There is growing concern at the impacts of intensification of pastoral grazing animal systems on water quality, with the main concern related to nitrate leaching.
There is a need to relate real-time nitrate leaching levels to subsequent water quality in nearby rivers and groundwater.
I'm interested in the methodologies and technologies that might be deployed to assess this issue on larger scales, for example in paddocks or catchments.
I know that Lincoln Ventures (or whoever are their successors) have developed/are developing a technique for real time measurement of water fluxes through the soil profile.
About 2 - 3 years ago Aqualinc put a research application in to MBI to develop a real time measurement technology for nitrate concentrations. Apparently there are technologies already available, but just need to be adapted. They were turned down and haven't reapplied.
The combination of fluxes and concentrations will allow you to real time measure nitrate losses.
Just a few million spent on this would likely crack it, and given the magnitude of the problem is long term a pretty good expenditure. You would still need Overseer in some form, but accuracy could be immeasurable improved.
Hi Gerald,
You may wish to look at this paper in Water Resources Research.
Steve
Nitrate in Groundwater and Water Sources used by Riparian Trees in an Agricultural Watershed: A Chemical and Isotopic Investigation in Southern Minnesota
Stephen C. Komor
Joseph A. Magner
Article first published online: 9 JUL 2010
DOI: 10.1029/95WR03815
Dear Sir, Following links may be useful for you
http://www.tandfonline.com/doi/pdf/10.1080/00288230709510290
http://www.fao.org/docrep/v2350e/v2350e0q.htm
Regards
Dear Gerald, this can be particularly difficult depending on whether you're talking streams, shallow groundwater, or deep groundwater where, for instance in Canterbury, the lag between loss and measureable increase could be 50+ years. This is the danger of not doing anything to mitigate losses or constrain development now because it may be many years before the full impact is apparent. There is technology now to read nitrate levels in runoff, streams or groundwater more or less instantly as it passes an in situ sensor but the main means used currently to measure cumulative N losses is using lysimeters. These capture what nitrate loss is occurring from a urine patch from a defined volume of soil. Its not perfect but is a reasonable facsimile. We can assess now the size of the nitrate loss occurring from a paddock but what happens after that depends on the soils and the underlying hydrology. Doesn't really answer your question but then its a really complicated issue. If we knew we could retire now!
Regards
Dear Gerald, We've studied the movement of nitrate between trees, crops and soil using N15 stable isotopic tracer. This is an effective and well-documented study material, but N15-enriched fertilizer is expensive. Anyway, keep on looking, and best wishes.
Gerald chased me offline, and suggests I put my response to him in this discussion.
I saw this on ResearchGate but did not respond because we are not able to provide real-time measurements of nitrate leaching or other N cycle processes using isotopes. Only those deep UV spectroscopy gadgets can do that for concentrations, and because of interferences I understand they need clean water and may still need some corrections. I haven't looked into them in a few years (and never bought one).
However, since you ask me, I'll reorient your question to what we can do. We can follow N from deposition in urine spots through to its eventual fate. Natural abundance isotope measurements can help a lot with understanding mass balance - how much N goes where? And so, if we follow a urine addition for a week or two, we then know what the losses look like in our isotope measurements if we see them in the atmosphere or in drains, streams, etc. It does take a few months to produce the results, but seems worth it.
I attach [the link to] a paper that was just accepted in Ag Ecosystem and Environment - the official preprints should be available within a few weeks. Naomi Wells was a PhD student with Tim Clough and me in the Land-to-Water-Nitrogen Transfers programme.
I think there would be value in doing more of this natural isotope tracing work, to build on what has already been learned from NzOnet EF studies.
doi.org/10.1016/j.agee.2014.10.001
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