doi:10.3723/ut.31.167 Underwater Technology, Vol. 31, No. 4, pp. 167–177, 2013 www.sut.org per Environmental properties of the water-filled Ojamo limestone quarry, southern Finland 1,2 2 1,3 1 2 Ari Ruuskanen* , Kimmo Karell , Solomon Viitasaari , Lari Järvinen and Pirkko Kekäläinen Pa Technical 1Luksia, Adult Education Institute of Western Uusimaa, 08100 Lohja, Finland 2University of Helsinki, Tvärminne Zoological Station, 10900 Hanko, Finland 3University of Helsinki, Department of Environmental Sciences, PO Box 65, Viikinkaari, 00014 Helsinki, Finland Abstract taken place (Ejsmont-Karabin, 1995). As a result of The present paper presents a survey of the water-filled the decomposition of organic material, anoxia and Ojamo limestone quarry, located in southern Finland and H2S formation may occur in the benthic region, abandoned c. 40 years ago. In order to estimate the bio- especially if water exchange and mixing is restricted geological state of the quarry, the geological and hydro- (Galas, 2003). graphic properties were measured, and phytoplankton and The Ojamo limestone quarry was abandoned in zoobenthos sampling was carried out by SCUBA diving. 1965. The quarry consists of an open-pit area and a Ojamo can be considered to be mesotrophic. The zoo- vast network of tunnels. After abandonment the benthos was lacking bivalves and insects. The Ojamo water mine slowly filled with groundwater and rainwater body had good oxygen values owing to its connection to the run-off, creating an artificial lake basin. The mine groundwater. has been submerged for more than 40 years. Dur- ing this period the aquatic flora and fauna have Keywords: quarry, limestone, SCUBA, hydrography, phyto- undergone succession. Biological properties in terms plankton, scientific diving, zoobenthos of benthic fauna, phytoplankton and hydrographic measurements of this artificial lake have not been 1. Introduction studied before. The present study examines the ecological state Abandoned quarry sites are often filled with ground- of the Ojamo quarry. Hydrographic properties of water and rainwater drainage, leaving behind an the water column and biota were measured in terms artificial lake basin. These man-made lake systems of phytoplankton and zoobenthos composition, as have been studied to document species assem- well as sediment type. blages and limnological properties (Cowell, 1960; Bogaert and Dumont, 1989; Shevenell et al., 1999; Galas, 2003; S´lusarczyk, 2003). 1.1. Site description Despite their artificial origin, the quarry reser- The Ojamo limestone quarry, N60°14,375’ voirs can display similar hydrographic properties E24°02,068’ (WGS84), is part of the Uusimaa Schist known to natural lakes, such as thermal stratifica- zone, which is formed by leptitic rocks and sedimen- tion (Cowell, 1960; Whittier et al., 2002; S´lusarczyk, tary carbonites (Kähkönen, 1998). Ojamo limestone 2003). However, the geomorphology left behind by is heterogeneous, and between the limestone layers previous mining processes shows strong differences lie silica-rich layers, as well as granite and amphibo- between quarry reservoirs and natural lakes, and lite dikes. The layers are thin, as is the whole forma- ultimately affects sediment type. Before submer- tion (Parras and Tavela, 1954). The main rock type sion by water, the quarry area undergoes a succes- of the mine area is coarse-grained calcitic limestone, sion of terrestrial plants (Davis et al., 1985). This is mostly composed of calcium carbonate (CaCO3). followed by a succession of aquatic flora and fauna The mine consists of an open quarry area and and, possibly, eutrophication status after filling has closed caves. Morphometric characteristics of the open part of the quarry are shown in Table 1. Below * Contact author. E-mail address: [email protected] the open-pit part of the mine, former mining shafts 167 Ruuskanen et al. Environmental properties of the water-filled Ojamo limestone quarry, southern Finland Table 1: The morphometric characteristics of the Ojamo quarry by terrestrial plants, such as trees and vegetation, Area 60,000m2 which formed small patches of forest. These 3–5m Length (max.) 312m tall trees are currently submerged but are still in Breadth (max.) 100m an erect position and hold foliage. The open quarry Max. depth (open part) 40m area has also been filled with aggregate, both Shore line 900m before and after being submerged. Dredging and Altitude above sea level 72m other construction work has been conducted in the area during the last 10 years also. The bottom of form a network spanning tens of kilometres in the lake is heterogenic in terms of geological mor- length altogether and reach a depth of 238m. The phology and sediment type. Primarily, the sediment shafts allow for groundwater upwelling to the open consists of solid and fragmented rocky bottom along part of the mine. The surface drainage area of the with patches of soft bottom in areas of former, more lake is small because of high relief. The open part or less decomposed, terrestrial vegetation. is divided into two semi-isolated areas by an old Temperature and light conditions of the water mine road which forms a wall reaching up to the body show seasonal variation. In winter, from depth of 0.5m (Fig 1). The Ojamo quarry site serves November to March/April, surface temperature as a training site for Finnish professional and sci- varies from 0°C to 2°C. There are, however, differ- entific diver programmes. Training takes place all ences depending on location. The rim parts of the year round. cave receive permanent ice cover, but the centre stays Before being abandoned and becoming filled with open on mild winters. This is because of an inflow water, the Ojamo mine was exposed to occupation of 4–5°C groundwater from tunnels located in the (a) 50m (g) O2 (mg/l) 012345678910 Submerged 0 (0.5m) mine road (h) O2 (mg/l) 1 I 0 1234 4 4,1 4,2 O 2 2 O2 (20m) 4,3 4,4 II VI (5m) 3 4,5 Depth (m) (30m) 4,6 III 4,7 4 4,8 Depth (m) T (5m) IV 4,9 N 5 5 V 5,1 0510 15 20 25 5,2 Temperature (ºC) 5,3 (b) (c) (d) (e) (f) O2 (mg/l) O2 (mg/l) O2 (mg/l) O2 (mg/l) O2 (mg/l) 012345678910 012345678910 012345678910 012345678910 012345678910 1 1 1 1 1 3 3 3 3 3 5 5 5 5 5 7 7 7 7 7 9 9 9 e 9 9 11 11 11 11 11 13 O 13 13 13 13 15 2 15 15 15 15 17 17 17 17 17 19 19 Depth (m) 19 19 Depth (m) 19 Depth (m) Depth (m) Depth (m) 21 Temperatur 21 21 21 21 23 23 23 23 23 25 25 25 25 25 27 27 27 27 27 29 29 29 29 29 31 31 31 31 31 0510 15 20 25 0510 15 20 25 0510 15 20 25 0510 15 20 25 0510 15 20 25 Temperature (ºC) Temperature (ºC) Temperature (ºC) Temperature (ºC) Temperature (ºC) Fig 1: (a) Bottom contours of the lake are shown with dashed lines, the number values in parentheses depicting the approxi- mate depth of a given area. Tunnel entrances are marked by the solid thick arrow. The graphs (b)–(h) display the levels of dissolved oxygen and temperature, and their relation to depth in 1m intervals. The line portraying the sampling location within the lake and roman numerals (I–VI) are symbols of the sampling points. Graph (h) represents a subsection of the graph (g) and illustrates the decline of dissolved oxygen concentration in 10cm intervals to point out extreme conditions. The grey area illustrates area of submerged forest 168 Underwater Technology Vol. 31, No. 4, 2013 middle part of the quarry (Fig 1). In March to April type of sampling carried out are shown in Table 2 when the air temperature rises, the surface water and Fig 1. All the samples were collected between warms, exceeding 24°C in July. During summer, a 26 and 30 July 2010. thermal stratification occurs at the depth of 10–15m. As a result of the submerged forests, a steep vari- Below the thermocline in the deepest part of the ation in geomorphology and a heterogenic bottom quarry, water temperature remains around 5°C. type, it would have been difficult to operate effectively A Secchi depth exceeds 13m during winter the traditional surface-operated sampling devices months from December to February and starts to in most areas of the benthos. Therefore, SCUBA decrease in March to April. This is because of the diving techniques were used to collect samples for turbidity from the inorganic material which flows qualitative measuring. with the surface run-off from melting snow into the Before sampling, several dives were executed to quarry. During the summer season from May to check the bottom quality in order to choose suita- August, the Secchi depth varies between 2m and ble sampling devices. Since the bottom was muddy 4m, depending on the intensity of the phytoplank- in some locations, buoyancy control was found to ton production. Fig 2 illustrates the development be imperative in maintaining the visibility and the of surface temperature and Secchi depth from bottom undisturbed. February to April 2010. When sampling, bottom guidelines were laid – The origin of the water in the quarry is most a method obtained from cave diving techniques – likely groundwater. The quarry has no clear inflow to orientate when carrying the sampling devices. sources. It is uncertain if there is a connection to The dives were made as buddy dives. Basic sam- Lake Lohjanjärvi, which is located above the mine plings took approximately 20 minutes each. Air was tunnel network.