Sexy science (or not)

By Marcus Wilson 03/06/2010 4

Slightly drifting away from physics this one, but it’s still science, so I shan’t apologise.

At this week’s Cafe Scientifique in Hamilton we had a great presentation from Louis Schipper, one of the soil scientists at the university here, on denitrification.   What’s that? Well, it’s quite important, so pay attention.

Louis gave us an interesting perspective on this problem. What do we (humans) need to do to live sustainably on this planet? – whatever thing it involves, we need to be consuming only one-earth’s supply of it. For some things, we need several earths to support us with our current practices. In this regard, what are our biggest problems? One, if I remember rightly, was biodiversity. Two was our use of nitrogen. And third was greenhouse gas emission / other climatic influencing effects.

Numbers one and three we are probably familiar with. I suspect most people recognise that species are becoming extinct at an alarming rate, even if we do only fret most about the LCMs (Large cute mammals – like the tiger and polar bear, not that I’d like to meet either in the wild.) And global warming is much discussed as well – I doubt there are many people in New Zealand who haven’t heard of it, even if they don’t appreciate the science of it.  (Can anyone supply any statistics here?)  But nitrogen?

Nitrogen is needed for plants to grow, and plants are needed for us to eat. About 40% of the people on this planet are supported by nitrogen that hasn’t been fixed from the air naturally (e.g. by clover). I think I got that right – if not I’m sure someone will correct me. (See – blogs do get ‘peer-reviewed’). This is unsustainable, and it leads to the problem of too much nitrate in the soil, which gets into our waterways and encourages algae to grow etc.

Anyway, my point is that global warming is a sexy science topic, and nitrogen use isn’t, though, on the number-of-earths scale, it is the bigger problem.  What exactly is it about one that has caused it to take off in the public imagination, that is lacking with the other?  Not sure. Is it scientist-and-public communication again?

Which leads me to the last point of my ramble, that The University of Waikato is hosting a mini-conference on  science-and-public communication events along the cafe scientifique lines. Should be a very interesting day – I’m really looking forward to it (Thursday 8 July). See



4 Responses to “Sexy science (or not)”

  • The paragraph starting “Nitrogen is needed for plants to grow” is surely the most important in this post, but I don’t feel like I understand it. I can see the questions marshalling in my head:

    1. The atmosphere is 70% nitrogen — how can we be running out?
    2. What is fixing, and what does clover have to do with anything?
    3. What is nitrate? Sounds like a nitrogen compound. So if we’re running out of nitrogen, how can we have too much nitrate?

  • Hmm. Ask Louis these ones. It’s not about running out of nitrogen, it’s about nitrogen ending up in places that is shouldn’t, and taking a long time to remove through natural processes. (Like global warming isn’t about running out of carbon, it’s (partly) about carbon ending up where it shouldn’t – in the atmosphere as CO2.) I think the basic thing is that when you stick nitrogen-based fertilizer into the soil around the plants, we end up with nitrate (a nitrogen compound) in the soil, which then ends up in the waterways. Sure, before man was around to stuff things up there would have been nitrate in the waterways, but it would be in equilibrium – the rate of its arrival being equal to the rate of its removal. But in some places the high use of fertilzer (plus waste from dairy farming) means nitrate is arriving in waterways much more quickly than it can be removed – i.e. giving long term build up in lakes (Louis also mentioned the Gulf of Mexico, which has a large and growing dead-zone from nitrates running down the Mississippi.) Something like that. Anyway, the point of my blog was that problem hasn’t really caught the public imagination.

  • Hi Repton,

    That ‘fixing’ think is nitrogen fixation, sucking nitrogen out of the air and making it into ammonia . Ammonia is essential for, well, pretty much everything but none of the so called ‘higher organisms’ can make it from the nitrogen in the atmosphere. Legumes (most notably clover) and a few other plants and even termites are nitrogen fixers, but they do that by having symbiotic relationships with bacteria.

  • If I understand Louis correctly, it’s not that we’re running out of nitrogen but that we’re using nitrates in an unsustainable manner.

    Plants can’t use nitrogen gas to make proteins, they require it in the form of nitrate (NO3-). This is a soluble molecule & gaseous nitrogen is ‘fixed’ into nitrate by a variety of bacteria (& also by lightning strikes!). Some of these bacteria live in a symbiotic relationship with clover & other legumes, which is why clover’s so useful in a pasture, because it adds nitrate to the soil (well, its bacterial symbionts do).

    In an unmodified-by-man environment, as Marcus says, nitrate in pretty much equals nitrate out – nitrates released through excretion, or when organisms die, are returned to the atmosphere as nitrogen through the actions of another set of bacteria (the ‘denitrifying’ bacteria).

    However, the problems arise when we add too much nitrate (in the form of fertiliser, & also as farming effluent etc) & unbalance the system. There’s too much for the denitrifying bacteria to handle & the extra ends up polluting waterways & encouraging algal blooms, which in turn use up all the oxygen in the water & can produce the ‘dead zones’ Marcus mentions. Nitrates can also pollute bore-supply drinking water & cause some rather nasty health problems, particularly in infants & young children. Hence the significance of Louis’ work on denitrification systems.

    You’re right, Marcus, it’s really strange that this one hasn’t caught on in the same way as global climate change. Maybe it needs a poster boy (or girl!)?

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