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

Table 13 Results of subgroup analyses for TN

	n^a	Ln R ± 1 SE	R	Median removal efficiency (%)	95 % confidence interval
All wetlands	38	−0.46 ± 0.05	0.63	37	29–43
Climate zone
Aw (equatorial savannah, dry winter)	1	−0.49 ± 0.21	0.61	39	7–60
Cfa (warm, fully humid, hot summer)	6	−0.47 ± 0.15	0.63	37	15–54
Cfb (warm, fully humid, warm summer)	19	−0.44 ± 0.08	0.64	36	23–46
Csa (warm, dry and hot summer)	3	−0.63 ± 0.02	0.53	47	44–50
Dfa (snow, fully humid, hot summer)	5	−0.61 ± 0.12	0.54	46	30–58
Dfb (Snow, fully humid, warm summer)	4	−0.31 ± 0.11	0.73	27	9–42
Wetland type
Combined horizontal	2	−0.33 ± 0.05	0.72	28	19–36
Free water surface	30	−0.46 ± 0.07	0.63	37	27–46
Horizontal subsurface flow	3	−0.56 ± 0.1	0.57	43	31–54
Riparian	3	−0.47 ± 0.11	0.63	37	22–50
Water type
Agricultural runoff	18	−0.45 ± 0.08	0.64	36	25–46
River/lake water	10	−0.39 ± 0.08	0.68	32	20–43
Sec. domestic Wastewater	6	−0.67 ± 0.1	0.51	49	38–59
Tert. domestic Wastewater	4	−0.29 ± 0.05	0.75	25	17–34
Wetland history
Created, formerly cropland	3	−0.45 ± 0.05	0.64	36	29–43
Created, formerly other land use	25	−0.49 ± 0.06	0.61	39	30–46
Restored, formerly drained cropland	6	−0.33 ± 0.12	0.72	28	9–44
Restored, formerly other land use	3	−0.49 ± 0.36	0.61	39	−23–70
Water regime
Continuous, variable	21	−0.54 ± 0.06	0.58	42	33–49
Intermittent, variable	1	−0.67 ± 0.27	0.51	49	12–70
Precipitation-driven	15	−0.43 ± 0.09	0.65	35	22–46
Intermittent, constant	1	−0.42 ± 0.1	0.66	34	19–47

ISSN: 2047-2382