Restoration of spawning grounds for trout and grayling in the river High-Rhine |
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| Authors: | M Zeh W Dönni |
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| Institution: | (1) Swiss Federal Institute for Environmental Science and Technology (EAWAG) and Swiss Federal Institute of Technology (ETH), Limnological Research Center, CH-6047 Kastanienbaum, Switzerland;(2) Present address: Water and Soil Protection Laboratory of the Canton of Bern, Schermenweg 11, CH-3014 Bern, Switzerland |
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| Abstract: | In January 1990 10 m3 of washed gravel (grain size 16–50 mm) were introduced in an impounded section of the River High-Rhine to test its potential as a spawning ground for salmonids. The process of infiltration of fine sediments into the gravel and subsequent clogging was monitored for three years. Levels of clogging of the gravel matrix were estimated and ranged from slight to moderately-heavy. The degree of clogging was lower in winter than in summer. Since no bedload transport was observed during the study period, flood events could wash out sediments from the top layer of the gravel bed only. An equilibrium diffusion technique using porewater samplers was employed to measure oxygen concentrations within the interstitial space during the spawning period ofThymallus thymallus (April),Salmo trutta fario andOncorhynchus mykiss (December till February). Oxygen concentration decreased with increasing depth and during the course of the study period. Oxygen concentrations measured as a reference in the interstitial of the confluence of the river Glatt were considerably lower than those of the new gravel bed. A wide range of O2 concentrations was found in winter 1991/92 and in spring 1992. This could be explained by the heterogeneous microstructure of the substrate. Successful embryonic and larval development of grayling in the gravel bed was observed in spring 1991 and 1992. However, no eggs or larvae of brown trout or rainbow trout were found. Habitat restoration projects for salmonids in impoundments of the High-Rhine are critically discussed. |
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| Keywords: | Rhine siltation clogging habitat restoration salmonids equilibrium diffusion technique porewater samplers |
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