2.2. Sediment and water sampling
Twelve sediment samples were collected by hand on March 24, 2010 from the center of Nanhu Lake, using perspex core tubes with lengths of 15 cm and internal diameters of 6.5 cm. Each perspex core tube had an injection hole at 4 cm from the bottom, whose diameter was 5 mm. The sediment core samples, with overlying water, were about 10 cm in thickness. All the perspex core tubes were immediately sealed at the top and bottom with silicone rubber bungs to keep the sediment structure intact. These tubes were then placed into boxes with ice and transported to the laboratory in Jinan University. The bungs on the top of the perspex core tubes were immediately removed when they arrived at the laboratory to allow the gas in the tubes to be exchanged with air. Overlying water in the sediment cores was siphoned from the tubes in order to regulate the thickness of sediment cores to 5 cm from the bottom of the tube, which kept the sediment surface 1 cm above the injection hole in the tube (Zhang et al., 2013). When needed, a 32P radiotracer, in the form of NaH232PO4, was injected into the sediments through the injection hole. One hundred and twenty five liters lake water were collected using plastic buckets from the center of Nanhu Lake for the experiments.