= Environmental impact
An <environmental impact> is a change in environmental conditions attributable to an activity or intervention. The change can concern <biodiversity>, <water> quality, <carbon storage> or another specified property of an <ecosystem>. Its sign and magnitude depend on the chosen outcome, spatial boundary and observation interval.
Causal interpretation requires a comparison: a change observed after an intervention might also reflect <climate> variation. A long-term grassland experiment directly varied <species richness> and followed annual aboveground <biomass> production. Higher <species richness> increased the temporal stability of total production, even though individual <species> could fluctuate more strongly.<Biodiversity and ecosystem stability in a decade-long grassland experiment by David Tilman and others>[Nature 441, pp. 629–632; experimentally imposed species numbers and temporal stability]{ref} The example shows why measuring an <environmental impact> requires identifying both the affected property and a credible comparison, rather than treating every environmental measurement as evidence of a particular cause.
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