Comparative study on endogenous release of nitrogen and phosphorus in Nansi Lake, China
南四湖内源氮磷释放的对比研究

Intact sediments and interstitial water were collected by sediment sampler and Peeper (pore water equilibriums) from different zones of Nansi Lake in August 2011, and the release of nitrogen and phosphorus in sediments were studied through static incubation and interstitial water molecule diffusion model. Results showed that nitrogen and phosphorus releasing rates from sediments were significantly different between zones of Nansi Lake in summer, with a general north-to-south decreasing trend. The release rates of NH4+-N and PO43--P through static incubation were 3.1~10.3 mg·m-2·d-1 and 0.3~2.7 mg·m-2·d-1, respectively. The release rates of NH4+-N and PO43--P from Nanyang Lake were significantly greater than other Lakes and this may be due to the serious pollution from the nearby Jining City to the Northern Nansi Lake. Centrifugation and Peeper method were used to obtain porewater in different sampling areas of Nansi Lake, and the releasing rates of sediment NH4+-N and PO43--P estimated by Fick's Law were 3.69~4.51 mg·m-2·d-1, 0.24~0.66 mg·m-2·d-1 and 2.54~4.16 mg·m-2·d-1, 0.04~0.51 mg·m-2·d-1, respectively. The releasing rates calculated by Peeper were about 20% higher than those by conventional centrifugal method. The spatial distributions of NH4+-N and PO43--P releasing rates estimated by static incubations and interstitial water molecule diffusion model were consistent, with the releasing rates of NH4+-N much higher than PO43--P. The R/F value of NH4+-N and PO43--P were 0.84~2.64 and 2.03~13.79, respectively. The results indicated that the release rates obtained by static incubations with intact sediment cores may be closer to the actual situation than those by interstitial water molecule diffusion model.