Coastal eutrophication is now recognised as a major environmental problem. Over the past three decades it has become apparent that increases in nutrient concentrations can lead to serious degradation of coastal ecosystems, particularly in areas that are densely populated. Progress in remedial action has been hampered in part by a lack of long-term records detailing the rate and direction of changes in nutrient concentrations of coastal ecosystems. This research developed a transfer function to reconstruct concentrations of total nitrogen (TN) from the palaeoecological record of diatom valves preserved within coastal sediments.
A 70-site calibration set, composed of percentage abundance counts of diatom taxa from surface sediments and corresponding water quality records, was constructed from sub-tidal sampling locations within Denmark. Canonical correspondence analysis (CCA) with forward selection indicated that five environmental variables explained a statistically significant proportion of the variation within the diatom data, with TN uniquely explaining 2.5 % of the variation.

Weighted averaging partial least squares (WA-PLS) was used to create a transfer function to reconstruct TN from fossil diatom counts. Application of the TN transfer function to a core from Roskilde Fjord, Denmark indicated that concentrations of TN had nearly doubled to 91 micro-m per litre between the turn of the 20th century and 1995. The most rapid increase in TN concentration was seen in the years post 1956, which corresponds to the post-war increase in the use of artificial fertiliser.

This research has indicated that Danish coastal sediments hold a record of recent environmental change as indicated by changes in the structure of fossilised diatom assemblages. The quantitative nature of the reconstruction allows the degree of change to be assessed in terms readily accessible to environmental managers, and so can be used to set targets for nutrient reduction schemes. The methodology also has applicability to the Water Framework Directive by providing means to determine conditions of minimal human impact on nutrient concentrations.