Phosphorus Dynamics in the Barnegat Bay
George
1
Keighton ,
David
2
Velinsky ,
Nathaniel
3
Weston
and Bhanu
2
Paudel
1Department
of Chemistry, College of Arts and Sciences, Drexel University, Philadelphia, PA
2Patrick Center for Environmental Research, Center for Academy Science, The Academy of Natural Sciences of Drexel University, Philadelphia, PA
3Department of Geography & the Environment, Villanova University, Villanova, PA
Abstract
It has been hypothesized that bay sediment is acting as a phosphorus reservoir, and the conditions present in the southern sections of the bay are causing phosphorus to be released more readily. Water and sediment samples were collected from six different stations
throughout the bay and its tributaries. The water samples were analyzed for dissolved and particulate phosphorus. Sequential sediment extraction was performed to analyze phosphorus speciation in the collected sediment samples. Benthic phosphorus exchange and
water column P production was identified by purging sediment cores of the six main bay stations with water collected from each station to measure benthic fluxes under oxic and anoxic conditions. The sediment extractions show that the bulk of sedimentary phosphorus is
bound up in the inorganic form, with high inorganic P in the central and southern bay. The P concentration gradient along the two sections of the bay was not evident in the benthic flux experiment, and no difference was apparent between oxic and anoxic conditions. The
findings suggest that sediments are the sink of phosphorus.
50
Introduction
45
July
0.06
July
October
0.05
October
40
Barnegat Bay is a shallow brackish estuary located along the coast of Ocean County, New Jersey. It is
separated from the Atlantic Ocean by a barrier island complex, except at Barnegat Inlet near the central part
of the bay. Depth ranges from 1 to 6 m. Major tributaries include Toms River, Cedar Creek and Metedeconk
River. Nutrient loadings of nitrogen and phosphorus, mainly from nonpoint sources, are a matter of concern
since changes in the N to P ratio can affect algal productivity. Despite heavier phosphorus (P) loadings from
tributaries in the northern sections of the Barnegat Bay, dissolved phosphorus concentration here is
significantly lower than in the southern Barnegat Bay. In this project, we seek to determine what
mechanisms are causing this anomaly.
Phosphorus (%)
P (µg/L)
35
30
25
20
15
0.03
0.02
0.01
5
0
0
MB1
MB2
MB3
MB4
MB5
MB6
MB1
MB2
MB3
MB4
MB5
MB6
Figure 4. Left: Surface water phosphate at sites MB1-MB6. Right: Sediment total phosphorus. More
P is uptaken in the sediments during the fall.
Figure 1. Sampling sites in the Barnegat
Bay and selected tributaries. Sites are
numbered from north to south, with 1
being the northernmost.
0.08
100
Loosely sorbed P
0.07
Phosphorus (%)
0.06
Percentage grain size fraction
Inorganic P
Organic P
0.05
0.04
0.03
0.02
Results
•Surface water phosphate data (Figure 4, left) confirmed
the initial observations of higher dissolved P
concentration in the southern Barnegat Bay
•Sediment total P (Figure 4, right) patterns matched the
trend seen in surface water P, supporting our hypothesis
that sediments are acting as a reservoir and potential
source of P to the water column.
•Inorganic P (Figure 5) represents by far the largest
fraction of sediment P, i.e. bound in detrital apatite or
some other mineral matrix.
•As one moves south through the bay, sediment
transitions from sand/gravel to a finer silt/clay
consistency (Figure 6). This may be linked to higher
surface area and increased P adsorption.
•A significant increase in phosphate uptake in the fall
sediment is seen compared to the samples collected
during the summer (Figure 3). This is especially
apparent at the central and southern collection sites.
90
Sand+Gravel
80
Silt+Clay
70
60
50
40
30
20
0.01
10
0
0
MB1
Figure 3. Water column phosphate
production in July and October.
Negative values indicate P uptake.
0.04
10
Method
Samples were collected during July and October 2014 sampling from the six stations in the bay (Figure 1).
Activities consisted of sediment coring and collection, taking water samples, and recording data captured by
a YSI EXO multi-probe water quality sonde. The SEDEX method, outlined in Figure 2, comprises 13 steps that
separate out five different reservoirs of phosphorus on particles using a series of chemical leaches of
increasing severity. The wet sediment was passed through a 125 µm sieve before being weighed out to 0.5g.
Extractions were then performed according to a modified implementation of SEDEX, using a multi-sample,
solid-phase extraction manifold (SPEXMan) approach. For six selected flux sites throughout the bay (MB1MB6), cores were filled with site water and purged with air or nitrogen to test for anoxic and oxic conditions.
2 oxic and 2 anoxic cores were tested for each site. Samples were analyzed using an Alpkem RFA300
colorimetric autoanalyzer.
0.07
MB2
MB3
MB4
MB5
MB6
Figure 5. A comparison of different fractions
of P. Most P is bound in the inorganic form.
MB1
MB2
MB3
MB4
MB5
MB6
Figure 6. Sediment grain size comparison
between field stations. Grain size becomes
finer as one moves further south.
Conclusion
Concentrations of phosphorus in the surface water and the sediment samples along the north-south
gradient confirmed the initial observations that became the impetus of the project. Summer flux data
suggested the water column may be acting as a source of phosphate under anoxic conditions.
Comparison of summer and fall data reveals a significant phosphorus uptake in the sediments during
the fall. Changes in sediment grain size across the bay may play a role in phosphorus uptake. Final
results are pending additional sampling and measurements to be performed in May 2015.
Acknowledgements
Figure 2. SEDEX scheme developed by
Ruttenberg (1992) for extracting different
forms of P from marine sediments.
The work completed on this project was made possible by funding from the New Jersey Department of
Environmental Protection. We are grateful for the field and laboratory support of many staff members
and volunteers: Paul Kiry, Roger Thomas, Paul Overbeck, Dane Ward, Lori Sutter, Gerard Ondrey,
Stephanie Dantos, Sarah Peterson, Kate Henderson, Ashley Seyfried, John O’Connor and Gavin Lewis