『Abstract
Phosphorus (P) release from bottom sediments can be a significant
source to the overlying water column, potentially maintaining
and enhancing algal growth and eutrophic conditions in lakes and
reservoirs. Thus, the objectives of this study were to: (1) measure
P flux under aerobic and anaerobic conditions from intact sediment
cores collected at Beaver Reservoir, northwest Arkansas, (2) evaluate
the spatial variability in measured sediment P flux under aerobic
and anaerobic conditions along the reservoir, and (3) compare
external and internal P loads to Beaver Reservoir. Six intact
sediment cores were collected at three sites representing the
lacustrine, transitional, and riverine zones during June 2003,
September 2003 and February 2004 and incubated for 21 days in
the dark at 〜22℃. Three cores from each site were incubated under
aerobic conditions and anaerobic conditions. Water samples were
collected from the overlying water column in each core daily for
the first five days and every other day thereafter and analyzed
for soluble reactive phosphorus (SRP). Water removed from the
core was replaced with filtered lake water, maintaining a constant
overlying water volume of 1 l. Sediment P flux under anaerobic
conditions (＜0.01-1.77 mg m-2 day-1) was
generally greater than that measured under aerobic conditions
(＜0.01-0.89 mg m-2 day-1). Some spatial
variability existed in sediment P flux where P flux was generally
greatest at the sites in the riverine and transitional zones.
Maximum sediment P flux was observed under anaerobic conditions
in cores collected from the transitional zone during September
2003. Average sediment P flux under aerobic conditions (0.09 mg
m-2 day-1) and anaerobic conditions (0.31
mg m-2 day-1) was greater than the external
P flux (0.05 mg m-2 day-1) estimated from
the Beaver Reservoir tributaries. Results showed that the annual
internal P load (7 Mg year-1) from bottom sediments
in Beaver Reservoir was less than 10％ of the annual external P
load (〜81 Mg P year-1). The internal P load was significant,
but it would not currently be cost effective to manage this P
source given the large surface area of Beaver Reservoir.
Keywords: phosphorus; bottom sediments; internal sources; aerobic
and anaerobic conditions』
1 Introduction
2 Materials and methods
2.1 Site description
2.2 Field and laboratory procedures
2.3 External load estimation
2.4 Data analysis
3 Results
3.1 Sediment phosphorus - June 2003
3.2 Sediment phosphorus flux - September 2003
3.3 Sediment phosphorus flux - February 2004
3.4 Internal phosphorus loads
3.5 External phosphorus loads using USGS data
4 Discussion
Acknowledgments
References