Spatiotemporal Variations of Chemical Compositions through Empirical Modeling in Bartlett Pond, Laredo, Texas

Abstract

Surface water samples were collected from a small, shallow wetland Bartlett pond in Laredo, Southern Texas, to investigate the factors controlling water quality parameters and their spatiotemporal variation within the ecosystem. The major cations and anions occurred in the following order: Na + ≫ Ca 2+ > Mg 2+ ≈ K + and HCO 3 − ≈ Cl − > SO 4 2 − ≫ NO 3 − ≫ PO 4 3 − , respectively. Marine aerosols were the primary source for most of the magnesium (76%) and sodium (73%) concentrations, while contributing only minor proportions of potassium (17%) and calcium (4.5%). In addition to contributions from marine aerosols, the weathering of minerals, primarily carbonate and siliciclastic, plays a key role in regulating the pond’s water chemistry. We observed strong seasonal control on chemical compositions but minor spatial variation trends within the pond. A comprehensive multivariate regression analysis was conducted to evaluate the biogeochemical controls on water quality in Bartlett Pond across seasonal cycles. Seventeen major physicochemical parameters including water temperature, pH, EC, TDS, major base cations (Ca 2+ , Mg 2+ , Na + , K + ), anions (Cl − , NO 3 − , SO 4 2 − , PO 4 3 − , HCO 3 − ), and other parameters such as Hardness, Alkalinity, SAR, and Boron were analyzed through 43 predictive models, yielding a total of 265 regression coefficients. The models explained substantial proportions of variance (R 2 = 0.64 to 1.00), revealing strong interdependencies among ionic constituents. Obviously, Total Dissolved Solids (TDS) and Electrical Conductivity (EC) exhibited robust predictive capacity for ionic strength, while NO 3 − , PO 4 3 − , and SAR emerged as sensitive indicators of both geochemical weathering and anthropogenic inputs. Phosphate appeared as a limiting nutrient, and nitrate drastically decreased during summer months, suggesting increased photosynthetic activities and consequently gross primary productivity (GPP) increases within this shallow pond. Seasonal variations reflected shifts between carbonate equilibrium, nutrient cycling, and evaporative concentration effects. The integrated regression framework provides quantitative insight into the hydrological-geochemical coupling governing small pond systems under variable seasonal influences.