Autumn leaves release VOCsAutumn frosts in deciduous foreststrigger significant releases of volatileorganic compounds (VOCs) fromleaves and may contribute to ground-
level ozone, according to new findingsfrom the Austrian Alps. The concentra-tion of natural VOCs after a hard frostwas 2-1/2 to 10 times more than theconcentration of VOCs from burningfossil fuels over one week in mid-November 1999.
After the first hard frost in Novem-ber 1999, scientists recorded dailypeaks of plant VOCs and found thatthey correlated with warm daytimeand freezing nighttime temperatures.
The same pattern of VOC releasewas observed in the lab when scien-tists froze and thawed leaves of clover,grass, fir, and larch from the forestsand fields surrounding Sonnblick. Theresearchers propose that frost destroysplant cells, which release wound com-pounds, such as hexanals, pentenol,and methylbutanals, in large amountswhen they thaw (Geophys. Res. Lett.2001, 28 (3), 507–510).
Modeling biodiversityGiven fears that biodiversity may bedeclining precipitously worldwide,ecologists have been scrambling to de-termine how numbers of variousspecies are changing. One of ecology’smore fundamental measures of biodi-versity is the mathematical relation-ship connecting “species richness” andthe test area in which a particularspecies has been laboriously counted.However, M. Crawley and J. Harral ofImperial College in the United
Kingdom find that the relationship isnot as simple as has been believed.
In this study, the British researchersstudied the flora in Berkshire Countyin southeastern England. All vascularplants, including native and alien,were counted, except those clearlyplanted. Replicated and randomizedplant data were collected in 11 differ-ent spatial scales, ranging from 0.01 to108 m2.
These zone data were fitted to themodel, in which species richness S isgiven by S = cAz, where c is the con-centration of species in an area A.The exponent z is typically believedto be ~0.25. However, the researchersfound a greater variation in the expo-nent. At small scales (<100 m2), z was0.1–0.2 and strongly habitat-depen-dent; at intermediate scales (1hectare to 10 km2), z jumped to0.4–0.5; and at the largest scales, z re-turned to the 0.1–0.2 range. Thesevariations suggest that different pro-cesses determine plant diversity atvarious spatial scales (Science 2001,291, 864–868).
Where does all the mercury go?Total mercury concentrations in tribu-taries of the Chesapeake Bay tend tobe higher under high-flow conditions,whereas methylmercury, the form thataccumulates in fish, is less dependenton flow rate, according to a new studyfrom the University of Maryland. Thefinding suggests that resuspension ofbed sediments or erosion of river-banks during high-flow conditions iscontributing inorganic mercury butlittle methylmercury.
Analyzing flow conditions, sus-pended particulate concentrations,and watershed characteristics of sixrepresentative Chesapeake Bay tribu-taries varying both in size and the ex-tent of urbanized areas surroundingthem, Nicole Lawson and colleaguesfind that the two most urbanizedrivers—the Potomac, which flowsthrough the Washington, DC, area andHerring Run, which flows through
Baltimore, MD—showed the strongestcorrelation between flow rates andtotal mercury concentrations.
Concentrations of other metalswith substantial anthropogenicsources—such as lead, nickel, andzinc—also seemed to depend on riverflow, whereas cadmium, copper, andchromium concentrations increasedonly slightly with flow rate. For most ofthe rivers, mercury was the metalmost strongly retained within the wa-tershed. Overall, the study results con-firm the importance of includinghigh-flow events in any sampling pro-tocol to determine the flux and water-shed yields of metals in rivers (WaterRes. 2001, 35 (2), 501–515).
Undigested particles inthe oceanNearly all organic matter formed atthe surface of the ocean is biodegrad-ed as it sinks toward the ocean floor. Asmall fraction of sinking particles,however, resists degradation and getsburied in the sediment, locking carbonaway from the atmosphere. New evi-dence reported by John Hedges of theUniversity of Washington and col-leagues could explain why some parti-cles remain untouched by hungrymicrobes, while others are ultimatelyrecycled into CO2.
Using solid-state 13C nuclear mag-netic resonance spectroscopy, the re-searchers characterized particulateorganic matter at ocean depths lowerthan possible using conventional ana-lytical techniques. Bulk samples ofplankton (0–100 m depth) and organicparticles in the upper (∼500–1000 m)and lower (3000–3500 m) water col-umns of the Pacific Ocean and theArabian Sea were found to be sur-prisingly similar in composition. Theresearchers suggest that some particu-late organic matter is shielded by sink-ing inorganic particles, like opal,calcium carbonate, and aluminosili-cates, which made up 80% of the massof all of the particles sampled (Nature2001, 409, 801–804).
Research�Watch
146 A � ENVIRONMENTAL SCIENCE & TECHNOLOGY / APRIL 1, 2001
APRIL 1, 2001 / ENVIRONMENTAL SCIENCE & TECHNOLOGY � 147 A
