Nitrogen and phosphorus levels in sediments from tropical Catatumbo river (Venezuela)

Nitrogen (N) and phosphorus (P) concentrations were determined in sediment samples along the bed of Catatumbo river in both Colombian and Venezuelan t erritories until the river outlet in Maracaibo lake. Total phosphorus was d etermined by digestion with HCl followed by analysis using the ascorbic aci d method and total nitrogen was done using the standard microkjeldahl metho d plus nitrate-nitrite. Ammonium, orthophosphate and nitrate were determine d using standard methods after extraction steps. The mean concentrations al ong the river bed were found in an interval of 0.035 and 1.492 mg g(-1) dry sed. for nitrogen and 0.027 and 1.039 mg g(-1) dry sed. for phosphorus at 95% confidence level. The mean molar ratio N/P in the river bed was 4.42 an d 3.46 for river outlet zones in the lake, which indicates that nitrogen is the limiting nutrient. For comparison with previous results of lake sedime nts from sites near the river outlet it was concluded that Catatumbo river is a significant source of nutrients to the Maracaibo Lake system because s ediment nutrients concentrations from Catatumbo river were higher than the ones in Maracaibo Lake. Statistic studies showed significant differences be tween countries, zones and similar behaviour in the river bed as related to the affluent rivers.