Teleconnection of Instream Total Organic Carbon Loads with El Niño Southern Oscillation (ENSO), North Atlantic Oscillation (NAO), and Pacific Decadal Oscillation (PDO)

Abstract

<abstract> <b>Abstract.</b> Recently, total organic carbon (TOC) load has attracted a great deal of attention from water quality managers because it can form disinfection byproducts (DBP) during chlorination of drinking water. TOC loads in streams are generally affected by the hydrologic characteristics of a basin. In addition to the basin characteristics, hydrologic characteristics are affected by climate variability associated with a number of the oceanic and atmospheric phenomena that operate at seasonal to multidecadal time scales. Consideration of these large-scale climate phenomena, such as the El Niño Southern Oscillation (ENSO), North Atlantic Oscillation (NAO), and Pacific Decadal Oscillation (PDO), are important for water quality managers because they can provide additional information for reducing TOC loads (and hence potential for DBP formation) in the drinking water supply. The objective of this study was to see if teleconnections exist between ENSO, NAO, PDO, and TOC loads. This study was conducted in the Big Creek watershed in southern Alabama in a series of steps. In the first step, model-simulated TOC loads were used to understand the effect of climate on TOC loads while keeping the land use and anthropogenic effects constant. In the second step, wavelet analysis, including cross wavelet analysis and wavelet coherence, was conducted to examine the correlation of ENSO, NAO, and PDO with TOC load in a time and frequency space. Analysis indicated that the common period of oscillations of various climate signals with TOC loads was detected even though NAO and PDO are decadal phenomena. Further, we examined the effects of ENSO, NAO, and PDO on large TOC loads using ten possible combinations of climate signals. TOC loads in El Niño winters and springs were significantly higher than in La Niña winters and springs, especially when ENSO was modulated with high (positive) NAO and high (positive) PDO. Similarly, TOC loads in El Niño or La Niña, occurring concurrently with high PDO and high NAO, were higher than TOC loads in neutral periods occurring concurrently with low (negative) PDO and low (negative) NAO. Interestingly, TOC loads in the La Niña phase were significantly higher than in the El Niño phase from August to October, especially when La Niña was modulated with high PDO and high NAO. Quantifying instream TOC loads with various climatic conditions is helpful for monitoring TOC loads and devising control measures.