Importance of long-term monitoring for detecting environmental change: lessons from a lowland river in south east England

摘要

Rising nitrate concentrations in rivers and groundwater in regions withintensive agriculture have been of concern for several decades. Long recordsof nitrate concentration are rare; in the UK, few pre-date 1974. Recordsfrom the River Stour from 1937 are analysed using moving-windows to explorethe effects of window width on trend detection and process inference.Nitrate concentrations rose sharply from the late 1950s in response towidespread ploughing of grassland, but have fallen since the early 1980s,suggesting that widespread nitrogen control measures, which were introducedafter the start of the downward trend, may not be the principal driver forrecent change. Short windows (5 years) are too noisy; longer windows (10, 15and 30 years) identify signals (i.e. trends) more reliably. Since systemresponse times can be of the order of 20–30 years, management decisions madeon shorter data sets (even up to 15 years) could be misleading.