Data collection
Water quality parameters were measured six times during the experimental period, on day 0, 27, 37, 44, 51 and 58. Conductivity, temperature and dissolved oxygen concentration (DO) were measured using a HACH portable multi-parameter meter (HQ40d, HACH, USA). Total nitrogen (TN) and total phosphorus (TP) were determined using spectrophotometry after digestion with K2S2O8 in an autoclave (120 °C, 1.1 kg cm-2) for 30 minutes, measuring at wavelengths 220 and 275 nm for TN, and 700 nm for TP (UV-2800, Unico, China, GB 11894-89, GB 11893-89). At the end of the experiment, water was sampled from each experimental container and filtered onto GF/C filters to analyze chlorophyll a (Chl a) content as an indicator of phytoplankton biomass. Periphyton Chl a content (µg Chl a per cm2 area) was determined by brushing off a 9 cm2 (3 × 3 cm) area in the middle of one side wall after draining the water, filtering the brushed water through Whatman GF/C filters. Chl a content was determined spectrophotometrically after ethanol extraction (HJ 897-2017). Snails in each container were collected manually and wet weight was determined. Ten P. crispuswere randomly selected in each container to measure internode length. All macrophytes were harvested with shoot and root separately cleaned and blotted dry to measure wet weight, after which they were dried in an oven at 60 °C for 48 hours. Dried plant samples were ground individually in a 2 ml tube on a mill (MiniBeadbeater-16, Biospec Products, USA). Plant total C and N were determined on an elemental NC analyzer (Flash EA 1112, CE Instruments, Italy). P content was determined by incinerating and digesting the organic P with K2S2O8 (same to water TP analysis), and then measuring the dissolved phosphate concentration on a spectrophotometer (Cleverchem380, DeChem-Tech., Germany).