Synchrony in catchment stream colour levels is driven by both local and regional climate

Abstract

Abstract. Streams draining upland catchments carry large quantities of carbon from terrestrial stocks to downstream freshwater and marine ecosystems. Here it either enters long-term storage in sediments or enters the atmosphere as gaseous carbon through a combination of biotic and abiotic processes. There are, however, increasing concerns over the long-term stability of terrestrial carbon stores in blanket peatland catchments as a result of anthropogenic pressures and climate change. We analysed sub-annual and inter-annual changes in river water colour (a reliable proxy measurement of dissolved organic carbon; DOC) using 6 years of weekly data, from 2011 to 2016. This time-series dataset was gathered from three contiguous river sub-catchments, the Black, the Glenamong and the Srahrevagh, in a blanket peatland catchment system in western Ireland, and it was used to identify the drivers that best explained observed temporal change in river colour. The data were also used to estimate annual DOC loads from each catchment. General additive mixed modelling was used to identify the principle environmental drivers of water colour in the rivers, while wavelet cross-correlation analysis was used to identify common frequencies in correlations. At 130 mg Pt Co L−1, the mean colour levels in the Srahrevagh (the sub-catchment with lowest rainfall and higher forest cover) were almost 50 % higher than those from the Black and Glenamong, at 95 and 84 mg Pt Co L−1 respectively. The decomposition of the colour datasets revealed similar multi-annual, annual and event-based (random component) trends, illustrating that environmental drivers operated synchronously at each of these temporal scales. For both the Black and its nested Srahrevagh catchment, three variables (soil temperature, soil moisture deficit, SMD, and the weekly North Atlantic Oscillation, NAO) combined to explain 54 % and 58 % of the deviance in colour respectively. In the Glenamong, which had steeper topography and a higher percentage of peat intersected by streams, soil temperature, the log of stream discharge and the NAO explained 66 % of the colour concentrations. Cross-wavelet time-series analysis between river colour and each environmental driver revealed a significant high common power relationship at an annual time step. Each relationship however, varied in phase, further highlighting the complexity of the mechanisms driving river colour in the sub-catchments. The estimated mean annual DOC loads for the Black and Glenamong rivers to Lough Feeagh were similar at 15.0 and 14.7 t C km−2 yr−1 respectively. The important role of past and current precipitation and, in particular, temperature emphasises the vulnerability of blanket peatland carbon stores to projected climate change and highlights the interaction of local and regional climate in controlling aquatic carbon export. Our results show that water colour (and hence DOC) concentrations can vary considerably between neighbouring catchments and also that regional-scale climatic drivers control the trends in intra- and inter-annual flux of DOC through the system. The combination of locally determined concentrations and regionally controlled fluxes produces aquatic DOC loads that vary over both the annual cycle and over multiple years.

13 Years of Storms: An Analysis of the Effects of Storms on Lake Physics on the Atlantic Fringe of Europe

“…While, on average, the influx of water from the inlets might have had a limited impact on the heat budget, it could still play an important biological role in the lake. Such events have potential to wash both particulate and dissolved substances from the catchment into the lake as described in other studies from the catchment [5,6,23,24,56]. The allochthonous carbon inputs that come into the lake with such events would be particularly important for the biology in the lake [57].…”

“…Lough Feeagh has an average pH of 6.7 and low alkalinity [5,23,24]. It is dystrophic and has medium to high concentrations of coloured dissolved organic matter resulting in brown lake water with low transparency (average Secchi depth 1.6 m).…”

Impacts of a record-breaking storm on physical and biogeochemical regimes along a catchment-to-coast continuum

“…In Lough Feeagh, the most notable shift was the sudden increase in surface water acidity following Desmond. This was likely a consequence of the mobilisation of organic matter from the predominantly peatland catchment area [ 37 ] with a potential contribution from the direct rainfall over the lake surface. Whilst Feeagh is normally slightly acidic, post-flood values were noticeably lower than the annual mean pH (6.1 compared to 6.6).…”

“…The Burrishoole catchment (~100 km 2 ) is a predominantly upland blanket peat, oligotrophic catchment located within the Nephin Beg mountain range on the west Atlantic coast of Ireland ( Fig 1 ). Rivers and streams are generally acidic or neutral and water chemistry depends on local and regional climate as well as surrounding soil composition in each of the sub-catchments [ 37 ]. Given its coastal proximity, the catchment generally experiences a temperate climate with mild winters (mean December-February 2005–18 air temperature of 6.0° C) and summers (mean June-August 2005–18 air temperature of 14.3° C) and a diurnal sea breeze with mean wind speeds of ~5 m s -1 [ 38 ].…”

Characterizing ventilation events in an anoxic coastal basin: Observed dynamics and the role of climatic drivers

“…However, as increased runoff also increased the depth of the surface layer, the renewal time decreased slowly with increasing freshwater input. Given the fast transit time of freshwater through the system, Furnace likely has a limited capacity to sequester quantities of dissolved organic carbon exported from the Burrishoole watershed, which drains a blanket peatland catchment (Doyle et al 2019).…”