Agrochemical asymmetry in the water–food nexus: Macro-level statistical associations from aquatic production in Australia

Agrochemical intensification is increasingly reshaping Australia’s aquatic food systems, yet the distinct long-run effects of pesticide and fertilizer use on aquaculture and fish production remain poorly understood within the water–food nexus. This study addresses this gap for Australia using annual data from 1990–2024 and an autoregressive distributed lag (ARDL) framework across three linked models of freshwater withdrawals, aquaculture production, and wild fish production, with robustness confirmed through FMOLS and CCR estimators. All findings are interpreted as macro-level statistical associations observed at the national aggregate scale; causal interpretation should await sub-national and spatially explicit analysis. Three key findings are observed. First, agricultural land expansion increases freshwater withdrawals more than proportionally: a 1% increase in agricultural land is associated with a 1.47% rise in water demand, indicating that irrigation efficiency cannot fully offset scale effects in the aggregate data. Second, pesticide use is positively associated with aquaculture (+1.60) and fish production (+0.48) — suggesting that it reflects production-system development rather than ecological damage alone, a pattern consistent with aggregate intensification trends, though the mechanisms require further investigation. T Third, fertilizer use shows strong negative long-run associations with aquaculture (−2.05) and fish production (−0.47), despite short-run gains. This pattern is consistent with ecological threshold theory, although causal attribution requires caution at this level of aggregation. These findings suggest that pesticide and fertilizer inputs should be examined separately rather than treated as a single agrochemical intensification category. The results also indicate that efficiency improvements may not fully offset land-use pressures in the aggregate Australian data. The findings suggest that water-allocation planning and agrochemical governance may benefit from greater attention to land-scale effects and cumulative nutrient pressures, while recognising the limitations of national-level time-series evidence.