Mangrove abundance, diversity, and productivity in effluent-rich estuarine portion of Butuanon River, Mandaue City, Cebu

Mangrove vegetation represents one of the most diverse and productive coastal ecosystems globally. However, mangroves located at the mouth of the Butuanon River (Class D) in Mandaue City are subjected to significant effluent discharge from surrounding urban areas. Despite this environmental stress, the impact of such pollution on mangrove health remains understudied. This study investigates the relationship between effluent and sediment parameters and mangrove diversity, abundance, and productivity along the Butuanon River. Five sampling stations were randomly established, where mangrove species identification, quantification, diversity assessment, productivity measurements, and physicochemical analyses (water and sediment) were conducted. Multivariate statistical analyses, including Detrended Correspondence Analysis (DCA), Non-Metric Multidimensional Scaling (NMDS), Analysis of Similarities (ANOSIM), and Pearson’s correlation, were employed to evaluate ecological patterns. Results indicate a decline in mangrove diversity, attributed to the dominance of Avicennia alba. Key physicochemical parameters such as water hardness, pH, salinity, and temperature exhibited an inverse relationship with mangrove abundance, diversity, and productivity, unlike biochemical oxygen demand (BOD). However, these parameters had minimal impact on the resilient A. alba. Productivity trends revealed higher mangrove productivity at upstream sites, decreasing toward the river mouth. These findings suggest that the Butuanon River’s mangrove ecosystem is critically degraded, with poor productivity and biodiversity loss driven by effluent pollution. Urgent remediation measures are needed to mitigate further ecological decline and preserve this vital coastal habitat.