Efficiency and dimensioning of riparian buffer zones in agricultural catchments

A strong linear correlation was found between the log-transformed load and retention of nitrogen and phosphorus in riparian buffer zones (r = 0.99 and 0.997, respectively). Analyses of N and P budgets in four riparian forests of varying age (two grey alder stands in Estonia and two riparian deciduous forests in USA) show a significant efficiency. Despite the different input load (72.9-110.4 kg N ha(-1) year(-1) and 2.5-3.0 kg P ha(-1) year(-1)), the outputs into streams from the alder stands systems were comparably low (9.0-13.2 and 0.38-0.62 kg ha(-1) year(-1)). The older forests from the USA showed less efficiency. Plant uptake of both N and P in younger stands was significantly higher than in older forests. Methods to determine the buffer zones' and buffer strips' width and their efficiency are presented. The testing of efficiency assessment in a watershed in Estonia demonstrated an expected efficiency of buffers. (C) 1997 Elsevier Science B.V.