USGS Home
Contact USGS
Search USGS

Bottom Sediment

Texture

Differences in sediment texture are associated with variations in sediment salinity and degree of waterlogging, that are important environmental variables in salt marshes (Brereton 1971). Of 27 references to sediment texture in habitats supporting S. maritimus, most list clay (Table 9). Several of these references also list muds which are presumably high in organic matter. More than half of the references for S. robustus list organic sediments.

Walker and Coupland (1970) surveyed vegetation on a variety of sediment types based on texture, organic content, and water-holding capacity. They found nearly all stands of S. maritimus on sticky alkaline clay. Ranwell (1972) identified clays with higher cation exchange capacities (10-40 mE) as favoring good growth of this bulrush, but he noted that the higher capacities also indicate increased concentrations of nutrients and calcium. Klavestad (1957) observed the most well developed stands of this species along estuarine shores where clays have inputs of freshwater. However, freshwater inputs may be less important where S. maritimus grows on peats (Jacobson and Jacobson 1989). Adam (1981) and Ewing (1986) described optimum substrates for S. maritimus as soft and anoxic or highly reduced. Moody (1978) noted especially high rates of pioneering on silts.

Several authors suggest that sediment texture is insignificant for S. maritimus or note that the species grows in a wide variety of sediment textures (Dix and Smeins 1967; Haslam et al. 1975; Looman 1981).

Barko et al. (1977) grew S. robustus on a variety of dredge spoils in a greenhouse and found much higher biomass of plants grown in clay than those grown in sand, probably because of its lower nutrient (N, P) content. They had no success growing this species in spoils that were mostly silty clay, probably because they had much higher free-water salinities. Baden et al. (1975) reported that S. robustus is mostly found on silts, but that sediment texture seemingly is unimportant. Dominance of S. maritimus on sandy or other easily eroded bottom sediments may depend on the intolerance of other plants to the erosive effects of wave or ice action at such sites (Tyler 1969).

In summary, predominantly clay sediments support most natural stands of S. maritimus, whereas clays and organic sediments support most stands of S. robustus. Nonetheless, in the absence of other limiting factors, both bulrushes probably can grow on all common textural types, except possibly on rubble, boulder, and stone.

Sedimentation and Disturbance

Scirpus maritimus invades silted tidal ponds in British Columbia and Oregon (Jefferson 1974; Moody 1978; Hutchinson 1982). These ponds accumulate silt after other emergents reduce tidal energy. Scirpus maritimus is also characteristic of emerging flats in European maritime areas undergoing land upheaval (Dijkema et al. 1984). Scirpus maritimus is exclusively an invader of mudflats in Oregon salt marshes; disjunct stands are rare at such sites (Eilers 1975). Seed production in these marshes is uncommon, probably because of excessive inundation periods. Although the distribution of S. maritimus in British Columbia may be controlled primarily by sediment moisture and salinity, invasion may be greatest where vegetation traps fine particles and raises sediment moisture (Hutchinson 1982). Stands of S. maritimus in erosional and depositional zones in Czechoslovakian impoundments differ mainly in stand density rather than height (Dykyjova 1986). Protection from wave action increases corm survival, but the effects of sediment deposition on corms are unknown (Foote 1988).

Both bulrush species flourish in severely disturbed sites such as blasted wetlands (Warren and Bandel 1968); borrow pits, canals, drainage ditches, and dredged spoil deposits (Palmisano and Newsom 1968; Palmisano 1970; Adam 1981; Newling et al. 1983; Palmer 1986); and ponds in coal strip-mines (Olson 1979; Fulton et al. 1983). Both species also grow in areas disturbed by agriculture (Smeins 1967; Bassett 1978; Podlejski 1981, 1982; Pederson and Van der Valk 1984; Ferren 1985) or construction (Nelson 1954; Ranwell 1972; Wolseley 1986; Krahulec et al. 1987; Capehart and Hackney 1989; Brostoff and Clarke 1993). Scirpus robustus naturally colonizes new deltas formed by floods (Fuller et al. 1985). Storm tides may be instrumental in the perpetuation of this species in coastal Louisiana, although severe hurricanes sometimes eliminate stands for at least a year (Beter 1957; Kimble 1958; Chabreck and Palmisano 1973). In the Phillipines, Bernasor and DeDatta (1986) found greater S. maritimus stem density in continuously wet rice fields than in farmed fields on alternate wet and dry regimes.

In summary, sexual reproduction and seedling establishment in these bulrushes are strongly related to the availability of unvegetated sediments. Both species are highly tolerant of natural and artificial disturbances to bottom substrates, although little is known about adaptations to such stresses.

Chemistry

Scirpus maritimus grows on saline sediments and on sandy beach ridges where salinities are low (Flowers 1934; Tsopa 1939, cited in Chapman 1974; Penfound 1953; Ferrari et al. 1985). Plants occupy wetlands with sediment interstitial water conductivities ranging from 1.3 to 120 mS/cm and with as much as 6.3% dry weight total salts (Table 10). More robust stands are usually where conductivities range from about 4 to 23.0 mS/cm (Smeins 1967; Lieffers and Shay 1982a; Ewing 1986) and sediments contain about 0.3-1.0% dry weight total salts (Ungar 1965). Plants may not produce achenes in well-drained, highly saline sediments (Ungar 1970). In prairie Canada, plants are absent from wetlands where interstitial water conductivities exceed 40 mS/cm and water tables regularly fall well below the sediment surface (Looman 1981). However, where water tables remain high, short sterile plants can survive for several years at conductivities three times higher. In Saskatchewan, populations of S. maritimus grow in saline gleysols where highest salt content occurs in the upper 30 cm (Dodd and Coupland 1966b). Production experiments with S. maritimus in sediment with added sodium chloride show maximum corm numbers at 5.6-6.9 mS/cm and maximum corm weights at 4.6-5.6 mS/cm (Mercado et al. 1971). Bassett (1978) showed that S. maritimus ranks fourth in mean sodium tolerance among the 38 most frequent species in a Camargue (France) pasture.

In the Canadian prairies, current- and previous-year water levels and salinity, rather than the ionic concentrations in bottom sediments, show best correlations with S. maritimus plant size, seed production, and density (Lieffers and Shay 1982b). In wetlands in this region, achenes germinate and seedlings grow on wet mudflats if sediment salinities are less than 20 mS/cm (Lieffers and Shay 1982b). Vigorous stands regularly occur in some of these wetlands when surface water is present during the growing season, because salts move from sediments to the water column. Stand establishment is greatly inhibited in other wetlands where salt content of sediments does not decrease when surface water is present and where water salinities continue to increase, probably because of inputs of saline groundwater. Under continuous flooding, such high salinities, particularly in central areas, can preclude the growth of any emergent hydrophytes (Lieffers and Shay 1983).

Scirpus maritimus usually occurs where sediment pH varies from 5.2 to 8.9 (Table 10), although an acidophilous subspecies in Europe grows where sediment pH is as low as 3.7 (Husak and Hejny 1978; Dykyjova 1986).

Sediments for S. maritimus are often described as eutrophic or high in organic matter (Daborn 1975; Haslam et al. 1975; Looman 1981). Scirpus maritimus biomass is markedly higher on nutrient-rich sediments, even though the plant is less influenced by nutrient availability than several other common genera of emergent hydrophytes (e.g., Phragmites, Glyceria, Sparganium, and Typha; Dykyjova 1986). Bassett (1978) found more robust stands of Scirpus maritimus in areas high in organic matter, potassium, and organic nitrogen but relatively low in pH. Podlejski (1981) found positive correlations between the number of leaves per stem and the total sediment nitrogen; leaf area-to-weight ratios correlated with amounts of sediment organic matter. High correlations between total nitrogen and organic matter suggest that high concentrations of both substances lead to plants with thicker stems and broader leaves (Podlejski 1981).

Karagatzides and Hutchinson (1991) found that the greater standing crops of S. maritimus on high marsh compared to low marsh more strongly correlated with the number of daylight hours of tidal exposure than with any of a wide variety of physical and chemical sediment variables. However, they noted that the length of tidal exposure may also relate to the chemical variables. For example, high marsh may yield large crops where decaying wrack raises levels of nitrogen and other nutrients, whereas the less exposed low marsh may have small crops because of reduced sediment nitrogen and greater potential for the production of toxic sulfides. Young corms may be especially vulnerable to sulfide poisoning if saline lakes flood during midsummer (Lieffers 1981).

Sediments supporting S. robustus are in saline and brackish wetlands (Palmisano 1970; Stalter 1973; Baden et al. 1975). Stands occur where interstitial water conductivities vary from 2.6 to more than 100 mS/cm (Table 10), but the optimum range seems to be about 4-28 mS/cm (Palmisano and Newsom 1968; Mall 1969; Palmisano 1970; Chabreck 1972). Plants at highest salinities probably are dormant (Miller 1962). The limit of sediment osmotic potential for S. robustus is about -3.5 MPa (Ustin et al. 1982).

Of 12 sediment and water chemistry variables studied by Palmisano (1967) in Louisiana wetlands, only sediment salt concentrations significantly correlated with the distribution of S. robustus. Most robust stands there occur where salt concentrations average about 15 mg/L. Mall (1969) considered sediment salt concentration the second most important factor, after length of sediment submergence, controlling the distribution of hydrophytes in a California wetland. There, aboveground biomass of S. robustus is highest where sediments are submerged for 7 to 8 months, mean annual sediment salt concentrations range from 8.6 to 28.0 g/L, and sediment organic matter is more than 40%. Mall (1969) noted that when mean annual salt concentrations in the sediments fall below 8 g/L, the number of plants is reduced, although growth rate remains high. Germination of S. robustus achenes is best in sediments with soluble salt concentrations of 9 g/L or less (Prevost and Gresham 1981). Mall (1969) noted greatest achene yields on sediments of 9.3 g/L salinity submerged for 7 months. However, Pearcy et al. (1982) and Pearcy and Ustin (1984) noted that this species competes best where salinities increase from spring to summer. They found no clear relation between achene production and salinity from year to year and questioned the predictive value of simple regressions between various production measurements and salinity.

Wilkinson (1970) grew S. robustus where sediment pH falls as low as 3.1, but where water pH remains 6.5 or higher. Prevost and Gresham (1981) found best achene germination where sediment pH ranges from 5.1 to 5.7. The ranges in concentrations of other chemicals in sediments supporting the two bulrushes are listed in Table 10.

Slope

The only information on the effect of slope on either of the two bulrushes seems to be that of Klavestad (1957), who found Scirpus maritimus restricted to bottoms that slope 10 degrees or less.