Ditches are indispensable in the Dutch lowlands, but their role in the climate is often overlooked. This thesis shows that ditches and their sediments can be active sources of greenhouse gases, particularly methane. Although ditches cover only a small part of the landscape, the oxygen-deprived conditions in the ditch sediment mean they can nevertheless contribute significantly to total emissions. The research shows that these emissions are not simply determined by surrounding land use or soil type, which leads to uncertainties when extrapolating emissions. It is precisely the conditions within the ditch itself that are important: the composition of the sediment, water quality, the presence of plants and management practices. Furthermore, emissions vary significantly over time, meaning that measurements taken only occasionally can give a distorted picture. For this reason, this research also involved the development of an automatic measuring device, BERTHA, which can measure greenhouse gases from ditches much more frequently and accurately than manual measurements. Furthermore, this thesis investigates what happens to sediment dredged from ditches. This material can also emit greenhouse gases. Climate-conscious water management therefore requires attention to be paid to the entire ditch: water, soil and dredged material.
Judith van der Knaap obtained a BSc in Health Sciences from Maastricht University and a BSc in Biology from Radboud University. She then went on to complete an MSc in Biology: Conservation and Restoration Ecology at Radboud University. From 2021 to 2025, she worked as a PhD candidate in the Ecology Department at Radboud University as part of the National Research Programme on Greenhouse Gases in Peat Meadows (NOBV). Her PhD research focused on the role of ditches and sediments in greenhouse gas emissions in the Netherlands. During her PhD programme, she presented her work at national and international conferences and to water managers. In 2024, she received the Christine Mohrmann Stipendium for promising female PhD students at Radboud University.