Hydrocarbon emissions from boat engines: Evidence of recreational boating impact on Loch Lomond

As with all internal combustion engines, the engines powering recreational craft emit hydrocarbons and their combustion products in exhaust, and thus have the potential to pollute waters on which they are used. Despite this, their impact is rarely considered. A model is presented which uses publishe d and empirical data to estimate potential hydrocarbon output from craft us ing Loch Lomond. Output from the model suggests that c.25 tonnes of unburnt hydrocarbons may have been discharged from craft into Loch Lomond in 1989 and, due to rising craft numbers, this may have since increased. Water analysis shows that hydrocarbons are detectable in the surface waters of Loch Lomond and that detected concentrations correlate with localised c raft activity on a single day. In replicated experiments, the quality of ar tificially contaminated water recovered over time as the volatile hydrocarb ons evaporated. The time for heavily contaminated water to reach half its i nitial pollutant concentration in these experiments was around 9 days. The potential for hydrocarbon contamination in inland waters that are heavily u tilised for recreational boating requires urgent examination.