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.

Production pathways for CH4 and CO2 in sediments of two freshwater ecosystems in south-eastern Poland.

This paper presents the results of research into pathways leading to the production of methane (CH4) and carbon dioxide (CO2) in sediments of two eutrophic reservoirs (Maziarnia and Nielisz), located in south-eastern Poland. In seeking to identify the pathways in question, use was made of analysis of stable carbon isotopes in CH4 and CO2 dissolved in pore water. This determined that CH4 is mainly produced through acetate fermentation, though the hydrogenotrophic methanogenic process may also be of importance, especially in deeper layers of sediments. Both the presence of autochthonous organic matter and increased pH values are shown to favour acetate fermentation. In turn, methanogenesis in sediments is assessed as capable of accounting for the generation of a considerable amount of CO2. Indeed, the role of methanogenesis in CO2 production is increasingly important further down in the layers of sediment, where allochthonous organic matter is predominant.

The influence of environmental factors on the carbon dioxide flux across the water-air interface of reservoirs in south-eastern Poland.

Studies concerning the emission of carbon dioxide (CO2) were carried out in 2009-2012 for six reservoirs located in four provinces of south-eastern Poland. The CO2 flux across the water-air interface was measured using the "static chamber" method. The measured fluxes of CO2 (FCO2) ranged from -30.64 to 183.78mmol/m2/day, and the average values varied in the range from -3.52 to 82.11mmol/m2/day. In most of the cases, emission of CO2 to the atmosphere was observed. The obtained values of CO2 fluxes were comparable to values typical for other temperate reservoirs. Analysis of the influence of selected environmental factors on the FCO2 showed that it depends on parameters characterizing both the sediments and surface water. The CO2 flux at the water-air interface was positively correlated with parameters of bottom sediments such as porosity, content of organic carbon and total nitrogen; and negatively with pH value and δ13C of organic carbon. In the case of the parameters characterizing surface water, positive dependences on the concentrations of nitrate and total nitrogen, and negative relationships with water temperature and chlorophyll a concentrations, were found.

Methane and Carbon Dioxide in the Sediment of a Eutrophic Reservoir: Production Pathways and Diffusion Fluxes at the Sediment-Water Interface.

The estimated diffusion fluxes of methane (CH4) and carbon dioxide (CO2) at the sediment-water interface in the Rzeszów Reservoir in southeastern Poland are presented. The relevant studies were conducted during 2009, 2010, and 2011. Calculated fluxes ranged from 0.01 to 2.19 mmol m-2 day-1 and from 0.36 to 45.33 mmol m-2 day-1 for methane and carbon dioxide, respectively. While the values for calculated diffusion fluxes of methane are comparable with those reported for other eutrophic reservoirs, much higher values were obtained here for carbon dioxide. The resulting values of δ13C-CH4 and the fractionation coefficients between methane and carbon dioxide (αCH4-CO2) suggest that methane in the sediment of the Rzeszów Reservoir is produced by acetate fermentation, while the hydrogenotrophic methanogenic process is of successively greater importance with increasing depth. In the top layer of the sediment, 24-72 % of CO2 came from methanogenesis, while the contribution made by the degradation of organic matter by methanogenesis to CO2 was greater in the deeper layer.

Determination of nitrate isotopic signature in waters of different sources by analysing the nitrogen and oxygen isotopic ratio.

A reference study on both the nitrogen content in waters and nitrogen and oxygen isotopic signatures characterising nitrate from different sources was conducted within the San River catchment area. Three kinds of catchments were studied: (1) forested and uncultivated; (2) artificially fertilised with nitrate; and (3) fertilised with manure and sewage. Moreover, atmospheric water was studied. The obtained values were found to be similar to others in the literature, with the exception of nitrate from the atmosphere, in regard to which influence reflecting the local conditions was to be noted. The isotopic signature of nitrate in the studied water results from the biogeochemical transformation of nitrogen compounds rather than from the mixing of different sources. The obtained results were statistically distinct and can be used as end-member values in further modelling studies connected with the management of nitrate in river waters, especially under middle-eastern European conditions.