Lake Nakuru, Kenya, is one of a series of saline–alkaline closed basin lakes in the eastern arm of the Rift Valley. The lake has been variously described as ‘the lake of a million flamingos’ and ‘the Worlds greatest ornithological spectacle’ and is bedrock to the areas’ tourism. The lake was designated a bird sanctuary in 1960, a National Park in 1968, first rhino sanctuary in 1987, first Kenyan Ramsar site in 1990, an Important Bird Area in 1999 and a world‐class national park in 2005. Over the last 40 years, its basin has been heavily settled, extensively cultivated, urbanized and industrialized. Environmental problems include poor agricultural practices, human encroachment, pollution, wildlife mortality/morbidity, human/wildlife conflicts, poverty, ethnic tensions and land clashes and lack of adequate legal and policy framework. Approaches to conservation have been initiated against identified existing problems and constraints. These approaches are (i) organizational and institutional development; (ii) hot spots and pollution loads management and (iii) catchment and park management. Constraints have been identified as unclear demarcation of responsibilities, lack of budget, skilled staff and know‐how and lack of environmental standards and regulations. The impacts of ecosystem changes on people’s lives and livelihoods are discussed.

Toxic trace metals have been implicated as a potential cause of recent flamingo kills at Lake Nakuru, Kenya. Chromium (Cr), copper (Cu), lead (Pb), and zinc (Zn) have accumulated in the lake sediments as a result of unregulated discharges and because this alkaline lake has no natural outlet. Lesser flamingos (Phoeniconaias minor) at Lake Nakuru feed predominantly on the cyanobacterium Spirulina platensis, and because of their filter-feeding mechanism, they are susceptible to exposure to particlebound metals. Trace metal adsorption isotherms to lake sediments and S. platensis were obtained under simulated lake conditions, and a mathematical model was developed to predict metal exposure via filter feeding based on predicted trace metal phase distributions. Metal adsorption to suspended solids followed the trend Pb k Zn Ͼ Cr Ͼ Cu, and isotherms were linear up to 60 g/L. Adsorption to S. platensis cells followed the trend Pb k Zn Ͼ Cu Ͼ Cr and fit Langmuir isotherms for Cr, Cu and Zn and a linear isotherm for Pb. Predicted phase distributions indicated that Cr and Pb in Lake Nakuru are predominantly associated with suspended solids, whereas Cu and Zn are distributed more evenly between the dissolved phase and particulate phases of both S. platensis and suspended solids. Based on established flamingo feeding rates and particle size selection, predicted Cr and Pb exposure occurs predominantly through ingestion of suspended solids, whereas Cu and Zn exposure occurs through ingestion of both suspended solids and S. platensis. For the lake conditions at the time of sampling (1.2 g/L suspended solids, 0.23 g/L S. platensis), predicted ingestion rates based on measured metal concentrations in lake suspended solids were 0.71, 6.2, 0.81, and 13 mg/kg-d for Cr, Cu, Pb, and Zn, respectively. Higher exposure doses are predicted when metal concentrations are determined from sediment concentrations rather than suspended solids concentrations. Also, decreases in the S. platensis population would increase the clearing rate of the flamingos and increase predicted metal exposure via ingestion of suspended solids. For example, with metal concentrations calculated based on average metal concentrations in lake sediments and S. platensis concentration of 0.06 g/L, exposure rates would be 13, 10, 4.4, and 38 mg/kg-d for Cr, Cu, Pb, and Zn, respectively. These ingestion rates, except for Cu, are significantly higher than the no observable adverse effects levels. Keywords-MetalToxicity Adsorption Filter feeding Flamingo Trace metal exposure model for filter-feeding flamingos

No abstract

T oxic trace metals have been implicated as a potential cause of recent flamingo kills at Lake Nakuru, Kenya. Chromium (Cr), copper (Cu), lead (Pb), and zinc (Zn) have accumulated in the lake sediments as a result of unregulated discharges and because this alkaline lake has no natural outlet. Lesser flamingos (Phoeniconaias minor) at Lake Nakuru feed predominantly on the cyanobacterium Spirulina platensis, and because of their filter-feeding mechanism, they are susceptible to exposure to particlebound metals. Trace metal adsorption isotherms to lake sediments and S. platensis were obtained under simulated lake conditions, and a mathematical model was developed to predict metal exposure via filter feeding based on predicted trace metal phase distributions. Metal adsorption to suspended solids followed the trend Pb k Zn � Cr � Cu, and isotherms were linear up to 60 �g/L. Adsorption to S. platensis cells followed the trend Pb k Zn � Cu � Cr and fit Langmuir isotherms for Cr, Cu and Zn and a linear isotherm for Pb. Predicted phase distributions indicated that Cr and Pb in Lake Nakuru are predominantly associated with suspended solids, whereas Cu and Zn are distributed more evenly between the dissolved phase and particulate phases of both S. platensis and suspended solids. Based on established flamingo feeding rates and particle size selection, predicted Cr and Pb exposure occurs predominantly through ingestion of suspended solids, whereas Cu and Zn exposure occurs through ingestion of both suspended solids and S. platensis. For the lake conditions at the time of sampling (1.2 g/L suspended solids, 0.23 g/L S. platensis), predicted ingestion rates based on measured metal concentrations in lake suspended solids were 0.71, 6.2, 0.81, and 13 mg/kg-d for Cr, Cu, Pb, and Zn, respectively. Higher exposure doses are predicted when metal concentrations are determined from sediment concentrations rather than suspended solids concentrations. Also, decreases in the S. platensis population would increase the clearing rate of the flamingos and increase predicted metal exposure via ingestion of suspended solids. For example, with metal concentrations calculated based on average metal concentrations in lake sediments and S. platensis concentration of 0.06 g/L, exposure rates would be 13, 10, 4.4, and 38 mg/kg-d for Cr, Cu, Pb, and Zn, respectively. These ingestion rates, except for Cu, are significantly higher than the no observable adverse effects levels.

The 18th World Lake Conference, entitled “Governance, Resilience, and Sustainability of Lakes for a Better Society” was held virtually from November 9th to 11th, 2022 at the University of Guanajuato, Mexico. This forum was designed with the primary objective of providing a space where scientists, professionals, students, managers, and practitioners could propose, share, and learn about studies, strategies, and actions which enhance the management of lakes around the world. Different activities were contemplated and scheduled in the organization of this forum, such as conferences, special sessions, technical sessions, and workshops where 194 distinguished investigators and participants shared the results of their research and the knowledge they have gained over the years.