Effective microorganisms-based bioremediation for improving water and sediment quality in Ponjavica Nature Park (Serbia): A case study of sustainable aquatic ecosystem restoration

Anthropogenic pressures are increasingly degrading protected freshwater ecosystems, particularly eutrophic systems affected by sediment accumulation. Although Effective Microorganisms (EM) have been proposed as an eco-friendly bioremediation approach, field-based evidence from protected freshwater systems under real management constraints remains limited. This study evaluated the effectiveness of EM-based treatment in improving microbiological and physicochemical water and sediment quality in Ponjavica Nature Park (Serbia), a protected eutrophic wetland exposed to long-term anthropogenic pressures. Water and sediment samples were collected before and after EM application to assess changes in key microbiological indicators and organic pollution parameters. The results showed measurable improvements in water quality following EM treatment. Total coliform counts decreased by up to 50% (5,860–6,440 MPN/100 mL), faecal coliforms ( Escherichia coli ) fell below detection limits (<100 MPN/100 mL), intestinal enterococci decreased to < 40 MPN/100 mL, and aerobic heterotrophic bacteria declined slightly. Biochemical oxygen demand (BOD 5 ) remained consistently below 3.0 mg O 2 /L, indicating effective microbial degradation of organic matter, while chemical oxygen demand (COD) ranged from 66.9 to 98.9 mg O 2 /L, with localised increases associated with sediment disturbance. Overall, water quality classification improved at several monitoring sites according to national standards. Rather than proposing EM as a substitute for conventional remediation technologies, this study demonstrates its potential to provide environmentally acceptable short-term improvements in water quality in protected freshwater systems where financial, technical, and ecological constraints limit engineering interventions. The applied approach offers a transferable framework for similar eutrophic and sediment-impacted aquatic environments.