Spatial relationship of groundwater–phosphorus interaction in the Kissimmee river basin, South Florida Y. Assegid, 1 A. M. Melesse 1 * and G. M. Naja 2 1 Department of Earth and Environment, Florida International University, FL, USA 2 Science Department, Everglades Foundation, Miami, FL, USA Abstract: Fluctuations of groundwater levels were used to predict soluble phosphorus concentrations. In-situ observations showed a decrease in soluble phosphorus during groundwater recession and an increase with groundwater rise. A spatial analysis of the simulated soluble phosphorus and groundwater levels indicated similarity of patterns (spatial correlation) 99% of the time. A geographically weighted multivariate analysis of soluble phosphorus using groundwater levels, phosphorus levels of the Kissimmee River, and distance from the Kissimmee River as predictors showed a goodness of fit(R 2 ) ranging from 0.2 to 0.7. Results indicated no significant difference between the simulated and observed soluble phosphorus levels at a p value of 0.01. Among the parameters, the groundwater level explained 70% of the soluble phosphorus variability. The distance to surface waterbodies and their phosphorus levels had significant weights only within a 5-km range from the waterbody. A model generalization is further required to simulate the spatiotemporal groundwater–phosphorus dynamics over meaningful temporal ranges – at least for 3 to 5years – for conclusiveness of the data. Copyright © 2014 John Wiley & Sons, Ltd. KEY WORDS soluble phosphorus; groundwater fluctuation; South Florida; Kissimmee River; weighted multivariate analysis Received 1 May 2013; Accepted 4 May 2014 INTRODUCTION Phosphorus (P) over-enrichment of natural waters has emerged as one of the leading causes of water quality impairment (Verhoeven et al., 2006). Increased P concentrations can lead to eutrophication causing exten- sive algal blooms, destroying aquatic life in affected areas, and posing a direct threat to humans (Conley et al., 2009). The rise in eutrophic events can be attributed to the rapid increase in intensive agricultural practices, indus- trial activities, and population growth which have increased nutrient flows into the environment (Bennett et al., 2001). This rapidly growing environmental crisis with worldwide impacts not only poses a direct threat to humans but also has economic consequences (Lu and Hodgkiss, 2004). Protecting and monitoring our freshwater ecosystems are major concerns for many local and state agencies because of expense and time requirements (Sawaya et al., 2003). Moreover, there is a high level of technical complexity and logistical problems involved with mon- itoring large systems as discussed by Harvey et al. (2004). Watershed-based models are alternative methods to assess levels of water quality parameters and transport in a large watershed with a high precision. In Chebud et al. (2011), soluble and sequestered P levels were simulated with a 13% error level using a watershed-based model called watershed assessment model or WAM. Gornak and Zhang (1999) also reported localized field scale models for estimation of nutrient dynamics involving different land uses. However, the high resolution of data required as inputs such as land use, management practices, soil types, and climatic data pose a challenge to make use of field scale models for operational prediction on a routine basis. A viable option would be the development of data-driven models (Chebud and Melesse, 2011; Chebud and Melesse, 2012) through the use of economical data acquisition techniques such as remote sensing (Chebud et al., 2012). South Florida (SF) ecosystem, encompassing a region of more than 67 000 km 2 representing a unique combina- tion of ecological diversity, is under intensified water management (canal dredging, channelization, and drain- age). This ecosystem is mainly governed by a vast wetland system, karst surficial hydrogeology, and an extended coastal boundary with the Atlantic Ocean. South Florida Water Management District (SFWMD) has an extensive monitoring network with over 1834 stations as *Correspondence to: A. M. Melesse, Department of Earth and Environment, Florida International University, FL, USA. E-mail: melessea@fiu.edu HYDROLOGICAL PROCESSES Hydrol. Process. (2014) Published online in Wiley Online Library (wileyonlinelibrary.com) DOI: 10.1002/hyp.10241 Copyright © 2014 John Wiley & Sons, Ltd.