Internal Nutrient Loading in Shelburne Pond Under Benjamin Ramcharitar , DongJoo Joung

Internal Nutrient Loading in Shelburne Pond Under
Ice Cover and Open Water
Benjamin
1
Ramcharitar ,
DongJoo
2
Joung ,
Jason D.
2
Stockwell , Andrew
W.
2
Schroth
1. Middlebury College, [email protected] 2. University of Vermont, [email protected], [email protected], [email protected]
Overview
Study Site
Hypothesis
• Hyper-eutrophic • No major tributaries
• Internally driven • Winter ice cover
Background
Phosphorus (P) is a limiting resource for primary production. Input
of P into lake ecosystems from point and non-point sources causes
eutrophication and harmful algal blooms (HABs).
Reactive phosphorus (RP) release from the sediment is governed by
the factors that control P sorption (O2, pH, temperature, and light)
to metals (Fe, Mn, Ca, Al) in the sediment. Under hypoxic or
anoxic conditions P is released into the water column due to
reductive dissolution of minerals in the sediment (internal loading).
Field
(1) Sediment cores
collected
(2) Water environmental
parameter data collected
by Sonde
(3) Water collected at
three depths (surface,
middle, and bottom)
Motivation
Internal nutrient loading under the ice is poorly studied in hypereutrophic systems. Nutrient dynamics under the ice may be
important for developing spring primary production (i.e.
blooms), particularly in systems without large riverine inputs.
The goal of this study was to test if nutrient loading and
corresponding environmental parameters differ under ice and
non-ice periods.
DO (mg/L)
Temp (°C)
Bottom Water Column
Concentration (ppb)
Labile Sediment Mn, Fe, Ca (mg/g)
Total Sediment Mn, Fe, Ca (mg/g)
Iron
Ice Thickness Chlorophyll a
Water P
Labile P
Total P
R2=0.08
Manganese
Water Fe
Labile Fe
Total Fe
Water Mn
Labile Mn
Total Mn
Environmental Changes
-During the ice period, thermal and dissolved oxygen (DO) stratification were established in the water, the stratification
dissipated in early non-ice periods, and developed again in June.
-The pH was lower in the ice compared to non-ice period.
 Probably related to oxygen consumption via microbial activity, developing reducing conditions at the sediment-water
interface during ice periods.
 Increased primary production and vertical mixing delivered DO in the water and increased pH during post ice until DO
and temperature stratification reset.
R2=0.65
R2=0.54
Labile Sediment P (mg/g)
Water Column-Sediment Interactions
R2=1.5E-5
R2=0.20
- In general, water column P and metals increased over time during ice periods with the exception of P in early January.
After ice melt the water column concentration decreased.
- In the same ice period (1/15-3/19) sedimentary P and metals had a decreasing trend.
 Sedimentary release of P and metals increased water column P and metals concentrations.
 Reductive dissolution of Fe/Mn as well as P, which was adsorbed onto Fe/Mn-(hydr)oxides
- In the post ice period P and metals concentrations decreased to the levels of their earlier low concentrations.
- Sudden increase of water column P and metals on March 19th
 Watershed water input (rain event prior to our sampling and evidenced by conductivity changes)
R2=0.13
R2=0.03
R2=0.52
R2=0.16
R2=0.17
Metal to P Regression
- Labile P was in good correlation with labile Fe and Mn regardless of seasons and with labile Ca only during ice periods.
 Dissolution of labile Ca phases as well as Fe/Mn-hydroxides under persistent anoxic sediment during ice release P.
Fe/Mn hydroxides may be more closely link to P distribution during post- ice due to rapid oxidation/reduction.
- Correlations of total P versus other total phase of metals were not significant
 Probably due to P partitioning into particulate organic matter, which was more than 20% of sediments.
Total Sediment P (mg/g)
<0.45µm Water Fe, Mn (ppb)
(1) Water filtered through (1) Ascorbic acid digestion for
Labile and Aqua Regia for
0.45 µm and 0.02 µm
Total P and Trace metals
membranes
(2) Analyzed for elemental
(2) Analyzed for elemental
concentrations using
concentrations using
ICP-OES
ICP-MS
Results and Discussion
R2=0.77
R2=0.24
Water Processing
Surface Sediment
Flux (mg/m2)
Post Ice
R2=0.52
Sediment Processing
Conclusion
R2=0.98
R2=0.63
R2=0.01
R2=0.07
 Sedimentary fluxes of P and metals are key for water column distributions particularly during ice periods.
 Sedimentary releases were controlled by redox conditions developed by thermal stratification and oxygen
consumption under ice.
 Runoff water inputs during early thaw periods may be important in addition to sedimentary release for spring
biological production.
 During post-ice, P was likely partitioning into particulate forms (particulate organic mater), which may explain the
increase in sedimentary release but lack of increase in dissolved P and metals in the water.
Acknowledgements
<0.45µm Water Column P (ppb)


I would like to thank Jason Stockwell, Andrew Schroth, DongJoo Joung, the Rubenstein Lab, and other lab members for support.
NSF REU program funded by award DBI-1358838. This research was also supported by a Pilot Grant from Vermont EPSCoR to JDS, DJJ and AWS.
Ice Thickness (cm)
Chl a (µg/L)
Water Column Depth (m)
Phosphorus
Metal To P Regression
Ice Period
Methods
Water Column-Sediment Interaction
Environmental Parameters
pH
Flux of P out of the sediment will be
greater during under-ice versus non-ice
periods due to stratification of DO by ice
which creates anoxic/hypoxic bottom
waters.