Temporal variations in dissolved organic carbon concentrations in upland and lowland lakes in North Wales

Over a period of 18 months, the dissolved organic carbon (DOC) concentration of a series of four lakes in North Wales was measured monthly. The lake catchment profiles consisted of an upland thin peat/soil (Llyn Cwellyn), an upland thin peat/soil associated with an adjacent area of small bog (Llyn Teyrn), an upland blanket bog (Llyn Conwy), and large lowland fen and fertile agricultural area (Llyn Cefni). The results examine the indirect effect of temperature and precipitation on the DOC concentrations found in the lakes fed by the catchments. The lowest DOC of the four sites was observed for Llyn Teyrn, varying from 1.2 to 3.30mg/L, and with the highest being recorded for Llyn Cefni (5.4510.83mg/L). Temperature and rainfall data were both collected. Correlations with the DOC exhibited significant relationships with temperature for three of the sampled lakes Cwellyn (r 0.490), Teyrn (r 0.640) and Cefni (r 0.472). Recomputation versus 30- and 60-day temperature lag times improved the correlation coefficients. The data showed weak and insignificant correlations for DOC versus rainfall for the three lakes, but the upland lake, Llyn Conwy, with its blanket bog catchment, did not demonstrate any statistical correlation with temperature, although it did show a significant correlation for DOC versus rainfall (r 0.553, P<0.05). Over the sampling period, although tentative relationships were found among temperature, rainfall and DOC levels, an indirect association tempered by site hydrology is suggested.