Assessment of nitrogen and phosphorus loading by atmospheric dry deposition to the Lagos Lagoon, Nigeria

Surface water pollution has been found to be considerably driven by the contributions of airborne particles, open-air waste burning and fossil fuel combustion, ammonia volatilization from excreta, fertilizer and derivatives from explosive factories. Atmospheric deposition into the Lagos Lagoon is suspected to be a major contributor to the nutrient levels of the lagoon. Atmospheric dry nutrient deposition was monitored at six stations around the Lagos Lagoon from January to June 2012 in order to estimate the contribution of atmospheric deposits into the lagoon’s nutrient cycles. Species of phosphorus (P) and nitrogen (N) in the lagoon water were analyzed by colorimetric methods. Mean [NO−3 + NO−2]-N was 3.08 ± 2.10 mg m−2 day−1 (0.55–8.73 mg m−2 day−1). The (NO−3 + NO−2)-N was only about 2 % of total N but [NH+4 + organic]-N was approximately 38 % of total N. Particulate N was about 60 % of total N. Average total N was 144 ± 94.9 mg m−2 day−1 (48.0–285 mg m−2 day−1). Average soluble reactive P was significantly lower than [NO−3 + NO−2]-N averaging about 0.12 ± 0.12 mg m−2 day−1. Soluble reactive P (SRP) was less than 2 % of total P but soluble organic P was about 86 % of total P. Particulate P accounted for about 12 % of total P. Average total P was 4.56 ± 10.1 mg m−2 day−1 (0.48–31.6 mg m−2 day−1). This study shows that atmospheric deposition of nutrients into the Lagos Lagoon is taking place and this may represent a considerable proportion of the total nutrient loading of the lagoon.