Seasonal CO2 fluxes from alpine river influenced by freeze-thaw in the Qinghai Lake basin, northeastern of the Qinghai-Tibet Plateau.

River CO2 emissions, which contribute 53 % of the basin's overall carbon emissions, are essential parts of the global and regional carbon cycles. Previous CO2 flux calculates are mostly based on single samples collected during ice-free periods; however, little is known about the effects of freeze-thaw cycles on the river CO2 flux (FCO2) of inland rivers in alpine regions. Based on one year-round monthly continuous field sampling, we quantified the FCO2 and determined their driving factors in typical rivers during different freeze-thaw periods in the Qinghai Lake Basin (QLB) using the thin boundary layer model (TBL) and the path analysis method. The findings indicated that (1) the average FCO2 in the typical rivers was 184.98 ± 329.12 mmol/m2/d, acting as a carbon source during different freeze-thaw periods, and showed a decreasing trend with completely thawed periods (CTP, 303.15 ± 376.56 mmol/m2/d) > unstable freezing periods (UFP, 189.44 ± 344.08 mmol/m2/d) > unstable thawing periods (UTP, 62.35 ± 266.71 mmol/m2/d); (2) pH, surface water temperature (Tw) and total alkalinity (TA) were the dominant controlling factors during different freeze-thaw periods. Interestingly, they significantly affected FCO2 more before completely frozen than after frozen, with Tw and TA changing from having promoting effects to having limiting effects; (3) in addition, dissolved carbon components indirectly affected FCO2, primarily through the indirect effects of pH and Tw in the UTP; wind speed (U) directly promoted FCO2 in the CTP; and Ca2+ and dissolved inorganic carbon (DIC) were susceptible to indirect effects, which promoted/limited the release of FCO2 in the UFP, respectively. Our results reveal the changes of FCO2 and the factors influencing it in inland rivers within alpine regions during different freeze-thaw periods, thereby offering valuable support for carbon emission-related studies in alpine regions.

Hydrogeochemical characteristics and recharge sources identification based on isotopic tracing of alpine rivers in the Tibetan Plateau.

Alpine rivers originating from the Tibetan Plateau (TP) contain large amounts of water resources with high environmental sensitivity and eco-fragility. To clarify the variability and controlling factors of hydrochemistry on the headwater of the Yarlung Tsangpo River (YTR), the large river basin with the highest altitude in the world, water samples from the Chaiqu watershed were collected in 2018, and major ions, δ2H and δ18O of river water were analyzed. The values of δ2H (mean: -141.4‰) and δ18O (mean: -18.6‰) were lower than those in most Tibetan rivers, which followed the relationship: δ2H = 4.79*δ18O-52.2. Most river deuterium excess (d-excess) values were lower than 10‰ and positively correlated with altitude controlled by regional evaporation. The SO42- in the upstream, the HCO3- in the downstream, and the Ca2+ and Mg2+ were the controlling ions (accounting for >50% of the total anions/cations) in the Chaiqu watershed. Stoichiometry and principal component analysis (PCA) results revealed that sulfuric acid stimulated the weathering of carbonates and silicates to produce riverine solutes. This study promotes understanding water source dynamics to inform water quality and environmental management in alpine regions.

Homogenization of microplastics in alpine rivers: Analysis of microplastic abundance and characteristics in rivers of Qilian Mountain, China.

Microplastics in remote areas has received increasing concern in recent years. However, studies on microplastics in alpine rivers and their affecting factors are still limited. In this study, we investigate the abundance and characteristics of microplastic in the surface water of five alpine rivers in Qilian Mountain, China. Utilizing sieve collection, digestion and density separation, along with microscopy and Raman spectroscopy analyses, microplastics were observed in all the water samples and the average abundance of microplastics was 0.48 ± 0.28 items/L, which was lower than in other freshwaters. Transparent (37.3%) and fibrous (72.1%) microplastics were predominant. Polypropylene (53.8%) was the most frequently identified polymer type. Analysis of similarities (ANOSIM) and linear discriminant analysis (LDA) based on microplastic shape, color, and polymer type showed that there was no significant difference in the microplastic characteristics among rivers of Qilian Mountain. The distance decay models revealed that the similarity in microplastics characteristics was not affected by changes in watershed characteristics, such as geographical distance, elevation, water quality, and land use. This finding suggests that the primary source of microplastics in Qilian Mountain rivers could be from dispersed origins. The results of this study indicated that despite remote alpine rivers suffering limited anthropogenic impacts, they were not immune to microplastics. However, in watersheds with lower intensity of human activity, the abundance and characteristics of microplastics in water bodies may be more uniformly distributed and controlled by diffusion conditions such as atmospheric transport or riverine transport. Our investigation unveils novel understanding of microplastic dispersion in secluded alpine territories, emphasizing the crucial need for managing atmospheric transport of microplastics within conservation areas.

Impact of river dynamics on the genetic variation of Gypsophila repens (Caryophyllaceae): a comparison of heath forest and more dynamic gravel bank populations along an alpine river.

Alpine rivers are, despite anthropogenic water flow regulation, still often highly dynamic ecosystems. Plant species occurring along these rivers are subject to ecological disturbance, mainly caused by seasonal flooding. Gypsophila repens typically grows at higher altitudes in the Alps, but also occurs at lower altitudes on gravel banks directly along the river and in heath forests at larger distances from the river. Populations on gravel banks are considered non-permanent and it is assumed that new individuals originate from seed periodically washed down from higher altitudes. Populations in heath forests are, in contrast, permanent and not regularly provided with seeds from higher altitudes through flooding. If the genetic structure of this plant species is strongly affected by gene flow via seed dispersal, then higher levels of genetic diversity in populations but less differentiation among populations on gravel banks than in heath forests can be expected. In this study, we analysed genetic diversity within and differentiation among 15 populations of G. repens from gravel banks and heath forests along the alpine River Isar using amplified fragment length polymorphisms (AFLP). Genetic diversity was, as assumed, slightly higher in gravel bank than in heath forest populations, but genetic differentiation was, in contrast to our expectations, comparable among populations in both habitat types. Our study provides evidence for increased genetic diversity under conditions of higher ecological disturbance and increased seed dispersal on gravel banks. Similar levels of genetic differentiation among populations in both habitat types can be attributed to the species' long lifetime, a permanent soil seed bank and gene flow by pollinators among different habitats/locations.

Occurrence and vertical distribution of Ca, Cl, Cr, Fe, Mn, Mo, K, Rb, Sr, S, Sn, and Zn in the skull bones of alpine bullhead (Cottus poecilopus) in the West Carpathians.

The aim of this study was to examine the contents of calcium, chlorine, chromium, iron, manganese, molybdenum, potassium, rubidium, strontium, sulfur, tin, and zinc in the bones of the alpine bullhead (Cottus poecilopus) related to its vertical distribution in the mountain river Javorinka. This river is located on the northern side of the High Tatras, the West Carpathians. Sampling took place during 2017, 2018, and 2019. One hundred three individuals of bullheads were collected. Only deceased individuals were selected for sampling; there was no deliberate harm to any sampled individuals. Weight, body length, and head length and width were measured. The amounts of Ca, Rb, and Mo were significantly dependent on the altitude and the fish size. At higher altitudes, there are smaller fish that colonize more inaccessible waters with smaller habitat flow options and these smaller fish contain relatively more Ca, Rb, and Mo in their skulls than large fish. The presence of Mn, Sr, and Zn was related to the altitude. Concentrations of Zn and Sr increase with altitude in the alpine bullhead skulls. The amounts of S, Cl, K, Cr, Sn, and Mo did not differ among fish living at different elevations.

[Seasonal Variations of DOM Spectral Characteristics in the Surface Water of the Upstream Minjiang River].

Alpine wetlands and valleys of northwestern Sichuan are the main catchment areas of Minjiang River, where dissolved organic matter (DOM) in surface waters comes mainly from the natural background environment. Sources and structure parameters of DOM are important for calibrating the flux and pattern of organic carbon exports from plateau wetlands and alpine rivers. In this study, surface water samples along the upstream Minjiang River were collected at the end of dry season (April) and rainy season (October). Excitation emission matrix (EEM) fluorescence spectroscopy coupled with parallel factor analysis (PARAFAC) was used to characterize seasonal variations of DOM along Minjiang River. Results showed fluorescence peaks (humic-like peaks A and C, protein-like peaks B and T) were different along the river. Peak A and peak C were more obvious at the end of dry season, while peak B and peak T were more obvious at the end of rainy season. PARAFAC produced a three-component model including two humic-like components[C1 (250-260/380-480 nm) and C2 (300-330/380-480 nm)] and one protein-like component[C3 (270-280/300-350 nm)], accounting relative intensity 48.68%-65.02% for C1, 23.17%-29.83% for C2, and 11.83%-21.53% for C3. Fluorescence components showed variations along the river more prominently in April than October, in which the most significant one was C1. Average fluorescence index (FI) values ranged from 1.4 to 1.9, indicating that DOM consisted of both autochthonous and allochthonous components. Moreover, higher degrees of humification, aromaticity and hydrophobicity were found in April than those in October, suggesting more terrigenous sources at the end of dry season and more biological sources at the end of rainy season. Additionally, chromophoric dissolved organic matter (CDOM)[a(355)] correlated significantly with humic-like substance[Fn(355)], which also indicated that DOM components originated from terrigenous input in the upstream Minjiang River. The results also showed significant positive correlation between C1 and C2 in April, with no significant correlation in October, which further proved that exogenous input and seasonal variations characterized DOM sources in the upstream Minjiang River.