The spatial distribution and characterization of phosphorus and nitrogen in a water-carrying lake: a case study of Lake Jiaogang, China.

The sources of P and N in water-carrying lakes include exogenous input and endogenous release. However, the influence of pollution from different sources on the dynamic distribution of N and P at the sediment-water interface in water-carrying lakes remains unclear. The objectives of this study were to investigate the differences in dynamic distribution characteristics of P compounds and N elements in Lake Jiaogang, a major water-carrying lake in eastern China. Four functional regions with different types of pollutant sources and different kinds of aquatic plants were selected to study the distribution of total P (TP), inorganic P, organic P, ammonium (NH4+-N), and nitrate (NO3--N). The results revealed that regions with internal-source pollutants contained the highest concentration of TP, Ca-P, and Fe-P with high concentrations. L-P, Al-P, mostly organic P, and soluble reactive phosphorous (SRP), the region with internal-source pollutants were lower than that with the imported-source pollutant. The concentration of dissolved NH4+-N showed high in regions with imported-source pollutants, however, in regions with internal-source pollutants, the dissolved NO3--N was with the highest concentration. Overall, P from upstream was still dominant in the sediments despite uptake by the aquatic plants. SRP showed high concentration in regions with imported-source pollutants due to the imported pollution and the improved bioavailability by plant root exudates. Feces and feed residues from aquatic livestock breeding resulted in the highest concentration of TN, NH4+-N, and dissolved NO3--N in the sediments of the region with internal-source pollutants. High concentrations of dissolved NH4+-N were due to the input of N from imported source pollutants. This study provides insights into the contributions of P and N to the eutrophication of the water-carrying lake.

Field observation and simulation experiments on nutrient transformation during phytoplankton-derived particulate matter deposition.

Phytoplankton-derived particulate matter (PPM) is the active component of the solid particles in eutrophic shallow lakes. To date, understanding of the degradation characteristics of PPM and the effect of degradation products on nutrient cycling in water are limited. In this study, field observations and simulation experiments were carried out to elaborate the nutrient transformation during phytoplankton-derived particulate matter deposition in the cyanobacterial blooming area of Lake Taihu. Results showed that the deposition of the PPM was strongly facilitated by the cyanobacterial bloom and the sediment resuspension. The main variation characteristics of phosphorus (P) species in PPM are shown in the increase of Ortho-P and the decrease of biodegradable phosphorus (Poly-P, DNA-P) during the deposition of PPM. The degradation of the PPM resulted in the release of dissolved nitrogen (N) and P to the water body. The conversion of easily degradable particulate N and P in the PPM to ammonium nitrogen (NH3-N) and soluble reactive phosphorus were believed to be responsible for this phenomenon. The cycling of nutrients and the cyanobacterial bloom status might therefore be altered because of the deposition and degradation of PPM. More considerations should be given on this process in future works.