Standpipe to determine permeability, dissolved oxygen, and vertical particle size distribution in salmonid spawning gravels /

Abstract

Excess sediment can profoundly effect the productivity of a salmon or trout stream (Cordone and Kelly, 1961; McNeil and Ahnell, 1964; McHenry et al., 1994). The habitat complexity of a stream may be greatly compromised if there is a high sediment supply and negative effects extend to spawning, egg and alevin survival, rearing habitat and adult holding habitat (Frissell, 1992). The Maine Atlantic Salmon Technical Advisory Committee (Dill et al., 2002) recognized sediment from "cumulative non-point source pollutants, including increased turbidity and sedimentation from land use factors" as a potential limiting factor for the Gulf of Maine Atlantic salmon. Atlantic Atlantic salmon fry prefer to hold stations over gravel substrate (1.6-6.4 cm), while salmon fry prefer to hold stations over gravel substrate (1.6-6.4 cm), while older parr prefer cobble or boulder substrate larger than 26 cm (Danie et older parr prefer cobble or boulder substrate larger than 26 cm (Danie et al., 1984). Armstrong et al. (2004) found that no age al., 1984). Armstrong et al. (2004) found that no age class of juvenile class of juvenile Atlantic salmon shows affinity for sand substrate. In a healthy stream, Atlantic salmon shows affinity for sand substrate. young salmon and trout hide in the interstitial spaces between cobbles and boulders to avoid predation and to avoid the extreme cold of winter surface flows (Heggenes, 1990). Waters (1995) found that excess fine sediment diminished Atlantic salmon habitat and also reduced food resources. Sediment caused a loss of pool depth, where both adults and juveniles may reside, and filled interstitial spaces between stream cobble and gravel blocking juvenile use of that area for cover, and decreased aquatic invertebrate production. Photo: Atlantic salmon parr rearing habitat. Photo by Melissa Halsted, SVCA. Atlantic salmon eggs and alevin have prolonged potential exposure to winter sediment transport because while eggs are laid in October or November, fry do not usually emerge until May of the following year, since low water temperatures prolong gestation (Baum, 1997). Atlantic salmon redds are usually 25 cm deep in the gravel and need a steady flow of clean, cold water to deliver oxygen and remove waste products. Soulsby et al. (2001) found in a Scottish River that when fine sediment less than 2 mm in size reached levels of 20%, egg mortalities were as high as 86%. Crisp and Carling (1989) compared fine sediment less than 1.0 mm in three streams in the United Kingdom and found average levels of 11% in the northeast, 8% in southwest Wales and 12% in Dorset. Individual samples rarely exceeded 20% fines. Chapman (1988) showed different responses to similar levels of fines from various field studies (Figure 5 from Chapman) and noted that laboratory experiments might not duplicate redd dynamics. Studies conducted in actual redds in Olympic Peninsula streams in Washington found that if more than 13% fine sediment (<0.85 mm) intruded into the redd, almost no steelhead or coho salmon eggs survived (McHenry et al., 1994). Barnard (1992) showed that fine sediment levels inside and outside coho salmon redds varied substantially in Freshwater Creek, a northwestern California watershed. Fines (<1 mm) averaged seven percent inside redds and 13% outside them, with no inside redd measurement in excess of 13%. Even if female salmon remove sediment from redds, Armstrong et al. (2004) note that transport of sediment during winter may re-infiltrate redds before fry emerged. Because the redd is a depression in the stream bed, it creates Venturi forces, drawing water down into the gravel. Fine sediment in suspension during storms may be sucked down into the redd. Particles of less than 6.4 mm have the potential to infiltrate redds and form a layer in the stream gravel that sometimes prevents emergence of fry (Lisle, 1989). Kondolf (2000), in a review of the literature, found that when fines (<6.4 mm) exceeded 30% salmonid emergence and survival was reduced by 50%. Barnard and McBain (1994) suggested that measuring permeability itself might be a quicker, and more cost effective, method of measuring sediment impacts on salmonids. Total suspended solids (TSS) and turbidity in the Gulf of Maine Atlantic salmon rivers are a concern (Dill et al., 2002) particularly in the Sheepscot River (Arter, 2004). High turbidity impacts the feeding ability of juvenile salmon, although it may also provide them some cover from predation if it occurs during periods of smolt migration (Danie et al., 1984). Dill et al. (2002) cited Newcomb and Jensen (1996) when noting "that more than 6 days of exposure to TSS greater than 10 mg/l is a moderate stress for juvenile and adult salmonids. A single day of exposure to TSS in excess of 50 mg/l is also a moderate stress." Sigler et al. (1984) found that turbidities of 25 nephlometric turbidity units (ntu) or greater caused a reduction in juvenile salmonid growth. The longer the duration of high turbidity the more damage is likely to fish and other aquatic organisms (Newcombe and MacDonald, 1991). As noted by Arter (2004): "Even moderate turbidity may affect a fish's ability to find food." Arter (2004) also recommended that any prospective sites for Atlantic salmon stocking be monitored for water quality, including turbidity. Photo: Finn Brook (at left) exhibits higher turbidity than the Sheepscot River. Photo by Melissa Halsted, SVCA. 128 KB Lisle (1981) noted that recovery of streams with high gradient proceeds much more rapidly following large flood events than ones with low gradient. Gulf of Maine rivers are of mild gradient particularly in their lower reaches; consequently, sediment may remain in storage for longer periods. Watts et al. (2003) noted the need for regional, strategic sediment monitoring to prevent damage to fisheries resources. Roads are recognized as a major sediment source potentially affecting Gulf of Maine Atlantic salmon rivers (Dill, 2002): "Seasonal roads are prone to NPS pollution due to erosion on the road surfaces, roadside ditches, or bank erosion at stream crossings. Of the NPs pollution sites identified in the Project SHARE database, most are eroding roads or stream crossings. These cause localized water quality and embeddedness problems in the salmon rivers." Photo Gully erosion on abandoned road in Sheepscot basin. Photo by Melissa Halsted, SVCA. See Roads and Upland Sediment Sources in Maine DPS Atlantic Salmon Watersheds Background page for more information.