Sub-Daily Temperature Heterogeneity in a Side Channel and the Influence on Habitat Suitability of Freshwater Fish

Abstract

Rising surface water temperatures in fluvial systems increasingly affect biodiversity negatively in riverine ecosystems, and a more frequent exceedance of thermal tolerance levels of species is expected to impoverish local species assemblages. Reliable prediction of the effect of increasing water temperature on habitat suitability requires detailed temperature measurements over time. We assessed (1) the accuracy of high-resolution images of water temperature of a side channel in a river floodplain acquired using a consumer-grade thermal camera mounted on an unmanned airborne vehicle (UAV), and (2) the associated habitat suitability for native and alien fish assemblages. Water surface temperatures were mapped four times throughout a hot summer day and calibrated with 24 in-situ temperature loggers in the water at 0.1 m below the surface using linear regression. The calibrated thermal imagery was used to calculate the potentially occurring fraction (POF) of freshwater fish using species sensitivity distributions. We found high temperatures (25–30 °C) in the side channel during mid-day resulting in reduced habitat suitability. The accuracy of water temperature estimates based on the RMSE was 0.53 °C over all flights (R2 = 0.94). Average daily POF was 0.51 and 0.64 for native and alien fish species in the side channel. The error of the POF estimates is 76% lower when water temperature is estimated with thermal UAV imagery compared to temperatures measured at an upstream gauging station. Accurately quantifying water temperature and the heterogeneity thereof is a critical step in adaptation of riverine ecosystems to climate change. Our results show that measurements of surface water temperature can be made accurately and easily using thermal imagery from UAVs allowing for an improved habitat management, but coincident collection of long wave radiation is needed for a more physically-based prediction of water temperature. Because of climate change, management of riverine ecosystems should consider thermal pollution control and facilitate cold water refugia and connectivity between waterbodies in floodplains and the cooler main channel for fish migration during extremely hot summer periods.

Threats of global warming to the world’s freshwater fishes

“…If species’ current distributions are confined by factors other than flow or water temperature (e.g., biogeographic dispersal barriers or anthropogenic pressures), species might be able to withstand larger temperature and flow extremes than inferred based on their current geographic range 27 , 28 . The same holds if species are able to adapt to new water temperature and flow conditions 16 or if fishes have the possibility to hide from extremes in micro-climatic refugia, for example due to water stratification or small-scale thermal heterogeneity 29 , which are not included in our hydrological model 21 . On the other hand, species’ range maps are relatively coarse representations of species occurrence, hence some species might be more affected than indicated by our results (i.e., if present-day climate extremes within their geographic range already preclude local occurrence).…”

Applications of Unmanned Aerial Systems (UASs) in Hydrology: A Review

“…In this case, a powered paraglider was employed to acquire the TIR images, which allowed to predict habitat diversity from temperature heterogeneity. More recently, Collas et al [41] obtained UAS-borne high resolution imagery of a river side channel using a consumergrade TIR camera to map sub-daily temperature heterogeneity and habitat suitability for native and alien fish species. The authors achieved an accuracy in water temperature estimates of 0.53 • over all flights, thus demonstrating the usefulness of UASs TIR imagery for temperature mapping and habitat management.…”

Assessing Habitat Suitability for Native and Alien Freshwater Mussels in the River Waal (the Netherlands), Using Hydroacoustics and Species Sensitivity Distributions

“…2). Then, the data were processed using SonarWiz 7.2 from Chesapeake Technology or Microsoft Excel, converted to POF predictions using R programming, and subsequently mapped using ArcGIS® software from ESRI [52,53,59,63].…”

“…For each LTD shore channel, the substrate type, water depth, and nearbottom flow velocity maps produced were used with the SSDs in order to calculate the POFs of native and alien freshwater mussels per pixel. SSDs provided predictions of habitat suitability (POFs) for each map pixel based on their unique abiotic parameter values [49,59]. This was completed by using the "calc" function from the raster package of R statistics to apply the SSDs on the abiotic condition maps based on the mean and standard deviation of the distributions [80].…”

“…Hydroacoustics, such as side-scan sonar (SSS), have been used for riverine habitat substrate mapping, including mussel beds, whereas acoustic Doppler current profilers (ADCPs) have been used to assess water depth-specific flow velocity in mussel habitats [26,[52][53][54][55][56][57][58]. By combining detailed spatial abiotic conditions measurements with available SSDs for native and alien freshwater mussels, a prediction of their POFs may be derived to evaluate the local suitability of habitat in river systems [38,44,45,59]. We hypothesize that shore channels along LTDs provided suitable habitats for native freshwater mussels due to favorable substrate type, water depth, and near-bottom flow velocity conditions.…”