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Frontiers in Freshwater Science ·

Volume 4 - 2026 | https://doi.org/10.3389/ffwsc.2026.1746686

Differences in potassium and chlorine incorporation in members of an alpine stream food web in the West Carpathians

  • Martin Janiga1,2
  • Marián Janiga1
  • Jakub Tuchyňa1
  • Patrik Pánik1
  • Zuzana Kompišová Ballová1*corresponding author
  1. 1Institute of High Mountain Biology, University of Žilina, Žilina, Slovakia
  2. 2Faculty of Humanities and Natural Sciences, University of Prešov, Prešov, Slovakia
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Abstract

High mountain streams are experiencing pronounced shifts in precipitation regimes and water chemistry; however, it remains unclear how organisms inhabiting these systems influence the transfer of chemical elements through food webs. We measured concentrations of potassium and chlorine in algae, grazing mayflies, predatory stoneflies, and Alpine Bullhead (Cottus poecilopus) across seasons in an alpine stream. Algae exhibited marked seasonal variation, with higher potassium accumulation during the main summer growth period despite relatively stable water concentrations. Grazing mayflies maintained stable potassium levels but showed increased chlorine during colder months when chlorine concentrations in water were elevated. Predatory stoneflies showed only minor seasonal variation, with a slight increase in potassium in winter. The Alpine Bullhead did not exhibit significant seasonal changes in potassium or chlorine accumulation in its skull. Following major flood events, potassium and chlorine concentrations tended to co-vary across trophic levels, whereas under baseflow conditions they often varied independently. These patterns suggest that different trophic groups regulate element accumulation according to their physiology, life history, and ecological roles. The decoupling of organismal and water chemistry indicates that environmental concentrations alone do not fully explain element distribution within alpine stream food webs. Our findings provide new insights into element dynamics and highlight the importance of biological mediation in high-mountain ecosystems under changing environmental conditions.

Keywords

1 Introduction

1.1 Ecological context and conceptual importance

Due to their catchment area, high mountain streams are extremely sensitive to the effects of global, regional, and local environmental impacts (Ballesteros-Cánovas et al., 2015). They reflect processes such as weathering, transboundary emissions, floods, etc. (Niedzwiedz et al., 2015). The response of alpine streams may lead to changes in interactions between species at different trophic levels, and the dynamics can be effectively monitored by accumulation of chemical elements in abiotic and biotic segments of food webs (Pastorino et al., 2019, 2020). The literature on chemical element accumulation in freshwater ecosystems is heavily biased toward heavy metals or potentially toxic elements (Miloškovič et al., 2022) while the negative potential effects of accumulation of macro- or micronutrients is studied less often. Potassium and chlorine are important nutrients whose levels in a stream can provide information on not only the life of the stream itself, but also its potential pollution (Perinajová et al., 2020). In sensitive high mountain ecosystems, potassium, and chlorine are washed out of mountain lakes during large floods (Hrivnáková, 2019; Hrivnáková et al., 2020), and previously accumulated amounts dissolve and are transported to mountain streams, where they are acquired by the biota. Relatively elevated levels of these elements are then found in lateral formations of the mountain streams (small channels with water circling backwards, stream margins, and small bays) affecting fish fry (Janiga and Janiga, 2023), but after large floods, the levels of these elements also increase in adult fish and other biota (Janiga et al., 2021). The dynamics of chlorine and potassium concentrations are typically not the same in high mountain streams. For example, in the glacial mountains of Central Asia, high levels of chlorine are found in water below glaciers (Solár and Janiga, 2023) while sites with higher levels of potassium in water are usually located 500 to 1,000 m lower in altitude (Janigová and Janiga, 2023).

1.2 Chemical patterns and empirical background

Chlorine is rarely found as pure chlorine and instead is commonly found in water as a compound (e.g., as chloride (Cl−) or part of salts, like NaCl, KCl, MgCl2, CaCl2). It is one of the major inorganic anions, or negative ions, in saltwater or freshwater. Chloride concentrations of between 1 and 100 mg/L are normally found in freshwater. According to the Water Research Institute, an official institution of the Slovak Republic that publishes water quality data, chloride levels in the Javorinka stream remains below 1 mg/L between 2022 and 2025, especially during the winter months. From July to September, however, the chloride content rises to 2.7 mg/L. Potassium levels in the water are even lower, with Javorinka drinking water reported at 0.27–0.3 mg/L (WRI, 2025). The ratio of potassium to chloride in alpine streams and watersheds typically varies depending on factors such as the region's geology, vegetation, precipitation patterns, and other hydrological factors. The K:Cl ratio in alpine streams is typically lower than in other environments. This is also the case in the Javorinka stream, where the amount of chlorine in the water is significantly higher than the amount of potassium, as measured in samples (WRI, 2025). Potassium is an essential plant nutrient commonly released into streams through weathering, while chloride is primarily influenced by atmospheric deposition and human activity. Low potassium availability is common in carbonate mountains, while chlorides are on the rise (WRI, 2025). Logging may cause initial leaching of nutrients, including potassium. Chlorides, mostly from atmospheric deposition, remain relatively stable. The result in recent years is that potassium is less abundant in streams than expected. This situation with potassium and chlorine is subsequently reflected in the stream's food chain.

1.3 Physiological and toxicological relevance and roles of potassium and chlorine in aquatic organisms

Potassium and chlorine levels in water are generally sufficient to meet basic nutritional requirements of fish, their dietary levels have a significant effect on fish growth (Kalantarian et al., 2013). For example, at low pH, chlorine uptake through the gill epithelium is reduced and dietary uptake of this element may be higher (Kopp et al., 2013). Chlorine is an essential element for living plants (Svensson et al., 2021) but is largely unbeneficial and even dangerous to the vitality of living organisms, and in fish causes several diseases. The excess of chlorine causes a significant decrease in body weight and body growth in freshwater fish (El-Bouhy et al., 2006). In macrozoobenthos in alpine streams, water enhanced absorption of chlorine could change species composition, for example, the abundance of chironomids may increase while mayflies decrease (Shenton et al., 2022). Adding chlorine as a disinfectant to natural water can result in the formation of chloroform and other carcinogenic or mutagenic compounds (Rook, 1974). Potassium is a macronutrient occurring naturally in plants and fruits and it is essential for organism physiology. Compared to other major elements in freshwater, potassium has a large ionic radius. This can interfere with protein structure, requiring cells to regulate potassium concentrations (De Angelis, 1992; Li et al., 2021). However, potassium and its salts may be toxic to freshwater animals, e.g., fish. Certain potassium compounds are strong oxidizing agent and are used in aquatic systems to treat diseases, parasites, and algae (Cruz and Tamse, 1989). Hyperkalemia is known to be lethal through disruption of cardiac function and depolarization of cell membranes in many aquatic organisms (Cripps et al., 2013; Cruz and Tamse, 1989). Potassium is a rubidium analogue, and the two substances can compete in fish (Peters et al., 1999). However, potassium itself acts as a nutrient for aquatic plants; its concentration in the streams is controlled by the chemical weathering of silicates, including minerals such as biotite, feldspar, and clay minerals. The amount of absorbed potassium and chlorine found in the Alpine Bullhead, the top predator fish of macrozoobenthos in alpine streams of the West Carpathians, depends on its diet and the biomass of consumed water invertebrates, as well as uptake of these elements directly through the water, by the gills (Janiga and Janiga, 2023; Terech-Majewska et al., 2016).

1.4 Trophic transfer/biological pathways through macrozoobenthos and algal uptake

The diet of Alpine Bullheads is comprised of mayflies (Ephemeroptera) including genus Ecdyonurus (family Heptagenidae) and bigger macrozoobenthic predators such as stoneflies (Plecoptera), including the species Perla grandis (Števove et al., 2019). Uptake of chemical elements in these spesies of macrozoobenthos is governed by water temperature, pH, overall water chemistry, tolerance to environmental contaminants (Goodyear and McNeill, 1999; Janiga and Janiga, 2023), but is mainly based on their functional feeding guilds (Pastorino et al., 2019; Santoro et al., 2009). The common diet of predator Perla grandis nymphs are nonbiting Chironomidae midges as well as smaller quantities of Heptageniidae larvae (Fenoglio et al., 2013). The biomass of Perla grandis in the diet of Alpine Bullheads is two times lower than the biomass of Ecdyonurus (Števove et al., 2019). The common diet of mayflies of the genus Ecdyonurus is mostly detritus, but also consists of biofilm, bacteria, diatoms, filamentous algae, and coccoid algae. This genus overwinters in the nymphal stage and belongs to the scraper feeding guild (Wögerbauer and Kelly-Quinn, 2013). The ability of algae, the diet of mayflies, to absorb chemical elements varies between species and between strains of a given species. Each chemical element also has a unique effect on the sorption capacity of different algal species (Mehta and Gaur, 2005). Chlorophyta, commonly known as the green algae, have significant accumulation capabilities, especially the Cladophora species, considered one of the best bioindicators in aquatic environments of chemical element pollution (Chmielewska and Medved, 2001). The successful use of periphyton for the assessment of water quality has been based on different taxonomic levels and functional groups (Chessman et al., 1999). Numerous studies have related periphyton communities and their species characteristics with habitat parameters such as water velocity, disturbance, water temperature and chemistry, substrate, and nutrient supply (Biggs et al., 1998; Cattaneo et al., 1997; Kann, 1978; Kuhn et al., 1981; Passy et al., 1999).

1.5 Seasonal dynamics, study system, and hypotheses

In the temperate zone, seasonal changes in temperature, pH, conductivity, and other water properties are among the most important phenomena affecting water chemistry (Solár et al., 2024). Elevated concentrations of nutrients such as chlorine or potassium can have lethal effects on aquatic organisms during large fluctuations in water temperature (Pastorino et al., 2022). The food chain we studied in the streams of Tatra National Park in the Western Carpathians consists of cyanobacteria/algae—mayflies—stoneflies—and Alpine Bullheads. The aim was to investigate how the flux of potassium and chlorine in this chain behaves in different seasons. In recent decades, increasing salinization of freshwater systems has been reported in many regions, mainly due to road de-icing salts and other anthropogenic sources (Kaushal et al., 2018). Because potassium and chloride are among the most responsive ions to salinization processes, they can serve as useful indicators of changes in the chemical regime of mountain streams. The cycling of these two chemical elements in the food chain of a high mountain stream can occur separately or together, reflecting common sources such as potassium chloride (KCl), which dissociates in water into the ions K? and Cl?. The analysis of the elemental concentrations in the different segments of the food chain in different seasons should give us a more detailed understanding of the process of potassium and chlorine accumulation in the high mountain stream. Based on current knowledge, we hypothesized that potassium and chlorine may interact in the river ecosystem through the coupled dynamics of the ions K+ and Cl−.

2 Materials and methods

2.1 Field sampling and laboratory analyses

For the purpose of this study, the Javorinka stream was monitored weekly from January 2019 through the end of December 2021. Javorinka is a typical mountain stream that originates in the pristine, undisturbed granitoid habitats of Tatra National Park in the Western Carpathians (Figure 1). Above the first village, Tatranská Javorina, Javorinka is joined by another important Tatra stream, the Medodoly, which drains the limestone springs of the Belianske Tatras. The carbonate bedrock of the Belianske Tatras, dominated by calcium carbonate (CaCO3), may contribute to water hardness and the ionic composition of the stream water. In the granite regions of the Tatra Mountains, streams typically contain around 1 mg/L of chlorides, whereas streams originating from the limestone Belianske Tatras region generally have higher concentrations, ranging from 2.6 to 3.5 mg/L (WRI, 2025). Javorinka is a mixture of these waters, as it has tributaries from both the granite and limestone parts, though most of its water comes from the granite bedrock (Solár et al., 2024). In the valley, spruce forest was disturbed by logging 10 years ago.

Location of the study area in the Javorinka stream catchment (Tatra National Park, Slovakia, Western Carpathians; highlighted in red), showing the sampling sites for water (blue circles), algae (green circles), macrozoobenthos – mayflies (yellow circles) and stoneflies (red circles), and Alpine Bullhead (brown circles).
Figure 1. Location of the study area in the Javorinka stream catchment (Tatra National Park, Slovakia, Western Carpathians; highlighted in red), showing the sampling sites for water (blue circles), algae (green circles), macrozoobenthos – mayflies (yellow circles) and stoneflies (red circles), and Alpine Bullhead (brown circles).

In the field, the following water parameters were weekly measured: water temperature (WT in °C), pH, and conductivity (COND in μS/cm), total dissolved solids (TDS in mg/L), dissolved oxygen content (DO in mg/L) and dissolved oxygen saturation (DO%). A portable multimeter (WTW 3430, GEOTECH, Weilheim, Germany) and compatible probes IDS pH electrode (SenTix 940–3), a conductivity electrode (TetraCon 925–3) and an optical oxygen electrode (FDO 925–3) were used. Then, water samples were collected in dark, sterile glass bottles (2 L). Samples were processed up to 12 h after sampling. In the laboratory, the following chemical variables were measured: nitrates (NO3−, mg/L), ammonia (NH3-N, mg/L), ammonium (NH4-N, mg/L), chlorides (Cl−, NaCl, mg/L), sulfates (S, SO42−, mg/L), phosphates (PO43- in mg/L), total phosphorus (TP, mg/L), and total hardness (CaCO3 in mg/L). The photometer meter YSI EcoSense 9500 (YSI Inc., OH, USA) was used. The relevant reagents were provided by PALINTEST Ltd. (Gateshead, UK). Field and laboratory measurements were performed three times, averaged, resulting in a relative standard deviation of less than 5% (Solár et al., 2024). The Slovak Hydrometeorological Institute, which is responsible for monitoring the flows in the Javorinka stream, provided the daily flow data.

The algae/cyanobacteria means the following systematic groups which were collected: (1) Hydrurus foetidus—is a cold-water alga (Class: Chrysophyceace) found in fast-flowing streams. The species appears to be of specific importance for the early emerging aquatic larvae of the macrozoobenthos (Klaveness, 2019). (2) Diatoma ehrenbergii (Class: Bacillariophyceace)—is almost always present in fibers of Hydrurus foetidus. Diatoms are often chosen to feed on by mayflies belonging to the genus Ecdyonurus. (3) Oscillatoria sp. (Class: Cyanophyceae) can easily handle sudden physical and chemical alterations of light, salinity, temperature, and nutrient composition. All groups have been determined with professional assistance of Dr. Hindáková (Institute of Botany, Plant Science and Biodiversity Centre, Slovak Academy of Sciences). Samples were collected periodically throughout each calendar month from 2019 to 2021 and 68 samples (winter 21, spring 15, summer 16, fall 16) were used for analyses. Two sampling sites were identified for sampling. The first included the river section between the villages of Tatranská Javorina and Podspády. This section is approximately 3 km long and lies between 930 and 970 m above sea level. The second section was near the village of Vojtasová (N 49°17′33.2′′, E 20°10′08.5′′). Here, the stream has a much softer and more gradual flow. The depth is constant along the entire length and the altitude varies between 850 and 865 m above sea level. Algal growth was more pronounced here and included the prevalence of macroscopic algae. All samples were cleaned immediately after collection to remove ingested invertebrates and larger soil particles. The samples were then allowed to dry naturally. The next step was to crush the dried samples into fine particles (5 μm). A cryomill was used to grind each sample for 40 s.

Macrozoobenthic invertebrates were sampled at two sites, the first at N 49°16′15.9′′; E 020°09′11.4′′; 962 m a.s.l. and the second (approximately 2 km downstream): N 49°17′52.4′′; E 020°09′40.9′′; 855 m a.s.l. Samples were collected periodically at the end of each calendar month (2019–2021). Macrozoobenthos was collected with a focus on Ephemeroptera (genus Ecdyonurus) and Plecoptera (Perla grandis). Seventy-nine samples of Ecdyonurus mayflies (winter 18, spring 19, summer 22, fall 20), 52 samples of Perla stoneflies (winter 9, spring 14, summer 15, fall 14) were obtained. All individuals were collected manually, with tweezers from rocks, with hands from water, or from substrate into plastic bottles filled with fresh water from the stream. In the laboratory, individuals were separated by species and air dried in a Petri dish. All individuals of a genus were analysed in a pooled sample. Sample size was determined by the number of individuals found (approximately 5 individuals for Perla and 20 individuals for Ecdyonurus) and averaged 0.5 g dry weight. Dried samples were ground into dust by hand.

The amounts of potassium and chlorine were measured in all samples using spectrometry DELTA XRF Professional with XRF WorkStation (Olympus Corporation, Tokyo, Japan). The XRF method determines the values of specific chemical elements (trace elements) in concentrations. The device was manually attached into the workstation and connected to a computer. Due to this method, we were able to proceed with a fast analysis of samples. Water samples were analysed in a special plastic cup. Each sample was analysed with the same X-ray exposure time (80 s) and the analysis was performed three times. The average of these three measurements was used in the results. XRF methodology can measure both bound and free chlorine in water. XRF has difficulty measuring light elements (such as Cl) in liquid samples, especially when air or light filters absorb their signal. Since the water was measured directly, we proposed partial readings instead of the full ionic content of Cl. Chlorine is volatile and does not fluoresce strongly under X-rays. From this perspective, we always expect higher K:Cl ratios. Measurements may reflect the relative abundance of solid-bound or suspended K and Cl rather than the full picture of dissolved ions in the stream, which we measured using photometry. However, XRF measurements of all samples are an excellent tool for comparing ratios in different time and space. They allow us to determine the local influence on water quality, e.g., whether it is affected by weathering (K), while the amount of chlorine is more influenced by climate, i.e., precipitation (Bergh and Compton, 2015; Maas et al., 2019). Using multivariate statistics, such as principal component analysis (see below), we can then interpret the phenomena and their variability. Granite and metamorphic rocks usually release more potassium through weathering; however, low K availability is common in karst or carbonate mountain catchments (Manning, 2010; WRI, 2025).

The powder from each sample of algae and cyanobacteria (5 μm particles) was measured three times for 240 s each against the initial reference plant material (NIST 1575a Pine Needles), the final value being the average of the three measurements. Macrozoobenthic invertebrates were also homogenized into powder and the potassium and chlorine content of each sample was measured in triplicate for 120 s. The result was the average of these measurements. To ensure the quality of the measurements of elements in macrozoobenthos, the instrument was permanently and continuously calibrated against a standard reference material beef liver (NCS ZC 71001).

Only naturally deceased individuals of Alpine Bullhead were collected from the stream. No fish were captured or sacrificed for the purposes of this study. They were gathered from the stream, in sections where macrozoobenthos, algae, and water samples were obtained. While no dead fish were discovered at one specific site, considering their presence in the surrounding environment, the areas where these deceased fish were located coincided with the sites where the collected species of macrozoobenthos and algae were present, in addition to where water measurements were recorded. With the help of students, the deceased individuals were collected, measured and weighed, and then placed in coolers. Two hundred five samples of bullheads (winter 13, spring 5, summer 22, fall 165) were analyzed. The carcasses were later used to measure potassium and chlorine levels in the skull. To achieve optimum measurement accuracy, each bullhead was carefully positioned head down in the focal point of the instrument. The samples were subjected to multi-beam measurements. Each measurement cycle consisted of three beams of 80 s each. This cycle was repeated three times. The results were then averaged. The lowest value recorded for a particular element represented the current detection limit of the spectrometer for that material. By applying this multi-test method to our bone samples, we were able to determine the minimum levels of each element that could be accurately measured by the instrument. Certified standard reference materials, including beef liver NCS ZC 71001 (CHNACIS, China) and bone meal (SRM 1486, Maryland), were used to verify the accuracy of this approach. Further methodological details are provided in Janiga and Janiga (2023).

2.2 Quality assurance

In spectrometry, the quality assurance depends on determination of the lowest Limit of Detection (LOD). We used a factory calibration, based on the Compton Normalization (CN). The CN algorithm is designed for achieving the exact LOD by company Innov-X Systems (Woburn, MA, United States). The LODs were determined for each measurement and for both elements K and Cl.

2.3 Statistics

PAST software, version 4.12, RRID: SCR_019129 (Hammer et al., 2001) was used to compare the mean values of element concentrations among seasons. The means were compared using the unequal-variance Welch version of ANOVA because the compared groups had unequal variances. Principal component analysis and the graphical design were performed in STATISTICA 12 software, RRID: SCR_014213.

3 Results

Table 1 shows the basic physical and chemical parameters of the Javorinka stream in the Tatra Mountains from 2019 to 2021. The stream is typical of those in the alpine zone. It is strongly influenced by karst bedrock, which results in a higher temperature and flow rate, as well as a lower TDS and conductivity in the summer. Additionally, there is a higher level of ammonia in the spring (see Tables 2, 3).

Table 1. Physical and chemical parameters of the Javorinka stream from weekly measurements (2019–2021).

Measured parameterNMeanSD
Flow/day (mean m3/s)1531.881.62
WT °C1535.312.82
pH1538.170.24
DO (mg/L)15011.680.88
DOS (%)150104.122.14
COND (μS/cm)153180.3341.14
TDS (mg/L)153181.5640.06
Chlorides Cl− (mg/L)1531.021.06
NaCl (mg/L)1531.711.76
Total hardness (mg/L as CaCO3)15383.8924.74
SO42- (mg/L)15314.3212.86
S (mg/L)1534.754.29
Ammonia N (mg/L)1530.060.07
Ammonia NH3-N (mg/L)1530.070.09
Ammonium NH4-N (mg/L)1530.070.09
Nitrates NO3- (mg/L)1532.500.88
Nitrates N (mg/L)1530.560.20
PO43- (mg/L)1530.380.43
Total P (mg/L)1530.130.14
K/Cl - XRF1530.680.07

Table 2. Principal component analysis—coordinates of variables.

VariableFactor 1Factor 2Factor 3Factor 4Factor 5
Flow/day (mean m3/s)0.67−0.020.180.02−0.26
WT °C0.790.190.020.030.22
pH−0.380.130.030.130.19
DO (mg/L)−0.77−0.13−0.05−0.08−0.21
DOS (%)−0.090.20−0.04−0.310.30
COND (μS/cm)−0.85−0.05−0.20−0.010.24
TDS (mg/L)−0.85−0.06−0.23−0.000.24
Chlorides Cl− (mg/L)−0.04−0.190.840.23−0.19
NaCl (mg/L)−0.05−0.190.850.22−0.16
Total hardness (mg/L as CaCO3)−0.79−0.05−0.140.110.17
SO42- (mg/L)−0.69−0.230.340.14−0.01
S (mg/L)−0.69−0.240.360.15−0.02
Ammonia N (mg/L)−0.120.930.28−0.070.03
Ammonia NH3-N (mg/L)−0.130.920.25−0.070.03
Ammonium NH4-N (mg/L)−0.120.930.27−0.060.07
Nitrates NO3- (mg/L)−0.510.120.12−0.42−0.06
Nitrates N (mg/L)−0.530.140.10−0.410.02
PO43- (mg/L)0.25−0.400.42−0.500.53
Total P (mg/L)0.25−0.400.43−0.500.53
Cl - XRF (ppm)−0.38−0.060.160.18−0.21
K - XRF (ppm)−0.070.040.090.720.44
K/Cl - XRF0.240.10−0.030.580.60
Variance in %26.114.611.29.27.6

Five factors with the highest variability, according to the measured physical and chemical properties of water. The most important coordinates of variables are in bold.

Table 3. A comparison of seasonal means of principal coordinates of samples (cases of factors 1 to 5 in PCA) and ratio K/Cl indices (Welch F test and LSD tests).

SeasonFactor 1Factor 2Factor 3Factor 4Factor 5K/Cl (ratio index)N – number of measurements
Winteraabaaaa (0.66)38
Springbbaaaa (0.67)37
Summercaaaab (0.71)39
Autumndaaaaa (0.67)39
Welch *F*157.75.010.621.561.143.75
*P*0.0000.0030.590.210.340.014

The letters (a–d) indicate the results of post hoc comparisons (LSD test), where identical letters denote no significant differences between seasons, while different letters indicate statistically significant differences (p < 0.05).

Factor 1 describes the variability in the physical properties of water. In summer, the water is warmest, with higher flow rates, lower conductivity, and lower TDS. Factor 2 is indicative of ammonia variability, with notably higher concentrations observed during the spring months (Table 3). Factors 3 through 5 determine the variability of chlorine and potassium; clearly, their occurrence in the stream is minimally related. Factor 3 is a unipolar vector that mainly characterizes the variability of chlorides, relatively independently of the other measured water parameters. The variability of potassium occurrence is characterized primarily by Factor 4, which independently increases or decreases its proportion in relation to chlorine. Factor 5 also indicates variability in potassium levels in water; in this case, an increase in potassium levels was accompanied by an increase in phosphate levels.

In the stream Javorinka, the concentrations of chlorine and potassium vary independently. Chlorides do not vary significantly throughout the year (Tables 2, 3), though they increase slightly in winter (Figure 2). However, levels of both chloride and potassium are low in the stream and are clearly influenced by the karst bedrock (Tables 1, 2). The presence of potassium in the stream is partially associated with phosphate-related phenomena (Table 2). Nevertheless, the relationship between potassium and phosphates in water remains independent of the seasons (Table 3). Overall, the ratio of potassium to chlorine increases in the summer (Table 3, Figure 2), indicating increased weathering. The variability of chlorides and the ratio of potassium to chlorides indicate a low level of dissolved KCl in this stream's water.

Seasonal chloride levels in the Javorinka stream partially show a slight increase in winter. In contrast, the ratio of potassium to chlorine rises mainly in summer, which indicates primarily weathering and the independent behavior of potassium and chlorine in the watercourse. Lines were created by negative exponential smoothing.
Figure 2. Seasonal chloride levels in the Javorinka stream partially show a slight increase in winter. In contrast, the ratio of potassium to chlorine rises mainly in summer, which indicates primarily weathering and the independent behavior of potassium and chlorine in the watercourse. Lines were created by negative exponential smoothing.

The notable variations in potassium levels in algae across different seasons (Figure 3A) indicate that algae absorb substantial quantities of potassium from the water during their primary growth phase, specifically in summer, when potassium concentrations in the algae reached their peak (Figure 2). No significant differences were observed between seasons in chlorine content in algae (Figure 3E). Scrapers (Ecdyonurus) take up potassium at a fairly constant rate throughout the year (Figure 3B), whereas chlorine is taken up by mayflies when there is a lot of this element in the water, mainly in autumn and winter (Figures 2, 3F). There were no significant seasonal differences in the amount of potassium (Figure 3C) or chlorine (Figure 3G) in the bodies of these predators—stoneflies (Perla). The Alpine Bullhead, another predator of macrobenthic insects in mountain streams, also showed no seasonal differences in potassium or chlorine accumulation in its skull (Figures 3D, H).

Mean (with ±0.95 confidence limits) concentrations of potassium (left) and chlorine (right) in the food web in the mountain stream Javorinka, the West Carpathians. Potassium – **(A)** algae/cyanobacteria (Welch *F* = 3.6, *df* = 30.01, ***p*** **=** **0.02**); **(B)** mayflies (Welch *F* = 1.9, *df* = 39.2, *p* = 0.16); **(C)** stoneflies (Welch *F* = 1.51, *df* = 25, *p* = 0.24); **(D)** Alpine Bullheads (Welch *F* = 1.1, *df* = 13.1, *p* = 0.38). Chlorine – **(E)** algae/cyanobacteria (Welch *F* = 1.2, *df* = 18.3, *p* = 0.35); **(F)** mayflies (Welch *F* = 3.06, *df* = 39.7, ***p* =** **0.04**), mayflies contained less chlorine in spring than in summer or autumn; **(G)** stoneflies (Welch *F* = 1.94, *df* = 23.3, *p* = 0.15); **(H)** Alpine Bullheads (Welch *F* = 1.2, *df* = 13.8, *p* = 0.33).
Figure 3. Mean (with ±0.95 confidence limits) concentrations of potassium (left) and chlorine (right) in the food web in the mountain stream Javorinka, the West Carpathians. Potassium – (A) algae/cyanobacteria (Welch F = 3.6, df = 30.01, *p* = 0.02); (B) mayflies (Welch F = 1.9, df = 39.2, p = 0.16); (C) stoneflies (Welch F = 1.51, df = 25, p = 0.24); (D) Alpine Bullheads (Welch F = 1.1, df = 13.1, p = 0.38). Chlorine – (E) algae/cyanobacteria (Welch F = 1.2, df = 18.3, p = 0.35); (F) mayflies (Welch F = 3.06, df = 39.7, **p = 0.04), mayflies contained less chlorine in spring than in summer or autumn; (G)** stoneflies (Welch F = 1.94, df = 23.3, p = 0.15); (H) Alpine Bullheads (Welch F = 1.2, df = 13.8, p = 0.33).

4 Discussion

4.1 K and Cl in alpine stream water

A wide range of aquatic organisms (e.g., phytoplankton, invertebrates, and fish) have historically been used in bioaccumulation studies (Augustine and Selunathi, 2018; Bian et al., 2016; Burgess, 2015) but information on the influence of natural potassium and chlorine on aquatic organisms living in alpine streams is limited (Stevenson, 2022). The synergistic effect of these two biogenic elements appears in stream water following large flood events (Janiga et al., 2021), and it is evident that potassium and chlorine oscillate in the water in the same way at certain times, as shown in research on high mountain rivers in Tian-Shan (Janigová and Janiga, 2023; Solár and Janiga, 2023). Outside of flood events, chlorine enters the watershed from high elevations independently of potassium (Nédeltcheva et al., 2006). While the fluctuation of potassium in Tatra mountain streams occurs largely due to flood events and in the summer (Hrivnáková, 2019; Janiga et al., 2021), chlorine in the water rises in the winter, related to its annual accumulation in air masses, snow deposition and subsequent weathering (Nédeltcheva et al., 2006). Similarly, higher ammonium concentrations observed in spring may be associated with snowmelt-driven runoff and the flushing of nitrogen compounds accumulated in soils and organic material during winter. Early spring runoff can enhance microbial mineralization and transport dissolved nutrients from the catchment into alpine streams (Williams et al., 2001). Potassium may increase downstream, as in some regions, the highest levels of potassium in stream water occur during winter (Sutcliffe and Carrick, 1973). High winter chlorine concentrations in mountain streams were also observed in other studies (e.g., Corsi et al., 2015). In alpine streams, increased chlorine often positively correlates with increases in rubidium and zinc (Janigová and Janiga, 2023; Pánik, 2024; Tuchyna, 2024), as these elements behave similarly in water. This phenomenon is often accompanied by similar variations of chlorine and ammonia (Janigová and Janiga, 2023) confirming independent annual oscillations of chlorine from potassium in high mountain waters. These metals are often present in dissolved form in the water and their abundance depends on local bedrock conditions (Neal et al., 1996). Potassium highly positively correlates to manganese and iron, and these elements mutually influence the food web of mountain stream biota (Janigová and Janiga, 2023; Pánik, 2024; Tuchyna, 2024).

4.2 Potassium in food web of alpine stream

4.2.1 Algae—food of macrozoobenthic srapers

Algae accumulate the most potassium in the summer (Talling, 2010). Oscillatoria cyanobacteria are sometimes responsible for this, as they are part of the photosynthesizing blue green phytoplankton, which pushes other groups (e.g., diatoms and green algae) out of rivers during extreme drought (Tuchyna, 2024). On the other hand, yellow algae Hydrurus foetidus has an undifferentiated potassium accumulation during the season (Tuchyna, 2024). Yellow algae are not suitable as food for scrapers. For aquatic insects including Ecdyonurus, the green algae of Ulotrix zonata (Kawecka, 1977) are a better food source than the yellow algae of Hydrurus, but a group of diatoms can make up as much as a quarter of the diet of Ecdyonurus (Kawecka, 1977). Hydrurus algae are the dominant food of other aquatic species, such as Trichoptera of the genus Hydropsyche (Kawecka, 1977). Oscillatoria can be toxic to Ecdyonurus, as it contains the toxin microcystin, and in high heat, cyanobacteria can kill Ecdyonurus (Bakr et al., 2022).

4.2.2 Macrozoobenthos – scrapers

Macrozoobenthic species possess many advantages as biondicators of water quality because they play an important role in nutrient cycling (Gabriels et al., 2010). This rationale is based on the observation that Ephemeroptera, Plecoptera, and Trichoptera are sensitive to increased contaminants in the water (Kiffney and Clements, 1994; Plafkin et al., 1989; Winner et al., 1980). Scrapers' diets consist of diatoms, parts of moss epidermis, and small pieces of algae and plant debris. Although the shape of Ecdyonurus jaws suggests predation, it is exclusively herbivorous, scraping flat surfaces of rocks and substrate or sifting food directly from the water (Rawlinson, 1939). Wögerbauer and Kelly-Quinn (2013) also mention filamentous algae as food, including Hydrurus foetidus. The seasonal cycle of potassium accumulation in Ecdyounurus larvae was balanced during the year. It is evident that potassium accumulates in these invertebrates independently of the food supply, because potassium levels in the algae were significantly higher in summer (Figure 3A), but potassium concentration in Ecdyonurus did not differ among seasons (Figure 3B). Additionally, in winter, the concentration of potassium in algae was very low, but not reflected in potassium levels found in the mayflies. A different food preference during this period may be one of the driving factors (Rawlinson, 1939).

4.2.3 Macrozoobenthos - predators

The accumulation of potassium in stoneflies points to a gradually decreasing trend of contamination during the year, but with no significant differences between seasons (Figure 3C). The potassium levels in Perla grandis indicate that this predator accumulates potassium from Ecdyonurus venosus in winter and hunts other prey during summer. In Borbera stream, its diet was mainly comprised of Diptera (Chironomidae), followed by Ephemeroptera (Baetis sp.), and in a lower percentage, Ephemeroptera (Heptageniidae) and Trichoptera (Hydropsychidae) (Cammarata et al., 2007). A study by (Tucker 1958) points to the accumulation of potassium during the year and shows increased values in invertebrates in winter, gradually decreasing during the year. He also remarks that in addition to its relation to dissolved organic matter, the degree of fluctuation appears to be governed to some extent by the size of the water basin, and inflowing streams. This may explain the tendency for a decrease in potassium levels in the body of Perla grandis in spring (Figure 3C). Studier and Sevick (1992) described accumulation of potassium in the predatory water bug Lepfocoris biviffafus and found that potassium accumulates more during spring than in summer.

4.3 Chlorine in food webs of alpine stream

4.3.1 Algae

Increased chlorination in the water enhances the removal of algae cells; their removal is reliant on chlorine dosage (Huang et al., 2021). In streams receiving increased chlorine amounts, the periphytic algal biomass and macroinvertebrate density may rapidly decrease (Aratani et al., 2007; Fukushima and Kanada, 1999). Tuchyna (2024) found that the amount of chlorine in Hydrurus foetidus algae is the highest in autumn and winter. This trend is somewhat visible in our study in autumn, but the differences among seasons were not statistically significant (Figure 3E). The variability of chlorine, particularly in algae of the genus Hydrurus, may be linked to climatic conditions, as the first algae to emerge following snowmelt is the “yellow” alga Hydrurus. In August, the phytoplankton bloom reaches its peak. Algal biomass in a habitat is a function of immigration, reproduction, death, emigration, and grazing rates. Dissolved solids, water conductivity, salinity, dissolved oxygen, temperature, pH, and light positively affect the growth rate algae and cyanobacteria (Ghalley et al., 2023; Stevenson, 2022; Tuchyna, 2022).

4.3.2 Macrozoobenthos – scrapers

A wide range of aquatic insects have historically been used in bioaccumulation studies. Differences among groups and their sensitivity to many chemical elements, including trace metals is well documented. In general, most Ephemeroptera scrapers are highly sensitive (Clements, 1991; Wiederholm, 1984). The absorption of chlorine in scrapers is seasonally linked to its earlier occurrence in algae. Our data indicate that while scrapers accumulate chlorine from algae, chlorine in algae gradually decreases during this period. Noble-Nesbiti (1990) observed that Sialis sp. in distilled water continuously loses chlorine ions from 0.15%−0.35% to 0.1% in 5 days, but these levels can be restored in a few days if larvae are transferred to water containing 1% NaCl. This may indicate that in late spring, during higher flows, mayflies show a significant lack of chlorine (Figure 3F) as it is washed away from their locality and restored where the flow gets lower (Hrivnáková, 2019). This supports our results, in which the highest concentration in water occurs in winter and fall. Ecdyonurus is not dependent on algae in summer and is probably not significantly affected by precipitation and floods, but it may be dependent on Hydrurus and its diatoms in autumn and winter.

4.3.3 Macrozoobenthos – predators

Food is an important vector element uptake in macrozoobenthos (Goodyear and McNeill, 1999; Luoma, 1983). Routes of contaminant uptake can be estimated by determining the distribution of chemical elements within animals (e.g., increased elements in the gills or the gut could suggest that they were taken up primarily from water or food, respectively (Hare et al., 1991; King and Davies, 1987). Interestingly, chlorine behaves differently than potassium in this regard, and this may indicate that these are not KCL but other compounds. Stoneflies contained less chlorine in spring and autumn than in summer or winter (Figure 3G). The increase in summer may indicate a higher level of food due to higher activity of possible prey. In freshwater insects there is a danger of gaining too much water from the environment and losing vital salts from the body due to the very low concentration of salts in fresh water. Osmotic inflow of water through the body surface can amount to 2%−10% of body weight daily at 20 °C (Noble-Nesbiti, 1990). The study also discussed flushing of salts such as chlorine during periods of increased flow. Särkkä et al. (1978) outlined the progression of chlorine across trophic levels within lake water ecosystems. This element was found to be the most concentrated in macrozoobenthos predators, regardless of certain fish species, a finding that was also corroborated in our study.

4.4 Role of fish predators (Alpine Bullheads)

Macrozoobenthos usually take up pollutants directly from water, sediments, and diet, and thus serve as a trophic link to higher food chain organisms such as fish and aquatic birds (Wayland and Crosley, 2006). Alpine Bullheads, like other freshwater fish, can accumulate various substances from their environment, including chlorine and potassium, which may derive from natural sources or anthropogenic activities. They generally absorb elements in two ways. Like other water creatures they absorb elements through their gills during respiration, and also absorb nutrients, elements, and pollutants in their diet. In the majority of freshwater fish, the branchial surface, rather than the body surface is the major site of K+ and Cl− exchange. Thus, for example, Rainbow trout (Oncorhynchus mykiss) are able to regulate potassium independently of diet (Haswell et al., 1980; Maetz, 1971; Sanders, 1979). Martemyanov (2001) explains a decrease in potassium concentration in more species of fish (mainly in Common roach, Rutilus rutilus) in muscle tissue and blood plasma during the breeding season as the fish prepare for water-salt homeostasis and stress situation. In our trend of concentration in potassium in Alpine Bullhead there was no significant difference in concentration between seasons, but the line curve shows a similar tendency to decrease in spring during the reproduction period (Figure 3D), which occurs between March and the end of May in Javorinka stream (Balon, 1966). Perinajová et al. (2020) write about the partially synergistic effect of potassium and chlorine behavior in Alpine Bullheads. They mention that these elements with sulfur variation and refused to confirm that these elements are present only in potassium chloride or sulfur salts. In bullhead bodies, Janiga (2020) described the inverse relationship between Zn and Sr in relation to K and Cl accumulation. If K and Cl increased, then Zn and Sr decreased and vice versa. The inverse concentration of K and Cl in relation to Zn and Sr in fish was different among seasons but did not depend on fish size. K and Cl increased and Zn and Sr decreased in warmer summer and autumn periods while Zn and Sr increased and K and Cl decreased in cold winter months. This factor clearly describes the seasonality of accumulation of these elements in Alpine Bullheads which is independent on the concentration of K and Cl in the water. To understand the accumulation of these biogens in Alpine Bullhead during seasons we need to investigate in detail the life cycle of their entire food spectrum (Števove et al., 2019). Alpine Bullhead are capable of changing their food strategy and direction to specialization if needed. Larvae of Simuliidae, Brachycentridae, Chironomidae and Hydropsychidae, and the crustacean Gammarus are the most abundant in their diet, though Heptagenidae (Ecdyonurus venosus) and Perliidae (Perla grandis) were also found as dietary components (Števove et al., 2019). The spectrum of this fish's diet is relatively wide likely explaining the lack of a significant correlation in potassium and chlorine accumulation in Alpine Bullheads among seasons. Alpine Bullhead are most abundant in streams between September and mid-October, and the largest individuals can be observed during this period. Potassium increases and summer water contamination declines significantly in the autumn, which may allow Alpine Bullhead to flourish, increase in abundance, and grow (Janiga and Janiga, 2023).

5 Conclusions

This research contributed to the knowledge of seasonal changes in the concentrations of potassium and chlorine through different segments of the food chain in the high mountain stream. Each of the studied food levels has its own way of accumulating potassium and chlorine. These elements often co-occur and accumulate in higher food chain levels during major flood events. During normal flows, they enter the water independently throughout the year and accumulate in different food orders, including algae, mayflies, stoneflies, and bullheads. This occurs in accordance with their physiological needs and the breadth of their food spectrum.

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Footnotes

Edited by: Davide Taurozzi, Roma Tre University, Italy

Reviewed by: Ataman Altug Atici, Yüzüncü Yil University, Türkiye

Richard Walker, University of Tennessee at Chattanooga, United States

Statements

Conflict of interest

The author(s) declared that this work was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

Funding

The author(s) declared that financial support was not received for this work and/or its publication.

Data availability

The datasets presented in this article are not readily available because they are owned by the University of Žilina and are subject to institutional licensing and intellectual property regulations. Data may be provided by the corresponding author upon reasonable request. Requests to access the datasets should be directed to Zuzana Kompišová Ballová, ballova1@uniza.sk.

Ethics approval

Ethical approval was not required for the study involving animals in accordance with the local legislation and institutional requirements because we collected carcasses of naturally deceased wild fish under the permission no. 99921/2018–6.3, issued by the Ministry of the Environment of the Slovak Republic, Department of State Nature and Landscape Protection, effective from 21 November 2018.

Author contributions

MartJ: Investigation, Visualization, Writing – original draft, Formal analysis, Data curation. MariJ: Visualization, Validation, Project administration, Writing – review & editing, Writing – original draft, Conceptualization, Investigation, Formal analysis, Supervision. JT: Writing – original draft, Data curation, Investigation. PP: Writing – original draft, Data curation, Investigation. ZKB: Supervision, Investigation, Writing – review & editing.

Acknowledgements

We would like to thank Michaela Perinajová, Tomáš Kubík, Martin Kompiš, Martina Haas, and other colleagues and students for their assistance in the field work. Special thanks are extended to Dr. Alica Hindáková for supporting the identification of algae and cyanobacteria groups. We are also indebted to Amanda Clarahan for English proofreading.

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Citation

Janiga, M., et al. (2026). Differences in potassium and chlorine incorporation in members of an alpine stream food web in the West Carpathians. Frontiers in Freshwater Science, Volume 4. https://doi.org/
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4 - 2026

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Copyright © 2026 Janiga, Janiga, Tuchyňa, Pánik and Ballová.

License: https://creativecommons.org/licenses/by/4.0/

*Correspondence: Zuzana Kompišová Ballová

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