Smits, A. P., Ruffing, C. M., Royer, T. V., Appling, A. P., Griffiths, N. A., Bellmore, R., et al ( 2019).Detecting Signals of Large‐scale Climate Phenomena in Discharge and Nutrient Loads in the Mississippi‐Atchafalaya River Basin. Geophysical Research Letters, 46. https://doi.org/10.1029/2018GL081166
Agricultural runoff from the Mississippi-Atchafalaya River Basin (MARB) delivers nitrogen (N) and phosphorus (P) to the Gulf of Mexico, causing hypoxia, and climate drives interannual variation in nutrient loads. Climate phenomena such as El Niño-Southern Oscillation (ENSO) may influence nutrient export through effects on river flow, nutrient uptake, or biogeochemical transformation, but landscape variation at smaller spatial scales can mask climate signals in load or discharge time series within large river networks. We used multivariate autoregressive state-space modeling to investigate climate signals in the long-term record (1979-2014) of discharge, N, P, and SiO2 loads at three nested spatial scales within the MARB. We detected significant signals of ENSO and land-surface temperature anomalies in N loads but not discharge, SiO2, or P, suggesting large-scale climate phenomena contribute to inter-annual variation in nutrient loads through biogeochemical mechanisms beyond simple discharge-load relationships.