Development of a family-level biotic index for environmental monitoring of nickel mining affected streams in Bataraza, Palawan, Philippines

Results of the study showed that nickel (2.47-5.02 mg/L) and iron (11.46-76.54 mg/L) were the only heavy metals in water that exceeded the DAO [Dep't of Environment and Natural Resources Administrative Order] standards (0.01 mg/L for both). In sediment samples collected from some stations in Togpon Creek, only Cr (139.76-588.02 mg/kg) and Ni (171.5-875.9 mg/kg) concentrations exceeded the Dutch Intervention Values of Cr (380 mg/kg) and Ni (210 mg/kg). The macroinvertebrates observed at the different stations belong to 10 Orders of Class Insecta (8) and Class Gastropoda (2). A total of 30 insect families were observed in the Orders: Coleoptera (8); Diptera (5); Ephemeroptera (6); Hemiptera (4); Lepidoptera (2); Odonata (2); Plecoptera (1); and Trichoptera (2). Two mollusk families were observed, Families Megastropoda and Neritinea. As expected, the reference station had the highest diversity index (3.37) and more macroinvertebrate families (28) than the impacted areas. No macroinvertebrates were collected from the station directly after the tailings pond. From about 50 m downstream of this station to about 680 m, the benthic macroinvertebrate community structure improved with the appearance of sensitive families such as Families Ephemeralidae and Letophlebiidae. By classifying the families into intolerant, tolerant and persistent, a biotic index was developed by giving a biotic value from 1 to 5 to each insect and mollusk family. The intolerant families (e.g. Ephemeralidae and Psephenidae) were given a 5, the tolerant families (e.g. Ryacophilidae and Calopterygidae) a 3 and the persistent families a 1 (e.g. Hydropsychidae and Dysticidae). Intermediate values of 4 and 2 were given to families which were less intolerant or less persistent. By estimating the biotic index from the sum of the biotic values of the insects and mollusks observed in a station and dividing the sum by the number of families considered, the biotic index derived can be compared to a range of values. When applied to the stations studied and compared to the Biological Working Monitoring Party, the biotic index developed was able to show differences in the quality of the environmental conditions