Tuesday, 23 November 2021

Rogoznica Dragon's Eye Lake Becoming Nationally Protected Nature Monument?

November 23, 2021 – Šibenik-Knin County assembly is formally launching the process to obtain the official protected status for Rogoznica Dragon's Eye Lake

On the shores of Šibenik-Knin County, a dragon is stirring. For as long as anyone can remember he has slept here. Famously, he rests next to the Adriatic and Marina Frapa, one of the most beautiful yacht harbours of the Mediterranean. Indeed, this giant - Rogoznica Dragon's Eye Lake - is one of the most iconic natural features of the mainland's coast.

He's at least 10, 000 years old, so local residents are used to having him around. However, he's recently become a lot more famous for two distinct reasons.

104171346_10158257158665930_2444010874871502806_n.jpg© Vlado Franolić

Firstly, the rise in drone photography has successfully unlocked the startling beauty Rogoznica Dragon's Eye Lake gifts this varied landscape. Secondly, over the last two decades a successive stream of scientific researchers have arrived to study these unique waters. They have poked and prodded, taken samples and photos. Their published findings have lead to the current awakening. Rogoznica Dragon's Eye Lake now looks set to become a nationally protected Nature Monument.

Today, 23 November 2021, Šibenik-Knin County assembly is formally launching the process to obtain the official protected status for Rogoznica Dragon's Eye Lake. Classification as a Nature Monument (Spomenik prirode or prirodna baština in Croatian) is sought to preserve the original natural values of a place or object. The protection is awarded because of the rarity, uniqueness or beauty of a natural monument, its value to science or its value to surrounding ecosystems. Rogoznica Dragon's Eye Lake meets each of those criteria.

Rogoznica Dragon's Eye Lake aka Zmajevo oko jezero

Autor-Dream-Division-Split-1_1600x900_0.jpg© Dream Division Split / Rogoznica TZ

This elliptical-shaped lake was formed after the end of the last ice age. After all the ice melted, sea levels rose a massive 100 metres. When that happened, the Adriatic penetrated through cracks in the wall of a sinkhole located on the Gradina peninsula. The sinkhole became Rogoznica Dragon's Eye Lake.

The lake has a maximum measured depth of 15 metres. It is surrounded on all sides surrounded by vertical rocks that range between 4 and 24 metres in height. These walls protect a unique hydrological and geomorphological phenomenon and ecosystem.

Below the water surface, the lake is connected to the open sea by a large cave. At the bottom of the lake is a thick bottom layer of hydrogen sulfide. This creates an environment that is, in parts, extremely low in oxygen. It also produces a meromictic lake - one which has layers of water that do not usually intermix.

This combination creates a challenging but unique set of conditions for the sea creatures and plants that inhabit the lake. Although, for the former, their residence can be somewhat transitory. From time to time, the lake waters become uninhabitable. Its sea creatures are forced to leave the lake en masse and head out into the open seas. They only return when the lake waters are purified.

To people of the locale, Rogoznica Dragon's Eye Lake has held a fame long before the drone cameras and scientists arrived. Myth and legend surround the lake and its formation. Some believe the sinkhole is actually a crater left by a falling meteor. Others say that long ago, a dragon really used to live here. The awarding of Nature Monument status ensures these entertaining stories will be retold long into the future.

If you want to read more about Rogoznica, read our Total Croatia guide here. And if you want to keep up with news from Šibenik-Knin County, keep an eye on Total Croatia News's tagged pages here

Tuesday, 6 October 2020

Rudjer Boskovic Institute Scientists Explain Loss of Oxygen in Dragon's Eye Lake

As Morski writes on the 5th of October, 2020, Rudjer Boskovic Institute scientists are busy investigating the disappearance of oxygen from the iconic Dragon's Eye Lake in Rogoznica. The Rudjer Boskovic Institute scientists studying the body of water in Rogoznica have recently noticed a change in the colour and smell of the lake. It is the occurrence of anoxia in the entire water column of the lake and the spread of toxic hydrogen sulfide. This natural process is favoured by extreme weather conditions, such as a sudden drop in atmospheric temperature.

Rogoznica Lake, more popularly known as the Dragon's Eye, is a natural phenomenon and a unique marine system in the Adriatic and the Mediterranean region. Recently, due to its physico-chemical and biological characteristics, it has been included on the map of about a hundred permanently stratified, anoxic (oxygen-free) and euxinic (free toxic sulfide in the water column) lakes in the world.

The main characteristic of the lake is seasonal stratification into an upper oxic layer, a middle layer or a chemocline coloured in purple, and a bottom anoxic layer characterised by complete darkness (due to there being absolutely no presence of light) and high concentrations of toxic ammonia and sulfide.

''Recently, the lake has suddenly mixed again, has become blurred, the smell of rotten eggs has spread, and the lake has changed from its usual transparent greenish-blue colour of the surface to an opaque greenish-gray. During the mixing of the water 'slayers, sulfide evaporation and oxidation has occurred in the lake, as well as the formation of polysulfide and elemental sulfur, which, due to high concentration and low solubility, appears in colloidal form, ie sediment in the water column, which changed the transparency and colour of the lake.

The process of mixing and oxidation of sulfides consumed all the oxygen in the lake, and the lake, as of the 27th of September, 2020, has remained completely oxygen-free. Such a condition has caused the death of  theflora and fauna,'' explained Dr. sc. Irena Ciglenecki-Jusic, Head of the Laboratory for Marine Physics and Water Systems Chemistry of the aforementioned institute.

This state of anoxia in the entire water column has been recorded three times so far, in September 1997, October 2011, and more recently in 2016. The lake has been the subject of natural science research by Rudjer Boskovic scientists in collaboration with colleagues from the Faculty of Science, University of Zagreb, the Centre for Sea and Coast in Dubrovnik and the Split Institute of Oceanography and Fisheries, as well as a team of international colleagues since way back in 1990.

The occurrence of anoxia in the entire water column of the lake is a natural process that occurs at irregular time intervals depending on the weather conditions. It is affected by extreme weather conditions, such as a sharp drop in the temperature of the atmosphere, which suddenly cools the salty surface layer of water. This layer of water sinks and mixes with water below which is rich in sulfide. In the last ten years, such sudden changes have become more frequent - scientists say.

''The recovery of the lake is long-lasting, especially in terms of biology, while the chemical processes more or less returns to the way it was within a month or so. According to current knowledge, biological recovery takes several years, but then there is re-mixing and that same life cycle starts all over again. However, it always begins from a new starting point, which is especially interesting for further specific research,'' explained Dr. Ciglenecki-Jusic.

The lake is considered a natural laboratory for monitoring changes in the environment, and in recent times has proven to be ideal for monitoring the transport and delivery of desert dust from the Sahara to the central Adriatic.

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