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December 2008
Welcome to the December edition of Fertile Minds, the monthly newsletter of Sydney Environmental & Soil Laboratory.
The staff at SESL wish all our clients and friends a safe Christmas break. Don't know what you want for Christmas? How about a photosynthetic slug? Read on!
If you have any questions you would like answered in Fertile Minds, please write to info@sesl.com.au. Or if you have any special requirements, we would be pleased to talk with you and tailor a package and price. Please contact the office on (02) 9980 6554 or write to us at info@sesl.com.au.
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In this issue
- The Loam Ranger – Plant poisoning
- The physics of mulches: how they work
- Waste regulation in NSW
- Drip irrigation may use more water, not less
- Did you know ... ? – Green sea slugs
The Loam Ranger – Plant poisoning
Dear Loam Ranger,
As a council officer I get called out to look at trees that the caller claims have been poisoned. What clues should I look for?
The deliberate killing of trees in either public or private areas without approval is illegal and is a particularly selfish and immoral crime, distressing to those who love trees and the green and leafy suburbs and towns in which they live. While prosecutions for cutting down trees illegally do occur, rarely is it possible to obtain the standard of proof required for prosecution for poisoning. We have, however, obtained direct evidence of the intentional killing of trees with herbicides and other means and would like to share our experience.
We get many requests, from both residents and councils, usually in suburban areas, to prove that their trees or other plants have been poisoned. These are often accompanied by more or less overt accusations directed at neighbours. While we have certainly had positive diagnoses of herbicide poisoning, the great majority of such requests either clearly do not involve herbicide or are too difficult to diagnose. This article summarises our experience.
Click here to find out what signs to look for in a poisoned tree (750 words, 3 minutes)
The physics of mulches: how they work
We all know that mulches benefit plant growth. The beneficial effects are more obvious in dry and hot climates. Mulches can sometimes provide nutrients, but most of the benefit is due to the physical processes at the ground surface. These can be summarised under three headings: Water infiltration, Water evaporation and Temperature damping.
Click here to learn how mulches work (750 words, 3 minutes)
Waste regulation in NSW
In a recent issue we looked at the broad changes to the NSW Protection of the Environment Operations Act 1997 (the POEO Act) that took effect from May 2008. For various reasons (largely, we think, because this is a new frontier for regulators), the application of the new regulations is changing rapidly. Since our last article, all exemptions to waste classification for reuse on land have been updated. This article updates the situation as it stands at the moment.
It is critical to recognise that the Act places responsibility on the waste generator, the waste transporter and the waste reuser to ensure that all waste generated, transported and reused is fit for purpose, does not pollute the environment or pose health hazards, and is licensed under the Act. Each and all of those people are liable.
All waste reuse must be licensed or specifically exempted.
Your waste (that is, what you have generated, are transporting or are reusing) may well already be exempted from the need for a licence. See below for a list of exemptions and links to more information. If it does not come under any of these categories, you will need to apply for a licence with the NSW Department of Environment and Climate Change (DECC). Sorting through the legislation, classifications, definitions and exemptions is a daunting task, but SESL has made it a priority to come to grips with the legislation and regulations. If you want, SESL will apply on your behalf, for either a licence or an exemption.
Drip irrigation may use more water, not less
Drip irrigation supplies plants with only as much water as they need, and none is wasted feeding weeds, leaching into the soil or evaporating into the air. So it must be good, right?
Well, paradoxically, a study published in the Proceedings of the National Academy of Sciences of the USA has found that drip irrigation could well lead to overuse of limited water resources (PNAS 105: 18215–18220; DOI: 10.1073/pnas.0805554105).
Authors Frank Ward and Manuel Pulido-Velazquez studied water use in the dry Upper Rio Grande Basin in the USA and Mexico, and looked at how changes in water use policies would affect actual water use. Their computer modelling showed that subsidies to growers who switched to drip irrigation would encourage the uptake of drip irrigation, as might be expected. But this would have two unintended consequences.
The first consequence would be that the higher productivity (more crop per drop) at less cost (on account of subsidy) would encourage growers to plant more area and so use up to 20% more water than before. The second would be that the hydrologic cycle would be interrupted, as all water applied by drip irrigation is lost to transpiration, and none is returned to the originating basin in groundwater flow or surface flow.
However, further studies taking into account different factors may yet prove otherwise. Nevertheless, water is a scarce and valuable resource, especially here in Australia, and a solution may lie in simultaneously maximising yield while minimising water use, rather than trying to use all the water available.
Click here for a link to download the PDF (250 words, 1 minute)
Did you know ... ? – Green sea slugs
Why don’t animals use photosynthesis?
The answer has always been that their ancestors never acquired the equipment the way plants did, and even if they had, their surface-area-to-volume ratio is too small to allow a surface of green tissue to feed the entire animal.
Now it turns out that at least one animal does photosynthesise.
A study published by the Proceedings of the National Academy of Sciences of the USA reports the discovery of photosynthesis by a sea slug, Elysia chlorotica (PNAS 105: 17867–17871; DOI: 10.1073/pnas.0804968105). Author Mary Rumpho and her colleagues discovered that when the sea slug ingests its food alga, Vaucheria litorea, instead of digesting everything, it takes the alga’s photosynthetic plastids and incorporates them into its own cells within the digestive tract.
On its own this is not enough, because the photosynthetic plastids, called chloroplasts in higher plants, depend for more than 90% of their proteins on the nuclear genome, not their own genome. So how do they do it?