Climate change significantly increases the frequency of storm events, which flush land pollutants, including phosphorus (P), into freshwater bodies. Understanding the biogeochemical transformation of P in dissolved and particulate forms during storm events is still challenging. The surface water samples were collected during the stormwater flow and the dry weather flow from the five study sites along the pH gradient for measurement of P species, including dissolved inorganic phosphorus (DIP) and dissolved organic P (DOP), colloidal organic and inorganic P (COP and CIP), particulate organic and inorganic P (POP and PIP). In dry weather flow, DIP levels rise due to low suspended particulate matter (SPM) concentrations (11–23 mg L^-1) and desorption from the particulate matter. In contrast, during stormwater flow, high SPM concentrations (25–65 mg L^-1) lead to the removal of DIP from the system through the adsorption onto fine sediments. A negative correlation was observed between the P partitioning coefficient (Kd) and both SPM (r = -0.2) and pH (r = -0.4), indicating strong particle reactivity between DIP and PIP during the storm events. Additionally, the correlation between benthic chlorophyll-a and DIP and PIP suggests that P uptake from different fractions influences the geochemical transformation of P during stormwater flow. This study shows that stormwater flow modifies P species shift between the particulate and dissolved phases, with urban and agricultural land uses influencing tributaries and mainstreams more than forested areas. These findings emphasize the relevance of stormwater dynamics and land use in freshwater P control. 
 

Phosphorus, freshwater, land use, streams, biogeochemical