Background. The Meycauayan River is considered one of the most severely polluted rivers in the Philippines due to heavy metal and organic pollution that has caused environmental degradation. Objectives. The aim of the present study was to provide insight on the current status of the Meycauayan River and outline an appropriate strategy to solve problems of organic and heavy metal contamination. Methods. The physical, chemical and biological characteristics of the water and sediments were analyzed and evaluated based on available local and international standards. Three sites (upstream, midstream and downstream) of the river were considered for the evaluation of water and sediment quality. Results. Dissolved oxygen, measured in the morning, was very low at the upstream sampling station (1.87 ppm) and even lower at the downstream site (0.49 ppm). The temperature for the three sites ranged from 28.03°C (upstream) to 30.75°C (downstream). Visual inspection indicated that the color of the water was gray upstream and midstream, and black at the downstream station. Biochemical oxygen demand exceeded the recommended limits of the Department of Environment and Natural Resources (DENR) of 7.0 ppm with values of 13.22 ppm (upstream) and 12.02 ppm (downstream). Chemical oxygen demand exceeded the limit of 20 ppm at the downstream site at 84 ppm. Dissolved oxygen did not reach the recommended limit of 5.0 ppm of the DENR. There was a high coliform count at both the upstream (3.5 × 104 colony-forming unit (cfu)/ml) and downstream (2.5 × 104) sites, which exceeded the limit of the United States Environmental Protection Agency (USEPA) of 126 cfu/100 ml. Heavy metals such lead (Pb), zinc (Zn), copper (Cu), manganese (Mn) and chromium (Cr) exceeded the severe effect level of the National Oceanic and Atmospheric Administration (NOAA), which could be detrimental to humans and aquatic life. The results of one-way analysis of variance showed significant differences (p <0.001) in pH, temperature, dissolved oxygen, conductivity, total dissolved solids, chemical oxygen demand, nitrates and phosphates for water quality and Pb, Zn, Cu, Mn and Cr for sediment quality across the study sites. Conclusions. The results of the present study indicate that the downstream site was more polluted, possibly due to the accumulation of pollutants coming from the upstream site. The deterioration of the Meycauayan River is a result of rapid industrialization, urbanization and population growth. Examination of the water quality of the Meycauayan River indicates that it is very polluted and requires an immediate solution. The results of the present study should be used as a basis for crafting strategies to rehabilitate the Meycauayan River. Competing Interests. The authors declare no competing financial interests. This study was funded by Pure Earth.

Background.Water quality in the Marilao-Meycauayan-Obando river system (MMORS) of Bulacan, the Philippines, is of great concern due to the pollution load from local industries. The river system is currently used as a source of water for the aquaculture industry in Bulacan.Objectives.In order to address organic and heavy metal pollution, several remediation strategies were tested in aquaculture ponds along the river system. Strategies such as phytoremediation (vetiver grass pontoons), application of probiotics and zeolite (with filtration as pre-treatment) were utilized in ponds to decrease or remove toxic pollutants in water and sediments.Methods.Two sites were chosen as the pilot remediation sites – ponds in Barangay Nagbalon, Marilao and Barangay Liputan, Meycauayan, Bulacan. Pond bottom preparation was done to improve the condition of the pond bottom sediments before stocking by adding zeolite. Physicochemical parameters of water such as dissolved oxygen (DO), temperature, pH, salinity, ammonia, phosphate, biochemical oxygen demand (BOD) and chemical oxygen demand (COD) were monitored throughout the culture period. Heavy metals in sediments and fish were monitored. Fish parameters such as average body weight and feed conversion ratio were determined.Results.The DO levels were below recommended levels in the morning and reached a supersaturated level in the afternoon. Ammonia and COD levels were above recommended limits. A decreasing trend was observed for ammonia levels in treatment ponds. In terms of the growth of milkfish, the pond with probiotics showed the highest growth and better feed conversion ratio in Nagbalon and in the phytoremediation pond in Liputan. Percentage survival of milkfish was much higher at Liputan. Copper, chromium, lead and manganese were detected in pond sediments. After application of zeolite, there was a decrease in lead levels throughout the culture period.Conclusions.The different remediation studies were compared in terms of cost, effectivity and application and phytoremediation (vetiver grass pontoons) was determined to be the most cost-effective remediation strategy.Competing Interests.The authors declare no competing financial interests.

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The Marilao-Meycauayan-Obando River System of Bulacan was included in the dirty 30 rivers list in the world by the Blacksmith Institute in 2008. The river system, which is heavily polluted with organic matter and heavy metal, plays an important role in the aquaculture industry in Bulacan. With this pollution, organisms are known to be affected. One of which are the microscopic plankton, which serve as a primary food for fishes and can be indicators of pollution. The study focused on the composition of the phytoplankton and zooplankton communities in fishponds along the MMORS. Horizontal towing of about 3 m long was done on the surface water of the pond to collect freshwater plankton using a net with a mesh size of 64 microns. The plankton samples were immediately fixed in 10% formalin solution and were identified and enumerated. The collection of samples was done during the dry (April 2015) and wet (June 2015) seasons. The major identified groups of phytoplankton belong to Bacillariophyta, Chlorophyta, Cyanophyta, Cryptophyta, and Dinophyta, whereas the zooplankton belongs to the group of Copepoda, Rotifera, and Isopoda for all the sampling collection. Statistical analysis showed that phytoplankton density has a significant positive correlation with zooplankton density and chemical oxygen demand. Indicator species such as Microcystis, which might cause minor fish kills in ponds, were observed. Other species such as Peridinium and Rhodomonas indicate discoloration in the water. Diatom species such as Nitzchia, Tabellaria, and Fragilaria indicate that the water is polluted because these are pollution-tolerant species. Brachionus, which is a zooplankton species, indicates organic pollution in water. The low diversity index of plankton on ponds indicates that the water is polluted. This study provides baseline information on the biodiversity of the plankton community, which is essential in aquaculture.

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