The period of autumn cold and the first frosts means that we are not always mindful of the progressive warming of the climate. A review of recent publications, several of which allude to the impact of climate change on aquatic ecosystems, will remind us of this. It seems that a lot revolves around temperatures in the Anthropocene era. We begin our review, however, with the work of Polish scientists who have attempted to estimate the degree of loss in invertebrate fauna and fish populations in the lower section of the Oder River as a result of the ecological disaster that hit this ecosystem in the summer of 2022. We also present a paper on the problem of microplastic pollution in flowing waters – how rivers recycle and transport plastic trash. We also recommend a comprehensive review of the potential use of algicidal bacteria to combat cyanobacteria, prepared by Polish scientists.

1. Quantifying a mass mortality event in freshwater wildlife within the Lower Oder River: Insights from a large European river

Szlauer-Łukaszewska A., Ławicki Ł., Engel J., Drewniak E., Ciężak K., Marchowski D. (2024). Quantifying a mass mortality event in freshwater wildlife within the Lower Odra River: Insights from a large European river. Science of The Total Environment, 907, 2024, 167898.

Moments before the publication of the current issue of Water Matters, the website of the prestigious journal Science of the Total Environment published a paper by a team of Polish scientists from several national scientific centers and organizations, presenting the results of a study of the population loss of invertebrate (mussels and snails) and vertebrate (fish and lampreys) fauna of the lower section of the Oder River after the ecological disaster of the summer of 2022. The authors show, based on their own surveys and estimates, that the mortality of the bivalve Unionidae in this section amounted to about 65 million individuals, a population decline of 88 percent. The most significant loss, on the order of 95 percent, was found for the native bivalve Anodonta anatina, while the invasive bivalve Sinanodonta woodiana declined by 15 percent. In addition, at least 147 million dead aquatic snails, mainly Viviparus viviparus, have been identified in coastal areas, indicating a population decline of 85 percent. The loss of ichthyofauna in the lower Oder River is estimated at 3.3 million fish, mainly ruffe(Gymnocephalus cernua), bream (Abramis brama) and perch(Perca fluviatilis), with an estimated total biomass of more than 1,000. t. In a 560-kilometer stretch of the river, the estimated fish mortality was 1,650 tons, a 60 percent decrease. Compared to pre-disaster levels. The rapid deterioration of the river’s ecosystem clearly indicates the need for further research into the adaptive capacity of the watercourse and its potential for regeneration.

The article, unfortunately, has not been published in open access, but I highly recommend anyone interested in the state of Poland’s second largest river to take the trouble to obtain it. This is an important addition to our existing knowledge of the state of the Oder River!

2. macroplastic fragmentation in rivers

Liro M., Zielonka A., van Emmerik T.H.M. (2023). Macroplastic fragmentation in rivers. Environment International, 180, 108186.

Do you remember the game of rubbing two pieces of Styrofoam against each other? A peculiar rasping sound was spreading, and bits of polystyrene were flying around. It turns out that rivers do the same with plastic – they act on the waste like mechanical shredders. By doing so, they become peculiar factories and transporters of micro- and nanoplastics. (We also wrote about the plastic model of the river in previous issues ofWater Matters). The problem of fragmentation of plastics that enter flowing waters has been looked at by scientists from Poland and the Netherlands, and their findings have just been published in the journal Environmental International. Based on a review of published experimental results and a conceptual model, the authors identify a number of factors that determine the breakdown of plastics into smaller particles. Trash made of various types of polystyrene, for example, food trays, forks and cups, and pieces of Styrofoam, turn into microplastics the fastest. Size and shape are also important – objects with a large surface area and low mass, such as pieces of film, are most susceptible to fragmentation. The intensity of mechanical grinding of trash depends on the energy of the water flow and the presence of obstacles in the channel, as well as the type and depth of the river. This process occurs with varying intensity in permanently flowing rivers, as well as intermittent and ephemeral rivers (we wrote about IRES in earlier issues ofWater Matters). The faster breakdown of plastic is also facilitated by increased exposure to UV radiation, which occurs in rivers devoid of natural riparian vegetation. The model created by the researchers can support the development of a method to quantitatively estimate the ” plastic footprint” ( plastic waste) of different plastics in different types of rivers.

3. Controls of thermal response of temperate lakes to atmospheric warming

Zhou J., Leavitt P.R., Rose K.C., et al. (2023). Controls of thermal response of temperate lakes to atmospheric warming. Nat Commun 14, 6503.

Global lakes are warming slower than surface air temperature due to accelerated evaporation

Tong Y., Feng L., Wang X., et al. (2023). Global lakes are warming slower than surface air temperature due to accelerated evaporation. Nat Water.

Almost at the same time, just two weeks apart, two papers were published by Chinese-American research teams on the rate of warming of lake waters due to climate change. The results of the two teams mutually confirm each other and lead to convergent conclusions – despite the globally recorded increase in the temperature of the surface layers of lake water today, in the future this rate will be slower than the warming of the atmosphere.

The first team, using data from 345 lakes located in temperate climates, showed a statistically significant (P

The second team, based on analysis of surface water temperature data over 92,000. lakes (using satellite remote sensing and numerical modeling), showed an average increase in global lake surface temperature of 0.24°C per decade from 1981 to 2020. This rate is statistically slower (P<0.05) than the change in air temperature (an average increase of 0.29°C per decade) over the same period. The loss of energy due to accelerated evaporation is mainly responsible for these differences (for more on this topic, see also the work of Wang et al., 2018.). Seemingly obvious, but in the article we have it demonstrated on hard data. The authors forecast further warming of the lakes over the next 80 years (2021-2099) if the greenhouse gas reduction scenario is not implemented. The results of both papers provide an important rationale for assessing the physical and biological responses of lakes to past and projected climate warming.

4. mesophotic coral bleaching associated with changes in thermocline depth

Diaz C., Foster N.L., Attrill M.J. et al. (2023). Mesophotic coral bleaching associated with changes in thermocline depth. Nat Commun 14, 6528.

Studies of the effects of climate change on aquatic organisms include the phenomenon of coral reef fading due to the loss of symbiotic algae under temperature stress. This problem is observed particularly intensively in the coral reefs of shallow ocean zones. However, it turns out that it also affects mesophotic coral ecosystems inhabiting deeper (30-150 m) and cooler waters (so-called “shadow reefs,” developing in zones where very little light reaches). Evidence of coral fading at a depth of 90 meters has been provided by a multidisciplinary study of Egmont Atoll in the Chagos Archipelago in the central Indian Ocean, conducted in 2019-2020 by a team of British scientists from the University of Plymouth. The authors showed that this phenomenon was linked to the continued deepening of the thermocline, triggered by the Indian Ocean Dipole (IOD). IOD is a phenomenon of surface water temperature anomalies between the eastern and western parts of the Indian Ocean that modifies surface wind fields, ocean currents and thermocline depths in a manner similar to El Niño in the South Pacific. The phenomenon described in the article is the deepest recorded case of coral fading, which occurred while there was no coral fading in shallow waters. The results of this work demonstrate the potential vulnerability of mesophotic coral ecosystems to thermal stress and underscore the need for increased oceanographic knowledge.

5. boom-bust cycles in gray whales associated with dynamic and changing Arctic conditions

Stewart J.D., Joyce T.W., Durban J.W. et al. (2023). Boom-bust cycles in gray whales associated with dynamic and changing Arctic conditions. Science 382(6667).

Climate change affects many global systems, but polar ecosystems are the most affected. Climatic effects affect short-lived species of lower trophic levels the most. Less recognized, however, is how long-lived and mobile species respond to rapid polar warming. This question was asked by US scientists who analyzed a database of more than 50 years of data on the abundance of the gray whale(Eschrichtius solidus, Polish name: gray walrus or gray swimmer) in the eastern North Pacific. The local population of this mammal was almost completely wiped out in the 19th century. As a result of hunting. Thanks to the introduction in 1947. A ban on commercial fishing, by 2016. A steady increase in the population to levels similar to those before the fishing season was observed. Most models assumed that gray whales would reach a relatively stable equilibrium. Stewart and co-authors challenged this assumption. They proved that the population of this cetacean shows rapid, episodic increases and decreases, and that these dynamics are closely linked to the availability of prey and the size of the ice cover on the feeding grounds. During periods when a decrease in the biomass of the food base (benthic invertebrates) was accompanied by an increase in the area of ice cover, gray whales showed increased mortality, which resulted in a population decline of 15 to 25 percent. This suggests that even mobile, long-lived species are vulnerable to the dynamically changing conditions that result from a warming Arctic. The findings of Stewart and co-authors indicate that despite the regulation of whaling, the recovery of whale populations in an era of rapidly changing climate may be more difficult than expected.

6 Algicidal bacteria against cyanobacteria: Practical knowledge from laboratory to application

Morón-López J., Serwecińska L., Balcerzak Ł., Glińska S., Mankiewicz-Boczek J. (2023). Algicidal bacteria against cyanobacteria: Practical knowledge from laboratory to application. Critical Reviews in Environmental Science and Technology.

And at the end of the current review, an article from a few weeks ago, but if anyone has missed it, I heartily recommend it. A team of researchers from two Lodz-based centers (the University of Lodz and the European Regional Center for Ecohydrology of the Polish Academy of Sciences) has taken up the topic of using bacteria to combat toxic algal blooms. The authors have comprehensively reviewed the existing knowledge on the basic aspects of searching for, isolating and determining potential algicidal bacteria that attack cyanobacteria. They also presented species interactions between these organisms and the mechanisms by which bacteria interact with different species of cyanobacteria. The article also presents the authors’ experimental findings on the sensitivity of nine freshwater cyanobacteria and two green algae to six different strains of bacteria with potent algicidal activity. The review indicates that promoting the microbial activity of indigenous algal bacteria through bioaugmentation (introduction of microorganisms) can be an effective method of inhibiting toxic cyanobacterial blooms. However, the authors emphasize that some key algal characteristics of the strains may be related to their pathogenic properties. Thus, the use of algicidal bacteria by bioaugmentation must be preceded by a thorough ecological risk and biosafety assessment.

Although the article is not openly available, but the smug authors are willing to share copies of their work, for which I thank them.

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