Spatiotemporal change of stream and wetland features over 140 years in an agricultural catchment in southern Sweden : an assessment of historical maps in GIS

Sammanfattning: The Swedish agricultural landscape has historically changed by draining wetlands and hydromorphological impacts by straightening and redirect watercourses. Drainage has been a part of Sweden’s agricultural history, dating back to the 13th century with its peak in the 19th and 20th centuries. Draining the landscape was necessary to create more arable land to support a growing population by increased food production. However, the drainage resulted in wetland loss and a change in natural stream morphology. As new legislation arose during the late 20th century, the drainage was regulated to protect wetlands and streams with Agenda 2030 and the respective Sustainable Development Goals (SDG). This study has assessed changes in wetlands and stream networks from the 19th century to the present time concerning drainage regulations in Tidan sub-catchment in southern Sweden. Historical maps and orthophotographs from the 19th- and 20th centuries were used with contemporary orthophotographs to assess these changes. The wetland area, land cover, stream length, and meandering degree were assessed by georeferencing and vectorizing the historical maps in ESRI ArcMap 10.8. The results indicate that the wetland area has reduced by 54% between the late 19th century and the present. The total change in stream length indicates changes in the length of individual streams, increased sinuosity, or an increase in the number of streams from the late 19th century to the present. The land cover of the wetlands shows a shift from open wetland towards forest-covered wetlands. However, these results should be interpreted with caution. There are uncertainties in the accuracy of the historic maps due to scale and the detail level compared to the orthophotographs used for later years. A historical map covering a large area has a lower level of detail and is less accurate due to the compromise of how much information to show. Hence wetlands area, stream length, and sinuosity index might not be represented equally between the different maps. It could not be concluded that the resulting changes are entirely human-induced, caused by natural changes, or inaccurate due to used material limitations. However, the result shows that a decrease in wetland area and changes in stream morphology have occurred.