We investigate the distribution of various fractions phosphorus (P) in sediments at the coastal area of Semarang City. Samples were collected from thirteen locations at the Banjir Kanal Barat, port and Banjir Kanal Timur. Sedimentary parameters such as sand, silt, clay, and organic carbon were analysed in order to find out their relation with various P fractions. The sediment types are predominantly sandy and silty with low clay content. Among all fractions (loosely bound/Ads-P), bound calcium/Ca-P), iron bound/Fe-P), and organic fraction/OP), Ca-P fractions constitute the largest portion (71.2 %) followed by iron-bound (17.0 %), organic fraction (10.4 %) and loosely bound (1.4 %). The bioavailable P fractions range from 20.2 % to 42.0 % of the total P (TP) content with average 28.8 %. Relatively high Ads-P content is observed in offshore locations with comparatively high mud percentage as compared with the near-shore locations. The order of abundance of the main forms of P in the Semarang coastal surface sediments is as follows: Ca-P > Fe-P > OP > Ads-P. The concentration of this fraction causes the abundance of chlorophyll-a from 9.09 to 21.09 mg/m3.
This research examines the eutrophication process mainly by considering the chlorophyll-a concentration. A simple linear model was used to determine the correlation between Chlorophyll-a and dissolved inorganic phosphate (DIP). The research was carried out on river mouths in the north coast of Central Java. The results of the linear model show that the relationship between chlorophyll-a and DIP follows the logarithmic model with the log [Chloa] = 1.52 + 1.60 log [DIP], R2 = 0.55. The model suggests that the high concentration of chlorophyll-a is related to dissolved inorganic phosphate concentrations. On the basis of the sufficient of conclusive evidence for these variables, the study sites with high stresses from several anthropogenic sources had higher chlorophyll-a than the sites that are relatively far from river mouths and lands.
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