A simple technique using wooden stakes to estimate vertical patterns of interstitial oxygenation in the beds of rivers

Silt and fine sediments from anthropogenic activities frequently clog river bed sediments, impairing vertical exchanged between stream and subsurface water. River managers need a simple technique to detect the extent of interstitial clogging and monitor the effectiveness of measures to reduce siltation. We evaluated the use of 30-cm long pine-wood stakes, inserted for 3-6 weeks in the sediments of four French rivers varying in interstitial clogging, to determine the association between changes in the colour of the wood and the adjacent interstitial conditions. There was a general association between depth to interstitial hypoxia and location of the colour change of the wooden stakes from brown to pale grey or black after 3-4 weeks. This change in colour also broadly matched interstitial contents of fine sediment, ammonium, and nitrate although the method could not reliably detect microscale zones of anoxia or short-term changes in dissolved oxygen. thus, its effectiveness lies in its use as a cheap, simple, and broad-scale indicator for collecting long-term integrated data of interstitial oxygenation in stream sediments with minimal disruption of the gravel bed, and appears an ideal tool for river managers and salmonoid fish biologists.