Evaluation of Quality of Bottom Sediments of Water Reservoir Poraj by Applying Sediment Quality Guidelines and Spiatal Analysis

S t r e s z c z e n i e Celem badań była ocena jakości osadów dennych zbiornika wodnego Poraj z zastosowaniem wytycznych dotyczących jakości osadów (ang. SQGs – Sediment Quality Guidelines) oraz analiz przestrzennych. Próbki osadów dennych zostały pobrane na podstawie regularnej siatki kwadratów zawierającej 46 punktów pomiarowych. Pobrane próbki zostały poddane analizom laboratoryjnym pod kątem zawartości metali śladowych, toksyczności oraz materii organicznej. Zawartość trzech metali śladowych przekroczyła odpowiadającą wartość PEC: Zn (22% próbek), Pb (17%) i Cd (17%). Porównując wartość PECQ, 17% próbek określa się jako prawdopodobnie toksyczne. Dla TEC w 76% badanego materiału nie wykryto toksyczności. Wartości PECQ zawierały się w przedziale od 0.04 do 2.08 z wartością średnią 0.38, PERI od 4.36 do 323.62 z wartością średnią 55.35. Wartość PERI ponad 150 została zaobserwowana w 17% próbek. Wyznaczono współczynnik determinacji pomiędzy badanymi wskaźnikami: PERI i PECQ (R2= 0.98), PECQ i TEC (R2= 0.99), PERI i TEC (R2= 0.98), PERI i PE (R2= 0.06), PECQ i PE (R2= 0.07). Niska wartość korelacji pomiędzy procentowym efektem toksyczności a analizowanymi wskaźnikami wskazuję na udział innych czynników wpływających na toksyczność osadów dennych zbiornika wodnego Poraj. Na podstawie rozkładów przestrzennych wyznaczono obszary z największym ryzykiem ekologicznym. K e y w o r d s : SQGs; Toxicity; Geographic Information System; Trace elements; Spatial distribution. 2/2018 A R C H I T E C T U R E C I V I L E N G I N E E R I N G E N V I R O N M E N T 141 A R C H I T E C T U R E C I V I L E N G I N E E R I N G E N V I R O N M E N T The Si les ian Univers i ty of Technology No. 2/2018 d o i : 1 0 . 2 1 3 0 7 / A C E E 2 0 1 8 0 3 2 K . R o z p o n d e k , R . R o z p o n d e k 142 A R C H I T E C T U R E C I V I L E N G I N E E R I N G E N V I R O N M E N T 2/2018 ronment are accumulated [1, 2]. The chemical composition of the matter lying on the bottom of water reservoirs is conditioned by both natural and anthropogenic factors. An important role is played, among others, by the geological structure of the basin, the type of soil cover, terrain and climatic conditions. Additionally, the chemical analysis of bottom sediments is a source of information on human activity in a given region [3]. The most frequently observed forms of anthropogenic impact affecting the quality of sediments are discharges of municipal and industrial sewage, atmospheric and gaseous pollution of the atmosphere as well as leaks from landfills. In agricultural areas, additionally, contaminants introduced into the basin of the reservoir (fertilisers, plant protection chemicals), as well as sewage sludge, which is used to fertilize the arable land [3, 4, 5]. As a result of the total effect of the presented factors, the material deposited on the bottom of water reservoirs may contain significant loads of organic (e.g. PAH, pesticides) and inorganic (e.g. trace elements) pollutants, which accumulate in sediments and may subsequently pose a threat to water quality due to remobilisation. A feature of these compounds is that they can remain active for a long period of time and constitute a secondary source of water contamination [6]. Modern studies on trace elements in bottom sediments are often related to ecological risk, toxicity evaluation, health risk caused by trace elements and geochemical cycling [7, 8, 9, 10]. Sediment quality guidelines (SQGs) and potential ecological risk index (PERI) are group of useful methods which allows assessment of pollution risk of an aquatic system by integrating total trace element content [9, 10, 11, 12, 13]. The main aim of this study was to evaluate the quality of bottom sediments of water reservoir Poraj by applying a set of sediment quality guidelines, potential ecological risk and spatial analysis. Toxicity effect and total trace element content were described in previous studies [2, 14]. 2. MATERIALS AND METHODS 2.1. Study area and bottom sediments sampling Sampling of bottom sediments from the Poraj Reservoir was conducted in August 2016. The analyzed reservoir is located in the Poraj and Koziegłowy municipality in the Myszków County, in the northern part of the Silesian Voivodeship. It has an area of 550 hectares. It was created in 1978 in order to build a reservoir of water for Huta Czestochowa. Currently, it is the subject of interest to local residents because it could be used for water sports and tourism, as well as recreation in the region [2, 14, 15, 16]. The Warta River is the main tributary directly supplying the Poraj water tank. For this reason, it substantially affects the quality of the water and bottom sediments of the reservoir. The waters of the river are polluted inter alia by sewage, which are supplied mainly from the area of Zawiercie and Myszków. They originate mainly from rural areas without a sewerage system. Domestic wastewater is directly introduced into the surface waters, which are located in the catchment area of the reservoir. Numerous resorts are present in the immediate vicinity of the lake, because of its recreational character. They constitute point sources of pollution, which directly participate in shaping the quality of water and sediment tank [15, 16]. Samples of bottom sediments were collected at 46 measuring points (determined by ArcGIS software) with depths ranging from 0.4 m to 7.4 m below the water table, Fig. 1. The research material was collected using a specialized hook for bottom sediments of Van Veen’s KC Denmark type [2, 14]. Figure 1. Water reservoir Poraj with the location of the measurement points EVALUATION OF QUALITY OF BOTTOM SEDIMENTS OF WATER RESERVOIR PORAJ ... E N V I R O N M E N T e 2/2018 A R C H I T E C T U R E C I V I L E N G I N E E R I N G E N V I R O N M E N T 143 2.2. Laboratory analysis The samples were first dried under dry-air conditions and then sieved through a 2 mm screen. They were then dried in an oven at 105°C to constant weight and ground in a vibrating mill until the grain size was lower than 0.2 mm [2, 14]. Prepared samples were used to determine the total trace element content in accordance to Polish Standard PN-ISO 10390:1997 and 11466:2002. Aqua regia (a mixture of concentrated hydrochloric acid and nitric acid in a volumetric ratio of 3:1) was used for trace element extraction (Zn, Cd, Pb, Ni, Cu, Cr). Mineralisation was carried out at 180°C, for 30 minutes in a high pressure microwave mineraliser from the German company Berghof GMBH. A plasma spectrometer (IRIS ICP-OES Thermo) was used to determine the trace element content. (Rozpondek, Wancisiewicz, 2016). Total nitrogen were determined by Kjedahl method. Organic matter content were determined in accordance to PN-ISO 11465:1999. Toxicity effect of bottom sediments was determined by Alivibrio fischeri bacteria bioassay using Microtox M 500 Analyzer (in accordance to PN-ISO 11348-2:2008). Water extracts were prepared by mixing one volume of bottom sediments and four of distilled water [17]. Total trace elements concentration, percentage toxic effect, organic matter and total nitrogen was described in previous studies [2, 14]. 2.3. Indexes of ecological risk Sediment quality guidelines (SQGs) were applied to evaluate the degree to which the sediment-associated chemical status might adversely affect aquatic organisms and to aid in the interpretation of sediment quality [9, 10, 18]. These guidelines have been widely used to screen sediment contamination by comparing sediment contaminant concentrations with the corresponding quality guidelines in aquatic ecosystems [9, 10, 11, 12, 17]. The assessment of sediment contamination with trace elements was based on threshold effect concentration (TEC) and probable effect concentration (PEC) methods. To determine potential risk to the benthic fauna, values of trace elements were compared to corresponding TEC and PEC values (Table 1). For each of the studies, trace elements concentration and mean PEC were determined (PECQ). PECQ was calculated by the average of the ratio of PEC of each element concentration. There are two crucial values for indication potential environmental risk: 0.5 and 1.0. If values of PECQ are lower than 0.5 then bottom sediments sample are predicted to be non-toxic. If it exceeds value of 1.0 then it indicates that the bottom sediments are predicted to be toxic and pose a threat to benthic fauna [10, 18, 19]. The potential ecological risk index (PERI) is also a method that allows assessment of potential harmfulness of trace elements contained in bottom sediments. The potential ecological risk index for trace elements was calculated based on the formula developed by Håkanson [20, 21]. It consists of: potential ecological risk of the trace elements, contamination factor, measured background values of the trace elements in studied area. The toxic response factor of the trace elements depends on the sedimentological toxic factor (STF) and bioproduction index (BPI) [20, 23, 24]. STF of individual elements is as follows: for Zn = 1; Cu, Pb, Ni = 5; Cr = 2, Cd = 30; [20, 21]. Bioproduction index is a factor that affects the bioavailability of trace elements. BPI was calculated as the nitrogen content in the regression line for the organic matter content value of 10% (Fig. 2) [20, 21]. The content of total nitrogen and organic matter was described in previous studies [2, 14]. The value of BPI was equal to 37.7. Contamination factor for each of the studied trace elements was estimated on the basis of geochemical background of the bottom sediments: Zn 48[mg·kg-1], Cu 6 [mg·kg-1], Ni, Cr 5 [mg·kg-1], Pb 10 [mg·kg-1] and Cd 0.5 [mg·kg-1] [10, 21, 22]. Table 1. Corresponding TEC and PEC values for studied trace elements [10] Parameter Zn Cd Pb Ni Cu Cr PEC 459 5 128 49 149 111 TEC 121 1 35.8 23 32 43.4 Figure 2. Total nitrogen content in the regression line for the organic matter content. R2=0.9336 K . R o z p o n d e k , R . R o z