Restoration of spawning grounds for trout and grayling in the river High-Rhine

Abstract

In January 1990 10 m 3 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 ou~ 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 of Thymallus thymallus (April), Sa/mo tr14ttafario and Oncorhynchus 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 0 2 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.

An experimental assessment of the effectiveness of gravel cleaning operations in improving hyporheic water quality in potential salmonid spawning areas

“…The few studies monitoring in situ oxygen concentrations in gravel streams report a high temporal and spatial variability of this parameter (e.g. Zeh and Dönni, 1994;Peterson and Quinn, 1996;Niepagenkemper and Meyer, 2002;Groves and Chandler, 2005). Surprisingly, even if the geomorphology at potential spawning sites seems to be suitable for reproduction of salmon, suboptimal DO concentrations in the pore water of gravel interstices may prevail (Niepagenkemper and Meyer, 2002).…”

“…Frequently occurring flood events can winnow out fine sediments and prevent an extensive microbial growth within the interstices of the gravel bed even if no bedload transport occurs (Zeh and Dönni, 1994). This results in an exchange of oxygen-rich surface water with the pore water of the hyporheic interstices, stressing the significance of a natural discharge regime for maintaining high instream-dynamics (Sear, 1993;Gibson, 2002;Mürle et al, 2003).…”

Comparison of methods for analysing salmon habitat rehabilitation designs for regulated rivers

“…Spawning habitat rehabilitation (SHR) is widely performed for regulated rivers in the western United States and other semi-arid regions globally (Zeh and Donni, 1994;Wheaton et al, 2004a;Gard, 2006;Elkins et al, 2007) to mitigate the decline in anadromous fish populations associated with dam impacts and excessive fishing (Yoshiyama et al, 1998;Graf, 2001). A component of SHR involves adding washed gravel and cobble, 8-256 mm in diameter, to a stream (aka gravel augmentation) to increase the quantity and quality of spawning habitat at a placement site (Harper et al, 1998;Wheaton et al, 2004a) as well as to provide coarse sediment to transport downstream where it may form diverse habitats .…”

The importance of morphodynamic processes at riffles used as spawning grounds during the incubation time of nase (Chondrostoma nasus)

“…Beyond such morphodynamic processes, Kappesser et al (2002) defined a Riffle Stability Index (RSI) which estimates the mobility of cobbles in riffles. The effects of restored riffles as spawning grounds, in accordance with the European Water Framework Directive, have been discussed in the scientific literature less for rheophilic cyprinids than for salmonids (Rubin et al, 2004;Zeh & Donni, 1994).…”