25 May 2018
Rubber Remedies for Carbon Sinks
Tropical forests trap atmospheric carbon in leaves. This carbon reaches the soil through decomposition. But forests are being transformed into agricultural lands and plantations. Soil is degraded by infrastructure development. Such human activities result in loss of organic carbon in soil.
Degraded land is often converted into rubber plantations in North East India. Researchers from the Assam University recently collaborated with South Africa to assess the impact of land use changes in North East India.
The team analysed organic carbon pools in soil samples collected from tropical forests, rubber plantations of different ages and degraded grasslands.
The research team ascertained the impact of land use changes on soil organic carbon. Organic carbon in soil is stored in two fractions as active and passive pools. Carbon in the active pool has a low residence time (2 to 5 years) compared to that of carbon in the passive pool (50 – 100 years). The carbon accumulation in the active pool depends on the availability of decaying matter.
The researchers measured carbon levels from both pools. Natural forests recorded the highest soil organic carbon stock followed by rubber plantations and grasslands.
In younger plantations, the carbon in active pools was higher than in the passive pools. Accumulation of carbon in passive pools increases when decomposition is impaired. So, older plantations had trapped stable soil organic carbon in passive pools.
Rubber plants contain a compound, tannin, in their leaves. Due to the priming effect, the leaf litter increases the levels of carbon in passive pools. The researchers thus found that older rubber plantations act as carbon sinks.
Degraded lands converted into rubber plantations can provide revenue as well as serve as carbon sink management, say the researchers.
Here is a case of agreement between economics and environmental concerns.
Sci. Total Environ., 624: 908-917 (2018)
Radiation Levels at Monazite Deposits
A case study from Kerala
Kerala boasts rich monazite deposits in its coastal areas. The ore contains thorium, increasingly used in nuclear power plants and projected to be the next generation nuclear fuel in India. But for local people, it spells unhealthy radiation levels.
Thorium decays to thoron, a radioactive isotope of radon. People in these areas are exposed to external radiation from the environment, and internal radiation from food, water and air. Normal radiation levels are less than 1.5 mGy per year. But the radiation in these areas is far higher.
Researchers from RCC Thiruvananthapuram, NBRCR Karunagappally, and three Japanese universities, measured the concentrations of radon, thoron and thoron derivatives in 183 houses in high background radiation areas and 76 houses in Control Areas,
There was no significant difference in dosage between the two areas. Less than a fifth of the total dose was due to radon. The indoor concentrations of radon was surprisingly low, compared to similar places elsewhere. While there is some increase in indoor concentrations in areas with high background radiation, there is no significant difference in inhaled air. The internal exposure due to inhalation appears to be ‘small, but not negligible, compared with the external exposure’. Scientists say that this could be attributed to the the large, open windows and high air ventilation in houses in this coastal area with warm climate.
An interesting point is that in spite of such high radiation levels, cancer incidence in the region is not as high as expected. Nor are there other expected abnormalities. There is some evidence that radiation exposure helps build radiation tolerance. But the molecular mechanisms that protect the people here are yet to be delineated.
Journal of Radiological Protection 37 (1): 111-126 (2017)