may be derived from the channel bottom or from the shore immediately adjacent 

 to the channel. Sand sediment is deposited at channel bends, either on 

 adjacent flats on the outsides of bends or as bar deposits on the insides of 

 bends, where current velocities decrease and drop their bedload. Sand flats 

 of the bar type are more well sorted than sheet deposits. Generally, bar type 

 sand flats are under the constant influence of unidirectional, or 

 bidirectional tidal currents that are of similar magnitude at high and low 

 tide and consist of fine to very fine sand. Over time these sand flat 

 environments also migrate landward, as nearshore deposits shift landward in 

 response to sea level rise (Timson, in preparation ) . The surface of these bar 

 deposits is mobile at all times in response to tidal current variability. 

 Sediments to depths of up to 8 inches (20 cm) may be mobilized and 

 transported several meters by tidal currents (Boothroyd and Hubbard 1975). 



Large sand flats in Maine are relatively few. Along the eastern coast of the 

 United States south of Maine low energy intertidal flats commonly are composed 

 of sand. In the characterization area, most of the source material for low 

 energy systems is silt and clay, which contribute to the extensive mud flats 

 found along the coast. The major sand flat areas in the characterization area 

 are Sagadahoc Bay and Heal Eddy near Georgetown (region 2) , Sprague Neck bar 

 in Machias Bay (region 6), Bailey's Mistake at Trescott (region 6), the spit 

 of South Lubec (region 6), and Clam Cove at Rockport (region 4). 



The benthic marine flora supported by sand flats is small in terms of biomass 

 and productivity in comparison with the rocky shore environment. Much of the 

 sand bottoms along the coast are not stable enough to support large macrophyte 

 populations. In areas that are extremely stable, small macroalgal populations 

 may appear for brief periods on sediment surfaces, such as small stones or 

 shells. Only small plants develop under these conditions and species 

 diversity is low. 



Invertebrate species living on sand flats in Maine include representatives 

 from sand beaches and mud flats (Larsen and Doggett 1978a). The species 

 listed in table 5-11 are the 12 most abundant species on sand flats, as 

 determined by a rank score analysis. Oligochaetes and nematodes are most 

 abundant and polychaetes and amphipods are relatively common. Two species 

 that are commercialy valuable and common to both sand and mud flats are the 

 bivalve soft-shelled clam and the polychaete sandworm. These species are 

 found in abundance, (up to 404 and 272 individuals/m , respectively) in many 

 locations . 



Larsen and Doggett (1978a) identified 71 species of invertebrates on the six 

 sand flats in the characterization area. At the 48 stations sampled, the 

 number of species varied from to 21, with a mean of approximately 12. In 

 species diversity sand flats rank fifth among the nine intertidal habitats 

 sampled by Larsen and Doggett (1978a). The mean faunal density on sand flats 

 is low but widely variable (Larsen and Doggett 1978a). The mean density is 

 1510 individuals/m 2 and the range is to l6,840/m . Sand flats in the 

 characterization area are therefore only slightly more densely populated than 

 sand beaches and rank eighth among the nine types of intertidal habitats 

 investigated. 



5-102 



