『Abstract
Different phosphorus fractions and metal element composition
of surficial sediments were measured on three occasions in 2005
and 2006 along a transect between Nyanza Gulf and offshore Lake
Victoria, in order to assess the potential for sediments to contribute
to the water column P concentrations in Lake Victoria. Total phosphorus
(TP), apatite phosphorus (AP), inorganic phosphorus (IP) and organic
phosphorus (OP) increased in sediments along the gulf towards
the main lake while the non-apatite inorganic phosphorus (NAIP)
increases were less defined. The longitudinal gradient of sediment
TP and its fractions in Nyanza Gulf is a result of high rates
of terrigenous input and resuspension and transport of the light,
phosphorus rich inorganic and organic matter towards the main
lake. TP in the sediment ranged from 812.7 to 1,738 mg/kg dry
weight (DW) and was highest in the Rusinga Channel, the exchange
zone between the gulf and the main lake. Ap was the most important
TP fraction, contributing between 35 and 57.3％ of TP. Ca content
in the sediment was strongly associated with TP and AP in the
sediment (r2 = 0.92 and 0.98, respectively) in the
gulf and the channel, indicating the importance of apatite in
controlling P availability in these zones. In the gulf and the
Rusinga Channel, the less bioavailable apatite phosphorus dominated,
whereas in the deeper main lake OP was the major fraction illustrating
the importance of anaerobic release of P from sediments and acceleration
of internal P loading in the main lake.
Keywords: Nyanza Gulf; Phosphorus fractions; Phosphorus recycling;
Surficial sediments』
Introduction
Methods and materials
Study area
Field sampling and laboratory analysis
Results
Water column properties
Surficial sediment fractions
Elemental composition and phosphorus association
Discussion
Spatial gradients of phosphorus fractions
Influence of terrigenous sediment input
Apatite-phosphorus association and P availability
Role of bottom sediment in internal P loading
Conclusions
Acknowledgments
References