DrDaniel Harrison

Much of my research is centered around anthropogenic supply of nutrient to marine ecosystems. Broadly I have been considering 2 cases; 1. Unintentional introduction of nutrients such as nitrogen, phosphorous, and silica into marine ecosystems, an example is the stormwater & wastewater entering Sydney Harbour from the urbanised catchment. 2. Proposals to intentionally introduce nutrients to the ocean for the purposes of restoring ocean productivity, sequestering carbon, or stimulating fisheries. Much of my work takes place at the Sydney Institute of Marine Science located at Chowder Bay on the harbour foreshore, of which the University of Sydney is one of four founding members.

Unintentional, introduction of nutrients to waterways such as Sydney Harbour result in changes to the ecosystem, however some changes may be beneficial under certain conditions, nutrients may lead to increased fisheries production, and increased marine diversity. It is well known that overloading marine ecosystems with nutrients can be responsible for negative outcomes such as eutrophication and harmful algal blooms. However much less studied is the case where inputs are lower and have not lead to eutrophication, I am interested in the effects and fate of nutrient inputs under these conditions. Does our anthropogenic influence play a role in maintaining the productivity and diversity we see in our harbour? Are we in fact inadvertently feeding our fish?

Artificial attempts to stimulate marine ecosystems would presumably seek to achieve a similar balance of increased productivity while avoiding eutrophication and harmful algal blooms. Could these ideas work? Are they technically feasible? How would they affect pelagic ocean ecosystems, and what are the potential risks and benefits? For two decades ocean iron fertilisation has been investigated as a potential low-cost method of sequestering massive amounts of carbon dioxide from the atmosphere. My PhD research has shown that while it may be possible to sequester some carbon at a low cost, various biogeochemical processes in the ocean work to lower the net benefit over the next 100 years, and on average the cost would actually be prohibitively high (Harrison, 2013). Close consideration of an alternative idea to provide the missing macronutrients (nitrogen, phosphorous, and silica), yields some counter-intuitive results, despite needing something like 10,000 times as much nitrogen as iron to stimulate productivity the biogeochemical processes are much more in favour of carbon sequestration, overall efficiency appears to be much higher and the cost lower than for iron, a good overview is given in Jones & Harrison (2013). The idea of artificially fertilising the ocean, or performing geoengineering to manipulate carbon dioxide levels or global temperature, towards pre industiral values is controversial. Although such dramatic measures may become increasingly more attractive if the planet continues on its current trajectory. There is much work to be done, to evaluate both the risks, and potential benefits of such ideas, as well as the technical feasibility, in this way policy makers of the future can be well informed.