Considering the data for all the rivers at the continental level, there has been little change in nitrate (NO3-N) concentrations between the two decades under comparison. Changes in the median value were not statistically significant. European rivers showed the highest nitrate loads transported to the marine environment. Comparing data from the two decades, North American and European rivers have remained fairly stable, while major river basins in South Central and Southeast Asia have recorded higher nitrate concentrations. Nitrate is a major nutrient, and excess levels can cause eutrophication with symptoms such as decrease in oxygen levels, algal blooms and reduced biodiversity.