Low grade rip rap weirs installed in agricultural surface drainage ditches manage downstream eutrophication by slowing water flow, allowing sediments time to settle out of the water column and phosphorus (P) to sorb to soil. A laboratory experiment was conducted in microcosm chambers to simulate increased hydraulic residence time caused by weirs and two field studies were conducted to compare experimental data with field data and determine sediment deposition rates. One field study monitored weirs monthly after installation and the other measured weirs of varying ages. Weirs retained significantly more water and sediment than controls. Longer inundation times led to abiotic factors known to release P during hydrologic flux, but did not translate to reduced P storage. By converting intermittently inundated sediments into more consistently saturated sediments, weirs function as a viable conservation practice for about a year until temporary P retention mechanisms and sediment retention capacities are reached.

Estimates of abundance are critical to manage and conserve waterfowl and their habitats. Most surveys of wintering waterfowl do not use probability sampling; therefore, development of more rigorous methods is needed. In response, I designed and evaluated an aerial transect survey to estimate abundance of wintering ducks in western Mississippi during winters 2002?2004. I designed a probability-based survey using stratified random and unequal probability sampling of fixed-width transects. To correct for visibility bias inherent in aerial surveys, I conducted an experiment to model bias and incorporated correction factors into estimation procedures to produce adjusted estimates. Bias-corrected estimates were most accurate. Precision of abundance estimates of total ducks met a priori goals (CV ≤ 15%) in 10 of 14 surveys. Based on a simulation study, the implemented survey design provided the most precise estimates, yet certain refinements remained possible. I also illustrated potential applications of survey results in the context of conservation and management of wintering waterfowl populations and habitats. I described patterns of abundance within and among winters, including a comparison with surveys conducted during winters 1988?1990 that revealed mallard abundance decreased 65% from the late 1980s. I developed a method to illustrate population abundance spatially for scientific and public education. I attempted to explain temporal variation in abundance estimates relative to variables potentially representing hypotheses explaining regional distributions of ducks. I concluded the data provided stronger support for factors related to energy conservation by ducks than factors related to energy acquisition. Finally, I determined associations between duck distributions and habitat and landscape features in accordance with the habitat-complex conceptual model. Landscapes with greater interspersion and diversity of wetlands attracted increased numbers of ducks, a though other factors such as wetland area also were important. I concluded that this study advanced methodologies to survey wintering waterfowl. Although improvements were warranted, I recommend this survey design for continued monitoring of wintering ducks in western Mississippi. Furthermore, I suggest habitat management on public and private lands should include complexes of seasonally flooded cropland, moist-soil, forested, and permanent wetlands to potentially increase wintering duck numbers in western Mississippi.

Grain sorghum provides energy-rich seeds for waterfowl. I conducted experiments in 22 sorghum fields in Arkansas, Mississippi, and Louisiana during falls 2006 – 2007 to evaluate abundance of ratoon grain (i.e., second crop after harvest), waste grain, and natural seeds. I also conducted surveys of wintering waterfowl in flooded croplands and moist-soil wetlands to evaluate if ducks and geese differentially used habitats. Fertilized plots in 2007 produced >4 times more ratoon grain (x = 219.57 ± 39.65 [SE] kg/ha) than other treatments. Fertilized plots in southern regions of my study area produced ~5 times more ratoon grain (x = 262.93 ± 50.28 kg/ha) than others. Mallards and other ducks used moist-soil wetlands (x >65 ducks/ha) more than other habitats. I did not observe geese using flooded sorghum. I recommend not manipulating sorghum stubble after harvest, fertilizing, and flooding it after ratoon grain has matured, and integrating moist-soil wetlands into agricultural lands.

Dramatic alterations have occurred on agricultural landscapes throughout North America, reducing the quantities of herbaceous habitat that once dominated field margins. A concomitant decrease of grassland bird populations paralleled these modifications. Conservation buffers, in the form of field borders, are a method of habitat establishment that effectively balances wildlife and landowner needs. Recent popularity of field borders led to their establishment throughout the southeastern US despite a paucity of knowledge regarding avian response to management regimes. This research evaluated wintering and breeding avian communities, as well as nesting ecology in response to field border establishment. Results indicated that birds utilize field borders for various life history requirements. Field borders provided enhanced avian benefits over traditional farm practices; and borders of widths >10 m were superior nesting habitat than more narrow borders. Based on these results, we strongly recommend field border establishment to enhance ecosystem integrity on farm landscapes.

Submitted by (lucia.rodrigues@ufrpe.br) on 2016-10-05T15:02:05Z No. of bitstreams: 1 Julio Jose do Nascimento Silva.pdf: 6372867 bytes, checksum: 695188902789532f6851de1b788672bc (MD5) / Made available in DSpace on 2016-10-05T15:02:05Z (GMT). No. of bitstreams: 1 Julio Jose do Nascimento Silva.pdf: 6372867 bytes, checksum: 695188902789532f6851de1b788672bc (MD5) Previous issue date: 2008-02-29 / Conselho Nacional de Pesquisa e Desenvolvimento Científico e Tecnológico - CNPq / The aim of this study was to evaluate the potential of the castor bean culture in an alluvial valley of Pernambuco Agreste. The research was conducted in the Nossa Senhora do Rosário farm, Pesqueira-PE. It was cultivated the BRS 188 – Paraguaçu castor bean, which according to the literature is suitable to the local conditions. The cultivation experiment started up on 15/03/2007, finishing his first stage on 31/10/07. In this period, the experiment was conducted on a dry condition, with only one irrigation application of 12 mm. Therefore, the soil and climate conditions were evaluated wider which where the culture was developed, such as soil texture, electrical conductivity of the saturation extract (CEes), average soil fertility, reference evapotranspiration (ET0). Based on the Tanque Class "A" and employing crop coefficient for castor bean suggested by culture FAO, it was estimated the crop evapotranspiration (ETc). The parameters evaluated were the height of the plants, stem diameter, leaf area index and productivity. All these parameters were estimated using descriptive statistics. It has been observed mean values of 1.48 dS.m-1 for CEes, before planting, and of 0.96 dS.m-1 at the end of the cycle, at sandy-loam area. The ETo average over the cycle was 2.98 mm.day-1 and ETc of 2.08 mm.day-1, while the average soil water matric potential was -27.97 kPa. By the end of1° cycle, the plants were 3.32 m tall with a diameter of 65 mm; regarding the estimation of the leaf area, a value of 4.42 m has been obtained of highest vegetative growth, and the approximate yield was 2900 kg.ha-1. On the other hand, it was also used geoestatistics techniques to observe the degree of dependency for the attributes and the spatial variability of soil, texture and CEes, and the attributes crop stem diameter and height of the plants. All parameters adjusted to a normal distribution, except free with the exception of stem diameter, for 200 days after sowing, showing a medium to low degree of spatial dependence. None of the variables showed pure nugget effect, adjusting to theoretical models for the semivariograms. The contour maps produced isolinhas the observation of the most heterogeneous areas, where a local management strategy can be developed. / Objetivou-se com este trabalho foi avaliar o potencial da cultura da mamoneira em vales aluviais no Agreste de Pernambuco. A pesquisa foi conduzida na Fazenda Nossa Senhora do Rosário, Pesqueira-PE. Utilizou-se a cultivar BRS 188 – Paraguaçu, que segundo a literatura se adequa às condições locais. O cultivo experimental iniciou-se no dia 15/03/2007, terminando seu primeiro ciclo no dia 31/10/07. Neste período, o plantio foi conduzido em regime de sequeiro, havendo apenas uma irrigação de salvação de 12 mm. Para tanto, foram avaliadas as condições edafoclimáticas em que se desenvolveu a cultura, como granulometria do solo, condutividade elétrica do extrato de saturação (CEes), fertilidade média do solo, evapotranspiração de referência (ETo). Pelo Tanque Classe “A” e adotando-se coeficiente de cultura para mamona da FAO, estimou-se a evapotranspiração da cultura (ETc). Os parâmetros avaliados da cultura foram a altura de plantas, diâmetro caulinar, índice de área foliar e produtividade. Todos estes parâmetros foram estimados por meio de estatística descritiva, onde se observou os valores médios de CEes de 1,48 dS.m-1, antes do plantio, e de 0,96 dS m-1 no final do ciclo, com classe textural franco arenosa. A ETo média durante o ciclo foi de 2,98 mm.dia-1 e a ETc de 2,08 mm.dia-1, enquanto o potencial matricial médio da águado solo foi de -27.97 kPa. As plantas alcançaram, até o final do 1° ciclo, 3,32 m de altura com diâmetro caulinar de 65 mm, no tocante à estimativa da área foliar, obteve-se valor de 4,42 m², no período de maior desenvolvimento vegetativo, e a produtividade estimada foi de 2900 kg.ha-1, média do experimento. Outrossim, utilizou-se também técnicas geoestatísticas para observar o grau de dependência e a variabilidade espacial dos atributos de solo, granulometria e CEes, bem como dos atributos de crescimento diâmetro caulinar e altura das plantas. Todos os parâmetros se ajustaram a uma distribuição Normal, com exceção do diâmetro caulinar aos 200 dias após a semeadura, e apresentou de médio a baixo grau de dependência espacial. Nenhuma das variáveis estudadas apresentou efeito pepita puro, ajustando-se modelos teóricos aos semivariogramas experimentais. Os mapas de isolinhas que foram produzidos permitiram observar regiões mais heterogêneas, onde um manejo localizado da área pode ser desenvolvido.

In 2019, the Mississippi River watershed had a record-long flooding, which was comparable with the 1927 Great Mississippi River Flood. This study leveraged this flooded condition to assess the flood tolerance of eastern cottonwood (Populus deltoides) and black willow (Salix nigra) planted as short rotation woody crops (SRWCs) on seasonally flooded marginal land of the Lower Mississippi Alluvial Valley (LMAV) in 2018. The survival/mortality prediction models developed by using hydrologic and environmental variables suggested that only high flood depth affected the survival of black willow. However, eastern cottonwood was threatened by flood depth, flood duration, and cumulative flooding temperature calculated by summing air temperatures while trees were flooded in 2019, 2020, and 2021. During the growing season, the models predicted that black willow could tolerate flood depth of 1.38 m in April, 1.52 m in May, and 0.74 m in June, while eastern cottonwood could tolerate 1.18 m in April, 0.86 m in May, and 0.85 m in June. Due to having higher flood tolerance thresholds, black willow had better survival and biomass production than eastern cottonwood. This study also identified critical physiological parameters that affected the biomass productivity of eastern cottonwood, black willow, and American sycamore (Platanus occidentalis). Results showed that the growth of black willow was driven by nitrogen per unit leaf area (R2 = 0.41 and P-value = 0.004) and photosynthetic nitrogen use efficiency (R2 = 0.27 and P-value = 0.03); American sycamore was determined by stomatal conductance (R2 = 0.68 and P-value = 0.04) and transpiration rate (R2 = 0.70 and P-value = 0.04); and eastern cottonwood was not affected by either water or nitrogen factors. Understanding physiological strategies of these species provides useful information when matching site-species for riparian restoration in the LMAV. This study also found that a SRWC plantation could mitigate agricultural runoff by removing 78 to 83% of nitrate-nitrogen and 70 to 73% of orthophosphate-phosphorus from the groundwater before discharge to the Yazoo River. Therefore, rather than abandoning these areas, establishing SRWC plantations for bioenergy on marginal cropland can mitigate agricultural nutrient runoff and improve the water quality of the LMAV.

This research investigated hydrologic connectivity, the intricate network of water pathways linking waterbodies, and its implications for biodiversity exchange in floodplains. Chapter 1 provides an exhaustive literature review encompassing factors influencing hydrologic connectivity, assessment approaches, scales, challenges, and management tools. Existing research often focuses on single scales and short-term periods, revealing a need for comprehensive multi-scale and extended temporal analyses. The absence of standardized definitions and methodologies in this field is also considered. Chapter 2 presents an innovative approach quantifying eight key connectivity metrics using remote sensing and GIS within the Lower Mississippi Alluvial Valley (LMAV). This adaptable method assesses connectivity between oxbow lakes and varying stream sizes, revealing spatial variability within the LMAV and enhancing scientific understanding of connectivity dynamics while ensuring portability. This research is crucial for effective ecosystem management and targeted conservation efforts, particularly regarding invasive species like the bigheaded carps (Hypophthalmichthys spp.).

This study identified marginal agricultural lands in the Lower Mississippi Alluvial Valley using crop yield predicting models. The Random Forest Regression (RFR) and Multiple Linear Regression (MLR) models were trained and validated using county-level crop yield data, climate data, soil properties, and Normalized Difference Vegetation Index (NDVI). The RFR model outperformed MLR model in estimating soybean and corn yields, with an index of agreement (d) of 0.98 and 0.96, Nash-Sutcliffe model efficiency (NSE) of 0.88 and 0.93, and root mean square error (RMSE) of 9.34% and 5.84%, respectively. Marginal agricultural lands were estimated to 26,366 hectares using cost and sales price in 2021 while they were estimated to 623,566 hectares using average cost and sales price from 2016 to 2021. The results provide valuable information for land use planners and farmers to update field crops and plan alternative land uses that can generate higher returns while conserving these marginal lands.