CARBON-DIOXIDE CONCENTRATION AND ATMOSPHERIC FLUX IN THE HUDSON RIVER

We made direct measurements of the partial pressure of CO2 (P-CO2) in the tidal-freshwater portion of the Hudson River Estuary over a 3.5-yr period. At all times the Hudson was supersaturated in CO2 with respec t to the atmosphere. P-CO2 in surface water averaged 1125 +/- 403 (SD) mu atm while the atmosphere averaged 416 +/- 68 mu atm. Weekly sample s at a single, mid-river station showed a pronounced and reproducible seasonal cycle with highest values (similar to 2000 mu atm) in mid-to- late summer, and lowest values (similar to 500 mu atm) generally in la te winter. Samples taken along the length of the 190-km section of riv er showed a general decline in CO2 from north to south. This decline w as most pronounced in summer and very slight in spring. Diel and verti cal variation were small relative to the standing stock of CO2. Over s ix diel cycles, all taken during the algal growing season, the mean ra nge was 300 +/- 114 mu atm. CO2 tended to increase slightly with depth , but the gradient was small, about 0.5 mu mol m(-1), or an increase o f 190 mu atm from top to within 1 m of the bottom. For a large subset of the samples (n = 452) we also calculated CO2 from measurements of p H and total DIC. Calculated and measured values of CO2 were in reasona bly good agreement and a regression of calculated versus measured valu es had a slope of 0.85 +/- 0.04 and an r(2) of 0.60. Combining our mea surements with recent experimental studies of gas exchange in the Huds on, we estimate that the Hudson releases CO2 at a rate of 70-162 g C m (-2) yr(-1) from the river to the atmosphere.