Chemical composition of interstitial water and diffusive fluxes within the diatomaceous sediment in Lake Myvatn, Iceland

Sigurdur Reynir Gíslason, Eydís Salome Eiríksdóttir, Jón Sigurdur Ólafsson

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20 Citations (Scopus)


The sub-arctic Lake Myvatn is one of the most productive lakes in the Northern Hemisphere, despite an ice-cover of 190 days per year. This is due to relatively high solar radiation, nutrient rich inflow waters, N 2 fixation and internal nutrient loading. In order to define direction and magnitude of diffusive fluxes, soil water samplers were used to collect interstitial water from 25150 cm depth, from within the diatomaceous sediment at the bottom of Lake Myvatn. Water depth at the sampling site was 225 cm. The pH of the interstitial water ranged from 7.16 to 7.30, while the pH of the lake water was 9.8010.00. The concentrations of most solutes were similar 16 cm above the bottom of the lake at the sampling site and at the lake outlet. The concentrations of NO 3, S, F, O 2, Al, Cr, Mo, V, U, Sn and Sb were higher in the lake water than in the interstitial water. They will therefore diffuse from the lake water into the interstitial water. The concentrations of orthophosphates, PO 4, and total dissolved P were highest at 25 cm depth, but Co and NH 4 concentrations were highest at 50 to 100 cm depth. Thus they diffuse both up towards the lake bottom and down deeper into the sediments. The concentrations of Na, K, Ca, Mg, Sr, Mn, Li and alkalinity were greater within the sediments than in the lake water and increased continuously with depth. The Si concentration of the interstitial water was higher than in the lake water, it was highest at 25 cm depth and decreased slightly down into the sediments. The concentration gradient was greatest for bicarbonate, HCO 3 -, 1.5×10 -7 mol cm -3 cm -1, and then in declining order for the solutes with the highest gradient; NH 4, Si, Na, Ca, Mg, -S (diffusion into the sediments), K, PO 4, Cl, Fe and Mn. The estimated annual diffusive flux of PO 4 for Lake Myvatn was 0.1 g P m -2 yr -1, about 10% of the total PO 4 input to Lake Myvatn. The H 4SiO 4° flux was 1.3 g Si m -2 yr -1, <1% of both the input and the annual net Si fixation by diatoms within the lake and the diffusive flux of dissolved inorganic carbon was 1% of the annual net C fixation by diatoms. Annual diffusive flux of NH 4 + was 1.9 g N m -2 yr -1 similar to the input of fixed N to the lake and 24% of the net N fixation within Lake Myvatn. Thus it is important for the nitrogen budget of Lake Myvatn and the primary production in the lake since fixed nitrogen is the rate determining nutrient for primary production.

Original languageEnglish
Pages (from-to)163-175
Number of pages13
JournalAquatic Ecology
Issue number2
Publication statusPublished - 2004

Bibliographical note

Funding Information:
We thank Árni Einarsson, director of the Myvatn Research Station, for his assistance and advice during the course of this study. Árni Einarsson, Philippe Van Cappellen, Terry Lacy, Ramesh D. Gulati and an anonymous reviewer improved this manuscript in many ways. Thanks also go to Freyr Tómasson, Birnir Jón Sigurdsson and Anna Diljá Sigurdardóttir at Lake Myvatn for their unstinting help in their free time. This study was financed by the Myvatn Research Station and the Science Institute, University of Iceland.

Other keywords

  • Concentration gradient
  • Fluxes of solutes
  • High productive lake
  • Sediment water interface
  • Soil samplers.


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