Overview

The contaminant assessment and management (or “Contam”) research area focuses on developing and implementing ENS technology to support a new observational strategy set in the context of mass and energy distributions and fluxes across a range of temporal and synoptic scales. The specific interest areas for Contam include soils, groundwater, and riparian systems. The Contam application domain is unique relative to other CENS applications in that it is concerned with enabling adaptive management of environmental problems through engineered responses triggered by ENS observations.

In 2006-07, our emphasis shifted dramatically from laboratory and small-scale testbeds to deployments in real environmental systems over meaningful scales in time and space. During the last 12 months alone, the Contam team, in collaboration with investigators from the Sensors, TEOS, NIMS and Systems groups, executed thirteen field deployments. Each deployment yielded significant contributions within days of completion, and more findings will emerge as we further analyze the data and share it with other researchers.

Groundwater. We also made progress on soil pylon sensor array design and validation. The soil pylon is a vertical array of soil sensors. It can be used to delineate mass and energy fluxes in subsurface systems through the integration of soil flow and transport simulators trained by feedback from the sensors. In Spring 2006, we executed a large-scale experiment at the Palmdale experimental agricultural site, which (1) tested the pylon performance under authentic conditions and (2) compared the CENS Sensor group’s potentiometric nitrate mini-sensors with larger, more expensive commercial models. Results of a controlled nitrate release demonstrated that the pylon is ready for deployment under unsaturated soil conditions. Both sensor types performed erratically during heavy irrigation events but stabilized immediately at the end of the events, and both sensors types accurately identified the arrival of nitrate pulses in the soil. Results from the mini-sensor suggested substantially different nitrate transport dynamics relative to the larger commercial model, pointing to sensor form factor as an important variable in achieving optimal coupling with the soil.

Rivers and streams. A major highlight of the Contam accomplishments was a large-scale deployment on a major river segment using multiscale ENS in terrestrial-aquatic systems design. For a second year, the confluence of the San Joaquin and Merced Rivers in Central California served as the testbed. CENS researchers successfully installed NIMS across a 70m wide portion of the river and measured coupled velocity and water quality distributions, including temperature, salinity (EC), dissolved oxygen, nitrate, ammonium, pH, and oxidation-reduction potential. By making measurements at two different points along the river, researchers collected data on river hydrodynamic mixing of unprecedented precision. The researchers have also found preliminary evidence to support the idea that will allow calculation of the river’s salt mass balance, with enough precision to identify relatively modest groundwater losses/gains from/to a river. Such groundwater accretions can significantly increase levels of pollutants flowing into the river in agricultural and industrial regions.

The multiscale ENS system along the San Joaquin included a network of stationary sensor arrays, known as a javelin array. In this major effort, more than 30 chemical (ammonium and nitrate) and 20 physical (water level and temperature) sensors were embedded in the shallow groundwater adjacent to the San Joaquin River in an effort to confirm whether groundwater-surface water interactions along this segment of the river involve significant nutrient exchange and biogeochemical cycling. This deployment was completed just prior to the publication of this report. But, preliminary results indicate the presence and cycling of nitrate and ammonium along the river. In addition to meeting the science objective, the deployment resulted in a unique dataset that compares chemical sensors reporting on the CENS wireless platform and another subset of the chemical sensors reporting on commercial dataloggers. The next step in this multiscale ENS system’s development is to orchestrate real-time collaborative and adaptive sampling with mobile (NIMS-based) and stationary (javelin-based) sensors.