Modelling the Water Table in a Bog

Abstract

Over the past five years, an ongoing study at INES, Lund University, have examined the encroachment of trees and vegetation into a bog ecosystem in northern Scania, Sweden. While several factors have been identified as contributing to this ecological transformation, including, nutrient availability, and climate, the hydrological aspect remains a key area of investigation. This thesis aims to deepen our understanding of how
the groundwater table in the bog changes over time in response to various environmental factors.

To achieve this aim, extensive fieldwork was conducted during the late winter and early spring, during 2023, to measure the water table and gather data on rainfall and evapotranspiration. The measurements were taken using a combination of manual techniques, such as pressure transducers, and automated data loggers. These measurements were then combined with existing data on the bog’s hydrological regime, as well as data
from SMHI (Sveriges meteorologiska och hydrologiska institut) covering the local area, to create a model of the groundwater table.

The model revealed several important insights into the hydrological dynamics of the bog. Firstly, it showed that the water table responds rapidly to rainfall, with a sharp increase in water levels observed following periods of heavy precipitation. Additionally, there is also occasionally an unknown source pushing the water tables to even higher levels. Secondly, it demonstrated the importance of evapotranspiration in regulating the water balance of the bog. Thirdly, it revealed a steady rate of water runoff, indicating that the bog acts as an important water regulator for the surrounding landscape.

These findings have important implications for the management and conservation of bogs and wetland ecosystems. The model created in this thesis allows forecasting of fluctuations in the groundwater table through numerical analysis of the given data, thus enabling the tracking of water table changes. Furthermore, the model can be adapted for use in other bogs and wetlands with minor adjustments, providing a valuable tool for future research in this field.

Popular Abstract

Water flow has been studied for decades by scientists in many fields of natural science for many reasons. It is necessary to have a solid understanding of physics, such as classical mechanics and fluid dynamics and have passed a number of levels in university mathematics in order to comprehend the movement of water.

Peat often develops as a result of incomplete decomposition of vegetation that grows in waterlogged environments. This is a result of either standing water, such as lakes or the edges of slow-moving watercourses, or areas that have consistently received heavy rainfall. Partially decomposed plant debris builds up and becomes densely compacted, which causes peat to form and alter the substrate’s chemical composition and physical characteristics. Peatlands or mires are the names for these ecological systems.

Peat typically forms when less organic matter is lost through decomposition than is gained through photosynthesis. The vegetation succession that results is known as hydrosere. Although these ecosystems are found all over the world, the Northern Hemisphere is where they are most prevalent. Fluid dynamics, hydrology, and chemistry have a significant influence on studies of peatlands. These ecosystems are also closely related to studies in biodiversity and vegetation.

Bogs and fens are two different types of peatlands. Although the two types of wetlands are very similar to one another, what sets them apart from is where they get their water from. While bogs are enclosed and only supplied with water by precipitation, fens are typically supplied with water from the ground water flow.

Long-term global climate change means that ice ages and their counterpart, interglacials, occur in even intervals over thousands of years. We are currently in the heating phase, the interglacial part, of this naturally occurring cycle. However, the global emission of greenhouse gases has been rising dramatically since the in-
dustrial revolution in the early 20th century, which raises the global temperature and affects all life on Earth. This subsequently leads to the unavoidable interglacial potentially peaking with a lot higher temperatures than without the influence of anthroprogenic presence.

This project focuses on vegetation encroaching on mires. The mire in question is known as Fäjemyren and is referred to as a bog. It is situated in the northern part of Scania, Sweden. One might anticipate that there will be few to no trees growing here because there are no nutrients added to it other than what is found in the precipitation. In some regions of Europe, the precipitation contains enough nitrogen and phosphor to supply bogs and fens with the minerals the vegetation need to flourish. Studies show a decline in these minerals in the precipitation in the majority of Scandinavian regions, dating as far back as the middle of the 20th century. Despite this decline, trees began moving in at Fäjemyren sometime in the 1960s, and as a result, the bog has lost up to 200 meters of wetland to forest.

Numerous factors, not to mention the fact that farmers turned peatlands into agricultural fields in the late 1800s and early 1900s, could have an impact. Could it be that climate change is to blame for the longer droughts, which helps the tree seedlings’ root systems to grow sufficiently and become hardy enough to withstand subsequent rainy periods?

The study at Fäjemyren explores various topics, and this thesis specifically focuses on developing a model to predict changes in groundwater levels over time. These changes are influenced by factors that vary daily and seasonally, such as rainfall, evaporation, water uptake by plants, and water runoff. By using data collected from instruments at the research site and information from the Swedish Meteorological and Hydrological Institute, it is indeed possible to make these predictions. Of course, the predictions aren’t perfect, as no data collection is ever flawless, whether it’s done by machines or humans. This model allows us to understand water flow in the area and might even spark a conversation about a possible fifth unknown factor contributing to the water supply in the bog.

• author: Bowley, Tobias
• supervisor: Moa Sporre; Veiko Lehsten
• organization: Department of Physics; Dept of Physical Geography and Ecosystem Science
• course: FYSK03 20231
• year: 2023
• type: M2 - Bachelor Degree
• subject: Physics and Astronomy
• language: English
• id: 9127664
• date added to LUP: 2023-06-20 09:27:42
• date last changed: 2023-06-21 09:32:35