Evaluating EM Mudball Density Effects on Ammonia Reduction in Stormwater Ponds

Abstract

Urban stormwater retention ponds are essential infrastructures for managing runoff. However, their functional performance is often compromised by elevated ammoniacal nitrogen (NH₃-N) concentrations resulting from nutrient accumulation, organic loading, and prolonged low flow conditions, particularly in tropical environments. This degradation not only affects water quality but also limits ecological functionality and long-term sustainability. While Nature-Based Solutions (NbS), such as Effective Microorganism (EM) mudballs, have gained cumulative consideration as low-cost and environmentally responsive remediation approaches, existing studies primarily focus on overall water quality improvements, with limited emphasis on the influence of application design parameters. In particular, the role of mudball density as a determinant of ammonia removal efficiency remains insufficiently explored, restricting the development of evidence-based and scalable implementation strategies. This study aims to explore the effect of EM mudball application density on ammonia reduction in a stormwater retention pond. The objectives are to determine changes in NH₃-N concentrations before and after the intervention, to identify spatial variations across the inlet, mid-pond, and outlet zones, and to assess the effectiveness of a defined mudball density in enhancing ammonia removal performance. A quantitative field-based approach was employed in a campus-scale stormwater retention pond characterised by low flow conditions. Water quality data were collected from three sampling points (n=3) representing functional zones. In-situ measurements were conducted using a multiparameter probe, focusing on NH₃-N as the primary indicator, with support from dissolved oxygen (DO), pH, temperature, and electrical conductivity (EC). A total of 1,365 EM mudballs were applied at an estimated density of 1.28 mudballs/m². Baseline and multiple post-intervention measurements were conducted to evaluate temporal and spatial treatment performance. The findings indicate a substantial reduction in NH₃-N concentrations, with a decrease of approximately 65%, demonstrating effective nutrient removal associated with enhanced microbial activity. Spatial analysis shows consistent reduction trends across all sampling zones, with greater responsiveness observed near inflow areas. Supporting parameters reveal moderate improvements in DO and reductions in EC of approximately 44%, while pH and temperature remained stable. However, the study is limited by a single-density approach and a short-term monitoring period, which constrain the identification of optimal thresholds. Nevertheless, the study provides empirical evidence linking mudball density to ammonia removal efficiency and offers practical implications for developing scalable, low-cost NbS strategies in urban stormwater management.