Comparing heterogeneity in floodplain soils of restored two-stage vs. unmaintained AG streams

Elizabeth Berg

Heterogeneity allows for niche partitioning and is therefore important in all ecosystems. In streams, this can be seen with the variety of heterogeneities as you go from reach level down. The variety of habitats can allow for a variety of organisms, increasing biodiversity. The same is true on a smaller scale in the streams for the microbiota. Heterogeneity in these streams will increase microbial processes, therefore, heterogeneity is very important. 

Picture3Trapezoidal ditch unmaintained for ten years

Healthy streams are more complex streams. This heterogeneity is occurring because the stream is interacting with its environment. When it floods, the floodplains are covered in water, increasing the surface area of the stream as well and thereby increasing microbial processing.In streams, we have hot spots and hot moments—the heterogeneity can occur both in time and in space. For example, you can see the variety in light, substrate size, and how a stream curves, as well as many other examples. Also in time, think of big rain storms and how much that affects little streams. Heterogeneity is affected by flow often in streams, so things like flood events can sort substrate or increase the width producing more interaction between the riparian zone and the stream.

Natural streams are extremely heterogeneous. These natural streams create their own floodplains and interact heavily with the terrestrial environment around them. However, human management often levels out streams, making them homogenous and standard. Imagine canals in a city. This reduces the microbial processes’ rates

However, now in the AG (agricultural) Midwest, we have a lot of trapezoidal ditches, created with the goal of draining fields quickly. These ditches were constructed without biology in mind. These take the water away from the fields, but look very little like a natural stream and have very little heterogeneity. There is little variety in the vegetation and the channel is very incised, reducing any floodplain that could be there.

Recently, some scientists have been working with farmers to create two-stage ditches in order to help reduce flooding on fields. These also recreate the floodplain that was once there by increasing the channel width. This increases the heterogeneity of the stream, and potentially can increase the soil quality as well. In addition, the restoration of the floodplain creates more surface area for microbial processes to occur.

Picture2Two-stage ditch dug out by back hoe

But, in the end, it took an unmaintained reach 10 years to get to this point and it still didn’t have the same level of soil quality that the new two-stage ditch had, but the two-stage ditch was created in a day. This means that building the two stage ditches can help jump start that process that the stream would do on its own and can create these good micro-habitats for microbiota more quickly. Overall, this increases the health of the stream faster and makes the stream a more natural environment. It is a good restoration method.Overall, the unmaintained ditch had lower soil quality than the two-stage ditch. This was most clear in the near stream portion of the stream, but was also true for the reach as a whole. Both reaches had extremely heterogeneous soil quality, they mimic a natural stream in this way. This likely is promoting a good environment for microbes to do their processing. Whether unmaintained or restored, they both lead to similar results of heterogeneity.