Coastal Ponds

Location Coastal lakes and ponds are distributed around the margins of the Antarctic continent, and are particularly abundant around the ice free areas of McMurdo Sound. These shallow coastal aquatic systems typically freeze solid over the winter months and cryoconcentrate the organisms in the ice, forcing the majority of the organisms, gases, and dissolved organic matter to the bottom (Figure 6). Most of the lakes studied are on Ross Island, east of McMurdo Sound near capes Evans, Royds and Bird.

Formation and diversity The coastal lakes and ponds occupy ice gouged areas in close proximity to McMurdo Sound (Figure 3). The main glacial groove in which the majority of the larger lakes at Cape Royds lie runs from Backdoor Bay along Blue Lake and branches off towards the coast with Clear, Coast, and Pony lakes. Two lakes at Cape Barnes, Sunk Lake, and Deep Lake, are found in a continuation of this same groove. These lakes range from freshwater to brackish with the ionic content enriched by precipitation, wind blown salt spray from the nearby sea, leaching from the volcanic rocks, and biologic inputs from penguins and sea birds. During the summer months, these ponds undergo varying degrees of melt depending upon snowpack and climatic conditions. The organisms that live in these coastal ponds experience extreme and often abrupt changes in light, temperature, water availability, salinity, and nutrients in contrast to those that live in the more stable inland meromictic lakes (Table 4).

Pony Lake is a shallow, eutrophic coastal pond located on Cape Royds. This lake is ice-covered except in mid-summer, when strong winds cause complete mixing of the water column. The lake is ^120 m long and 70 m wide, and 1-2 m deep. The source of water is snow, and water is lost by both ablation (from the snow and ice cover) and evaporation in mid-summer. Ice cover typically persists until late December. The pond is saline (^0.21 ppt), as a result of proximity to the sea and accumulation of salts by ablation. Phytoplankton are abundant (Chl a 28-140 mg l_1) with the dominant alga being the chlorophyte Chlamydomonas intermedia. There is a penguin rookery along the eastern shore and the lake has high nutrient concentrations. DOC concentrations range from 10 mg carbon per liter during the early season to as high as 110 mg carbon per liter during the height of the algal blooms.

Table 4 Comparison of ecological parameters in phytoplankton communities of Antarctic coastal ponds (i.e., Pony Lake, Blue Lake) and inland meromictic lakes (i.e., Lake Bonney, Lake Vanda)

Parameter

Coastal lakes and ponds

Meromictic lakes

Habitat stability

Low, experiences catastrophic changes

High, predictable

Growth season

Weeks

Months

Nutrient supply

High, C, N, P in excess

Low, growth limiting

Strategies

r-Selection (opportunistic, fast growing, rapid

K-selection (in equilibrium highly efficient, slow

population shifts)

population shifts)

Niche breadth

Wide, broad tolerances

Narrow, specialists

Species diversity

Low

High

Productivity

High

Low

Adapted from Vincent WF and Vincent CL (1982) Response to nutrient enrichment by the plankton of Antarctic coastal lakes and the inshore Ross Sea. Polar Biology 1: 159-165.

Adapted from Vincent WF and Vincent CL (1982) Response to nutrient enrichment by the plankton of Antarctic coastal lakes and the inshore Ross Sea. Polar Biology 1: 159-165.

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