Author: uset

3C - Channel Catchments Cluster

3C - Channel Catchments Cluster

Spatiotemporal distribution of trace elements
in estuarine and coastal sediments: The
Solent area as a case studies

J. Richir*, J.M. Pini, S. White, G.J. Watson (* jonathan.richir@port.ac.uk)
Institute of Marine Sciences, School of Biological Sciences,
University of Portsmouth, Ferry Road, Portsmouth, PO4 9LY, UK

Introduction
The Solent is a natural west-to-east channel separating the Isle of White and the coast of the county of Hampshire in the central part of the Channel (Fig. 1). It is also a European Marine site with protected habitats and species. The Solent is subject to many anthropogenic pressures, specifically towards the highly industrialized city area of Southampton. No scientific-based spatiotemporal trends have been published so far regarding the contamination of this threatened area. Therefore, this study aimed to provide, for the first time, an assessment of the contamination of the sediments of the Solent waters with trace elements.

Itchen estuary

Esso refinery

Solent’s eastern end

a) Esso refiney

Fig. 1 - Map of the Solent area showing the 32 sites monitored for trace elements. The 3 contrasted red sites Itchen estuary, Esso refinery and Solent’s eastern end are discussed regarding their sediment contamination with Zn, Cu and Hg in the Fig. 2.

Material and methods
Existing databases requested for the South of England from the Environment Agency (EA) and the British Oceanographic Data Centre (BODC; MERMAN project) were mined for TEs in the < 63 µm sediments of the Solent waters.
The 32 sites retained were GIS-mapped (ArcMAP; Fig. 1) and graphs were plotted (GraphPad Prism; Fig. 2a-c) for each site and TE, i.e. mainly As, Cd, Cr, Cu, Fe, Pb, Hg, Ni and Zn. The corresponding monitored period of time covered 22 years, from 1992 to 2013.
Sediment TE concentrations were compared to reference values, i.e. Sediment Quality Guidelines (SQG) and background levels (BL).

http://www.telegraph.co.uk/; Photo: Solent News

Fig. 2 - Temporal evolution of Zn, Cu and Hg concentrations in the < 63 µm sediments sampled a) in front of the Esso refinery (above graphs and picture), b) in the Itchen estuary (right graphs and picture) and c) at the eastern end of the Solent channel (below graphs and picture), between 1992 and 2013 .
TE concentrations were compared to their respective Canadian SQG values (CCME, 1999). The guidelines consist of threshold effect levels (TEL; orange dashed line) and probable effect levels (PEL; red dashed line) :
below the TEL, adverse effects on the biota rarely occur;
between the TEL and the PEL, adverse effects on the biota may occasionally occur;
above the PEL, adverse effects on the biota are frequent.
Zn, Cu and Hg concentrations were also compared to their natural BL (black dotted line). BL values were calculated as equal to the 20 percentile values (Rainbow, 2011 - Sci Total Environ) of the global dataset built with estuarine, coastal and open sea TE concentrations reported for sediments monitored by the EA or under the MERMAN project. Sediments with TE concentrations below their respective BL values (in the 0-BL value blue range of concentrations) can be considered as unpolluted.
Hg concentrations below the detection limit (DL) of the analytical techniques used were considered as half the DL values. The DL on the Hg graphs of the Esso refinery and the Solent’s eastern end sites (black dashed line) is the median DL value reported for these sites.

c) Solent’s eastern end

b) Itchen estuary

http://www.panoramio.com/

Results and discussion
The sediment TE pollution in the Solent waters displayed an important spatial variability (Fig. 2a-c), presumably linked to the spatial distribution of pollutant anthropogenic sources. The TE pollution decreased on the whole during the 22 year survey time interval (e.g. the Esso refinery site; Fig. 2a), although this general downward trend could not be generalized to all the monitored sites (e.g. the Itchen estuary; Fig. 2b). TE levels, above their background range of concentrations, still often remained above SQG values and therefore could adversely affect the living organisms.

http://www.panoramio.com/

Conclusion
The mining of existing environmental databases is a relevant way to monitored the TE contamination on a wide spatiotemporal scale, and to transfer back relevant information to managers and policymakers on the efficiency of the implementation of environmental directives.