Lagoa das Sete Cidades
Encyclopedia
Lagoa das Sete Cidade is a twin-lake
situated in the crater of a massive crater on the Portuguese
archipelago
of the Azores
. It consists of two ecologically-different small-lakes connected by a narrow passage (and crossed by a bridge), located inside a dormant volcano
on the western third of the island of São Miguel
. The Lagoa das Sete Cidades part of a natural landscape of communitarian interest: it is the largest body of water in the region and one of the most important freshwater resources in the archipelago.
and sorcerer
, who lived exclusively for his daughter, Antília, and who would not let the Princess speak to anyone. Apart from the King, the Princess was raised by an old nurse, after the Queen had died. As the years progressed, the princess grew-up to be a beautiful young woman and able to attract the attentions of any boy in the kingdom. However, the King restricted her movements to the castle and garden, and few ever saw her. But, un-intimidated by her father, and with the help of the nurse, she escaped to the local hills and valleys, as her father slept after his lunch. During one of her escape adventures, she heard a song: the music was beautiful and enchanted her to follow it to its origins. Hiding from view, the princess found a young shepard playing a flute, sitting on top of a hill. For weeks she returned, listening to the young shepard, until she was discovered behind some bushes. The shepard boy fell in love with the princess, and they continued to meet afterwards, talking, laughing and enjoying each other's company, until the boy decided to ask the princess in marriage.
Early in the morning, the couple knocked on the door of the Castle, and asked the servants to speak to the King. Very nervous but determined, the shepard asked the King for his daughter in marriage. Reacting angrily, the King refused and expelled him from the Castle, and forbade his daughter from seeing the young boy. Not wishing more ill-feelings, she followed the orders of her father, but met secretly with the shepard that afternoon in order to tell him that he would never see him again. Antília and the shepard boy cried all afternoon, embracing, and their tears formed two beautiful lakes, one green, for the Princess's eyes were green, and the other blue, for the shepard's eyes were likewise colored.
, pyroclasts
and trachyte
and basalt
ic lava
s. It is a stratovolcano
constructed from alternating phases of explosive and effusive ejecta, from dominantly basaltic pre-caldera eruptions, a trachytic caldera-forming stage and a post-caldera stage consisting of alternating trachytic and basaltic eruptions. The caldera-forming eruption was triggered by a basaltic injection into a shallow trachytic magma chamber.
These geomorphological structures allowed varying hydro-chemical properties and produced many types of springs
and water circulation networks (Coutinho et.al., 1996). Generally, formations with good hydrodynamic properties include areas with lava flows, basaltic pyroclasts and/or pumice
, while solidified Ignimbrite
s, conditioned by high temperatures and paleo-soils, such as ash, have produced impermeable conditions. The aquifers are dependent on reduced permeability, or secondary volcanoes with hydro-geological significant volumes. Consequently, the accumulation of ash at the bottom of the craters and caldera have conditioned the formation of lakes.
Although, hydrologically, the Lagoa das Sete Cidades is one lake (it is only divided by a bridge), most refer to it in terms of two separate bodies: Lagoa Verde and Lagoa Azul. Literally, the Green Lake and the Blue Lake (respectively), they are named for the reflect pigment of bodies: each side of the lake reflects the sunlight in different colors.
s and algae in the water bodies. The eutrophication
of the Lagoa das Sete Cidades lakes, due to nutrient enrichment was enhanced by human agricultural and domestic activities, began to be noticed in 1987 and led to the implementation of a monitoring program. Measurements taken at the time, that included the examination of Carlson's Trophic state index
, the measure of Chlorophyll
, inorganic nitrogen
and phosphorus
in the water column were made, showing increases in all measures. While phytoplankton populations varied throughout the year in the Lagoa Azul, the presence of phytoplankton in the Lagoa Verde persisted annually, dominated by Cyanobacteria. When temperature, light and nutrient availability are adequate to phytoplankton growth, surface waters may host algae or cyanobacteria blooms. In eutrophic waters, cyanobacteria often dominate the summer and early autumn phytoplankton, while during winter and spring they are replaced by diatoms.
As the existence of a eutrophication process in Sete Cidades lake was already known since the 1980s, the rise of cyanobacteria blooms was not unexpected by 2000. Although average total phosphorus concentration inside the lake was not very high, concentrations found in winter samples proved that there was an important run-off of fertilised water from the watershed. High levels of cynotoxins were found in 2002 in the Blue Lake. Lake water within the watershed is not potable, but recreational use, like swimming and windsurfing, were common practices, although advisories were placed along the lakes to warm of bloom toxicity and associated health dangers.
Although the state of the lake's water quality has improved since 2000, Cyanobacteria blooms have negatively affected the situation in the lake. Consequently, the Regional Government began preparation of a new territorial examination of the situation within the crater. The Plano de Ordenamento da Bacia Hidrográfica da Lagoa das Sete Cidades (POBHLSC) () was implemented to evaluate the conditions of the lake, establish methods of interdiction and monitorization of landuse initiatives.
Lake
A lake is a body of relatively still fresh or salt water of considerable size, localized in a basin, that is surrounded by land. Lakes are inland and not part of the ocean and therefore are distinct from lagoons, and are larger and deeper than ponds. Lakes can be contrasted with rivers or streams,...
situated in the crater of a massive crater on the Portuguese
Portugal
Portugal , officially the Portuguese Republic is a country situated in southwestern Europe on the Iberian Peninsula. Portugal is the westernmost country of Europe, and is bordered by the Atlantic Ocean to the West and South and by Spain to the North and East. The Atlantic archipelagos of the...
archipelago
Archipelago
An archipelago , sometimes called an island group, is a chain or cluster of islands. The word archipelago is derived from the Greek ἄρχι- – arkhi- and πέλαγος – pélagos through the Italian arcipelago...
of the Azores
Azores
The Archipelago of the Azores is composed of nine volcanic islands situated in the middle of the North Atlantic Ocean, and is located about west from Lisbon and about east from the east coast of North America. The islands, and their economic exclusion zone, form the Autonomous Region of the...
. It consists of two ecologically-different small-lakes connected by a narrow passage (and crossed by a bridge), located inside a dormant volcano
Volcano
2. Bedrock3. Conduit 4. Base5. Sill6. Dike7. Layers of ash emitted by the volcano8. Flank| 9. Layers of lava emitted by the volcano10. Throat11. Parasitic cone12. Lava flow13. Vent14. Crater15...
on the western third of the island of São Miguel
São Miguel Island
São Miguel Island , nicknamed "The Green Island", is the largest and most populous island in the Portuguese Azores archipelago. The island covers and has around 140,000 inhabitants, 45,000 of these people located in the largest city in the archipelago: Ponta Delgada.-History:In 1427, São Miguel...
. The Lagoa das Sete Cidades part of a natural landscape of communitarian interest: it is the largest body of water in the region and one of the most important freshwater resources in the archipelago.
Legend
The ancient story, recounts the tale of a bad-tempered widower King and his daughter in a Kingdom in the Western Sea. He was a King, Lord of AlchemyAlchemy
Alchemy is an influential philosophical tradition whose early practitioners’ claims to profound powers were known from antiquity. The defining objectives of alchemy are varied; these include the creation of the fabled philosopher's stone possessing powers including the capability of turning base...
and sorcerer
Sorcerer
-Gaming:* Sorcerer , a 2002 tabletop role playing game made by Ron Edwards* Sorcerer , a 1984 interactive fiction computer game made by Infocom...
, who lived exclusively for his daughter, Antília, and who would not let the Princess speak to anyone. Apart from the King, the Princess was raised by an old nurse, after the Queen had died. As the years progressed, the princess grew-up to be a beautiful young woman and able to attract the attentions of any boy in the kingdom. However, the King restricted her movements to the castle and garden, and few ever saw her. But, un-intimidated by her father, and with the help of the nurse, she escaped to the local hills and valleys, as her father slept after his lunch. During one of her escape adventures, she heard a song: the music was beautiful and enchanted her to follow it to its origins. Hiding from view, the princess found a young shepard playing a flute, sitting on top of a hill. For weeks she returned, listening to the young shepard, until she was discovered behind some bushes. The shepard boy fell in love with the princess, and they continued to meet afterwards, talking, laughing and enjoying each other's company, until the boy decided to ask the princess in marriage.
Early in the morning, the couple knocked on the door of the Castle, and asked the servants to speak to the King. Very nervous but determined, the shepard asked the King for his daughter in marriage. Reacting angrily, the King refused and expelled him from the Castle, and forbade his daughter from seeing the young boy. Not wishing more ill-feelings, she followed the orders of her father, but met secretly with the shepard that afternoon in order to tell him that he would never see him again. Antília and the shepard boy cried all afternoon, embracing, and their tears formed two beautiful lakes, one green, for the Princess's eyes were green, and the other blue, for the shepard's eyes were likewise colored.
Geography
The lake is situated within the caldera of the Sete Cidades Massif, an ancient volcano built on various layers of ashVolcanic ash
Volcanic ash consists of small tephra, which are bits of pulverized rock and glass created by volcanic eruptions, less than in diameter. There are three mechanisms of volcanic ash formation: gas release under decompression causing magmatic eruptions; thermal contraction from chilling on contact...
, pyroclasts
Tephra
200px|thumb|right|Tephra horizons in south-central [[Iceland]]. The thick and light coloured layer at center of the photo is [[rhyolitic]] tephra from [[Hekla]]....
and trachyte
Trachyte
Trachyte is an igneous volcanic rock with an aphanitic to porphyritic texture. The mineral assemblage consists of essential alkali feldspar; relatively minor plagioclase and quartz or a feldspathoid such as nepheline may also be present....
and basalt
Basalt
Basalt is a common extrusive volcanic rock. It is usually grey to black and fine-grained due to rapid cooling of lava at the surface of a planet. It may be porphyritic containing larger crystals in a fine matrix, or vesicular, or frothy scoria. Unweathered basalt is black or grey...
ic lava
Lava
Lava refers both to molten rock expelled by a volcano during an eruption and the resulting rock after solidification and cooling. This molten rock is formed in the interior of some planets, including Earth, and some of their satellites. When first erupted from a volcanic vent, lava is a liquid at...
s. It is a stratovolcano
Stratovolcano
A stratovolcano, also known as a composite volcano, is a tall, conical volcano built up by many layers of hardened lava, tephra, pumice, and volcanic ash. Unlike shield volcanoes, stratovolcanoes are characterized by a steep profile and periodic, explosive eruptions...
constructed from alternating phases of explosive and effusive ejecta, from dominantly basaltic pre-caldera eruptions, a trachytic caldera-forming stage and a post-caldera stage consisting of alternating trachytic and basaltic eruptions. The caldera-forming eruption was triggered by a basaltic injection into a shallow trachytic magma chamber.
These geomorphological structures allowed varying hydro-chemical properties and produced many types of springs
Spring (hydrosphere)
A spring—also known as a rising or resurgence—is a component of the hydrosphere. Specifically, it is any natural situation where water flows to the surface of the earth from underground...
and water circulation networks (Coutinho et.al., 1996). Generally, formations with good hydrodynamic properties include areas with lava flows, basaltic pyroclasts and/or pumice
Pumice
Pumice is a textural term for a volcanic rock that is a solidified frothy lava typically created when super-heated, highly pressurized rock is violently ejected from a volcano. It can be formed when lava and water are mixed. This unusual formation is due to the simultaneous actions of rapid...
, while solidified Ignimbrite
Ignimbrite
An ignimbrite is the deposit of a pyroclastic density current, or pyroclastic flow, a hot suspension of particles and gases that flows rapidly from a volcano, driven by a greater density than the surrounding atmosphere....
s, conditioned by high temperatures and paleo-soils, such as ash, have produced impermeable conditions. The aquifers are dependent on reduced permeability, or secondary volcanoes with hydro-geological significant volumes. Consequently, the accumulation of ash at the bottom of the craters and caldera have conditioned the formation of lakes.
Although, hydrologically, the Lagoa das Sete Cidades is one lake (it is only divided by a bridge), most refer to it in terms of two separate bodies: Lagoa Verde and Lagoa Azul. Literally, the Green Lake and the Blue Lake (respectively), they are named for the reflect pigment of bodies: each side of the lake reflects the sunlight in different colors.
Human impacts
In the mid-20th Century, the destruction of forested areas and their transformation into grassland and pasture in the natural catchment area of the lake, increased the run-off of nutrients, particularly phosphorus and nitrogen, from the steep land. Lacking a domestic sewage system until recently, the community of Sete Cidades contributed to gradual pressures on the ecosystem, resulting in an over-abundant development of rooted aquatic macrophyteMacrophyte
A macrophyte is an aquatic plant that grows in or near water and is either emergent, submergent, or floating. In lakes macrophytes provide cover for fish and substrate for aquatic invertebrates, produce oxygen, and act as food for some fish and wildlife....
s and algae in the water bodies. The eutrophication
Eutrophication
Eutrophication or more precisely hypertrophication, is the movement of a body of water′s trophic status in the direction of increasing plant biomass, by the addition of artificial or natural substances, such as nitrates and phosphates, through fertilizers or sewage, to an aquatic system...
of the Lagoa das Sete Cidades lakes, due to nutrient enrichment was enhanced by human agricultural and domestic activities, began to be noticed in 1987 and led to the implementation of a monitoring program. Measurements taken at the time, that included the examination of Carlson's Trophic state index
Trophic state index
The quantities of nitrogen, phosphorus, and other biologically useful nutrients are theprimary determinants of a body of water's trophic state index...
, the measure of Chlorophyll
Chlorophyll
Chlorophyll is a green pigment found in almost all plants, algae, and cyanobacteria. Its name is derived from the Greek words χλωρος, chloros and φύλλον, phyllon . Chlorophyll is an extremely important biomolecule, critical in photosynthesis, which allows plants to obtain energy from light...
, inorganic nitrogen
Nitrogen
Nitrogen is a chemical element that has the symbol N, atomic number of 7 and atomic mass 14.00674 u. Elemental nitrogen is a colorless, odorless, tasteless, and mostly inert diatomic gas at standard conditions, constituting 78.08% by volume of Earth's atmosphere...
and phosphorus
Phosphorus
Phosphorus is the chemical element that has the symbol P and atomic number 15. A multivalent nonmetal of the nitrogen group, phosphorus as a mineral is almost always present in its maximally oxidized state, as inorganic phosphate rocks...
in the water column were made, showing increases in all measures. While phytoplankton populations varied throughout the year in the Lagoa Azul, the presence of phytoplankton in the Lagoa Verde persisted annually, dominated by Cyanobacteria. When temperature, light and nutrient availability are adequate to phytoplankton growth, surface waters may host algae or cyanobacteria blooms. In eutrophic waters, cyanobacteria often dominate the summer and early autumn phytoplankton, while during winter and spring they are replaced by diatoms.
As the existence of a eutrophication process in Sete Cidades lake was already known since the 1980s, the rise of cyanobacteria blooms was not unexpected by 2000. Although average total phosphorus concentration inside the lake was not very high, concentrations found in winter samples proved that there was an important run-off of fertilised water from the watershed. High levels of cynotoxins were found in 2002 in the Blue Lake. Lake water within the watershed is not potable, but recreational use, like swimming and windsurfing, were common practices, although advisories were placed along the lakes to warm of bloom toxicity and associated health dangers.
Although the state of the lake's water quality has improved since 2000, Cyanobacteria blooms have negatively affected the situation in the lake. Consequently, the Regional Government began preparation of a new territorial examination of the situation within the crater. The Plano de Ordenamento da Bacia Hidrográfica da Lagoa das Sete Cidades (POBHLSC) () was implemented to evaluate the conditions of the lake, establish methods of interdiction and monitorization of landuse initiatives.