Thar She Blows: of Saharan Dust and Marine Productivity

By Charlie Whittaker

The Sahara Desert is not something you would usually associate with abundant life and vibrant algal blooms. It is one of the most arid and inhospitable areas in the world, representing the largest subtropical hot desert on the planet. And at well over 9,400,000 square kilometres- i.e. about the size of the United States, it is perhaps one of the most inhospitable areas globally. To say that it is unwelcoming to life is an understatement of epic proportions.

The Sahara Desert (credit mtsrs)

The Sahara Desert (credit mtsrs)

However, the desert is in fact one of the cornerstones of continued survival of one of the most abundant groups of organisms on the planet: the phytoplankton. This vast swathe of barren land is actually responsible for a dazzlingly complex and diverse ecosystem albeit thousands of miles away.

Tiny flecks of sand, red in colour due to the abundance of the element iron, are picked up the winds floating across the sand dunes, and in turn, carried thousands of miles westwards on the air currents. These tiny grains of iron rich sand then land in the ocean off the West coast of Africa, where they are responsible for sustaining a astounding array of life. Though individually insignificant and of little relevance, the sheer scale of their deposition makes them a globally relevant input- it is estimated that something in the region of 1015g/year get deposited courtesy of these Saharan winds Westwards. That’s 1012kg, or 1 billion tonnes!

A phytoplankton bloom in the Southern Ocean (credit ESA)

A phytoplankton bloom in the Southern Ocean (credit ESA)

But why all the fuss about iron though? Iron represents a fundamental micronutrient required as a cofactor for the enzymes of a ubiquitous number of different phytoplankton, from cyanobacteria to coccolithophores and diatoms to dizaotrophs. In particular, iron acts as an essential constituent of the enzyme nitrogenase, responsible for the fixation of atmospheric nitrogen. The photosynthetic organisms present in this group are globally significant in terms of the fixation of carbon dioxide from the atmosphere. These so called “forests of the ocean” contribute as much to the control of CO2 levels as tropical rainforests.

Given their dependence on iron then, there has been considerable interest in the concept of “iron seeding” the oceans as a means of generating blooms of these photosynthetic organisms. Such a sudden population rise would lead to increased CO2 drawdown and may have the potential to mitigate, at least in part, some of the consequences of continual anthropogenic mediated CO2 release into the atmosphere. Efforts doing this are still in progress but who would have thought the Sahara Desert, byword for desolate, bleak and lifeless, may have acted as the inspiration for one of the most ambitious biogeoengineering projects currently underway.

Eyes in the Sky: Agriculture and the Rise of Satellite Technology

By Sophie Harrington

When you think of farming, satellites probably aren’t the first thing that comes to mind. Yet in the coming years, farming may be more and more tied to the information gathered by satellites orbiting the globe. New technologies are being developed to integrate precision satellite data with farming practices around the world. These techniques hold the potential for not only increasing the efficiency and yields of farms, but also to reduce the environmental impact of intensive farming.

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The future of agriculture? (credit NASA Goddard Space Flight Center)

In the United Kingdom, a group of companies known as the Courtyard Partnership are hoping to revolutionize farming by providing in depth data from satellite imaging and soil analysis. By providing farmers with information on soil variation across their fields the group hopes to facilitate increases in yield while at the same time allowing the use of more environmentally friendly farming practices.

Soil brightness scanning by satellites provides information on soil texture, moisture, and organic composition which enable farmers to make distinctions between different soil types. This in turn allows soil inputs to be calibrated based on the specific soil “zone” determined through the combination of satellite imaging and soil sampling on the ground. Initially this could allow farmers to reduce wasted fertiliser by applying the optimum amount for each soil zone..

Later on, satellite images can also be used to provide data on chlorophyll cover, the pigment in plants which gives them their green colour. This acts as a proxy for plant nitrogen levels, which influence chlorophyll content. If the chlorophyll is lower than ideal, this can be compensated for by increasing fertilizer input. At the same time, the satellite images also provide data on the “Normalised Difference Vegetation Index” (NVDI). This provides a measure of crop growth (or “thickness” on the ground).

Fertiliser spreading on field

The Courtyard Partnership hopes to reduce the use of fertilizers through a better understanding of soil properties. (credit kitching71)

With this data, farmers are more able to monitor the total health and growth of their crops on a large scale. Indeed, the digital files containing the satellite data, and thus the corresponding chlorophyll and NVDI levels, can be tied to the farm machinery, allowing automatic changes in inputs ranging from seeds to fertiliser. This type of high precision data has the potential to dramatically decrease pollution and fertiliser waste. According to the Courtyard Partnership, use of such techniques could lead to savings of 45 tonnes of carbon dioxide emissions, as well as significant decreases in fertilizer use.

Considering the serious environmental consequences that have stemmed in part from the industrialization of farming, such techniques seem promising. The extensive application of fertilizers since the Green Revolution of the 50s and 60s have indeed led to increases in agricultural production, but at serious costs. Fertilizer runoff into rivers and streams has been implicated in significant algal blooms. The dead zone of the Gulf of Mexico arises from the nitrogen and potassium fertilizer runoff polluting the Mississippi river. The resulting algal blooms cause hypoxia, or low oxygen levels, killing off much of the marine life in the area.

The concept of using satellites in agriculture may seem alien for now, but if we want to solve our problems on the ground we may be best off looking to the sky.