Although largely invisible to the human eye, large numbers of diatoms can be found on the soil surface. These diatoms are known to reflect local environmental conditions, but until recently, relatively little was known about their response to changing weather conditions.
Diatoms are microscopic, unicellular algae and form one of the most common and diverse algal groups in both freshwaters and marine environments. Because they are photosynthetic and because of their high abundances, they play a large role and often overlooked role in the exchange of gasses between the atmosphere and biosphere. It has been estimated that they are responsible for as much as 20% of the total oxygen production on Earth. Given their relation to local environmental factors (Antonelli et al., 2017), there is growing interest in the use of diatoms in hydrology as potential tracers for overland flow (Pfister et al., 2019).
To investigate how soil diatoms vary both spatially and temporally, diatom samples were taken at 16 predefined sampling locations across the 249 km2 Attert basin in Luxembourg. Observations were taken at approximately monthly intervals over the period December 2017 to November 2018, resulting in a total of 192 samples. The sampling thus covered the 2018 summer drought, which was as severe in Luxembourg as it was in The Netherlands (see also Buitink et al. 2020). Diatoms in each of these samples were analyzed for species composition (a very labor intensive process, see Foets et al. 2020a), while the algal abundances were then derived from pigment analysis using High-Performance Liquid Chromatography.
The results indicate that diatom productivity is mainly controlled by factors related to soil moisture availability (Foets et al., 2020a). This leads to strong seasonal changes, and a strong reduction in diatom productivity during drought. In contrast, the concentration of green algae remained stable over the course of the study period. In addition to vegetation, drought can thus have large impacts on other parts of the ecosystem and their exchange with the atmosphere that are often overlooked. Future research will have to quantify the contribution of diatoms and other algae to the total gas exchange.
Further reading
Antonelli, M.; et al. (2017), On the potential for terrestrial diatom communities and diatom indices to identify anthropogenic disturbance in soils. Ecological Indicators, 75, 73–81, doi:10.1016/j.ecolind.2016.12.003.
Buitink, J., et al. (2020), Anatomy of the 2018 agricultural drought in The Netherlands using in situ soil moisture and satellite vegetation indices. Hydrol. Earth Syst. Sci., https://doi.org/10.5194/hess-2020-358, accepted.
Foets, J.; et al. (2020a), Temporal and spatial variability of terrestrial diatoms at the catchment scale: controls on communities. PeerJ, 8, e8296, doi:10.7717/peerj.8296.
Foets, J.; et al. (2020b), Temporal and spatial variability of terrestrial diatoms at the catchment scale: controls on productivity and comparison with other soil algae. PeerJ, 8, e9198, doi:10.7717/peerj.9198.
Pfister, L; et al. (2017), Terrestrial diatoms as tracers in catchment hydrology: A review. WIREs Water, 4, e1241, doi:10.1002/wat2.1241.