Lower Mississippi River Alluvial Valley Research Articles

Identification of Dominant Warm-Season Latent Heat Flux Patterns in the Lower Mississippi River Alluvial Valley

Warm-season precipitation in the Lower Mississippi River Alluvial Valley (LMRAV) is heavily dominated by the rates of evapotranspiration and surface heat fluxes and is a primary water resource for agriculture. However, the stochastic nature of LMRAV warm-season thunderstorms makes precipitation forecasts challenging. The Weather Research and Forecasting Hydrologic (WRF-Hydro) model, coupled with the multi-parameter Noah land surface (Noah-MP) model, has improved estimates of important warm-season precipitation process. Given the widespread agriculture and dominance of crop and forested landscapes over the region, proper assessment of land use / land cover (LULC) is critical in predicting warm-season precipitation patterns. The objective of this study is to quantify simulated latent heat flux sensitivity (important for warm-season precipitation) to temporally updated LULC datasets. Both the model default and annually updated LULC conditions were used to initialize a 16-year WRF-Hydro simulation from which warm-season latent heat flux estimates were obtained. Annual root mean square difference was computed at each gridpoint. Cluster analysis preprocessed with kernel principal component analysis was used to identify spatial RMSD structures that quantified sensitivity to updated LULC conditions. Results showed the largest impacts occurred directly in the LMRAV and for points slightly east and revealed a meteorological link between these regions.

A century of precipitation trends in forest lands of the Lower Mississippi River Alluvial Valley

Variations in long-term precipitation trends due to climate forcings have been observed in many parts of the world, exacerbating hydrological uncertainties to predicting droughts, floods, water resource availability, and ecosystem services. The Lower Mississippi River Alluvial Valley (LMRAV) is an important economic region of the midsouth USA, which is prone to natural disasters from extreme climate events and is known historically for cyclic flooding events and, within the last 20 years, for groundwater level declines. However, our knowledge of long-term precipitation trends in this region is fragmented. Using 100-year historic daily precipitation data from six stations of forest lands along with multivariate statistical analysis, we found that there were significant increasing trends (p ≤ 0.05) in annual precipitation near the south coastal area of the LMRAV and only marginally increasing trends in the northern area. Spatial variation in seasonality was observed at the decadal scale with increasing trends in fall near the coastal area and in spring around the north area. In addition to becoming wetter, the coastal area also experienced higher precipitation intensity with shorter return period over the past 100 years. These findings are useful to water resource managers for adapting to changing climate conditions in the LMRAV.

Assessing the sensitivity of lower atmospheric characteristics to agricultural land use classification over the Lower Mississippi River Alluvial Valley

The Lower Mississippi River Alluvial Valley (LMRAV) is a key agricultural area within the USA, and although it receives a substantial level of annual rainfall, irrigation remains a requirement to sustain high productivity. Since a large percentage of irrigation comes from limited groundwater sources, predictions of surface and lower atmospheric characteristics associated with convective rainfall processes are critical for planning and managing water resources. While numerical weather models are a key tool in this prediction effort, there is considerable error in the models associated with the correct categorization of regional land use. This is especially true for the LMRAV, where most agricultural land is defined as dry cropland despite the extensive use of irrigation. To improve the accuracy of regional model simulations over the LMRAV, this study investigates the sensitivity of changing the dominate land use category from dry to irrigated cropland within a high-resolution Weather Research and Forecasting (WRF) model simulation. Based on a 5-month simulation (May–Sept. 2016) over the LMRAV, results of the study show that replacing dry cropland with irrigated cropland leads to substantial variations in the low-level thermal and moisture balances. In general, the northern LMRAV was shown to have the greatest increase (decrease) in latent (sensible) heat flux in August and September, with a corresponding increase in 2-m dew point temperature where latent heat flux increased. Additionally, boundary layer heights were shown to decrease over the northern LMRAV over the simulation, likely a result of decreased temperatures resulting from a dampened sensible heat flux.

Identify temporal trend of air temperature and its impact on forest stream flow in Lower Mississippi River Alluvial Valley using wavelet analysis

Characterization of stream flow is essential to water resource management, water supply planning, environmental protection, and ecological restoration; while air temperature variation due to climate change can exacerbate stream flow and add instability to the flow. In this study, the wavelet analysis technique was employed to identify temporal trend of air temperature and its impact upon forest stream flows in Lower Mississippi River Alluvial Valley (LMRAV). Four surface water monitoring stations, which locate near the headwater areas with very few land use disturbances and the long-term data records (60–90 years) in the LMRAV, were selected to obtain stream discharge and air temperature data. The wavelet analysis showed that air temperature had an increasing temporal trend around its mean value during the past several decades in the LMRAV, whereas stream flow had a decreasing temporal trend around its average value at the same time period in the same region. Results of this study demonstrated that the climate in the LMRAV did get warmer as time elapsed and the streams were drier as a result of warmer air temperature. This study further revealed that the best way to estimate the temporal trends of air temperature and stream flow was to perform the wavelet transformation around their mean values.

Fishes in Paleochannels of the Lower Mississippi River Alluvial Valley: A National Treasure

Fluvial geomorphology of the alluvial valley of the Lower Mississippi River reveals a fascinating history. A prominent occupant of the valley was the Ohio River, estimated to have flowed 25,000 years ago over western Tennessee and Mississippi to join the Mississippi River north of Baton Rouge, Louisiana, 750–800 km south of the present confluence. Over time, shifts in the Mississippi and Ohio rivers toward their contemporary positions have left a legacy of abandoned paleochannels supportive of unique fish assemblages. Relative to channels abandoned in the last 500 years, paleochannels exhibit harsher environmental conditions characteristic of hypereutrophic lakes and support tolerant fish assemblages. Considering their ecological, geological, and historical importance, coupled with their primordial scenery, the hundreds of paleochannels in the valley represent a national treasure. Altogether, these waterscapes are endangered by human activities and would benefit from the conservation attention afforded to our national parks and wildlife refuges.

Identification of recharge zones in the Lower Mississippi River alluvial aquifer using high-resolution precipitation estimates

Summary Water resources in the lower Mississippi River alluvial valley play a critical role in agricultural productivity due to the widespread use of irrigation during the growing season. However, the unknown specifics of surface–atmosphere feedbacks in the region, along with diminishing groundwater availability and the non-sustainable trend in irrigation draws from the alluvial aquifer, makes it difficult for water resource managers to make sound decisions for future water sustainability. As a result, it is crucial to identify spatial and temporal associations between local rainfall patterns and groundwater levels to determine the influence of precipitation on regional aquifer recharge. Specifically, it is critical to define the recharge zones of the aquifer so that rainfall distribution can be used to assess potential groundwater recovery. This project addresses the issue of defining areas of recharge in the lower Mississippi River alluvial aquifer (LMRAA) through an assessment of historical precipitation variability using high-resolution radar-derived precipitation estimates. A rotated principal component analysis (RPCA) of both groundwater and precipitation data from October through April is used to define locations where aquifer levels show the greatest variability, with a stepwise regression approach used to define areas where rainfall and groundwater levels show the strongest association. Results show that the greatest recharge through direct rainfall is along the Tallahatchie River basin in the northeastern Mississippi Delta, with recharge along the periphery of the LMRAA likely a result of direct water flux from surface hydrologic features.

Potential tree and soil carbon storage in a major historical floodplain forest with disrupted ecological function

Floodplain forests are extremely productive for agriculture and historical floodplain forests have been converted to prime agricultural land throughout the world, resulting in disruption of ecosystem functioning. Given that flooding may increase with climate change and reforestation will increase resiliency to climate change, we tested whether reforested floodplains also have great potential to store carbon and the effects of even modest increases in forested acreage on carbon storage. To calculate potential aboveground biomass in the Lower Mississippi River Alluvial Valley (LMAV) of the United States, we determined current and historical tree biomass used density estimates and diameter distributions from tree surveys and relationships between diameter and biomass from current forests. To calculate potential soil organic carbon if the landscape was forested, we used soil organic matter from soil surveys of the agricultural landscape, and multiplied the carbon by a factors of 1.25, 1.5, and 1.75 based on published reports of soil carbon increases due to afforestation. Our results showed that area-weighted mean biomass density (trees ≥12.7 cm in diameter) for historical forests was 300 Mg/ha, ranging from 228 Mg/ha to 332 Mg/ha by ecological subsection, based on the most conservative diameter distribution. Mean biomass density for current forests was 97 Mg/ha, ranging from 92 Mg/ha to 111 Mg/ha. Mean carbon density for agricultural soils was 96 Mg/ha, whereas combined tree and soil carbon densities varied from 169 Mg/ha to 317 Mg/ha; soil carbon accounted for 0.5–0.7 of total carbon density. Historical forested carbon storage in the Missouri LMAV was about 234 TgC, with the most conservative diameter distribution and assuming 80% forest coverage. Current forested carbon storage in the Missouri LMAV is about 2% of historical storage, at 5 TgC in 30,000 ha of forests, but may reach 23 TgC if forested extent almost triples, with the addition of 50,000 ha of marginal agricultural land, and carbon storage increases in trees and soil. The entire LMAV currently stores 97 TgC in forests and reasonable carbon storage for the entire LMAV may be about 335 TgC, based on increased carbon storage and reforestation of 600,000 ha of marginal agricultural land, which would double the current forested extent. Although 335 TgC storage for the LMAV is only about 1.5 times greater than historical carbon storage of the Missouri LMAV, doubling the forested extent will increase other ecosystem functions, including carbon storage, flood abatement, and reduction of fertilizer pollution in the Gulf of Mexico.

Assessment of Spatial Rainfall Variability over the Lower Mississippi River Alluvial Valley

Abstract A large portion of the lower Mississippi River alluvial valley (LMRAV) relies on irrigation from the regional alluvial aquifer for crop sustainability, which is expensive both in terms of water resources and farmer expenditures because of the large volume of water necessary to maintain crop production. As a result, knowledge of the seasonal frequency and distribution of precipitation over the LMRAV is critical for water resources management, the development of irrigation strategies, and economic planning. This project addresses the need for a detailed assessment of regional precipitation patterns through the use of rotated principal component analysis (RPCA) of high-resolution gridded radar-derived rainfall data, which provides quantification of the spatial and temporal characteristics of rainfall over the LMRAV from 1996 to 2011. Results of the project show that precipitation depths over the LMRAV are generally lower and more variable than adjacent eastern areas throughout the year, although there is substantial variability between seasons. This pattern seems to be influenced more by variations during the cool season (January–March), which has a higher overall precipitation depth and lower spatial variability than the warm season (July–September). Results further indicate that warm season rainfall is generally lower and less predictable over the LMRAV as compared to the cool season, which may be detrimental to regional water resources since irrigation planning and permitting is heavily based on seasonal rainfall predictions.

Impacts of reforestation upon sediment load and water outflow in the Lower Yazoo River Watershed, Mississippi

Among the world's largest coastal and river basins, the Lower Mississippi River Alluvial Valley (LMRAV) is one of the most disturbed by human activities. This study ascertained the impacts of reforestation on water outflow attenuation (i.e., water flow out of the watershed outlet) and sediment load reduction in the Lower Yazoo River Watershed (LYRW) within the LMRAV using the US-EPA's BASINS-HSPF model. The model was calibrated and validated with available experimental data prior to its application. Two simulation scenarios were then performed: one was chosen to predict the water outflow and sediment load without reforestation and the other was selected to project the potential impacts of reforestation upon water outflow attenuation and sediment load reduction following the conversion of 25, 50, 75, and 100% of the agricultural lands with most lands near or in the batture of the streams. Comparison of the two simulation scenarios (i.e., with and without reforestation) showed that a conversion of agricultural land into forests attenuated water outflow and reduced sediment load. In general, a two-fold increase in forest land area resulted in approximately a two-fold reduction in annual water outflow volume and sediment load mass, which occurred because forests absorb water and reduce surface water runoff and prevent soil erosion. On average, over a 10-year simulation, the specific water outflow attenuation and sediment load reduction were, respectively, 250m3/ha/y and 4.02metric ton/ha/y. Seasonal variations of water outflow attenuation and sediment load reduction occurred with the maximum attenuation/reduction in winter and the minimum attenuation/reduction in summer. Our load duration curve analysis further confirmed that an increase in forest land area reduced the likelihood of a given sediment load out of the watershed outlet. This study suggests that reforestation in or around the batture of streams is a useful practice for water outflow attenuation and sediment load reduction.

Use of Aquaculture Ponds and Other Habitats by Autumn Migrating Shorebirds Along the Lower Mississippi River

Populations of many shorebird species are declining; habitat loss and degradation are among the leading causes for these declines. Shorebirds use a variety of habitats along interior migratory routes including managed moist soil units, natural wetlands, sandbars, and agricultural lands such as harvested rice fields. Less well known is shorebird use of freshwater aquaculture facilities, such as commercial cat- and crayfish ponds. We compared shorebird habitat use at drained aquaculture ponds, moist soil units, agricultural areas, sandbars and other natural habitat, and a sewage treatment facility in the in the lower Mississippi River Alluvial Valley (LMAV) during autumn 2009. Six species: Least Sandpiper (Calidris minutilla), Killdeer (Charadrius vociferous), Semipalmated Sandpiper (Calidris pusilla), Pectoral Sandpiper (C. melanotos), Black-necked Stilt (Himantopus himantopus), and Lesser Yellowlegs (Tringa flavipes), accounted for 92% of the 31,165 individuals observed. Sewage settling lagoons (83.4, 95% confidence interval [CI] 25.3-141.5 birds/ha), drained aquaculture ponds (33.5, 95% CI 22.4-44.6 birds/ha), and managed moist soil units on public lands (15.7, CI 11.2-20.3 birds/ha) had the highest estimated densities of shorebirds. The estimated 1,100ha of drained aquaculture ponds available during autumn 2009 provided over half of the estimated requirement of 2,000ha by the LMAV Joint Venture working group. However, because of the decline in the aquaculture industry, autumn shorebird habitats in the LMAV may be limited in the near future. Recognition of the current aquaculture habitat trends will be important to the future management activities of federal and state agencies. Should these aquaculture habitat trends continue, there may be a need for wildlife biologists to investigate other habitats that can be managed to offset the current and expected loss of aquaculture acreages. This study illustrates the potential for freshwater aquaculture to provide habitat for a taxa at risk. With the rapid growth of aquaculture worldwide, the practices of this industry deserve attention to identify benefits as well as risks to wildlife.

A Role for Agroforestry in Forest Restoration in the Lower Mississippi Alluvial Valley

Agroforestry options are explored for restoring important functions and values of bottomland hardwood (BLH) forests in the lower Mississippi River Alluvial Valley (LMAV). Agroforestry practices can augment the size and quality of BLH habitat, provide corridors between BLH areas, and enable restoration of natural hydrologic patterns and water quality. Agroforestry practices are designed primarily to benefit agriculture, which may appeal to farmers in the region. Profit potential from some agroforestry practices is currently competitive with agricultural crops and production forestry on marginal agricultural lands in the LMAV. Lack of experience with agroforestry in this region hinders adoption, but emerging markets for biofuels and ecosystem services could enhance future prospects. Concepts are presented for how agroforestry can be located and designed for restoring BLH forest functions and values in the LMAV and thereby contribute to achieving goals for ecological restoration.

Analysis of a Warm-Season Surface-Influenced Mesoscale Convective Boundary in Northwest Mississippi

Abstract The lower Mississippi River alluvial valley in southeastern Arkansas, northeastern Louisiana, and northwestern Mississippi is characterized by widespread agriculture with few urban areas. Land use is predominantly cultivated cropland with minimal topographic variation; the eastern edge of the alluvial valley is defined by a rapid, although small, change in elevation into a heavily forested landscape, however. This change in land use/land cover has been shown to potentially enhance precipitation through generation of a weak mesoscale convective boundary. This project defines the influence of the land surface on associated precipitation processes by simulating a convective rainfall event that was influenced by regional surface features. Analysis was conducted using a high-resolution simulated dataset generated by the Weather Research and Forecasting Model (WRF). Results show that the strongest uplift coincides with an abrupt low-level thermal boundary, developed primarily by a rapid change from sensible to latent heat flux relative to the agricultural and forested areas, respectively. In addition, surface heating over the cultivated landscape appears to destabilize the boundary layer, with precipitation occurring as air is advected across the land cover boundary and the associated thermal gradient. This information can be used to define and predict surface-influenced convective precipitation along agricultural boundaries in other regions where the synoptic environment is weak.

Patterns of differentiation among endangered pondberry populations

Pondberry, Lindera melissifolia, is an endangered and partially clonally reproducing shrub species found in isolated populations that inhabit seasonally wet depressions in forested areas of the lower Mississippi River alluvial valley and southeastern regions of the United States. With eleven microsatellite loci, we quantified population genetic differentiation and diversity among 450 genets in 10 locations distributed across pondberry’s range. We used estimates of F st and Jost’s D est to measure genetic differences between populations and between geographic regions. The largest pairwise regional difference was found between eastern and western regional population groups (F st = 0.23, D est = 0.67), with the northern-most population groups in each region exhibiting larger divergence from each other than the southern-most population groups. Genetic diversity was lowest in the Sand Pond Conservation Area (A e = 1.9, H e = 0.36), which was the northern-most pondberry population, and highest in the Francis Marion National Forest (A e = 4.1, H e = 0.69), although we identified only 17 genets in that admixed population. Following adjustments for estimated null allele frequencies, we identified heterozygote excess in four eastern populations and found no evidence for inbreeding in any population. The observed patterns of differentiation indicate a phylogeography that exhibits an Appalachian Mountain discontinuity coupled with northward migrations along the Southern Atlantic Coastal Plain and into the Mississippi Alluvial Plain. The genetic consequences of this proposed phylogeographical structure may affect selection of germplasm sources for population reestablishment programs across pondberry’s range.

Multilocus patterns of nucleotide polymorphism and demographic change inTaxodium distichum(Cupressaceae) in the lower Mississippi River alluvial valley

Studies of the geographic patterns of genetic variation can give important insights into the past population structure of species. Our study species, Taxodium distichum L. (bald-cypress), prefers riparian and wetland habitats and is widely distributed in southeastern North America and Mexico. We compared the genetic variation of T. distichum with that of its close relative, Cryptomeria japonica, which is endemic to Japan. • Nucleotide polymorphisms of T. distichum in the lower Mississippi River alluvial valley, USA, were examined at 10 nuclear loci. • The average nucleotide diversity at silent sites, π(sil), across the 10 loci in T. distichum was higher than that of C. japonica (π(sil) = 0.00732 and 0.00322, respectively). In T. distichum, Tajima's D values were each negative at 9 out of 10 loci, which suggests a recent population expansion. Maximum-likelihood and Bayesian estimations of the exponential population growth rate (g) of T. distichum populations indicated that this species had expanded approximately at the rate of 1.7-1.0 × 10(-6) per year in the past. • Taxodium distichum had significantly higher nucleotide variation than C. japonica, and its patterns of polymorphism contrasted strikingly with those of the latter, which previously has been inferred to have experienced a reduction in population size.

Habitat associations of chorusing anurans in the Lower Mississippi River Alluvial Valley

Amphibian populations have declined worldwide. To pursue conservation efforts adequately, land managers need more information concerning amphibian habitat requirements. To address this need, we examined relationships between anurans and habitat characteristics of wetlands in the Lower Mississippi River Alluvial Valley (LMAV). We surveyed chorusing anurans in 31 wetlands in 2000 and 28 wetlands in 2001, and measured microhabitat variables along the shoreline within the week following each survey. We recorded 12 species of anurans during our study. Species richness was significantly lower in 2000 than 2001 (t-test, P < 0.001) and correlated with an ongoing drought. We found species richness to be significantly greater at lake sites compared to impoundment, swale, and riverine sites (ANOVA, P = 0.002). We used stepwise regression to investigate the wetland types and microhabitat characteristics associated with species richness of chorusing anurans. Microhabitat characteristics associated with species richness included dense herbaceous vegetation and accumulated litter along the shoreline. Individual species showed species-specific habitat associations. The bronze frog, American bullfrog, and northern cricket frog were positively associated with lake sites (Fisher’s Exact Test, P < 0.05), however wetland type did not significantly influence any additional species. Using bivariate correlations, we found that six of the seven most common species had significant associations with microhabitat variables. Overall, our findings support the view that conservation and enhancement of amphibian communities in the LMAV and elsewhere requires a matrix of diverse wetland types and habitat conditions.

Evaluation of Reforestation in the Lower Mississippi River Alluvial Valley

AbstractOnly about 2.8 million ha of an estimated original 10 million ha of bottomland hardwood forests still exist in the Lower Mississippi River Alluvial Valley (LMAV) of the United States. The U.S. Fish and Wildlife Service, the U.S. Forest Service, and state agencies initiated reforestation efforts in the late 1980s to improve wildlife habitat. We surveyed restorationists responsible for reforestation in the LMAV to determine the magnitude of past and future efforts and to identify major limiting factors. Over the past 10 years, 77,698 ha have been reforested by the agencies represented in our survey and an additional 89,009 ha are targeted in the next 5 years. Oaks are the most commonly planted species and bare‐root seedlings are the most commonly used planting stock. Problems with seedling availability may increase the diversity of plantings in the future. Reforestation in the LMAV is based upon principles of landscape ecology; however, local problems such as herbivory, drought, and flooding often limit success. Broad‐scale hydrologic restoration is needed to fully restore the structural and functional attributes of these systems, but because of drastic and widespread hydrologic alterations and socioeconomic constraints, this goal is generally not realistic. Local hydrologic restoration and creation of specific habitat features needed by some wildlife and fish species warrant attention. More extensive analyses of plantings are needed to evaluate functional success. The Wetland Reserve Program is a positive development, but policies that provide additional financial incentives to landowners for reforestation efforts should be seriously considered.

CHANNEL MIGRATION AND REGENERATION OF BALD CYPRESS IN WESTERN TENNESSEE

Bald cypress (Taxodium distichum) regeneration was examined in the bottomland forest of the lower Hatchie River in western Tennessee. Bald cypress is found mostly in abandoned meanders. Its absence along the active channel indicates that colonization begins after the meander cuts off, creating an oxbow lake. Analysis of the size, the age, and the spatial structure of the stands indicates that the individuals first establish along the margins of the lake, and then colonize the interior as the lake fills in and new surfaces are exposed. Bald cypress will dominate abandoned meanders for several centuries. However, it will not regenerate in stands with a well-developed forest canopy. Bald cypress is eventually replaced by shade tolerant species and, therefore, only rarely occurs on older surfaces. Channel migration and the subsequent creation of oxbows will maintain bald cypress as a major component of bottomland forests. However, many of the major streams in the lower Mississippi River alluvial valley have b...

Old River: Foundation Design

The low-sill structure, the overbank control structure, and the navigation lock that are being constructed for the diversion control of the Old River are founded on a variety of soil types that are typical of those found in the lower Mississippi River alluvial valley. Detailed descriptions are given of the foundation conditions for the low-sill structure, which is a gated weir having its base approximately 50 ft below the ground surface and which is founded on silty soils that extend another 50 ft below the structure. Important considerations in design were excavation dewatering, seepage control, design of pile foundation, and preload fills at the abutments to minimize settlements.