Abstract
Using ecological signature of biological integrity as a measure of performance, the reclamation efficiency of waste stabilization ponds was evaluated over a period of four years in a tropical sewage treatment plant – cum fish culture consisting of two anaerobic, two facultative and four maturation ponds located serially across the sewage effluent gradient. The four maturation ponds were used for batch culture of fish. Samples of surface and bottom water as well as surface sediment were collected twice a month from different ponds of the system and examined for some nutrient cycling bacteria, primary production, chlorophyll content of micro-algae, phytoplankton, zooplankton abundance, fish growth and water quality parameters. Computation of ecological signature using aerobic mineralization index for heterotrophic and ammonifying bacteria revealed steady increase across the sewage effluent gradient. The heterotrophic and ammonifying bacterial populations appeared to have a direct function with the concentrations of chemical oxygen demand of water. The sum of total scores for different optimal conditions for fish growth increased as a function of the distance from the source of effluent implying that ecological resilience of the waste stabilization ponds has been accomplished by the sedimentation, chelation, and biological functional attributes mediated through redundancy of different subsystems, selfpurification capacity of the system as a whole.
Highlights
Resilience, related to self organized behaviour of the ecosystems over time and space, is regulated by keystone structuring process as well as redundancy behaviour of species
This phenomenon is well depicted in a waste stabilization pond which is characterized by the dominant assemblages of primary producers or rooted macrophytes, grazing pressure and physical disturbances include light and temperature [Holling, 1973; Ludwig et al, 1996; Weaver et al, 1996] or excessive nutrient loading that causing eutrophication
The values of gross primary productivity of phytoplankton (GPP), community respiration (CR), net primary productivity of phytoplankton (NPP) as well as chlorophyll content of microalgae were significantly higher (P < 0.05) in the facultative ponds compared to maturation ponds (Table 1)
Summary
Resilience, related to self organized behaviour of the ecosystems over time and space, is regulated by keystone structuring process as well as redundancy behaviour of species. Cardinale et al [2000] has nicely modelled how spatial heterogeneity interacts with temporal disturbance to modify the relationship between species diversity and ecosystem productivity. It is further documented that the bacterial functional redundancy may be a useful indicator of soil quality and ecosystem functioning [Yin et al, 2000]. This phenomenon is well depicted in a waste stabilization pond which is characterized by the dominant assemblages of primary producers or rooted macrophytes, grazing pressure and physical disturbances include light and temperature [Holling, 1973; Ludwig et al, 1996; Weaver et al, 1996] or excessive nutrient loading that causing eutrophication
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