Assessment of Ecological Importance and Anthropogenic Change of Subaquatic Springs in Ancient Lake Ohrid

Biljana Jordanoska1, Trajče Stafilov1 and Alfred Johny Wüest2

 

 

1 Institute of Chemistry, Faculty of Science, SS. Cyril and Methodius University, Arhimedova 5, 1000 Skopje, Macedonia, e-mail: This e-mail address is being protected from spambots. You need JavaScript enabled to view it

2 Eawag, Swiss Federal Institute of Aquatic Science and Technology, Seestrasse 79, CH 6047 Kastanienbau, Switzerland, e-mail: This e-mail address is being protected from spambots. You need JavaScript enabled to view it

 

 

Abstract

Apart from their contribution in the water balance of Lake Ohrid, Republic of Macedonia, subaquatic springs are also expected to affect the water quality. A simple experiment was developed and applied to subaquatic spring in Kališta region (south-east of Kališta village, in the north-western part of the Lake) and at the spring at Veli Dab (eastern side of the Lake) based on physicochemical spring water properties. Different sampling methods were established with the aim of uncovering a more suitable way of sampling pure subaquatic spring water. The goal was to test these findings and adapt them for further analysis with higher temporal and measurement related resolution. Measurements were also aimed at gathering additional knowledge and methodology for characterizing the hydrogeology of the watersheds. Of interest was information on the general chemical composition of spring water, interactions between aquifer and groundwater and on the origins of groundwater. Integration of this knowledge adds to a better understanding on how and what kind of groundwater is delivered to Lake Ohrid. The obtained results show that the examined springs are rich in nutrients and, comparing to Lake water, exhibit temporal variations in temperature, pH, conductivity and dissolved oxygen. Investigated springs have a very constant flow, as well as water quality.

Keywords: Lake Ohrid, subaquatic springs, sampling, water quality

 

 

Introduction

 

Lake Ohrid is located in the central Balkan Peninsula (Southeast Europe) on the border between Albania and Macedonia. With a maximum length and width of 30.3 and 15.6 km, respectively, the lake covers a surface area of 358 km2, reaches a maximum depth of 288.7 m and a volume of 55 km3 (Table 1, Figure 1). With a limnological age of likely 4 to 10 million years, it is one of the oldest lakes in Europe (Wagner, 2008). Lake Ohrid is a steep-sided graben of rift formation (Albrecht, 2008a).

Different to most other inland waters, Lake Ohrid is mostly fed by subaquatic and surface springs which play a significant role in the formation of this unique system. From a water balnce poit of view, an inflow ratio of ~50% of total spring discharge into Lake Ohrid was estimated which equals to estimated ~25% of total inflow for subaquatic springs (Matzinger et al. 2006b). Upstream Lake Prespa (Figure 2) discharges lake water by underground flow which feeds certain springs in the Lake Ohrid region.

Spring lakes systems are very unique and special ecosystems. The specific ecology of Lake Ohrid reflects conditions of its catchment, its eco-climatological setting and is strongly dependent on subaquatic springs (Matter et al., 2010).

The important role of subaquatic springs in the Lake's development has been mentioned in other lakes, such as Lake Kivu, Lake Cadagno (Tonolla et al., 2005, Schmid et al., 2010). Lake Ohrid is an oligotrophic lake; it is inhabited with more than 200 endemic and relic forms of organisms. 

Clearly the most spectacular quality of the Lake is its impressive endemism and subaquatic springs which contribute to and support its biodiversity, as several endemic organisms are found exclusively close to the springs (Stanković, 1960; Šapkarev et al., 1988; Salemaa, 1994).

While considerable knowledge has been acquired on various aspects of the Lake Ohrid ecology over the past decades, the subaquatic springs were not considered, as their existence is only known from a few recent observations and from indirect water balancing (Wüest, 2005). Knowing a small catchment area of the Lake it can be presumed that subaquatic springs are numerous, but their distribution is unknown. In shallow zones, several subaquatic spring inflows have been described in the past (e.g., Gilbert and Hadzisce 1984). In recent years, subaquatic spring inflows were also detected at large depths (Matzinger and Wüest 2004). Input of pure spring waters (Matzinger et al., 2006a; Jordanoska et al., 2010, 2012) is important for the oligotrophic status of Lake Ohrid and its subsequent low algae productivity. All previous findings postulate that the subaquatic springs have a significant influence on the overall physicochemical properties of Lake Ohrid by supplying nutrients and dissolved oxygen at different depths and by creating distinctly different, but constant boundary conditions for the organisms near the springs.

Explanation of hydrogeological relations, correlation and circulation of subaquatic spring water is very difficult task, and sometimes includes a lot of assumptions. Although contribution of these springs to the water balance the Lake Ohrid has been calculated, there is still little knowledge on the physics and chemistry of water that seeps from the lake floor. Very little is known about the flux in the seepage of such water, the path and processes that it passes. Because of theirs complex flow paths, difficult collection and limited in depth analysis, little data exists that would identify springs of conservation concern, although rare species associated with springs have been detected.

The objective of this paper is to describe the experimental observation that uses physicochemical data to improve localization and characterization of subaquatic springs and its hydrology as well as best and uniform way of sampling the pure spring water. It was shown that these springs presented temporal variations in temperature, pH, conductivity and dissolved oxygen (DO) compared to lake water (Kunz, 2006), so these parameters were used as tracers by vertical profiling in the water column. The physical characterization of subaquatic springs involves mainly their influence on local turbulence and stratification, as well as the horizontal distribution of spring water, the sources and factors controlling ground water and surface water quality including a discriminating natural background and anthropogenic impact. Characterization of the subaquatic springs is an important contribution for protection and preservation of Lake Ohrid. Here, we present the basic physicochemical compo­sitions of two different spring waters, and the potential implications on aquatic organisms living nearby.

 

Table 1: Characteristic of Lake Ohrid and its water balance (Matzinger et al., 2006b)

Tab01

 

Fig01

Figure 1: Map of Lake Ohrid.Bathymetry with 25 m contour intervals and marked surface and subaquatic sources (Albrecht, 2008)

 

Fig02

Figure 2: Ohrid and Prespa Lakes and their watershed boundaries (Gorsevski, 2008)