MEPS 446:31-44 (2012)  -  DOI: https://doi.org/10.3354/meps09488

ABSTRACT: Recovery of microphytobentos (MPB) and benthic processes were followed during 23 d after sediment deposition simulating the effects of 1 wk of nearby dredging or construction work. Cores of natural intact sediment in an outdoor flow-through system were exposed to daily depositions of 1.5 mm fine-grained sediment over 7 d (total load 10.5 mm). Porosity, chlorophyll a (chl a; proxy for MPB biomass), denitrification and sediment−water fluxes of oxygen and inorganic nutrients were measured during day and night on 6 occasions. After deposition stopped, chl a in the uppermost 3 mm of the sediment had decreased to 25% of that in the controls, started to increase linearly, probably due to upward migration of diatoms, but did not converge with the control cores in the course of the experiment. The linear increase of chl a indicated a recovery of algal biomass after ~50 d. The proportion of large sigmoid diatoms increased in the deposition cores and this change in MPB composition remained over the 23 d. Deposition resulted in higher porosity and increased flaking of the newly established algal mat. Deposition generally increased release or decreased uptake of nutrients, though effects on nitrate flux and denitrification were less clear. Although alga-related functions (oxygen production and nutrient fluxes in light) recovered faster than algal biomass, the faster recovery of the integrated system function in the dark reflected the impact of deposition on MPB. Sediment deposition in microtidal areas may imply disturbances for MPB, threatening the food supply for grazers and deposit feeders, and, in the end, fish that use the shallow areas as nurseries.

KEY WORDS: Microphytobenthos · Sediment deposition · Oxygen flux · Nutrient flux · Denitrification · Resilience