Evaluation of Nitrate, fDOM, and Turbidity Sensors in New Hampshire Streams

A state-of-the-art network of water quality sensors was established in 2012 to gather year-round high temporal frequency hydrochemical data in streams and rivers throughout the state of New Hampshire through the NH EPSCoR project. This spatially-extensive network includes eight headwater stream and two main-stem river monitoring sites, spanning a variety of stream orders and land uses. We evaluated the performance of nitrate, fluorescent dissolved organic matter (fDOM), and turbidity sensors included in the sensor network and the data is shared here.

Nitrate sensors were first evaluated in the laboratory for interference by different forms of dissolved organic carbon (DOC), and then for accuracy in the field across a range of hydrochemical conditions. Turbidity sensors were assessed for their effectiveness as a proxy for concentrations of total suspended solids (TSS) and total particulate C and N, and fDOM as a proxy for concentrations of dissolved organic matter. Overall sensor platform performance was also examined by estimating percentage of data loss due to sensor failures or related malfunctions. Although laboratory sensor trials show that DOC can affect optical nitrate measurements, our validations with grab samples showed that the optical nitrate sensors provide a reliable measurement of NO3 concentrations across a wide range of conditions. Results showed that fDOM is a good proxy for DOC concentration (r2=0.82) but is a less effective proxy for dissolved organic nitrogen (r2=0.41). Turbidity measurements from sensors correlated well with TSS (r2=0.78), PC (r2=0.53) and PN (r2=0.51).

自2012年起，一项尖端水质传感器网络在纽黑文州通过NH EPSCoR项目得以建立，旨在全年收集高时间频率的水文化学数据，涵盖该州各大溪流与河流。该网络覆盖范围广泛，包括八个源头溪流和两个主河道监测站点，跨越了多种溪流等级和土地利用类型。我们对传感器网络中包含的硝酸盐、荧光溶解性有机物质（fDOM）和浊度传感器的性能进行了评估，并将相关数据在此共享。硝酸盐传感器首先在实验室中进行了不同形态溶解性有机碳（DOC）干扰的评估，随后在多种水文化学条件下进行了现场准确性的测试。浊度传感器则被评估其作为悬浮颗粒物总量（TSS）和总颗粒碳氮含量的代理效能，而fDOM则被评估其作为溶解性有机物质浓度的代理效能。此外，通过估算由于传感器故障或相关故障导致的数据丢失百分比，对整体传感器平台性能进行了考察。尽管实验室传感器试验表明DOC可能影响光学硝酸盐测量，但我们的现场抓取样品验证显示，光学硝酸盐传感器在广泛条件下提供了可靠的NO3浓度测量。结果显示，fDOM是DOC浓度的良好代理（相关系数r2=0.82），但作为溶解性有机氮的代理效能较低（相关系数r2=0.41）。传感器测得的浊度与TSS（相关系数r2=0.78）、PC（相关系数r2=0.53）和PN（相关系数r2=0.51）具有良好的相关性。