The Use of Multisource Optical Sensors to Study Phytoplankton Spatio-Temporal Variation in a Shallow Turbid Lake

Abstract

Lake water quality monitoring has the potential to be improved through integrating detailed spatial information from new generation remote sensing satellites with high frequency observations from in situ optical sensors (WISPstation). We applied this approach for Lake Trasimeno with the aim of increasing knowledge of phytoplankton dynamics at different temporal and spatial scales. High frequency chlorophyll-a data from the WISPstation was modeled using non-parametric multiplicative regression. The ‘day of year’ was the most important factor, reflecting the seasonal progression of a phytoplankton bloom from July to September. In addition, weather factors such as the east–west wind component were also significant in predicting phytoplankton seasonal and diurnal patterns. Sentinel 3-OLCI and Sentinel 2-MSI satellites delivered 42 images in 2018 that successfully mapped the spatial and seasonal change in chlorophyll-a. The potential influence of localized inflows in contributing to increased chlorophyll-a in mid-summer was visualized. The satellite data also allowed an estimation of quality status at a much finer scale than traditional manual methods. Good correspondence was found with manually collected field data but more significantly, the greatly increased spatial and temporal resolution provided by satellite and WISPstation sensors clearly offers an unprecedented resource in the research and management of aquatic resources.

First Evaluation of PRISMA Level 1 Data for Water Applications

“…The sites represent a rather wide range of water types and trophic conditions but also atmospheric turbidity. In particular: (1) the Zeebrugge site in the North Sea is representative of turbid nearshore waters [ 40 ]; (2) the Lucinda site is located in tropical coastal waters in Eastern Australia, dominated by non-algal particulates and CDOM [ 41 , 42 ]; (3) the Casablanca site in the Western Mediterranean Sea is representative of open ocean chlorophyll-a dominated waters [ 43 ]; (4) the Bahia Blanca site in the southern Atlantic coast is representative of high suspended loads induced by widespread erosion and strong tidal currents [ 44 ]; (5) the Acqua Alta Oceanographic Tower (AAOT) of Venice in the northern Adriatic Sea is representative of moderately sediment dominated waters [ 45 , 46 ]; (6) finally, Lake Trasimeno has shallow turbid waters with recurrent sediment resuspension and moderate to high bloom of phytoplankton, including cyanobacteria species [ 47 ].…”

“…AERONET-OC is instrumental in satellite ocean colour validation activities through standardized measurements performed at different sites with a single measuring system and protocol, calibrated with an identical reference source and method, and processed with the same code [ 48 , 49 , 50 ]. In recent years, AERONET-OC has also supported the radiometric characterization of Landsat-8 and Sentinel-2 for aquatic applications [ 33 , 34 , 35 , 36 , 37 , 38 , 39 , 40 , 41 , 42 , 43 , 44 , 45 , 46 , 47 , 48 , 49 , 50 , 51 , 52 ] and, even if for a limited set of bands, we have considered this network very relevant also for PRISMA.…”

“…The WISPStation is an autonomous radiometer system developed by Water Insight B.V. (Wageningen, The Netherlands). The system is calibrated relative to a reference instrument (calibrated in a certified laboratory using a lamp and an integrating sphere with NIST traceable calibrations) and its usefulness in gathering quality-controlled water reflectance data has been demonstrated over a variety of inland waters [ 47 , 48 , 49 , 50 , 51 , 52 , 53 ]. The WISPStation contains two sets of sensors, measuring both the radiance and irradiance near instantaneous at high frequency in the spectral range of 350–900 nm every 15 min.…”

“…(3) the Casablanca site in the Western Mediterranean Sea is representative of open ocean chlorophyll-a dominated waters [43]; (4) the Bahia Blanca site in the southern Atlantic coast is representative of high suspended loads induced by widespread erosion and strong tidal currents [44]; (5) the Acqua Alta Oceanographic Tower (AAOT) of Venice in the northern Adriatic Sea is representative of moderately sediment dominated waters [45,46]; (6) finally, Lake Trasimeno has shallow turbid waters with recurrent sediment resuspension and moderate to high bloom of phytoplankton, including cyanobacteria species [47]. Table 2.…”

Innovative Water Quality and Ecology Monitoring Using Underwater Unmanned Vehicles: Field Applications, Challenges and Feedback from Water Managers

“…While there has been a rapid development of unmanned tools and sensors for environmental monitoring and inspections in recent years [26][27][28][29][30], it is not yet clear if the use of these methods by water managers in their daily practice, and the extent to which they can replace or complement existing techniques, should be further explored. There still seems to be technical, social, legislative and operational limitations and barriers for the large-scale use of this technology.…”