Date of Award
12-1-2025
Degree Name
Master of Science
Department
Geology
First Advisor
Lefticariu, Liliana
Abstract
Riparian wetlands serve as transition areas connecting terrestrial and aquatic ecosystems, providing vital functions in maintaining water quality and habitat for diverse array of organisms. A comprehensive understanding of the interaction between surface water (SW) and groundwater (GW) in riparian wetlands is crucial for the management of these ecologically significant habitats. However, the interactions between SW and GW are often only partially constrained particularly with respect to their effects on water chemistry and nutrient cycling.In this study I utilized geochemical and hydrological approaches to examine the dynamics of surface water and groundwater interactions within the riparian wetlands of the Dogtooth Bend, a region along the Mississippi River in Alexander County, Illinois. The study involved the collection of surface water and groundwater from six riparian wetlands namely Grand Lake (GL), Bayou Stony (BS), Lake Milligan (LM), Big Cypress (BC), Central Bend (CB) and Santa Fe (SF), from the August 2022 to November 2023. Additional surface water samples were collected from the Mississippi River at Thebes Illinois and the Horseshoe Lake (HSL), located northwest to the studied wetlands in southern Illinois. To evaluate the spatial and temporal hydrological and geochemical trends, various parameters were measured both in the field and in the laboratory. In the field, I assessed the presence of surface water and groundwater and when the water was present, I measured the water level elevation in the wells. Collected water samples were assessed for physico-chemical attributes, including pH, temperature, dissolved oxygen (DO), oxidation reduction potential (ORP) using the YSI 626904 ProDSS instrument sensor. In the laboratory, I measured the concentration of ammonia (NH3), hydrogen sulfide (H2S), ferrous iron (Fe2+), and alkalinity using Hach® methodologies. The concentration of chloride (Cl-), sulfate (SO42-), and nitrate (NO3- ) was determine using Thermo Fisher Integrion HPIC system in unison with a Dionex AS-DV auto sampler. Quantification of total organic carbon (TOC), total nitrogen (TN) and total phosphorus (TP) concentrations was carried out at the J.F. Costello Confluence Field Station Environmental Chemistry Laboratory at the National Great Rivers Research and Education Center located in Alton Illinois. The TOC values were determined by analyzing the unfiltered water samples via a VarioTOC select combustion analysis while the TP and TN measurements were made utilizing the methods described in the National Environmental Methods Index ID I-4650-03. The stable isotopes of water (δ2HVSMOW and δ18OVSMOW)) and dissolved nitrate (δ15NNO3- and δ18ONO3- ) were determined by the UC Davis Stable Isotope Facility using standard methods. To provide a more robust data set from which to inform my interpretations of the hydrological and geochemical trends in the riparian wetlands at Dogtooth Bend, I added to my data previously collected from 2021 to 2022 at the same locations by Genz (2023). The isotopic signature of water samples from the SR-SW, CB-SW and SF-SW are similar to those of local precipitation suggesting a meteoric origin. Nitrate (NO₃⁻) concentrations show varying correlation patterns across Dogtooth Bend, indicating site-specific nutrient transfer pathways. Strong correlations (SR-GW and SR-SW, r = 0.89) suggest active surface–groundwater interaction, while negative correlations (e.g., LM-GW and LM-SW, r = -0.44) imply limited connectivity and distinct nitrate sources. The isotope data analysis for δ15NNO3- and δ18ONO3- shows that the sources of nitrate were fertilizers, precipitation and soil organic N. TN and TP concentrations varied significantly among sites, with correlation analyses indicating possible links to mineralization, redox cycling, and Fe²⁺ interactions. Notably, strong correlations between TP and Fe²⁺ (r = 0.82) highlight redox-driven phosphorus mobilization, while TN correlations varied widely, reflecting localized biotic and abiotic nitrogen cycling. Cl⁻ concentrations shows high statistical significance between surface and groundwater at sites such as Tbebes vs. GL-GW (P = 0.00) and THEBES vs. SR-GW (P = 0.00), while showing no significant differences with CB-GW (P = 0.89), suggesting localized recharge or mixing patterns. Similarly, SO₄²⁻ showed strong differences across some sites (GL-GW and BC-GW, r = 0.45), with weak positive correlations indicative of redox-driven transformations. This overall complex interplay of external influences, direct hydrological pathways, and active biogeochemical processes, including coupled Fe2+/TP cycling ultimately drives the observed geochemical variations and similarities in GW and SW across the Dogtooth Bend wetlands. These findings highlight the importance of integrated surface water and groundwater management in wetland conservation, as site-specific processes can influence nutrient transport, water quality, and ecological function.
Access
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