Abstract:
Fresh water is essential to human life and known by their richest species diversity and but
pollution from different sources is one of major stressor. The aim of this study was to assess
thewater quality in some selected wetlands in Lake Tana sub Basin using physicochemical
parameters and macro invertebrate assemblage.The study was conducted on six selected sites
during thedry and wetseasons of the year 2020. Macroinvertebrates were sampled from littoral
zone at sampling depth of 0.25-0.5 m using standardized kick sampling with a hand D-net (28 cm
x 30 cm) and a horizontal transect. All the physico-chemical parameters, except salinity and
Chlorophyll-a, showed a significant (p<0.05) temporal variation and the values ranged 6.8 - 7.3,
20.1-24.6 ℃, 5.4-6.1 mg/l, 110.8-129.6 ppm, 121-156.9μs/cm, 0.72-1.36 mg/l and 0.36-0.95 mg/l
for pH, temperature, dissolved oxygen, total dissolved solids, conductivity, nitrate and
phosphate, respectively. The highest pH value (7.4±1.0) was recorded in the Ras Abay River
mouth as well as the highest NO
3
(1.75±0.9 mg/l) and PO
(1.44±0.69 mg/l) was recorded in
Megech and Gumara River mouth, respectively. A total of 7,247 macro invertebrate individuals
belonging to 49 families and 77 genera were collected. The total number of individuals present
at each site ranged from 878 at Megech site to 1669 at Wonjeta, and 3,190 and 4057 during wet
and dry seasons,respectively. Tubificidae was the most abundant family (1,568 individuals)
followed by Thiaridae (626 individuals), Caenidae (575 individuals), Coenagrionidae (499
individuals) and the least Lestidae (479 individuals) family.Gumara and Megech River mouths,
and sites around Bahir Dar town were moderately and highly polluted compared to other
minimally polluted sites. Generally,rural areas with high agricultural activities such as crop
farming and livestock grazing as well as urban areas which directly release domestic wastes into
the lake affected water quality of the specific areas. Species diversity, species composition and
evenness indexvalues of macroinvertebrates were low at highly disturbed agricultural sites and
followed by urban impacted sites. Therefore,agricultural, domestic and industrial wastes should
be treated before being released into the lake and solid waste disposal in and around the Lake
Tana and its tributary rivers should be discouraged.