Characteristics of Atmospheric Deposition during the Period of Algal Bloom Formation in Urban Water Bodies

Abstract

Urban water bodies are limited by poor mobility, small surface areas, and little water supply; thus, they are sensitive to atmospheric nutrient inputs, especially during the optimal period of algae growth. This study investigated the impact of atmospheric deposition on the Quyang urban water body in Shanghai. Observations that coupled atmospheric organic matter, nitrogen and phosphorous and the actual urban water body (nutrient availability and Chlorophyll-a concentrations (Chl-a)) were conducted during spring and summer. Atmospheric total organic carbon (TOC), total nitrogen (TN), ammonia (N-NH4+) and total phosphorus (TP) deposition ranged from 35–81, 3–40, 0.79–20.40 and 0.78–0.25 mg m−2 d−1, respectively. The soluble N/P molar ratios of the bulk deposition (ranging from 56–636) were well above the Redfield ratio (N/P = 16). Nutrient inputs from atmospheric deposition have been suggested to be a strong factor for increasing the likelihood of P limitation in the water bodies. The actual loads to small, shallow urban water bodies were assessed and found to be ~50, 130, 130 (the N-fixation contributes to the atmospheric deposition inputs especially during the spring), and 80% of TOC, TN, N-NH4+, and TP, respectively, representing nutrients transferred into the water phase. The maximum primary production (evaluated as Chl-a) stock resulting in a 2-m-deep water column from the above inputs ranged from 2.54–7.98 mg Chl-a m−3. As a continuous source of nutrients, atmospheric deposition should not be underestimated as a driving force for urban water body eutrophication, and it potentially influences primary production, especially during the optimal algae growth period.