1. During the four days July 27-30, 2004, the estuary systems of the Merrimac (NH,MA), Androscoggin-Kennebec (NH,ME), Penobscot (ME) and Pleasant (ME) rivers were surveyed using both continuous and discrete collection methods. These basins represent a wide variety of land use patterns, population densities, and river-borne chemical transport signatures. We suspected that differences in basin properties would lead to variability in carbon export and processing. Hunt, C.W., Salisbury, J., Vandemark, D., Campbell, J.W., McGillis, W.R. University of New Hampshire chunt@cisunix.unh.edu Figure 2. R/V Camden Belle Figure 4. Flow-through system equipped to measure Fl-Chl, Fl- CDOM, beam attenuation, DO, Temp, and Salinity. Seawater is pumped through the system from below the boat at a rate of 20L/min. Coastal Ocean Observation and Analysis www.cooa.unh.edu University of New Hampshire Panel 1- Observed pCO2 versus salinity in the Merrimac River Panel 2 - Conservative pCO2 versus salinity based on conservative mixing of H (hydrogen ion calculated from pCO2) and total alkalinity (Talk). Concentrations of Talk and pCO2 at S=0 were measured in the rivers on the date of the cruise, while a seaward endmember was taken from our Gulf of Maine database. The endmember concentrations of Talk and H were allowed to mix conservatively across the salinity gradient. Using the carbonate equilibrium equations (Pilson 1998, K1 and K2 values of Cai and Wang 1998) with our observed temperature and salinity, we estimated the pCO2 gradient. Panel 3 - The residual pCO2 concentration is the difference between the observed and conservative pCO2. The residual contains information about the biological production and destruction of organic matter. When the residual is negative the system tends to be productive (autotrophic) and when it is positive the system tends to be a net consumer of organic matter (heterotrophic). Figure 1. Maps of the population density, Dissolved Inorganic Nitrogen (DIN) Flux, and Dissolved Organic Carbon (DOC) Flux for the four surveyed watersheds. Fluorescence-based retrievals of chlorophyll-a (Panel 1) and DOC (Panel 2) from our flow-through system. Large differences in the distributions of constituent concentrations are apparent between the systems. Differences in riverine fluxes of carbon and nutrients between the rivers are the likely source of this spatial variability in constituent behavior. The covariance of the residuals suggests there is information linking the fluorescence-retrieved constituents to apparent net production. We infer from these plots: 1. The Merrimac is strongly contributing to autotrophy particularly at low salinities. 2. The Kennebec is mildly autotrophic to neutral. 3. The Penobscot is contributing to moderate autotrophy at low salinities and then becomes nearly neutral at higher salinities. 4. The Pleasant is contributing to strongly heterotrophic conditions. Several constiuent-pCO2 relationships can be seen in the data suggesting the two are linked. Notable is the strong negative covariance between the chlorophyll and pCO2 residuals in the Merrimac, supporting the notion that phytoplankton production is responsible for the pCO2 draw-down. Also interesting is the positive trend between the DOC and pCO2 residuals in the heterotrophic Pleasant Estuary, suggesting that autochronous carbon is the source of excess heterotrophy in the Pleasant. Conclusions Although these 4 drainage basins and their associated estuaries are proximal and share the same climatic biome, we see major differences in terms of estuarine function. We believe these differences are attributable to biogeochemical responses to land-derived nutrients, labile carbon and autochronous carbon inputs. Ancillary data (nutrient analyses) and future cruise work (including oxygen and nitrogen gas tension) will help confirm or refute our hypotheses. References Cai W.-J. and Wang Y. (1998) The chemistry, fluxes and source of carbon dioxide in the estuarine waters of the Satilla and Altahama Rivers, Georgia. Limnol. Oceanogr. 43, 657-668. Pilson, M.E.Q. (1998). An Introduction to the Chemistry of the Sea. Prentice Hall, Upper Saddle River, New Jersey. Considerable differences can be seen between the estuaries in both the estimated and observed pCO2 curves. We hypothesize that these difference are biogeochemical responses to nutrients and labile carbon delivered to the estuaries from the drainage basins. (see attribute maps) Residuals of pCO2 are shown in red, chlorophyll-a in green, and DOC in blue Figure 5. Estimation of the pCO2 residual Figure 6. Chlorophyll and DOC data across salinity gradients in four estuary-plume systems Figure 7. Plots of Conservative and Observed surface pCO2 Figure 8- Plots of Conservative and Observed Chlorophyll-a, DOC, and pCO2 in four estuary- plume systems Figure 3. Fast equilibrator for continuous pCO2 measurements.