Sunbiggin Tarn & Moors & Little Asby Common SSSI water quality monitoring survey

Maberly, Stephen C.; De Ville, Mitzi M.; James, J. Ben; Keenan, Patrick O.; Thackeray, Stephen J. ORCID: 2020 Sunbiggin Tarn & Moors & Little Asby Common SSSI water quality monitoring survey. Lancaster, UK Centre for Ecology & Hydrology, 44pp. (UKCEH ref. LA/07228/1, UKCEH Project no. 07228) (Unpublished)

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Report to Friends of the Lake District and Natural England. 1. Sunbiggin Tarn is a small marl lake on the Orton fells in North West England, where there is concern about nutrient levels and consequent algal growth that places the lake in an ecologically unfavourable state. This work was designed to investigate the causes of this nutrient enrichment based on monthly samples from seven inflow streams and the lake between April 2019 and February 2020 and a depth profile measured in mid-summer. 2. There are several lines of evidence for calcite precipitation in the tarn during summer. Alkalinity in summer is lower than in the winter; the tarn alkalinity in the winter is similar to the inflowing streams but lower than the streams in the summer; calculations show that the calcite was highly oversaturated in summer; finally, data from the Environment Agency from 2004 to 2006 show summer concentrations of dissolved calcium are about half that of winter concentrations. 3. There is some evidence for internal loading of total phosphorus during the summer since surface concentrations in May, June and July are higher than at other times of years. More frequent depth profiles would be needed to determine if this resulted from internal loading. The current data and calculations suggest that anoxia-triggered release of phosphorus from the sediment is likely to be more important than release of phosphorus from apatite dissolution at depth in producing the high concentrations of soluble reactive phosphorus measured at the bottom of the tarn. 4. The concentration of total phosphorus in the tarn seems to be consistent with the stream concentrations, although the effects of any groundwater inputs are unknown. In contrast, there is a large loss of total nitrogen within the tarn since the concentrations are much lower in the tarn than the inflowing streams. 5. The concentrations of total phosphorus in 2019-2020 was lower than in 2003 and 2004-2006 and the mean and median concentrations of phytoplankton chlorophyll a were lower in 2019-2020 than in 2004-2006 but slightly higher than in 2003. There is therefore some suggestion that the ecological conditions in the tarn are improving. 6. The concentrations of nitrate in the tarn are unlikely to inhibit charophyte growth directly but could have an indirect effect by stimulating phytoplankton and epiphytic algae growth that could shade the charophyte beds. The generally low concentrations of nitrogen in the tarn suggest that this is unlikely. Rather primary production could be limited by nitrogen rather than phosphorus, at least in some seasons. 7. More detailed, targeted future investigations are suggested to address some of the uncertainties noted in order to produce more evidence-based knowledge for the conservation and management of Sunbiggin Tarn.

Item Type: Publication - Report
UKCEH and CEH Sections/Science Areas: Pollution (Science Area 2017-)
Water Resources (Science Area 2017-)
Funders/Sponsors: Friends of the Lake District, Natural England
NORA Subject Terms: Ecology and Environment
Date made live: 20 Oct 2020 11:22 +0 (UTC)

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