Modify crop farming practices in watershed to reduce pollution: freshwater marshes

How is the evidence assessed?
  • Effectiveness
  • Certainty
  • Harms

Study locations

Key messages

  • One study evaluated the effects, on vegetation in freshwater marshes, of modifying crop farming practices in the watershed to reduce pollution. The study was in the USA.


  • Community composition (1 study): One replicated, site comparison study in the USA reported that freshwater marshes being restored by abandoning cropland in the watershed (along with removing topsoil from the marshes) contained a different overall plant community, after 1–12 years, to both natural and degraded marshes nearby.
  • Overall richness/diversity (1 study): The same study reported that freshwater marshes being restored by abandoning cropland in the watershed (along with removing topsoil from the marshes) contained fewer wetland plant species, after 1–12 years, than nearby natural marshes.




About key messages

Key messages provide a descriptive index to studies we have found that test this intervention.

Studies are not directly comparable or of equal value. When making decisions based on this evidence, you should consider factors such as study size, study design, reported metrics and relevance of the study to your situation, rather than simply counting the number of studies that support a particular interpretation.

Supporting evidence from individual studies

  1. A replicated, site comparison study around 2010 of 48 ephemeral freshwater marshes in Nebraska, USA (O’Connell et al. 2013) reported that marshes undergoing restoration (surrounding cropland abandoned and agricultural topsoil removed) contained a different plant community to natural marshes (surrounded by permanent grassland) and degraded marshes (surrounded by cropland), with lower cover of wetland perennial plants and fewer wetland perennial species than the natural marshes. Results summarized for this study are not based on assessments of statistical significance. After 1–12 years, the overall plant community composition differed between restored, natural and degraded marshes (data reported as a graphical analysis). Perennial wetland species were underrepresented in restored marshes (43% cover; 10.1 species/marsh) compared to natural marshes (56% cover; 13.0 species/marsh). However, restored marshes had greater cover of these species than degraded marshes (35% cover; species richness not reported). Annual wetland species were “slightly” overrepresented in restored marshes compared to natural marshes in terms of abundance (data reported as a graphical analysis only). However, there was a similar number of these species in restored marshes (8.2 species/marsh) and natural marshes (8.0 species/marsh). Methods: Around 2010, vegetation was surveyed in 48 ephemeral playa marshes (along two transects crossing each marsh, in both the cool and warm seasons). Sixteen of the marshes were undergoing restoration under the Wetland Reserve Program. This involved abandoning the surrounding cropland and removing eroded agricultural topsoil from the marshes. The study does not distinguish between the effects of these interventions. Of the remaining marshes, 16 were in natural catchments and 16 were in degraded, farmed catchments.

    Study and other actions tested
Please cite as:

Taylor N.G., Grillas P., Smith R.K. & Sutherland W.J. (2021) Marsh and Swamp Conservation: Global Evidence for the Effects of Interventions to Conserve Marsh and Swamp Vegetation. Conservation Evidence Series Synopses. University of Cambridge, Cambridge, UK.

Where has this evidence come from?

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Marsh and Swamp Conservation

This Action forms part of the Action Synopsis:

Marsh and Swamp Conservation
Marsh and Swamp Conservation

Marsh and Swamp Conservation - Published 2021

Marsh and Swamp Synopsis

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