#potamology

[probablyasocialecologist]

We have forgotten what a 'natural' river even looks like

In praise of messy rivers.

Why have we forgotten what our natural rivers look like? In the UK and most other developed economies, the network of streams and rivers have been managed, and physically altered in some cases, for more than 1,000 years to support more farms and later more industry. It is no wonder most people do not realise that the rivers they grew up with, fish in, swim in, or simply walk along are nothing like the natural ecosystems they once were. History and culture has evolved around modified river systems. In Britain, for instance, 1,000 years of change has meant 97% of rivers are fragmented by barriers like weirs. Things accelerated after World War I with 36% of the river network of England and Wales, some 35,500km, subject to major modifications. And these are only the documented changes – much more was routinely maintained such as the annual removal of silt or vegetation.

[mostly-history]

Lake Baikal (October 1999), from the OrbView-2 satellite.

Lake Baikal is a rift lake in southern Siberia, between Irkutsk Oblast to the north-west and Buryatia to the south-east.  It formed as an ancient rift valley about 25 – 30 million years ago, hence its long crescent shape.

With 22 – 23% of the world's surface freshwater, Lake Baikal is the largest freshwater lake in the world, in terms of volume.  It is also the oldest and deepest lake in the world, and the 7th-largest lake in terms of surface area.  It contains more water than the North American Great Lakes combined.

Several rivers flow directly into Lake Baikal, but it is drained only by the lower Angara River, which flows northwards from the lake's south-western shore to join the Yenisei River.

Below the lake is the Baikal Rift Zone.  At 8 – 11km below the surface, it is the world's deepest continental rift.  About 7km of sediment rests on the rift floor, so the lake bottom is just over 1km below sea level.

The fault zone is seismically active, with hot springs in the region, and earthquakes every few years.  The rift itself is active, and widens about 2cm a year.

[yourthomasjefferson]

Please join me today (Saturday 3 October), from 1–2pm, for a presentation on waterways in the United States during my lifetime. This theme is in conjunction with the Smithsonian's "Water - Ways" traveling exhibit. (Registration via the link in my bio) . . . #ThomasJefferson #YourThomasJefferson #rivers #potamology #limnology #science #water #history #maritime #foundingfather #American #18thcentury #reenactor #lookalike #virtual #theater #speaker https://www.instagram.com/p/CF4xw6pDpdp/?igshid=8fq14y6uj6oc

[mostly-history]

Lake Baikal and the Angara River (Russia, April 2012).

The Angara River, known as the “daughter of Baikal”, is the only river flowing out of Lake Baikal.  Even during the coldest parts of winter, this part of the river never freezes, and it is the only place in Northern Asia where birds will stay during the winter.

The water temperature in Lake Baikal changes only up to 300 – 500m below the surface.  Below that, it stays at 4°C the whole year round.  At the beginning of the lower Angara River (where it drains the lake), the water flows only from the lower depths of the lake.  It isn't until at least 2km away from the lake that the Angara can get cold enough to freeze.

[mostly-history]

Lake Baikal (November 2001) from the Terra satellite.

This true-colour image shows winter advancing on the region.  To the north, rivers are freezing over, appearing as white ribbons in the photo.  Snow dusts the southern part of the Central Siberian Plateau, while the mountains to the north of Lake Baikal are covered in snow. The lake isn't frozen yet, and neither is the Angara River, which flows out of the lake from its south-western corner.

[mostly-history]

Napo River from the air – natural colour image (January 2002) and radar image (March 2013).

These photos show forested wetlands around the river in Ecuador and Peru.  The first image was taken from the Landsat 7 satellite on a rare cloud-free day.

The radar image was taken on a NASA Gulfstream C-20A aircraft.  Yellow, orange and blue indicate areas where vegetation has probably been inundated with flood waters beneath the forest canopy.  Green areas are relatively healthy forest vegetation, while the roughness of the texture can indicate whether it is tree cover or deforested grassland or swamp.  The black parts are the open water of the Napo River and its tributaries.

Areas of open water are very dark because most of the radar waves bounce off the water and don't return to the radar.  Forested areas, on the other hand, reflect a lot of radar energy back to the antenna, so they are bright.

Areas that are sometimes or semi-permanently inundated often have different vegetation and animal species.  Changes in wetlands are indicators of climate change, and inundated wetland areas are sources of methane.

[mostly-history]

The Angara River near Talzy at Lake Baikal (Irkutsk Oblast, Russia).

Talzy is about 25km from the lake's south-western shore, where it empties into the Lower Angara River.  The Angara then flows northwards into the Yenisei, which continues northwards until it reaches the Arctic Ocean.

[mostly-history]

Angara River (Russia, 1978).

This photo was taken from the upper working platform of the Ust-Ilimsk power plant, from a height of about 100m.