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Pond skimmer
Last words past and present at newscientist.com/lastword
THE LAST WORD Off the rails I was looking out of a train window at the live rail on the adjacent track during a heavy rainstorm. This made me wonder how much electrical power is lost across the wet ceramic supports. Is it enough to cause a significant voltage drop in the locality where the rain is falling?
n My experience is with electricity supply, but the principles involved in the transmission of high-voltage electricity in heavy rain are similar to those in electrified rail systems. Rather than speaking about power being “lost”, it makes more sense to talk about the electrical current leaking across the ceramic supports or the insulators. It should be noted that, contrary to the impression one might get from television, rainwater is a fairly poor conductor of electricity. The track insulators are also designed in a special shape so there is no continuous wet surface between the live conductor and earth. These factors make the leakage current small compared with, say, the current drawn by a train starting from rest. Peter Smith Long Ashton, Somerset, UK
recently flooded the nearby road, overflowing into my garden and the pond. The next morning the algae had gone. What was in the floodwater that managed to clear the algae?
n “Pea-soup” algae are generally single-celled species, plus others that clump in twos and fours. Populations explode when sunshine and nutrients combine in warm conditions – Daphnia and similar organisms that graze on algae are barely able to thin the ranks. The resultant pea soup may look repellent, but is often a healthy community that is enthralling to view under
“The pea soup may look repellent, but it is often enthralling to view under a microscope”
I have a garden pond that suffers from “pea-soup” algae. A thunderstorm
a microscope. To clear the water, key nutrients such as phosphates must be reduced. Floodwater might wash out a pond or cause the algae to die through pollution. Dead cells will sink or form a scum, leaving the rest as clear water. Possible toxic pollutants include roadside herbicides, salt or tarry phenolics from asphalt on recently surfaced roads. Furthermore, heavy traffic sprinkles roads with exhaust dust and rubber powder. Tyre rubber contains toxic organic compounds and metals such as zinc, with the dust having a huge surface-tovolume ratio that permits rapid release of poisons into the water. In fact, it is a common (although
The writers of answers that are published in the magazine will receive a cheque for £25 (or US$ equivalent). Answers should be concise. We reserve the right to edit items for clarity and style. Please include a daytime telephone number and an email address if you have one. New Scientist retains total editorial control over the published content. Reed Business Information Ltd reserves all rights to reuse all question and answer material that has been
submitted by readers in any medium or in any format and at any time in the future. Send questions and answers to The Last Word, New Scientist, 110 High Holborn, London WC1V 6EU, UK, by email to [email protected] or visit www.newscientist.com/topic/lastword (please include a postal address in order to receive payment for answers). Unanswered questions can also be found at this URL.
Pond skimmer
ill-advised) practice to put old tyres into ponds to clear them of unwelcome organisms. However, it actually increases the nutrient supply and invites cyanobacterial blooms that are far less welcome than any pea soup. Jon Richfield Somerset West, South Africa n Algae do well in a neutral to slightly alkaline environment, at a pH of about 7 or 8. At this level they take up nutrients such as phosphate and nitrate easily. All rain is acidic. Carbon dioxide makes up about 0.04 per cent of air and it dissolves in clouds and falling rain to form carbonic acid, giving natural unpolluted rain a pH of about 5.5. Air-polluting gases such as the oxides of sulphur and nitrogen further reduce the pH of rain. Normal amounts of rainfall on the surface of a pond would decrease its pH, but it is buffered by carbonates and bicarbonates – naturally occurring alkaline chemicals in water. However, a deluge of rainwater would have defeated the pond’s buffering capacity, lowering its pH. An acidic pH can damage algal cell walls, thus causing the overnight algal demise in this case. Because pond plants use up the excess carbon dioxide during photosynthesis, the pond’s pH will start to return to normal. But pond owners should not be tempted to use acid to get rid of algal blooms because it could
have disastrous consequences for pond flora and fauna. David Muir Science Department Portobello High School Edinburgh, UK n As photosynthetic organisms, algae will tend to cluster close to the surface of the pond to capture maximum light (just as trees in a dense woodland have most of their leaves at the top). So, although the water may appear as “pea soup”, it is probably much clearer towards the bottom. The storm water pouring into the pond causes it to overflow. And the overflow comes from the top layers of water. It is also possible the storm water, having fallen from a height and being colder than the pond water, sank rapidly, enhancing the effect. So perhaps it is nothing in the storm water itself. Within a week, I’ll bet it turned just as pea-soupy as it was before. Alistair Scott Gland, Switzerland
This week’s question I know that face
I’ve seen several archaeological shows in which skulls are built up to create “real-life faces”. How valid is this? Has anyone tested the procedure by giving people a complete, contemporary skull when a picture exists of the person, and seeing how it compares to the recreated image? Ian Wardrop Houghton, Adelaide, Australia
Question Everything The latest book of science questions: unpredictable and entertaining. Expect the unexpected Available from booksellers and at newscientist.com/questioneverything
THE LAST WORD Off the rails I was looking out of a train window at the live rail on the adjacent track during a heavy rainstorm. This made me wonder how much electrical power is lost across the wet ceramic supports. Is it enough to cause a significant voltage drop in the locality where the rain is falling?
n My experience is with electricity supply, but the principles involved in the transmission of high-voltage electricity in heavy rain are similar to those in electrified rail systems. Rather than speaking about power being “lost”, it makes more sense to talk about the electrical current leaking across the ceramic supports or the insulators. It should be noted that, contrary to the impression one might get from television, rainwater is a fairly poor conductor of electricity. The track insulators are also designed in a special shape so there is no continuous wet surface between the live conductor and earth. These factors make the leakage current small compared with, say, the current drawn by a train starting from rest. Peter Smith Long Ashton, Somerset, UK
recently flooded the nearby road, overflowing into my garden and the pond. The next morning the algae had gone. What was in the floodwater that managed to clear the algae?
n “Pea-soup” algae are generally single-celled species, plus others that clump in twos and fours. Populations explode when sunshine and nutrients combine in warm conditions – Daphnia and similar organisms that graze on algae are barely able to thin the ranks. The resultant pea soup may look repellent, but is often a healthy community that is enthralling to view under
“The pea soup may look repellent, but it is often enthralling to view under a microscope”
I have a garden pond that suffers from “pea-soup” algae. A thunderstorm
a microscope. To clear the water, key nutrients such as phosphates must be reduced. Floodwater might wash out a pond or cause the algae to die through pollution. Dead cells will sink or form a scum, leaving the rest as clear water. Possible toxic pollutants include roadside herbicides, salt or tarry phenolics from asphalt on recently surfaced roads. Furthermore, heavy traffic sprinkles roads with exhaust dust and rubber powder. Tyre rubber contains toxic organic compounds and metals such as zinc, with the dust having a huge surface-tovolume ratio that permits rapid release of poisons into the water. In fact, it is a common (although
The writers of answers that are published in the magazine will receive a cheque for £25 (or US$ equivalent). Answers should be concise. We reserve the right to edit items for clarity and style. Please include a daytime telephone number and an email address if you have one. New Scientist retains total editorial control over the published content. Reed Business Information Ltd reserves all rights to reuse all question and answer material that has been
submitted by readers in any medium or in any format and at any time in the future. Send questions and answers to The Last Word, New Scientist, 110 High Holborn, London WC1V 6EU, UK, by email to [email protected] or visit www.newscientist.com/topic/lastword (please include a postal address in order to receive payment for answers). Unanswered questions can also be found at this URL.
Pond skimmer
ill-advised) practice to put old tyres into ponds to clear them of unwelcome organisms. However, it actually increases the nutrient supply and invites cyanobacterial blooms that are far less welcome than any pea soup. Jon Richfield Somerset West, South Africa n Algae do well in a neutral to slightly alkaline environment, at a pH of about 7 or 8. At this level they take up nutrients such as phosphate and nitrate easily. All rain is acidic. Carbon dioxide makes up about 0.04 per cent of air and it dissolves in clouds and falling rain to form carbonic acid, giving natural unpolluted rain a pH of about 5.5. Air-polluting gases such as the oxides of sulphur and nitrogen further reduce the pH of rain. Normal amounts of rainfall on the surface of a pond would decrease its pH, but it is buffered by carbonates and bicarbonates – naturally occurring alkaline chemicals in water. However, a deluge of rainwater would have defeated the pond’s buffering capacity, lowering its pH. An acidic pH can damage algal cell walls, thus causing the overnight algal demise in this case. Because pond plants use up the excess carbon dioxide during photosynthesis, the pond’s pH will start to return to normal. But pond owners should not be tempted to use acid to get rid of algal blooms because it could
have disastrous consequences for pond flora and fauna. David Muir Science Department Portobello High School Edinburgh, UK n As photosynthetic organisms, algae will tend to cluster close to the surface of the pond to capture maximum light (just as trees in a dense woodland have most of their leaves at the top). So, although the water may appear as “pea soup”, it is probably much clearer towards the bottom. The storm water pouring into the pond causes it to overflow. And the overflow comes from the top layers of water. It is also possible the storm water, having fallen from a height and being colder than the pond water, sank rapidly, enhancing the effect. So perhaps it is nothing in the storm water itself. Within a week, I’ll bet it turned just as pea-soupy as it was before. Alistair Scott Gland, Switzerland
This week’s question I know that face
I’ve seen several archaeological shows in which skulls are built up to create “real-life faces”. How valid is this? Has anyone tested the procedure by giving people a complete, contemporary skull when a picture exists of the person, and seeing how it compares to the recreated image? Ian Wardrop Houghton, Adelaide, Australia
Question Everything The latest book of science questions: unpredictable and entertaining. Expect the unexpected Available from booksellers and at newscientist.com/questioneverything