Mississippi-Atchafalaya River Basin Research Articles

Assessing the potential to decrease the Gulf of Mexico hypoxic zone with MidwestUSperennial cellulosic feedstock production

AbstractThe goal of this research was to determine the changes in streamflow, dissolved inorganic nitrogen (DIN) leaching and export to the Gulf of Mexico associated with a range of large‐scale dedicated perennial cellulosic bioenergy production scenarios within in the Mississippi–Atchafalaya River Basin (MARB). To achieve this goal, we used Agro‐IBIS, a vegetation model capable of simulating the biogeochemistry of row crops, miscanthus and switchgrass, coupled withTHMB, a hydrology model capable of simulating streamflow andDINexport. Simulations were conducted at varying fertilizer application rates (0–200 kg N ha−1) and fractional replacement (5–25%) of current row crops with miscanthus or switchgrass across theMARB. The analysis also includes two scenarios where miscanthus and switchgrass (MRXandMRS, respectively) each replace the ca. 40% of maize production currently devoted to ethanol. Across the scenarios, there were minor reductions in runoff and streamflow throughout theMARB, with the largest differences (ca. 6%) occurring for miscanthus at the highest fractional replacement scenarios in drier portions of the region. However, differences in totalMARBdischarge at the basin outlet were less than 1.5% even in theMRXscenario. Reductions inDINexport were much larger on a percentage basis than reductions in runoff, with the highest replacement scenarios decreasing long‐term meanDINexport by ca. 15% and 20% for switchgrass and miscanthus, respectively. Fertilization scenarios show that significant reductions inDINleaching are possible even with application rates of 100 and 150 kg N ha−1for switchgrass and miscanthus, respectively. These results indicate that, given targeted management strategies, there is potential for miscanthus and switchgrass to provide key ecosystem services by reducing the export ofDIN, while avoiding hydrologic impacts of reduced streamflow.

Prioritizing conservation for the reduction of Gulf hypoxia using an environmental performance index

The annual growth of hypoxia in the Gulf of Mexico is largely attributed to agricultural nutrient loadings that originate from the Mississippi/Atchafalaya River Basin (MARB). To effectively target conservation efforts throughout the entire MARB in order to reduce Gulf hypoxia, strategies to rank areas according to their impact on both agricultural production and ecosystem services are extremely important. In this paper, we utilize an Environmental Performance Index (EPI) to rank regions within the MARB according to their environmental performance, that is, their ability to produce agricultural outputs while minimizing nutrient loadings to the Gulf of Mexico. We compare our index rankings to previously used rankings of delivered yields alone and find the spatial distribution of rankings changes considerably when accounting for agricultural productivity. For example, the Corn Belt regions of central Iowa and northern Illinois no longer make up the lowest performing regions of the MARB after accounting for their high levels of agricultural production. Instead, regions along the Missouri river including central Missouri, western Iowa, and southeastern South Dakota as well as areas near the Ohio river including southern Illinois, western Kentucky, and southern Ohio now count among the lowest performing regions using the EPI ranking scheme. We suggest that incorporation of economic production value into large-scale prioritization of agricultural conservation within the MARB is essential to effectively reduce Gulf hypoxia while maintaining food security from efficient farm production.

Cost-effective targeting of conservation investments to reduce the northern Gulf of Mexico hypoxic zone.

A seasonally occurring summer hypoxic (low oxygen) zone in the northern Gulf of Mexico is the second largest in the world. Reductions in nutrients from agricultural cropland in its watershed are needed to reduce the hypoxic zone size to the national policy goal of 5,000 km(2) (as a 5-y running average) set by the national Gulf of Mexico Task Force's Action Plan. We develop an integrated assessment model linking the water quality effects of cropland conservation investment decisions on the more than 550 agricultural subwatersheds that deliver nutrients into the Gulf with a hypoxic zone model. We use this integrated assessment model to identify the most cost-effective subwatersheds to target for cropland conservation investments. We consider targeting of the location (which subwatersheds to treat) and the extent of conservation investment to undertake (how much cropland within a subwatershed to treat). We use process models to simulate the dynamics of the effects of cropland conservation investments on nutrient delivery to the Gulf and use an evolutionary algorithm to solve the optimization problem. Model results suggest that by targeting cropland conservation investments to the most cost-effective location and extent of coverage, the Action Plan goal of 5,000 km(2) can be achieved at a cost of $2.7 billion annually. A large set of cost-hypoxia tradeoffs is developed, ranging from the baseline to the nontargeted adoption of the most aggressive cropland conservation investments in all subwatersheds (estimated to reduce the hypoxic zone to less than 3,000 km(2) at a cost of $5.6 billion annually).

Effects of Agricultural Conservation Practices on N Loads in the Mississippi–Atchafalaya River Basin

A modeling framework consisting of a farm-scale model, Agricultural Policy Environmental Extender (APEX); a watershed-scale model, Soil and Water Assessment Tool (SWAT); and databases was used in the Conservation Effects Assessment Project to quantify the environmental benefits of conservation practices on cropland. APEX is used to simulate conservation practices on cultivated cropland and Conservation Reserve Program land to assess the edge-of-field water-quality benefits. Flow and pollutant loadings from APEX are input to SWAT. SWAT simulates the remaining noncultivated land and routes flow and loads generated from noncultivated land, point sources, and cropland to the basin outlet. SWAT is used for assessing the effects of practices on local and in-stream water-quality benefits. Each river basin is calibrated and validated for streamflow and loads at multiple gauging stations. The objectives of the current study are to estimate the effects of currently existing and additional conservation practices on total N (TN) loads in the Mississippi-Atchafalaya River Basin (MARB) and draw insights on TN load reductions necessary for reducing the hypoxic zone in the Gulf of Mexico. The effects of conservation practice scenarios on local and in-stream (riverine) water quality are evaluated. Model results indicate that conservation practices currently on cropland have reduced the TN losses to local waters between 20 and 59% in the six river basins within MARB and the TN load discharged to the Gulf by 17%. Further water-quality improvement can be obtained in the MARB with additional conservation treatment.

Estimating the Effects of Agricultural Conservation Practices on Phosphorus Loads in the Mississippi-Atchafalaya River Basin

<abstract><title><italic>Abstract.</italic></title> Agriculture in the Mississippi-Atchafalaya River basin (MARB) is important in terms of both the national economy and the nutrients discharged to the basin and the Gulf of Mexico. Conservation practices are installed on cropland to reduce the nutrient losses. A recent study by the Conservation Effects Assessment Project (CEAP) determined the effects of agricultural conservation practices on water quality in the MARB. A modeling framework consisting of a farm-scale model (Agricultural Policy Environmental Extender, APEX), a watershed-scale model (Soil and Water Assessment Tool, SWAT), and databases was used. APEX was used to simulate the conservation practices on cropland and Conservation Reserve Program (CRP) land and assess the edge-of-field water quality benefits. The predicted flow and loads from APEX were input to SWAT, and SWAT was used to simulate the watershed processes and estimate the local and instream water quality benefits. The model was used for scenario assessment after calibration and validation for streamflow and loads. Recent studies indicate that phosphorus influences the formation of the hypoxic zone in the Gulf of Mexico. The major objectives of this article are to: (1) estimate and discuss the effects of currently existing and additional conservation practices on total phosphorus (TP) loads in the MARB, and (2) assess how TP loads discharged by the conservation scenarios can achieve the recommended annual P target for hypoxia reduction. Results indicated that current conservation practices on cropland have reduced TP losses to local waters by 13% to 52% in six basins within the MARB and reduced the TP load discharged to the Gulf of Mexico by 22%. Additional P load reduction is likely required to reach the annual P target for hypoxia reduction.

Spatial Variability in Nutrient Transport by HUC 8, State, and Subbasin Based on Mississippi/Atchafalaya River Basin SPARROW Models

Nitrogen (N) and phosphorus (P) loading from the Mississippi/Atchafalaya River Basin (MARB) has been linked to hypoxia in the Gulf of Mexico. With geospatial datasets for 2002, including inputs from wastewater treatment plants (WWTPs), and monitored loads throughout the MARB, SPAtially Referenced Regression On Watershed attributes (SPARROW) watershed models were constructed specifically for the MARB, which reduced simulation errors from previous models. Based on these models, N loads/yields were highest from the central part (centered over Iowa and Indiana) of the MARB (Corn Belt), and the highest P yields were scattered throughout the MARB. Spatial differences in yields from previous studies resulted from different descriptions of the dominant sources (N yields are highest with crop-oriented agriculture and P yields are highest with crop and animal agriculture and major WWTPs) and different descriptions of downstream transport. Delivered loads/yields from the MARB SPARROW models are used to rank subbasins, states, and eight-digit Hydrologic Unit Code basins (HUC8s) by N and P contributions and then rankings are compared with those from other studies. Changes in delivered yields result in an average absolute change of 1.3 (N) and 1.9 (P) places in state ranking and 41 (N) and 69 (P) places in HUC8 ranking from those made with previous national-scale SPARROW models. This information may help managers decide where efforts could have the largest effects (highest ranked areas) and thus reduce hypoxia in the Gulf of Mexico.

SPARROW Models Used to Understand Nutrient Sources in the Mississippi/Atchafalaya River Basin

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, including inputs from wastewater treatment plants (WWTPs), and calibration sites throughout the MARB. Previous studies found that highest N and P yields were from the north-central part of the MARB (Corn Belt). Based on the MARB SPARROW models, highest N yields were still from the Corn Belt but centered over Iowa and Indiana, and highest P yields were widely distributed throughout the center of the MARB. Similar to that found in other studies, agricultural inputs were found to be the largest N and P sources throughout most of the MARB: farm fertilizers were the largest N source, whereas farm fertilizers, manure, and urban inputs were dominant P sources. The MARB models enable individual N and P sources to be defined at scales ranging from SPARROW catchments (∼50 km) to the entire area of the MARB. Inputs of P from WWTPs and urban areas were more important than found in most other studies. Information from this study will help to reduce nutrient loading from the MARB by providing managers with a description of where each of the sources of N and P are most important, thus providing a basis for prioritizing management actions and ultimately reducing the extent of Gulf hypoxia.

Nutrient loads exported from managed catchments reveal emergent biogeochemical stationarity

Complexity of heterogeneous catchments poses challenges in predicting biogeochemical responses to human alterations and stochastic hydro‐climatic drivers. Human interferences and climate change may have contributed to the demise of hydrologic stationarity, but our synthesis of a large body of observational data suggests that anthropogenic impacts have also resulted in the emergence of effective biogeochemical stationarity in managed catchments. Long‐term monitoring data from the Mississippi‐Atchafalaya River Basin (MARB) and the Baltic Sea Drainage Basin (BSDB) reveal that inter‐annual variations in loads (LT) for total‐N (TN) and total‐P (TP), exported from a catchment are dominantly controlled by discharge (QT) leading inevitably to temporal invariance of the annual, flow‐weighted concentration, = (LT/QT). Emergence of this consistent pattern across diverse managed catchments is attributed to the anthropogenic legacy of accumulated nutrient sources generating memory, similar to ubiquitously present sources for geogenic constituents that also exhibit a linear LT‐QT relationship. These responses are characteristic of transport‐limited systems. In contrast, in the absence of legacy sources in less‐managed catchments, values were highly variable and supply limited. We offer a theoretical explanation for the observed patterns at the event scale, and extend it to consider the stochastic nature of rainfall/flow patterns at annual scales. Our analysis suggests that: (1) expected inter‐annual variations in LT can be robustly predicted given discharge variations arising from hydro‐climatic or anthropogenic forcing, and (2) water‐quality problems in receiving inland and coastal waters would persist until the accumulated storages of nutrients have been substantially depleted. The finding has notable implications on catchment management to mitigate adverse water‐quality impacts, and on acceleration of global biogeochemical cycles.

Analysis of Nutrient Removal Costs in the Chesapeake Bay Program and Implications for the Mississippi-Atchafalaya River Basin

Analysis of Nutrient Removal Costs in the Chesapeake Bay Program and Implications for the Mississippi-Atchafalaya River Basin

Coastal change and hypoxia in the northern Gulf of Mexico: Part I

Abstract. The Committee on Environment and Natural Resources (CENR) has identified the input of nutrient-rich water from the Mississippi/Atchafalaya River Basin (MARB) as the prime cause of hypoxia in the northern Gulf of Mexico and the prime means for its control. A Watershed Nutrient Task Force was formed to solve the hypoxia problem by managing the MARB catchment. However, the hypoxic zone is also experiencing massive physical, hydrological, chemical and biological changes associated with an immense river-switching and delta-building event that occurs here about once a millennium. Coastal change induced hypoxia in the northern Gulf of Mexico prior to European settlement. It is recommended that for further understanding and control of Gulf hypoxia the Watershed Nutrient Task Force adopt a truly holistic environmental approach which includes the full effects of this highly dynamic coastal area.

Isotopic Evidence of Nitrate Sources and Denitrification in the Mississippi River, Illinois

Anthropogenic nitrate (NO3-) within the Mississippi-Atchafalaya River basin and discharge to the Gulf of Mexico has been linked to serious environmental problems. The sources of this NO3- have been estimated by others using mass balance methods; however, there is considerable uncertainty in these estimates. Part of the uncertainty is the degree of denitrification that the NO3- has undergone. The isotopic composition of NO3- in the Mississippi River adjacent to Illinois and tile drain (subsurface drain) discharge in agricultural areas of east-central Illinois was examined using N and O isotopes to help identify the major sources of NO3- and assess the degree of denitrification in the samples. The isotopic evidence suggests that most of the NO3- in the river is primarily derived from synthetic fertilizers and soil organic N, which is consistent with published estimates of N inputs to the Mississippi River. The 1:2 relationship between delta18O and delta15N also indicate that, depending on sample location and season, NO3- in the river and tile drains has undergone significant denitrification, ranging from about 0 to 55%. The majority of the denitrification appears to have occurred before discharge into the Mississippi River.

The Distribution of the Subspecies of Sceloporus undulatus (Sauria: Iguanidae) in Louisiana

Examination of 349 Louisiana specimens of Sceloporus undulatus substantiates the presence of two subspecies in the state. Sceloporus u. undulatus inhabits areas east, and S. u. hyacinthinus areas west and north of the Mississippi- Atchafalaya river basin. The absence of specimens from the Mississippi-Atchafalaya river basin may indicate a lack of intergradation in Louisiana. In spite of extensive literature on taxonomy and distribution of Sceloporus undulatus (Latreille), little is known about the distribu- tion of the subspecies within Louisiana. Smith (1938), who last re- viewed this species in its entirety, recognized two subspecies in the state: S. u. undulatus in southeastern Louisiana, and S. u. fasciatus (= hyacinthinus fide Smith, 1948) in northwestern Louisiana. This conclusion was based on specimens from only three localities in north- western Louisiana; Smith had none from any other part of the state. Recent authors (Cagle, 1952; Conant, 1958; Keiser and Wilson, 1969) have accepted this Louisiana distributional picture. Smith (1938) distinguished the two subspecies primarily by mean differences in numbers of dorsal scales. Populations with a mean dorsal scale count of 36 or less were assigned to undulatus and those with 37 or more to fasciatus. My study was undertaken to determine the distribution and extent of intergradation of S. u. undulatus and S. u. hyacinthinus in Louisi- ana. METHODS AND MATERIALS. Three hundred and forty-nine lizards were ex- amined. Data recorded were sex, color pattern, snout-vent length, number of dorsal scales (DS), number of scales around the body (SAB), and number of femoral pores (FP). Scale counts were made according to the methods outlined by Smith (1946). Sex was determined by examination of the postanal scales, which are larger in males than in females.