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The effects of water table drawdown and catchment management on DOC export and water quality

Willis, Naomi (2009) The effects of water table drawdown and catchment management on DOC export and water quality. PhD thesis, Prifysgol Bangor University.

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Abstract

The intention of this study was to investigate the two most significant sources of dissolved organic carbon (DOC) to drinking water supplies; peatlands and algae. For two drinking water reservoirs in north Wales, Llyn Cefni and Llyn Alaw, markedly different seasonal trends were recorded, and these were linked to contrasting aspects of the lake's catchment and the meteorological conditions experienced during the two surveys. For Llyn Cefni, the DOC signatures for the inflowing streams and lakes correlated significantly, Afon Erddreiniog (R2=0.585, p<0.01) and Afon Cefni (R2=0.784, p<0.001), indicating a strong flux of terrestrial DOC into the lake from a nearby peatland. Much less of a seasonal trend in DOC was recorded at Llyn Alaw, with concentrations averaging 10.7 mg L 1, reflecting the absence of a peaty catchment. DOC derived from autochthonous production was also shown to be influential. Both lakes experienced nitrate depletion during the summer of the surveys, falling from 12.7 mg L-1 in Llyn Cefni and 6.5 mg L"' in L lyn Alaw to undetectable levels, suggesting extreme eutrophy, although the lack of detectable phosphate at Llyn Alaw may be why the growth of algal blooms was much less prevalent than at Llyn Cefni. A new type of floating constructed wetlands (FCW) was shown to Offer a potential solution 'to the production of algal blooms in the reservoirs, whereby over a four-week period, the FCWs were able to reduce algal growth by 80%, through sequestration of the key nutrients nitrate and phosphate and possibly due to the direct inhibitory properties of phenolic compounds on the algae. Furthermore, it was discovered that 8 Phragmites aus/ralis plants is the ideal number to maximise nutrient uptake and minimise algal growth in 70 litres of water. Studies in Finland and Malaysia were undertaken to highlight the importance of peatland management practices, as' vast areas of the world's boreal and tropical peatlands have been drained for agricultural purposes. The study in Finland showed that although there was no consistent response in DOC export potential with drainage across the sites of contrasting nutrient status, a significant correlation was observed between DOC and the water content of the soil, R2 = 0.59 (p< 0.001), indicating that as the water-table height falls the DOC export potential of the soil increases. It was also considered that the trend in DOC is driven by changes in soil pH and the resulting suppression of the key carbon regulating enzyme phenol oxidase; where acidity has increased following drainage phenol oxidase activity has declined and the concentration of DOC released has increased, conforming the view that phenol oxidase acts as an `enzymic latch' in peatlands. The study in Malaysia recorded a 40% greater export potential of DOC from the oil palm soil and more than twice the DOC concentration in drainage waters compared to the undisturbed peat soil. The activity of the key hydrolytic enzyme ß-glucosidase was 25% higher in the oil palm soil than the undisturbed peat. This may be due to an improved soil organic matter quality at the oil palm site and suggests that increased activity of this enzyme may have been crucial for mobilising DOC from the soil matrix. The repercussions of these studies are discussed with emphasis on the potential impacts of a changing climate.

Item Type: Thesis (PhD)
Subjects: Degree Thesis
Departments: College of Natural Sciences > School of Biological Sciences
Degree Thesis
Date Deposited: 14 May 2015 05:17
Last Modified: 14 Apr 2016 15:28
URI: http://e.bangor.ac.uk/id/eprint/4493
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