Effects of Future Land Use Variability on Nutrient Loads in a Fast-Urbanizing Landscape

Abstract

Urbanization, driven by population growth, alters watershed hydrology and nutrient runoff. However, the complex interplay between urbanization and nutrients in regional watersheds remains an open question. This study assessed how urbanization affects streamflow, total nitrogen (TN), and total phosphorus (TP) loads in six diverse Florida watersheds covering an area of 10,600 km². This was carried out by introducing 2070 land use/land cover (LULC) projections to a watershed hydrology/water quality model. We investigated how different levels of urban density, as a proxy for urbanization patterns, affect streamflow and nutrient variability. Results indicate that urban land could increase from 14% to 27% in 2070. This expansion could lead to monthly streamflow increases of 0%–36%, based on watershed and urbanization patterns. Future TP loads could change by −8% to +140%, with decreases attributed to LULC transitions from high-use fertilizer agriculture to low/medium density residential classes. Projected TN loads are more consistent, with simulated changes of −1% to +26%. Among LULC transitions, the largest increases in TP and TN are caused by potential urbanization of freshwater wetlands. This study provides knowledge relevant to regions undergoing similar urbanization trends, enabling managers to make better land development plans with water quality considerations. It also contributes a detailed modeling framework that can be adopted even with the use of different LULC datasets and software.