Lina Polvi Sjöberg – Geomorphic complexity and sediment

Geomorphic complexity and ecological processes and interactions in stream restoration

I am interested in understanding the natural form and processes of streams, which can be used to restore degraded streams to a more ‘natural’, self-sustaining form. The regional focus of most of my recent research is northern Sweden, where most streams, large and small, were severely altered to facilitate timber floating and are now undergoing different types of restoration to increase habitat quality and quantity.

There are several aspects of natural stream processes that my research focuses on. First, geomorphologists know a lot about how alluvial streams form and change, which are those that are self-formed in sediment (sand, gravel, boulders) that has been transported and deposited by the stream itself. But in northern Sweden most streams are semi-alluvial, meaning that some of the sediment that makes up the stream’s bed and banks came from somewhere else than the stream itself, namely glacial deposits of coarse cobbles and boulders. Therefore, the classical equations and processes used to predict channel form do not apply in northern Sweden. In the MorphoRest project, I am analyzing how sediment moves and how we can predict natural channel form in semi-alluvial streams. Second, I am interested in how complexity of streams can be quantified and how this impacts ecological characteristics and processes— how is overall geomorphic complexity best quantified? Does geomorphic complexity automatically translate into increased biodiversity of instream organisms or riparian vegetation, or possibly higher quality of ecosystem processes?

Finally, in the BioRest project, which I am co-leading together with Christer Nilsson, we are taking a look at how larger landscape-scale processes and features impact the biotic recovery of restored site. Streams are unique in the landscape in that they are not separate, discrete features, but they connect the entire landscape from the mountains to the sea. Water, sediment, animals, and seeds move downstream (and animals such as fish even move upstream) at different speeds and are caught or deposited in different sections of the stream system, which influences how a specific section of a stream looks like, in terms of the ecology and geomorphology. In northern Sweden, we have different types of stream segments that alternate throughout the stream system, including turbulent rapids with coarse sediment, slow-flowing meandering sections, and lakes. In the BioRest project, we are working to figure out how restored stream sections recover based on how the stream section fits into the larger landscape and stream system.

Most of my past research has focused on the connection between physical processes in streams (how water flows and sediment shape how the stream looks like) and ecological characteristics and processes. For example, in Colorado, USA, I have examined the role of geomorphology in determining the width of the riparian zone, and the role of beaver and plants in forming how the stream behaves and looks like. I believe that in order to best manage the amazing natural resource that streams are we need to understand how streams work from both a geomorphic and ecological point of view, as well as interactions between them.


Surveying the channel with a total station to quantify complexity

A restored stream in northern Sweden with coarse boulders, instream wood, and opened side channels

A restored stream in northern Sweden with coarse boulders