Spring changes in a farm pond plankton community structure and the effects of chemical enrichment on population growth

The benefits of fertilizing farm ponds are well known. For example, Swingle and Smith (1941) found production of fish could be doubled at a reasonable cost by providing a supplemental energy source (commercial fertilizers and cottonseed meal). An additional benefit ascribed to fertilizing ponds is a decrease in rooted aquatic plants as a result of nutrient competition from plankton blooms. But the use of a fertilizer can be an expensive, wasteful process If none of its ingredients is the factor limiting plankton growth. Further, additions at the wrong time, or of the wrong amounts, can do damage. Most commercially prepared fertilizers are made up of various percentages of nitrate, phosphate and sulfate. However, in many instances adding other chemicals such as manganese (Henderson, 1949), molybdenum (Goldman, 1960), and silicate (Ryther and Guillard, 1959) has increased plankton populations. Ryther and Guillard also found one or more components of their iron and trace mineral mixture increased plankton in sea water. Because of these problems, I undertook this research to determine: 1) the changes taking place in plankton abundance and species composition with time, and 2) some of the potential causes of these changes, especially nutrient additions.