A novel approach to measure nutrient fluxes in permeable sediments

Around the globe, the coastal ocean is of immense importance, as it provides critical functions for the environment, society and economy. Sediments play a fundamental role in the wellbeing of the coastal ecosystems as they are able to convert, store and release chemical compounds that affect and control life. For example, sediments are a major sink for oxygen, but it is also suggested that coastal sediments are very important in the recycling of nutrients, a process that controls primary production, but also plays a role in the production of algal blooms or low oxygen conditions in coastal waters. However, due to the specific geophysical characteristics of many coastal sediments (i.e. they often are composed of loose sand grains), measurements that quantify the nutrient exchange between the sediments and water column are very difficult and hence the recycling capacity of nutrients in these sandy sediments is not well quantified, even though it is likely to be highly important.

Here we propose a proof-of-concept study to develop a new capability to quantify the exchanges of nutrients between different types of sandy sediments and the water column. To achieve this, we will adapt a well-known technique to measure oxygen exchange between sediments and the water column (i.e. so called benthic chambers). We will equip these flux exchange recorders with novel miniaturized sensors that autonomously can measure nutrient concentrations in an enclosed volume of water. We will also integrate them with sensors measuring water flow and sediment bed properties. We first will verify the functioning of the new approach in the laboratory and then demonstrate it in a real-world scenario. For this we have chosen an area along the UK South Coast, that is known for high nutrient levels, caused by agricultural discharges, wastewater, urban runoff and sewer overflows, and where high nutrient inputs historically already led to algal blooms and low oxygen concentrations in the water column. This novel capacity can produce knowledge that is urgently needed to sustain a healthy environment and manage our natural resources and on the longer-term can be adapted to measure other geochemical species, e.g. other pollutants and in different environments.