Chapter 3: Physiochemical Characteristics of Ponds
Claude E. Boyd and Christopher A. Boyd
Pond management often is viewed as a fish management effort. However, many other factors including physical and chemical influences must be considered by pond managers. Water sources should be selected and manipulated to maintain water levels in ponds—but without causing excessive flushing. Waters should be of high quality to avoid stressing fish, and they should contain sufficient alkalinity and nutrients to support enough natural productivity for the desired level of fish production. Plankton blooms should be dense enough to create adequate turbidity to prevent aquatic plants from becoming troublesome, but not so abundant as to cause low nighttime dissolved oxygen concentration. Sediment accumulation should be minimized to avoid loss of water depth and pond volume, and bottom soil condition should be suitable for good growth of fish food organisms. Moreover, the natural beauty of ponds and their surroundings should be preserved.
This chapter is an overview of physiochemical characteristics of ponds and their watersheds. Its purpose is to supplement discussions of pond management practices in other chapters.
A unit watershed is the smallest land surface area discharging water at a given point. First-order streams have no tributaries, and the land area that delivers water to an intermittent or permanent, first-order stream is a unit watershed (Wesche and Isaak 1999). Ponds usually are superimposed into unit watersheds. The land area delivering water to a higher order stream often is called a watershed, but this area is more precisely described as a stream basin or catchment.
Watersheds vary from a few to several hundred hectares in area. Constructed ponds become an integral part of watershed structure and function. The contour of the portion of the watershed that is flooded usually determines the basic morphometry of the pond, although specific habitat features can be created during the construction process. Water balance and water quality in a pond are affected by its watershed, and a pond influences the amount and quality of water discharged from its watershed.