Modelling of ecological status of Polish lakes using deep learning techniques

Since 2000, after the Water Framework Directive came into force, aquatic ecosystems' bioassessment has acquired immense practical importance for water management. Currently, due to extensive scientific research and monitoring, we have gathered comprehensive hydrobiological databases. The amount of available data increases with each subsequent year of monitoring, and the efficient analysis of these data requires the use of proper mathematical tools. Our study challenges the comparison of the modelling potential between four indices for the ecological status assessment of lakes based on three groups of aquatic organisms, i.e. phytoplankton, phytobenthos and macrophytes. One of the deep learning techniques, artificial neural networks, has been used to predict values of four biological indices based on the limited set of the physicochemical parameters of water. All analyses were conducted separately for lakes with various stratification regimes as they function differently. The best modelling quality in terms of high values of coefficients of determination and low values of the normalised root mean square error was obtained for chlorophyll a followed by phytoplankton multimetric. A lower degree of fit was obtained in the networks for macrophyte index, and the poorest model quality was obtained for phytobenthos index. For all indices, modelling quality for non-stratified lakes was higher than this for stratified lakes, giving a higher percentage of variance explained by the networks and lower values of errors. Sensitivity analysis showed that among physicochemical parameters, water transparency (Secchi disk reading) exhibits the strongest relationship with the ecological status of lakes derived by phytoplankton and macrophytes. At the same time, all input variables indicated a negligible impact on phytobenthos index. In this way, different explanations of the relationship between biological and trophic variables were revealed.

Effects of multiple stressors on cyanobacteria abundance vary with lake type

Blooms of cyanobacteria are a current threat to global water security that is expected to increase in the future because of increasing nutrient enrichment, increasing temperature and extreme precipitation in combination with prolonged drought. However, the responses to multiple stressors, such as those above, are often complex and there is contradictory evidence as to how they may interact. Here we used broad scale data from 494 lakes in central and northern Europe, to assess how cyanobacteria respond to nutrients (phosphorus), temperature and water retention time in different types of lakes. Eight lake types were examined based on factorial combinations of major factors that determine phytoplankton composition and sensitivity to nutrients: alkalinity (low and medium-high), colour (clear and humic) and mixing intensity (polymictic and stratified). In line with expectations, cyanobacteria increased with temperature and retention time in five of the eight lake types. Temperature effects were greatest in lake types situated at higher latitudes, suggesting that lakes currently not at risk could be affected by warming in the future. However, the sensitivity of cyanobacteria to temperature, retention time and phosphorus varied among lake types highlighting the complex responses of lakes to multiple stressors. For example, in polymictic, medium-high alkalinity, humic lakes cyanobacteria biovolume was positively explained by retention time and a synergy between TP and temperature, while in polymictic, medium-high alkalinity, clear lakes only retention time was identified as an explanatory variable. These results show that, although climate change will need to be accounted for when managing the risk of cyanobacteria in lakes, a "one-size fits-all" approach is not appropriate. When forecasting the response of cyanobacteria to future environmental change, including changes caused by climate and local management, it will be important to take this differential sensitivity of lakes into account.

Temperature Effects Explain Continental Scale Distribution of Cyanobacterial Toxins

Insight into how environmental change determines the production and distribution of cyanobacterial toxins is necessary for risk assessment. Management guidelines currently focus on hepatotoxins (microcystins). Increasing attention is given to other classes, such as neurotoxins (e.g., anatoxin-a) and cytotoxins (e.g., cylindrospermopsin) due to their potency. Most studies examine the relationship between individual toxin variants and environmental factors, such as nutrients, temperature and light. In summer 2015, we collected samples across Europe to investigate the effect of nutrient and temperature gradients on the variability of toxin production at a continental scale. Direct and indirect effects of temperature were the main drivers of the spatial distribution in the toxins produced by the cyanobacterial community, the toxin concentrations and toxin quota. Generalized linear models showed that a Toxin Diversity Index (TDI) increased with latitude, while it decreased with water stability. Increases in TDI were explained through a significant increase in toxin variants such as MC-YR, anatoxin and cylindrospermopsin, accompanied by a decreasing presence of MC-LR. While global warming continues, the direct and indirect effects of increased lake temperatures will drive changes in the distribution of cyanobacterial toxins in Europe, potentially promoting selection of a few highly toxic species or strains.

Sensitivity of plankton indices to lake trophic conditions

Herein, we report the response of indices based on phytoplankton and zooplankton and their combination to different nutrient concentrations in lakes. The study was carried out in ten lakes in northeastern Poland. Integrated samples were collected from the epilimnion during the summer of 2012-2013. Secchi disk visibility (SD), total phosphorus (TP), total nitrogen (TN), and chlorophyll a were used as proxies for eutrophication. We calculated 16 plankton indices: two phytoplankton indices, six crustacean indices, five rotiferan indices, two zooplankton diversity indices, and one combined phytoplankton and zooplankton index. Among them, nine indices with the strongest correlations with TP were selected: percentage share of Crustacean species indicative of high trophy in the indicative group's numbers (IHTCRU), percentage share of Rotifera species indicative of high trophy in the indicative group's numbers IHTROT, Crustacean ratio of biomass to numbers B/NCRU, phytoplankton trophic index (TITP+TN), Margalef's index, percentage share of cyclopoid biomass in total biomass of Crustacea (CB), Rotifera numbers (NROT), biomass of Cyclopoida (BCY), and ratio of the cyclopoid biomass to the biomass of Cladocera (CY/CL). The sensitivity of the normalized values of these indices to proxies of eutrophication was tested. IHTCRU, IHTROT, and B/NCRU were the most sensitive and gave the strongest responses at lower TP concentrations (<35 μg/L). The phytoplankton trophic index, TITP+TN, together with the zooplankton-based Margalef's index and CB were very sensitive in both low (<35 μg/L) and high (>60 μg/L) TP conditions. On the other hand, NROT, BCY, and CY/CL were slightly sensitive at low TP concentrations while their reaction was notable at high TP concentrations. A similar pattern of response was observed for TN concentration and SD visibility.

Different defense strategies of Dendrolimus pini, Galleria mellonella, and Calliphora vicina against fungal infection

The resistance of Galleria mellonella, Dendrolimus pini, and Calliphora vicina larvae against infection by the enthomopathogen Conidiobolus coronatus was shown to vary among the studied species. Exposure of both G. mellonella and D. pini larvae to the fungus resulted in rapid insect death, while all the C. vicina larvae remained unharmed. Microscopic studies revealed diverse responses of the three species to the fungal pathogen: (1) the body cavities of D. pini larvae were completely overgrown by fungal hyphae, with no signs of hemocyte response, (2) infected G. mellonella larvae formed melanotic capsules surrounding the fungal pathogen, and (3) the conidia of C. coronatus did not germinate on the cuticle of C. vicina larvae. The in vitro study on the degradation of the insect cuticle by proteases secreted by C. coronatus revealed that the G. mellonella cuticle degraded at the highest rate. The antiproteolytic capacities of insect hemolymph against fungal proteases correlated well with the insects' susceptibility to fungal infection. The antiproteolytic capacities of insect hemolymph against fungal proteases correlated well with the insects' susceptibility to fungal infection. Of all the tested species, only plasmatocytes exhibited phagocytic potential. Exposure to the fungal pathogen resulted in elevated phagocytic activity, found to be the highest in the infected G. mellonella. The incubation of insect hemolymph with fungal conidia and hyphae revealed diverse reactions of hemocytes of the studied insect species. The encapsulation potential of D. pini hemocytes was low. Hemocytes of G. mellonella showed a high ability to attach and encapsulate fungal structures. Incubation of C. vicina hemolymph with C. coronatus did not result in any hemocytic response. Phenoloxidase (PO) activity was found to be highest in D. pini hemolymph, moderate in G. mellonella, and lowest in the hemolymph of C. vicina. Fungal infection resulted in a significant decrease of PO activity in G. mellonela larvae, while that in the larvae of D. pini remained unchanged. PO activity in C. vicina exposed to fungus slightly increased. The lysozyme-like activity increased in the plasma of all three insect species after contact with the fungal pathogen. Anti E. coli activity was detected neither in control nor in infected D. pini larvae. No detectable anti E. coli activity was found in the control larvae of G. mellonella; however, its exposure to C. coronatus resulted in an increase in the activity to detectable level. In the case of C. vicina exposure to the fungus, the anti E. coli activity was significantly higher than in control larvae. The defense mechanisms of D. pini (species of economic importance in Europe) are presented for the first time.