In situ nutrient enrichment:: Methods for marine benthic ecology

Nutrient enrichment of marine sediments or the water column has been used to study plant nutrient limitation and its cascading effects on community structure. Here we develop methodological recommendations for in situ enrichment. We review 18 published enrichment methods. Nutrient concentrations varied through time and among sites, with sediment depth, distance from the source, 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 comparative field experiments we applied a coated slow-release fertilizer in the sediment and the water column and followed nutrient concentrations over time. We recommend coated fertilizer pellets; because they provide gradual nutrient release, allow for realistic nutrient gradients, and even application but we emphasize that nutrient concentrations need to be monitored through time.