Planktonic index of biotic integrity based on nutritional characteristics: a case study in Gwangyang and Jinhae bays, Korea

Abstract

To assess the responses of planktonic organisms to pollutants in the coastal ecosystems of Gwangyang and Jinhae bays (Korea), we investigated seasonal changes in various biological factors during the period from 2010 to 2012. Based on the characteristics of nutrient uptake by planktonic organisms under the coastal pollution conditions, we focused on four major parameters: total phytoplankton, harmful algal bloom (HAB) species, heterotrophic bacteria (HB) and Escherichia coli to develop a planktonic index of biotic integrity (P-IBI). The threshold values for total phytoplankton, HAB species and HB were based on the zero Z-score following normal distribution of the data for each parameter during the three years. Based on this approach, the threshold values were: 1.2 × 106 cells L&#8211 1 for total phytoplankton 3.3 × 104 cells L&#8211 1 for HAB species and 1.7 × 106 cells mL&#8211 1 for HB. Five grade levels for the P-IBI were established, based on the zero Z-scores. The E. coli data were not normalized, and the threshold value for this parameter was based on the USEPA guideline for E. coli and the Korean Ministry of Oceans and Fisheries guideline. For Gwangyang Bay, the annual integrated score for the P-IBI in 2010 was better than in the other years of the study. Inorganic and organic pollution sources acted to lower the P-IBI scores in 2011 and 2012, respectively. In Jinhae Bay, the P-IBI for the inner part of Masan Bay was Grade IV&#8211 V, indicating unhealthy conditions relative to the central and western parts, where the P-IBI varied from Grade II to III. The P-IBI values for Gwangyang and Jinhae bays were mostly rated as Good (Grade II) or Fair (Grade III), except for a few stations in the semi-enclosed areas of the inner part of Jinhae Bay. Consequently, the P-IBI for Gwangyang Bay indicated ecological conditions better than or equal to those in Jinhae Bay. The P-IBI in each bay indicated a change to unhealthy status during the rainy periods of spring and summer, whereas during winter and autumn the index indicated healthy conditions.