The effects of powerboat emissions on the water quality of Loch Lomond

GE Environmental Sciences;QH301 Biology

Bannan, Mark ; Adams, Colin E.

University:University of Glasgow

关键词: GE Environmental Sciences;    QH301 Biology;   

Others  :  http://theses.gla.ac.uk/5325/1/1999BannanPhD.pdf

来源: University of Glasgow

【 摘 要 】

Recently, there has been increased concern about the potential impact ofpowerboating on freshwater ecosystems. In the case of Loch Lomond, such concern ledto the commencement of a programme of boat counting surveys in 1989. In thesesurveys, it was found that maximum boat numbers are increasing in Loch Lomond. As alogical progression from these surveys, the present study examined the impact ofpowerboat chemical pollution on the water quality of Loch Lomond.In the first stage of this study, the scale of powerboat pollution was assessed.This was achieved by constructing a simple mathematical model to estimate the totalannual discharge of hydrocarbons (HCs) from powerboat emissions into Loch Lomond.By using boat census data and published information about the emission rates ofdifferent types of powerboat engines, the total annual input for Loch Lomond wasestimated at 25.50 tonnes in 1989 and this input has greatly increased since then. Thisindicates that there is real potential for hydrocarbon (HC) pollution of Loch Lomondfrom powerboat operation. Most of the HC material discharged emanated fromspeedboats powered by outboard motors.To identify and quantify HC pollutant compounds entering water from outboardengines, Gas Chromatography-Mass Spectrometry (GC-MS) analysis was performed onwater subject to a controlled pollution discharge from an outboard motor. Altogether, 47compounds were detected in this exhaust-polluted water (EPW), with most of thesebeing volatile aromatic HCs, such as benzene and alkylated benzenes.Water samples were also taken from three sites in Loch Lomond on twooccasions: once in winter, during negligible boat activity and once in summer, at a timeof high powerboat activity. No HCs were detected in winter, but some volatile aromaticHC compounds were clearly detectable in summer. These compounds were the same asthose most abundant in EPW and found in similar relative proportions. Further experiments in this study involved the analysis of a large number ofwater samples. To enable this, it was necessary to develop an appropriate new methodfor the analysis of powerboat exhaust pollutants, which are mostly aromatic HC. Allaromatic HCs fluoresce and the new method involved fluorescence spectroscopyanalysis, following sample purification by normal-phase column chromatography. Thistechnique is non-destructive allowing subsequent confirmatory analysis by GC-MS. Itwas found that the new method was fast, precise, highly sensitive and specific to volatilearomatic HCs.The capability of measuring HCs in a large number of samples allowedpreviously unfeasible experiments investigating:1) The geographical distribution of powerboat exhaust HCs in Loch Lomond.2) The depth profile of powerboat exhaust pollutants in the top 1.5 m of the watercolumn.3) Recovery of water quality, following peak weekend boat activity in summer.It was found that:1) Volatile aromatic HCs from powerboat exhaust are detectable over much of LochLomond on days of heavy powerboat activity, with concentrations of up to 37 ug.l"occurring.2) Pollutant HCs are found at depths of at least 1.5 m, and are not confined to thesurface microlayer (100 urn), The HC distribution with depth was mostly uniform inthe field and this was confirmed in controlled experiments in a tank.3) Recovery of water quality was difficult to demonstrate in the field, possibly aspollution incidents occur continually during summer.4) HC concentration declined in controlled experiments, in which water was subjectedby a controlled pollution discharge from an outboard motor. The time taken for theHC concentration to reach 50 % of the initial HC loading varied but wasapproximately 7 - 9 days.The toxicity of EPW was investigated by performing 24 hour LC50 (LethalConcentration for 50 % of test organisms) tests, using the water flea, Daphnia magna(an international standard test organism). The mean LC50 recorded in this study,expressed as the total concentrations ofHC compounds, was 3.72 mg.l". Previous studies suggest that multiplying the Le50 for D. magna by anapplication factor of 0.001 gives an approximate safe level of a pollutant. Using datacollected in this study, a safe level of exhaust He compounds of 3.72 Jlg.r1 wouldresult. In summer, during times of high powerboat activity, such levels are exceeded atmany locations in Loch Lomond.The current study has shown that He pollution from a relatively small number ofinefficient powered recreational craft using Loch Lomond poses a potential threat to themaintenance of water quality.