Seasonal variations of water physicochemical characteristics in Qinhuangdao City aquaculture area and their effects on cultured organisms

To reveal seasonal variation patterns of physicochemical characteristics in an aquaculture area and their effects on cultured organisms of Qinhuangdao City, Hebei Province, fifteen sampling points were established in study area, including aquaculture ponds, water inlets, and drainage outlets, for fixed-point monitoring over a one-year period（May 2023 to April 2024）．Physicochemical parameters such as water temperature, pH, dissolved oxygen concentration, and ammonia nitrogen concentration were measured, and their relationships with cultured organisms growth were analyzed．Results showed that aquaculture water physicochemical parameters exhibited significant seasonal variations and spatial differences, with the most evident water quality deterioration occurring during summer aquaculture peak season．Ammonia nitrogen and nitrite nitrogen were main parameters exceeding standards, with maximum concentrations reaching 2.35 mg/L and 0.24 mg/L respectively, both exceeding tolerance thresholds of cultured organisms．Downstream waters in aquaculture area reached severe eutrophication（I_TL(∑)>70）in summer．Survival rate of Pacific white shrimp showed a strong negative correlation with ammonia nitrogen concentration（r=−0.814, P<0.01）, while dissolved oxygen exhibited a significant positive correlation with growth of cultured organisms（r=0.573～0.756, P<0.01）．Water quality parameters showed obvious threshold effects on cultured organisms, with significant inhibition of growth and survival when dissolved oxygen concentration fell below 5 mg/L and ammonia nitrogen concentration exceeded 1.2 mg/L．Based on these findings, it is recommended to reduce adverse effects of seasonal water quality fluctuations on cultured organisms by reasonably regulating culture density, optimizing feeding management, strengthening water purification, and establishing early warning mechanisms．A scientific basis for aquaculture water quality management and production practices in Qinhuangdao City was provided through these research results．