The use of diversity indices for local assessment of marine sediment quality

Diversity indices are commonly used to measure changes in marine benthic communities. Although diversity indices give a good understanding of how biological communities respond to changes in sediment, responses of these indices can vary because of small sample sizes, and insensitive responses can result from an inappropriate choice of test community. This study focused on species density and two indices of community structure and explored how they respond to variations in sediment characteristics in our target region, Japan, and in two local areas within this region. Our analysis of the Japanese regional dataset showed a decrease in species density and the dominance of a few species as sediment conditions degraded. Local case studies showed that species density responded to sediment degradation at sites where the community was variable. However, the indices for community structure sometimes became misleading because of inaccurate estimates with small sample sizes, and could become insensitive because of masking by community variability. We conclude that species density is a sensitive indicator of change for marine benthic communities, but that indices of community structure should only be used when there is a sufficient sample size and a test community is distinguishable from other coexisting communities.

Distribution of Heavy Metals in Surface Sediments of the Bay of Bengal Coast

The concentrations of major (Si, Al, Ca, Fe, and K) and minor (Cd, Mn, Ni, Pb, U, Zn, Co, Cr, As, Cu, Rb, Sr, and Zr,) elements in the surficial sediments were studied in an attempt to establish their concentration in the Bengal coast. It was revealed that the majority of the trace elements have been introduced into the Bengal marine from the riverine inflows that are also affected by the impact of industrial, ship breaking yard, gas production plant, and urban wastes. The concentration of heavy metals was measured using Atomic Absorption Spectroscopy and Energy Dispersive X-ray fluorescence instruments. The highest concentrations for several trace elements were thus recorded which generally decrease with distance from the coast. It was observed that the heavy metal concentrations in the sediments generally met the criteria of international marine sediment quality. However, both the contamination factor and pollution load index values suggested the elevation of some metals’ concentrations in the region. Constant monitoring of the Bengal coast water quality needs to be recorded with a view to minimizing the risk of health of the population and the detrimental impacts on the aquatic ecosystem.

Distribution and accumulation of heavy metals in surface sediments from a subtropical bay affected by the Special Economic Zone, China

The concentrations of nine metals (Cd, Cr, Cu, Ni, Mn, Pb, Zn, Fe, and Al) in surface sediments from 14 sampling sites in Shantou Bay were determined in order to understand current metal levels and spatial distribution due to the rapid development of the Shantou Special Economic Zone. Results showed that metal concentrations in surface sediments varied from 0.31 to 1.74 mg kg–1 for Cd, 35.98 to 74.19 mg kg–1 for Cr, 24.43 to 79.24 mg kg–1 for Cu, 428.45 to 809.87 mg kg−1 for Mn, 16.91 to 31.51 mg kg−1 for Ni, 35.59 to 64.84 mg kg−1 for Pb, 84.91 to 246.51 mg kg−1 for Zn, 2.93 to 3.93% for Fe, and 5.25 to 9.28% for Al. Although all metal concentrations in sediments meet Chinese National Standard Criteria for Marine Sediment Quality, both enrichment factor (EF) and geo-accumulation index (Igeo) show Pb and Cd pollution existed in the upper and middle bay, and pollution of other metals is also recorded in some sites depending on the sources; river input, sewage discharge, and port activities are the main sources of pollutant to the bay.