Hydrology, water chemistry and organic matter in peatland pools and headwater streams

Abstract

  Peatland pools that result from human activities (e.g. disturbance from building roads, or rewetting) have different hydrology to pools that have formed naturally. This impacts on biogeochemical processes within the pool. Studies of peatland pools in the Flow Country (Scotland, UK) showed artificial pools had a smaller surface area than natural pools, but natural pools were shallower and had less variable depth than artificial pools. During storm events, the artificial pools had a significantly larger response to rainfall input. The site with artificial peat pools had more variable water table depths within the peat than the site with natural pools. There were also differences in biogeochemistry between the natural and artificial pools: natural pools had lower organic carbon (OC) and dissolved CO2 concentration than artificial pools, and there was a higher carbon turnover in natural pools. Similar to peatland pools, small headwater streams are hotspots for OC processing. In a study of 200 small peatland water bodies across the UK (headwaters, streams and pools, with catchment area less than 1 km2 and at least 70% peat cover), the mean dissolved OC (DOC) concentration was 24 mg C L-1 (95% CI: 21-27), but in pools, the mean DOC concentration was higher, 34 mg C L-1. Dissolved organic matter (DOM) elemental composition was also significantly different from pools, headwaters and small streams. As a result of these studies, two samples of DOM (one from natural and one from an artificial pool) were analysed using FT-ICR MS. There were 11,424 molecular formulae identified in the two samples. There were 6,167 individual compounds in DOM from the artificial pool, of which 29% were unique to that pool (not found in the natural pool); there were 5,257 compounds in the natural pool DOM, of which 17% were unique to that pool. There were differences in structural indicators (e.g. double bond equivalent) and average size (e.g. m/z) of DOM compounds unique to each pool. These studies have shown how catchment-scale peatland condition is detectable on the molecular level, causing differences in organic matter structure, which will have implications for carbon turnover, processing and transport, and GHG emissions from peatland water.