WWW.WAS.ORG • WORLD AQUACULTURE • SEPTEMBER 2014 61 Pond Succession and Aging Watershed or hill ponds are constructed by building a dam across a valley and using runoff from the surrounding watershed to fill them. As ponds age, they fill with sediment in the form of soils and organic matter. Leaves and woody debris may fall into ponds or be washed in from the watershed. Eventually ponds will fill in and turn into shallow wetlands and then to dry land, if the basins are not emptied of material. This process is referred to as pond or lake succession. Man-made impoundments may be particularly vulnerable to rapid succession, inasmuch as the dam and shoreline are constructed of compacted, heavy clay soils that are prone to erosion. Wind-driven wave action and human activity in the watershed may hasten dam and bank erosion. Aging ponds tend to accumulate soft sediment deposits near the shoreline that reduces water depth. Excessive growth of aquatic plants and algae, which thrive in shallow waters, add more organic matter to ponds when they die. Low dissolved oxygen and other water quality problems may develop under these conditions. Aquaculture production and harvesting, irrigation, aesthetics and recreational activities may be affected by the deteriorating pond environment. When these conditions become severe or unmanageable, the pond will require renovation or abandonment. The effective “life” of a pond or how long it can be managed Pond Renovation: A Brief Overview Forrest Wynne properly before renovation is required depends on many factors. Orientation and exposure to prevailing winds, land use in the watershed, slope, soil types, annual rainfall and vegetative cover of surrounding land influence the rate that soil and organic matter enters a pond. For instance, a wellmanaged recreational pond may last 50 years or more before it needs renovation. If managed improperly, construction in the watershed, farming practices and livestock activity may greatly increase soil erosion and unwanted nutrients that wash into the pond. Proper land management practices, including vegetated buffer strips, will help reduce these problems. Levee-type aquaculture ponds are constructed where relatively flat land is available and a reliable source of water (typically groundwater) is used to fill them (Avery 2010). These ponds have minimal watersheds and shallow depths of 1.5 to 1.8 m to allow seining and to improve water quality (Steeby and Avery 2002). Intensively managed levee ponds may require renovation every 7-10 years. Sediment from eroding levees accumulates, making seine-harvest of fish difficult. Eventually, the crown of eroding levees may narrow to the point of making farm vehicle travel unsafe. (CONTINUED ON PAGE 62) FIGURE 1. Silt removal with a small bulldozer. FIGURE 2. Tractor with pan on levee.
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