Some IGERT members have formed a small paper discussion group on the resilience and management of saline systems. These unique systems exist both in Nebraska and Austria, and we are curious about how the two compare. Two different threats related to salt and aquatic systems are predicted to become more serious in the coming decades: the loss of naturally saline lakes, and the anthropogenic salinization of freshwater lakes. We will visit examples of both of these situations in Austria. First, we visit a freshwater system influenced by salt.
Members of the saline systems discussion group travel to Hallstatt, in the western part of Austria near Salzburg. Hallstatt is part of the Salzkammergut, or “salt kingdom,” where salt has been mined for thousands of years, providing the region with economic stability and a vital natural resource. The region is also characterized by several freshwater lakes. Our mission is to learn more about how these two natural resources coexist and their socio-economic connection.
The town of Hallstatt seems tiny from the ferry, hugging the shores of the lake Hallstättersee and creeping up the surrounding mountains. The town has about 1,000 permanent inhabitants. Every morning, two fishermen cruise the lake with nets and return with the catch of the day for the locals and restaurants to prepare for dinner. Swans, introduced to the lake to please Empress Elisabeth when she would vacation here; today they cruise the lake looking for handouts from the peasant tourists.
We ascend a nearby mountain to visit the local salt mine. Hallstatt has been a mining center since about 7,000 years ago, and this is thought to be the oldest salt mine in the world. Neolithic people mined the salt to preserve meat; this area became one of the first known human settlements, and its archaeological importance is recognized by an era of time named after it (Hallstatt Era 800-400 BC).
|Roman ruins underneath a sports shop in town.|
We enter the salt mine through a tunnel dug in the 1700s, and descend to where the salt is located. The salt was deposited in layers from seawater periodically evaporating during the Mesozoic Era. The deposit is rich with iron from the seawater, giving the salt a red color. (Thanks to the guide for being so patient with all of our geology questions!)
|Entrance to the salt mine.|
|Salt deposits in the mine.|
The mine has continuously functioned through the millennia. The mining techniques adapted with technology, and today the salt is mined by being dissolved into water under pressure. The salt is then transported as brine through pipes 40 km to the town of Ebensee, where it is placed in evaporative pools to extract the salt.
|The evolution of brine pipes.|
|An old brine pipe.|
The system is so efficient that the mine only employs 28 workers total. Because of the loss of jobs in the mining industry, young people have left town for opportunities elsewhere; the population has shrunk by half, and many of the houses have become rental properties for tourists.
Hallstättersee receives wastewater discharges from the mine through one of its tributaries. On two occasions in the last few decades, the brine pipes burst leaks, releasing large amounts of brine into the lake. News reports suggested that the brine sank to the bottom immediately and therefore had no impact on the lake; we were interested in the effects of sudden intense additions salt on the benthic ecosystem. Our discussion papers found that the brine spills caused ectogenic meromixis (the lake stops mixing during “turnover” periods) and hypoxia (low or no oxygen) in the deeper regions of the lake which showed temporary die-off of benthic fauna. Even though one brine spill was much larger than the other, the lake took the same amount of time to recover from the shock by flushing the salt out of its basin (3 years, or 6 times its water residence time).
As far as we can tell, culturally and economically, though the lake is beautiful, here salt is king. The lake is lucky that it has the natural ability to respond quickly to the occasional “oops” of large brine spills, because the salt isn’t going anywhere soon.
(Photos by Victoria)