near-bottom water level are detected, and the methylmercury content in the sediments ... This results in repeated water pollution, which can last for many years.
ISSN 1068-3739, Russian Meteorology and Hydrology, 2010, Vol. 35, No. 9, pp. 611–618. Ó Allerton Press, Inc., 2010. Original Russian Text Ó Yu.A. Fedorov, A.E. Ovsepyan, V.B. Korobovb, I.V. Dotsenko, 2010, published in Meteorologiya i Gidrologiya, 2010, No. 9, pp. 44–54.
Bottom Sediments and Their Role in Surface Water Pollution with Mercury (with a Special Reference to the Northern Dvina River Mouth and the Dvina Bay of the White Sea) Yu. A. Fedorova, A. E. Ovsepyana, V. B. Korobovb, and I. V. Dotsenkoa a
b
Southern Federal University, ul. Zorge 40, Rostov-on-Don, 344090 Russia Arkhangel'sk Center for Hydrometeorology and Monitoring of Environment with Regional Functions ul. Mayakovskogo 2, Arkhangel'sk, 163020 Russia Received May 29, 2008
Abstract—Mercury content in bottom estuarine sediments of the Northern Dvina River and the Dvina Bay of the White Sea is studied. Major regularities of the behavior of the metal and its compounds in bottom sediments of the water area are defined. The role of lithological composition, pH and Eh of the environment, the presence of hydrogen sulfide for determining the content and forms of the mercury presence in the bottom sediments of the region are studied. The sediments related to technogenic formations are specified. The paths and forms of mercury coming from bottom sediments to the near-bottom water level are detected, and the methylmercury content in the sediments is calculated.
DOI: 10.3103/S1068373910090050
INTRODUCTION The peculiarity of bottom sediments is their ability to sequestrate mercury and its compounds and in the case of changing physicochemical and hydrodynamic environmental conditions to bring them partly back to the water column. This results in repeated water pollution, which can last for many years. Generally, the most toxic mercury forms are released from bottom sediments. Such events nonplus the ecologists, as against the background of the all-in-all trouble-free state of the aquatic environment and absence of visible pollution sources one observes the bursts of very high concentrations of mercury and its compounds. As the Northern Dvina estuarine area refers to the bodies, for which mercury is an element of characteristic pollutants [6, 7, 12, 14], the urgency is obvious to study the changes in content of this metal and its compounds in the bottom sediments in the region as a factor that can have an adverse effect on the surface water quality. It should be also added that such long-term and large-scale mercury measurements from the bottom sediment area and depth are done for the first time. METHODS OF COLLECTION, PREPARATION, AND ANALYSIS OF SAMPLES Several expeditions were organized and realized on the rivers and water reservoirs of northern Russia in 2004–2007 to study the peculiarities of changes in mercury content in water and bottom sediments. The modified methodology of sample collection, preparation, and measurement for the mercury content was tested earlier on different water bodies of Russia [1, 4, 12]. The samples were taken with a bottom scoop and/or a tube of a State Oceanographic Institute design aboard ship Aisberg-2 in the surface (0–5-cm depth) and subsurface (5–10 cm) sediment layers. More than 150 samples were taken at 18 monitoring stations (the scheme of sampling stations see in [12]). Most mercury measurements were performed with the help of an atomic absorption method in the cold vapor of the certified Laboratory of the Southern Federal University. The frequency control of the results obtained was performed in the Federal State Unitary Geological Enterprise (FSUGE) Yuzhgeologiya and Hydrochemical Institute of Roshydromet. The measurement error was 10–15%. pH and Eh, methane and organic carbon content were also measured in bottom sediments. 611
612
FEDOROV et al.
Changes in pH, Eh, methane, organic carbon, and mercury content in bottom sediments Characteristic of bottom sediments Sand of different dimensionality, re-washed, often with technogenic material (glass, concrete, plastics, etc.) Silty sand differently polluted with wastes from pulp-and-paper production Silty sand, sandy silt, generally with a smell of hydrogen sulfide Argillaceous silt with a smell of hydrogen sulfide
Corg , %
Hg, mg/g of dry mass
Methylmercury, ng/g of dry mass (calculated)
Eh, mV
pH
CH4, mg/g of wet mass
–22.9...73.0 20
7.71–7.80 7.74
0.27–0.30 0.28
0.12–1.04 0.4
0.04–0.09 0.045
0.045–1.57 –
–64.4...–107.2 6.93–7.33 –78 7.05
0.03–5.4 1.56
0.5–6.07 1.28
0.02–0.15 0.09
0.09–3.15 –
0.11–21.0 3.78–27.95 0.21–0.37 6.9 0.29 2.03–45.5 11.1–40.3 0.10–0.80 14.8 14.2 0.35
0.87–23.2 – 1.05–28.0 –
–92.8...–150 –110 –96.5...–176 –130
6.71–7.17 6.90 6.58–7.56 6.9
Note: Characteristic of groups of bottom sediments is given according to [4].
RESULTS AND THEIR CONSIDERATION Mercury concentration in bottom sediments of the estuarine area of the Northern Dvina River and the Dvina Gulf of the White Sea varied within 0.02–0.80 mg/g of dry mass amounting on average to 0.135 mg/g of dry mass [6, 13]. Very high mercury concentrations were detected in bottom sediments of internal channels crossing the town of Arkhangel'sk. It should be said that these values were excluded from average concentration calculations. Changes in mercury concentration by levels were as follows. In the 0–5-cm layer the mercury content varied from 0.02 to 0.48 mg/g of dry mass, on average it amounted to 0.11 mg/g of dry mass; in the 5–10-cm layer the minimum content was 0.02 mg/g of dry mass, the maximum content was 0.8, the average content was 0.16 mg/g of dry mass. In the upper reaches of the estuarine area of the Northern Dvina River, mercury concentration changed in a narrow interval of values and approached the minimum (0.04–0.05 mg/g of dry mass). At the Port Bakaritsa station, 51 km away from the sea edge of the delta, mercury content in the bottom sediments reached comparatively high values (up to 0.37 mg/g of dry mass). At the next station of Vershina, downstream of the delta, the mercury concentration decreases approximately by 10 times accounting for 0.03 mg/g of dry mass. The mercury content in the bottom sediment of the Solombala Island station increased up to 0.2 mg/g of dry mass. When moving along Maimaksa channel, over the bottom sediment area from the station Port Ekonomiya to the Mud'yugskii Island station, mercury concentration increases from 0.05 to 0.18–0.22 mg/g of dry mass. A special attention, when studying the estuarine area, was given to the Kuznechikha channel with Solombala pulp-and-paper plant on its left bank and thermal power plant (TPP) and cement mill on its right bank. Total mercury in bottom sediments of the Kuznechikha channel changed from 0.04 to 0.21 mg/g of dry mass. The comparison of mercury content near the right and left banks of the Kuznechikha channel shows that total mercury concentration increases near the left bank both upstream and downstream of the point of the waste water discharge by the Solombala pulp-and-paper plant and TPP. The levels increased significantly near the right bank only at Lesozavod No. 29 station (it is the maximum for the Kuznechikha channel). The station is located much down the stream, undergoes the influence of waters from the Yuras channel, which according to several indicators is the most polluted body. Here, one of the highest mercury concentrations in the water, both in the surface and in the near-bottom layers, is detected [12, 16]. In the 5–10-cm level of bottom sediments, the maximum and average total mercury content is approximately 1.5–2 times larger than at the upper level. This can be indicative both of favorable conditions of accumulation of the metal and its compounds during the formation and/or redistribution along the bottom sediment section and of mercury income from the upper sediment level to the water column when hydrochemical conditions change. RUSSIAN METEOROLOGY AND HYDROLOGY
Vol. 35
No. 9
2010
BOTTOM SEDIMENTS AND THEIR ROLE
613
Fig. 1. A total mercury distribution (mg/g of dry mass) in bottom sediments of the estuarine area of the Northern Dvina River at levels of (a) 0–5 cm and (b) 5–10 cm. (1) >0.3; (2) 0.2–0.3; (3) 0.1–0.2; (4)
