The McMurdo Dry Valleys and other desert oases on the coast of East Antarctica are essentially "plant-free" environments. As a result the dissolved organic material (DOM) present in the water of the dry valley lakes and streams is derived only from the breakdown of biomass originally produced by microbes, e.g. algae and bacteria.
These microbes grow in the water column of the lakes, such as Lake Fryxell in Taylor Valley (Fig.1), and form mats that cover the streambeds. Studies by MCM scientists have shown that this microbial DOM has chemical characteristics that are distinct from those of DOM derived from leaf litter on the forest floor or from wetland plants which can give water a yellow-color. Based on these chemical differences, a simple spectroscopic measurement (the fluorescence index, FI) was developed (McKnight et al. 2001). This index has been used by many scientists to understand processes that control carbon and nutrient cycling in diverse aquatic and soil ecosystems and can be used to design in situ sensors. For example, studies using the index have shown that in lakes DOM can become more "microbial" in character during summer blooms of algae (Miller et al 2009).