Comparison of sampling methodologies for nutrient monitoring in streams: uncertainties, costs and implications for mitigation

摘要

Eutrophication of aquatic ecosystems caused by excess concentrations ofnitrogen and phosphorus may have harmful consequences for biodiversity andposes a health risk to humans via water supplies. Reduction of nitrogen andphosphorus losses to aquatic ecosystems involves implementation of costlymeasures, and reliable monitoring methods are therefore essential to selectappropriate mitigation strategies and to evaluate their effects. Here, wecompare the performances and costs of three methodologies for the monitoringof nutrients in rivers: grab sampling; time-proportional sampling; andpassive sampling using flow-proportional samplers. Assuming hourlytime-proportional sampling to be the best estimate of the "true" nutrientload, our results showed that the risk of obtaining wrong total nutrient loadestimates by passive samplers is high despite similar costs as thetime-proportional sampling. Our conclusion is that for passive samplers toprovide a reliable monitoring alternative, further development is needed.Grab sampling was the cheapest of the three methods and was more precise andaccurate than passive sampling. We conclude that although monitoringemploying time-proportional sampling is costly, its reliability precludesunnecessarily high implementation expenses.