Introduction Field: • Vertical temperature-O2 profile: YSI meter • Water clarity: Secchi Disk • pH and conductivity: Hydrolab Multimeter • Water sampling: peristaltic pump, in-line filtered (Whatman GF/F) chlorophyll-a • Water chemistry on filtered lake water

Nutrient Dynamics and Primary Productivity in a Biomanipulated Eutrophic Lake Shampa A. Panda1,2, Steve Di Lonardo1 and John D. Wehr1

1: Louis Calder Center - Biological Field Station, Fordham University, Armonk, NY 10504, 2: University of North Carolina at Chapel Hill, Chapel Hill, NC 27514

Question

Management History

Methods

Laboratory: • Chlorophyll-a • Water chemistry

• NH4+

• NO3-

• TDN • PO4

3-

• TDP

Discussion

Results: Water Chemistry

Phosphorus Uptake

• Max P uptake in +P treatment • Uptake dependent on biomass • Similar trend for all P forms:

• PO43- (P = 0.086, F=3.63, r2= 0.193)

• TDP (P = 0.009, F= 10.57, r2= 0.514)

Nitrogen Uptake

• Max N uptake in +P treatment • Uptake dependent on biomass • Similar trend for all N forms:

• NH4+ (P = 0.001, F = 66.54, r2 = 0.689)

• NO3- (P = 0.001, F = 21.31, r2 = 0.703)

• TDN (P = 0.329, F = 21.31, r2 = 0.703)

• Algal biomass (chlorophyll-a) co-limited by N and P.

• Nutrient (both N and P) uptake limited by P concentration.

Cultural eutrophication due to N and P loading has led to degraded water quality in lakes worldwide. This study was conducted on suburban North Lake, in Armonk, NY. It has been monitored for the past ten years for water clarity, chemistry, algal biomass, and phytoplankton community structure. North Lake receives nutrients from runoff over impervious surfaces, nuisance wildlife, and human activity. The lake experienced dense aquatic vegetation and high algal biomass over many years. An algal bloom following the addition of triploid grass carp to manage vegetation indicated the need for a detailed study of nutrient effects on algal blooms and primary productivity.

1. Which nutrient drives algal blooms in North Lake? • Nitrogen • Phosphorus • Nitrogen + Phosphorus

Results: Algal Biomass

• Max algal biomass in N+P treatment • Similar trend for all experiments

• Exp. 1 (6-25-11) N: F = 29.18, P = 0.001 P: F = 34.74, P = 0.001 NP: F = 22.63, P = 0.002

• Exp. 2 (7-10-11) N: F = 1.91, P = 0.225 P: F = 1.56, P = 0.267 NP: F = 0.50, P = 0.512

• Exp. 3 (7-24-11) N: F = 25.91, P = 0.015 P: F = 26.78, P = 0.014 NP: F = 23.80, P = 0.016

Jilian Decker, Alissa Perrone, Sarah Whorley, North Lake Committee, Louis Calder Biological Field Station at Fordham University, National Science Foundation

Acknowledgments

Experimental Design R1 R2

R3

• Experimental Duration: 96 hours • Treatments:

• Control • Nitrogen • Phosphorus • Nitrogen + Phosphorus

C

N

P

NP

C N P NP ++ +- +- --

Nitrogen + −

Phos

phor

us

−

+

Increasing primary productivity

• 1999 (carp stocked) • 2001-4 • 2005-6 ( SAV) • 2006 (hypolimnetic drawdown) • 2007 • 2008 (carp restocked) • 2009-10 ( algal biomass)

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