Monitoring Sediment and Water Chemistry in Small Remote Aquatic Systems in East Sepik Province, Papua New Guinea

Small rivers are complex ecosystems facing threats from human activities and climate change. Therefore, studying the sediment and water chemistry of several streams in the East Sepik Province of Papua New Guinea will enhance our understanding of the characteristics of remote aquatic systems. We found high total organic carbon (OC) and vanillic acid to vanillin ratio, (Ad/Al)v, and high dissolved CH4, indications of methanogenesis, at some locations. High sediments inorganic carbon and high total alkalinity (TA) and SiO2 in the water were characteristic of carbonate minerals at other locations. Some locations showed high dissolved oxygen (DO), and low dissolved CH4, dissolved inorganic carbon (DIC), and partial pressure of CO2 (pCO2), indicating autotrophic condition. Other sites showed remarkably low DO and high pCO2, dissolved CH4, nutrient, and DIC, indicating heterotrophy and possibly anoxic condition. These findings reveal that even small remote aquatic systems of the areas sampled exhibit high variability in their sediment and water chemistries, probably due to human activities and different watershed morphology. Furthermore, higher dissolved NO3−, NO2−, N2O, PO43−, SiO2, TA, DIC, pCO2, DOC, particulate OC, and nitrogen were found at lower salinity, and vice versa, indicating the importance of mixing from seawater in diluting materials and affecting the autotrophy/heterotrophy in these systems.