Publication Abstract

Nitrogen Cycling in the Southern North Sea: Consequences for Total Nitrogen Transport

K. Weston, T.D. Jickells L. Fernand and E.R. Parker

Nitrate and ammonium uptake rates were measured during a series of cruises in the well mixed region of the southern North Sea from February- September. Water column integrated uptake rates ranged between 0.01 and 8.7 mmol N m^-2 d^-1 and 0.01 and 12.2 mmol N m^-2 d^-1 for nitrate and ammonium respectively with ammonium uptake dominating after the phytoplankton spring bloom in May. A moored buoy continuously measuring nitrate and chlorophyll a and moored current meters were also deployed in the central southern North Sea in the region of the East Anglian plume – a permanent physical feature of higher suspended load. This enabled the flux of water and hence of nutrients across the southern North Sea to be determined and an assessment of the contribution of freshwater nutrients to the flux to be made. A simple box model is developed to relate the phytoplankton uptake of nitrate and ammonium to the flux of nitrate, ammonium and particulate organic matter (POM) across the southern North Sea. This showed the importance of the plume region of the North Sea in processing of nitrogen with nitrate dominating total nitrogen transport prior to the spring bloom snd transport of nitrogen as ammonium, nitrate and POM in approximately equivalent amounts during summer. The box model also demonstrates more generally the need to assess nitrogen transport as nitrate, ammonium and POM if an improved understanding of the impact of nutrient input in shelf seas is to be achieved.

Reference:

K. Weston, T.D. Jickells L. Fernand and E.R. Parker (2004) Nitrogen Cycling in the Southern North Sea: Consequences for Total Nitrogen Transport. Estuarine, Coastal and Shelf Science, 59(4): 559-573.