Sedimentation Patterns of Multiple Finnish Lakes Reveal the Main Environmental Stressors and the Role of Peat Extraction in Lake Sedimentation

Samu E Valpola,Tommi Kauppila,Antti E K Ojala,Jari Mäkinen,Tuija Vähäkuopus

doi:10.3390/geosciences10080313

Abstract

Human land-use activities, especially in the peatlands, are under consideration as the mitigation and lowering of CO2 emissions from land-use practices is needed to address climate change. In Finland, approximately one third of the land surface is covered by peatlands, and around 50% of peatlands are ditched for forestry. Another 3% of peatlands are used for agriculture and approximately 1% for peat extraction. The effects of these different land-use practices, including changes in sediment depositional rates and sediment quality, need to be identified. This study analyzed 51 lakes that were subdivided into two groups: (1) a group of impacted lakes in which peat was recently extracted from the catchments and (2) a reference group consisting of lakes where peat had not been extracted from the basin, but in which other land-use activities had occurred. The overall aim of the study was to investigate if peat extraction caused excessive delivery and deposition of dry and organic matter in lakes that are located in their immediate downstream catchment areas. Differences in sediment accumulation were defined by comparing the overall sediment thickness and recent (post 1986) sedimentation levels to identify if there were differences in the sediment chemical composition or rate of organic matter deposition between groups and to identify possible land-use stressors that could explain the possible differences in sediment chemical assemblages or sedimentation rates. The results show moderate (cm scale) sedimentation rates in both impacted and reference lakes after 1986, while sediment chemical assemblages indicated the erosion and input of mineral soils to all of the studied lakes, rather than the input of organic materials. No statistically significant correlations were observed between selected environmental variables and the recent accumulation rates of carbon and dry matter. Moreover, significant changes in the stressors potentially affecting the chemical assemblages of pre- and post-disturbance sediments were not observed.

Highlights

Human land use directly affects more than 70% of the global ice-free land surface [1]
Of the sub-bottom surveys, a total of lakes were ranked as good in their quality, lakes were ranked as average quality, and 15 lakes were ranked as poor quality
The results clearly show that there is no significant difference in the quality of acoustic sub-bottom profiles between the impacted and reference lakes

Summary

Introduction

Human land use directly affects more than 70% of the global ice-free land surface [1]. These activities impact peatlands that are important in the climate change context due to their significance in the cycling and storage of carbon (e.g., [2,3]). Impacts of anthropogenic activities on the Earth’s surface worldwide had begun by 10,000 to 8000 years ago [4,5]. Jenny et al [6] showed that a significant portion of the Earth’s surface shifted to human-driven soil erosion 4000 years ago, long before deforestation and land-use practices were affected by industrialization. In Finland, approximately one third of the land surface is covered by peatlands and Geosciences 2020, 10, 313; doi:10.3390/geosciences10080313 www.mdpi.com/journal/geosciences

Objectives

Methods

Results

Discussion

Conclusion