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Edge-of-field monitoring focuses on identifying and reducing agricultural sources of excess nutrients which can threaten the health of streams, rivers, and lakes. Edge-of-field monitoring assesses the quantity and quality of agricultural runoff and evaluates the effectiveness of conservation practices that aim to reduce nutrient loss.
Edge-of-field (EOF) monitoring sites are installed at the edge of agricultural fields, either on the field surface or using subsurface tiles, where runoff can be intercepted and channeled through monitoring equipment before it enters the natural stream system. EOF sites monitor both runoff quantity and quality.
EOF monitoring often uses a nested-basin study design where both individual field runoff and larger subbasin streams are monitored. By monitoring at multiple scales, both the immediate effect of a conservation practice on a single field and the cumulative effect on the larger watershed can be evaluated. Year-round monitoring utilizes natural rainfall/snowmelt conditions to measure not only the quantity of nutrient loss but also the timing. This information allows event-timing-based options for strategic nutrient application and adaptive implementation to be evaluated.
WHY DO EOF MONITORING?
Historically, monitoring for conservation-practice assessment has been done at the watershed scale, but those evaluations are often complicated by land-use variability and in-stream processes, which often require a long study duration. By monitoring runoff from an individual field, we can evaluate the direct impacts of agricultural activities and the effectiveness of conservation practices. The benefits of EOF monitoring include:
WHAT DOES EOF MEASURE?
Data collected at edge-of-field sites includes:
Loads and yields are calculated by combining sample concentrations and runoff quantity to determine the amount of each consituent leaving the field. This is critical for evaluating the effectiveness of conservation practices.
Surface EOF monitoring sites are located in areas where runoff exits agricultural fields or in nearby streams where the fields directly drain. A typical EOF surface site consists of:
SUBSURFACE TILE SITES
Subsurface tile EOF monitoring sites are typically located at drainage tile outlets, in a ditch or stream, or in-line with the subsurface tile system. A typical EOF subsurface tile site consists of the same equipment as the surface sites with some differences due to the requirements of the subsurface location:
FLEXIBLE MONITORING STRATEGIES
Like any monitoring effort, EOF has its challenges, and the USGS collaborates with producers and partners to develop rigorous monitoring strategies that are both flexible and adaptable. Each site brings its own complexities and opportunities, such as:
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