Contribution of non-carbonate anions to total alkalinity and overestimation of <i>p</i>CO<sub>2</sub> in New England and New Brunswick rivers

Abstract

Abstract. Total alkalinity (TAlk) has long been used to evaluate the buffering capacity of aquatic systems. TAlk has also been used, together with measurements of either pH or dissolved inorganic carbon (DIC), to indirectly estimate the partial pressure of carbon dioxide (pCO 2 ) in inland waters, estuaries, and marine systems. These estimates typically assume that carbonate and bicarbonate ions comprise nearly all the species contributing to TAlk; however, other inorganic and organic acids have the potential to contribute significant noncarbonate alkalinity. To evaluate the potential for error in using TAlk to estimate pCO 2 , we measured pH, TAlk, and DIC in samples of river water. Estimates of pCO 2 derived from TAlk and pH measurements were higher than pCO 2 estimates derived from DIC and pH by 13-66 %. We infer that this overestimate is due to the presence of significant noncarbonate alkalinity (NC-Alk). This study also describes the relative proportions of carbonate-and non-carbonate alkalinity measured in 15 river systems located in northern New England (USA) and New Brunswick (Canada). NC-Alk represents a significant buffering component in these river systems (21-∼100 % of TAlk), and failure to account for NCAlk (which cannot directly contribute to pCO 2 ) leads to the overestimation of carbon dioxide release to the atmosphere.

Comparison of the alkalinity and calcium anomaly techniques to estimate rates of net calcification

“…As mentioned previously, mussels excrete a significant proportion of N as organic wastes. Dissolved organic compounds are believed to substantially contribute to seawater total alkalinity (Kim & Lee 2009) and have been shown to be a significant buffering component in organic-rich river systems (Hunt et al 2011). Release of dissolved organic carbon (DOC) was measured during our experiment (data not shown) but cannot account for this missing process.…”

CO2 Input Dynamics and Air–Sea Exchange in a Large New England Estuary

“…Annual river discharge in 2005 was the highest measured for the Kennebec river in 24 years, and the second-highest in the Androscoggin river for 82 years of record. Elevated river discharge delivers large fluxes of CO 2 and DOC to estuaries, resulting in elevated CO 2 fluxes from the estuary (e.g., Hunt et al 2011). Additionally, elevated river flow in 2005 reduced the overall surface salinity in the estuary, and since lower salinity is generally associated with high pCO 2 in the Kennebec estuary, the higher proportion of lowsalinity waters in the estuary resulted in elevated fluxes of CO 2 from the estuary as a whole.…”

“…Inclusion of these noncarbonate species in calculations to derive carbonate parameters can result in the overestimation of pCO 2 and CO 2 concentration. To account for this, we followed the methodology of Hunt et al (2011) to derive TAlk DIC-pH from DIC and pH NBS measurements, with the resulting difference between measured TAlk and TAlk DIC-pH representing non-carbonate alkalinity (NC-Alk). All TAlk data presented in this work have been corrected for NC-Alk at levels that will be discussed later.…”

The sensitivity of estuarine aragonite saturation state and pH to the carbonate chemistry of a freshet-dominated river

“…Fraser River TA thus appears to be produced primarily by carbonate weathering in the upper watershed, diluted by low-TA seaward tributaries, and flow-dependent. There are no data in the Fraser River region to date that determine organic acids and bases that may contribute significantly to TA, as they do in some coastal areas (Cai et al, 1998;Koeve and Oschlies, 2012;Kim and Lee, 2009;Hernández-Ayón et al, 2007) and rivers (Hunt et al, 2011;Kennedy, 1965). Carbonate alkalinity is esti- mated to be as low as 10 % of TA in the Congo (Wang et al, 2013) and Kennebec rivers (Hunt et al, 2014).…”