Diatoms are found everywhere, especially in water and soil. The contribution that they make to the natural economy of the earth is enormous. It has been estimated that their photosynthesis traps 20,000,000,000 tonnes of carbon each year – more than all of the world’s rainforests put together!
Diatoms use silica to build their cells, which is like glass: in a way, they live in ornamented glass houses. Their shapes are surprisingly variable, and the different types of holes and lines are precisely positioned.
Their diverse shapes and patterns of beautifully arranged pores can be seen by light microscopy, while fine structures and marks sculptured on the cell walls can only be seen using electron microscopy. They have evolved over the years to adapt to harsh natural environments: fossil evidence suggests their origin even before the early Jurassic, around 200 million years ago and are widely distributed and diversified microorganisms (ca. 100.000 species) on Earth’s surface.
Nearly all diatoms are microscopic – cells range in size from 2 µm to 500 µm – half a millimetre. The biggest diatoms are about the width of a human hair. Scientists use light microscopes (LM) or scanning electron microscopes (SEM) to view diatoms.
When diatoms are viewed with a light microscope, the silica cell walls appear transparent (because we are seeing through glass).
When diatoms are viewed with a scanning electron microscope, the cells appear opaque, because we are seeing the surface of the cell with electrons.
Why do some diatoms prefer certain landscapes or soil types to others?
Depending on whether we look at the soil in forests, grassland or fields – some diatoms are found only in one type of these soils. Why is this?
“In the soil found in forests, diatoms have a stable microhabitat. In 2021, we showed that a disturbance in the soil – for example farming, rather than seasonal changes, is the reason for why some diatom communities are not found in agriculture soil,”Diatom expert & researcher Carlos Wetzel explains, adding that there is no particular visible unique character that belongs to a diatom and their preference for habitats.
For many types of diatoms found in water, scientists have figured out these diatoms respond to human impacts, which ones prefer more polluted or clean water and more. Luxembourg monitors its rivers since the early 2000’s using diatoms within the water framework directive, and scientists have figured out how long it takes diatoms in water to adapt to new water quality conditions. For soil, this knowledge is still to be gained – only few scientists have studied diatoms in soil. Carlos Wetzel from LIST is one of them. Carlos has been studying diatoms for around 20 years and is behind all the diatom images on this page. Let’s discover more below!
Diatoms paint a picture of the health of the soil in Luxembourg
Diatoms have been an object of study for researchers in Luxembourg for nearly 20 years. Typically, diatoms are studied in water – they are for example abundant on the slippery green/brownish algae found on rocks by the water. A researcher at the Luxembourg Institute of Science and Technology, Carlos Wetzel, is looking at them in the soil to paint a picture of the health of the soil in Luxembourg.
Carlos has travelled all over Luxembourg to collect nearly 300 samples from three types of soil: forest, grassland and arable soil (e.g agricultural fields).
“Recently, environmental metabarcoding has opened up a completely new way to evaluate microbial diversity in natural environments. The method provides data on many organisms that have so far escaped our attention as they are hard to identify with traditional methods, which is often the case regarding diatoms.”Carlos Wetzel explains. Diatoms excel in forming such tiny structures, which are nanometer scale (1/1,000,000 of a millimeter) and amazingly elegant! Carlos captures stunning, colourful images of diatoms showing their intricate shapes. One of his images was awarded in the first FNR Science Image Competition.
Carlos Wetzel’s project aims to assess soil conditions (in terms of human impact and fertility) by combining molecular approaches and microscopic techniques to unravel the diversity of these microorganism on soil, providing an overview on their diversity, their functional importance, how they respond to human impact and how they could be applied as bioindicators. The overall goal is to create a biological quality index against which future degradation and improvements can be measured, monitored and better understood.
“Besides being the baseline for developing and creating an index to help eventual soil monitoring, the results gained from our project will serve as baseline for many further studies involving soil biodiversity,”Carlos explains.
The insight gained from looking at diatoms can help scientists, farmers and policy makers make a better strategy for manure management, land use, and management practices.
Why is it important to look at the soil in Luxembourg?
While there is research going on in Luxembourg that looks at other aspects of the soil, there is little nationwide or EU biological data on soil structure.
Bad soil is expensive: Soil degradations, such as pollution, soil organic carbon loss, biodiversity loss, acidification, erosion or compaction, could lead to millions of euros worth of costs for Luxembourg, each year.
It is important not to compress the soil too much: Water, nutrients and organisms need to flow between the top and lower layers of soil – if the soil is compacted by heavy machinery under inadequate soil conditions, this flow is restricted, which has bad consequences: Without a healthy soil structure, it is harder for the soil to mitigate the impacts of climate change, support plant growth and resilience to droughts.
The diatom metrics knowledge being gained in research projects such as the one led by Carlos Wetzel at LIST could be incorporated into soil monitoring programmes and so help preserve our soil – because after all, it takes 1,000 years to make one centimetre of soil.
This research project is supported by a grant from the FNR’s CORE programme, which awards grants for research in priority areas for Luxembourg.