Aquatic publication review (35)

Modern science is providing increasing evidence of how dynamic and vulnerable our aquatic ecosystems are to change. From variability in the length of the river network, to the impact of human activities on water quality, to the contribution of birds associated with aquatic habitats to nutrient supply, each of these issues has conservation implications. Modern technologies, including DNA metabarcoding, can help better monitor ecosystems, but science can also find solutions to everyday challenges, such as cooking an egg perfectly.

1. prancevic J. P., Seybold H., Kirchner J.W., (2025). Variability of flowing stream network length across the US. Science 387, 782-786

With climate change and the alarming hydrological situation in Poland, it is becoming a very likely possibility that some of our rivers and streams will become ephemeral ecosystems. The phenomena we have read about in reports from other countries may soon affect us. The appearance and disappearance of flow in rivers makes the length of the river network variable. Just how much, was checked by American scientists who analyzed the variability of river network length across the continental United States. To do so, they used semi-mechanistic models and water gauge measurements and topographic data from nearly 15,000 catchments.

They found that the median stream network in the US is five times longer under high annual flow conditions than under low flow conditions, with variability in river network length in some areas more dynamic than in others. They proved that this depends on regional differences in both hydroclimatic conditions and network flexibility in response to pressures. It is worth being aware of such phenomena, as it may soon turn out that we also have fewer rivers in our country than we think.

2 Imbert A., Boulêtreau S., Beisel J.-N., Cucherousset J., (2025). Quantitative estimates of nutrient inputs from angling baits in lakes supporting different recreational fisheries. Fisheries Management and Ecology; 0:e12802

The fact that anglers are not indifferent to the aquatic environment has been written about many times. We, too, have pointed out the irresponsible practice of this form of recreation as one of the cardinal sins of the ignorant tourist. The availability of works that quantify the problem is limited. All the more interesting are the results of estimating the effect of anglers’ use of groundbait on the increase in water trophy in the lakes of southwestern France, published in Fisheries Management and Ecology.

The authors of the study analyzed angling activity, including seasonal and annual dynamics, the quantity and quality of bait, and the amount of nitrogen and phosphorus introduced into the waters with three forms of angling: specialized roach fishing, specialized carp fishing (carp angling) andput-and-take fishing. Both the type and quantity of bait used and the supply of nutrients introduced with it varied according to the type of angling use, with the supply of nutrients ranging from 0.5-10.2 kg of nitrogen and 0.1-1.6 kg of phosphorus per hectare per year.

Specialized roach fishing was the least taxing, while carp fishing was the most taxing. The three forms of fishing also differed in the number of days spent on the lake and the season of greatest activity. This study showed that the ecological consequences of bait use differed among recreational fishing methods, which can be used to regulate the use of fishing baits.

3 Clausen, P., Lauridsen, T.L., Pedersen, C.L., et al. (2025). Are increasing roosting waterbird numbers responsible for eutrophication of shallow lakes? Examples from a Danish Ramsar site. Hydrobiologia 852, 389-410

But lest we say that only humans are accelerating eutrophication, we should also remember the contribution of natural inhabitants of aquatic ecosystems to the process. The Water Framework Directive expects member states to reduce the supply of nutrients from allochthonous sources in order to improve water quality. But what about when ecosystem inhabitants themselves are the source of eutrophication? Several Danish lakes have been exempted from having to meet WFD targets precisely because of the supply of nutrients by waterbirds. Danish hydrobiologists at Aarhus University have asked themselves whether such an exemption was made right.

They analyzed data onroosting bird abundance and nutrient loads from catchments and atmospheric deposition from four brackish lakes located in Ramsar sites and EU Birds Directive Special Protection Areas to estimate the relative contribution of nutrients from increasing numbers of waterbirds roosting on these lakes to the total balance of nutrient loads.

The results indicated that in the case of three lakes, nocturnal birds (mainly geese) were the source of only 0.2-0.4 percent of the total nitrogen supply (0.3-1.2 kg N/ha/year) and 0.6-2.0 percent of the total phosphorus supply (0.04-0.12 kg P/ha/year). In contrast, in the fourth clear-water lake, with no direct inflow or outflow, they accounted for as much as 14 percent and 76 percent, respectively. These results confirm the need for individual assessment of nutrient supply in relation to the total nutrient balance before lakes are exempted from meeting WFD environmental targets due to presumed natural loading from waterbirds.

4 Macher T.-H., Beermann A. J., Arle J., et al. (2025). Fit for purpose? Evaluating benthic invertebrate DNA metabarcoding for ecological status class assessment in streams under the Water Framework Directive. Water Research, 272, 122987

With the pressure on aquatic ecosystems, there is also a growing demand for ever faster, more efficient and cost-effective methods of monitoring their condition, including biotic components. In EU countries, biomonitoring is primarily based on morpho-taxonomic methods. DNA metabarcoding is a novel and promising approach for rapid and efficient assessment of aquatic ecological status, but before it can be implemented, it needs to be calibrated and the results made compatible with traditional taxonomic determination methods.

German scientists tested the feasibility of such calibration and implementation of metabarcoding for assessing the status of flowing waters in the context of WFD objectives. Analysis of 170 samples including benthic invertebrates, determined by traditional and metabarcoding methods, showed high (70 percent) concordance of results. Metabarcoding allowed the identification of a larger number of small invertebrate taxa, but in terms of the proportion of EPT indicator taxa (mayflies, fork-worms, caddisflies) the proportions were similar. Ecological status classes obtained by different methods were highly correlated (^R2 0.74, Spearman’s rho 0.86). The classifications also showed high agreement, regardless of whether the abundance of organisms or P/A (present/absent) data was used. This study indicates the great usefulness of barcoding methods in supporting water biomonitoring and complementing traditional methods with techniques based on DNA analysis.

5. di Lorenzo, E., Romano, F., Ciriaco, L. et al. (2025). Periodic cooking of eggs. Commun Eng 4, 5

Did you know that even cooking an egg can be approached scientifically? In early February, a serious journal from the Nature stable – Communication Engennering – published an article by Italian chemists who studied the conditions for perfect egg cooking. The whole difficulty of this process is due to the two-phase nature of the product: the white and the yolk, which require different cooking temperatures. This means the need to separate the two components in the heat treatment process, or to accept a thermal compromise to the detriment of taste and texture.

However, scientists have shown that it is possible to cook the white and yolk at two temperatures without separating them, using a batch cooking technique. It involves transferring an egg every 2 minutes from boiling water to 30 degrees Celsius water in 8 repetitions, taking a total of 32 minutes. This method not only optimizes the texture and nutrients of eggs, but also points to new cooking techniques and ways to process materials.

[1] DOI: 10.1126/science.ado2860[2] https://doi.org/10.1111/fme.12802[3] https://doi.org/10.1007/s10750-024-05475-9[4] https://doi.org/10.1016/j.watres.2024.122987[5] https://doi.org/10.1038/s44172-024-00334-w