Vertical hydraulic exchange and the contribution of hyporheic community respiration to whole ecosystem respiration in the River Lahn (Germany)

Abstract

To quantify the contribution of hyporheic community respiration to whole running-water ecosystem respiration in a cultural landscape setting, we studied the vertical hydraulic exchange in riffle-pool sequences of the River Lahn (Germany). We used flow through curves from four tracer experiments to estimate flow velocities in the surface and subsurface water. Generally, vertical exchange velocities were higher in riffle sections and a high temporal variability was observed (range of values 0.11-1.08 m day -1 ). We then used (1) the exchange velocities and (2) time series of dissolved oxygen concentration in surface and subsurface water to calculate hyporheic respiration. Hyporheic respiration was estimated in a range of 10-50 mg O 2 m -3 day -1 for the upper sediment layer (first 20 cm). It was much lower in the deeper sediment layer (20-40 cm), ranging from 0 to 10 mg O 2 m -3 day -1 (volumes are volumes of interstitial water; the average porosity was 20%). We determined primary production and respiration of the biofilm growing on the sediment by modelling dissolved oxygen concentration time series for a 2,450 m long stream reach (dissolved oxygen concentrations with diurnal variations from 8 to 16 mg L -1 ). Modelled respiration rates ranged from 2 to 21 g O 2 m 2 day -1 . All information was integrated in a system analysis with numerical simulations of respiration with and without sediments. Results indicated that hyporheic respiration accounted for 6 to 14% of whole ecosystem respiration. These values are much lower than in other whole system respiration studies on more oligotrophic river systems.

Alteration of key hyporheic functions through biological and physical clogging along a nutrient and fine‐sediment gradient

“…High vertical exchange flows with a mean of À1·45 and À0·26 m day À1 (exchange between SW and 15 cm below the SW/GW interface) were observed at the upstream and midstream sites, respectively, comparable with those of former studies at similar river types with vertical exchange flows ranging from À4·8 † to À0·11 † m day À1 (Pusch and Schwoerbel, 1994;Ingendahl et al, 2009). High vertical exchange flows with a mean of À1·45 and À0·26 m day À1 (exchange between SW and 15 cm below the SW/GW interface) were observed at the upstream and midstream sites, respectively, comparable with those of former studies at similar river types with vertical exchange flows ranging from À4·8 † to À0·11 † m day À1 (Pusch and Schwoerbel, 1994;Ingendahl et al, 2009).…”

Suspended sediments in the Kharaa River catchment (Mongolia) and its impact on hyporheic zone functions

“…This knowledge is necessary for a quantitative understanding and process based numerical studies across gradients of controlling factors (cf. Ingendahl et al 2009). …”

Complex hydromorphology of meanders can support benthic invertebrate diversity in rivers

“…However, of these two factors, hydraulics is the primary characteristic shaping aquatic habitat for invertebrates, since it influences (Ambühl, 1960). The boundary layer, which is determined by near-bed flow and roughness, defines the strength of lift and drag forces acting on benthic invertebrates (Statzner, 1988), in addition to habitat conditions in the interstitial space of subsurface sediments (Ingendahl et al, 2009). Hydraulic characteristics also determine the following factors in providing suitable aquatic habitat: (i) sediment particle size distribution; (ii) sediment movement and bedload transport; (iii) accumulation and resuspension of fine particulate organic matter; and (iv) growth of biofilm and submerged macrophytes.…”