Aquatic publication review (24)

The end of the vacation season and entry into the new school year coincided with the appearance of several publications touching on methodological issues. Researchers show how the outcome of a study depends on the method adopted, whether for estimating methane emissions from marshes, assessing water security in watersheds, or determining fish age from otoliths. We also present a paper describing mercury isotope studies that have identified oxidation pathways for this element in such remote corners of the globe as the Arctic Ocean.

It turns out that even there, mercury can pose a significant threat to aquatic organisms. Research by scientists from Portugal, in turn, shows how analysis of the fossil record allows us to understand the dynamics of changes in the species composition of marine organisms due to events such as the Messinian salt crunch in the Mediterranean Sea over 5 million. years ago. Perhaps we should use this experience to evaluate the Oder salt crisis?

1. wetland hydrological dynamics and methane emissions

Cui S., Liu P., Guo H. et al. (2024). Wetland hydrological dynamics and methane emissions. Commun Earth Environ 5, 470.

Swamps and other wetlands are an important source of atmospheric methane, but the variability of their hydrological conditions makes estimates of the balance of this greenhouse gas subject to high uncertainty. A review of the issue, conducted by researchers from Denmark’s Aarhus University in collaboration with scientists from China and published in Communication Earth & Environment, presents an analysis of the patterns of groundwater level fluctuations and their impact on the uncertainty in methane flows in more than 30 wetlands.

The analysis considers a number of key determinants of methane production and emissions, such as heterogeneity in soil redox potential, changes in substrate availability and alternative electron acceptor pools, the impact of different methane transport pathways, and nonlinear responses of biological assemblages and activities of methanogens and methanotrophs to water level fluctuations. This review aims to improve the accuracy of wetland methane emission reports by more accurately assessing biogeochemical kinetics under hydrological fluctuations.

2. near surface oxidation of elemental mercury leads to mercury exposure in the Arctic Ocean biota

Lim S.H., Kim Y., Motta L.C. et al. (2024). Near surface oxidation of elemental mercury leads to mercury exposure in the Arctic Ocean biota. Nat Commun 15, 7598.

Mercury (Hg) is a common trace metal that exists in the atmosphere mainly in gaseous Hg(0) and oxidized Hg(II) forms, formed by oxidation of gaseous mercury or released by emissions. The Hg(0) form is unabsorbable, and the condition for its bioavailability is oxidation to Hg(II). The long-distance transport of mercury by air and the accelerated effects of global warming pose a serious threat to remote polar regions, such as the Arctic, where an increase in the concentration of this element is observed. Once mercury Hg(II) enters ecosystems through wet and dry deposition, it is taken up by organisms, which can lead to its accumulation in the food chain.

To study the oxidation of atmospheric mercury in the Arctic Ocean, the researchers measured the ratio of its isotopes in zooplankton, Arctic cod, total gas fraction, sediments, seawater and snow cover from the Bering Strait, Chukchi Sea and Beaufort Sea. They used Δ200Hg to distinguish between Hg(0) and Hg(II). The results of their analysis indicate that, as in other oceans, mercury in open ocean waters and Arctic biota comes mainly from atmospheric Hg(II) deposition and riverine export.

However, while in oceans at temperate latitudes positive Δ200Hg is mainly due to oxidation of Hg(0) in the troposphere, in the Arctic Ocean waters terrestrial vegetation, coastal halogens (bromine radicals) and sea salt aerosols are responsible for bioavailable Hg(II). This study identifies new sources and pathways of biochemical transformations in which Hg(0) becomes a potential ecological threat to the Arctic Ocean biota.

3. Struggling with fish age, a comparison of otolith preparation techniques to unravel age and growth of boarfish

Silva M.I., Martins R., Sequeira V. et al. (2024). Struggling with fish age, a comparison of otolith preparation techniques to unravel age and growth of boarfish, Capros aper (Linnaeus, 1758). Sci Rep 14, 20282.

To rationally manage the commercial exploitation of fish populations, it is necessary to properly identify their stocks, species structure and age dynamics. One of the common methods of estimating the age of fish is the analysis of otoliths, i.e. elements of the fish’s equilibrium-auditory organ, located in the inner cerebrum (endoneurocranium). Methods for studying these structures are not standardized. Portuguese researchers compared the techniques used to prepare otoliths to estimate the age ofcapros (Capros aper), which led to divergent results.

By comparing two methodologies for studying the aging of sagittal otoliths (whole otoliths and cross-cut otoliths), the researchers showed that analyzing whole structures gives more reliable results. The maximum age of the fish determined by this method was 15 years. The growth pattern developed indicated a biphasic pattern, with a faster initial rate until about 2.4 years of age, which then slowed during sexual maturation. Given the lack of a standard age analysis protocol for this species and existing inconsistencies regarding technique and maximum estimated age, the authors stress the need to implement a standardized research protocol to ensure comparability of results.

4. the marine biodiversity impact of the Late Miocene Mediterranean salinity crisis

Agiadi K. Hohmann N., Gliozzi E., et al. (2024). The marine biodiversity impact of the Late Miocene Mediterranean salinity crisis. Science 385, 986-991.

Studying the history of water bodies allows us to better understand the taxonomic structure of the organisms that inhabit them and to recognize the factors shaping them. An international team of scientists conducted a comprehensive analysis of the ecological effects of the Mediterranean Sea’s separation from the Atlantic, which took place in the Miocene between 5.97 and 5.33 million years ago. This event, known as the Messinian Salinity Crisis(MSC), led to a near-total drying up of the sea, leaving only a few hypersaline lakes, similar to today’s Dead Sea. The goal of this work was to determine whether the MSC may have led to the extinction of the Mediterranean biota, and to quantify changes in the area’s species richness and beta-diversity before, during and after the crisis.

Based on the fossil record, scientists have shown that of the more than 2,000. distinguished marine species (both endemic and non-endemic) recorded since the Messinian period, only 86 endemic species survived into the Pliocene, while 693 presumably endemic Mediterranean species disappeared.

Few marine species were recorded in the first stage of the MSC (5.97 to 5.6 Ma), even fewer in the last stage (5.5 to 5.33 Ma), when freshwater and brackish-water species migrating from Paratethys (the now-defunct Sarmatian Sea) were also found. Analysis of the fossil record before and after the MSC indicates the extinction of the Mediterranean biota during the crisis. Recognizing how the MSC transformed Mediterranean ecosystems makes it possible to quantify biotic recovery after ecological crises, and the model proposed by the authors can be adapted to analyze similar phenomena in other geographic, geological, oceanographic and climatic regions. Perhaps it will be useful in our country for assessing the effects of the salt crisis on the Oder River?

5. upwind moisture supply increases risk to water security

Posada-Marín J., Salazar J., Rulli M.C. et al. (2024). Upwind moisture supply increases risk to water security. Nat Water.

Another paper that demonstrates how the methodological assumptions made affect the study’s outcome and inference concerns how to approach water security assessments in catchments. Water risk estimates usually take into account upstream risks that result in a decrease in downstream water availability. However, some studies also indicate the validity of including vulnerability to wind direction in the model. There is growing interest in including wind dependence in risk assessment because precipitation over large areas of land (large catchments) can be modified by wind-induced changes in the amount and timing of evaporation of water to the atmosphere.

Based on a global water security risk assessment conducted for 379 transboundary hydrological basins, the researchers compared the results of two approaches: anupstream perspective and anupwind perspective. The traditional upstream perspective analyzes threats and geophysical vulnerability within the basin boundaries. The upwind perspective focuses on threats and geophysical vulnerability in areas that contribute to the basins’ moisture supply (i.e., the precipitation catchment, including from outside the surface catchment). It turns out that considering moisture supply increases water security risk by more than 30 percent. relative to the traditional approach. This study points to the need to include moisture dependence and wind direction in global water risk assessments.