Aquatic publication review (22)

It’s the middle of summer, the heat is pouring from the sky, so it’s hard to avoid references to works describing the effects of high temperatures on the aquatic environment. And these have appeared in particular abundance in recent weeks. Since water is a common destination for our vacation getaways, we talk a lot in the holiday literature review about how climate warming is affecting various aspects of the structure and functioning of aquatic and water-dependent ecosystems. There will be drought, flooding, rising water column temperatures, increasing water fertility and the possibility of purification by macrophytes when stimulated by artificial underwater light. And also about how salinity and flow changes in urban watercourses affect aquatic communities. Let’s hurry to spend our vacations by the waters, they degrade so fast!

1. emergence of lake conditions that exceed natural temperature variability

Huang L., Woolway R.I., Timmermann A. et al. Emergence of lake conditions that exceed natural temperature variability. Nat. Geosci. (2024).

It will probably surprise no one to find out that due to climate change, the surface temperature of the lakes is forecast to increase significantly. This, in turn, can cause changes in the distribution of thermally sensitive aquatic species. Scientists have investigated this phenomenon using the results of daily projections of the CESM2-LE(Community Eart System Model ver. 2 Large Ensemble) for a set of historical (1850-2014) and future (2015-2100) simulations. The results indicated that global warming will cause thermal changes in the water column, leading to the emergence of new conditions with no contemporary counterparts(non-analogous, i.e., with temperatures outside the range of natural variability, with no analogues today or in the past).

Non-analog conditions will occur first in lakes located at low latitudes. For colder lakes, in northern cool regions or southern temperate regions, non-analog conditions are expected to occur only if warming exceeds ~4.0 °C. These changes are likely to significantly affect their habitability, leading to a change in the taxonomic composition of freshwater communities. The phenomenon is expected later this century.

2. Severe droughts reduce river navigability and isolate communities in the Brazilian Amazon

Santos de Lima L., Silva F.E., Dorio Anastácio P.R. et al. (2024). Severe droughts reduce river navigability and isolate communities in the Brazilian Amazon. Commun Earth Environ 5, 370.

With climate change, not only are water thermals changing, but above all the problem of drought is intensifying, and this has serious implications for the functioning and safety of entire communities. In the study, the results of which were published in Communications Earth & Environment, the researchers analyzed the situation of Brazilian communities living in the Amazon basin during the extreme droughts that hit the area between 2000 and 2020. The results show that the droughts in 2005, 2010 and 2016 were the most severe, with low water levels lasting more than a month longer than usual.

Such droughts disrupt inland water transportation and isolate local populations, limiting access to basic commodities (food, fuel, medicines) and essential services (health care, education). Given this new reality, Amazonian countries must develop long-term mitigation, adaptation and disaster response strategies to ensure the food and health security of populations living in these regions. It turns out that relying on water transportation at a time of widespread deficits in this medium can have completely unintended consequences.

3. rising seas could cross thresholds for initiating coastal wetland drowning within decades across much of the United States

Osland M.J., Chivoiu B., Grace J.B. et al. (2024). Rising seas could cross thresholds for initiating coastal wetland drowning within decades across much of the United States. Commun Earth Environ 5, 372 (2024).

Due to climate change, it dries out some and floods others. Accelerated sea level rise poses a threat to coastal areas, but the extent and projected time horizon of these inundations are not sufficiently recognized. U.S. scientists analyzed three alternative scenarios for relative sea level rise: medium-low, intermediate and medium-high (corresponding to 0.5; 1.0 and 1.5 meters of average sea level rise by 2100 compared to a 2000 baseline) for areas including Washington and 22 U.S. coastal states along the Pacific Ocean, Gulf of Mexico and Atlantic Ocean.

The results showed that there is a large spatial variation in the relative rate of sea level rise, which affects the potential timing and extent of coastal inundation thresholds. The high rate of relative sea level rise identifies areas that are already sinking or may begin to sink in the coming decades, including large areas in the Mississippi River Delta, Greater Everglades, Chesapeake Bay, Texas, Georgia and the Carolinas. The results indicate areas where action should be taken to prepare for the transformational changes of the coast.

4 Acceleration of phosphorus weathering under warm climates

Guo L., Xiong S., Mills B.J. et al. (2024). Acceleration of phosphorus weathering under warm climates. Sci. Adv. 10, eadm7773.

Another major effect of a warming climate is an increase in the fertility of surface water. It turns out that this is not only due to increased evaporation and reduced water dilution of pollutants, but also due to accelerated release of phosphorus from the geological substrate through chemical weathering. The global climate plays a significant role in controlling the speed at which this process takes place. Based on an analysis of temperature and phosphorus data in surface soils (0 to 30 cm) around the world, it was shown that the release of this element actually increases at high average annual temperatures (with a variation of ~12°C).

A number of other factors were also analyzed, such as precipitation, runoff, biome, lithology, absolute altitude and slope. The main regulators of phosphorus mobility appeared to be climatic factors (mainly temperature), although the contribution of non-climatic factors was also significant. Increasing the supply of nutrients with warming is a critical part of the Earth’s natural thermostat. The potential acceleration of phosphorus loss from soils as a result of anthropogenic climate warming could threaten agricultural production and terrestrial and marine ecosystems, and is likely to contribute significantly to increased ocean anoxia in the near future.

5. Underwater light source changes nitrogen and phosphorus removal pathways by Vallisneria spinulosa Yan growth system

Zhao J., Zhou X., Fan C. et al (2024). Underwater light source changes nitrogen and phosphorus removal pathways by Vallisneria spinulosa Yan growth system. npj Clean Water 7, 59.

In an era of widespread scarcity of good-quality water, all methods of purification, especially those based on natural solutions, are of particular importance. One method is to use aquatic plants with high purification capacity. A limitation to its use is the usually high turbidity of polluted waters, which hinders plant colonization and limits its effectiveness. Chinese scientists have conducted a study on the possibility of using artificial underwater light to increase the efficiency of colonization and purification of waters by an underwater vascular plant from the frog family, Vallisneria spinulosa Yan.

The introduction of an underwater artificial light source increased the clonal reproduction capacity of this species, and thus significantly increased the amount of total nitrogen, total phosphorus and nitrate nitrogen loads removed. The underwater light source significantly reduced the abundance of microorganisms on the leaves of V. spinulosa, and also reduced most of the nitrifying(Nitrosomonadaceae) and denitrifying(Nitrospira, Comamonadaceae and Rhodocyclaceae) bacteria in the system. However, the proportion of some cyanobacteria and photosynthesizing bacteria increased.

After about 2 months of experimentation, V. spinulosa reached a height that allowed it to use natural light, so its artificial source could be removed, reducing maintenance costs of the plant. The use of solar power can significantly reduce the cost of the method, which has proven to be an effective way to stimulate the growth of underwater plants under severe shading conditions.

6. Assessing the response of an urban stream ecosystem to salinization under different flow regimes

Pimentel I.M., Baikova D., Buchner D. et al, (2024). Assessing the response of an urban stream ecosystem to salinization under different flow regimes. Science of The Total Environment, 926, 171849.

Urban watercourses are subject to a variety of anthropogenic impacts, but salinity remains a key stressor. Climate change is expected to exacerbate the problem, which is due to, among other things. From changes in flow parameters. However, the effects of salinity and flow velocity on urban watercourses are still poorly understood, as experiments considering multiple stressors are often conducted in non-urbanized areas. A team of aquatic ecologists and hydrobiologists from the University of Duisburg-Essen conducted mesocosm experiments using repeated pulses of salinity (NaCl) along a gradient (from 0 to 2.5 mS/cm) in conjunction with normal and reduced flow velocities (20 cm/s vs. 10 cm/s) on the recently renaturalized Boye River, which flows through a highly urbanized area in western Germany.

Based on a comprehensive assessment of several groups of organisms (benthic macroinvertebrates, eukaryotic algae, fungi, parasites) and ecosystem functions (primary production, organic matter decomposition), the researchers showed that a reduction in flow velocity had a pervasive effect, causing changes in the communities of almost all analyzed organisms (except fungi) and inhibiting organic matter decomposition. Salinity, on the other hand, mainly affected the communities of mobile organisms, increasing the migration of invertebrates by drift and reducing the reproduction of fungi.

The authors stipulate that the relatively small impact of salinity shown in their study is most likely due to the long-term impact of this pressure on the ecosystem (for more than 30 years), which has allowed the organisms to adapt. Nevertheless, in order to preserve the integrity of the ecosystem and prevent its deterioration, the management of urban streams should prioritize the provision of minimum freshwater flows by limiting water withdrawals in conjunction with the restoration and preservation of hydromorphology. Comprehensive analysis of multiple groups of organisms makes it possible to establish salinity thresholds, exceeding of which requires mitigation measures.