## 2 Materials and Methods  
### Study Site and High-Frequency Monitoring  
Lough Feeagh, in the Burrishoole catchment (Figure 1), is a monomictic lake, which has a maximum depth of 45 m and a mean depth of 14.5 m. It lies at an altitude of 14.5 m above sea level,has a surface area of 3.95 km\({}^{2}\) and its water retention time is \(\sim\)164 days (5\(-\)6 months) [65]. Feeagh is classified as a dystrophic lake [66] due to its low nutrient concentrations and primary productivity, but high colour and dissolved organic carbon concentrations, with TN values of 0.32-0.51 mg N-L-1, TP values between 3.70 and 28.76 \(\upmu\)g P-L-1, Chl \(a\) values of 0.1-2.61 \(\upmu\)G Chl \(a\)-L-1 and colour and DOC ranging from 45.33 to 105 mg Pt-L-1 and 6.83 to 12.18 mg C-L-1, respectively, in 2018 (n = 26). The Burrishoole catchment is situated on the northwest Atlantic coast of Ireland, in County Mayo (Figure 1). The area of the catchment is approximately 90 km\({}^{2}\) and the geology is primarily composed of granite, gneiss and schist [67]. The system comprises 45 km of low-productive and poorly buffered shallow streams draining into the sea in the northeast corner of Clew Bay, on the Atlantic coast [68]. The streams form two main sub-catchments comprising the two main inflow rivers to Lough Feeagh, the Glenamong and Black rivers (Figure 1). The presence of small amounts of dolomite and wacke in the eastern part of the catchment has a marked effect on the buffering capacity of the Black river compared with the Glenamong [69]. A terminal moraine, marking the boundary between metamorphic and sedimentary rock-types, separates the largest freshwater lake, Lough Feeagh, from the lagoonal estuary, Lough Furnace [70] (Figure 1). The land cover in the catchment comprises 64% blanket bog  
Figure 1: Location of the Burrishoole catchment on the west coast of Ireland. Lough Feeagh is the main freshwater lake and the two main inflow rivers characterise the Glenamong and Black river sub-catchments. The squares represent the Automatic River Monitoring Stations (ARMS) and the star the Automatic Water Quality Monitoring Station (AWQMS). The location of Met Éreann weather station (Newport Furnace) is marked with an arrow. with a peat depth ranging from 0.5 to 2 m [71]. In addition, 23% of the land is used for commercial afforestation. The remaining area comprises reduced extensions of native oak woodland, natural grasslands and agricultural land [70]. The Marine Institute (MI) maintains an Automatic Water Quality Monitoring Station (AWQMS) on Lough Feeagh (Coordinates; 53.95, \(-\)9.58) [72] and Automatic River Monitoring Stations (ARMS) on the Glenamong (Coordinates: 53.96, \(-\)9.60) and Black (Coordinates: 53.97, \(-\)9.58) rivers (Figure 1). The MI also measures water level on the Glenamong river downstream of the ARMS every 15 minutes using a data logger (Orpheus mini, OTT Hydromet, Germany). An established rating curve has been used to convert water level into stream flow. To measure Black river discharges, the 'drainage area ratio method' was used [73]. Feeagh AWQMS collects high-frequency sensor information every 2 minutes. Vertical temperature profiles were measured using 12 platinum resistance thermometers (PRTs: Lab facility PT100 1/10 DIN 4 wire sensor, Labfacility Ltd., UK) at 2.5, 5, 8, 11, 14, 16, 18, 20, 22, 27, 32, and 42 m. The AWQMS has a multiparameter probe (Hydrolab Data Sonde 5x, OTT Hydromet, UK) at 0.9 m from the surface to measure temperature and DO. Sensors on the AWQMS are cleaned fortnightly and DO on the sonde is calibrated once per month. Wind speed was measured in the AWQMS (2.3 m above lake surface level) with an anemometer (Vector Instruments A100L2-WR, Windspeed Ltd., UK). Data from the AWQMS is available from 2004 onwards. More information about the deployed sensors in the buoy can be found in the GitHub Data Repository [74].