Tidal and meteorological induced nutrient (N, P) dynamics in the micro-tidal Ho Bugt, Danish Wadden Sea

Tidal and meteorological induced variations in nutrient dynamics are important at all depth intervals in the Ho Bugt estuary. In the tidal channels, nitrate concentrations may vary ±20% and total nitrogen concentrations even more due to sedimentation/resuspension effects during the tidal cycle. On tidal flats, nutrient and carbon contents of the deposited material depend strongly on meteorological conditions and may vary 0.7% TC, 0.1% TN and 0.4%c TP from week to week. Trapped material 0.65 m above the bottom of the tidal flat always contained more nutrients than tidal flat sediments indicating that fine-grained material does not stay for long on the bottom. On salt marshes, the nutrient content of deposited material increases from the salt marsh edge (5 g N kg−1 and 1.5 g P kg−1) to the distal part (9 g N kg−1 and 2.5 g P kg−1), whereas seasonal variations appear to be small. Total (tidal flat+salt marsh) deposition of nutrients for the area is estimated to 426 ton N y−1 and 117 ton P y−1. This may be compared to a terrestrial input of 2200 ton N y−1 and 48.5 ton P y−1 indicating that the estuary acts as a filter for the terrestrial supply to the open sea and that import from the open sea plays cm important role in the nutrient budget especially for the particle bound P.