Due to the cumulative effects of rapid urbanization, population growth and climate change, many inland and coastal water bodies around the world are experiencing severe water pollution. To help make land-use and climate change adaptation policies more effective at a local scale, this study used a combination of participatory approaches and computer simulation modeling. This methodology (called the “Participatory Watershed Land-use Management” (PWLM) approach) consist of four major steps: (a) Scenario analysis, (b) impact assessment, (c) developing adaptation and mitigation measures and its integration in local government policies, and (d) improvement of land use plan. As a test case, we conducted PWLM in the Santa Rosa Sub-watershed of the Philippines, a rapidly urbanizing area outside Metro Manila. The scenario analysis step involved a participatory land-use mapping activity (to understand future likely land-use changes), as well as GCM precipitation and temperature data downscaling (to understand the local climate scenarios). For impact assessment, the Water Evaluation and Planning (WEAP) tool was used to simulate future river water quality (BOD and E. coli) under a Business as Usual (BAU) scenario and several alternative future scenarios considering different drivers and pressures (to 2030). Water samples from the Santa Rosa River in 2015 showed that BOD values ranged from 13 to 52 mg/L; indicating that the river is already moderately to extremely polluted compared to desirable water quality (class B). In the future scenarios, we found that water quality will deteriorate further by 2030 under all scenarios. Population growth was found to have the highest impact on future water quality deterioration, while climate change had the lowest (although not negligible). After the impact assessment, different mitigation measures were suggested in a stakeholder consultation workshop, and of them (enhanced capacity of wastewater treatment plants (WWTPs), and increased sewerage connection rate) were adopted to generate a final scenario including countermeasures. The main benefit of the PWLM approach are its high level of stakeholder involvement (through co-generation of the research) and use of free (for developing countries) software and models, both of which contribute to an enhanced science-policy interface.

The widespread microplastic occurrence has invaded both marine and freshwater ecosystems. However, most studies are focused on marine microplastics and there is still insufficient knowledge and understanding of microplastics in freshwater ecosystems like small lakes. Known as one of the largest contributors of plastics to the aquatic environment, the Philippines has begun ventures on studying microplastic pollution, although, still, there are no accurate figures on the extent of the microplastic problem in the country, especially in its freshwater environment. In this study, a comparative assessment of microplastic concentration and characterization between Lake Yambo, an ecotourism and rural lake, and Lake Sampaloc, an aquaculture and urbanized lake, in San Pablo City, Laguna, Philippines was conducted through microplastic isolation and optical examination. Results revealed that the average microplastic concentration in Lake Sampaloc and Lake Yambo ranges from 483 to 989 n/m3 and 344 to 789 n/m3, respectively. Generally, the sampling sites in Lake Sampaloc had a higher mean concentration of microplastics than those in Lake Yambo. The key features of the microplastics detected in the surface waters of the studied lakes are fibrous, colored, and small-sized (<2 mm). In addition to proving the assumption that there are more microplastics observed in a highly-populated or urbanized freshwater ecosystem like Lake Sampaloc, this study also contributed to the meager evidence that microplastics are present even around scarcely-populated lakes like Lake Yambo. The outcome of this study is relevant for the local government unit (LGU) of San Pablo to make sustainable environmental policies regarding plastic waste management and disposal.