From Highs to Lows: Changes in Dissolved Organic Carbon in a Peatland Catchment and Lake Following Extreme Flow Events

Eleanor Jennings,Tadhg Moore,Caitriona Nic Aonghusa,Martin Rouen,Russell Poole,Norman Allott,Mary Dillane,Elizabeth Ryder,Donald C Pierson,Elvira De Eyto

doi:10.3390/w12102843

Abstract

The concentration of dissolved organic carbon (DOC) in freshwater catchments has implications for carbon availability in downstream lakes and for water supplies. The links between catchment hydrology and stream and lake DOC concentrations are, however, still not fully understood. Much of the literature has been from catchments with organo-mineral soils, with fewer studies from upland peat sites. We used high-frequency fluorescence data, a proxy for DOC, to investigate 1. the relationship between stream discharge and concentration in a blanket peat catchment during extreme high flows and 2. the relationship between inflow and in-lake estimated DOC concentrations. We found that for approximately two thirds of extreme events, there was a decrease in stream DOC concentration (i.e., a dilution) on the rising limb rather than an increase (i.e., a flushing out of DOC from terrestrial stores). Flushing events dominated only in summer when concentrations in the stream were also increasing. In comparison to the stream, concentrations in the downstream lake were less variable, and peaks and troughs were damped and lagged. Replicating these patterns and processes in DOC models would be critical in order to provide appropriate simulations in response to shorter- and longer-term changes in climate, and thus inform future catchment and lake management.

Highlights

The concentrations of dissolved organic matter (DOM) in surface waters have come under increased scrutiny in recent years due to reports of upward trends in many regions [1,2,3,4]
Understanding the movement of carbon through freshwater systems is critical for the identification of uncertainties in global carbon budget estimations [6], while removal of DOM from water sources remains a major challenge in drinking water treatment [7]
While much of the literature has emphasized a positive relationship between stream discharge rates and dissolved organic carbon (DOC) concentrations i.e., where there is a flushing of DOC from the peat soil and a subsequent increase in stream concentrations [9,10,11,12], other studies have reported no increases at higher discharge rates, or even a decrease in stream DOC levels [13,14]

Summary

Introduction

The concentrations of dissolved organic matter (DOM) in surface waters have come under increased scrutiny in recent years due to reports of upward trends in many regions [1,2,3,4]. Water 2020, 12, 2843 carbon (DOC), have implications both for carbon supply to downstream aquatic systems and global carbon cycling. Understanding the movement of carbon through freshwater systems is critical for the identification of uncertainties in global carbon budget estimations [6], while removal of DOM from water sources remains a major challenge in drinking water treatment [7]. Greater insight into when dilution dominates over flushing in a given system, and when and why both dilution and flushing events occur, is fundamental for understanding the aquatic carbon cycle, and in particular the supply of carbon to downstream lakes

Methods

Results

Discussion

Conclusion