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

Abstract

Dissolved oxygen (DO) conditions within the hyporheic zone were investigated in a gravel stream (River Sieg) in North Rhine Westphalia, Germany, populated in the spawning season by recurring migratory fish species, like Atlantic salmon (Salmo salar L.) and sea trout (Salmo trutta trutta L.). The gravel bed was cleaned at three sites in an area of approximately 150 m 2 to a depth of 50 cm, reducing the quantity of grains <2 mm to below 0.2%. DO concentrations in cleaned and uncleaned sediments were monitored in situ at 10, 20 and 30 cm sediment depth from the end of November 2001 to the end of April 2002. DO showed only minor fluctuations at the cleaned sites and steadily decreased at all uncleaned sites over time. Fine sediment accumulation over 5 months in the cleaned sites was comparable to the proportion of material within the bed prior to the experimental cleaning and probably influenced the DO concentrations of the hyporheic water. Decreasing DO concentrations at all sites coincided with increasing water temperatures towards the end of the study period. The cleaning operation significantly improved the conditions of DO in the hyporheic zone of the three study sites.

Inter‐disciplinary perspectives on processes in the hyporheic zone

“…The need to develop and implement techniques to facilitate the rehabilitation and restoration of surface water and groundwater interaction within the HZ as part of 'holistic' river management strategies has been advocated (Boulton, 2007). Examples of this in practice are currently limited (Sarriquet et al, 2007;Kasahara and Hill, 2008;Meyer et al, 2008) and the restoration of surface water and HZ interactions remains an ongoing goal for future research. The major reason for this shortcoming is the current lack of integrated inter-disciplinary conceptual understanding of HZ ecohydrological and biogeochemical functioning.…”

Low flow controls on benthic and hyporheic macroinvertebrate assemblages during supra‐seasonal drought

“…In the 40 absence of flushing flows, fine sediments (<2 mm in size) 41 may be deposited onto the bed, infiltrating and potentially 42 clogging the interstices within the benthic and hyporheic 43 zones (Brunke, 1999). This reduces the competency of 44 exchange processes and the porosity and permeability 45 of the sediments (Bo et al, 2007;Meyer et al, 2008) with consequences for the supply of dissolved solutes and hyporheic oxygen (Youngson et al, 2004). It also reduces living space for larger hyporheic invertebrates as well as sediment-associated benthos.…”

Transport of nonsorbing solutes in a streambed with periodic bedforms

“…Various advective models (collectively called the pumping exchange model, PEM) 24 have been developed previously for quantifying the mass exchange across the streambed with bedforms [42,46,47]. The essence of these models is an assumption of advection alone in transporting solute through flow tubes.…”

“…Solute exchange between the hyporheic zone and the stream affects significantly the stream water quality and ecology. For example, eggs of salmonids deposited in the gravel bed of a stream rely on dissolved oxygen (DO) transferred from the overlying water to survive and hatch [3,24]. On the other hand, if dissolved organic carbon is also transferred into the gravel bed and competes for DO, the pore water quality in the bed can deteriorate, affecting the salmonids' reproduction [25].…”