Fp910

Parts of bulk soil were used for measuring the physical and chemical properties. The soil water content (SWC) was measured by soil mass loss before and after drying at 105 °C for 12 h. After the soil was dried, mixed, and sifted using a 2 mm sieve, the soil organic matter (SOM), total N (TN), total P (TP), total potassium (TK), available N (AN), available P (AP), available K (AK), electrical conductivity (EC), and pH were measured according to Zhang et al. [19 (link)]. Briefly, SOM was measured by the potassium dichromate oxidation method. The TN content was determined via Kjeldahl digestions. The TP and TK contents were measured after digestion in concentrated HNO₃ with inductively coupled plasma optical emission spectrometry (iCAP 6300, Thermo Elemental, San Jose, CA, USA). The alkaline hydrolysis method was applicated to measure the AN content. The AP level was measured colorimetrically with the ascorbic acid/molybdate method after extracting using HCl/NH₄F. The AK was extracted via NH₄OAc and measured by a flame photometer (FP910, PG Instruments Co., Ltd., Lutterworth, UK). Soil EC was measured in a 1:5 (w/v) soil: water mixture using an EC meter (DDSJ-319L, INESA Scientific Instrument Co., Ltd., Shanghai, China). Soil pH was measured in a 1:2.5 (w/v) soil:water mixture using a pH meter (PHSJ-6L, INESA Scientific Instrument Co., Ltd., Shanghai, China).

Water transparency was measured in the field using Secchi disc. Water temperature, dissolved oxygen (DO), electric conductivity (EC) and water pH were measured according to APHA³⁸ . DO was measured using JENWAY instrument (9500, UK), while, EC was measured using conductivity meter (JENWAY, 4520). Whereas, pH was measured using pH meter (JENWAY, 3510).
Nitrogen (N) was estimated by using the micro-Kjeldahl method, and phosphorous (P) was established using a spectrophotometer (CECIL CE 1021) by applying indophenol blue and molybdenum blue methods, respectively. The samples were deep frozen until further analysis of inorganic elements. Potassium (K) was determined using a flame photometer (FP910-PG Instruments), following Allen³⁹ . Some heavy metals; zinc (Zn), cobalt (Co), and lead (Pb) were selected according to previously studies, which revealed that P.stratiotes could be assumed as a biomonitor and bioaccumulator for these particular heavy metals^{36 ,44 (link)–47} . Zn, Co, and Pb were determined using an atomic absorption spectrophotometer (Shimadzu AA-6200) following the Standard Methods for Examination of Water and Wastewater⁴¹ . The detection limits for the targeted heavy metals ranged from 0.01 to 0.2 µg/L.