Sensor-Equipped Unmanned Surface Vehicle for High-Resolution Mapping of Water Quality in Low- to Mid-Order Streams

Abstract

Longitudinal profiling of water quality via the deployment of sensors from watercraft has advanced the understanding of spatial patterns in large rivers and lakes; however, a similar approach in low- to mid-order streams is lacking. To fill this gap, we developed an unmanned surface vehicle (USV)-water quality measurement platform (the “AquaBOT”). The components of the AquaBOT included a nitrate sensor, multiparameter sonde (temperature, conductivity, turbidity, dissolved oxygen, chlorophyll), quantum sensor, and global positioning system (GPS) mounted to a small pontoon-style USV. The AquaBOT was tested in four streams and rivers in Iowa and Tennessee. All measured water quality parameters varied longitudinally, and greater ranges were generally observed along the low-order, agriculturally influenced streams in Iowa. Nitrate, in particular, was spatially heterogeneous. For example, during one run in early June, concentrations ranged from 10.5 to 12.5 mg N L–1 along a 2.3 km reach and hotspots were observed directly downstream of some tile drains. The spatial resolution of AquaBOT data collected in June was 10× higher than grab sampling data, and measurements were collected in less time and at a comparable cost. The AquaBOT can complement existing measurement approaches and will lead to advancements in understanding the processes driving water quality along the stream-to-river continuum.

Sub-Liquid and Atmospheric Measurement Instrument To Autonomously Monitor the Biochemistry of Natural Aquatic Ecosystems

“…Some of the field sites, including saline lakes, may host salt crusty deposits on lake surface, making the floating platform’s maneuvering tricky. Several works have investigated and proposed solutions with the use of simple camera ,, or ultrasound sensors for detecting and navigating around such obstructions. Long-term deployments also impose restrictions on recalibration due to possible degradation of the sensors (higher in a corrosive saline environment).…”

High Resolution Mapping of Nitrate Loads of a Reservoir Using an Uncrewed Surface Vehicle: Potential Opportunities and Challenges

“…Potential opportunities of high‐resolution mapping through a remotely operated vehicle of water quality along rivers were explored in early 2010s (Casper et al., 2012). Recently, uncrewed underwater and surface vehicles have been used for water quality mapping, particularly for mixing processes of water (Amran et al., 2020; Griffiths et al., 2022; Honek et al., 2020). Surveys of these vehicles are cost efficient to maintain and measure water quality and quantity regularly (e.g., sub‐weekly and weekly intervals).…”

Novel, Ultralight Platform for Mapping Water Quality Parameters in Low-Order Streams

“…Similarly, remotely operated drone watercraft can become encumbered or damaged in shallow water or on submerged obstructions that are difficult to see from a distance; they also require the operator to maintain line-ofsight contact with the drone to avoid obstacles and respond to problems. 11 Having a drone operator on the bank of a ditch or stream may be complicated by private land ownership or other challenges to accessing the site. The unoccupied niche for many smaller streams and ditches requires a sampling platform that is small enough to be maneuvered around obstacles but large enough to support an instrumentation payload and an operator who can monitor instruments and respond to changing field conditions.…”

“…Optical sensors that are capable of making high-frequency measurements have permitted more accurate quantification of watershed-scale pollutant loading and allowed insights into concentration–discharge relationships to characterize watershed behavior. , In addition to high-frequency monitoring from fixed positions in a watershed, others are advancing the state of the science by developing approaches for water sampling from moving platforms. In marine systems, this approach has been applied to develop solute maps and track movement of water masses. − More recently, both passive (drifting) platforms and powered boats have been employed to sample estuarine and riverine environments. − …”

“…These limitations also preclude the effective use of a canoe, especially during low flow conditions because even though a canoe is relatively small and lightweight when compared against other boats, it is still large enough to be ineffective in small streams. Similarly, remotely operated drone watercraft can become encumbered or damaged in shallow water or on submerged obstructions that are difficult to see from a distance; they also require the operator to maintain line-of-sight contact with the drone to avoid obstacles and respond to problems . Having a drone operator on the bank of a ditch or stream may be complicated by private land ownership or other challenges to accessing the site.…”