Sediment storage in the shallow hyporheic of lowland vegetated river reaches

Abstract

Abstract:Excessive fine sediment deposition on the river channel bed together with colmation of finer sediments within the hyporheic are now linked to the degradation of the aquatic habitats of gravel bed rivers in permeable catchments. Previous studies of chalk rivers (associated with outcrops of calcareous rock) have demonstrated the important role of aquatic vegetation in trapping fine sediment on the river channel bed. This research investigated the spatio-temporal patterns and composition of fine sediment stored in two vegetated river reaches, in the Frome and Piddle catchments, Dorset (UK), with contrasting hydrological regimes, in order to establish the importance of aquatic vegetation in controlling the magnitude and timing of sediment storage in chalk rivers.Monthly mapping of macrophyte and sediment cover at the two sites (Maiden Newton and Snatford Bridge, 2003-2004) revealed a cyclical pattern of sediment storage related to the growth and die-back of aquatic vegetation peaking at 66Ð8 kg m 2 in July 2003 at Maiden Newton, and 23Ð5 kg m 2 in October 2003 at Snatford Bridge. Sediment was stored within gravels and beneath vegetation in the margins and mid-channel locations at both sites. Significantly more sediment was stored beneath vegetation than within gravels. The spatio-temporal pattern of sediment storage at the reach scale and the composition of the stored sediments reflected the growth patterns and functional form (flexibility) of the dominant macrophytes Ranunculus penicillatus subsp. pseudofluitans (water crowfoot) and Rorippa nasturtium aquaticum (watercress). Finally, the paper discusses the implications of reach-scale patterns in sediment storage for contaminant storage.

Asynchronicity of fine sediment supply and its effects on transport and storage in a regulated river

“…Heppell et al 2009), although the median particle size (D 50 = 164 μm) is greater than other studies (e.g. Marttila and Kløve 2014;7-60 μm).…”

“…Walling et al 2003;Collins and Walling 2007a, b). Others have observed mixed patterns, arguing for the importance of cycles of vegetation growth and senescence (Heppell et al 2009) or the greater influence of flow conditions and local channel characteristics (Marttila and Kløve 2014). The latter authors also found that, in a catchment exploited for peat and wood in central Finland, the high volumes of sediment delivered by headwater tributaries were quickly conveyed downstream; similar dynamics have been reported in Mediterranean streams (Francke et al 2014;Piqué et al 2014).…”

“…Walling et al 2002; 23,400 g m −2 ) or lowland rivers (e.g. Heppell et al 2009; 66,800 g m −2 ) while low values are found in small urbanised catchments (e.g. West Midlands, Lawler et al 2006;50-110 g m −2 ) and chalk streams (Acornley and Sear 1999).…”

Scaling down hyporheic exchange flows: from catchments to reaches

“…A variety of herbs, shrubs and trees grow in stream channels, increasing bed roughness and driving specific relationships with hydraulic conditions and the development of preferential flow pathways (Corenblit et al, 5 2007). Vegetation also alters stage-discharge relationships that affect hyporheic flow (Champion and Tanner, 2000;Harvey et al, 2003;Heppell et al 2009). Jones et al (2008) demonstrated that in-channel vegetation restructures hyporheic flow patterns by creating temporally dynamic deviations of hydraulic gradients.…”

Recent advances and future directions in soils and sediments research

“…Recent flume-based and field studies (e.g. Wharton et al 2006;Heppell et al 2009;Harvey et al 2011;Jones et al 2011;Salant 2011) have also demonstrated that both macrophytes and periphyton are important in controlling sediment deposition and resuspension within river channels. According to Harvey et al (2011) "physical-biological interactions and resulting effects on sediment and nutrient redistribution are arguably some of the principal drivers of ecological function and hydrogeomorphic evolution of aquatic systems….. and deserve more study".…”