In situ nutrient enrichment: Methods for marine benthic ecology

Nutrient enrichment of marine sediments or the water column has been used t o study plant nutrient limitation and its cascading effects on community st ructure. Here we develop methodological recommendations for in situ enrichm ent. We review 18 published enrichment methods. Nutrient concentrations var ied through time and among sites, with sediment depth, distance from the so urce, fertilizer type and load. Combining available data, we could predict an increase in sediment porewater phosphate (r(2) = 0.48) but not ammonium (r(2) = 0.07) concentrations in a multiple regression model. In three compa rative field experiments we applied a coated slow-release fertilizer in the sediment and the water column and followed nutrient concentrations over ti me. We recommend coated fertilizer pellets; because they provide gradual nu trient release, allow for realistic nutrient gradients, and even applicatio n but we emphasize that nutrient concentrations need to be monitored throug h time.