Fate of heavy metals in ecosystems of dam reservoirs: Transport, distribution and significance of the origin of organic matter.

In this article, a multivariate analysis of the parameters determining the transport and fate of selected heavy metals in the water - bottom sediment interface was carried out. The studies were carried out in the summer season of 2019 at Nielisz Reservoir (southeastern Poland, Lublin Voivodeship). Finally, a previously unknown factor related to the quality of organic matter was identified. Autochthonous organic matter was shown to promote the accumulation of the studied heavy metals. To date, the significance of the origin of organic matter in the context of the transport and fate of heavy metals in retention reservoirs has rarely been reported in the scientific literature. More than that, this factor was not considered an important component in the process of heavy metal deposition in bottom sediments. However, it turns out that not only the quantity of organic matter, but also its quality plays an important role in the circulation of heavy metals in retention reservoir ecosystems. It was found that autochthonous organic matter promotes the accumulation of the studied heavy metals. It can be assumed that, in a sense, it plays the role of a catenary ("hub") controlling the fate of heavy metals in the water-sediment system. It has also been conjectured that, in a sense, OMS may reflect the potential for heavy metal assimilation by aquatic vascular plants (mainly of the C3 group). Plants with a photosynthetic pathway similar to the C3 group generally have a much lower enrichment in the 13C isotope (δ13C from -38‰ to -22‰). In our case, the lowest δ13C-TOCS value was -24.05‰, and the average for the whole reservoir was -21.53‰. In addition, it was observed that quantitative changes in the isotopic composition of total organic carbon δ13C-TOCS, corresponded with changes in the content of the heavy metals studied in entrapped sediments.

Significance of organic matter in the process of aggregation of suspended sediments in retention reservoirs.

It is crucial to have a comprehensive understanding of the process by which suspended sediment (SS) in water is aggregated and deposited to ensure the proper use and management of storage reservoirs. The present study was an investigation into the varied granulometric composition of accumulated sediment, as well as an examination of the amounts of organic matter present and its origins. This study aimed to determine what underpins the process of aggregation of sediment suspended in reservoir water. The results of the study, as also analysed using multivariate statistics, reveal a process of sediment aggregation dependent not only on the amount of organic matter but also on its origin. Greater production of autochthonous organic matter was shown to be associated with an intensified process of suspended sediment flocculation, confirming that the metabolism of a reservoirs' aquatic organisms influences the granulometric composition of suspended sediment.

Sediment methane production within eutrophic reservoirs: The importance of sedimenting organic matter.

While temperate reservoirs can be a significant source of atmospheric methane (CH4), knowledge of the role they play in global emissions of the gas remains limited in line with extreme temporal and spatial variability noted both within and between reservoirs. There is also still no clear identification of the environmental factors influencing the emission of this gas to the atmosphere. This article presents the results of research into the influence of sedimenting matter on CH4 emission from the surface of different zones of reservoirs. The research were conducted in 2018-2019 within Maziarnia and Nielisz Reservoirs - two artificial bodies of water of eutrophic status both located in SE Poland. Their diffusive CH4 fluxes at the water-air interface were measured using the "static chamber" method, while sediment traps monitored the rate of accumulation of sedimenting matter in bottom sediments (US). The CH4 fluxes noted at the reservoirs proved highly variable, both temporally and spatially, ranging from 0.02 to over 2500 mmol/m2·d. Determined accumulation indexes were in turn in the 13.61-618.49 g/m2·d range. Nevertheless, CH4 flux was found to correlate significantly with sedimentation index (US), with highest observed values for both reservoirs noted in river zone, while the lowest characterise the lacustrine zone. On this basis, it was hypothesised that sedimentation index may prove a useful tool in estimating CH4 emissions from reservoirs, with the reverse relationship also likely to apply. Furthermore, the key factor found to be responsible for the aforementioned temporal and spatial variations in CH4 emissions is primary production, whose subsequent sedimentation supplies sediments with easily-degradable organic matter. The results presented here contribute to an understanding of environmental factors that may influence spatial variation in CH4 production and can be useful to serve determinate of potential methods by which to reduce emissions this gas from managed systems such as reservoirs.