EFFECTS OF GRAVELING ON THE PRIMARY PRODUCTIVITY, RESPIRATION AND NUTRIENT FLUX OF 2 ESTUARINE TIDAL FLATS

This study was conducted in Puget Sound, USA, and investigated the eff ect of graveling intertidal mud and sandflats to enhance clam producti on on the benthic assemblage structure, primary productivity, respirat ion, and nutrient flux. The study was conducted between spring and aut umn (1991), the period of greatest productivity and plant standing sto ck in Puget Sound. Graveled and control plots were established in the low intertidal zone on a mud flat in a protected embayment (Chapman Co ve) and an exposed sandflat (Semiahmoo Bay). Gravel altered benthic as semblage structure, respiration, and nutrient flux rates. Graveled plo ts contained more surface coverage of sessile animals and seaweeds. Ne t productivity (NP), which differed relatively little between graveled and control plots, was negative for all but one sampling at the prote cted embayment plots. In contrast, NP was always positive at the expos ed sandflat plots. The respiration rate was 13 to 57% greater in the g raveled plot at Chapman Cove than in the adjacent control plot, and 7 to 54% greater in the gravel plot than the control plots at Semiahmoo Bay. Heterotrophy was greater in the graveled plots, as reflected by a lower net productivity to respiration ratio. Effects of graveling on water quality parameters such as dissolved oxygen and inorganic nitrog en concentrations were not detected. Graveling sandy and mud beaches i ncreases secondary productivity, which is associated with increased ra tes of remineralization and release of dissolved nutrients to the wate r column.