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Sedimentary Characteristics, Biological Zonation and Physical Processes of the Tidal Flats of Iqaluit, Nunavut

2002; Springer Nature (Netherlands); Linguagem: Inglês

10.1007/978-94-017-2037-3_10

2215-0072

Janis E. Dale, Shannon R. Leech, S. B. McCann, Glenda M. Samuelson,

Arctic and Antarctic ice dynamics

Tidal flats in temperate areas tend to be dominated by tidal processes, resulting in distinct sedimentary characteristics and associated flora and fauna. Fewer studies exist in arctic regions where the classic form of temperate tidal flats is less obvious. This paper discusses the sedimentary characteristics, biological zonation, and dominant physical processes affecting the subarctic, macrotidal tidal flats near Iqaluit, Nunavut. Tidal, wave, and ice processes dictate the development of tidal flat morphology and the distribution of organisms. The semi-diurnal tides average 7.8 m above low, low tide (ALLT), with large tides of 11.6 m ALLT. The two high and two low tides are experienced daily, even during ice cover that averages 8 to 9 months of the year. Tidal currents move sediment, biota, raft ice floes with their sediment or boulder-rich load, and affect water temperature and salinity at the bed. All of these factors limit the distribution of flora and fauna. Exposure indices generated from tidal data, reveal two critical tidal heights around 4.0 m and 7.5 m ALLT. The boundary between motile and less motile (sedentary) fauna occurs around 4.0 m ALLT, and 7.5 m ALLT marks the limit of most marine flora and fauna, with the rare exception being Fucus evanescens. The effectiveness of wave action is restricted to ice free periods. Thus the sorting of sediment by wave action is limited to a few months each year. Ice floes also dampen wave action. The longer the ice-free period the greater the degree of sorting of the intertidal deposits after the disruptive effects of ice formation. The tidal flats are divided into six morphological zones and three closely associated biological zones. Fauna of the upper flat and beach areas are hardy and freshwater tolerant. Many are highly motile, opportunistic species that recolonize the area after ice breakup. These zones are the most intensively affected by ice action. There is a gradual change in fauna from highly motile species to more sedentary ones towards the lower end of the middle flat. Below 2.2 m ALLT, the tidal flat has smaller sizes and decreasing numbers of boulders. In addition, this area has the highest diversity and species richness due to increasing numbers of sedentary infauna such as Mya truncata, larger tubiculous polychaetes and the anemone Tealia sp. Anthropogenic effects are most apparent on the flats nearest the town-centre, at sites proximal to the sewage lagoon, dump sites and areas graded by the hamlet for vehicular traffic. Reduced species richness, diversity and evenness values characterize the invertebrate population at these sites. Elsewhere communities appear stable and show no statistically significant difference from studies in the 1980s.