The relative effects of water depth, fetch and other physical factors on the development of macrophytes in a small southeastern US pond

Abstract

Aerial photography obtained during the growing seasons of 1979, 1982, 1985, 1988, and 1992 were used in a geographic information system to analyze the development of the floating-leaved macrophyte community in Pond B, an 87 ha, 12 m deep former cooling pond at the Savannah River Site that displays the water chemistry and fluctuating water levels typical for small southeastern reservoirs and ponds. The 1979 photograph was panchromatic. The later photography was natural color. Digitally-scanned photographs were: (1) classified using image processing software into the categories of macrophytes present or macrophytes absent (i.e. water); (2) compared across years to measure the rates and patterns of macrophyte development; and (3) compared to measures of water depth, sediment slope steepness, aspect, and fetch to relate patterns of macrophyte development to physical factors. The area occupied by floating-leaved macrophytes increased from 3.2 ha in 1979 to 19.9 ha in 1992, when macrophytes occupied 84.1% of the area ≤2 m deep and 56.3% of the area 3 m deep. The rates of macrophyte development were consistently slower in areas of greater water depth and greater fetch. The effects of slope and aspect were less than those for depth and fetch. Greater slopes initially enhanced but later slowed macrophyte development. Rates of development were greater for aspects facing the sun. The rate of macrophyte development was not correlated with proximity to existing vegetation.