Renata Gruca-Rokosz

The significance of denitrification in relation to external loading and nitrogen retention in a mountain reservoir

Nitrogen retention (Nret) and denitrification were studied in the mesotrophic Solina reservoir (south-east Poland) between spring and autumn in 2002 and 2003. Nret was calculated on the basis of the input-output mass balance. The rate of denitrification was measured using the 15N isotope pairing technique in two types of areas; in deep areas, where the bottom sediment makes contacts with the hypolimnion (Dprof), and in the unstratified shallows (Dlitt). The calculated daily load of removed nitrogen (Dtot) varied somewhat from 11.0 to 19.1 mg N m–2 day–1 with a standard deviation of 3.0 mg N m–2 day–1. The limited oscillation noted for Dtot results from the major participation of the deep areas of the reservoir, which are characterised by stable Dprof, as distinct from Dlitt, which varied seasonally from 5.8 mg N m–2 day–1 in November to 109.9 mg N m–2 day–1 in August. The primary factor limiting the denitrification rate was temperature, the other being availability of substrates, mainly organic matter. Nitrogen retention ranged seasonally between –25.0 and 175.9 mg N m–2 day–1. The contribution of denitrification to Nret ranged from 9.0% to 49.8% (mean 16.4%). On average, only 4.9% of the nitrogen external load was denitrified (range 2.6–7.9%, s.d. 1.5%). After comparing obtained data with others available in the literature, we concluded that reservoirs, estuaries and highly-loaded lakes in a river system experience a more limited contribution of Dtot to Nload than is the case in natural lakes.

Carbon and nitrogen and their elemental and isotopic ratios in the bottom sediment of the Solina-Myczkowce complex of reservoirs

Carbon and nitrogen and their elemental and isotopic ratios in the bottom sediment of the Solina-Myczkowce complex of reservoirs The studies concerned the ecosystem of the Solina-Myczkowce cascade of reservoirs. While the elemental C:N ratio was higher in the Solina Reservoir branches and in the Myczkowce Reservoir (>10), the values for stations located near the Solina Dam were low (<10). Markedly, the lowest values for δ13C were noted in the Myczkowce Reservoir (-28.5‰), and these contrasted with the higher values found in the Solina Reservoir (ca. -27‰). δ15N varied from 2‰ in the upper Solina to above 3.5-4‰ downstream. While the data obtained indicate the autochthonous origin of sedimentary matter, primary production influences the properties of the bottom sediments in the lower part of the Solina reservoirs.

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.

Denitrification in the sediment of a eutrophic reservoir measured with the isotope pairing technique

Denitrification in the sediment of a eutrophic reservoir measured with the isotope pairing technique Denitrification rates in the bottom sediment of the Rzeszów Reservoir (southeastern Poland) were measured using the isotope pairing technique. At the stations studied rates were reported in the range of about 26 to 610 μmol N2 m-2 h-1, with the figures generally highest in summer. Simple and multiple regression analyses of relationships with selected abiotic factors gave rise to a model that revealed a statistically significant influence on rates of denitrification in the bottom sediment of the Rzeszów Reservoir due to concentrations of nitrate in overlying water, temperature, and the organic matter content in the sediment. The present study confirms that nitrate concentration in the overlying water is the main factor controlling sedimentary denitrification.

The distribution and isotopic composition of carbon and nitrogen as indicators of organic-matter fluxes in the Solina Reservoir (south-east Poland)

The feasibility of using carbon and nitrogen isotope ratios of sediment organic matter (OM) to elucidate the source and fate of bottom sediment was studied in the Solina Reservoir (south-east Poland). Horizontal and vertical changes in OM, total organic carbon (TOC) and total nitrogen (TN) content, as well as δ15N and δ13C values, in bottom sediments were analysed to establish the extent to which these sediments are terrestrial or internal in origin. Increased proportions of TOC along with slight decreases in TN were noted in the surface layer of shallow water sediment compared with the profundal sites. Upstream shallower C : N and δ15N values amounted to ~15 and ~2‰, respectively, pointing to the allochthonous origin of the OM. In turn, profundal C : N ratios of less than 10 and δ15N values of ~4‰ indicated autochthonous sediment. Values for δ13C did not differ between stations and ranged from –27.39 to –27.66‰. It is therefore suggested that the sediment from the upper shallower stations contains more allochthonous, refractory OM, whereas the profundal stations have planktonic OM enriching the sediment. This combined with the vertical distribution observed for δ15N signalled an intensification of eutrophication over the past few years.

Spatial Diversity Characterising Certain Chemical Substances in Sediments of Besko Reservoir

The article reports the conducted analyses of certain chemical parameters characterising the sediments of Poland’s Besko Reservoir. Specifically, determinations concerned the pH value, percentage organic matter (OM), total organic carbon (TOC), total nitrogen (TN), carbonates (CO3 2-), total phosphorus (TP) and its fractions, as well as heavy metals (Fe, Al, Cr, Cu, Ni, Cd, Zn, Mn). The sediments have a slight alkaline reaction, with pH values correlating positively with the high content of carbonates. The sediments have low organic matter content, while organic carbon accounts for about 30% of OM. The values for the C:N ratio point to an allochthonous origin for organic matter. The analysis of phosphorus fractionation showed that inorganic phosphorus (IP) is predominant at every research station. The lowest percentage for a fraction was in turn obtained for NAIP. This testifies to a slight anthropogenic impact of the catchment area. The sediments can be classified as of the 2nd purity class (according to PIG), due to their highest concentration of chromium. According to Müller’s classification, the sediments can be classified as purity class 3 (i.e. with moderate contamination). The values noted for the EF coefficient confirm a very strong enrichment by chromium ions. In addition, chromium, copper, nickel and cadmium have a negative effect on aquatic organisms. The results show that the sediments can be used for example in building and maintaining hydraulic structures.

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.

A Preliminary Study Into the Possibility of δ13C Being Used as a Sensitive Indicator of the Trophic and Hydrobiological Status of Aquatic Ecosystems

There is a need to search for additional indicators allowing for more accurate identification of both the trophic status of waters as well as its chemical and biological consequences. The work detailed in this paper involved a preliminary analysis pertaining to the possibility of using an isotopic index in association with the values for trophic and saprobic indicators in describing a dam reservoir experiencing a far-reaching eutrophication. The water samples for the physicochemical analysis were collected from three sites along the axis of the dam reservoir in Rzeszów three times during the spring and summer of 2013. The results sustained the classification of the Reservoir’s waters as hypertrophic, irrespective of the particular zone sampled. While phytoplankton blooms characterised by reference to the numbers of organisms per unit volume of water were also similar throughout the Reservoir, diversification in terms of taxonomic composition was to be noted, given the occurrence of cyanobacteria among the dominant diatoms in the area close to the dam. This presence was accompanied by enrichment of the Reservoir’s suspended organic matter with carbon of the heavier 13C isotope. On this basis, the δ13C isotopic index can be regarded as a potentially useful indicator allowing for more accurate identification of both the level and the nature of the ongoing trophic degradation in bodies of water.

Diffusive Fluxes of CH4 and CO2 at the Sediment-Overlying Water Interface in Reservoir Ecosystems

The work detailed here concerned the CH4 and CO2 fluxes at the sediment-overlying water interface in Maziarnia and Nielisz Reservoirs, SE Poland. The research in question was conducted in the period of 2009–2011, the samples of sediment and overlying water were collected at two stations located in the upper and lower parts of each reservoir. The concentrations of CO2 and CH4 in pore water and overlying water were measured with the headspace method, using a Pye Unicam gas chromatograph (PU-4410/19) equipped with a methane analyzer allowing low CO2 concentrations to be detected. Diffusive fluxes of the analyzed gases at the sediment-overlying water interface were calculated on the basis of Fick’s first law, and were found to range from -0.01 to 3.48 mmol×m-2×d-1 for CH4 and from -1.27 to 47.02 mmol×m-2×d-1 for CO2. Comparable fluxes elsewhere typify the reservoirs experiencing far-reaching eutrophication. No dependent relationships were found between the values calculated for fluxes and either season of the year or sediment characteristics.