The current review of the aquatic literature probably cannot begin other than with the native publication in Nature. It addresses the impact of damming rivers on fish microhabitats. The team of authors is mainly from Poland, but the problem is of global importance, although it is presented on a European scale. There were also papers on other ills of aquatic and wetland ecosystems, such as the deoxygenation of flowing waters and the deteriorating conservation status of Europe’s amphibians. Scientists are also asking whether fish and invertebrates feel pain, and whether snow is likely to be white again in the future.

1. over 200,000 kilometers of free-flowing river habitat in Europe is altered due to impoundments

Parasiewicz P., Belka K., Lapinska M. et al, 2023 Nat Commun 14, 6289.

In the era of the Anthropocene, the need to take measures directed at river restoration/revitalization, in order to restore or preserve their habitats and biodiversity, is becoming evident worldwide. On a European scale, the problem was looked at by an international team of scientists, most of them from Poland, who developed a conceptual model of the impact of barriers on fish habitat. The researchers assessed the impact on fish microhabitats of six types of barriers (dams, weirs, sluices, culverts, fords and ramps) using data from nearly 5,500. positions on the rivers of Europe.

Their results, freshly published in Nature Communication, indicate that more than 200,000. km (10 percent of the length) of previously free-flowing rivers have been transformed by partitioning. The greatest habitat changes are caused by dams, weirs and sluices, although the intensity of their impact varies regionally due to differences in the height, type and density of their locations, as well as their biogeographic location. This work has provided water managers with a tool that will enable them to predict the potential environmental benefits or losses that can be expected as a result of barrier management on rivers, as well as to prioritize these actions.

2. widespread deoxygenation in warming rivers

Zhi W., Klingler C., Liu J. et al, 2023. Nat. Clim. Chang.

Staying on the topic of anthropogenic transformation of river ecosystems for a while longer, it is necessary to mention the work of Zhi and co-authors. Published in Nature Climate Change, the text addresses the phenomenon of deoxygenation of flowing waters. While it is commonly observed in oceans and lakes, it is far less expected in flowing waters, especially the shallower ones. Analyzing daily data from 1981-2019 on water temperature and dissolved oxygen concentrations in 580 rivers in the United States and 216 in Central Europe, using a deep learning approach, the authors found sustained warming in 87 percent. watercourses and deoxygenation in 70 percent.

Interestingly, rivers are currently warming and deoxygenating faster than oceans, although slower than lakes. In general, the rate of deoxygenation of rivers today is 1.6 to 2.5 times higher than in the past, which will have significant consequences for water quality and the functioning of aquatic ecosystems.

3. Ongoing declines for the world’s amphibians in the face of emerging threats

Luedtke J.A., Chanson J., Neam K., et al, 2023 Nature.

The consequences of the impact of anthropogenic pressures on aquatic ecosystems are observed widely and in many aspects. An article by more than 100 researchers has just been published in the journal Nature, presenting the results of the second Global Amphibian Assessment (GAA2, Global Amphibian Assessment). The first such assessment was published in 2006. It indicated that due to habitat loss and overexploitation of populations, the conservation status of more than half of the species studied had deteriorated between 1980 and 2004, and 48 percent of the species were considered endangered. Under GAA2, completed in June 2022, the number of amphibian species on the IUCN Red List was increased by more than 2,000, bringing the total to 8011 species of varying threat status (92.9 percent of all described species, an increase of 39.9 percent compared to 2004).

According to the researchers, amphibians are currently the most endangered class of vertebrates (40.7 percent of species worldwide are endangered), and the status of their populations is deteriorating globally, especially for salamanders and neotropical areas. The main reasons for this situation are climate change and habitat loss. Reversing the prevailing trend requires increasing funding for amphibian protection and taking immediate corrective action.

4. Reasons to Be Skeptical about Sentience and Pain in Fishes and Aquatic Invertebrates. Reviews in Fisheries Science & Aquaculture

Diggles B. K., Arlinghaus R., Browman H. I., et al, 2023.

If we’re staying on the topic of vertebrates, the journal Reviews in Fisheries Science & Aquaculture has published a very intriguing article on how fish and invertebrates feel (or don’t) pain. The problem is important because its definition lies at the heart of the legislation regulating the welfare of these animals. These regulations require the use of scientifically validated criteria, and the lack of such criteria risks creating interpretive problems.

The paper’s authors present ten arguments that they believe justify skepticism about the ability of fish and invertebrates to feel pain (such as, for example, the lack of reproducible empirical evidence, the use of arbitrary criteria, the devaluation of the concept of welfare, the high risk of unintended consequences, or the dangers of applying the precautionary principle) to guide legislators, policymakers and the scientific community and to draw attention to the need for a high level of scientific evidence for any indicators of aquatic animal welfare, particularly those required by legislation.

The paper’s authors emphasize that they identify themselves as animal welfare advocates, and the issue they raise is not about choosing between welfare or not, but rather about ensuring that important decisions are based on sound scientific evidence. Of course, the approach presented in the paper may raise objections or at least skepticism from animal rights activists, but it is worth noting that the authors here do not appeal to moral issues or empathy, but to the need to ensure objective scientific standards.

In doing so, they make no secret of the fact that this is crucial not only for the welfare of aquatic animals, but also for global food security. You can disagree (I wasn’t entirely convinced by the article), but it’s worth reading, if only to broaden your horizons with a different, very formal view of the interpretation of the issue of how animals feel pain.

5. Valorization of Spirodela polyrrhiza biomass for the production of biofuels for distributed energy

Romanowska-Duda Z., Piotrowski K., Szufa S. et al, 2023 Sci Rep 13, 16533.

The use of aquatic organisms for human consumption goes beyond food security. For example, aquatic plants in the cilia family Lemnaceae have great potential as biofuel material. For this reason, scientific interest in this group of plants has increased significantly in recent years. A team of scientists from Poland and Greece conducted a study on the effects of salt stress on the growth and development of multi-rooted spirodela Spirodela polyrhiza (It is a pity that in the article the name is systematically spelled wrong!) and the valorization of the biomass of this species for biofuel and energy production in a circular economy. Spirodela is a tiny, unrooted vascular plant with leaves floating on the surface of the water, with a habit somewhat resembling an eyelash.

It turns out that this species has a high ability to store starch under certain unfavorable growth conditions, such as salt stress and nutrient deficiency. The analysis of individual parameters of growth and development of S. polyrhiza, in the experiment conducted by the authors, indicates new possibilities for the use of this group of plants in biofuel and bioethanol production.

6. a cleaner snow future mitigates Northern Hemisphere snowpack loss from warming

Hao D., Bisht G., Wang H. et al, 2023 Nat Commun 14, 6074.

Finally, something in reference to the coming winter. With the heating season just getting underway, the topic of air pollution from combustion products is returning like a boomerang, including in terms of climate impact. One of the effects of smog is a change in the color of the snow cover. Light-absorbing soot particles ( black carbon), deposited on the snow, cause it to darken, melt faster, and consequently cause regional climate change. The problem was looked at by a U.S. team of researchers from the Pacific Northwest National Laboratory in Richland, USA, working under Hao, who analyzed projections of changes in combustion product deposition and its impact on the rate of snow melt under the two SSP (Shared Socioeconomic Pathways) scenarios analyzed through 2081-2100.

Compared to the 1995-2014 period, the authors predict a decrease in the intensity of soot deposition and a decrease in the rate of snow cover loss (using the Tibetan Plateau as an example), which is linked to a projected decrease in air pollution from combustion products, mainly under the sustainable development path (SSP1-2.6). Does this mean we can expect cleaner snow in the future?

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