Mississippi River Alluvial Plain Research Articles

Integrated surface and groundwater modeling to enhance water resource sustainability in agricultural watersheds

Management of water resources is essential to maintain sustainable agricultural productivity and preserve groundwater and surface ecosystems. The long-term sustainability of these systems depends on the understanding of complex surface-groundwater flow interactions at different temporal and spatial scales, and the impacts of agricultural practices on water use. To support these efforts, an integrated AnnAGNPS-MODFLOW modeling technology is proposed and evaluated. It combines the capability of the AnnAGNPS model to detailed characterization of farming practices with groundwater flow estimation tools of the MODFLOW model. The AnnAGNPS-MODFLOW model was evaluated in Upper Sunflower River watershed at the Lower Mississippi River Alluvial Plain. The integrated modeling technology in conjunction with observed values of streamflow at the outlet and well water levels were used to estimate irrigation strategies with application rates varying in time and space at field scale. Utilization of improved irrigation characterization have provided evidence of the sensitivity of streamflow and groundwater levels to irrigation strategies. Simulation results indicate that a reduction of irrigation application rates by 20–40% can impact aquifer long-term water levels. This finding supports the need to investigate more efficient irrigation strategies to promote the aquifer sustainable use. The proposed technology provides a management tool critical to understanding and evaluating the impact of agricultural practices, irrigation, and aquifer recharge strategies that are important to sustaining water resources in irrigated agricultural watersheds.

Mapping annual irrigation from Landsat imagery and environmental variables across the conterminous United States

Identifying the location of irrigated croplands and how they change over time is critical for assessing and managing limited water resources to navigate such challenges as local to global water scarcity, increasing demands for food and energy production, and environmental sustainability. Although efforts have been made to map irrigated area for the U.S., multi-year nationwide maps at field-relevant resolutions are still unavailable; existing products suffer from coarse resolution, uncertain accuracy, and/or limited spatial coverage, especially in the eastern U.S. In this study, we present an approach to map the extent of irrigated croplands across the conterminous U.S. (CONUS) for each year in the period of 1997–2017. To scale nationwide, we developed novel methods to generate training datasets covering both the western and eastern U.S. For the more arid western U.S., we built upon the methods of Xie et al. (2019) and further developed a greenness-based normalization technique to estimate optimal thresholds of crop greenness in any year based on those in USDA NASS census years (i.e., 1997, 2002, 2007, 2012, and 2017). For the relatively humid eastern states, we collected data on the current status of center pivot irrigated and non-irrigated fields and extended these sample points through time using various indices and observational thresholds. We used the generated samples along with remote sensing features and environmental variables to train county-stratified random forest classifiers annually for pixel-level classification of irrigated extent each year and subsequently implemented a logic-based post-classification filtering. The produced Landsat-based Irrigation Dataset (LANID-US) accurately reconstructed NASS irrigation patterns at both the county and state level while also supplying new annual area estimates for intra-epoch years. Nationwide pixel-level locational assessment further demonstrated an overall accuracy above 90% across years. In the 21-year study period, we found several hotspots of irrigation change including significant gains in the U.S. Midwest, the Mississippi River Alluvial Plain, and the East Coast as well as irrigation declines in the central and southern High Plains Aquifer and the southern California Central Valley, Arizona, and Florida. The resulting 30 m resolution LANID-US products represent the finest resolution account of nationwide irrigation use and dynamics across the United States to date. The developed approach, training data, and products are further extendable to other years (either before 1997 or after 2017) for continuous monitoring of irrigated area over CONUS and are spatially applicable to other regions with similar climate and cropping landscapes.

Methods to quality assure, plot, summarize, interpolate, and extend groundwater-level information—examples for the Mississippi River Valley alluvial aquifer

Large-scale computational investigations of groundwater levels are proposed to accelerate science delivery through a workflow spanning database assembly, statistics, and information synthesis and packaging. A water-availability study of the Mississippi River alluvial plain, and particularly the Mississippi River Valley alluvial aquifer (MRVA), is ongoing. Software (visGWDBmrva) has been released as part of the study that demonstrates groundwater informatics for the aquifer. Considerable water-level data collected by multiple agencies over a seven-state area exist (18,903 wells; 287,272 measurements [April 22, 2019]). Data and metadata quality assurance methods, basic statistics, hydrograph visualization, outlier identification, hypothesis testing, and time-series modeling are described. Two approaches (generalized additive models [GAMs] and support vector machines [SVMs]) are used for data interpolation and extension to monthly water-level estimates. Numerical congruence between GAM and SVM estimates will be useful to limit inclusion of monthly estimates from subsequent science activities.

Trends in Land Use, Irrigation, and Streamflow Alteration in the Mississippi River Alluvial Plain

The Mississippi River Alluvial Plain is a critical region for agricultural production in the United States, providing the majority of the nation’s rice, catfish, and cotton. Although it is a humid region, high agricultural yields are maintained through irrigation from groundwater and surface water sources. Heavy groundwater extraction has led to cones of depression in the alluvial aquifer in both Arkansas and Mississippi. This study explores the link between increasing irrigation and streamflow alteration within the alluvial plain. Changing land use patterns were evaluated utilizing the USDA Census of Agriculture datasets to determine changes in land-use, irrigation, and crop yield from 1969 to 2017. Temporal land use patterns set the background for the analysis of sixteen long-term streamflow records from the USGS, which were assessed using the Indicators of Hydrologic Alteration (IHA) software to determine changes in low flow patterns in rivers overlying the Mississippi River Valley alluvial aquifer. Most streamflow records had significant hydrologic alteration with respect to low flow conditions, including higher frequency of low flow events, lower annual minima, or a declining base flow index. Changes in streamflow coincide with areas of massive increases in irrigated cropland area. This study provides further context for the tradeoffs between intensive agricultural production and agroecosystem sustainability.

Genetic Structure Among Hibernacula of the Endangered Gray Bat (Myotis grisescens)

In an attempt to fill knowledge gaps relating to genetic structure in the endangered gray bat (Myotis grisescens), we investigated geographic patterns in multilocus microsatellite DNA (msDNA) genotypes and mitochondrial DNA (mtDNA) haplotype frequencies across eight primary hibernacula. Isolation-by-distance (IBD) was absent in the msDNA data and no bottlenecks were detected, with genotypic diversity (A R = 6.52, H o = 0.64) and overall genetic differentiation (F ST = 0.024, P < 0.001) being comparable to other Myotis and North American vespertilionids. Genetic structure (ΦCT = 0.063, P < 0.001) among groups of populations (K = 2) was observed. We also identified a pattern of slight east-west regional genetic structure, likely attributable to the natural barrier of the Mississippi River Alluvial Plain, in the haplotype data (ΦCT = 0.086, P < 0.05), along with moderate IBD (r = 0.486, P < 0.05). Though genetic differentiation among populations was generally low, significant interpopulation genetic structur...

Simultaneous determination of mercury and organic carbon in sediment and soils using a direct mercury analyzer based on thermal decomposition–atomic absorption spectrophotometry

The purpose of this work was to study the feasibility of using a direct mercury analyzer (DMA) to simultaneously determine mercury (Hg) and organic matter content in sediment and soils. Organic carbon was estimated by re-weighing the sample boats post analysis to obtain loss-on-ignition (LOI) data. The DMA-LOI results were statistically similar (p<0.05) to the conventional muffle furnace approach. A regression equation was developed to convert DMA-LOI data to total organic carbon (TOC), which varied between 0.2% and 13.0%. Thus, mercury analyzers based on combustion can provide accurate estimates of organic carbon content in non-calcareous sediment and soils; however, weight gain from moisture (post-analysis), measurement uncertainty, and sample representativeness should all be taken into account. Sediment cores from seasonal wetland and open water areas from six oxbow lakes in the Mississippi River alluvial flood plain were analyzed. Wetland sediments generally had higher levels of Hg than open water areas owing to a greater fraction of fine particles and higher levels of organic matter. Annual loading of Hg in open water areas was estimated at 4.3, 13.4, 19.2, 20.7, 129, and 135ngcm−2yr−1 for Beasley, Roundaway, Hampton, Washington, Wolf and Sky Lakes, respectively. Generally, the interval with the highest Hg flux was dated to the 1960s and 1970s.

The Limnology of a Mississippi River Alluvial Plain Oxbow Lake Following the Application of Conservation Practices

From 1995 and 2011, Beasley Lake watershed near Indianola, MS, was subjected to a variety of conservation measures designed to reduce water velocity, erosion and discharge of sediment laden water. Water quality monitoring during the period indicated a number of long term trends and relationships between the parameters measured. Conservation practices reduced sediments and nutrients during the course of the study that resulted in increased Secchi visibility and chlorophyll a. Annual mean dissolved oxygen decreased slightly over time and was strongly dependent upon temperature, and weakly associated with varying salinity and pH. Total phosphorus, ammonium nitrogen and nitrate nitrogen showed significant downward trends from 1995 through 2011. Chlorophyll a concentration was significantly dependent upon total nitrogen but not phosphate, indicating nitrogen limiting conditions. Watershed based conservation practices significantly changed the long term water quality of Beasley Lake by reducing sediment and nutrients, increasing water clarity and boosting primary production as indicated by chlorophyll a.

Effects of agricultural conservation practices on oxbow lake watersheds in the Mississippi River alluvial plain

Agricultural lands are considered to be a major source of nonpoint source pollutants such as sediment, pesticides and nutrients in the United States. Conservation practices have been tested for their effectiveness in reducing agricultural related pollutants on smaller scales, but farm watershed scale assessments of these practices are limited and few of these have evaluated the impacts on downstream ecology. Several projects focused on oxbow lake watersheds in the Mississippi River alluvial plain were designed to utilize working farms to evaluate primary pollutants in water resources and to identify conservation practices that are most effective in reducing the transport of those pollutants in surface and ground water on a watershed scale. Major findings of these studies include: (1) conservation practices reduced sediment in oxbow lakes, resulting in improved water clarity, plankton growth, and fish stocks; (2) total phosphorus in lakes decreased between 39&amp;ndash;50% following application of conservation practices; (3) conservation tillage and cover crops reduced NO&lt;sub&gt;3&lt;/sub&gt;-N losses by 73%, sediment losses by 70; and (4) riparian areas mitigated the transport of sediment in runoff and enhanced the degradation of pesticides.

Relationships Between Water Table and Model Simulated ET

This research was conducted to develop relationships among evapotranspiration (ET), percolation (PERC), groundwater discharge to the stream (GWQ), and water table fluctuations through a modeling approach. The Soil and Water Assessment Tool (SWAT) hydrologic and crop models were applied in the Big Sunflower River watershed (BSRW; 7660 km(2) ) within the Yazoo River Basin of the Lower Mississippi River alluvial plain. Results of this study showed good to very good model performances with the coefficient of determination (R(2) ) and Nash-Sutcliffe efficiency (NSE) index from 0.4 to 0.9, respectively, during both hydrologic and crop model calibration and validation. An empirical relationship between ET, PERC, GWQ, and water table fluctuations was able to predict 64% of the water table variation of the alluvial plain in this study. Thematic maps were developed to identify areas with overuse of groundwater, which can help watershed managers to develop water resource programs.

Periphyton responses to nutrient and atrazine mixtures introduced through agricultural runoff

Agricultural runoff often contains pollutants with antagonistic impacts. The individual influence of nutrients and atrazine on periphyton has been extensively studied, but their impact when introduced together and with multiple agricultural pollutants is less clear. We simulated a field-scale runoff pulse into a riverine wetland that mimicked pollutant composition typical of field runoff of the Mississippi River Alluvial Plain. Periphyton biomass and functional responses were measured for 2 weeks along a 500 m section. Additionally, laboratory chamber assays were used to identify potential periphyton changes due to nutrients, atrazine, and their interactions. Generally, nutrients stimulated, and atrazine reduced chlorophyll a (Chl a) in chambers. In the wetland, nutrient and atrazine relationships with periphyton were weaker, and when found, were often opposite of trends in chambers. Total nitrogen (TN) was inversely related to Chl a, and total phosphorus was inversely related to respiration (R) rates. Atrazine (10-20 μg L(-1) in the wetland) had a positive relationship with ash-free dry mass (AFDM), and weakened the relationship between TN and AFDM. Wetland periphyton biomass was better correlated to total suspended solids than nutrients or atrazine. Periphyton function was resilient as periphyton gross primary production (GPP)/R ratios were not strongly impacted by runoff. However, whole-system GPP and R decreased over the 2-week period, suggesting that although periphyton metabolism recovered quickly, whole-system metabolism took longer to recover. The individual and combined impacts of nutrients and atrazine in complex pollutant mixtures can vary substantially from their influence when introduced separately, and non-linear impacts can occur with distance downstream of the pollutant introduction point.

Evaluation of Surface and Radar-Estimated Precipitation Data Sources Over the Lower Mississippi River Alluvial Plain

The Mississippi River floodplain in northwestern Mississippi and eastern Arkansas, often referred to as the Mississippi Delta, is extremely important for regional economic stability and growth due to the widespread agriculture in the area. Precipitation is often the limiting factor in crop production, and thus knowledge of precipitation variability is essential. The region is unique in currently having three sources of precipitation observations: (1) multi-sensor precipitation estimates from the National Weather Service (NWS) NEXRAD network; (2) surface observations from NWS recording stations; and (3) surface observations from U.S. Department of Agriculture (USDA) Soil Climate Analysis Network (SCAN) recording stations. For meteorological and climatological precipitation research, quantitatively defining the biases associated with available precipitation data sources is critical in selecting which source to use for a given application. Results of this research indicate that the multi-sensor data are in best agreement with surface observations during the cool season (October-March) when stratiform precipitation dominates, whereas only moderate correlations exist during the warm season. Additionally, overall bias values among the data sources decrease after 2002, at which point the remotely sensed and surface-based estimates show improved agreement.

Preemergence Herbicides Effect on Growth and Yield of Early-Planted Mississippi Soybean

The objective of this research was to evaluate the impact of full and reduced rates of PRE herbicides, applied alone or in combination, on growth and yield of selected April-planted soybean varieties in the lower Mississippi River alluvial flood plain. Field studies were conducted in 2001 and 2002 at Stoneville, MS, to evaluate the effects of preemergence (PRE) herbicides on growth and yield of early-planted soybean. Main plot factor was PRE grass herbicide. Sub-plot factor was PRE broadleaf herbicide. Sub-sub-plot factor was soybean variety. Soybean injury 8 weeks after treatment (WAT) in 2001 under cool and wet growing conditions ranged from 11 to 31% when PRE broadleaf herbicides were applied alone. Pendimethalin alone caused 31% soybean injury 8 WAT. Soybean injury with PRE combinations of pendimethalin at 1120 g ai/ha and broadleaf herbicides ranged from 29 to 49%. Soybean injury with flumioxazin alone was 26 to 31% compared to 38 to 49% with mixtures of S-metolachlor and flumioxazin. Conditions after planting were warmer and drier in 2002 than 2001, but all herbicide treatments still resulted in noticeable soybean injury. Soybean injury from PRE broadleaf herbicides tended to be less with the sulfonylurea-tolerant soybean (STS) variety, especially in 2001. Averaged across PRE grass herbicides, soybean yield was reduced both years by metribuzin at 694 g ai/ha and sulfentrazone + chlorimuron at 231 + 38 g ai/ha. Averaged across PRE broadleaf herbicides, pendimethalin reduced soybean yield 4% in 2001 and S-metolachlor reduced soybean yield 3% in 2002.

Pesticide Body Residues of Hyalella azteca Exposed to Mississippi Delta Sediments

This article discusses pesticide residues in the sediments of the Lower Mississippi River Alluvial Plain of Arkansas and Mississippi related to bioaccumumulation by the freshwater crustacean Hyalella azteca. According to the authors, most of these pesticides are the result of agricultural runoff and consist of both current use and legacy or discontinued pesticides. Three types of watersheds were investigated including National Wildlife Refuge, Best Management Practices (BMPs) and watersheds where the total maximum daily load of legacy pesticides exceeded guidelines. They concluded that BMPs have little if any impact on pesticide sequestration and few available current-use insecticides but greater legacy compounds accumulated in H. azteca tissues

Cotton and corn rotation under reduced tillage management: impacts on soil properties, weed control, yield, and net return

A 6-yr rotation study was conducted from 2000 to 2005 at Stoneville, MS to examine the effects of rotating glyphosate-resistant (GR) and non-GR (conventional) cultivars of cotton with corn under reduced tillage conditions on soil properties, weed control, crop yield, and net return. There were four rotation systems (continuous cotton, continuous corn, cotton–corn, and corn–cotton) for each non-GR and GR cultivar arranged in a randomized complete block design with four replications. Field preparation consisted of disking, subsoiling, disking, and bedding in the fall of 1999. After the fall of 2000, the experimental area received no tillage operations except rebedding after harvest each year to maintain reduced tillage conditions. A glyphosate-based program in GR cultivars and a nonglyphosate-based program in non-GR cultivars were used for weed management. Soil organic carbon in the top 5-cm depth progressively increased from the first year to the sixth year, regardless of rotation. In 2005, organic carbon was higher in corn grown continuously and in rotation compared to continuous cotton, partly due to higher plant residues from corn compared to cotton. Control of most grass and broadleaf weeds was sufficient to support cotton and corn production, regardless of rotation and herbicide program. Control of yellow nutsedge was reduced in continuous non-GR cotton; this apparent weed species shift toward yellow nutsedge was mitigated by breaking the cotton monocrop with corn. Plant populations of both GR and non-GR cotton rotated with corn were similar to that of continuous cotton suggesting cotton stand establishment was not affected by corn residues from the previous year. Cotton yield increased every year following rotation with corn by 10–32% in the non-GR cultivar, and by 14–19% in the GR cultivar compared to continuous cotton. Similarly, corn yield increased by 5–13% in non-GR cultivar and by 1–11% in the GR cultivar when rotated with cotton. As a result, net returns were higher from rotation management as compared with monoculture in both crops. This study demonstrated that alternating between cotton and corn is agronomically feasible and a sustainable option for farmers in the lower Mississippi River alluvial flood plain region who are looking for simple cultural practices that provide economic and environmental benefits.

Residual Effects of Fall Deep Tillage on Soybean Yields and Net Returns on Tunica Clay Soil

Seed yield of monocrop soybean [Glycine max (L.) Merr.] grown on nonirrigated clay soils in the Mississippi River alluvial flood plain has been consistently low and marginally profitable. Deep tillage (subsoiling) of certain clayey soils in the fall when the soil profile is dry significantly increases yields and net returns from this production system. Yields and net returns were evaluated for seven deep‐till treatments and a conventional‐till treatment that was disked annually (C). The deep‐till treatments included subsoiling annually and once every second, third, fourth, and fifth year (DT1, DT2, DT3, DT4, and DT5, respectively), Paratill annually (PT1), and profile modification every fifth year (MP). Over the 5‐yr study, DT1 produced the greatest yield (3452 kg ha−1), which was 1016 kg ha−1 (42%) above the average yield from C (2436 kg ha−1). Yields from DT2, DT3, and PT1 were virtually identical and averaged only 198 kg ha−1 (5–6%) less than the average yield from DT1, whereas yields from DT4 and DT5 averaged 291 kg ha−1 (9%) and 613 kg ha−1 (18%) less. Net returns from DT1 ($436 ha−1) averaged the highest, whereas returns from C ($220 ha−1) were the lowest. Net returns from DT2 and DT3 were within 5% of the net returns from DT1, whereas net returns from the DT4, DT5, PT1, and MP treatments respectively averaged 9, 26, 9, and 31% less than returns from DT1. Thus, fall deep tillage should be performed at least once every 3 yr to maximize and sustain higher yields and net returns from soybean grown on nonirrigated Tunica clay (clayey over loamy, smectitic, nonacid, thermic Vertic Haplaquept).

A Decision‐Support System for Prioritizing Restoration Sites on the Mississippi River Alluvial Plain

Conversion of forested wetlands to agricultural use and the resulting fragmentation of the landscape has led to concerns for the functional integrity of the Mississippi River Alluvial Plain ecosystem. We describe an effort spearheaded by The Nature Conservancy to initiate a multi‐decade partnership dedicated to creating and implementing a viable, cooperative, landscape‐level restoration project in the Mississippi River Alluvial Plain. Important phases of the process during the first 5 years were (1) initiation of the development of an extensive network of partners, including state and federal agencies, private land owners, conservation groups, academicians, and other interested citizens; (2) development of a geographic information system (GIS) for the entire extent of the ecosystem; and (3) for one watershed, the Tensas basin in northeastern Louisiana, refinement of a high resolution GIS to generate more detailed land‐use conversion statistics to demonstrate the feasibility of a semi‐objective, landscape‐scale restoration planning procedure, including methodology for prioritization of existing wetland forest patches and areas most suitable for reforestation and connection via corridors.

Use of the index of biotic integrity to assess physical habitat degradation in warmwater streams

Indices of biotic integrity (1131) were computed for two annual fish collections from 27 locations along the bluffline bordering the Mississippi River alluvial plain in northwestern Mississippi. Study sites exhibited varying degrees of physical habitat degradation due to accelerated channel erosion. Objectives of index application were to quantify existing environmental quality and to test the IBI as a tool for relating fish population characteristics to physical degradation. Physical habitat data were collected concurrently with fish at all sites, and physical habitat descriptors were compared with the IBI scores and component metrics.

Distribution of nitrogen in soils of the southern Mississippi river alluvial plain

Abstract Nitrogen (N) dynamics in the agriculturally important alluvial soils of the southern Mississippi Delta are not well understood, and little information is available regarding the amounts of various forms of N present in these soils. Profiles of nine alluvial soils were selected to represent the principal agricultural acreage in the southern Mississippi Delta. Soils were sampled by horizon to a depth of 150 cm and the distribution of various N fractions were characterized. Forty‐one additional chemical, physical and mineralogical properties were measured, and regression techniques were used to determine if these soil properties were related to N distribution in the highly heterogeneous soils typical of this region. These profiles contained 11.6 to 26.5 Mt N/ha (average 18.8 Mt N/ha). The surface 15 cm contained an average of 4.8 Mt N/ha and accounted for about 26% of the profile N. Most of N in the surface 15 cm was recovered as organic N (78.4–87.4%), and the balance recovered primarily as nonexch...

Net Returns from Eight Irrigated Cropping Systems on Clay Soil

Considerable research has been conducted on the agronomic relationships of cropping systems adapted to the clay soils of the lower Mississippi River floodplain (30°-37° North latitude); however, only a few studies included the determination and evaluation of net returns. An 8-yr study (1984-1991) was conducted on a Tunica clay (clayey over loamy, montmorillonitic, nonacid, thermic Vertic Haplaquept) to determine net returns above specified costs from eight nonirrigated cropping systems. The cropping systems included 1) monocrop corn (Zea mays L.) ; 2) monocrop soybean [Glycine max (L.) Merr.] ; 3) monocrop grain sorghum [Sorghum bicolor (L.) Moench.] ; 4) biennial rotation of corn and soybean ; 5) biennial rotation of grain sorghum and soybean ; 6) continuous wheat (Triticum aestivum L.)-soybean doublecrop ; 7) biennial rotation of corn and wheat-sobyean doublecrop ; and 8) biennial rotation of grain sorghum and wheat-soybean doublecrop. Cropping systems that included grain sorghum as a component produced the highest average net returns. Average net returns per acre from grain sorghum-soybean ($76), grain sorghum and wheat-soybean doublecrop ($64), and monocrop grain sorghum ($60) systems were significantly higher than from the monocrop soybean ($25), monocrop corn ($-9), and corn and wheat-soybean doublecrop ($16) systems. Average net returns per acre from the wheat-soybean doublecrop ($48) and the corn-soybean ($42) systems were similar and in the intermediate range. Data indicate that monocrop corn and soybean systems and the corn-wheat-soybean system are not profitable when grown in nonirrigated environments on clay soils in the lower Mississippi River alluvial plain.

Cropping Systems for Clay Soil: Irrigated and Nonirrigated Soybean Rotated with Corn and Sorghum

In the Mississippi River alluvial plain, soybean [Glycine max (L.) Merr.] is the primary crop. Seed yields of soybean grown under monocultured, dryland conditions in this region are usually lower than needed for profitable production. Experiments were conducted from 1985 through 1990 on Tunica clay (clayey over loamy, montmorillonitic, nonacid, thermic Vertic Haplaquept) near Stoneville, Mississippi, to determine the response of soybean to rotation with corn (Zea Mays L.) and sorghum [Sorghum bicolor (L.) Moench] under irrigated (I) and nonirrigated (NI) conditions