The Mara Project, in collaboration with colleagues from the University of Antwerp, the Botanic Garden Meise, the Swedich Museum of Natural History, GFZ German Research Center for Geosciences, and the Cary Inistitute of Ecosystem Studies has published a paper on the role of Hippos in moving silicon from savana graslands into aquatic ecosystems where it can have large impacts on primary production.
Schoelynck, J., A.L. Subalusky, E. Struyf, C.L. Dutton, D. Unzué-Belmonte, B. Van de Vijver, D.M. Post, E. J. Rosi, P. Meire, P. Frings. 2019. Hippos (Hippopotamus amphibius): the animal silica pump. Science Advances 5:eaav0395. doi:10.1126/sciadv.aav0395
https://www.youtube.com/watch?v=dTyUNPCUgvs&feature=youtu.be
https://www.sciencenews.org/article/hippo-poop-cycles-silicon-through-east-african-environment