Seasonal variability of dissolved nutrients in the Humber-Ouse estuary, UK

Measurements of dissolved nitrate, silicate, phosphate, nitrite and ammoniu m in the Humber-Ouse Estuary, UK, are presented for the period March 1993 t o December 1996, The nutrient data are consistent with independent measurem ents made in the freshwater, non-tidal River Ouse and with earlier measurem ents made in the coastal zone. Nitrate, nitrite and silicate always exhibit ed mid-estuarine maxima, whereas this was not the case for phosphate during summer and early autumn. The mean and standard deviations (SD) of the nitr ate and nitrite maxima were 515+/-90 mu M and 9+/-3 mu M, respectively, tak en over the whole record. The mean and SDs of the silicate and phosphate ma xima were 120+/-50 mu M and 11+/-4 mu M, respectively. The nitrate peak, wh ich was well defined during summer and early autumn, correlated closely wit h a strong turbidity maximum (TM). The nutrient distributions were greatly influenced by physical transport (strong correlation between the location o f the nutrient maxima and the freshmater-saltwater interface, FSI) and wast ewater and freshwater nutrient inflows (spatial 'grouping' of maxima locati ons). Mid-estuarine nutrient inputs were derived from river sources in the middle-to-upper estuary and were subsequently advected and mixed over a lar ge area. A description and interpretation of the seasonal variability of th e dissolved nutrients is given, although it is recognized that the various physical and biochemical influences can only be separated quantitatively th rough the application of numerical modelling techniques. (C) 1999 Elsevier Science Ltd. All rights reserved.