Using the Planning and Management Model of Lakes and Reservoirs (PAMOLARE) as a tool for planning the rehabilitation of Lake Chivero, Zimbabwe

The objective was to determine the applicability of the Planning and Management Model of Lakes and Reservoirs (PAMOLARE) as a tool in predicting and managing changes in Lake trophic status, using Lake Chivero (Zimbabwe) as a case study. The model was used to estimate the effect of nutrient reduction under three management scenarios, which were: the use of the existing management system (used as the baseline scenario), the use of natural wetlands and the combination of efficient wastewater treatment systems and wetlands. Modelling parameters were gathered through, 2010 field data, literature review and information acquired from responsible authorities. The current trophic status of Lake Chivero was evaluated by analyzing different physico-chemical variables from the lake's major and minor tributaries. Physico-chemical parameters measured were dissolved oxygen, turbidity, conductivity, total dissolved solids, pH, temperature, total nitrogen, total phosphorus and chlorophyll-a. The results indicated that Lake Chivero was hypereutrophic, with a mean phosphorus concentration of 2.77 mg L−1 and a mean nitrogen concentration of 3.21 mg L−1. Most physico-chemical parameters differed significantly with (P ≤ 0.05) with sampling site. The phosphorus contribution from non-point sources was estimated to be about 493 tonnes per annum compared to 634 tonnes per annum from point sources. About 40,000 ha of wetlands would have the capacity to remove up to 80,000 tonnes of phosphorus and about 99,700 tonnes of nitrogen per annum. The results of the model scenario runs revealed that phosphorus in the lake water could decrease from 2.77 to 0.22 mg L−1 over 6.5 years. Nitrogen levels in the lake water also could decrease from 3.16 to 3.06 mg L−1 over 4 years. The notable trends indicated that the model could be used as a tool for planning the management of Lake Chivero.