Unraveling characteristics and drivers of ambient nutrient uptake in small streams worldwide
摘要
Nutrient uptake in streams is crucial for regulating the nutrient loads to large water bodies downstream from the watershed. However, a greater understanding of the characteristics and environmental driving factors of ambient nutrient uptake in small streams (discharge [Q] < 100 l s−1) draining catchments with different land-use practices worldwide is still needed. To address this need, we conducted a meta-analysis that included 370 individual experimental observations from 53 published studies. Our findings indicated that streams with high background nutrient concentrations (e.g., agriculture and urban streams) generally exhibited longer ambient uptake lengths (Sw-amb), higher ambient uptake rates (Uamb), and lower ambient uptake velocities (Vf-amb) of nutrients than those with low background nutrient concentrations (e.g., forest and mountain streams). Community respiration (CR), ambient nitrate-nitrogen (NN) concentration, and Q were crucial factors influencing ambient ammonium-nitrogen (AN), NN, and soluble reactive phosphorus (SRP) uptake in streams, respectively, based on a random forest analysis. Moreover, results from partial least squares path modeling revealed that the stream type could indirectly influence the Vf-amb by impacting other environmental factors (e.g., Q, water pH, water temperature, or ambient nutrient concentrations). Overall, our findings enhance the understanding of characteristics of ambient nutrient uptake in different types of small streams on larger scales and provide insights into the complex relationships between environmental factors and ambient nutrient uptake.