| | | 20.3 Limiting nutrients in Lake Malawi, Victoria and Tanganyika |
While P is the nutrient most often limiting algal growth and biomass in most fresh water systems, this is not necessary the case in tropical lakes. In Lakes Malawi, Tanganyika, and Victoria, concentrations of N and P in surface waters are low (Figure 3). Talling and Talling (1965) suggested that low nitrate concentrations in Lake Victoria indicated a potential for N limitation. While phytoplankton in Lake Victoria appears slightly deficient in N, neither N nor P appears to be limiting, based on Redfield ratios. Similarly, particulate nutrient ratios in Lake Malawi suggest N and P deficiency. Evidence suggests that photosynthesis in Lake Victoria is now light limited, but in Lake Malawi Guildford et al. [203] found that phytoplankton growth is rarely controlled by light. Little work has been done to identify limiting nutrients in Lake Tanganyika, but the fact that the N: P regeneration ratio is close to 16:1 [220], the optimal ratio for phytoplankton, suggests that also this lake is not limited by these nutrients.
| | | 20.3 Limiting nutrients in Lake Malawi, Victoria and Tanganyika |