Table 2. The mean relative abundance of dominant species (above 1% of total abundance), mean (range) species richness of diatoms observed across the 24 sites in the Gilgel Gibe watershed and their saprobity (Sapr) and trophic state (Trop) status.

Species	Sapr	Trop	Dry season		Wet season
			AIS	UIS	AIS	UIS
Achnanthidium minutissimum (Kützing) Czarnecki	β-meso	diff	5.1	1.7	12.7	6.2
Achnanthidium subhudsonis (Hustedt) H. Kobayasi			5.7		2.1	0.2
Adlafia bryophila (Petersen) Moser Lange-Bertalot & Metzeltin	olig	meso	4.0		0.1	0.5
Adlafia minuscula (Grunow) Lange-Bertalot	β-meso	oli	1.1		2.6	0.7
Fragilaria ulna (Nitzsch.) Lange-Bertalot	α-meso/poly	diff	0.3	0.4	2.0	5.5
Gomphonema gracile Ehrenberg	olig	meso	2.9	4.5	2.0	1.8
Gomphonema minutum (Ag.)Agardh	β-meso	eut	6.8	6.7	2.5
Gomphonema parvulum (Kützing) Kützing	α-meso/poly	eut	13.5	28.5	11.4	16.9
Gomphonema pumilum (Grunow) Reichardt & Lange-Bertalot	_	diff	10.0		16.5	2.0
Halamphora montana (Krasske) Levkov			0.9	0.9	1.6	2.8
Luticola mutica (Kützing) D.G. Mann			1.5		1.6	1.7
Navicula cryptocephala Kützing	α-meso	diff	2.2	3.8	1.9	1.3
Navicula gregaria Donkin	α-meso	eut	2.4	0.1	2.1	1.0
Navicula rostellata Kützing			3.2	1.9	0.3	0.6
Navicula schroeteri Meister	β-meso	eut	7.3	2.5	2.2
Nitzschia palea (Kützing) W.Smith	poly	hyper	6.2	21.0	7.9	30.8
Pinnularia obscura Krasske	olig	_	2.0		6.6	0.9
Surirella angusta Kützing	β-meso	eut	2.2	0.7	0.5
Richness			29.4 (23–37)	18.5 (14–25)	22.3 (14–32)	24.2 (13–34)

AIS = agriculture impacted sites [18], UIS = urban impacted sites [6], βmeso = β-mesosaprobous, αmepo = α-meso/polysaprobous, αmeso = α-mesosaprobousand, poly = polysaprobous, olgo = oligosaprobous, diff = in different, meso = mesotrophic, oli = oligotrophic, eut = eutrophic, hyper = hypereutrophic.