Aquatic publication review (32)

Small mid-field reservoirs are a very important element of the agricultural landscape. They are not only refugiums of flora and fauna or regulators of the microclimate, but also filterers of excess nitrogen. The effectiveness of such ecosystems in removing this element has been studied in China by scientists there. Since winter is on the calendar, the topic of glaciers could not be missed – it turns out that their role in shaping the Earth’s topography and climate due to erosion is greater than that of rivers. These, in turn, have been changing their hydrological patterns in recent years, but the changes have been uneven across sections of the watercourses.

Scientists came to interesting conclusions by comparing the diversity and taxonomic composition of the microbiome of surface and subsurface environments, as well as marine and terrestrial environments. In turn, an analysis of the conservation status of more than 23,000 taxa of freshwater fauna included in the IUCN Red List shows that_1/4 of them are threatened with extinction. I don’t think any of us are surprised by this fact.

1 Shen W., Zhang L., Ury E.A. et al. (2025). Restoring small water bodies to improve lake and river water quality in China. Nat Commun 16, 294 [1].

Nature restoration is not only of conservation importance, but above all supportive in restoring natural resources and processes that are crucial to our functioning. Researchers in China proved this by studying the role and effectiveness of small inland water bodies as filterers of excess nitrogen from agriculture. Analysis of satellite data from an area of 10 major river basins in mainland China from 1995 to 2015 shows that the number of reservoirs has declined by 43 percent, with the most dramatic decline, both in number and area, found in reservoirs less than^104.5m2 (3.16 hectares), located in agricultural areas.

Currently, China’s reservoirs remove 986 kilotons of nitrogen per year, accounting for 3 percent of the surplus of this element in the landscape. The authors showed that restoring 7 percent of the area of small reservoirs (a total of 2.3 million hectares) could increase nitrogen removal up to 21 percent (211 kilotons per year) nationally, while restoring the same area as a single, large water body would contribute only 5 percent. This is due to the greater efficiency of small reservoirs (90 kg/ha/year) compared to those larger than^104.5m2 (32 kg/ha/year). This study underscores the tangible economic and environmental benefits of restoring small reservoirs in agricultural landscapes.

2 Feng D., Gleason C. J. (2024). More flow upstream and less flow downstream: The changing form and function of global rivers. Science 386, 1305-1311 [2].

Variability in the physical and hydrological conditions of rivers along their continuum from source to mouth determines erosion patterns, sedimentation, energy distribution and ecological communities. Climate change and associated modifications to the hydrological regime can transform the existing functioning of these dynamic ecosystems. Two U.S. scientists, Feng and Gleason, mapped daily flows in some 2.9 million rivers around the world to determine how they have changed over the past few decades. They showed that from 1984 to 2018, average flow volumes in source sections increased, while those in estuary sections decreased. These changes, among others, have increased the frequency of 100-year floods in sections closer to the sources, while the flood potential of downstream regions has remained constant.

3. Wilner J.A., Nordin B.J., Getraer A., et al. (2024). Limits to timescale dependence in erosion rates: Quantifying glacial and fluvial erosion across timescales. Sci. Adv. 10, eadr2009 [3].

Earth’s topography and climate are the result of opposing processes – uplift and erosion. In terms of the latter phenomenon, there is an ongoing scientific debate to resolve whether rivers or glaciers are the more effective factor. Researchers at Dartmouth College in Hanover, USA, conducted a comparative analysis of river and glacial erosion rates, supplemented by numerical experiments, through which they showed that globally, average rates of glacial erosion exceed those of river erosion by an order of magnitude over time, and that this difference cannot be explained by Sadlerian deviations or variability due to slope, precipitation or latitude.

The authors also test the hypothesis that the so-called Sadler effect, according to which geologic indicators show an inverse relationship with the time scale of measurement, includes de facto three separate effects: thickness measurement error, erosion-deposition error and the error of not observing rest intervals. These findings confirm the occurrence of increased erosion rates after cooling and Cenozoic glaciation, and reveal the importance of glacial erosion on the scale of millennia and the entire orogenesis.

4 Ruff S. E. et al. (2024). A global comparison of surface and subsurface microbiomes reveals large-scale biodiversity gradients, and a marine-terrestrial divide. Sci. Adv. 10, eadq0645 [4].

Subsurface environments are among the largest habitats for microbial life on Earth, but their differences from surface environments have not been well studied so far, mainly because of a lack of data to distinguish between microbiomes living in different places. And this is where genetics comes to the rescue.

The international team of biologists used an extensive analytical database of more than 1,000 metabarcoding data sets for archaeons and bacteria and 147 metagenomes from a variety of widely dispersed environments to conduct an analysis of microbiome differences and similarities between surface and subsurface environments, as well as marine and terrestrial environments. Surface data included water samples from oceans and lakes and shallow sediment samples, while subsurface data came from boreholes or mines and included deep sediments, aquifers and fractured fluids.

Microbial diversity in the marine and terrestrial microbiomes has been shown to be similar at local and global scales. However, the taxonomic composition of the communities differs significantly between sea and land, confirming the generally accepted phylogenetic division. In contrast, community composition between surface and subsurface environments showed a high degree of similarity, indicating some continuum of diversity. Differences in microbial life thus appear to be greater between land and sea than between surface and subsurface. The authors point to differences in the taxonomic composition of microbial communities, but emphasize similar microbial diversity for the Earth’s subsurface and surface environments.

5 Sayer C.A., Fernando E., Jimenez R.R. et al. (2025). One-quarter of freshwater fauna threatened with extinction. Nature [5].

Already the title of the article is so telling, in fact, you might not want to read any further. A quarter of freshwater fauna is threatened with extinction. Hands up who is surprised! To date, global extinction risk assessments have not included any freshwater species groups, and have primarily used data on terrestrial quadrupeds to guide environmental policy and set conservation priorities.

In order to identify the extinction risk, distribution, conservation requirements, key habitats and pressure factors of freshwater fauna species, a team of scientists conducted an analysis of the conservation status of more than 23,000 taxa, including tenth-generation taxa (crayfish, crabs and shrimp), fish and dragonflies, based on the IUCN Red List. Nearly_1/4 of the species (24 percent) are at high risk of extinction, a level comparable to that of terrestrial quadrupeds (23 percent).

The highest percentage of endangered species (30 percent) was found in the shellfish group, compared to 26 percent for freshwater fish and 16 percent for dragonflies. Among all endangered freshwater species, as many as 54 percent are becoming extinct due to pollution, 39 percent due to dams and hydrological disturbances from water withdrawals, 37 percent due to land use change, including the effects of agricultural activities, and 28 percent due to ecological invasions and diseases. Most species (84 percent) are affected by more than one threat.

The priority areas identified for the protection of terrestrial quadrupeds largely mirror those for freshwater fauna, but given the differences in key threats and habitats, it cannot be assumed that meeting the needs of quadrupeds is sufficient to protect freshwater species at the local scale. This proves that a case-by-case approach to each group of organisms is necessary.

[1] https://doi.org/10.1038/s41467-024-55714-9

[2] DOI: 10.1126/science.adl5728

[3] DOI: 10.1126/sciadv.adr2009

[4] DOI: 10.1126/sciadv.adq0645

[5] https://doi.org/10.1038/s41586-024-08375-z