or antibiotic sensitive isolates of A. baumannii was observed. Rotifers contributed to the removal of all tested bacteria, particularly in SW. Rotifers were able to remove 5.5 ± 1.3 log CFU/mL of A. baumannii in SW and 3.5 ± 1.7 log CFU/mL in DNB. Additionally, no intracellular growth of A. baumannii inside A. vaga was detected. In wastewater treatment plants and drinking water facilities, grazing by rotifers might be useful for the removal of emerging human pathogens such as A. baumannii from water.