Nitrogen species distributions in the Ria d e Arousa, NW Spaln, during the upwelling season are strongly affected by the influence of shelf wind stress on water circulation. Intermittent northerly winds forced large volumes of nitrate-nch Eastern North Atlantic Central Water Into the ria ulth a fortnightly per~odlclty and led to net commun~ty production maxima supported by external nitrate. Net commun~ty production in the central segment of the estuary was hlgh (average 251 m g m-2 d.' of nitrogen] However, only 2 0 % of the total nutrient input was net taken up due to rapid water exchange. An lntenslve culture of hanging mussels favoured dissolved organic nitrogen formation (58% of net community production) and particulate organic nitrogen sedimentation (21 % of net communlty production, or 50% of net particulate organic n ~t r o g e n formation). Consequently, more than 7 5 % of the net d~ssolved+particulate organic nltrogen production was exported from the central segment, with a dlssolved/partlculate ratio of -3. In addition, 4 0 % of phytoplankton gross primary productlon was internally recycled by pelagic+benthic ammonificat~on in the central segment, mainly during prolonged upwelllng relaxations Low rates of particulate organic nltrogen sedimentation and low levels of conversion to dissolved organic nltrogen were observed during the development of a red tide assemblage. This appears to be held evidence of limited filtration by mussels in the presence of these organisms. A strong reversal in the resldual circulation occurred In mld-October, during the transltlon from northerly to southerly winds Ammonium released from the estuarine sediments, at a high average net rate of 162 mg N m-2 d-', was exported towards the shelf.
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Rosón et al. (1996) studied this question.