Walker River distributed temperature sensing, thermal infrared imaging, and temperature modeling data

Watershed-scale stream temperature models are often one-dimensional because they require fewer data and are more computationally efficient than two- or three-dimensional models. However, one-dimensional models assume completely mixed reaches and ignore small-scale spatial temperature variability, which may create temperature barriers or refugia for cold-water aquatic species. Fine spatial and temporal resolution stream temperature monitoring provides information to identify river features with increased thermal variability. We used distributed temperature sensing (DTS) to observe small-scale stream temperature variability, measured as a temperature range through space and time, within two 400 meter reaches in summer 2015 in Nevada’s East Walker and mainstem Walker Rivers. Thermal infrared (TIR) aerial imagery collected in summer 2012 quantified the spatial temperature variability throughout the Walker Basin. We coupled both types of high resolution measured data with simulated stream temperatures to corroborate model results and estimate the spatial distribution of thermal refugia for Lahontan cutthroat trout and other cold-water species. Temperature model estimates were within the DTS measured temperature ranges 21% and 70% of the time for the East Walker River and mainstem Walker River, respectively, and within TIR measured temperatures 17%, 5%, and 5% of the time for the East Walker, West Walker, and mainstem Walker Rivers, respectively. DTS, TIR, and modeled stream temperatures in the mainstem Walker River nearly always exceeded the 21°C optimal temperature threshold for adult trout, usually exceeded the 24 °C stress threshold, and could exceed the 28 °C lethal threshold for Lahontan cutthroat trout. Measured stream temperature ranges bracketed ambient river temperatures by -10.1 to +2.3 °C in agricultural return flows, -1.2 to +4 °C at diversions, -5.1 to +2 °C in beaver dams, -4.2 to 0 °C at seeps. To better understand the role of these river features on thermal refugia during warm time periods, the respective temperature ranges were added to simulated stream temperatures at each of the identified river features. Based on this analysis, the average distance between thermal refugia in this system was 2.8 km. While simulated stream temperatures are often too warm to support Lahontan cutthroat trout and other cold-water species, thermal refugia may exist to improve habitat connectivity and facilitate trout movement between spawning and summer habitats. Overall, high resolution DTS and TIR measurements quantify temperature ranges of refugia and augment process-based modeling.

流域尺度的河流水温模型多采用一维架构，相较于二维或三维模型，其所需数据更少且计算效率更高。然而，一维模型假设河段完全混合，忽略了小尺度空间温度变异性——而这类变异性可能为冷水水生生物构建温度屏障或提供热避难所。具备精细时空分辨率的河流水温监测，可用于识别热变异性升高的河流特征。2015年夏季，我们针对内华达州东沃克河与沃克河干流的两段400米河段，采用分布式温度传感（Distributed Temperature Sensing, DTS）观测了以时空温度范围为表征指标的小尺度河流水温变异性。2012年夏季采集的热红外（Thermal Infrared, TIR）航空影像，可量化沃克盆地全域的空间温度变异性。我们将这两类高分辨率实测数据与模拟河流水温数据相结合，用以验证模型结果，并估算拉洪塔切喉鳟（Lahontan cutthroat trout）及其他冷水水生生物的热避难所空间分布格局。水温模型的估算值与DTS实测温度范围的匹配率，在东沃克河与沃克河干流分别为21%与70%；而与TIR实测温度的匹配率，在东沃克河、西沃克河与沃克河干流分别为17%、5%与5%。沃克河干流的DTS、TIR实测及模拟河流水温，几乎均超过了成体鳟鱼的21℃最优温度阈值，通常超过24℃的胁迫阈值，且可能突破拉洪塔切喉鳟的28℃致死温度阈值。不同河流特征处的实测河流水温范围与环境水温的偏差区间为：农业退水区为-10.1℃至+2.3℃，引水口处为-1.2℃至+4℃，海狸坝区域为-5.1℃至+2℃，渗流点处为-4.2℃至0℃。为明晰这类河流特征在暖期对热避难所的调控作用，我们将各特征对应的水温波动区间叠加至对应位置的模拟河流水温数据中。基于该分析，本研究区域内热避难所的平均间距为2.8千米。尽管模拟河流水温通常过高，难以支撑拉洪塔切喉鳟及其他冷水水生生物的生存，但热避难所的存在可提升栖息地连通性，助力鳟鱼在产卵场与夏季栖息地间移动。综上，高分辨率的DTS与TIR实测数据可量化热避难所的温度范围，并为基于过程的水温建模提供有效补充。