Phosphorus distribution among selected abiotic and biotic components of two KwaZulu-Natal estuaries, South Africa.
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Date
2013
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Abstract
Phosphorus is an essential element since it controls primary productivity in aquatic ecosystems and
its excess can lead to eutrophication in receiving systems. The aim of this project was to determine
phosphorus distribution in biotic and abiotic nutrient pools of two KwaZulu-Natal estuaries.
Samples of dissolved inorganic phosphorus (DIP), particulate phosphorus (PP), phytoplankton,
microphytobenthos, zooplankton, macrozoobenthos and sediment were collected in the temporarily
open/closed Mpenjati (MP) and permanently open Mlalazi Estuary (ML) during May (ML),
September (MP) and November (ML+MP) using standard methods. Chlorophyll a concentrations as
well as species richness, abundance and biomass of zooplankton and macrozoobenthos were
analysed. Living and non living nutrient pools were analysed for phosphorus and were compared
between stations, sampling sessions, estuaries and taxa.
Zooplankton abundance and biomass in the Mlalazi Estuary was higher during May than
November. In the Mpenjati Estuary highest zooplankton abundance and biomass was recorded
during September than November. No significant differences were apparent in abundance (p =
0.217) and biomass (p = 0.974) of zooplankton between the two estuaries. Macrozoobenthos
abundance and biomass in the Mlalazi Estuary was higher during May than November. In the
Mpenjati Estuary macrozoobenthos abundance and biomass was higher during November than
September. Significant differences in abundance (p = 0.003) and biomass (p = 0.020) were apparent
between the estuaries.
Sediment to a depth of 10 cm comprised the highest phosphorus biomass than any other nutrient
pool in both Mlalazi (4871.1 mgP·m⁻² ± 5888.9 SD) and Mpenjati (2578.6 mgP·m⁻² ± 1828.0 SD)
estuaries followed by DIP (120.5 mgP·m⁻² ± 177.7 SD and 5.9 mgP·m⁻² ± 6.1 SD respectively). In
both estuaries, the lowest phosphorus biomass was contained in zooplankton with both estuaries
containing zooplankton P biomass of 0.001 mgP·m⁻² ± 0.002 SD. Particulate phosphorus and DIP
concentrations were higher in the upper reaches in both estuaries indicating that rivers were the
main sources of this nutrient in these systems. The Mlalazi Estuary had higher nutrient levels than
the Mpenjati Estuary. Such elevated nutrients can be enhanced by the continuous river flow into the
permanently open estuary. In both estuaries, no significant differences were apparent in
zooplankton and macrozoobenthos P content between different taxa.
Description
M.Sc. University of KwaZulu-Natal, Durban 2013.
Keywords
Phosphorus., Estuaries--KwaZulu-Natal., Biotic communities--KwaZulu-Natal., Eutrophication., Theses--Marine biology., Mpenjati Estuary (KwaZulu-Natal), Mlalazi Estuary (KwaZulu-Natal)