Shiga Prefecture, Lake Biwa Pearls
Episode 1
Circulating Continuously for 4.4 Million Years: A Rich Reservoir Since Ancient Times.
Lakes, varying in size, are depressions formed on Earth. Each is a unique water body, most of which disappear within about 10,000 years. However, some endure remarkably longer, like Lake Biwa, Japan's largest freshwater lake.
Lake Biwa's origins trace back approximately 4.4 million years, believed to have formed from water accumulating in the ground following a major earthquake-induced collapse. Initially located further south than its present location in what is now the Iga-Ueno region, surrounded by metasequoia forests, it was a warm marshland where apparently elephants, rhinos, and even crocodiles thrived. When the continent and the Japanese archipelago separated 3.2 million years ago, it drifted to the area spanning from present-day Shiga to Mie prefectures. Lake Biwa migrated to its present location, undergoing significant transformations over the following 2.8 million years. Its vast waterfront disappeared only to be replaced by swamps and rivers which appeared in the southern half of what is now Lake Biwa. Climate shifts saw the disappearance of metasequoia forests and the lake expanding northward, eventually settling into its current form around 400,000 years ago. Lake Biwa is continuously migrating northward, anticipated to connect with the Sea of Japan in the distant future.
Typically, lakes dry up within about 10,000 years, yet Lake Biwa persists. Why? It owes its longevity to ongoing crustal movements, facilitating its renewing life cycle amidst climate and ecosystem changes. Small cycles gather and interact which form larger cycles. The larger cycles are supported by smaller cycles which have sustained Lake Biwa's 4.4 million-year history of life cycles.
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One of the Rare Ancient Lakes of the World
Lakes with a history of over 100,000 years, harboring endemic species, are referred to as "ancient lakes." Lake Biwa is one of only about 20 such "ancient lakes" in the world. Moreover, it is a miraculous ancient lake that originated 4.4 million years ago. The reason for its remarkable longevity lies in tectonic movements. Typically, lakes become shallower over thousands to tens of thousands of years, turning into marshlands as the water becomes murky. However, Lake Biwa continues to exist due to tectonic movements, sinking by 1 millimeter each year, and receiving fresh water from numerous rivers, keeping it perpetually fresh.
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Lake Biwa Supported Human Lives All Along
Humans began living around Lake Biwa approximately 26,000 years ago, during the later stages of the Paleolithic period. Since then, activities have continued uninterrupted. This indicates just how abundant the blessings of Lake Biwa were. Over 100 archaeological sites lie in the waters of Lake Biwa, containing artifacts from the Jomon (ca. 10,500 - ca. 300 B.C.) to Edo (1603 -1868) periods, submerged due to rising water levels and tectonic movements. Fishermen fishing have pulled up pottery, and Jomon pottery has been caught in fishing nets. Mokkan, or inscribed wooden tablets and remnants of shrines have also been discovered.
Among the notable large cycles is "Lake Biwa's Deep Breath," where approximately 27.5 billion tons of stored water circulates almost annually. During midwinter, the water near the surface cools and sinks into the lake. This triggers convection currents, which causes the lake water to circulate widely and mix evenly. When the oxygen-rich surface water reaches the lake bed, creatures like izasa, shrimp, and ikecho-gai, find it easier to thrive. Much like humans take deep breaths to intake oxygen, Lake Biwa also inhales oxygen, exchanging breaths with the environment.
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Various Activities Connected by Rivers
Lake Biwa is nestled in a basin surrounded by mountains towering over 1,000 meters high. Water gushes from the mountains in all directions, forming 117 Class A rivers that flow into Lake Biwa, which fill its basin while there are only two outlets, the Seta River and Lake Biwa Canal. Therefore, it remains abundantly replenished. The volume of water in Lake Biwa is 27.5 billion cubic meters. This water is used for the water supply in the Kinki area, supporting the lives of 14.5 million people. Each of the 117 major rivers also supports numerous forms of life and livelihoods. In the mountainous area, animals quench their thirst from the water sources, and river fish traverse the clear streams. Near human settlements, tea plantations stretch out, and in some areas, waterways are laid out for household use. Further downstream, sake breweries and textile factories rely on water, canoeists gather near the river mouths and sightings of wild birds seeking lake fish are common.
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Lagoons: Children of Lake Biwa
Like small potatoes connected to a large potato, Lake Biwa is surrounded by several small, scattered lakes connected by waterways and rivers like umbilical cords. These are naiko, or lagoons. There are 23 ancient lagoons and 10 new ones. The lagoons were originally part of Lake Biwa but were formed by the accumulation of sediment carried by waves and rivers. Consequently, they tend to be more nutrient-rich than Lake Biwa itself, making them ideal habitats for newly hatched fish and shellfish, such as hommoroko and ikecho-gai.
The creatures living at the bottom of the lake actually play a role in a small cycle. For example, the ikecho-gai. This bivalve, known as the mother shell of freshwater pearls, grows to about 20 centimeters in size. This shellfish possesses water purification capabilities. Ikecho-gai feed on aquatic phytoplankton. They draw in lake water, ingest phytoplankton, filter the water, and return it to the lake. In other words, ikecho-gai themselves serve as water filtration systems. Although their contribution may seem modest in a large lake, they rely on the lake water to live while helping keep it clean.
Lake Biwa harbors various small and unique organisms, forming interconnected cycles: fish and shellfish found exclusively in this lake, migratory birds that visit every year, waterside plants, the people who live there, and so on. In some cases these various flora and fauna interact with each other to form cycles.
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Over 60,000 Migratory Birds
Lake Biwa is home to over 100,000 waterfowl and is registered under the Ramsar Convention as an internationally important wetland. Among them, over 60,000 are migratory birds. Flying thousands of kilometers, they arrive at Lake Biwa. The summer birds include swallows and reed warblers. In spring, they come from islands in Southeast Asia to raise their offspring. The winter birds include ducks and tundra swans. At the beginning of autumn, they cross the frozen Sea of Okhotsk from Siberia. From high in the sky, they see Lake Biwa sparkling, and the birds descend towards the lake surface. "Hello again," after six months. Thus, escaping the severe cold, the birds fish and rest their wings, gathering strength for their spring departure.
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66 Species of Fish and Shellfish Found Nowhere Else in the World
Lake Biwa is home to 66 species of endemic organisms, including subspecies and varieties. Endemic species are living organisms found nowhere else in the world, unique to a particular place. Creatures that have inhabited the area for millions of years or those that have continued to evolve here still thrive today. For example, the Biwa trout, known as the "jewel of Lake Biwa," has been present here for 430,000 years. Its majestic presence almost makes it seem like a living testament to the history of Lake Biwa. Ikecho-gai used in the cultivation of Lake Biwa pearls are also endemic bivalves of Lake Biwa. Fossils of ikecho-gai have been found in the sedimentary layers known as the Katata Formation, suggesting they have inhabited the lake since a period between 1.4 million to 400,000 years ago when Lake Biwa was shallower and narrower than it is today.
Let's take a closer look at the reed and its surroundings. Reeds are plants commonly found in Lake Biwa and its surrounding lagoons, thriving both in water and on land. The water level of Lake Biwa rises during spring snowmelt and the rainy season. Submerged reeds assist in nurturing the lake's inhabitants' offspring. Splashing around in the water are fish like carp and crucian carp, laying their eggs at the base of the reeds. Among the reeds, little grebes build floating nests and rear their young. From summer to fall, reeds spread their roots on land, forming lush colonies that grow to nearly 4 meters in height. Harvest mice and reed warblers build nests, while swallows that have fledged from their nests roost in the reed colonies.
Reeds also lend a helping hand to human life. They are used as materials for sudare, or blinds, and thatched roofs. During spring festivals, large, beautiful torches made from bundled reeds are indispensable. There are temples and shrines that have been roofing with local reeds for centuries.
Only with human intervention can reeds grow healthily, and will disappear if left untouched. Each winter they are cut, then the cuttings are burned on the ground. The flames engulfing the reed beds are a traditional sight in this region. The burning disinfects the earth, and the ashes fall to the ground, becoming fertilizer for the next sprout and ensuring robust growth. Thus, the seasons are renewed.
What a single reed or a single ikecho-gai can achieve may seem modest in the grandeur of nature. However, no matter how small, every entity has been indispensable for Lake Biwa's 4.4 million years of existence. Small and unique beings gather, interweaving in a delicate balance, sustaining the cycle of life.
That's Lake Biwa—an exuberant reservoir of life, a celebratory lake for creatures on its small island.
Now, the spotlight should be on Lake Biwa's pearls on this festive stage. The luminous glow akin to moonlight and the diverse forms are gifts created by the abundant cycles of Lake Biwa, captivating our hearts as beautiful and mysterious jewels since ancient times. Stay tuned for the next installment, unraveling the timeless tale of Lake Biwa's pearls. (To be continued)
