Exploring factors driving organic carbon burial and storage in small constructed ponds : an experimental approach

• Main Author: Taylor, Scott
• Other Authors: Cooke, David ; Deary, Michael
• Published: Northumbria University 2017
• Subjects: 620; F800 Physical and Terrestrial Geographical and Environmental Sciences
• Online Access: https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.757248

The significance of ponds in the terrestrial carbon cycle has received increasing attention in recent years. Evidence suggests that ponds exhibit rates of biogeochemical cycling orders of magnitude greater than larger water bodies and, cumulatively, the storage of organic carbon (OC) in small ponds may equal or possibly surpass that of large water bodies. This project furthers our understanding of OC storage within ponds, combining survey and experimental approaches to accurately quantify sediment carbon stocks and accumulation rates. It incorporates four distinct, yet complimentary components aiming to: i) Evaluate the accuracy of estimating OC storage in entire ponds from sediment cores; ii) Monitor physicochemical dynamics and quantify OC storage across newly constructed ponds; iii) Quantify OC storage across a suite of mature ponds and assess the impact of vegetation community development; iv) Identify variations in microbial communities between different ponds in relation to sediment physicochemistry and vegetation coverage, exploring the implications for OC storage and burial. Carbon stocks were surveyed in 12 mature ponds across an experimental field site at Druridge Bay, Northumberland. Comprehensive historical ecological data was used to separate these ponds into three distinct groups based on hydrology and vegetation. One pond was selected from each of the resulting three groups and exhumed in its entirety to accurately quantify OC storage. Three sediment cores were taken beforehand in a novel attempt to evaluate the percentage difference between sediment core estimates and whole pond sediment OC storage. Whole pond exhumation suggests that the three ponds stored between 1565 – 2288 g OC m2, whilst results from the cores alone gave estimates within a 10-15% range. A further three ponds from each group were selected to quantify burial rates using sediment cores. Results suggest the ponds have stored between 1413 – 4459 g OC m2 over 20 yrs, equating to around 67 – 212 g OC m2 yr-1. OC storage was greater in ponds that had undergone the fastest establishment of vascular plant communities. Three new ponds were constructed at the Druridge site. Physicochemical parameters were monitored at approximately fortnightly intervals across a period of three years. All three ponds were hyper-eutrophic, dominated by algae. However, OC storage was negligible, further suggesting that OC burial is only significant upon the establishment of vascular plant communities. Sediment samples were subject to 16s rRNA analysis to identify microbial communities involved in carbon cycling. Variations in microbial community composition between ponds were observed and showed complex relationships with sediment physicochemistry and vegetation coverage. Microbial diversity was significantly higher in ponds storing more OC. Ponds dominated by Juncus vegetation, had lower diversity and a greater abundance of facultative anaerobic bacteria, and stored less OC. The intense rates of OC burial observed in this study demonstrate the functional capacity of constructed ponds to operate as significant sinks of OC. High rates of OC accumulation compared to the surrounding terrestrial landscape highlights the potential for their construction across landscapes to act as versatile, yet effective carbon mitigation features.