The environmental quality of coastal ecosystems is an issue of growing international attention. Estuarine organic matter is derived from a multitude of natural and anthropogenic allochthonous and autochthonous sources that originate across a freshwater continuum. Various point and diffuse sources, such as discharges of treated and untreated sewage as well as urban and agricultural run-off, contribute significantly to the deterioration of the water and sediment quality of aquatic ecosystems. The EU Water Framework Directive requires all surface waters to fulfil the criterion of “good ecological status” by the end of 2021, this status is defined with reference to undisturbed conditions. Within heavily impacted coastal areas with no prior monitoring of baseline data assessing these reference conditions will be inherently difficult. Understanding near-pristine conditions within estuaries provides reference sites for assessing natural variability of organic and inorganic chemical parameters which in turn will provide baseline conditions for management to allow them to distinguish between changes caused by human and those that are natural.
A fine scale survey of metals, nutrients and lipid biomarkers was investigated within an estuary that was perceived to be of relatively pristine condition. The data obtained has been used to assess existing models that aimed to define elevated versus baseline concentrations. The majority of the data focused on the sediment fraction due to its importance as a historic sink of organic and inorganic compounds which in turn enables an understanding of the potential inputs from both natural and anthropogenic sources. Regional geochemical baseline models were constructed for metals and nutrients to enable an understanding whether the organic and inorganic compounds were from natural or anthropogenic origins. The lipid biomarkers were utilised to establish the origin of the organic matter. Within the Conwy estuary there were a number of locations that yielded higher concentrations that were deemed above background levels, these have been discussed to highlight potential sources of contamination. A proportion of locations sampled fell below those that were deemed enriched for metals, nutrients and lipids resulting in concentration ranges of pristine conditions which other contaminated estuaries can refer to.