Role of hydrodynamic conditions on quantity and biochemical composition of sediment organic matter in sandy intertidal sediments (NW Atlantic coast,Iberian Peninsula)

摘要

Ten beaches subjected to different wave action exposure were studied on the northwest coast of the Iberian Peninsula.According to descriptions of beach types (from very sheltered to very exposed)given by McLachlan (1980),five of the beaches studied were classified as sheltered and the other five as exposed beaches.The biochemical composition (proteins,lipids and carbohydrates)of sedimentary organic matter was analysed from the surface sediment down to a depth of 25 cm,between July and September 1997,at three tidal levels:high,medium and low,at ebb tide.Biochemical compound concentrations were significantly higher in the sheltered than in hte exposed beaches.Concentrations were,on average two,three and four times higher in the sheltered than in the exposed beaches.Concentrations were,on average two,three and four times higher (for proteins,carbohydrates and lipids,respectively)in sheltered than in exposed sediments.The low hydrodynamic conditions of hte sheltered beaches favoured the settlement of sedimentary organic matter.This is supported by the higher protein to carbohydrate ratio found in te exposed (12.3),in contrast with the sheltered locaities (5.2).Sheltered but not exposed sediments were characterised by clear vertical profiles of protein,carbohydrate and lipid concentrations,with values on top approximately twice as high as in the deeper sediment layers.On the other hand,there were significant differences in the biochemical compounds concentratins among tidal levels for both groups of intertidal localities,except for the protein concentrations in sheltered localities.Biochemical compound concentrations were higher at medium and low tidal levels for both sheltered and exposed beaches.In the three tidal levels,there was a significant negative relationship between the biopolymeric carbon and the intertidal slope.Thus,the biopolymeric carbon concentration decreased as the intertidal slope increased.