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Silt, Turbidity and Suspended Sediments in the Aquatic Environment: An Annotated Bibliography and Literature Review – 1995. Kerr, S. J. Ontario Ministry of Natural Resources

Author:  Kerr, S.J. 1995. Silt, turbidity and suspended sediments in the aquatic environment: an annotated bibliography and literature review. Ontario Ministry of Natural Resources, Southern Region Science & Technology Transfer Unit Technical Report TR-008. 277 pp.

Summary: The impacts of siltation and suspended sediments on water quality and resident aquatic organisms is one of the most common problems facing resource managers today. Most construction activities in or near a watercourse have the potential to result in decreased shoreline stability and/or an increase in siltation, suspended sediments and turbidity.

This annotated bibliography was prepared in response to requests from several Ontario Ministry of Natural Resources biologists and technicians. Almost 1,200 references are cited. Abstracts, summaries or extracts of each paper are included whenever possible.

The impacts of siltation and suspended sediments on water quality and resident aquatic organisms is one of the most common problems facing resource managers today. Most construction activities in or near a watercourse have the potential to result in decreased shoreline stability and/or an increase in siltation, suspended sediments and turbidity.

(A) Sources of Suspended Solids

(ii) Dams and Reservoirs – act as settling basins for silt and other suspended materials – recreation and aesthetics impaired; – aquatic habitat lost.

(x) Roads – road construction and associated culvert installation result in dramatic short term increases in suspended sediment; massive soil erosion and sediment production from logging roads (dependent on whether road has paved or gravel surface); disruption and/or removal of riparian vegetation; significant increases in turbidity and suspended solids; destabilized shoreline and sediment from backfill associated with bridge construction and stream crossings.

In addition to various impacts on aquatic organisms, suspended materials in the water column have other physical and chemical effects. Suspended solids adsorb and concentrate trace metals and other contaminants and can transfer them from terrestrial to aquatic environments thereby increasing their bioavailability to aquatic life (Murty 1986; Persaud and Jaagumagi 1995). Turbidity causes light to be scattered and absorbed rather than transmitted in a straight line. Thus, light penetration is reduced. Turbid water also absorbs heat so an increase in suspended sediment can cause water temperatures to increase (Marcus et al. 1990). The reaeration of surface waters has been found to decrease as the average suspended sediment concentration increased (Alonso, McHenry and Hong 1973).

Impacts of Silt and Suspended Sediments

There are numerous direct and indirect impacts of silt, suspended sediments and associated turbidity (see Appleby and Scarratt 1989; European Inland Fisheries Advisory Commission 1965). These include changes to water quality, reduced light penetration diminished recreational values and aesthetics as well as direct and indirect impacts to fish, invertebrates, aquatic plants.

Changes in Water Quality

Suspended sediments can alter taste, odor, temperature and abrasiveness of water (Oschwald 1972) and reduce levels of dissolved oxygen particularly in deeper, thermally stratified lakes (Appleby and Scarratt 1989; Cramer 1974). Increases in sediment inputs have also been noted to decrease pH at the substrate-water interface of streams (Lemly 1982). A decrease in water clarity is another obvious change resulting from an increase of suspended solids.

Reduced Light Penetration

Increased turbidity, associated with suspended solids, reduces the penetration of sunlight. This in turn reduces photosynthetic activity (Marzolf and Arruda 1980; McCubbin et al. 1990; Meyer and Heritage 1941; Persaud and Jaagumagi 1995) and limits primary production (Gliwicz 1986; McCubbin et al. 1990; Munavar et al. 1991; Murphy et al. 1981; Wilson 1957).

Impacts on Aquatic Plants

Impacts to aquatic macrophytes vary from none (Edwards 1969) to the decrease of loss of various species (Moss 1977; Robel 1961). Documented effects include physical damage to leaves (Lewis 1973), reduction in photosynthetic activity (Chandler 1942; Chapman 1962; Ward 1992; Warren 1971), slower growth rate (Lewis 1973), and a
reduction in the maximum depth of colonization (Canfield et al. 1985; Garrard and Hey, 1988).

Impacts on Invertebrates

Tolerance of various aquatic invertebrates varies according to the species however a wide range of impacts have been documented:

Reduced Feeding Activity – Filter feeding invertebrates are generally less tolerant of turbid conditions than other aquatic species. Increases in suspended sediment concentration (to 50-100 mg/1) decreased ingestion rates to potential starvation levels (Arruda, Marzolf and Faulk 1983). Suspended clay was found to reduce Daphnia feeding rates (Kirk 1991 b; McCabe and O’Brien 1983). Under highly turbid conditions, mussels and clams usually close their shells. Either the mussel cannot feed or silt laden food is rejected as pseudofaeces and the animal starves (Ellis 1936). Turbid conditions may also result in a reduction of food quality (i.e., leaf litter) for benthic macroinvertebrates (Forbes, Magnusson and Harrell 1981).

(ii) Toxicity and Direct Mortality – Suspended sediments have been found to be acutely toxic to amphipods (Forbes, Magnusson and Harrell 1987). Silt layers, 1/4 – 1 inch in thickness, can produce a high mortality in some freshwater mussels (Ellis 1936). “Red mud” was found to increase mortality rates of a planktonic copepod (Paffenhofer 1972). Koenings et al. (1990) demonstrated that turbidity reduced Daphnia survival.

(iii) Impede/Alter Movements – Sediment additions in a Northwest Territories river increased the numbers of different macrobenthos drifting downstream (Rosenberg and Wiens 1978). Similar observations on movements and colonization were also reported on Emerald Creek, Idaho (Leudtke and Brusven 1976).

(iv) Altered Species Composition and Abundance – There is considerable evidence to indicate that changes in the abundance and composition of invertebrate communities are associated with increases in suspended solids and turbidity. Gammon (1970) found that suspended loads between 40-120 mg/1resulted in a 25% reduction in macroinvertebrate density; at a sediment load of more than 120 mg/l, macroinvertebrate density decreased by 60%. Standing stocks of Daphnoid zooplankton have been reduced at elevated turbidities in Lake leRoux, South Africa, and in an Amazonian floodplain lake (Carhalho 1984). Insect densities (drift and benthos) were found to be smaller in stream riffles with large amounts of sediment (Bjornn et al. 1974). Densities of Chironomids decreased in abundance by 90% after a release of suspended solids downstream from Guernsey Reservoir, Wyoming (Gray and Ward 1982). Erman et al. (1977) reported that invertebrate diversity in sediment California stream were greatly reduced for a period of at least ten years following logging activities. Stream invertebrate densities have been reduced in areas sedimented from upstream construction activities (Bowlby et al. 1987; Tebo 1955). Productivity of aquatic insects declined by 85% due to increased suspended solids in a stream below a gravel dragline operation (McKee and Wolf 1963). Algal biomass has been reduced in highly turbid waters (Cooper and Lipe 1992). Increased turbidity below a Camel River tributary was attributed for the elimination of some macroinvertebrates and the low diversity of
others (Nuttal 1972). Similar observations were noted in a Virginia reservoir (Samel 1973). Changes in species composition have also been documented (Lenat et al. 1981). Lemly (1982) noted that species richness and diversity of filter feeding benthic insects were significantly reduced in areas polluted by elevated sediment inputs. Chutter (1969) concluded that there could be considerable changes in the invertebrate fauna in flowing waters associated with levels of silt and sediment which did not completely smother them. The abundance and distribution of mayflies, clams and bryozoans are some species which have been documented to respond negatively to turbid waters (Cooper 1987). Cuker (1987) noted a species shift in algal communities associated with increased turbidity.

(v) Physiological Changes – The most harmful effect of suspended solids on invertebrates is the clogging of their filter feeding apparatus and digestive organs. Other physiological impacts associated with increased suspended sediments include reduced fecundity and brood size (Kirk 1992), retarded development of eggs and larvae (Appleby and Scarratt 1989; McKee and Wolf 1963) and increased water pumping rates (Appleby and Scarratt 1989).

(vi) Decreased Primary Productivity – Increased levels of suspended sediment coupled with high flows can remove algae from substrates resulting in a reduction in biomass (Alabaster and Lloyd 1980). Lloyd (1985) concluded that an increase in turbidity of 25 NTU (Nephelometric Turbidity Units) in shallow, clear-water systems may potentially reduce stream productivity by 13-50% or more and be associated with an increase in suspended sediment concentration of approximately 25-100 mg/l. A 5 NTU increase in turbidity in clear-water systems may reduce the primary productivity by 3-13% or more and be associated with an increase in suspended sediment concentration of approximately 5-25 mg/1. In Lake Erie, turbidity was found to influence composition, size, duration and time of occurrence of phytoplankton pulses and vertical distribution of microcrustacea (Chandler 1942). Turbid water can also limit the production of zooplankton (Committee Restoration of Aquatic Ecosystems 1992; Hart 1987).

(vii) Growth Rates – Probably as a result of reduced feeding activity as well as diminished food value, growth rates are often delayed or reduced in many organisms (Appleby and Scarratt 1989; Kirk 1992; Paffenhofer 1972).

Impacts on Fish

Probably the most research on the impacts of silt and suspended sediment sediments on aquatic organisms has involved fish. Some of the most comprehensive work has been done by C. P. Newcombe (1986a, 1986b, 1994a, 1994b) and this material is highly recommended for more detailed information. Generally, tolerance varies considerably between different fish species, the various particle sizes and types, and water quality parameters (including temperature). For example, larger particles having greater angularity have generally been found to be more lethal than smaller and smoother particles (Appleby and Scarratt 1989; Newcombe 1994b). Smaller particles lack the mass to cause mechanical damage to gill tissue but are capable of stimulating mucous production in the gill epithelium (C. P. Newcombe, British Columbia Ministry of Environment, Lands and Parks, Victoria, British Columbia. V8V 1X4). There is also evidence (Goldes 1983) that fine particles are phagocitized and can become distributed through the tissues of the fish. The effects of suspended sediments on fish is also influenced by water temperatures with more severe impacts occurring at higher water temperatures. This phenomena is probably a function of reduced activity (and metabolic rate) at cooler temperatures as well as the fact that saturation concentration of dissolved oxygen is an inverse function of water temperature. Impacts are based on intensity which Newcombe (1986a) defines as the product of concentration of suspended sediment multiplied by the duration (hours) of exposure of the organism. On this basis, he developed a Stress Index. The Stress Index is based on the natural logarithm of the product of suspended solid concentration (mg/1) and duration of exposure (hours). The resulting value is expressed in terms of Newcombe also identified three basic categories of effect: behavioral (transient), sublethal and lethal. The index can then be used to rank anticipated effects (Table 2). It is important to realize that average severity of effects differ among fish species as well as life history stage. In addition, the onset of ill effects is often abrupt and can occur at relatively low concentrations and brief duration of exposure.

Younger life stages of fish are usually the most vulnerable and more severely impacted (Alexander and Hansen 1986; Appleby and Scarratt 1989; Newcombe 1994b). Generally, the larval stage appears to be the more sensistive than the egg or juvenile stages (Appleby and Scarratt 1989). Newcombe (1994b) also concluded that exposed fish eggs are generally more sensitive (and vulnerable) than eggs buried in the substrate.

Table 2: Ranking of effects of suspended sediments on fish and aquatic life.

Rank Category of Effect Description of Effect

  1. Increased coughing rate
  2. Alarm reaction; avoidance reaction
  3. Behavioral Effects Avoidance response; abandonment of cover
  4. Reduction in feeding rates
  5. Impaired homing
  6. Poor condition of organism
  7. Moderate habitat degradation
  8. Physiological stress and histological changes
  9. Sublethal Effects Reduction in growth rates
  10. 0-20% mortality
  11. 20-40% mortality
  12. 40-60% mortality; severe habitat degradation
  13.  60-80% mortality
  14. Lethal Effects > 80-100% mortality

Source: Newcombe and MacDonald (1991)

There have been some benefits observed from increased suspended sediments in aquatic ecosystems. These include increased protection to prey fish from predators (Bruton 1985; Doan 1941; Godin and Gregory undated) as well as the predators themselves (Gregory and Northcote 1993), increased production for some species such as channel catfish (Homer 1956), enhanced fishing success for species including eels (Deelder 1970), assisted feeding Impacts to fish will be summarized under the following categories: movements and avoidance, feeding impairment, physiological changes, sedimentation of spawning beds, growth rates and production/abundance.

(i) Movements and Avoidance – Although not all fish avoid turbid waters, elevated turbidity or levels of suspended solids often induce avoidance reactions and may modify natural movements and migrations of many fish species. McLeay et al. (1984) found that Arctic grayling were displaced at suspended sediment concentrations of 300 mg/1 or greater. Juvenile salmonids have been known to leave channels containing sedimented substrate which did not provide interstitial spaces for winter refuge (Bjornn et al. 1974; Hillman, Griffith and Platts 1987; Marcus et al. 1990; Sigler, Bjornn and Everest 1984 ). In fact, the abundance of juvenile salmon in pools of small streams declines in direct proportion to the amount of habitat lost to sedimentation (Bjornn et al. 1977). Gammon (1970) reported that fish vacated stream pools after deposits of sediment accumulated but returned after winter floods had removed sediment deposits. Erman and Lignon (1988) found that three spine stickleback and prickly sculpin numbers were significantly reduced in areas exposed to a frequent flow of water laden with fine sediments. Paramagian (1991) concluded that sediment was a major habitat factor limiting the viability of smallmouth bass populations in Iowa.

Other behavioral changes have been observed. In some species, the tendency to migrate has been noted to decrease with increasing water turbidity (Appleby and Scarratt 1989). Berg and Northcote (1985) reported that, at high turbidities, dominance hierarchies broke down and territories were not defended.

Under turbid conditions Heimstra et al. (1969) noted that social hierarchies in green sunfish were disturbed. In Lake Texoma (Oklahoma-Texas), behaviour of larval shad and freshwater run were altered by an inflow of turbid water. Larval shad became concentrated near the surface while larval drum were distributed throughout the water column in contrast to their normal concentration near the bottom (Matthews 1984). Similarly, vertical migrations of herring, which are related to light intensity, have been disrupted (Appleby and Scarratt 1989).

(ii) Feeding Impairment – Reduced light penetration affects sight feeding fish by reducing efficiency of prey location (Berg and Northcote 1985; Godin and Gregory undated; Vinyard and O’Brien 1976; Zettler and Carter 1986). Turbidity can reduced the feeding of predatory fish even under abundant food conditions (Gregory 1991; Vinyard and O’Brien 1976). Miller and Menzel (1986) reported a negative relationship between water transparency and muskellunge feeding activity. Turbidity from suspended clay particles significantly reduced the feeding rate of bluegills on Daphnia (Gardner 1981). The feeding rate of Arctic grayling has been impaired at increased sediment concentrations (McLeay et al. 1987).
Larval striped bass consumed 40% fewer prey in water having suspended solids concentrations of 200-500 mg/1(Breitburg 1988). A reduction in feeding activity of juvenile coho salmon was noted at suspended sediment concentrations of 300 mg/1(Gregory and Northcote 1993). Redding et al. (1987) reported that feeding rates of yearling coho salmon and steelhead was reduced at high (2-3 gm/1) of suspended solids. After two hours of exposure to turbidity of 3 5 ppm, cutthroat trout in an Idaho river stopped feeding (European Inland Fisheries Advisory Council 1965). As suspended sediment concentrations increased, Johnson and Wildish (1982) noted a depression in the feeding rate of larva herring.
For Pacific herring, Boehlert and Morgan (1985) found that the incidence and intensity of maximum feeding occurred at levels (500-1000 mg/1) of suspended solids significantly greater than controls (0 mg/1). At higher levels of suspended solids feeding decreased. They hypothesized that suspensoids may have acted to improve visual contrast thereby increasing feeding efficiency.

Physiological Changes – Several species of fish have been found to be relatively tolerant of high suspended sediment concentrations (Petticord 1976). Fish can tolerate short episodes of extremely high levels of suspended sediment by exuding a protective mucus on the skin and gills. This mucus traps and continually removes trapped particles but comes at a metabolic cost which places the fish under stress (Committee Restoration Aquatic Ecosystems 1992; Persaud and Jaagumagi 1995). For a direct effect or mortality to occur the levels of suspended solids must be very high and dissolved oxygen relatively low. Excessive levels of silt clog opercular cavities and irritate gills leading to respiratory difficulties and poor health (Phillips 1971). At very high turbidities, sediment-clogged gills cease to function as oxygen exchange sites and the fish dies from a combination of anoxemia and carbon dioxide retention (Ritchie 1972). In a study with green sunfish, Hokel and Pearson (1976) found that ventilation rates increased under highly turbid conditions to compensate for reduced respiratory efficiency while maintaining a constant oxygen uptake.

In most cases, elevated suspended sediments have sublethal effects. These may include increased fin rot and body abrasion (Herbert and Merkens 1961; Ritchie 1972), paler coloration (McLeay et al. 1984), delayed maturation (Reynolds et al. 1988), elevated cough frequency (Servizi and Martens 1992), elevated microhematocrit (packed red blood cell volume), hemoglobin concentration and red blood cell counts (Appleby and Scarratt, 1989; Redding et al. 1987) and decreased tolerance rates and time to death when exposed to other environmental stressors (Appleby and Scarratt 1989; McLeay et al. 1984; Redding et al. 1987).

(iv) Sedimentation of Spawning Beds – Perhaps one of the most well known impacts is the sedimentation of fish spawning grounds. Generally, silt which settles on/into spawning substrate prevents successful incubation and hatching of fish eggs requiring a clean surface. Sediment clogs the interstitial spaces in gravel reducing water flow and, hence, oxygen availability to eggs which ultimately causes them to suffocate (Doudoroff 1957; McQuinn et al. 1983; Peters 1965; Ventling-Schwank and Livinstone 1994). Other impacts include a reduction in spawning activity (Saunders and Smith 1965), reduced adhesiveness in sauger eggs (Doan 1941), accumulated toxic metabolites around incubation eggs (McCubbin et al. 1990; Phillips 1971), delayed and/or reduced emergence (Hausle and Coble 1976; Sheppard et al. 1984) and blocked fry emergence (McCubbin et al. 1990; Phillips 1971; Shaw and Maga 1943).

There has been considerable study to quantify these impacts. In an experiment involving white perch and striped bass, Morgan et al. (1983) found increased levels of sediment (> 0.8 mm) slowed egg development and eventually resulted in mortality. Silt deposition of 1 mm per day in two South Dakota lakes was associated with a 97% mortality of pike embryos (Hassler 1970). Increased turbidity and sedimentation has also been found to reduce spawning and incubation success of yellow perch (European Inland Fisheries Advisory Council 1965; Thorpe 1977), pikeperch (European Inland Fisheries Advisory Council 1965) and lake whitefish (Fudge and Bodaly 1984). Survival to emergence of salmonid eggs relates negatively to the percentage of small fines in redds (Chapman 1988; Phillips 1971; Reiser and White 1988; Shaw and Maga 1943; Shelton and Pollock 1966; Tappel and Bjornn 1983). Bjornn et al. (1977) suggested that when the percentage of fine sediment exceeds 20-30% in spawning riffles, survival and emergence of salmonid embryos begins to decline Erman and Lignon (1988) recorded that incubating rainbow trout eggs had significantly lower survival rates (30.7% and 41.8% respectively) at sites exposed to silted water than those (61.4%) in clean water. In a South Wales river, 98-100% rainbow trout egg mortality was attributed to heavy siltation. In Bluewater Creek, Montana, Peters (1967) reported that the best (97%) survival of trout eggs occurred where stream discharges were stable and sediment concentrations were low. Langer (1980) reported a reduction in survival of chum salmon eggs at suspended sediment concentrations of 97 mg/1.

(v) Altered Growth Rates – Generally, an increase in suspended solids results in reduced growth rates. This has been documented for Arctic grayling (McLeay et al. 1987), crappies (Buck 1956), coho salmon (Sigler, Bjornn and Everest 1984; Smith and Sykora 1976), rainbow trout (Sigler, Bjornn and Everest 1984), brook trout (Sykora, Smith and Synak 1972), and largemouth bass (Buck 1956). Concentrations at which reduced growth rates have been documented range from 50 mg/l (Herbert and Richards 1963) to 130 mg/1 (Buck 1956).

(vi) Production/Abundance – Increasing sedimentation and turbidity suppress fish production. The standing crop of fish in a small southern Ontario stream was reduced from 24 to 10 kg/ha as a result of increased suspended solids associated with highway construction (Barton 1977). In a study of 23 streams in England, there was an average of 2-5 fish/1000 feet of sediment polluted stream compared with 16-27 fish/1000 feet of unpolluted stream (Ritchie 1972). Homer (1956) found that the average weight of fish from clear-water farm ponds was 1.7 times greater than ponds having intermediate turbidity and 5.5 times greater than muddy ponds. In rivers with suspended solid concentrations of 1000-6000 ppm china-clay wastes, brown trout densities were approximately 1/7 of populations in clean (60 ppm) streams (Herbert, Alabaster and Lloyd 1961). A reduction in sand bedload resulted in a 28% increase in brown trout and rainbow trout production (Alexander and Hansen 1983). Alexander and Hansen (1986) also reported that a 4-5 fold increase in sand sediment into Hunt Creek, Michigan, resulted in a significant reduction in brook trout abundance. Reduced standing crops of brook trout have also been associated with siltation in Ellerslie Brook (Saunders and Smith 1965).

Buck (1956) documented the changes in centrarchid production associated with varying turbidities:

< 25 mg/l (clear) – centrarchid yield 161.5 lb./acre
25-100 mg/1 – centrarchid yield 94.0 lb./acre
> 100 mg/l (muddy) – centrarchid yield 29.3 lb./acre

In addition to an actual decrease in productivity, the diversity of fish stocks is also reduced with increasing suspended sediment concentration (European Inland Fisheries Advisory Council 1965; Garrard and Hey 1988). Marcuson (1968) documented changes in the trout:coarse fish ratios in Bluewater Creek, Montana, with decreases in suspended sediment. These shifts result from an alteration in the composition and diversity of the aquatic community to those more tolerant of increased turbidity (often “less desirable” species).

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