The chemistry of suspended particulate matter, Firth of Forth

• Main Author: Holmes, Gary Sturgeon
• Published: University of Edinburgh 1978
• Subjects: 551.9
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.652522

The Firth of Forth is a wide, shallow, marine-dominated coastal embayment on the east coast of Scotland. The concentration of suspended particulate matter ranges from <1 mg 1-1 at the seaward end to >30 mg 1-1 in the west, with intermediate values along the south shore and in bottom waters. Studies of the major-element chemistry (Al, Si, Ca, Fe, Ti, IC, Mg, P and S) of local suspended matter are reported. An attempt is made to account for the observed areal, vertical and temporal changes in the chemistry of this material in terms of its concentration, gross composition, mineralogy, particle size characteristics and the partitioning of major elements among terrigenous, biogenic and organic components. The extent to which these factors are influenced by hydrodynamic processes and resuspension of bottom sediments is examined. Suspended matter in the Forth is dominated by terrigenous debris, particularly to the west. Locally, variations in inter-element ratios of this material as a function of water depth indicate increasing particle size and loading of terrigenous matter in bottom waters. Particulate Al resides almost exclusively in detrital aluminosilicates. All the elements examined are present to some degree in the terrigenous fraction, their abundance relative to Al being a function of particle size-specific mineralogy. Biogenic associations of Si, Ca (skeletal debris) and P (organics) are quantified. Pollutant phases of particulate P and Fe occur in direct association (organics and possibly ferriphosphates) and in independent forms (sewage organics and ferruginous waste). Seaward and northward flux of particulate matter occurs in surface waters, ensuring some dispersal of pollutant material and mixing with terrigenous debris. As this settles, however, it is subject to net landward transport in the bottom waters along with material winnowed from local sediments. Some degree of hydrodynamic sorting of particles is expressed in their chemistry. Relative to the amount of material in suspension, only negligible escape of particulate matter from the Forth appears to occur.