ENVSCI 201: Lecture 6 - Can We Restore Freshwater Systems?

Restoration Goals

Typically, most goals focus on biodiversity of the stream. Then it is followed by channel stability, riparian habitat, in-stream habitat, and water quality.

Restoration Methods

Most methods aim at modify the stream’s morphology and hydrology. Others may focus on riparian restoration. Typically these efforts are on a smaller scale rather than a larger scale.

Riparian Zone Importance

Riparian zones act as a buffer zone for incoming runoff water. They help to regulate the temperatures, sediments, pollutants, and energy of incoming runoff. They also provide an energy input with its detritus as well as provide habitats.

Riparian reconstruction is typically one method for restoration. The width and length of these efforts may have implications on how effective they are, but we are lacking data as most riparian reconstructions are done on a smaller scale (which doesn’t show as much change).

Riparian Replanting

Typically done in urban streams, when the riparian zone is restored by replating specific plants. Successfully doing this is supposed to bring all the benefits that comes with having a riparian zone (energy input, shading, regulation, filteration, etc)

However, it’s effectiveness depends on how the land is actually used around it. The presence of subsurface pipings that directly flow water into stream, going past the riparian zone, completely misses the point of having a riparian zone.

Riparing Fencing

Typically used in agricultural streams where the riparian zone is fenced off from the stock animals. Riparian replanting also tends to occur to restore the riparian zone.

This has the same benefits and limitations as the riparian replanting of urban streams. It also has the added benefits of preventing erosion and nutrient inputs as the fence prevents animals from going near the stream and disturbing the soils.

Ghost of Land Use Past

As talked about before, the effectiveness of these restoration efforts heaving rely on the historical land use of the stream and surrounding area. For example, historical agricultural land-use may mean more sediments in streams which may create problems during restoration efforts and or to the ecological health of the stream

Typically, these efforts tend to improve ecological health somewhat. But we are severely lacking data to state a clear relationship.

Rain Gardens

Green areas that allow for some runoff to infiltrate into the ground instead of being directed into streams through subsurface piping. It uses the concept of bioretention and act as water sinks essentially.

They help to filter incoming particles from runoff, absorb incoming contaminants, increase infiltration into the ground, and also delay stormwater pulses. They tend to have overflow inlets that may directly source runoff into streams when rainfall is too intense

Man-made Habitats/Streams

Man-made habitats or streams are also made, typically with a lot of physical land modification and dredging. These efforts are aimed at creating suitable habitats and streams for organisms to come in and colonise.

Daylighting

It’s a movement of resurfacing the previous grounded and piped streams. A lot of streams are piped and placed underground. This also applies the same concept of create habitat but instead of new habitat, it’s the restoration of old ones.

They’re supposed to restore streams so that daylight can reach them, the connection between hyporheic zone and stream is reestablished, and riparian zones are restored.

These tend to be extremely expensive and time consuming. The effectiveness of these efforts also depends on the goals of daylighting, whether it is more for the cultural aspect or for the ecological component

Field of Dream Hypothesis

It states that if habitat is made (whether new or restored), organisms will come back, colonise, and settle within it. Whether or not organisms comes back to a restored area depends on that area’s connectivity with other already established areas.

Organisms need to be able to successfully disperse from established areas to these newly restored areas, or else they just won’t come.

Nitrogen Cycle in Agricultural Lands

The normal nitrogen cycle is heaving modified and disturbed when agricultural practises are in play.

There is an extra input of nitrogen in the soils (typically from fertilsers and animal waste in the form of ammonium). The ammonium in the soil tends to stick to the soil as it is positively charged. Any unused ammonium is converted into nitrates through nitrification. Nitrates are negatively charged and are therefore easily leached out. The excess ammonium typically means excess nitrates that end up in bodies of water.

Dinitrification is then the final step that converts nitrates back into nitrogen gases.

Nitrification Inhibitors

Work by blocking the nitrification of excess ammonium and mineralisation of animal waste. While it proved to be effective, it had implications as there were questions whether it could work on a larger scale and its possible threats in ending up in dairy/food products.

Two Stage Ditch

When the surrounding floodplain is modified so that there is a step down right before the stream, creating a minifloodplain (typically with riparian plants as well).This is done to help slow down the incoming runoff as well allow the land to better retain various nutrients and contaminants.

It also created anoxic and saturated conditions that allowed for more denitrification, preventing more nitrates from entering the stream.

Scale of Solutions vs. Scale of Problems

Typically, the actual problems that we face are a lot larger than the solutions we apply. Streams are huge and can stretch for kilometres, going past through many different land-uses, have many different disturbances along the way, and so on and so forth.

Typically, we tackle restoration on a lot smaller scale such as on a local scale where we address the stream’s health in a small region. However, there have been efforts to focus restoration on entire catachments as well.