Emmanuel Mgimwa

Introduction
The influence of physical-chemical variables on phytoplankton and lesser flamingo (Phoeniconaias minor) abundances have been studied in the East African Rift Valley Soda lakes such as Bogoria (Ballot et al., 2004, Schagerl & Oduor 2008, Tebbs et al., 2013, & Robinson, 2015), Nakuru (Ballot et al., 2004, Schagerl & Oduor 2008, Robinson 2015, & Krienitz et al., 2016), Elementaita (Ballot et al., 2004, Schagerl & Oduor 2008, Robinson, 2015), Oloidien (Robinson, 2015) and Manyara (Kihwele et al., 2014). However, there are no studies on the influence of physical-chemical variables on phytoplankton and lesser flamingo abundances at lake Natron despite being the only important and regular breeding area for the East African lesser flamingo populations (Baker & Baker 2002, & Wildlife Division, 2010). Although migration and erratic movements of lesser flamingo has been documented (Baker 1997, & Baker & Baker, 2002), a sizeable number of flamingos has been found to stay at lake Natron throughout the year. The migrating lesser flamingos spend time at lake Natron before and after the breeding season (October - February but can breed throughout the year if conditions are favourable) making it important to understand the productivity levels of the phytoplankton and the underlying physical-chemical variables.

This study investigated the relationship of the lesser flamingo and phytoplankton abundances and how the physical-chemical variables (dissolved oxygen, water turbidity, pH, nitrate (NO3-), ammonium (‎NH4+) and phosphate (PO43-)) affect Chlorophyll-a abundance at lake Natron. The study used Chlorophyll-a as a measure of phytoplankton and selected physical-chemical variables with the greatest influence on the phytoplankton's primary productivity.

Conclusion
Findings from this study suggest that annual fluctuation in the lesser flamingos numbers in lake Natron is triggered by phytoplankton abundance whose primary productivity is influenced by physical-chemical variables in the lake waters. In turn, these changes are mainly due to both anthropogenic activities and weather changes within the lake basin and its surroundings.
The observed trend in physical-chemical variables at the three study lagoons is a result of the spatial distribution of freshwater sources from Pinyinyi, Engaresero and Ewaso Ng’iro rivers and the dilution effect from rainfall and evaporation. The importance of the hydrological balance for the productivity of lake Natron is of paramount for the survival of the lesser flamingos. Being a closed (no river flowing from this lake) and transboundary ecosystem, any hydrological changes will impact the limnology and, in turn affect phytoplankton productivity.