Larval odonates as bioindicators of cattle grazing and water quality at prairie wetlands

Vegetation near wetlands is precious habitat for odonates such as dragonflies and damselflies. Odonates could therefore be a prime indicator of the ecological impact of cattle grazing near wetlands. Christine completed a study of 27 prairie potholes in south-eastern Alberta with different cattle grazing scenarios. The study investigated the suitability of odonates as biological indicators, or bioindicators, of the impact of cattle grazing on wetland water quality, vegetation structure, vegetation diversity, and the aquatic macro-invertebrate communities at prairie wetlands.

As Christine's thesis states,

Cattle are given free access to prairie wetlands in the study area as a source of drinking water and supplementary forage. Cattle were commonly observed targeting their grazing efforts on wetland vegetation and effectively removing most of the emergent vegetation (e.g. Typha latifolia and Scirpus sp.). Unrestricted cattle access to wetlands is a well-established management strategy that has arisen [from] convenience and economy rather than ecological study. It has been demonstrated that keeping cattle out of wetlands and providing on-site watering troughs can improve cattle health and weight gain, and in turn increase ranchers' profits.

The impacts of cattle grazing include:

• Changed plant species composition, including decreased richness and vegetation density
• Disrupted ecosystem function, such as nutrient cycling and succession
• Changed ecosystem structure, such as vegetation height and soil erosion

The picture below shows the difference between heavily grazed and un-grazed wetlands. Deferred grazing refers to grazing that only allows cattle to graze after waterfowl have nested, and their young are fledged.