Groundwater Connection with Landscape

The depth of the water table is partly responsible for different plant species occupying different positions along the slopes from hill to valley, as only the drought tolerant plants can live on the hills in arid regions and water tolerant plants live near streams (Figure 14). In lowland discharge areas of arid climates, water is lost to the atmosphere by evapotranspiration causing salt to accumulate. Such settings develop salt-tolerant vegetation.

Riparian Forest along Sonoita Creek


Pantanal Mato-Grossense National Park
Figure 14 – The depth to the water table can influence the types of vegetation growing in a place. a) In a water stressed environment such as Arizona, United States, trees grow along the stream corridor where the water table is shallow, while desert shrubs and grass grow on the hills where the water table is too deep for plant roots to reach (The Old Pueblo, 2014. “Riparian Forest along Sonoita Creek, southwest of Patagonia Lake, part of which can be seen in the center of the photo” by The Old Pueblo is licensed under CC BY-SA 4.0). b) In places with too much water such as the Pantanal wetlands in Mato Grosso do Sul, Brazil, trees are found on hills where their roots have room to grow in the oxygen rich unsaturated zone above the water table, whereas near the lake shores, the groundwater table is so close to the ground surface that tree roots can’t get sufficient oxygen because there is little if any air in the pores of the soil (Wikimapia, 2020. “Pantanal Mato-Grossense National Park” by Wikimapia is licensed under CC BY 4.0).

The water table occurs everywhere beneath us and when humans change the landscape shape, the vegetation, or purposefully drain groundwater for farming and construction, we change the depth to the water table. This often has problematic consequences for humans and ecological systems. However, we are able to predict consequences before we make changes so as to make informed decisions about our actions. Depending on the predicted consequences, we may decide not to proceed or we may redesign the changes to reduce the adverse effects.

The depth of the water table can have a strong impact on how the land responds to heat. For example, in hot dry areas of Australia where eucalyptus trees are the native vegetation, the natural position of the water table is deeper below land surface than after the eucalyptus trees are cleared for crops. This occurs because the trees consume soil moisture capturing infiltrating water, resulting in minimal groundwater recharge. After the trees are cleared, the crops consume less groundwater so recharge increases and the water table rises. When the water table is near the ground surface, water evaporates leaving dissolved substances behind to form salt precipitates that accumulate in the soil rendering the land unfit for crops. Soil salinization is a cause of cropland loss each year around the globe. In many agricultural regions, management of land use to avoid salinization is key to agricultural productivity.

Another example of water table depth influencing the landscape is the occurrence of wildfires as described by Elbein (2019) in his Pulitzer Prize winning National Geographic article “Tree Planting Programs Can Do More Harm Than Good.” He explains that a shallow water table in wetlands can make the difference between normal wildfires and infernos that cause massive destruction. This was the case in the Fort McMurray wildfire in Alberta, Canada, in 2016, which was the costliest wildfire in Canada’s history. Mossy bogs, a type of wetland known as a peatland, cover an immense part of northern Canada and Russia. Peat is composed of partially decayed organic material such as moss. Peatlands contain large amounts of carbon that is gradually sequestered from the atmosphere over thousands of years. As peat forms, it supports fewer of the typical trees (black spruce in the Alberta case). With fewer trees, more recharge reaches the water table so the water table moves closer to the surface. The shallow water table makes the peatland resilient after wildfires. Peatlands commonly experience low‑intensity fires and are able to recover the carbon lost during the fire in a relatively short period of time because the shallow water table prevents the fire from burning deeply into the peat. When peatlands were drained for the purpose of creating a spruce forest in the Fort McMurray area, an environmental adjustment occurred: the black spruce trees used more water, the water table declined, the shallower peat was replaced by a drier moss species (kindling instead of fire retardant), the large trees became a huge store of fuel, and then the Fort McMurray wildfire ensued. Intensely burned peatlands require long periods of time to recover the carbon released to the atmosphere by the fire (Figure 15). The media attributed this fire to the extremes of nature related to climate change without recognition that human intervention in the shallow groundwater flow system played a key role in the event.


Figure showing how the depth of the water table can influence the impact of forest fires on landscape.
Figure 15 – Scientists studied the landscape after the 2016 Fort McMurray Fire and found that where the water table was lowered by humans beneath peatlands so they could plant a black spruce forest, the fire was more intense and burned deeper, causing large loss of carbon that took 1000s of years to store (after Elbein, 2019; image Wilkinson, 2018).


Groundwater in Our Water Cycle Copyright © 2020 by The Authors. All Rights Reserved.