# Presentation: 662003

## An interdisciplinary study of land-sea carbon coupling between thePenobscot River and Gulf of Maine 

- William M. Balch & Collin Roesler- *Bigelow Laboratory*
- Andrew Barnard*, **WET Labs*
- Thomas G. Huntington, *USGS, Augusta, ME*
- Huijie Xue, *University of Maine Orono*
-  George R. Aiken, *USGS Boulder, CO*

## Acknowledgements

- Respective lab groups
- Dave Drapeau, Bruce Bowler, Emily Booth, Laura Windecker, Heidi Franklin, Rois Langner, Dan Abraham, Kenna Butler, Yi Du
- NASA IDS

## Overview

- Introduce the study area
- Follow DOC from watershed to coastal sea
- Discuss quantity and quality of DOC
- Optical proxies for using remote sensing to estimate DOC concentrations
- 3-D circulation modeling results
- Summarize

## In a recent paper on the Gulf of Maine’s optical properties, we showed that the Gulf is “CaseII-dissolved” all the time and “Case II particulate”  about half the time...

## The DOC “Tea Bag” Analogy

- Soil build-up of particulate organic carbon/leaf litter during growing season-  “the tea leaves”
-  Precipitation soaks POC- “the steep”
- DOC is extracted- “the brew”
- Transformations enroute- “binds to other POC, mineral surfaces (i.e. stains your teeth), is metabolized (digested)”
- Remaining DOC is carried downstream to the ocean...some of which is visible, some not, but it is a large pool!

## But the plot thickens...

- There are different ways to brew your tea
- The downstream ocean has its own source of DOC (some of which is colored)
- Which DOC dominates in river-impacted coastal waters?
- What is the fate of the terrestrial vs marine DOC? (...fundamental to the Case II vs Case I distinction)

## The birth of terrestrially impacted, Case II-dissolved water...We start way upstream in the Penobscot River...

- 

- 

- 

- West Enfield

## Penobscot River empties into Penobscot Bay...

## Penobscot Bay then empties into the Gulf of Maine

## Are the tributaries of the Penobscot equal  in their DOC concentration?

## “When you brew your tea is everything...”

- “Summer tea”

- “Iced tea”

## Timing is everything...

_**Jan-May**_
- Frozen ground
- Fast runoff does not penetrate frozen sediments...poor “steep”
- Temperature does affect the leaching cold water “bad brew”

- _June-December_
- End of growing season with lots of accumulated carbon
- Runoff percolates in earth...good “steep”
- Warm temperatures enhance microbial breakdown of leaf litter, “good steep”, “good brew”

## Put daily discharge, measured DOC concentration as function of flow rate & time of year, one can model the daily DOC flux...

**Notes:**
Measured (magenta points) and estimated (blue line) daily fluxes of DOC for the Penobscot River at Eddington.  The green line is the measured daily discharge, the secondary Y-axis (left hand side) has  been offset for clarity. 

## Optical proxies for DOC in the river...fluorescence of DOC

## Penobscot River-seasonally variable relationship between discharge and CDOM fluorescence...

-    CDOM Fluor (ppb QS)

-     Discharge (cfs)

- Eddington CDOM fluor
- Discharge W. Enfield

**Notes:**
Our working hypothesis is that during high flow periods, the material transport rate exceeds the transformation rate and that we can observe clear land use/coverage signals within Penobscot Bay and the coastal waters. However, during low flow periods, transformation exceeds transport and these signals may be degraded within the Bay, and may be more related to the coastal ocean endmembers. 

## CDOM Excitation/Emission fluorescence spectra vary with land use...

- Pleasant River
- Agricultural watershed

- Passadumkeag
- Wetland

- Ex(nm)

- Em(nm)

- Em(nm)

- Ex(nm)

**Notes:**
Figure 6. Spectrofluorometric analysis of dissolved samples from July 2004. Examples of excitation/emission matrices for two sites typical of A. agricultural and B. wetland coverages. Symbols indicate spectral points where peaks were observed throughout the stations.  

## Ex/Em properties vary with the watershed...

- Different Penobscot
- Watersheds

- % Aerial Coverage Wetland

- peak ratio
- (Ex/Em 265/475 : 225/430)

- F (QS eq)

- EX200:EM300

**Notes:**
C. Peak height (Ex 220, Em 300) for each station. Note the four highest values are about a factor of two greater than the next highest peak. These are located at stations downstream of watershed characterized by retention waters where significant transformation occurs. The next five stations with indistinguishable peak heights are all associated with agricultural watersheds. The remaining stations exhibit decreasing peak heights are those found in the northern watersheds typical of forest and lumbered land cover. Thus this peak appears sensitive to CDOM breakdown products. D. Relation between peak ratio (Ex/Em 265/475 : 225/430) and the percent of areal coverage of the subwatershed by wetlands. A significant correlation is observed both with and without the high value point.

## In line ferry data from Penobscot Bay...strong inverse relation between apg425 and salinity

- Salinity

-      apg425

- S     a
- 30   9
- 15  4.5
- 0     1

## How much of the DOC that makes it down the river, through the bay and into the Gulf of Maine?

- First two years of our IDS study we were very lucky:
-    2004- Dry year
-    2005 THE wettest year on record
- Allowed a good contrast in the quantity and quality of the DOC that came out into the Gulf of Maine

## How much does the [DOC] change from Penobscot Bay to the Gulf of Maine?

## How does the quality of the DOC change from Bay to Gulf?

- SUVA
- (10-3 m2 mgDOC-1; 254nm)

## Space time plot for DOCin the Gulf of Maine

## SUVA (DOC specific absorption cross section)

- x10-3
- m2 (mg DOC)-1

- Sargasso
- Value=0.8

- Strong EW gradient

## Going back 8 years with agp412 ...2004 and 2005 indeed were  extraordinary years...

- ‘05
- ‘04
- ‘03
- ‘02
- ‘01
- ’00
- ’99
- ‘98

- Wettest

- Dry

## They were extraordinary years for optical scattering, too...

- ‘05
- ‘04
- ‘03
- ‘02
- ‘01
- ’00
- ’99
- ‘98

- Wettest

- Dry

## Aqua estimates at the mouth of Penobscot Bay

**X**

**X**

- P<0.001

**X**

**X**

## We have combined the DOC Export along with 3d circulation model of H. Xue to model the DOC distribution

## It is clear that in the Gulf of Maine, transformations are occurring in CDOM plotted against salinity...

## Summary

- The relation between discharge rate and DOC concentration shows two different relationships, a winter-spring and summer-fall pattern
- The fluorescence properties of CDOM provide information on watershed type
- DOC quantity drops gradually from the upper watershed through Penobscot Bay
- DOC quality (SUVA) is high throughout the Penn Bay and drops dramatically as water exits into the GoM suggesting a loss in aromaticity

## Summary

- During dry year (’04) and wet year (’05)  no influence of Gulf of St. Lawrence water entering GOM and affecting CaseII dissolved conditions.
- Dry year (’04) showed major loss of CDOM in mid Gulf...photooxidation?
- Aqua-derived DOC values look reasonable
- Clear evidence of nonconservative CDOM behavior in the Gulf
- Have modeled 3-D DOC flow.  Future plans to incorporate DOC non-conservative transformations

## Thank you!

## How do three of the biggest watersheds compare in the concentration of their DOC (tea)?

**Notes:**
Figure 3 shows that the three rivers follow a similar seasonal pattern where DOC reaches a minimum during Spring snowmelt and increases through the summer and fall and declines during the winter.   For this figure the storm sampling that was conducted only on the Penobscot River is not shown.  The Penobscot River has higher DOC concentrations than the other rivers and the Kennebec River has slightly higher DOC concentrations than the Androscoggin.  DOC concentration decreases along and axis from the northeast towards the Southwest.