EVALUATION OF CLIMATIC AND PHYSICAL CONTROLS AND THE INFLUENCE OF ENSO EVENTS ON LONG-TERM WEATHERING AND CO2 CONSUMPTION ACROSS THE PANAMA CANAL WATERSHED

Empirical studies over the past two decades have documented the importance of small mountainous rivers (SMRs), particularly those in the tropics, on global silicate weathering and associated CO₂ consumption budgets. Despite this important contribution to understanding silicate weathering, field studies for these locales are typically based on one to two years of data, thus leaving undetermined the strength of observed relationships between weathering fluxes and controlling parameters over the longer term. Furthermore, the corresponding lack of long-term data prevents determination of the impact that multi-year or decadal climate patterns, such as the Pacific Decadal Oscillation or El Niño Southern Oscillation (ENSO), can have on weathering fluxes. This study addresses this knowledge gaps through an evaluation and analysis of a high-temporal frequency, 17-yr hydrochemical dataset for 8 sub-basins of the Panama Canal Watershed (PCW) collected between 1998 – 2015 by the Panama Canal Authority. Annual and long-term river cation contents (Ca²⁺, Mg²⁺, K⁺, Na⁺) and associated CO₂ consumption values are compared to variables such as mean annual rainfall and temperature, stream gradient, and land use/land cover to not only identify controls, but also determine their strength of relationship over annual and decadal time scales. Annual cation yields and CO₂ consumption values by watershed, and over time, and are amongst the middle to upper range of those values recorded for tropical SMRs worldwide. Strongly positive statistical relationships were documented between cation yields and forest cover and precipitation, whereas negative relationships were observed between cation yields, mosaic land cover, and temperature. Furthermore, cation yields in all watersheds exhibit a positive statistically temporal correlation with La Niña events. These findings emphasize the strong impact that long-term datasets have on identifying short-term influences on chemical weathering and in determining accurate long-term chemical weathering rates and CO₂ consumption values in ENSO influenced regions.