Study

Ecology of water-level manipulations on a northern marsh

Actions

This study is summarised as evidence for the following.

Action Category

Lower water level to restore/create freshwater marshes from other land uses

Action Link
Marsh and Swamp Conservation

Raise water level to restore degraded freshwater marshes

Action Link
Marsh and Swamp Conservation
  1. Lower water level to restore/create freshwater marshes from other land uses

    A replicated, before-and-after study in 1949–1957 in a freshwater wetland in Minnesota, USA (Harris & Marshall 1963) reported that following drawdown of water levels, emergent wetland vegetation colonized the site. Over five years of drawdown, stands of tall emergent plants like softstem bulrush Scirpus validus, cattails Typha spp. and sedges Carex spp. developed on approximately 5,000 acres of 12,000 acres that were previously open water. Elsewhere, exposed mudflats were colonized by species such as marsh fleabane Senecio congestus and red goosefoot Chenopodium rubrum (area not quantified). The study suggested several related factors that affected the type of vegetation that developed, e.g. month of drawdown, soil type (mineral or peat), speed of drying, seed availability, and presence of algal mats. Herbaceous wetland communities present in the first year of drawdown were largely replaced by upland weeds, then woody species, over the following four years. Methods: At some point between 1949 and 1957, water levels were lowered in seven separate wetland pools to stimulate growth of emergent and moist-soil wetland vegetation. Two pools supported islands of emergent vegetation before drawdown. Observations were made after 1–5 years of drawdown in each pool (further details not reported).

    (Summarised by: Nigel Taylor)

  2. Raise water level to restore degraded freshwater marshes

    A replicated study in 1949–1957 in a freshwater wetland in Minnesota, USA (Harris & Marshall 1963) reported that the effects of reflooding on emergent plant abundance depended on the water level and species. Statistical significance was not assessed. In areas with deep water (>15 inches in summer, after reflooding), the density of all emergent plant species declined (e.g. softstem bulrush Scirpus validus: 7.1 stems/ft2 after 1 year of reflooding then 0 stems/ft2 after four years of reflooding; cattails Typha spp.: 0.8 stems/ft2 vs 0.4 stems/ft2). In areas with shallow water (0–10 inches in summer, after reflooding), the density of softstem bulrush and spikesedge Eleocharis palustris declined (9.6–10.3 stems/ft2 after one year vs 0.1–0.3 stems/ft2 after four years) whilst the density of cattails and sedges Carex spp. increased (1.0–1.5 stems/ft2 vs 2.2–2.5 stems/ft2). Methods: At some point between 1949 and 1957, water levels were raised in four separate wetland pools that had been drawn down for the previous 1–5 years. Vegetation was surveyed between one and four years after reflooding, in stands initially dominated by each plant species but with different post-reflooding water depths.

    (Summarised by: Nigel Taylor)

Output references

What Works in Conservation

What Works in Conservation provides expert assessments of the effectiveness of actions, based on summarised evidence, in synopses. Subjects covered so far include amphibians, birds, terrestrial mammals, forests, peatland and control of freshwater invasive species. More are in progress.

More about What Works in Conservation

Download free PDF or purchase
The Conservation Evidence Journal

The Conservation Evidence Journal

An online, free to publish in, open-access journal publishing results from research and projects that test the effectiveness of conservation actions.

Read the latest volume: Volume 18

Go to the CE Journal

Discover more on our blog

Our blog contains the latest news and updates from the Conservation Evidence team, the Conservation Evidence Journal, and our global partners in evidence-based conservation.


Who uses Conservation Evidence?

Meet some of the evidence champions

Endangered Landscape Programme Red List Champion - Arc Kent Wildlife Trust The Rufford Foundation Save the Frogs - Ghana Bern wood Supporting Conservation Leaders National Biodiversity Network Sustainability Dashboard Frog Life The international journey of Conservation - Oryx British trust for ornithology Cool Farm Alliance UNEP AWFA Butterfly Conservation People trust for endangered species Vincet Wildlife Trust