Table 1. Pollution Indices Used in the Present Study and Their Classifications.

pollution indicators	procedures of calculation and classifications
geoaccumulation index (Igeo)21−23	Igeo = Log2(Ci/(1.5 × Bi))
	Ci is the measured value of heavy metal (i) in the sediments, Bi is the geochemical background value of the heavy metal (i) in sedimentary rocks, Bi is using the background value of soil inorganic elements in Guangdong Province during “The 7th Five-Year Plan” (Co = 7.0 mg/kg, V = 65.3 mg/kg, Cu = 17 mg/kg, Pb = 36 mg/kg, Ni = 14.4 mg/kg, As = 8.9 mg/kg, Cd = 0.056 mg/kg, and Hg = 0.078 mg/kg),24 and the 1.5 is the coefficient to decrease the effects of variations in the background values; Igeo can be divided into seven grades:
	Igeo ≤ 0	0 < Igeo ≤ 1	1 < Igeo ≤ 2	2 < Igeo ≤ 3	3 < Igeo ≤ 4	Igeo > 4	Igeo > 5
	unpolluted	unpolluted to moderately polluted	moderately polluted	moderately to heavily polluted	heavily polluted	heavily to extremely polluted	extremely polluted
contamination factor (CF)23,25,26	CF = Ci/Cn
	Ci is the heavy metal (i) content measured in sediments, and Cn is the reference value of heavy metal (i) in the study using the background value of soil inorganic elements in Guangdong Province during “The 7th Five-Year Plan”; CF values can be divided into four groups:
	CF < 1	1 ≤ CF < 3		3 ≤ CF < 6	CF ≥ 6
	low contamination	moderate contamination		considerable contamination	very high contamination
potential ecological risk index (RI)25,26
	Eri is the potential ecological risk coefficient of single heavy metal (i), pointing to the ecological risk level of a single pollutant, and Tr is the response factor of the heavy metal toxicity coefficient in the order Co = Cu = Pb = Ni = 5, V = 2, Cu = 5, Pb = 5, Ni = 5, As = 10, Cd = 30, and Hg = 40. The degree of ecological risk can be classified into the following levels:
	Eri < 40	40 ≤ Eri < 80	80 ≤ Eri < 160	160 ≤ Eri < 320		Eri ≥ 320
	low risk	moderate risk	strong risk	very strong risk		extreme risk
	RI < 150	150 ≤ RI <300	300 ≤ RI < 600	RI ≥ 600
	low risk	moderate risk	strong risk	very strong risk