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Causal Attribution of Coastal Water Clarity Degradation to Nickel Processing Expansion at the Indonesia Morowali Industrial Park, Sulawesi

Sandy Hardian Susanto Herho, Alfita Puspa Handayani, Iwan Pramesti Anwar, Faruq Khadami, Karina Aprilia Sujatmiko, Doandy Yonathan Wibisono, Rusmawan Suwarman, Dasapta Erwin Irawan

Abstract

Indonesia's nickel ore export ban has driven rapid expansion of smelting and hydrometallurgical processing capacity at the Indonesia Morowali Industrial Park (IMIP), now the world's largest integrated nickel processing complex, on the coast of Central Sulawesi. Whether this industrialization has degraded the adjacent marine environment remains unquantified. We apply Bayesian structural time-series (BSTS) causal inference to a multi-decadal, multi-sensor satellite ocean color record of the diffuse attenuation coefficient at 490 nm, $K_d(490)$, to test for a causal link between IMIP expansion and nearshore turbidity change. A consensus structural breakpoint, a significant posterior causal effect estimated against a Banda Sea counterfactual, and a distribution-free placebo rank test collectively establish that coastal water clarity deteriorated after the transition from initial nickel pig iron production to hyper-expansion of high-pressure acid leaching facilities for battery-grade nickel. Satellite-derived land cover analysis independently corroborates this timing, showing substantial built-area growth and concurrent tree cover loss within the IMIP footprint. The resulting euphotic zone shoaling occurs in oligotrophic waters supporting high marine biodiversity, where even moderate optical degradation may impair coral photosynthesis and compress depth-dependent reef habitat. These findings quantify a marine environmental cost absent from Indonesia's mineral downstreaming policy discourse and demonstrate a transferable, satellite-based quasi-experimental framework for causal impact assessment at coastal industrial sites in data-limited tropical settings.

Causal Attribution of Coastal Water Clarity Degradation to Nickel Processing Expansion at the Indonesia Morowali Industrial Park, Sulawesi

Abstract

Indonesia's nickel ore export ban has driven rapid expansion of smelting and hydrometallurgical processing capacity at the Indonesia Morowali Industrial Park (IMIP), now the world's largest integrated nickel processing complex, on the coast of Central Sulawesi. Whether this industrialization has degraded the adjacent marine environment remains unquantified. We apply Bayesian structural time-series (BSTS) causal inference to a multi-decadal, multi-sensor satellite ocean color record of the diffuse attenuation coefficient at 490 nm, , to test for a causal link between IMIP expansion and nearshore turbidity change. A consensus structural breakpoint, a significant posterior causal effect estimated against a Banda Sea counterfactual, and a distribution-free placebo rank test collectively establish that coastal water clarity deteriorated after the transition from initial nickel pig iron production to hyper-expansion of high-pressure acid leaching facilities for battery-grade nickel. Satellite-derived land cover analysis independently corroborates this timing, showing substantial built-area growth and concurrent tree cover loss within the IMIP footprint. The resulting euphotic zone shoaling occurs in oligotrophic waters supporting high marine biodiversity, where even moderate optical degradation may impair coral photosynthesis and compress depth-dependent reef habitat. These findings quantify a marine environmental cost absent from Indonesia's mineral downstreaming policy discourse and demonstrate a transferable, satellite-based quasi-experimental framework for causal impact assessment at coastal industrial sites in data-limited tropical settings.
Paper Structure (10 sections, 34 equations, 8 figures)

This paper contains 10 sections, 34 equations, 8 figures.

Table of Contents

  1. Introduction
  2. Data
  3. Methods
  4. LULC Change Analysis
  5. Exploratory Analysis of Oceanographic Time Series
  6. Structural Break Detection
  7. BSTS Causal Impact Estimation
  8. Results
  9. Discussion
  10. Conclusion

Figures (8)

  • Figure 1: Geospatial context of the study domain. (a) Location of IMIP (red circle) within the Indonesian archipelago; the dashed rectangle delineates the study area. (b) Tolo Bay and the western Banda Sea at 15 arc-second bathymetric resolution (SRTM15+V2), showing the impact zone (red box) directly offshore of IMIP and the control zone (blue box) in the open Banda Sea. The color scale denotes elevation and bathymetry in meters.
  • Figure 2: Annual LULC maps of the IMIP impact zone derived from Sentinel-2 at 10 m resolution for (a) 2017 through (h) 2024. Eight classes are shown: water (blue), trees (dark green), flooded vegetation (light green), crops (orange), built area (red), bare ground (tan), clouds (gray), and rangeland (yellow-green).
  • Figure 3: Three-level intensity analysis of LULC transitions in the IMIP impact zone, 2017--2024. (a) Interval-level: annual change intensity $S_t$ for each year-pair; the dashed line marks $U_{\mathrm{int}}$. (b) Category-level: gain (right) and loss (left) intensities; dashed lines mark $U_{\mathrm{cat}}$. (c) Transition-level: selected intensities for built area gain sources and tree cover loss sinks; dashed lines mark the uniform thresholds. Red bars denote active/targeted transitions; gray bars denote dormant/avoided transitions.
  • Figure 4: Monthly climatology of the entire study area (1998--2024) for (a) $K_d(490)$ ($\times 10^{-2}$ m$^{-1}$), (b) SST ($^{\circ}$C), and (c) SSS (PSU). Points and error bars show the median and 95% bootstrap confidence interval ($B = 10{,}000$); shading denotes the IQR.
  • Figure 5: Monthly $K_d(490)$ ($\times 10^{-2}$ m$^{-1}$) for the impact zone (red) and control zone (blue), January 1998 to December 2024. The orange dashed line marks first smelter commissioning (April 2015); the purple dash-dotted line marks the export ban (January 2020).
  • ...and 3 more figures