How can we maintain healthy river ecosystem?

The challenge

Water temperature and dissolved oxygen (DO) are both fundamentally important to the biological health of rivers, and therefore to the delivery of the Water Framework Directive objectives to enhance and maintain the quality of European waters. Many species are tolerant only of specific water temperature ranges. Variations in daily and seasonal water temperatures are important factors in determining the distribution of aquatic organisms.

The solution

Dissolved oxygen is an important indicator of river health and used by regulators as part of the classifications for good chemical status. The overall level of oxygen in a river is a balance between reaeration at the water surface and loss of oxygen in satisfying chemical and microbial oxygen demands in the water column or from the river bed.

The water quality model QUESTOR was applied in a stepwise manner (adding modelled processes or additional data) to simulate the flow, water temperature and dissolved oxygen concentrations along a 14 km reach. The aim of the stepwise model building was to find the simplest process-based model which simulated the observed behaviour accurately.

A simulation of both water temperature and dissolved oxygen at an hourly resolution was developed.

Resulting benefits

The resulting model is still very much a prototype that needs to be tested against other data sets and in other conditions. However the results obtained show promise in giving an insight into how flow, nutrient and radiation regimes combine to influence the growth of macrophytes. Such an insight can inform the future management of rivers, e.g. whether increased shading could be a local method of controlling macrophyte growth, and whether nutrient reduction will be effective in controlling in-stream primary productivity. Understanding controls on primary production can make a significant contribution to the objective of improving, or maintaining, healthy river ecosystems.