Why Is Lake Ohrid So Clear?

In dreams, clarity is the ability to see and explore, to experience miracles beyond normal consciousness. Possibilities expand into strange, wonder-filled forms as the rules of existence follow alternative paths to unexpected conclusions.

In UNESCO Lake Ohrid, clarity has the same effect. But the lucid dream becomes a full, active reality.

Light and Depth

The ancient symbol of life, light travels distantly in Lake Ohrid. Water transparency stretches up to 21m [1], and the lake’s euphotic zone — the area receiving enough light for photosynthesis — extends down to 150m due to its exceptional purity [2]. While the water is always thrillingly  clear, the winter months offer the greatest clarity [3].

Yet the story doesn’t end there. Light’s deep dive into Lake Ohrid opens entire habitats for wildlife to exploit. Different species have been able to evolve and adapt to underwater spaces that wouldn’t be viable in less light-filled lakes, creating new opportunities for the development of life on Earth [4].

A photon’s journey beneath Lake Ohrid’s waves is therefore into a world of its own making…

Ljupco Lepi 19

Beautiful Freak

But why is Lake Ohrid so deliciously pristine? Ironically, water clarity is not such a transparent topic. Many diverse factors can  impact the clearness of any lake from comparative waviness to whether the water is dyed by surrounding soils. As we have seen, it even varies by season.

Yet one reason makes Lake Ohrid stand out: its beautifully freakish inflow. Unlike many inland waters, comparatively little liquid supply comes overland from sediment-shouldering rivers — less than 10% before the River Sateska was diverted in the 60s [2]. Instead, the biggest individual sources (more-or-less 50%) are rare and mysterious underground pathways that run through karstic Mount Galichica on the lake’s eastern shore and emerge as coastal and sublacustrine springs.

These subterranean channels bring waters from both rainfall and Lake Ohrid’s sister, Lake Prespa, on the other side of the mountain, but they store away some of the waters’ nutrients (about 65% of phosphorous) along the way [5]. By doing so, they help to hold back a process known as eutrophication, which can instigate algal growth and cause water clarity to diminish. At the same time, by running through underground rock, water avoids accumulating some of the impurities that an overground journey would risk.

Ljupco Lepi 18

It’s a fine balancing act. If all the nutrients were blocked, there would have been little to support the creation of Lake Ohrid’s rich underwater world over the past thousands of years [4], especially at the springs, which are often micro-metropolises for unique species [6]. Luckily, although it cannot be expected to protect Lake Ohrid alone, the underground filter system so far judges things pretty well [5], shielding enough nutrients to prevent severe overload but not so many that it disrupts ecosystems.

The spring system has another trick up its sleeve too. Entering the lake, the spring waters are cold so they tend to plunge deep in summer, which takes those limited nutrients away from the surface level, where they would otherwise set off light-blocking processes. This contrasts with the rivers, whose water often flows in at a higher level [3].

And the story doesn’t end there. Alongside karstic channels that deliver premium-grade water through Mount Galichica to bubble up in Lake Ohrid springs, the elite natural infrastructure for water clearness also includes Studenchishte Marsh, which acts as an additional buffer to prevent overenthusiastic nutrients entering the lake[7].

The consequence is optimum clarity for beauty and wildlife both, just like in an incredible dream…

References

  1.  M. Talevska, D. Petrovic, D. Milosevic, T. Talevski, D. Maric & A. Talevska (2009) Biodiversity of Macrophyte Vegetation from Lake Prespa, Lake Ohrid and Lake Skadar, Biotechnology & Biotechnological Equipment, 23:sup1, 931-935.
  2. Matzinger, A., Schmid, M., Veljanoska-Sarafiloska, E., Patceva, S., Guseska, D., Wagner, B., Muller, B., Sturm, M., and Wuest, A. (2006) Eutrophication of ancient Lake Ohrid: Global warming amplifies detrimental effects of increased nutrient inputs, Limnol. Oceanogr., 52, 338–353.
  3. Matzinger, A., Spirkovski, Z., Patceva, S., Wuest, A. (2006) Sensitivity of ancient Lake Ohrid to local anthropogenic impacts and global warming. Journal of Great Lakes Research 32: 158—179.
  4. Matzinger, A. (2006) Is anthropogenic nutrient input jeopardizing unique Lake Ohrid? – Mass flux analysis and management consequences, Doctoral Thesis submitted to the Swiss Federal Institute of Technology Zurich.
  5. Matzinger, A.,  Jordanoski, M., Veljanoska-Sarafiloska, E.,  Sturm, M., Müller, B. , and Wüest, A. (2006) Is Lake Prespa jeopardizing the ecosystem of ancient Lake Ohrid? Hydrobiologia 553:89–109.
  6. Jordanoska, B., Stafilov, T., Wüest, A. (2013). Assessment of ecological importance and anthropogenic change of subaquatic springs in ancient Lake Ohrid. Water Research and Management, 3(2): 9-17.
  7. Albrecht, C. and Wilke, T. (2015) Lake Ohrid – A Paradise in Peril (article for Fokus magazine)

Main Photo: Kliment A. Inline Photos: Ljupco Lepi

 

 

 

 

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