Dissolution of Diatom Frustules and Recycling of Amorphous Silicon in Lake Michigan

Abstract

We measured the concentration of diatom frustules and amorphous silicon per gram of dry sediment at 5-m intervals in the upper water column (0–40 m), in sediment traps placed at 37 and 60 m below the surface, and in a sediment core. The average concentration of frustules per gram of dry suspended sediment in the water column was 3.14 × 108. The 37 and 60 m trap sample averages were 1.16 × 108 and 5.03 × 107 frustules/g dry sediment, respectively. Subsamples from the sediment core averaged 6.31 × 106 frustules/g dry surficial sediment. The average proportion of amorphous silicon/g dry sediment was 8.6% in the water column, 7.7% in the 37 m traps, 6.0% in the 60 m traps, and < 2.0% in subsamples from the sediment core. The major fraction of amorphous silicon produced annually as diatom frustules was decomposed before incorporation in the permanent sediment. A comparison of the annual silicon requirement for diatom production and silicon inputs showed that the watershed contributes < 5.0% of the dissolved reactive silicon required for annual diatom production. These observations suggest that recycling of biogenic silicon provides the major source of soluble reactive silicon required for diatom blooms in Lake Michigan. Key words: Lake Michigan, diatoms, sedimentation, sediment traps, dissolution, deposition, silicon, sources, sinks, recycling

High concentrations of amorphous, biogenic Si (BSi) in the sediment of a small high-latitude lake: implications for biogeochemical Si cycling and for the use of BSi as a paleoproxy

“…The concentrations of DSi in the interstitial water of the top part of the sediment profile in Lake Kuutsjärvi (21-24 mg l -1 , Fig. 4) were high compared to these values and to other values measured from the uppermost layers of lake sediment profiles (Harriss 1967;Bailey-Watts 1976;Nriagu 1978;Cornwell and Banahan 1992;Parker et al 1977;Peinerud 2000), where values above 20 mg l -1 were mostly found only at 10-20 cm sediment depth. As supersaturation of the sediment interstitial water with DSi is a factor retarding further dissolution (cf.…”

Measured and predicted fluxes of biogenic silica in Lake Michigan1

“…Apparently a large fraction of the material sedimented during April-June was inorganic materials that are suspended during winter circulation and thermally mixed periods in spring. Parker et al (1977) found that the fraction of biogenic silica in monthly sediment trap samples decreased from 3 1% in May to 6% in October, and then increased slightly in November.…”

“…Fee (1973) found that primary production rates were about twice as large in the nearshore as the average of 130 g C~rn-~*yr-' in offshore waters. Parker et al (1977) estimated annual primary production of 100 g C*m-2* yr-' at ANL 5, which is representative of Fee's offshore rate, and an annual silica requirement for offshore diatom production of 114 g Si02*m-2.yr-1. We calculated a biogenic silica flux at ANL 5 of 110 g Si02.…”

Interactions between climate and landscape drive Holocene ecological change in a High Arctic lake on Somerset Island, Nunavut, Canada

“…As the diatoms died and were removed from the water column or surface sediments, the silica was recycled, leading to few remains in the sediment. Extensive dissolution and silica recycling has been observed in more productive temperate systems (e.g., Parker et al 1977aParker et al , 1977bNriagu 1978;Conley et al 1988;Ryves et al 2013) and in Alaska (Cornwall and Banahan 1992). The increased terrestrial vegetation production, along with the continual presence of permafrost, may have reduced input of silica to the lake.…”