Identifying anthropogenic nitrogen loading in Maryland’s Coastal Bays using stable isotope analysis of biological indicators

Ben Fertig, Tim JB Carruthers, William C Dennison, Adrian B Jones, Francis Pantus, Ben Longstaff

AERS March 14, 2008

δ15N in biological indicators identifies nitrogen source in Maryland’s Coastal Bays

•  Where do terrestrial sources of nitrogen to Maryland’s Coastal Bays come from?

•  Do spatial patterns of δ15N in biological indicator species resemble conventional water quality monitoring?

•  How does macroalgae δ15N respond to a pulse of nitrogen?

•  Can δ15N in oysters be interpreted similarly to that of macroalgae?

Stable isotopes indicate nitrogen source

Stable isotopes indicate nitrogen source

Coastal Bay watersheds dominated by agriculture and forest

Nutrient monitoring and biological indicators provide different information

Jones et al. 2004 http://www.ian.umces.edu/pdfs/md_coastal_bays_report.pdf

Spatial patterns of δ15N in macroalgae and oyster biological indicators

Sample preparation – my daily grind!

Gills Mantle

Muscle

Dry tissues Grind samples

Pack in tin

Dissection 60˚C Oven

Mass spectrometer

Physical parameters vary by region (2006)

Precipitation before and during deployments varied among 2004, 2006, 2007

Precipitation before and during deployments varied among 2004, 2006, 2007

Precipitation before and during deployments varied among 2004, 2006, 2007

Biological parameters respond to nutrient pulse events (2006)

Short-term integration (macroalgae δ15N) too quick to provide patterns inside regions (2006)

but between regions, St. Martin R., Johnson Bay highest (May)

May July 7.4

(0.1)

6.2 (0.4)

7.6 (0.5)

6.7 (0.3)

7.0 (0.2)

6.8 (0.2)

6.8 (0.2)

6.3 (0.3)

Oyster δ15N (longer integration period) showed both regional and small scale patterns

δ15N was higher in 2007 in all oyster tissues

Within regions, spatial patterns vary over time

How does δ15N compare to other systems?

Ecosystem Indicator species δ15N (‰) Reference Delmarva coastal bays

Macroalgae Oyster

4.0 – 9.1 5.1 – 10.6

This study

Chesapeake Bay

Oyster 7.3 – 16.5 Fertig, unpublished

California estuaries

Macroalgae 9.5 – 17.0 Cohen and Fong 2006

Moreton Bay, Australia

Macroalgae < 3 – > 9 Costanzo et al. 2004

Western Australia

Macroalgae Filter feeders

6.3 – 12.8 10.1 – 13.0

Gartner et al. 2002

Manning R. (Australia)

Oyster 5.8 – 9.9 Piola et al. 2006

Conclusions •  Biological indicators provide additional information to

conventional water quality monitoring

•  Nitrogen from both agricultural runoff and septic sources are important to Delmarva’s Coastal Bays

•  Delmarva coastal bays δ15N within global ranges, and on the lower end of the spectrum found in Chesapeake Bay

•  Because macroalgal δ15N signal responds quickly to rainfall, regional patterns are washed out

•  Oyster δ15N responds more slowly, providing finer spatial patterns, tissues provide different temporal integrations

Acknowledgements Judy O’Neil

Thomas Fisher Jeff Cornwell Cindy Palinkas

Kris Beckert Lois Lane

Mike Owens David Needham Emily Nauman Mike Malpezzi Moncie Wright

Brian Sturgis Courtney Schupp

Roman Jesien

Cathy Wazniak Matthew Hall

Jay Charland Ron Piling

UC Davis Stable Isotope Facility

Suspended particulate matter δ15N was highest in Johnson Bay

Quantifying denitrification in Maryland’s Coastal Bays

•  Additional analysis to previous assessments

•  Transects along three bays

•  Sediment slurries

•  Indirect acetylene inhibition

•  Measuring N2O intermediary after 24 h

•  Potential measured after spike with 100 µM nitrate

Denitrification present in St. Martin River and Johnson Bay

Potential denitrification changes along transects in St. Martin River and Johnson Bay

Nitrogen could enter Johnson Bay in multiple ways – which is most important?