An Assessment of the Effects of Canalization on the Water Quality and Birdlife in Lake Naivasha

Abstract

Lake Naivasha which is approximately 150 km2, supports large scale production of flowers for the European market. This has significantly raised the water abstraction levels with the horticulture farms around the lake digging canals with which to draw irrigation water from the lake. The aim of the study was to assess whether canalization of the shoreline significantly affects water quality and birdlife distribution in Lake Naivasha. The specific objectives of the study were to assess the intensity of shoreline canalization and the canal density around the lake. To demonstrate whether unique patterns of in shore canalization exhibited within the lake significantly impacted the water quality and correlate this to wetland birdlife. The method used to achieve the objective, was first to map all the canals on the shoreline using GPS, analyse water quality parameters at every canal point and assess lakeshore birdlife distribution at these canals. The canals were then grouped according to the aggregation pattern observed into a Southern, Northern and Eastern Zone. The findings of the study revealed that the southern part of the lake had 60% of shoreline canals, 26 in number, some with a width of up to 25 and 30 meters. The northern part of the lake had one canal, with four others on the northwestern side; all these were between 5-10 meters wide. 13 canals on the eastern side of the lake exhibited the highest density in terms of proximity of canals with the widest canals measuring 20 meters. The true western side had no canals. Water quality means for the Eastern, Southern and Northern side were: TDS at 184 mg/l, 166 and 160mg/l for the DO, 73.7, 89.9 and 83.7, whereas pH 9.1, 8.7 and 8.8 respectively during low water levels. The width of canals and their proximity to one another had significant impact on the water quality and on birdlife distribution on the shoreline. Bird counts were highest on the northern side and lowest on the eastern side and there was a distinguishable water quality pattern in the different zones. The study revealed an inverse relationship between canalization and birdlife distribution on the shoreline. Low water quality was observed from data collected in areas with the highest canal density, which was postulated to impinge negatively on the biotic factors that sustain birds within the lake leading to fewer bird counts in areas of high canal density. It was also observed that canalized areas disrupted the pristine and tranquil ecosystem that birds need. There is an urgent need to get policy makers to enact regulations that limit inshore abstraction canal numbers and sizes. Horticultural farms should be limited to only one canal per farm to aid in improving the ecosystem integrity. It is apparent, Lake Naivasha risks suffering irreparable degradation in the next prolonged drought season if canalization effects are left unmitigated.