Sensitivity of stoichiometric ratios in the Mississippi River to hydrologic variability

Leong, D. N.; Donner, Simon D.; Hassan, Marwan A.; Gabor, R. S.; Drummond, Jennifer

doi:10.1002/2013jg002585

Cited by 14 publications

(14 citation statements)

References 38 publications

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“…This variation is due almost entirely to decreased DIN in dry years and seems to occur in all agricultural watersheds up to about 80% agricultural land use. This is similar to the results of Leong et al (2014) who analysed the statistical relationship between Si : DIN and water discharge in rivers draining many basins across the Mississippi River watershed. Their results suggested that high discharge could increase DIN : Si by about 4% across the basin.…”

Section: Discussionsupporting

confidence: 88%

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Low ratios of silica to dissolved nitrogen supplied to rivers arise from agriculture not reservoirs

2016

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Coastal marine systems are greatly altered by toxic marine algae, eutrophication and hypoxia. These problems have been linked to decreased ratios of dissolved silica to inorganic nitrogen (Si : DIN) delivered from land. Two mechanisms for this decline under consideration are enhanced nitrogen (N) fertiliser losses from agricultural lands or Si sequestration in reservoirs. Here we examine these mechanisms via nutrient concentrations in impoundments receiving water from 130 watersheds in a landscape representative of the agriculture that often dominates coastal nutrient inputs. Decreased Si : DIN was correlated with agriculture, not impoundment. Watersheds with > 60% agricultural land yielded highest DIN, whereas Si was uncorrelated with agricultural intensity. Furthermore, eutrophic lakes were dominated by Cyanobacteria that use little Si, so reservoirs did not diminish Si : DIN. Instead, Si : DIN increased slightly as reservoir residence time increased. These data suggest that impoundments in agricultural watersheds may enhance the water quality of coastal ecosystems, whereas fertiliser losses are detrimental.

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Section: Discussionsupporting

confidence: 88%

“…This is similar to the results of Leong et al . () who analysed the statistical relationship between Si : DIN and water discharge in rivers draining many basins across the Mississippi River watershed. Their results suggested that high discharge could increase DIN : Si by about 4% across the basin.…”

Section: Discussionmentioning

confidence: 99%

Low ratios of silica to dissolved nitrogen supplied to rivers arise from agriculture not reservoirs

2016

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“…S1. The general correspondence in results between this study and that of Leong et al () is due in part to the fact that both use the same nutrient load data from the U.S. Geological Survey. But the analytical approaches are quite different, which provides strengthened confidence in the conclusion that mass of nutrient loads and stoichiometry of nutrient loads respond differently to hydrological conditions.…”

Section: Discussionsupporting

confidence: 78%

“…S1). Leong et al () reported that, for both the Arkansas River and the Red River, DSi had a stronger nonlinear response to increasing discharge than did N. If DSi is more strongly affected by discharge than is N, then it would generate the inverse relationship between the N‐ICEP and discharge shown in Supporting Information Fig. S1.…”

Section: Discussionmentioning

confidence: 99%

Stoichiometry of nitrogen, phosphorus, and silica loads in the Mississippi‐Atchafalaya River basin reveals spatial and temporal patterns in risk for cyanobacterial blooms

Royer

2019

Limnology & Oceanography

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Ratios of nitrogen (N), phosphorus (P), and dissolved silica (DSi) influence how algal communities respond to nutrient loading, and DSi limitation can facilitate cyanobacterial dominance. The indicator of coastal eutrophication potential (ICEP), described previously by other researchers, predicts production by diatoms vs. nonsiliceous taxa based on deviation of nutrient loads from the Redfield ratio of 106C:16 N:20Si (N‐ICEP) or 106C:1P:20Si (P‐ICEP). The ICEP was calculated for the Mississippi‐Atchafalaya River basin, and four subbasins: the Ohio‐Tennessee, Missouri, Upper Mississippi, and Arkansas‐Red basins from 1979 to 2015. The P‐ICEP indicated a stoichiometric imbalance that favored cyanobacteria for all but the Arkansas‐Red subbasin. The N‐ICEP indicated conditions favorable for cyanobacteria in the Upper Mississippi, Ohio‐Tennessee, and the northern Gulf of Mexico. Agriculture is the predominant land use in the Upper Mississippi and Ohio‐Tennessee subbasins and these subbasins controlled the stoichiometry of the nutrients delivered to the northern Gulf of Mexico. The imbalance in N, P, and DSi inputs to the Gulf was greatest during spring and early summer, and in most years transitioned to favoring diatoms by August or September. Comparing the 1980–1994 and 2001–2015 periods, there was a significant increase in the P‐ICEP for the Upper Mississippi, Ohio‐Tennessee, and Missouri subbasins that appeared to arise mainly from increased P loading to surface waters in the those basins. The ICEP revealed patterns in stoichiometry of N, P, and DSi loads among the major tributaries to the Mississippi River, and an increasing risk of cyanobacterial blooms for inland waters in much of the Mississippi‐Atchafalaya River basin.

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“…The Mermentau and Vermilion Rivers also had lower DOC:TP, DOC:DIP, Si:TP, and Si:DIP ratios than the Calcasieu River. The differences in those ratios can influence primary production and the composition of plankton communities in these rivers, individually or in combination, as such influence was found by other researchers [40,41].…”

Section: Land Use Effects On Phosphorus Fluxessupporting

confidence: 58%

Phosphorus Fluxes from Three Coastal Watersheds under Varied Agriculture Intensities to the Northern Gulf of Mexico

2018

Water

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This study aims to evaluate recent total phosphorus (TP) and dissolved inorganic phosphorus (DIP) transport from three coastal rivers-the Calcasieu, Mermentau, and Vermilion Rivers-that drain watersheds with varied agriculture intensities (21%, 67%, and 61%, respectively) into the northern Gulf of Mexico, one of the world's largest summer hypoxic zones. The study also examined the spatial trends of TP and DIP from freshwater to saltwater along an 88-km estuarine reach with salinity increasing from 0.02 to 29.50. The results showed that from 1990-2009 to 2010-2017, the TP fluxes for one of the agriculture-intensive rivers increased while no significant change was found for the other two rivers. Change in river discharge was the main reason for this TP flux trend. The two more agriculture-intensive river basins showed consistently higher TP and DIP concentrations and fluxes, as well as higher DIP:TP ratios than the river draining less agriculture-intensive land, confirming the strong effect of land uses on phosphorus input and speciation. Longitudinal profiles of DIP along the salinity gradient of the estuarine reach displayed characteristic input behavior. Desorption of DIP from suspended solids and river bed sediments, urban inputs, as well as stronger calcium carbonate and phosphorus co-precipitation at the marine endmember could be the reasons for such mixing dynamics.

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Sensitivity of stoichiometric ratios in the Mississippi River to hydrologic variability

Cited by 14 publications

References 38 publications

Low ratios of silica to dissolved nitrogen supplied to rivers arise from agriculture not reservoirs

Low ratios of silica to dissolved nitrogen supplied to rivers arise from agriculture not reservoirs

Stoichiometry of nitrogen, phosphorus, and silica loads in the Mississippi‐Atchafalaya River basin reveals spatial and temporal patterns in risk for cyanobacterial blooms

Phosphorus Fluxes from Three Coastal Watersheds under Varied Agriculture Intensities to the Northern Gulf of Mexico

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