Freshwater ecosystems in the northern Murray-Darling Basin face increasing pressure from altered hydrology, agricultural intensification and chemical pollution. Despite significant investment in environmental water delivery, long-term monitoring indicates that native fish and yabby (Cherax destructor) populations in the Gwydir River show little recovery. These limited responses suggest that stressors beyond water availability may be constraining ecosystem recovery. Yabbies are a key macroinvertebrate in this system, supporting fish populations as a major prey resource and contributing to aquaculture and local food supply. Pesticide exposure has the potential to alter fatty acid (FA) profiles in yabbies, disrupt lipid metabolism, and induce oxidative stress, thereby reducing their nutritional value and ecological function.
This study assessed water quality, pesticide occurrence, and yabby abundance across 18 sites spanning three hydrological zones of the Gwydir River catchment. Water samples collected were screened for over 450 pesticide compounds and various water quality parameters. Yabbies were collected using baited traps deployed overnight at each site. Of the 450+ compounds screened, 13 were detected, predominantly herbicides including Diuron, Metolachlor, Terbuthylazine-desethyl (metabolite of terbuthylazine) and Ametryne, consistent with broadacre cropping land use. Diuron concentrations approached ANZG 99% species protection guideline values at several mid-catchment sites. Principal Component Analysis of water quality revealed a clear spatial gradient, with mid-catchment agricultural sites characterised by elevated nutrients, turbidity, and pesticide detections. Yabby abundance varied markedly, with highest catches at mid-catchment sites. Another field sampling in September and forthcoming analyses of yabby tissue FA profiles and pesticide bioaccumulation will determine whether sub-lethal biochemical impacts are occurring in these populations. This integrated approach linking water chemistry, contaminant screening, and organism-level biomarkers will provide novel insights into how agricultural contaminants affect basal food resources and inform improved management of river health.