Saprobic Trophic Approach as a Biological Indicator for Eutrophication Management in Cengklik Reservoir, Boyolali, Central Java

Eutrophication is a serious environmental problem in tropical reservoirs, triggered by human activities like floating net cages and agriculture activity. Its consequences, such as massive water hyacinth growth, directly threaten sustainable water resources and impede the achievement of SDGs 6 and 14. This study assessed the saprobic trophic approach as a sensitive indicator for monitoring eutrophication in Cengklik Reservoir, Boyolali. Analysis utilized secondary water quality data (DO, BOD, nitrate, and phosphate) to evaluate the organic pollution load. Results indicated the reservoir water conditions tend to be mesosaprobic and chronic eutrophication confirming a moderate to high organic pollution load. Strong correlations were found between high nitrate/phosphate concentrations and the observed saprobic levels, supporting the visual evidence of abundant water hyacinth. The saprobic trophic approach is confirmed as an effective biological indicator that complements water chemistry. Long-term trend data (BOD, DO, Nitrate, Phosphate 2020-2024) is an innovative decision support tool for water resource monitoring and management. Policy and governance implications: this swift, ecological indicator provides crucial data for evidence-based decision-making and stricter pollution control policies on nutrient discharge. Routine monitoring with this approach is vital for achieving sustainable water governance and supporting SDGs 6.3 (water quality) and 14.1 (nutrient pollution reduction) in the Cengklik Reservoir.