Understanding the role of river restoration in maintaining good water quality

We are used to living with our back turned to the environment. In particular, related to rivers, we usually enjoy them without any interest on their quality. We don't usually go further than to check if the water seems clean, if it looks clear and looks good to swim on it. However, the river is more than that, it is a whole ecosystem where external factors cause dramatic changes to water quality and that in turn affects us.

Rivers are naturally dynamic; they flood adjacent lands, erode their banks and bed, and move sediment around. However, human activities have affected them causing changes on the river and increasing risk of flooding as well as may effect on the habitat diversity. This is why, river restoration is achieving strength as an alternative way to protect ecosystem health, preserve water resources and provide flood protection.

This issue is a global problem, affecting all parts of the world. To have a better understanding of river restoration projects and their effect of water quality, , Vidhya Chittoor Viswanathan, early stage researcher in ADVOCATE Project , in tandem with Professor Mario Schirmer have published recently a paper titled " Water quality deterioration as a driver for river restoration: a review of case studies from Asia, Europe and North America ".

This review is aimed at transferring lessons learned from various restoration projects focusing on water quality improvement from different parts of the world. To achieve this, restoration projects aimed at water quality amelioration through river restoration are chosen from four countries across three continents (Europe, Asia and North America).

In general terms, the situation is as follows, the rivers from industrialized countries have been subjected to spills, overuse or the misuse of them, decreasing their quality. Several restoration projects around the world were found to focus on water quality amelioration through river restoration. However, there is a major lack of understanding of the biogeochemical processes affected by river restoration. The Thur River in Switzerland is used as example, to test river restoration's influence on water quality on a river reach and catchment scale.

The river Thur in Switzerland is a tributary of the Rhine. It is a highly dynamic river in a catchment with no reservoirs to control its dynamic discharge patterns. The landuse also varies significantly in the pre-demoninantly agricultural catchment, which is 61 % agriculture, 30 % forest and only 9 % urban. As the lower part of the Thur River was often flooded by melt water in Spring, the river restoration was considered to be an alternative flood protection measure by the Cantonal authorities. The 2km stretch river restoration project in the lower part of the river was completed in 2003. Although, it was mainly done for flood protection it is also expected to improve water quality and provide ecological improvement by increasing habitat diversity as well.

That sounds great; on the other hand, as most restored rivers are not monitored at all, it is difficult to predict consequences of restoration projects or analyse why restoration projects fail or are successful.Evaluating the success of this river restoration is often restricted in large catchments due to a lack of high frequency water quality data, which are needed for process understanding. Vidhya Chittoor has developed a study in the framework of ADVOCATE Project where these challenges were addressed by looking at the diurnal and seasonal changes in flow and water quality and measuring water quality parameters including dissolved oxygen (DO), temperature, pH, electrical conductivity (EC), nitrate and dissolved organic carbon (DOC) with a high temporal frequency (15 minutes - 1 hour). In addition, the stable isotopes of water (δD and δ18O-H2O) as well as those of nitrate (δ15N-NO3-and δ18O-NO3-) were also measured to follow changes in water quality in response to the hydrological changes in the river.Finally, this study may be found in further detail on the paper titled " Does river restoration affect diurnal and seasonal changes to surface water quality? A study along the Thur River, Switzerland ", whose author is Vidhya Chittor Viswanathan . This paper is still in press.

Chittoor Viswanathan, V., & Schirmer, M. (2015). Water quality deterioration as a driver for river restoration: a review of case studies from Asia, Europe and North America Environmental Earth Sciences DOI:10.1007/s12665-015-4353-3