Sources for Bottom Water Phosphates and Suspended Sediments in - - PowerPoint PPT Presentation

Sources for Bottom Water Phosphates and Suspended Sediments in Southern Cayuga Lake, New York

Prabighya Basnet Hobart & William Smith Colleges Geneva, NY

Outline of Today’s Presentation

• Introduce Problem Under Investigation
• Experimental Design
• Field & Laboratory Analyses
• Results

– CTD Data – Laboratory Data

• Implications
• Recommendations

Cayuga Lake Phosphates & Suspended Sediments

2005 - 2007 Mean Phosphate 2 4 6 8 10 12 H

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k a n e a t e l e s Average Phosphate (SRP, ug/L, P)

2005 Surface 2006 Surface 2007 Surface 2005 Bottom 2006 Bottom 2007 Bottom

The Concern

• Upwelling of Bottom Water

– Hypolimnion Phosporus – Upwelled to Surface – Fertilizes Algal Growth – Degrades Water Quality – Especially Southern End

• Upwelling Mechanisms

– Cornell’s Lake Source Cooling – Internal Seiche Activity – Waves & Surface Currents

• Induce Localized Upwelling

2007 CTD Profiles Site D

Fluorescence Subsurface Algae Turbidity Surface & Nepheloid

Probable Sources of Sediment

(and attached Phosphates?)

to the Nepheloid Layer

• Fluvial

– Suspended Sediments & Phosphates from Runoff Events, esp. in Spring

• Resuspension by Waves

– Suspended Sediments & Phosphates from Southern Shelf

• Settling Dead Algae

– Especially in Summer – Bacteria Release SRP

Spring Runoff Events

Photos by Bill Hecht

Study Design: Fieldwork

Eight Sites

• Two Sites, A & C, just
• ffshore of Taughannock

and Salmon Creeks

• Six sites along a mid-lake

transect

– Sites 1 & 2 Finger Lakes Survey – Sites B, D, E & G extend mid-lake southward from Site 2

• Sampling each site once

every 2 weeks

• May through October

Methods

CTD Profile - SeaBird CTD SBE-25 SeaLogger

Profiles of Conductivity, Temperature, pH, Dissolved Oxygen, Turbidity, and Fluorescence

Water Samples

Surface Water Mid Depth (40m above the lake floor) Bottom Water (within a few m of the lake floor)

Onsite Analyses

Vertical and Horizontal Plankton Tow Secchi Disk Depth Conductivity, Temperature & pH Dissolved Oxygen & Alkalinity Titrations

Laboratory Analyses

Total Phosphate (TP) Soluble Reactive Phosphate (SRP) Nitrate Chlorophyll-a Total Suspended Sediments (TSS) Major Ion Concentrations.

CTD Turbidity Profiles

Deepest Sites Impact by Wind & Runoff? Sources

Highest After Wind Events May & Early June Profiles Wind & Runoff Events Runoff Event? No Rain Episode Increases - Minimal Accumulation Site 1 Minimal Contribution from Algae

Phosphates: TP (uniform) and SRP (high in bottom)

Total Phosphate - 2008

5 10 15 20

1S 1M 1B 2S 2M 2B B/S B/M B/B D/S D/M D/B E/S E/M E/B G/S G/M G/B

Sites TP (P, ug/L)

Dissolved Phosphate - 2008

2 4 6 8 10 12 14 16

1S 1M 1B 2S 2M 2B B/S B/M B/B D/S D/M D/B E/S E/M E/B G/S G/M G/B

Sites SRP (P, ug/L) 2005 - 2008 Mean Phosphate 2 4 6 8 10 12 H

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k a n e a t e l e s O t i s c

• Average Phosphate (SRP, ug/L, P)

2005 Surface 2006 Surface 2007 Surface 2008 Surface 2005 Bottom 2006 Bottom 2007 Bottom 2008 Bottom

2006 - 2008 Mean Total Phosphates 5 10 15 20 25 H

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k a n e a t e l e s O t i s c

• Phosphate (TP, ug/L, P)

2005 No Data 2006 Surface 2007 Surface 2008 Surface 2005 No Data 2006 Bottom 2007 Bottom 2008 Bottom

Large Hypolimnetic SRP Reservoir

Recycling of Algal Matter?

Chlorophyll-a (high surface) & Total Suspended Sediments (high bottom)

2005 - 2008 Mean Chlorophyll-a 1 2 3 4 5 H

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• Average Chlorophyll-a (ug/L

2005 Surface 2006 Surface 2007 Surface 2008 Surface 2005 Bottom 2006 Bottom 2007 Bottom 2008 Bottom

2005 - 2008 Mean Total Suspended Solids 1 2 3 4 H

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k a n e a t e l e s O t i s c

• Average TSS (mg/L)

2005 Surface 2006 Surface 2007 Surface 2008 Surface 2005 Bottom 2006 Bottom 2007 Bottom 2008 Bottom

Chlorophyll-a - 2008

1 2 3 4 5 6 7 8

1S 1M 1B 2S 2M 2B B/S B/M B/B D/S D/M D/B E/S E/M E/B G/S G/M G/B

Sites Chlorophyll-a (ug/L)

Total Suspended Solids - 2008

1 2 3 4 5 6 7 1S 1B 2S 2B B/S B/B D/S D/B E/S E/B G/S G/B Site TSS(mg/L)

Recycling of Algal Matter?

Secchi Disk Depths CTD Fluorescence Data

2005 - 2008 Mean Secchi Disk Depth 1 2 3 4 5 6 7 8 9 10

H

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• Aveage Secchi Depth (m)

2005 2006 2007 2008

Secchi Disc Depth - 2008

1 2 3 4 5 6 1 2 B D E G Depth (m)

North to South Decrease in Water Clarity Algal biomass below epilimnion

Phosphate vs. Suspended Solids Linked?

TP vs TSS

R2 = 0.05

5 10 15 20 25 2 4 6 8 10 TSS (mg/L) TP (ug/L)

Phosphate Recycled Algal Matter? New Phosphate << Recycled Phosphate

SRP vs TSS

R2 = 0.01

2 4 6 8 10 12 14 16 2 4 6 8 10 TSS (mg/L) SRP (ug/L)

Implications

• Suspended Sediments at Lake Floor are probably

related to resuspension events by wind, runoff events, and less importantly settling algae.

• Phosphates not linked to Suspended Sediments

– Other Sources of Phosphate to Lake? – Missed Early Spring Runoff Contributions? – Primarily Recycled Phosphorus by Bacteria? – High Phosphate in Hypolimnion an Ongoing Problem

• Suggests that the inhabitants of the area must

reduce their phosphate input in the lake.

• Must Decrease Long Term Phosphate Sources
• Phosphate Sources from Other Work

– Spring Runoff from Agricultural & Urban Areas (50%) – Wastewater Treatment Facility Inputs (~45%) – Lake Source Cooling (3%) – Septic Systems (??)

Recommendations

Thanks - Questions?

2008 Crew 2008 Crew