Carbon and nutrient cycling at the sediment-water boundary in western Lake Superior

Organic carbon and nutrient settling rates, benthic recycling rates, and material burial rates were measured in the western arm of Lake Superior. Organic carbon settling rates, measured using particle- intercepting sediment traps, averaged 2.3 mmol m(-2) day(-1) over the course of the experiment. Measured particle settling fluxes exhibit a minimum during winter and a maximum during spring. Sediment oxygen uptake rates measured throughout the basin average 2.2 +/- 0.8 mmol m(-2) day(-1) (n = 16) and nitrate, soluble reactive phosphorus, and silicic acid efflux rates average 0. 15 +/- 0.07 (n = 25), 0.005 +/- 0.006 (n = 23), and 1.34 +/- 0.4 mmol m(-2) day(-1) (n = 26), respectively. Sediment solid-phase, particle settling rate, and benthic efflux data demonstrate that organic carbon, nitrogen, and biogenic silica are recycled at the sediment-water interface with an efficiency of similar to 60% or greater in western Lake Superior. In contrast to these constituents, phosphorus recycling efficiency is lowest at sites close to the two major river inputs of (similar to 10%) and highest at our deepest site (similar to 40%). Despite these low recycling efficiencies for phosphorus, the benthic flux of phosphorous is an essential and dominant component to the lake's annual internal budget contributing similar to 50% of the total annual phosphorus inputs to the water column.