WWW.WAS.ORG • WORLD AQUACULTURE • MARCH 2015 67 occurring or widespread cropping of water hyacinth and/or other aquatic plants is warranted. This may include adapting the cultivation of already-farmed aquatic plants to any water depth and perhaps, if required, using some type of potted floating medium to support roots. Therefore, for aquatic plants, especially water hyacinth, it is beneficial to develop uses so that their removal will be attractive and eventually their agriculture become economical. Other than experimenting with many existing aquatic plant species, including freshwater macroalgae, it may be a promising line of research to find or develop water hyacinth strains without or with low calcium oxalate concentration or simple treatments to remove it. This may represent the right step to convert troublesome ‘aquatic weeds’ into valuable and high-yielding ‘aquatic crops,’ while obtaining environmental and biodiversity services from its farming, including perhaps biodiversity enrichment or fisheries enhancement, as described for tropical seaweed farming (Radulovich et al. 2015). Conclusions Overall, cropping on water surfaces using land crops or eventually developing the cultivation at any depth of aquatic plants as crops may be a viable option that can be implemented sustainably and, perhaps most beneficially, using only water evaporated from the surface of lakes and other freshwater bodies with or without plants. Implementing this approach to the extensive lake surfaces in tropical countries could become a major source of sustainable food, particularly in view of growing limitations imposed by climate change and the increasing demand for food from growing populations. Notes Ricardo Radulovich,* Schery Umanzor and Rebeca Mata, Department of Agricultural Engineering, University of Costa Rica, San Jose, Costa Rica. Desiree Elizondo, Grupo Cabal, Managua, Nicaragua. * Corresponding author: Ricardo Radulovich, Department of Agricultural Engineering, University of Costa Rica, San Jose, Costa Rica. Phone (+506) 8315-0613. Email: ricardo. radulovich@ucr.ac.cr. The research reported here was supported by grant 134-01 from Grand Challenges Canada and by the University of Costa Rica. References Benton, A.R., W.P. James and J.W. Rouse. 1978. Evapotranspiration from water hyacinth (Eichhornia crassipes (Mart.) Solms) in Texas reservoirs. Water Resources Bulletin 14:919-930. Castine, S.A., S.S. Sellamuttu, P. Cohen, D. Chandrabalan and M. Phillips. 2013. Increasing productivity and improving livelihoods in aquatic agricultural systems: A review of interventions. Working Paper AAS-2013-30, CGIAR Research Program on Aquatic Agricultural Systems, Malaysia. CIA (Central Intelligence Agency). 2014. The World Factbook. www.cia.gov/library/publications/the-world-factbook/ FAO (Food and Agricultural Organization of the United Nations). 1998. Crop evapotranspiration - Guidelines for computing crop water requirements. FAO Irrigation and Drainage Paper 56. FAO, Rome, Italy. Finch, J. and A. Calver. 2008. Methods for the quantification of evaporation from lakes. World Meteorological Organization’s Commission for Hydrology, CEH Wallingford, UK. Idso, S.B. 1981. Relative rates of evaporative water losses from open and vegetation covered water bodies. Journal of the American Water Resources Association 17:46-48. Irfanullah, H.Md., Md.A. Kalam Azad, Md. Kamruzzaman and Md. Ahsalun Wahed. 2011. Floating gardening in Bangladesh: a means to rebuild lives after devastating flood. Indian Journal of Traditional Knowledge 10:31-38. Madramootoo, C.A. and H. Fyles. 2010. Irrigation in the context of today’s global food crisis. Irrigation and Drainage 59:40-52. Mohamed, Y.A., W.G.M. Bastiaanssen, H.H.G. Savenije, B.J.J.M. van den Hurk and C.M. Finlayson. 2012. Wetland versus open water evaporation: An analysis and literature review. Physics and Chemistry of the Earth 47-48:114-121. Radulovich, R. 2010. Marine agriculture: land plants cropped floating at sea. World Aquaculture 41(4):43-46. Radulovich, R. 2011. Massive water savings from producing food at sea. Water Policy Journal 13:547-554. Radulovich, R., S. Umanzor, R. Cabrera and R. Mata. 2015. Tropical seaweeds for human food, their cultivation and its effect on biodiversity enrichment. Aquaculture 436:40-46. Timmer, C.E. and L.W. Weldon. 1967. Evapotranspiration and pollution of water by water hyacinth. Hyacinth Control Journal 6: 34-37. Van Der Weert, R. and G.E. Kamerling. 1974. Evapotranspiration of water hyacinth (Eichhornia crassipes). Journal of Hydrology 22:201-212. FIGURE 11. Fast growth of aquatic ‘crops’ planted by tying to a floating widely-spaced net after two weeks (a) and after two months (b). The two bands of small water hyacinth plants outgrew water lettuce after two months.
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