Lake Tovel: A Natural Laboratory between Ecology and Evolution
The mysterious story of the red waters that disappeared, revealing complex ecological interactions
Introduction: The Mystery of the Red Waters
In the dark waters of an alpine lake, for much of the twentieth century, a biological mystery unfolded that would fascinate scientists and visitors for decades. Lake Tovel, located in the heart of the Adamello Brenta Nature Park in Trentino, is not only a scenic jewel with crystal clear waters, but a true natural laboratory where ecology and evolution have written an extraordinary chapter.
Until 1964, during warm summers, the lake turned a vibrant blood-red color, a spectacular phenomenon that inspired legends and, subsequently, in-depth scientific investigations 1 2 .
Today, the disappearance of that phenomenon tells us an even more fascinating story about how ecosystems respond to environmental changes of natural and anthropogenic origin.
Location
Adamello Brenta Nature Park, Trentino, Italy
Size
370,000 m² surface area at 1,178 m altitude 1
The Environmental Stage: A Unique Ecosystem
Origins and Physical Characteristics
Lake Tovel is the largest natural basin within the Adamello Brenta Park 1 . Its basin was formed from glacial origins, later shaped by a major landslide that, obstructing the outflow stream, widened the basin by submerging an ancient forest .
Even today, on the lake bottom, the trunks of that ancient submerged forest are visible, a silent testimony to the geological dynamics that continue to characterize this environment .
The crystal clear waters of Lake Tovel today
Life in the Lake
Despite the cold waters and winter freezing period, the lake hosts a surprisingly rich biological community. Among the fish species are the Arctic char (Salvelinus alpinus), the Minnow (Phoxinus laevis) and the Bullhead (Cottus gobio) 3 .
Arctic Char
Salvelinus alpinus
Minnow
Phoxinus laevis
Mountain Frog
Amphibian species
Tovellia Sanguinea: The Protagonist of an Evolutionary Drama
Scientific Discovery
For decades, the reddening phenomenon remained shrouded in mystery. The first documented reports date back to the English mountaineer Douglas William Freshfield in 1864, who noted: "In the center, the water is dark blue like an Egyptian night; around the edge, the fallen pine trunks are scattered disorderly on the bottom and tinge the edge of the lake with an intense red" 3 .
Only in the late 1930s, after years of research, was the culprit identified with certainty: an alga, initially named Glenodium Sanguineum and later renamed Tovellia sanguinea 2 6 .
Tovellia sanguinea
Dinoflagellate algae responsible for the red coloration
Adaptive Evolutionary Mechanism
Tovellia sanguinea is not a simple pigment, but the result of a sophisticated evolutionary adaptation. This alga, to protect itself from the strong ultraviolet radiation typical of high altitudes, produces an oil rich in carotenoids 2 .
These pigments, which spread in the water when the alga blooms in large quantities, are the same that color carrots and autumn leaves, and give the lake its characteristic blood-red tint 2 .
The phenomenon was triggered when the surface water temperature reached its peak during the hottest summer hours, creating ideal conditions for the massive reproduction of the alga 2 6 .
Adaptation Mechanism
UV Radiation
High altitude exposes the lake to intense ultraviolet radiation
Algal Defense
T. sanguinea produces carotenoid-rich oils as protection
Blooming
Mass reproduction during warm summer days releases pigments
Red Coloration
Carotenoids spread through water, creating the red lake effect
The Natural Experiment: The Disappearance of the Red
Hypothesis and Observation
1964 marked a turning point: from that year, the reddening phenomenon occurred irregularly, then disappeared completely around the 1980s 2 . The disappearance of such a conspicuous event created a unique natural experiment, allowing scientists to study complex ecological interactions.
For years, the most credited hypothesis was that of pollution caused by urban settlements 2 .
Timeline of the Red Phenomenon
Discovery of the True Cause
It was only around the 2000s that more in-depth studies revealed the true cause. Research demonstrated that livestock grazing around the lake, practiced intensively until the 1960s, played a fundamental role.
Livestock excrement, rich in nitrogen and phosphorus, constituted a natural fertilizer that, washed into the lake, provided the essential nutrients for the massive reproduction of Tovellia sanguinea 2 8 .
When grazing was interrupted, these nutrients were lacking, depriving the alga of its ecological "fuel" and preventing blooms of sufficient intensity to color the lake 1 6 .
Comparison of Ecological Conditions Before and After 1964
| Factor | Red Period (Until 1964) | Current Period |
|---|---|---|
| Livestock Presence | Intensive grazing 2 8 | Absent or minimal grazing 1 |
| Nutrient Input | High (nitrogen and phosphorus from excrement) 2 8 | Low 8 |
| T. sanguinea Bloom | Massive and visible 1 | Present, but minimal and not visible 6 |
| Lake Color | Blood red in summer 6 | Blue-green 1 |
Research Methodologies and Scientific Tools
The study of Lake Tovel and its ecosystem required the use of various scientific disciplines and cutting-edge methodologies.
Limnological Monitoring
Limnological monitoring represents the heart of research on the lake. Scientists conducted seasonal sampling of water to track fundamental physical-chemical parameters. This practice allowed establishing a direct correlation between the cessation of grazing, the decrease in nutrients, and the decline of algal blooms 2 8 .
Key Parameters Monitored in Lake Tovel
| Parameter | Measurement Method | Ecological Significance |
|---|---|---|
| Nutrient Concentration (N/P) | Chemical analysis of water samples | Determines primary productivity and algal bloom potential 8 |
| Tovellia sanguinea Biomass | Microscopic counting and DNA analysis | Directly indicates the extent of the population of the red-causing alga |
| Water Transparency (Secchi Disk) | Secchi disk | Measures water clarity, influenced by plankton and sediments |
| Surface and Deep Temperature | Multiparameter probes | Determines lake stratification and preferred habitat of T. sanguinea 2 |
Genetic and Taxonomic Analysis
Molecular biology techniques were crucial for accurately identifying the responsible organism. DNA analysis confirmed that the alga Tovellia sanguinea is a dinoflagellate, a microorganism known for its blooms, sometimes toxic, in marine and aquatic environments .
Study of Historical Archives
A fascinating aspect of the research was the use of archival sources. At the Mountain Library of the Society of Trentino Alpinists (SAT), precious historical testimonies were traced, such as the article by mountaineer Nepomuceno Bolognini from 1875 and the translation of Freshfield's work, which helped date and describe the phenomenon in the 19th century 3 .
Scientist's Toolkit - Materials and Reagents for Research
- Multiparameter probes - Measure in situ temperature, pH, dissolved oxygen, conductivity
- Plankton nets - Collection of phytoplankton and zooplankton samples from different depths
- DNA extraction kits - Isolate genetic material from planktonic organisms for identification
- Optical and electron microscope - Identification and counting of algal species, study of cell morphology
- Spectrophotometer - Measure chlorophyll-a concentration and nutrients in water samples
- Historical archives and satellite data - Provide long-term temporal context and analysis of land use changes
Conclusion: A Disappeared Phenomenon, A Lesson That Remains
The story of Lake Tovel is much more than the simple chronicle of a disappeared chromatic phenomenon. It is a powerful case study on how an ecosystem responds in a complex and interconnected way to changes, whether natural or anthropogenic.
The alga Tovellia sanguinea is not extinct; it still survives in the lake waters, a living relic of a not-too-distant past . Its story teaches us that the balance of ecosystems is delicate and dynamic.
Today, Lake Tovel, with its crystal blue-green waters, remains an open-air laboratory for the study of biodiversity conservation and the effects of climate change 7 . Its legend, that of Princess Tresenga whose blood tinged the waters, continues to live on 2 8 .
Lake Tovel Today
While the red phenomenon has disappeared, the lake continues to be an important site for ecological research and conservation efforts in the Alpine region.
But perhaps, the most fascinating story is the real one, told by science: the story of a tiny alga that, feeding on the waste products of mountain domestic life, wrote one of the most incredible pages of Alpine ecology.