Predicting Nutrient Distribution Patterns in Some Coastal Lagoons in Ghana Using Mike 3 Model
Date
2019-07
Authors
Journal Title
Journal ISSN
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Publisher
University of Ghana
Abstract
The study assesses the levels of phosphate, nitrate and ammonia in water and sediments from the
Mukwe, Sakumono II, Gao and Laloi lagoons situated within the central coast of Ghana alongside
other physicochemical parameters (pH, Dissolved Oxygen, Total Dissolved Solids and
Temperature). Data collected over a six-month period was used in calibrating and predicting
nutrient concentrations in the Sakumono II and Gao lagoons using the MIKE 3 model. High pH
measurements beyond USEPA and Ghana’s EPA permissible limits of 6.5 to 8.5 and 6.0 to 9.0,
respectively, were recorded in the Sakumono II and Mukwe lagoons whiles Gao and Laloi
recorded pH values within these permissible limits. With the exception of the Laloi lagoon which
had an average dissolved oxygen value of 5.1mg/l, dissolved oxygen concentration in all the other
lagoons were lower than the EPA and WHO permissible limits of 5.0mg/l to 6.5mg/l and 5.0mg/l
to 6.0mg/l, respectively. Total Dissolved Solid measurements in all the lagoons were above the
EPA permissible limit of 500mg/l. Phosphate, nitrate and ammonia concentrations in all the four
lagoons were generally above Ghana’s EPA and USEPA permissible limits. Discharge rates
measured were highest for the Laloi lagoon and lowest for the Gao lagoon, which may be linked
to the width and depth of the lagoons. Sediment nutrient concentrations were used together with
the instantaneous sediment discharge formula to calculate the rate of discharge of sediment nutrient
for the four lagoons. The results indicated that sediment nutrient concentration has a positive
correlation with sediment discharge rate. Apart from few discrepancies in the results which was
caused by poor rainfall data and non-point discharges, the correlation analysis indicated that MIKE
3 model was able to generally predict nutrient concentrations and show the distribution patterns in
the Sakumono II and Gao lagoons. Average sediment nutrient concentrations recorded for phosphate during the dry and rainy season for Sakumono II, Mukwe, Gao and Laloi lagoons were
(0.121 and 0.128mg/kg), (0.146 and 0.113mg/kg), (1.42 and 1.22mg/kg) and (0.112 and
0.103mg/kg) respectively. The average sediment nutrient concentrations recorded for ammonia
during the dry and rainy season for Sakumono II, Mukwe, Gao and Laloi lagoons were (37.18 and
25.85 mg/kg), (41.49 and 37.46mg/kg), (4.58 and 4.31mg/kg) and (41.74 and 40.93mg/kg)
respectively. The average sediment nutrient concentrations recorded for nitrate during the dry and
rainy season for Sakumono II, Mukwe, Gao and Laloi lagoons were (14.54 and 11.55mg/kg),
(15.15 and 15.41mg/kg), (3.83 and 3.46mg/kg) and (13.22 and 11.77mg/kg) respectively. Average
sediment discharge rates recorded in the Sakumono II, Mukwe, Gao and Laloi lagoons for
ammonia, nitrate and phosphate were (0.00000399 m3/s, 0.00000133m3/s and 0.0000000143m3/s),
(0.0000377m3/s, 0.0000126m3/s and 0.00000131m3/s), (0.000021m3/s, 0.0000073m3/s and
0.0000000746m3/s) and (0.00001624m3/s, 0.0000537m3/s and 0.0000000465m3/s) respectively.
Description
MPhil. Marine Science
Keywords
Ghana, Coastal Ecosystems, Lagoons, Anthropogenic Pollution