PS 36-3 - Tracking spatial distribution of tributary inputs in the surface waters of an oligotrophic lake

Abstract: Tributary inputs influence lake spatial heterogeneity by acting as major sources of external loading that can alter both physical and chemical lake characteristics. Loading through tributary inflows can vary both temporally, due to weather and seasonality, and spatially due to surrounding land use. Here we evaluate the spatial distribution of tributary inputs, as indexed by specific conductance, in oligotrophic Lake Sunapee, NH, following both single day storm events and sustained, multi-day rain events as tracked in the PRISM Climate Group online database. We use a combination of new technologies and manual sampling techniques including an autonomous surface vehicle, Catabot, to measure horizontal patterns in specific conductance at the lake surface; Onset HOBO data loggers for specific conductance deployed at the inflow of three tributaries into the lake; and manual vertical profiles using a YSI ProDSS sonde along a transect extending into the lake from the tributary inflows to capture vertical patterns. Deployments of Catabot on Lake Sunapee in summers 2021 and 2022 revealed a spatial gradient in specific conductance with higher concentrations located in closer proximity to tributary inflows. Spatial patterns in specific conductance varied, with steeper gradients observable during some months of the sampling period, notably in mid- to late-summer. While we are still working to fine tune our statistical approach to relate precipitation patterns to the observed spatial distributions, preliminary results show that visually steeper gradients in specific conductance aligned with periods of heightened precipitation. Time series from data loggers in tandem with manual vertical profiles in summer 2022 also suggest that specific conductance gradients decreased in relation to tributary inflows into the lake. This suggests that factors such as wind disturbance and other forms of mixing need to be considered when teasing apart the influence of precipitation events on spatial distribution of tributary inputs. As our project is still underway, we seek feedback and suggestions for strengthening our analyses.