Fig 4 - uploaded by Dale Robertson
Content may be subject to copyright.
Sources of nutrients to the Gulf of Mexico for (A) nitrogen and (B) phosphorus.  

Sources of nutrients to the Gulf of Mexico for (A) nitrogen and (B) phosphorus.  

Source publication
Article
Full-text available
Nitrogen (N) and phosphorus (P) loading from the Mississippi/Atchafalaya River Basin (MARB) has been linked to hypoxia in the Gulf of Mexico. To describe where and from what sources those loads originate, SPAtially Referenced Regression On Watershed attributes (SPARROW) models were constructed for the MARB using geospatial datasets for 2002, includ...

Contexts in source publication

Context 1
... N sources in the MARB, as identified by the MARB SPARROW model, include farm fertilizers, manure from confined animals, additional agricultural input from legume crops, atmospheric deposition, WWTPs, and urban areas (Fig. 4 and Table 3). This model did not specifically identify contributions from unconfined animal operations, commercial and industrial point sources, forested areas, or natural/background sources (discussed later); therefore, inputs from these sources would be incorporated into other defined sources or represented as model error. Overall, ...
Context 2
... P sources in the MARB, as identified by the MARB SPARROW model, include farm fertilizers, total manure, WWTPs, urban and forested areas, channels in large streams, and deeply weathered loess soils (Fig. 4). This model did not specifically identify contributions from atmospheric deposition, www.agronomy.org • www.crops.org • www.soils.org commercial and industrial point sources, or natural background sources; therefore, they would be incorporated into the other defined sources or represented as model error. Agricultural inputs (manure and ...

Similar publications

Article
Full-text available
The goal of this research was to quantify the relative impact of hydrologic and nitrogen source changes on incremental nitrogen yield in the contiguous United States. Using nitrogen source estimates from various federal data bases, remotely sensed land use data from the National Land Cover Data program, and observed instream loadings from the Unite...

Citations

... Intensification of US Maize Belt agroecosystems has been accompanied by a simplification of crop rotations, largely to maizesoybean (Glycine max L. Merr.) or continuous maize production (Liebman et al., 2013;Aguilar et al., 2015). Accompanying the increased flux of P inputs and outputs in these grain cropping systems are unintentional P losses via erosion and runoff from agricultural fields to surface waters that compromise water quality from local to continental watershed scales (Smith et al., 2018), most notably the Mississippi River watershed (Robertson and Saad, 2013;Robertson et al., 2014). In maize-based systems, much work has evaluated the effects of P management, largely P application rates, on the distribution of P across pools of varying availability (e.g., Liu et al., 2008;Luo et al., 2017;Arruda Coelho et al., 2019), revealing strong effects of P input rates on P fractions characterized by enrichment of inorganic P (P i ) pools in surface soils (generally < 30 cm depth). ...
Article
Developing meaningful agroecosystem soil P inventories necessitates moving beyond single measures of readily extractable inorganic P (Pi) limited to surface depths. We drew on a long-term (36 year) experimental field trial in the US Maize Belt (northwestern Illinois) to evaluate how crop rotation [maize-maize (Zea mays L.) vs maize-soybean (Glycine max L. Merr.)] and N fertilization (0 vs 269 kg N ha⁻¹) impact P dynamics throughout the soil profile by using sequential fractionation and phosphatase activity assays, contextualized by soil P stocks and agronomic P balances. Distribution of P fractions by depth (0–15, 15–30, 30–60, 60–90 cm) indicate that management effects were limited to the surface soil layers (0–30 cm). Soil P fractions differed more by depth than by experimental treatments. Long-term N fertilization significantly decreased pH concurrently with labile organic P (Po) and phosphodiesterase activity. Soil labile inorganic P (Pi) was two-fold lower under N fertilization compared to zero N fertilization, reflecting greater yield and thus P export via grain harvest. Under N fertilization, integration of soybean elevated soil phosphodiesterase activity and decreased water-extractable Po. Higher stocks of soil Po than labile Pi at surface depths (0–30 cm) corroborated a hypothesized appreciable pool size of soil Po relative to the labile Pi pool to which most agronomic assessments are limited. Large negative agronomic balances over the 36-year period (−426 to −945 kg P ha⁻¹) are suggestive of legacy P from pre-experiment manure application and high native P stocks, with net P export equivalent to 11–35% of soil P stocks at 0–90 cm depth at the initiation of the experiment. These results contribute to a better understanding how N fertilization and rotation practices influence soil P cycling and stocks, thereby informing P budgets for comprehensive agroecosystem P management.
... In addition, nitrate export from the Upper Mississippi River System is an important contributor to Gulf of Mexico hypoxia (Turner and Rabalais, 2003;Crawford and others, 2019). TN and TP are delivered to the Upper Mississippi River System mainly from nonpoint sources such as runoff, tributary loads, and groundwater rather than point sources like wastewater treatment effluent as a result of large efforts to reduce phosphorus and nitrogen in wastewater Saad, 2013 and. Some transformation and uptake of these nutrients can occur in the river itself, especially in off-channel areas, which reduces the effect of excess nutrients to organisms locally and downstream. ...
Full-text available
Chapter
This report assesses the status and trends of selected ecological health indicators of the Upper Mississippi River System (UMRS) based on the data collected and analyzed by the Long Term Resource Monitoring element of the Upper Mississippi River Restoration program, supplemented with data from other sources. This report has four objectives: providing a brief introduction of the UMRS, including its significance, history, modern-day stressors, and recent research; using ecological indicators to describe the status of the river system and where and how it has changed from circa 1993 to 2019; discussing management and restoration implications of these changes; and highlighting the fundamental role of long-term monitoring in the understanding, management, and restoration of large-floodplain rivers. The data were collected in the six Long Term Resource Monitoring element study reaches that spanned much of the UMRS and the various gradients contained therein. These study reaches included Navigation Pools 4, 8, 13, and 26; the part of the Unimpounded Reach of the Upper Mississippi River between Grand Tower and Cairo, Illinois; and the La Grange Pool on the Illinois River. The indicators included in this report describe the status and trends for the hydrology, geomorphology, floodplain vegetation, water quality, vegetation, and fishes of the UMRS. Many of the indicators of river ecosystem health changed significantly over the nearly 30 years of our evaluation. However, there was substantial spatial variability in the magnitude and timing of those changes among study reaches. Few indicators changed everywhere or nowhere; most indicators changed in some reaches but not others. The quantitative assessments of these indicators describe how the conditions of the river differ across hydrogeomorphic and climate gradients and through time and are intended to support the restoration and management of the UMRS.
... In addition, nitrate export from the Upper Mississippi River System is an important contributor to Gulf of Mexico hypoxia (Turner and Rabalais, 2003;Crawford and others, 2019). TN and TP are delivered to the Upper Mississippi River System mainly from nonpoint sources such as runoff, tributary loads, and groundwater rather than point sources like wastewater treatment effluent as a result of large efforts to reduce phosphorus and nitrogen in wastewater Saad, 2013 and. Some transformation and uptake of these nutrients can occur in the river itself, especially in off-channel areas, which reduces the effect of excess nutrients to organisms locally and downstream. ...
Full-text available
Chapter
This report assesses the status and trends of selected ecological health indicators of the Upper Mississippi River System (UMRS) based on the data collected and analyzed by the Long Term Resource Monitoring element of the Upper Mississippi River Restoration program, supplemented with data from other sources. This report has four objectives: providing a brief introduction of the UMRS, including its significance, history, modern-day stressors, and recent research; using ecological indicators to describe the status of the river system and where and how it has changed from circa 1993 to 2019; discussing management and restoration implications of these changes; and highlighting the fundamental role of long-term monitoring in the understanding, management, and restoration of large-floodplain rivers. The data were collected in the six Long Term Resource Monitoring element study reaches that spanned much of the UMRS and the various gradients contained therein. These study reaches included Navigation Pools 4, 8, 13, and 26; the part of the Unimpounded Reach of the Upper Mississippi River between Grand Tower and Cairo, Illinois; and the La Grange Pool on the Illinois River. The indicators included in this report describe the status and trends for the hydrology, geomorphology, floodplain vegetation, water quality, vegetation, and fishes of the UMRS. Many of the indicators of river ecosystem health changed significantly over the nearly 30 years of our evaluation. However, there was substantial spatial variability in the magnitude and timing of those changes among study reaches. Few indicators changed everywhere or nowhere; most indicators changed in some reaches but not others. The quantitative assessments of these indicators describe how the conditions of the river differ across hydrogeomorphic and climate gradients and through time and are intended to support the restoration and management of the UMRS.
... In addition, nitrate export from the Upper Mississippi River System is an important contributor to Gulf of Mexico hypoxia (Turner and Rabalais, 2003;Crawford and others, 2019). TN and TP are delivered to the Upper Mississippi River System mainly from nonpoint sources such as runoff, tributary loads, and groundwater rather than point sources like wastewater treatment effluent as a result of large efforts to reduce phosphorus and nitrogen in wastewater Saad, 2013 and. Some transformation and uptake of these nutrients can occur in the river itself, especially in off-channel areas, which reduces the effect of excess nutrients to organisms locally and downstream. ...
Full-text available
Technical Report
This report assesses the status and trends of selected ecological health indicators of the Upper Mississippi River System (UMRS) based on the data collected and analyzed by the Long Term Resource Monitoring element of the Upper Mississippi River Restoration program, supplemented with data from other sources. This report has four objectives: providing a brief introduction of the UMRS, including its significance, history, modern-day stressors, and recent research; using ecological indicators to describe the status of the river system and where and how it has changed from circa 1993 to 2019; discussing management and restoration implications of these changes; and highlighting the fundamental role of long-term monitoring in the understanding, management, and restoration of large-floodplain rivers.
... In addition, nitrate export from the Upper Mississippi River System is an important contributor to Gulf of Mexico hypoxia (Turner and Rabalais, 2003;Crawford and others, 2019). TN and TP are delivered to the Upper Mississippi River System mainly from nonpoint sources such as runoff, tributary loads, and groundwater rather than point sources like wastewater treatment effluent as a result of large efforts to reduce phosphorus and nitrogen in wastewater Saad, 2013 and. Some transformation and uptake of these nutrients can occur in the river itself, especially in off-channel areas, which reduces the effect of excess nutrients to organisms locally and downstream. ...
Full-text available
Chapter
This chapter reports the patterns and drivers of improved water clarity in the Upper Mississippi River from 1993-2019, https://pubs.usgs.gov/of/2022/1039/ofr20221039.pdf
... Prior to industrialisation, the The Mississippi River basin is the third biggest basin in the world, covering approximately 41% of the contiguous United States [19], and is the major source of freshwater and nutrients to the Gulf of Mexico [20]. Ref. [21] approximated the amount of nitrogen delivered to the Gulf of Mexico from the Mississippi River basin. They identified six sources of nitrogen, viz., chemical fertilisers, atmospheric deposition, manure, fixation and other legume sources, urban effluent, and wastewater treatment facilities, which account for 41,26,10,9,7, and 7%, respectively. ...
Full-text available
Article
Biological processes of rivers are strongly influenced by concentration and fluxes of nitrogen (N) levels. In order to restrain eutrophication, which is typically caused by urbanisation and agricultural expansion, nitrogen levels must be carefully controlled. Data from 2013 to 2017 were gathered from 26 sub-catchments in the Mississippi River basin to assess the effects that catchment size, land cover, and precipitation can have on the discharge and total nitrogen (TN) and how TN yields deviate from a generalised local trend. The findings indicated that land cover and precipitation had a determinative effect on area-weighted discharge (Qarea). More specifically, Qarea had significant positive (directly proportional) relationships with precipitation, forest, and urbanised land cover, and significant negative (inversely proportional) relationships with grassland/pasture and scrub/shrub land covers. Concurrently, the TN concentration significantly increased in the presence of agricultural land cover, but significantly decreased in forest land cover. The TN yield (TN concentration × Qarea) was largely determined by Qarea because the latter was observed to fluctuate more dramatically than concentration levels. Consequently, the TN yield exhibited the same relationships that Qarea had with precipitation and land covers. The TN yield changed significantly (p < 0.05) and positively with instantaneous discharge across all sites. Nevertheless, the rate of TN yield variations with discharge displayed a significant (p < 0.0001) negative (r2 = 0.80) relation with the catchment size. Ultimately, this study used discharge readings to facilitate the prediction of TN concentrations and yields across various catchment areas in the Mississippi River basin and provided a robust model for future research in this area.
... Although N has received more attention (Jones et al. 2018), P export has been viewed by some researchers as a potential limiting nutrient in phytoplankton growth in many freshwater ecosystems and coastal waters (USEPA 2007;Sylvan et al. 2006;Hecky and Kilham 1988). Watershed sources of total P (TP; sum of particulate and dissolved P) to river systems can vary, but nonpoint sources such as soil erosion, farm fertilizers, and manure, along with point source discharge of urban wastewater, are thought to comprise the largest TP contributions (Jacobson et al. 2011;Robertson and Saad 2013). ...
... In 2019, the "dead zone" reached 18,005 km 2 , significantly exceeding the Hypoxia Task Force's goal. Robertson and Saad (2013) estimated that 41 % of N delivered to the Gulf originated from farm fertilizer applications. ...
... Numerous studies have investigated Hypoxia in the Gulf of Mexico, N export from agriculture, and strategies to reduce nutrient losses from cropland in the MRB (Ribaudo et al., 2001;Rabotyagov et al., 2010;Robertson and Saad, 2013;Kling et al., 2014;Rabotyagov et al., 2014;White et al., 2014;Jones et al., 2018;Marshall et al., 2018). Previous findings indicate that two sub-basins of the MRB, the Upper Mississippi River Basin (UMRB) and the Ohio-Tennessee River Basin (OTRB), where intensive corn-soybean rotations rely on high use of N fertilizers and/or manure nitrogen inputs, deliver a disproportionate share of N loadings from crop production to the Gulf of Mexico White et al., 2014;Jones et al., 2018;Marshall et al., 2018). ...
Full-text available
Article
An integrated hydro-economic agricultural land use model was developed with endogenous and spatially explicit crop planting, nitrogen (N) fertilizer use and irrigation in the Mississippi River Basin (MRB). We used the model to quantify the effects of energy and N fertilizer prices on N runoff to the Gulf of Mexico. Results show a modest effect of energy costs and a more substantive impact of N fertilizer costs on N delivered to the Gulf of Mexico. A 30 % reduction (increase) in N fertilizer price leads to a 3.5 % and 1.5 % increase (2.9 % and 1.5 % decrease) in N use and runoff, respectively. The model was also used to estimate the opportunity cost of N runoff abatement. The opportunity cost of reducing N runoff from crop production to the Gulf by 45 % is estimated to be $6 billion annually, which corresponds to an average cost of $29.3 per kg of N runoff reduction. The results show heterogeneities in the optimal N runoff reduction efforts across counties within the MRB, demonstrating the significance of a targeted abatement strategy.
... The mechanistic mass-balance framework of SPARROW enables a relatively complete accounting of the nutrient sources and their delivery downstream, implying the overall inputs and delivery of these sources to monitoring locations in streams is reasonably estimated with the individual source and combination of delivery variable coefficients. However, the individual land-to-water delivery factors, such as BMP variables, included in a final calibrated SPARROW model and controlling model-computed delivery of each source to the stream may not represent all the factors operating in an actual ecosystem, complicating the determination of their individual causative effects (Robertson and Saad 2013). Evaluation of BMP land-to-water delivery variables was conducted in three steps. ...
... Loss of P from agricultural lands to water bodies is a major concern in the Midwestern U.S. because of its negative impact on aquatic environments such as eutrophication (Carpenter et al., 1998;Gronberg and Arnold, 2017;Robertson and Saad, 2013;Robertson et al., 2014;Sharpley and Withers, 1994) and the development of hypoxic zones (Diaz and Rosenberg, 2008). Concentrations of dissolved reactive P (DRP) and TP are high enough (e.g., greater than 0.01 mg L − 1 ) to induce eutrophication in downstream water bodies (McDowell et al., 2015;Radcliffe et al., 2015;Rowe et al., 2016;USEPA, 2018). ...
Article
Legacy phosphorus (P) has accelerated the subsurface transport of colloidal P (CP) in intensively managed agricultural soils in the Midwestern U.S. Because of its high P sorption capacity and mobility, understanding the depth sequence distribution of mobile CP and its speciation in the soil profile is critical in assessing total P(TP) loss to protect the water quality of adjacent water bodies. In this study, physicochemical properties of water-extractable colloids (WECs) from the soil profile at 0–180 cm were characterized using conventional wet chemical analysis. Solution P-31 nuclear magnetic resonance spectroscopy (NMR), P and Fe K-edge X-ray absorption spectroscopy, and transmission electron microscopy were also used to understand P speciation and mineralogy of CP. Percent recovery of WECs per bulk soil increased more than three times with increasing depth. Considering mildly alkaline pH of pore water and negative zeta potential (−21 ± 4 mV) of WECs (size: 1.65 ± 0.45 μm), the transport of P rich WECs (TP: approximately 210–700 mg kg⁻¹) were facilitated from surface to subsoils. Generally, TP in WEC decreased with increasing depth. Interestingly, WECs in subsoil contain organic P (OP) as much as 60 mg kg⁻¹. NMR analysis clearly showed the presence of OP monoesters, OP diesters, and orthophosphate in these particles. Both orthophosphate and OP species interacted with iron oxyhydroxides, calcite, and aluminol functional groups of gibbsite and or phyllosilicates. The study showed the availability of WECs from surface to subsoils that carry orthophosphate as well as OP in legacy P impacted agricultural soils in the Midwestern U.S.