Abstract:
Frequent monitoring of water quality (WQ) is a crucial activity. WQ problem is a big
challenge in Lake Tana now and in the future. Turbidity affects WQ by hindering the entrance
of light in the water column. This affects aquatic life such as different fish species. Therefore,
this study aims to analyze turbidity dynamics in terms of spatiotemporal over Lake Tana
using Moderate Resolution Imaging Spectroradiometer (MODIS) surface reflectance product.
The traditional in-situ measurement to monitor at fixed geographical locations and time
intervals might not be representative for whole lake. Remote sensing can take over this
problem in accessing as a global extent and frequently measured. MODIS products such as
MOD09Q1 are atmospheric and geometric corrected and available in 250m spatial resolution.
This research validated the algorithm using MOD09Q1 product with observed turbidity (R2 =
0.754). Mann-Kendall trend test is conducted and it is found that, there is an increased trend
hence the quality of lake becomes deteriorate. The statistical performance measurement such
as RMSE, MAE, and PBIAS were compute their values are 80.73 NTU, 53.51% and -0.37%
respectivelyt. The valuesshowa good relationship between observed versus simulated.
Seasonal turbidity variation also occurred highest in June and lowest in December. It varies
from 1.2 – 950 NTU. The result is agreed with 5.1 - 989 NTU which is conducted on Lake
Tana from August 2011 to July 2012. But it is contrast with other Ethiopian lake like Hawassa
Lake having 8.20 - 87.3 NTU. Similarly, disagree with standard value, according to WHO the
lake turbidity is should be <5 NTU to be productive.
The hotspot analysis shows hotspot and cold spotsoccurred around the (major river inlets and
shore) and center of the lake respectively. ANOVA was carried out for seasonal and hotspot
areas and the result have shown that, it is statistically significant for seasonal and hotspot
areas turbidity with p is <0.001. There is a statistical significance difference among the means
of seasons as well as hotspot areas at 95% CI.Therefore, remote sensing technique offers a
better and efficient tool for mapping the dynamic trend of spatial and temporal turbidity over
Lake Tana using semi-analytical generic single band algorithm.