Influence of Commercial-Scale Seaweed Cultivation on Water Quality: A Case Study in a Typical Laver Culture Area of the Yellow Sea, North China

Seaweeds are important to marine ecosystems through biogeochemical processes. Laver are the most widely farmed seaweeds with the largest culture area in China. This study analyzes the water quality characteristics in a large-scale laver culture area (Taoluo) by comparing a small-scale laver culture area and non-culture areas, thereby assessing the changes in water quality due to large-scale laver cultivation. Particulate organic carbon and/or dissolved organic carbon decreased while the total suspended solid increased seasonally or with the distance from the coast. The concentrations of total nitrogen as well as dissolved inorganic nitrogen and phosphorus were generally higher near the shore and decreased seasonally in Taoluo. Substantial spatial variation in nutrient parameters between culture and non-culture sites was observed. Moreover, significant variations between culture and non-culture sites on a spatio-temporal scale were mostly observed in December compared with September and October. Furthermore, more clusters were found in December based on the water quality characteristics in various sampling sites using a hierarchical clustering analysis. These results suggested that more spatial deviation in water quality parameters between culture and non-culture sites were found in December; thus it can be hypothesized that the changes in water quality due to large-scale cultivation for laver was likely to occur in northern China in winter, i.e., the period of best growth status for the cold-temperate species of laver (e.g., Neopyropia yezoensis). We hope that this study can help to further understand the effects of seaweed farming on marine environments.