A Buoy for Continuous Monitoring of Suspended Sediment Dynamics

Abstract

Knowledge of Suspended Sediments Dynamics (SSD) across spatial scales is relevant for several fields of hydrology, such as eco-hydrological processes, the operation of hydrotechnical facilities and research on varved lake sediments as geoarchives. Understanding the connectivity of sediment flux between source areas in a catchment and sink areas in lakes or reservoirs is of primary importance to these fields. Lacustrine sediments may serve as a valuable expansion of instrumental hydrological records for flood frequencies and magnitudes, but depositional processes and detrital layer formation in lakes are not yet fully understood. This study presents a novel buoy system designed to continuously measure suspended sediment concentration and relevant boundary conditions at a high spatial and temporal resolution in surface water bodies. The buoy sensors continuously record turbidity as an indirect measure of suspended sediment concentrations, water temperature and electrical conductivity at up to nine different water depths. Acoustic Doppler current meters and profilers measure current velocities along a vertical profile from the water surface to the lake bottom. Meteorological sensors capture the atmospheric boundary conditions as main drivers of lake dynamics. It is the high spatial resolution of multi-point turbidity measurements, the dual-sensor velocity measurements and the temporally synchronous recording of all sensors along the water column that sets the system apart from existing buoy systems. Buoy data collected during a 4-month field campaign in Lake Mondsee demonstrate the potential and effectiveness of the system in monitoring suspended sediment dynamics. Observations were related to stratification and mixing processes in the lake and increased turbidity close to a catchment outlet during flood events. The rugged buoy design assures continuous operation in terms of stability, energy management and sensor logging throughout the study period. We conclude that the buoy is a suitable tool for continuous monitoring of suspended sediment concentrations and general dynamics in fresh water bodies.

Processes of flood‐triggered detrital layer deposition in the varved Lake Mondsee sediment record revealed by a dual calibration approach

“…This might be explained by summer stratification favouring long‐distance transport of fine‐grained suspended matter in the upper water column to the depocentre by mesopycnal flows (Sturm and Matter, ; Desloges and Gilbert, ; Schiefer, ; Hodder et al ., ). Moreover, lake internal currents, recorded during an ongoing monitoring study in Lake Mondsee (Mueller et al ., ), could have a potential effect on mesopycnal flows (Sturm and Matter, ; Giovanoli and Lambert, ; Schiefer, ). Although the generation of lake internal currents might be specific in Lake Mondsee (Mueller et al ., ) because of the characteristic basin morphology and the position of the discharging river inflows, an influence of internal currents for sediment distribution must be considered for all larger lake systems.…”

Hydrological and sedimentological processes of flood layer formation in Lake Mondsee

“…The combination of river gauges and monitoring buoys was designed to track hydro‐sedimentary dynamics, i.e. runoff generation and sediment transport, continuously from the head catchments to the lake (Mueller et al ., ).…”

“…Lake Mondsee catchment and monitoring set‐up including (i) four stream gauges equipped with devices for measuring precipitation, water level, air and water temperature, electrical conductivity, turbidity and automated water sampling, (ii) four monitoring buoys within the lake for multilevel water current and turbidity monitoring (Mueller et al ., ) and (iii) two sediment trap chains equipped with three integral traps in different water depths, one sequential trap at the lake floor and thermistors in different water depths. Additional rain gauges in the catchment conducted by the hydrographic services of Upper Austria and Salzburg are also indicated.…”

Adjusting the Frequency of Automated Phosphorus Measurements to Environmental Conditions

“…STRAUSS & STAUDINGER (2007) estimated that during an earlier flood in August 2002, almost half of the total annual phosphorus load from the River Fuschler Ache entered Lake Mondsee. The increase of particle input into the lake (considerably during the 2013 flooding event) was confirmed by MUELLER et al (2013). Even during meteorologically 'normal' years, up to 80% of the total phosphorus load of Lake Mondsee originated from single events in the snow melting period from February to March, and occasional (2-3 times per year) heavy rainfall (>50 mm d -1 ) in summer (STRAUSS & STAUDINGER 2007).…”