THE CARBON DYNAMICS OF CONTRASTING FRESHWATER PONDS

Lake carbon-storage is an emerging climate and environmental research theme. Small lakes are increasingly recognised as receiving disproportionately high carbon-inputs potentially causing rapid carbon-emissions, making them atmospheric CO2 and/or CH4 sources. However, little research investigates carbondynamics in ponds smaller than 0.01-hectare, despite these being most numerous. This research aimed to determine whether small ponds in the UK are carbon sinks, or atmospheric carbon sources. An intensively farmed-catchment pond, a nearby unpolluted forest-catchment pond (Oxfordshire) and a nutrient-impoverished peatland pond (Surrey) were sampled monthly from May 2011 to August 2012. Headspace gases were sampled from floating flux-chambers to measure watersurface carbon-emissions. Gas samples, and in situ gas-concentrations were analysed using membrane-inlet quadrupole mass spectrometry (QMS). Carboninputs were sampled by loss-on-ignition analysis of sediment-trap contents. Decomposition-rates were also measured (by QMS) at successive depths in sediment-cores collected from each site. Loss-on-ignition was conducted to determine depth-related carbon-content and bulk-density increase, inferring compaction and burial-rates. Emissions and inputs data were analysed statistically to compare site-related and temporal variations. Environmental predictor-response relationships were investigated using time-series, PLSR and dummy-coded panelregression analyses. Each pond received several orders of magnitude greater organic carbon-inputs than their water-surface carbon-emissions, despite rapid decomposition-rates. Inputs were functions of both land-use and weather-events. CO2 emissions were lowest and CH4 highest at the forest-catchment pond, with net burial responding to substrate-supply. The farm and peatland ponds had similar emissions, responding mostly to temperature-variations. In situ gas-concentration profiles indicated watercolumn storage of CO2 and CH4 in the peatland-pond. Carbon-inputs did not predict emissions, demonstrating that emissions were not substrate-limited. Influential predictor-variables included temperature and peak-windspeeds. Small ponds are numerous, increasing worldwide, and may represent most global liquid freshwater surface-area. They are easily constructed, holding promise for carbon-sequestration. However, pond carbon-cycling responded to storminess and temperature-extremes, making them vulnerable to projected anthropogenic climate-forcing.

Grantor dc:publisher

Oxford Brookes University

Year dc:date

2017

Author dc:creator

• Shaw, Maisie Ruth Helena

Contributors dc:contributor

• Pearce, Deborah
• Biggs, Jeremy

Statement dc:rights

• All rights reserved

Language dc:language

en

DOI dc:identifier

https://doi.org/10.24384/nshn-mq54

OAI identifier oai:identifier

tle:453136f7-b166-4b18-a2f6-7e731a81efe6:d6bd9758-527a-46cd-bfe2-c433766e8fca:1