Furthermore, there is often a time-lag between the application of nutrients to land and nutrient losses being detected in surface waters, which can span decades following changes in farming practice:
Ar ben hynny, yn aml mae oedi rhwng gwasgaru maethynnau ar y tir a chanfod colledion maethynnau mewn dŵr wyneb, sy'n gallu rhychwantu degawdau yn dilyn newidiadau mewn arferion ffermio: