Spatio-temporal patterns and predictions of size-fractionated chlorophyll a in a large subtropical river, China

Figures & data

Figure 1. The Pearl River, including its three main tributaries (West, North and East River) and the Pearl River Delta system. Sampling sites are represented by black dots: FK-Fengkai, DQ-Deqing, ZQ-Zhaoqing, QQ-Qingqi, ZT-Zuotan, WH-Waihai, XW-Xinwei, XL-Xiaolan, XT-Xiaotang, BJ-Beijiao, LH-Lanhe, HL-Hengli, CC-Chencun, SQ-Shiqiao, LHS-Lianhuashan and ZJQ-Zhujiangqiao.

Table 1. Sampling site coordinates.

Location	Station	Longitude	Latitude
West River	FK	111°30′26.6′′	23°23′15.7′′
	DQ	111°48′30.4′′	23°8′13.8′′
	ZQ	112°27′36.3′′	23°02′43.5′′
	QQ	112°47′11.0′′	23°10′14.5′′
	ZT	113°03′26.0′′	22°48′46.6′′
	WH	113°09′20.3′′	22°36′14.5′′
	XW	113°16′41.5′′	22°22′45.6′′
Central PRD	XL	113°17′17.9′′	22°38′13.8′′
	XT	112°57′51.1′′	23°05′27.4′′
	BJ	113°11′54.5′′	22°54′04.1′′
	LH	113°19′53.4′′	22°49′15.2′′
	HL	113°27′02.5′′	22°44′05.4′′
	CC	113°14′55.7′′	22°58′15.1′′
	SQ	113°24′49.0′′	22°55′24.2′′
City center	LHS	113°30′37.0′′	23°00′58.0′′
	ZJQ	113°13′16.5′′	23°08′12.6′′

Figure 2. Non-metric multidimensional scaling (NMDS) model based on size-fractionated chlorophyll a. Group 1 (G1), West River; Group 2 (G2), central Pearl River Delta; Group 3 (G3), Guangzhou city center; PRD, Pearl River Delta.

Figure 3. (a) Chlorophyll a concentration and (b) the percentage of each size fraction of phytoplankton in G1 (West River), G2 (central Pearl River Delta) and G3 (Guangzhou city center).

Figure 4. Results from the LDA analysis on correlations between clusters (Groups 1, 2 and 3) and environmental variables showing: (a) the distribution and overlap of clusters in F1 and F2 dimensions, and (b) the distribution of water quality parameters corresponding to F1 and F2.

Table 2. Species with greater than 5% occurrence in the three groups: G1 (West River), G2 (central Pearl River Delta) and G3 (Guangzhou city center) waters.

Species name	G1 (%)	G2 (%)	G3 (%)
A. granulata	35.68	46.65	63.98
Melosira sp.	18.02	9.07	–
Melosira varians	7.68	5.73	–
Peridinium sp.	5.62	–	8.33
Protoperidinium sp.	–	–	7.09

Table 3. Environmental factors measured at G1 (West River), G2 (central Pearl River Delta) and G3 (Guangzhou city center) (mean values across sampling sites for each group).

Environmental factors	G1	G2	G3
SiO4^4− (mg L^−1)	3.62	3.96	4.61
NH4^+ (mg L^−1)	0.15	0.20	1.80
NO3^− (mg L^−1)	1.39	1.50	2.38
NO2^− (mg L^−1)	0.07	0.12	0.29
NH3 (mg L^−1)	0.01	0.01	0.07
TN (mg L^−1)	2.39	2.77	6.72
PO4^3− (mg L^−1)	0.02	0.02	0.03
COD (mg L^−1)	2.84	3.19	6.44
DO (mg L^−1)	7.21	6.44	3.99
Salinity (‰)	0.49	0.55	0.86
pH	7.92	7.83	7.64
TDS (ppt)	0.4	0.5	0.9
Orp (mv)	106.8	82.3	85.4
Temperature (°C)	24.0	24.9	25.5
Transparency (cm)	46	52	31
Width (m)	617	421	334
Light (lx)	6720	6730	2482

Table 4. Temporal variation in physico-chemical factors and Chl-a related to the spatial pattern (mean values across all sampling sites) G1 (West River), G2 (central Pearl River Delta) and G3 (Guangzhou city center).

Group	Factors	Mar-2015	Jun-2015	Sep-2015	Dec-2015	Jun-2016	Dec-2016
G1	Width (m)	560	716	638	588	609	619
	Trans (cm)	113	26	45	63	13	52
	Orp (mv)	130.9	84.68	69.79	129.12	136.88	72.69
	Chl-a (µg/L)	3.18	2.17	1.68	1.70	2.24	2.15
G2	Width (m)	473	503	442	296	413	303
	Trans (cm)	83	32	53	57	10	53
	Orp (mv)	106.34	56.33	57.28	116.66	132.4	72.9
	Chl-a (µg/L)	5.18	5.27	4.47	4.75	6.70	4.43
G3	TN (mg L^−1)	4.54	4.23	4.08	6.61	6.06	17
	NO3^- (mg L^−1)	2.08	1.97	2.03	2.32	2.91	3.3
	COD (mg L^−1)	6.08	4.45	4.75	13.95	4.99	4.78
	DO (mg L^−1)	5.41	5.65	1.8	3.94	4.49	1.2
	Chl-a (µg/L)	59.95	30.11	25.44	13.01	13.88	18.57