![]() ![]() The results indicate that (1) annually, the mean NO 2- + NO 3- and orthophosphate loads showed a steady increase during 1996–1999, a persistent level during 2000–2007, and a moderate increase during 2008–2016 (2) seasonally, NO 2- + NO 3- and orthophosphate in MARB in spring and summer were higher than those in autumn and winter. This study investigated the annual and seasonal variations in nutrient loads (NO 2- + NO 3- and orthophosphate) delivered to the Gulf of Mexico from the Mississippi-Atchafalaya River Basin (MARB) and examined the water quality variations. We detected significant signals of El Niño–Southern Oscillation and land–surface temperature anomalies in N loads but not discharge, SiO 2, or P, suggesting that large–scale climate phenomena contribute to interannual variation in nutrient loads through biogeochemical mechanisms beyond simple discharge–load relationships. Here, we used multivariate autoregressive state–space modeling to investigate climate signals in the long–term record (1979–2014) of discharge, N, P, and SiO 2 loads at three nested spatial scales within the more » Mississippi–Atchafalaya River Basin. Climate phenomena such as El Niño–Southern Oscillation 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. = ,Īgricultural runoff from the Mississippi–Atchafalaya River Basin delivers nitrogen (N) and phosphorus (P) to the Gulf of Mexico, causing hypoxia, and climate drives interannual variation in nutrient loads. Given the essential nature of this more » river junction to the society, transportation, and commerce of the United States, improved attribution of discharge increases may lead to future management strategies that are broadly impactful. enlargement processes on avulsion dynamics at this site. ![]() These findings highlight the importance of A.R. Significant lacustrine delta deposition in A.R. was slightly erosional during this period, and therefore hindered the A.R. between 19 can account for 35% of the water discharge increase, and was also an important control on shear stress distribution. can account for 73% of the water discharge increase. Simulations show that erosion of the upper A.R. We then isolate how several key changes to the system affected discharge partitioning and stage at the A.R.-M.R. Here, we develop and validate a hydrodynamic model of flow partitioning through the historic channel network. Natural and anthropogenic causes of this discharge annexation are difficult to disentangle. ![]() The Atchafalaya River’s (A.R.) partial annexation of discharge from the M.R., particularly between 19, prompted warnings of a rapid river avulsion and the construction of the Old River Control Structure to regulate flow. The modern Mississippi River (M.R.) Delta is plumbed by the Mississippi and Atchafalaya rivers, setting water and sediment dispersal pathways for Earth’s fifth-largest river system. ![]()
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