Vertical Distribution of Heavy Metals in Coastal Sediment: A Record of the Changing Input in the Estuarine of the Semarang Flood Canal

Abstract

Sediment plays an important role in archiving contaminant like heavy metals and could
record metal contamination in sediment due to land-based input such as flood canals of Semarang. This
study was to understand the changing record of heavy metals’ contamination in coastal sediment and to
assess the sediment quality. Two core sediments, from two different sites, were collected up to 80 cm in depth
and, subsequently, sectioned within a 5 cm interval. A digestion system followed by AAS measurement, was
used to determine the metal concentrations, Enrichment Factor (EF) was applied to assess sediment quality.
The sediment fraction and metals concentration revealed the changing of input and deposition process along
sediment cores in East Flood Canal (EFC) and West Flood Canal (WFC). There was an alteration of
sediment composition in which the proportion of sediment composition moved to finer size in EFC and a
pulse of coarser-finer-coarser size of sediment composition was observed in WFC. In general, higher
concentrations of Fe, Cd, Cu, Ni and Zn were observed differently with Pb concentration. Ni along both
sediment cores was unenriched (EF<1), whereas Cd, Cu, Pb, and Zn were classified minor to moderate
enrichment. Thus, the source and deposition processes of these Fe, Cd, Cu, Ni and Zn were different
compared with those of Pb.

Keyword: flood canal, Semarang, heavy metal, Enrichment Factor

Sedimen memiliki peran sebagai tempat penyimpanan bahan pencemar seperti logam berat dan studi
atas pencemaran logam berat dalam sedimen di banjir kanal kota Semarang belum banyak dilakukan. Sehingga
tujuan dari penelitian ini adalah untuk mengetahui sejarah pencemaran dengan melihat distribusi vertikal kemudian
menilai status logam berat dalam sedimen di muara banjir kanal barat dan banjir kanal timur kota Semarang. Untuk
menjawab tujuan penelitian, telah dilakukan pengambilan 2 sampel sedimen inti hingga kedalaman 80 cm kemudian
sedimen tersebut diambil tiap interval 5 cm. Metode peleburan yang diikuti pengukuran dengan AAS dilakukan
untuk mengukur konsentrasi logam dan Enrichment Factor (EF) dihitung untuk menilai kualitas sedimen. Fraksi
sedimen dan konsentrasi logam berat menunjukkan perubahan masukan dan proses deposisi di sepanjang sedimen inti
yang dianalsis dari Banjir Kanal Timur (BKT) dan Banjir Kanal Barat (BKB). Tampak adanya perubahan
komposisi sedimen dimana sedimen di EFC cenderung menjadi lebih halus sementara tampak adanya fluktuasi
komposisi sedimen di WFC dari kasar-halus-kasar. Masing-masing logam menunjukkan pola yang berbeda
walaupun konsentrasi Fe, Cd, Cu , Ni dan Zn tinggi tampak di periode energi yang lebih tinggi dan konsentrasi Pb
tinggi teramati sema periode energi rendah. Ni di kedua sedimen inti masih berada pada konsentrasi alami
(EF<1),tetapi Cd, Cu, Pb dan Zn telah mengalami pengayaan minor hingga moderat. Informasi tersebut dapat
menunjukkan sumber dan proses deposisi Fe, Cd, Cu, Ni dan Zn berbeda dengan Pb.

Kata kunci: Banjir kanal, Semarang, logam berat, Enrichment Factor.