Abstract
Sub-arctic Lake Myvatn is one of the most productive lakes in the Northern Hemisphere, despite an ice cover of 190 days per year. In situ, transparent and dark flux chambers were used for direct measurements of benthic fluxes of dissolved oxygen, nutrients, silica and certain metals, taking into account primary production and mineral precipitation. The range of benthic flux observed for dissolved oxygen (DO), dissolved inorganic carbon (DIC), ammonium, ortho-P, silica, calcium, and magnesium was 45.89 to 187.03, 99.32 to 50.96, 1.30 to 1.27, 0.51 to 0.39, 62.3 to 9.3, 33.82 to 16.83, and 23.93 to 7.52 mmol m -2 d -1, respectively (negative value indicating flux towards the lake bottom). Low benthic NH 4 + and ortho-P fluxes were likely related to benthic algal production, and aerobic bottom water. Ortho-P fluxes could also be controlled by the dissolution/precipitation of ferrihydrite, calcite, and perhaps hydroxyapatite. The negative silica fluxes were caused by diatom frustule synthesis. Benthic calcium and magnesium fluxes could be related to algal production and dissolution/precipitation of calcium and/or Ca,Mg-carbonates. Fluxes of DO, DIC, pH and alkalinity were related to benthic biological processes. It is likely that some of the carbon precipitates as calcite at the high pH in the summer and dissolves at neutral pH in the winter. Mean of the ratio of gross benthic DIC consumption and gross benthic DO production was 0.94 ± 0.18, consistent with algal production using NH 4 + as N source. During the summer weeks the water column pH remains above 10. This high pH is caused by direct and indirect utilisation of CO 2, HCO 3 -, CO 3 2, H 4SiO 4 ° and H 3SiO 4 by primary producers. This study shows that in shallow lakes at high latitudes, where summer days are long and the primary production is mostly by diatoms, the pH is forced to very high values. The high pH could lead to a positive feedback for the Si flux, but negative feedback for the NH 4 + flux.
| Original language | English |
|---|---|
| Pages (from-to) | 191-208 |
| Number of pages | 18 |
| Journal | Aquatic Ecology |
| Volume | 38 |
| Issue number | 2 |
| DOIs | |
| Publication status | Published - 2004 |
Bibliographical note
Funding Information:We thank Á. Einarsson, H.R. Ingvason, E.S. Eiríks-dóttir, P. Frogner, Th.L. Thórarinsson and A. Hjartar-son for their invaluable assistance with deployment and recovery of benthic flux chambers, sampling and chemical analysis in the lab, and R.C. Aller for introducing us to the benthic chamber technique at the beginning of this study. We thank T.G. Lacy, S. Arnórsson, J. Ólafsson and two anonymous reviewers for their constructive criticism on an earlier version of this manuscript. This project was supported by The Icelandic Research Council (Grants 0005200 and 996230099), as well as by the Myvatn Research Station, the National Energy Authority, the Science Institute, University of Iceland, and the University of Akureyri, Iceland.
Other keywords
- Benthic chambers
- Benthic primary production
- Positive and negative feedbacks
- Sedimentwater interface
- Solute fluxes