Nitrogen, phosphorus, and iron colimitation of phytoplankton communities in the nearshore and offshore regions of the African Great Lakes

Physical–chemical measurements in the water column along a transect through a tilapia cage fish farm in Lake Malawi, Africa

“…The C:N, C:P and N:P ratios generally decline from north stations, through the cages to the south stations (Table 3) although water current direction changed from southerly between January and April to northerly between May and July. The C:N, C:P and N:P ratios in the seston suggest moderate deficiency for both N and P by criteria of along the 10 km study transect and agree with many studies which have generally described Lake Malawi as seasonally P and N limited (Hecky et al, 1996;Guildford et al, , 2003Guildford et al, , 2007North et al, 2008;Gondwe et al, 2008). Consequently, high discharges of both N and P into the lake could, in principle, increase algal biomass commonly measured as chlorophyll concentration in the water column.…”

“…Similar losses of between 70% and 80% C, N and P have been reported from temperate cages by Gowen and Bradbury (1987), Holby and Hall (1991), Hall et al (1990Hall et al ( , 1992 and Kaushik (1998). In Lake Malawi algal growth may be seasonally limited by both N and P (Guildford et al, 2003;North et al, 2008); therefore, both nutrients being added by cage operations have the potential to stimulate eutrophication.…”

Responses of lake phytoplankton to micronutrient enrichment: a study in two New Zealand lakes and an analysis of published data

“…Our analysis of published data did not include results for secondary micronutrient limitation, and this phenomenon was not detected in Lake Waihola or Lake Mahinerangi. However, an increasing number of recent studies lend further support to the importance of micronutrients, particularly iron, in limiting lake phytoplankton productivity in the presence of sufficient N and P (Guildford et al, 2003;Sterner et al, 2004;North et al, 2007North et al, , 2008.…”

Some distinctive subject contributions from tropical Africa to fundamental science of inland waters

“…Experimental tests with phytoplankton, reviewed by Talling and Lemoalle (1998) and Guildford et al (2003), partly support the thesis of widespread N limitation (e.g., Moss 1969), but others have supported a predominant P limitation , Kalff 1983, albeit largely from evidence with lower temperatures at considerable altitude in Kenya. There is some evidence for both types of limitation from the C:N:P ratios in particulate matter in African waters (e.g., Dufour et al 1981, from several physiological tests (North et al 2008), and from the seriation of total P concentration in relation to algal abundance as chlorophyll a (Kalff 1983, Talling 1992, which may differ from regressions based on temperate lakes (Huszar et al 2006). In large lakes, relationships can differ between offshore and inshore regions and implicate iron (Fe) as a co-limiting nutrient (North et al 2008).…”

“…There is some evidence for both types of limitation from the C:N:P ratios in particulate matter in African waters (e.g., Dufour et al 1981, from several physiological tests (North et al 2008), and from the seriation of total P concentration in relation to algal abundance as chlorophyll a (Kalff 1983, Talling 1992, which may differ from regressions based on temperate lakes (Huszar et al 2006). In large lakes, relationships can differ between offshore and inshore regions and implicate iron (Fe) as a co-limiting nutrient (North et al 2008). In the Sudanese Nile system, there were suggestive correlations between the first cessation of population increase and observed mortality in dense populations of the diatom Aulacoseira granulata and the depletion of inorganic N Talling 1958, Talling et al 2009).…”