The Marginal Algae of Certain Ponds, with Special Reference to the Bottom Deposits

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Abstract
Bottom deposits in the littoral regions of ponds bear a growth of algae on or near the surface. This flora constitutes a separate community independent of and not derived either from the planktonic or epiphytic communities. The presence or absence of such a community is determined by the degree of stability of the deposit and upon its position in the pond. Shallow exposed areas are barren. Almost all of the algae are capable of movement. The structure, depth and organic content of the deposits vary from pond to pond and in different areas of the same pond. With high organic content, great depth of deposit, and marked stagnation, Eugleninae and other flagellates become predominant on submerged deposits while certain diatoms and Oscillatoria become dominant in uncovered deposits in summer and autumn. Factors affecting the algal flora are structure, depth, and organic content of the deposits, seasonal variation in exposure and disturbance and in the nature of the deposits, variation in rainfall from yr. to yr. and during the year and variation in pH. The smaller the body of water the more important are the bottom deposits as a factor controlling the flora of the whole pond. The various marginal deposits possess the capacity without enrichment to produce a flora containing the majority of the algae found in those areas in nature. A list of algae identified is included.