The skeletal material of hard corals records past pollution events according to a new study.
Coral cores from four enormous and elderly corals of the Porites genus collected from different reef environments off Bali, Indonesia, have been shown to contain different levels of a form of nitrogen.
The four reefs were each exposed to different amounts of nitrogenous pollution, and the corals found in each habitat had levels of organic delta(15)N in their skeletal material in accordance to the amount of nitrogen in the water. "We suggest that skeletal organic delta(15)N can serve as a recorder of past nitrogen sources..."
The paper, which has just been published in the journal Marine Pollution Bulletin, shows a timeline in the pollutant levels of Indonesia reefs.
The team says: "Skeletal delta(15)N in the agriculturally exposed coral declined from 10.7+/-0.4 per thousand in 1970-1971, when synthetic fertilizers (-0.8 per thousand+/-0.2 per thousand) were introduced to Bali, to a depleted "anthropogenic" baseline of 3.5 per thousand+/-0.4% in the mid-1990s. delta(15)N values were negatively correlated with rainfall, suggesting that marine delta(15)N lowers during flood-bourn influxes of waste fertilizers.
"Reef cores exposed to untreated sewage in terrestrial discharge were enriched (7.8 and 7.3+/-0.4 per thousand), while the offshore core reflected background oceanic signals (6.2+/-0.4 per thousand).
"Delta(15)N, N concentration, and C:N systematics indicate that the N isotopic composition of skeletal organic matter was generally well preserved over 30 years."
For more details see the paper: Marion GS, Dunbar RB, Mucciarone DA, Kremer JN, Lansing JS, Arthawiguna A (2005) - Coral skeletal delta(15)N reveals isotopic traces of an agricultural revolution. Mar Pollut Bull. 2005 Sep ; 50(9): 931-44.