The Chemical Composition of Precipitation and Its Significance to the Nutrient Budget of Lake Malawi

Relative to other sites studied in Africa, precipitation on the southwestern shore of Lake Malawi is dilute with regard to most constituents, except Ca2+ and HCO 3 − https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9780203748978/6f625601-b027-4df5-afef-f7e4441303c5/content/eq131.tif"/> , and has a chemical composition similar to that observed for remote, non-marine locations. Relatively high NH 4 + https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9780203748978/6f625601-b027-4df5-afef-f7e4441303c5/content/eq132.tif"/> /cation and NO 3 − https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9780203748978/6f625601-b027-4df5-afef-f7e4441303c5/content/eq133.tif"/> /anion ratios indicate a moderate influence of biomass burning on rain chemistry, while a high mean Ca2+ concentration suggests extensive soil deflation. Rain pH averaged ~6, and was controlled almost entirely by Ca(HCO3)2 concentration. Phosphorus in rain appears to originate as aerosols, but the ultimate source is uncertain. It is suggested that soluble nitrogen and sulfate, which were correlated, are produced by biomass burning. Atmospheric deposition is estimated to account for 33% of new P and 72% of new N input into Lake Malawi (excluding N fixation). If the upward flux of nutrients from the monimolimnion is accounted for, atmospheric deposition accounts for 6% of P input to the surface mixed layer, while the atmospheric N contribution remains 72%. A comparison of nutrient input ratios with nutrient concentration ratios in the surface mixed layer suggests that nitrogen is recycled more efficiently than phosphorus within the surface waters of Lake Malawi.