How effective are created or restored freshwater wetlands for nitrogen and phosphorus removal? A systematic review

Table 14 Results of subgroup analyses for TP

	n^a	Ln R ± 1 SE	R	Median removal efficiency (%)	95 % confidence interval
All wetlands	51	−0.62 ± 0.08	0.54	46	37–55
Climate zone
Aw (equatorial savannah, dry winter)	18	−0.89 ± 0.14	0.41	59	46–69
Cfa (warm, fully humid, hot summer)	7	−0.53 ± 0.16	0.59	41	19–58
Cfb (warm, fully humid, warm summer)	16	−0.39 ± 0.15	0.68	32	9–50
Csa (warm, dry and hot summer)	1	−0.85 ± 0.54	0.43	57	−22 to 86
Dfa (snow, fully humid, hot summer)	3	−0.14 ± 0.24	0.87	13	−38 to 46
Dfb (snow, fully humid, warm summer)	6	−0.57 ± 0.19	0.57	43	17–62
Wetland type
Combined horizontal	2	−1.22 ± 0.29	0.3	70	47–84
Free water surface	47	−0.64 ± 0.08	0.53	47	37–56
Riparian	2	0.31 ± 0.25	1.36	−36	−122 to 17
Water type
Agricultural runoff	35	−0.58 ± 0.1	0.56	44	31–54
Agricultural + urban runoff	1	−0.18 ± 0.5	0.84	16	−120 to 69
River/lake water	6	−0.49 ± 0.24	0.61	39	1–63
Sec. domestic wastewater	4	−1.13 ± 0.28	0.32	68	43–82
Tert. domestic wastewater	5	−0.66 ± 0.18	0.52	48	26–64
Wetland history
Created, formerly cropland	13	−0.79 ± 0.08	0.45	55	46–62
Created, formerly other land use	29	−0.69 ± 0.10	0.50	50	38–60
Restored, formerly drained cropland	6	0.15 ± 0.21	1.16	−16	−77 to 24
Restored, formerly other land use	3	−0.45 ± 0.15	0.64	36	14–53
Water regime^b
Constant	8	−0.92 ± 0.25	0.4	60	34–76
Continuous, variable	17	−0.79 ± 0.11	0.45	55	43–64
Intermittent, constant	6	−0.81 ± 0.1	0.44	56	45–64
Precipitation-driven	14	−0.23 ± 0.07	0.79	21	8–31

R = load out/load in
^aWhere n = 1 the SE is based on the within study variance only
^bRestored wetlands on former drained cropland have been removed from these calculations

ISSN: 2047-2382