Carbon dynamics in a Boreal land-stream-lake continuum during the spring freshet of two hydrologically contrasting years

H Miettinen,A Ojala,M Rantakari,J Pumpanen

doi:10.1007/s10533-020-00648-9

Abstract

We studied in 2013 and 2014 the spring carbon dynamics in a Boreal landscape consisting of a lake and 15 inflowing streams and an outlet. The first year had weather and a hydrological regime typical of past years with a distinct spring freshet connected with the thaw of the average snowpack. The latter year had higher air temperatures which did not permit snow accumulation, despite similar winter precipitation. As such, there was hardly any spring freshet in 2014, and stream discharge peaked in January, i.e., the conditions resembled those predicted in the future climate. Despite the hydrological differences between the years, there were only small interannual differences in the stream CO2 and DOC concentrations. The relationship between the concentrations and discharge was stronger in the typical year. CO2 concentrations in medium-sized streams correlated negatively with the discharge, indicating dilution effect of melting snowpacks, while in large-sized streams the correlation was positive, suggesting stronger groundwater influence. The DOC pathway to these streams was through the subsurface soil layers, not the groundwater. The total amount of carbon transported into the lake was ca. 1.5-fold higher in the typical year than in the year with warm winter. In 2013, most of the lateral inputs took place during spring freshet. In 2014, the majority of inputs occurred earlier, during the winter months. The lateral CO2 signal was visible in the lake at 1.5 m depth. DOC dominated the carbon transport, and in both years, 12% of the input C was in inorganic form.

Highlights

Inland waters, such as streams, rivers, and lakes play an essential role in the carbon (C) cycle at the catchment as well as the global scale (Aufdenkampe et al 2011; Battin et al 2009; Cole et al 2007)
We studied the relationship between concentrations of CO2 and dissolved organic carbon (DOC) and discharge in different years with streams divided into size groups with correlation analysis
Our findings have significant implications for the understanding of C dynamics in an interface of Boreal lentic and lotic ecosystems, especially under future climatic conditions where snow may not persist throughout the winter, emerging from this intensive two-year study with distinctively different winter and spring freshet

Summary

Introduction

Inland waters, such as streams, rivers, and lakes play an essential role in the carbon (C) cycle at the catchment as well as the global scale (Aufdenkampe et al 2011; Battin et al 2009; Cole et al 2007). Aquatic ecosystems connect hydrologically to terrestrial ecosystems, and terrestrially fixed C transported to lakes is processed therein, becoming deposited into the sediments and released to the atmosphere in gaseous form (Battin et al 2009). This transport and release of C is important in the Boreal region, where water bodies are abundant and cover a substantial part of the landscape (Verpoorter et al 2014). Organic C of terrestrial origin contributes to 30–80% of the C released from lakes to the atmosphere (Algesten et al 2003; Jonsson et al 2007)

Methods

Results

Discussion

Conclusion