Past 20-years environmental record in the coastal area of Rote Island, East Nusa Tenggara; Evidence from the variation of trace metals anthropogenic in annual banding of coral skeleton of Porites lutea

Abstract

Changing in the concentrations of trace metals in coastal seawater is in parallel with variations of human activities and geochemical processes. Coral skeleton is an excellent archive of metal proxies to monitor water quality as the trace metals incorporate to the skeleton. To study the response of trace metals in coastal seawater to human activities, the coral skeleton of Porites lutea (KR1 and KR2) from Rote Island, Kupang, East Nusa Tenggara, one of the passageways of Indonesian Throughflow (ITF) were used. Corals were drilled vertically using pneumatic tool with diameter 5 cm. The core was cut into 4 mm thick slabs, rinsed with aqua-bidest in an ultrasonic bath, and oven-dried. Sample were then x-rayed using digital radiography to determine the age and annual banding. Sub-samples were collected from each of annual banding using a hand-held drill. The powder of sub-samples were digested with acid and Milli-Q water and analyzed with Inductively Coupled Plasma-Optical Emission Spectrometer (ICP-OES) for determining of anthropogenic trace metals Cu, Pb, Zn, As, Cd and Cr. Contamination factor was used to assess the pollution degree of the coral. Based on the x-ray radiography, the linear extension rates of KR1 and KR2 are decrease from past 20 years with the average are 1.7 cm/year and 1.4 cm/year, respectively. The average of concentrations of trace metals in KR1 and KR2 followed the order of Cu>Cd>Zn>Cr>Pb>As, and their vertical profiles are slightly increase in the past-20 years. Moreover, the average of concentration all trace metals in KR2 are a bit higher than KR1 which maybe the KR2 is closed to the mainland compare to the KR1. The contamination factors of trace metals are in the level of non-pollution to moderate pollution.