Assessment of ecosystem changes in response to freshwater inflow of the Kromme River estuary, St. Francis Bay, South Africa: A network analysis approach
Baird, D.J.; Heymans, J.J. (1996). Assessment of ecosystem changes in response to freshwater inflow of the Kromme River estuary, St. Francis Bay, South Africa: A network analysis approach. Water S.A. 22(4): 307-318
In: Water S.A. Water Research Commission: Pretoria. ISSN 0378-4738; e-ISSN 1816-7950, meer
We present results on changes which occurred at the ecosystem level over a period of 10 years in the relatively pristine Kromme River estuary, St. Francis Bay, South Africa. Carbon flow models were constructed for the estuary based on data collected before 1984 and again during the period 1988 to 1992. The first data set was collected during a period of regular and substantial freshwater inflow (average of about 117 x 106 m3a), and the second set after the impoundment of the river in 1984 and the resultant decrease in freshwater inflow to less than 2 x 106 m3 per annum. The salinity regime changed from one with gradient (35 to 15) to a homogenous one where the salinity remained virtually constant at 35 and higher since the construction of the dam in 1984. The flow models were analysed and global system properties, such as the total system throughput, the magnitude and structure of cycling, development capacity, ascendancy and relative ascendancy, were used to assess whether the system has undergone change due to reduced freshwater inflow rates since 1984. Results showed that while some of the biotic compartments increased in biomass and abundance, others declined. Based on the results we conclude that the estuary has changed from a plankton-dominated system to one dominated by submerged benthic vegetation and macrobenthic invertebrates in response to reduced freshwater inflows.
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