Tuesday, October 2, 2012
Lake Baikal - in deep water?
Lake Baikal in central Asia is one of the natural wonders of our planet. Known as the 'Galapagos of Russia', it contains a unique flora and fauna - most of the 2000 plus plants and animals that live in its deep waters are endemic - found nowhere else.
A top predator in the lake, Pusa sibirica, is one of the world's very few species of freshwater seals, and up to 40 per cent of Baikal's species have not even been described yet. It is a major biodiversity hotspot, declared a World Heritage Site by the UN in 1996.
Baikal's endemic species have evolved over tens of thousands, perhaps millions, of years, to occupy niches that may never have been disturbed before the last three or four decades.
The lake's unique ecology stems from its physical properties. Baikal is the oldest lake in world; it started forming over 25 million years ago when a fissure in the continent began to open up. It is also the planet's deepest lake, averaging 744m deep and going down to 1642m in places, due to a tectonic pulse that made the rift's shoulders rise up while the bottom continued to deepen.
Astonishingly, Lake Baikal accounts for over a fifth of all surface fresh water on Earth, outside polar ice caps and glaciers. And unlike other deep lakes, it contains dissolved oxygen right down to the bottom.
This is because cold surface water regularly flows deep into the lake, driven by strong winds and complex differences in water temperature. This lets animals thrive at all depths, and ensures that nutrients are efficiently recycled. Baikal's great age and stable deep-water environments created evolutionary conditions that led to the extraordinary numbers of endemic species found there today.
Industrial development on the shores of the lake gave rise to Russia's first environmental movement in the 1960s. The most infamous development was the construction of the Baikal Paper and Pulp Mill (BPPM) which produces hundreds of thousands of tonnes of bleached pulp a year and discharges pollutants such as sulphates and organic chlorine compounds into the lake. Many other toxic compounds have come from mining, agriculture and general population growth.
Extracting a mud core from the lake.
I started working on Lake Baikal 20 years ago with a team of scientists from UCL, University of Liverpool and the Limnological Institute at Irkutsk, to investigate the effects of pollution from urbanisation and the BPPM. We had no long-term pollution records, but because particles in the water, including pollutants, eventually sink to the bottom of the lake, we had a natural archive of lake mud which we could study by extracting a mud core.
Specifically we looked for changes in diatoms - microscopic algae in a silicon shell which sit at the base of the food chain. Some diatoms are more sensitive to pollution than others, so we can determine the impact of past pollution by looking at species changes preserved in the lake mud. We found small changes in diatom species in a few shallow water areas, which may have been caused by increased nutrients like nitrogen in the water, linked to population growth and agriculture - for example from fertilisers running off nearby farmland. We also found evidence of pollution from burning fossil fuels though this did not affect the diatoms.
Since then, the threats to Lake Baikal have increased because of the exploitation of valuable minerals and energy resources in Baikal's vast drainage basin - more than twice the size of the UK because of the Selenga River that extends into northern Mongolia. We also know that global warming is directly affecting ice cover and surface-water temperature in the lake.
In turn these changes have influenced small organisms living in the open water, including tiny plants and animals (respectively known as phytoplankton and zooplankton). Warmer temperatures are also melting frozen soils (permafrost) in the drainage basin, releasing further nutrients into the lake. Human activity from industry and agriculture raises nutrient input even more.
This rise in nutrients means more algae of more different kinds are found in the lake, which in turn influences other aquatic species. So it is essential to understand these changes now, before they become too great and irreversibly damage this unique ecosystem.
We have assembled a new team to investigate these threats by studying isotopes of silicon (Si), which controls the growth of diatoms at the base of the food chain, and can tell us about nutrient levels in the lake.
Because Baikal is so enormous, we will spend a lot of time on a research ship next summer, taking samples of water and algae at many locations along a line running from north to south, and from the surface water right down to the depths. We will also do fieldwork in March, when the lake is covered by ice. Winter working conditions are extreme - temperatures can drop to below -30°C, and to access the water you have to dig through meter-thick ice.
The freshwater seal Pusa sibirica.
An important goal is to place modern-day nutrient uptake in the lake into a much longer historical context, so we will extract new sediment archives especially for this project. Working on the ice will give us a very stable platform from which to drop special coring equipment attached to metal cables down through the water, into the mud, and then to pull them back up again with a motorised winch.
We know from previous experience that just 50cm of lake mud can give us a historical record going back over 1000 years.
Baikal is still relatively pristine. Yet real threats remain, including discharge of pollutants into the Selenga River, direct pollution of the lake from the BPPM, and global warming.
Because water stays in the lake for around 400 years, pollutants entering now could build up for centuries to come. Protective measures have already been taken, including the 'Baikal Law', designed to regulate environmental and economic activities in the drainage basin. However, these have had limited success - the BPPM closed down for a couple of years because of environmental concerns, but it reopened in 2010 to much controversy.
The lake's future is still wide open, as economic activity continues to grow along its coastline and in its drainage basin. Global warming could also alter its delicate balance of species. Our research will help provide the knowledge that's needed to understand this still-unspoiled jewel in Russia's crown.