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Assessing Trends in Nutrient Concentrations in Coastal Shelf Seas: a Case Study in the Irish Sea |
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| Authors: | R J Gowen D J Hydes D K Mills B M Stewart J Brown C E Gibson T M Shammon M Allen S J Malcolm |
| Institution: | a Aquatic Systems Group, Agricultural and Environmental Science Division, Department of Agriculture for Northern Ireland, Newforge Lane, Belfast, BT9 5PX;b Natural Environment Research Council, George Deacon Division, Southampton Oceanography Centre, Empress Dock, Southampton, SO14 3ZH;c CEFAS, Pakefield Road, Lowestoft, Suffolk, NR33 OHT;d University of Liverpool, Port Erin Marine Laboratory, Port Erin, Isle of Man, IM9 6JA;e Biometrics Division, Department of Agriculture for Northern Ireland, Newforge Lane, Belfast, BT9 5PX |
| Abstract: | Single point time-series data collected in the Irish Sea since 1954 by Allen et al. (1998) have been re-evaluated using more recent data and areal winter surveys of the Celtic and Irish Seas. Survey data illustrate the heterogeneity of nutrient distributions with N (≈28 μM) and P (2·0 μM) enrichment of the eastern Irish Sea relative to the western Irish Sea (7–8 μM N and 0·7 μM P). Salinity nutrient relationships demonstrate distinct regional differences throughout the two seas. Trends in the Isle of Man time-series are unlikely to have resulted from changes in analytical procedures and personnel. Concerns over data quality cannot be resolved and there are no independent data to validate the time-series. Including more recent data shows P has declined since the late 1980s and N concentrations have remained stable since the mid 1970s. The absence of a Si trend is consistent with limited anthropogenic influence on riverine Si concentrations. Trends in N and P are consistent with changes in riverine concentrations of these two nutrients and the biogeochemical processes controlling their cycling in shelf waters. Denitrification is the most likely reason for offshore Irish Sea concentrations of N being lower than expected. |
| Keywords: | eutrophication nutrients Irish Sea time-series analysis |
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