Abstract
Floodplains and river corridor wetlands may be effectively managed for reducing nutrients and carbon. However, our understanding is limited to the reduction potential of these natural riverine systems. This study utilized the long-term (1978–2004) river discharge and water quality records from an upriver and a downriver location of the Atchafalaya River to quantify the inflow, outflow, and inflow–outflow mass balance of total Kjeldahl nitrogen (TKN = organic nitrogen + ammonia nitrogen), nitrate + nitrite nitrogen (NO3 + NO2), total phosphorous (TP), and total organic carbon (TOC) through the largest river swamp basin in North America. The study found that, over the past 27 years, the Atchafalaya River Basin (ARB) acted as a significant sink for TKN (annual retention: 24%), TP (41%), and TOC (12%), but a source for NO3 + NO2 nitrogen (6%). On an annual basis, ARB retained 48,500 t TKN, 16,900 t TP, and 167,100 t TOC from the river water. The retention rates were closely and positively related to the river discharge with highs during the winter and spring and lows in the late summer. The higher NO3 + NO2 mass outflow occurred throughout spring and summer, indicating an active role of biological processes on nitrogen as water and air temperatures in the basin rise.
Highlights
The Atchafalaya River pours approximately 182 km3 of water into the Gulf of Mexico (GOM) each year, representing about 24% of the total freshwater inflow to the world’s ninth largest ocean from theU.S continent
Many studies have demonstrated that microbial degradation and photochemical oxidation have played an important role in the removal of terrestrial dissolved organic carbon (DOC) in coastal waters [18,19,20,21,22]
Using terrestrially derived lignin phenols as bio-markers, Benner and Opsahl [24] found that photo-oxidation was the major removal process of the terrestrial DOC, and that the photochemical reactions mainly occurred in higher salinity waters, while flocculation and microbial degradation were more dominant in terrestrial
Summary
The Atchafalaya River pours approximately 182 km of water into the Gulf of Mexico (GOM) each year, representing about 24% of the total freshwater inflow to the world’s ninth largest ocean from the. This river is a major distributary that carries, during most years, 25%–35% of the Mississippi River’s flow and the entire Red River into GOM. Despite contributing nearly one third of the Atchafalaya’s flow, the Red River has been found to export only a marginal amount of nitrate nitrogen (~3%) to the Atchafalaya River [1]. The nutrient enrichment, especially nitrate nitrogen, has been attributed to exacerbating coastal water eutrophication, favoring harmful algal blooms, aggravating oxygen depletion and altering marine food webs in the northern Gulf of Mexico [3,5,6,7,8]
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