Analysis of Material Loading to Cannonsville Reservoir: Advantages of Event-Based Sampling

ABSTRACT

Eight years of monitoring data are reviewed and analyzed for the West Branch of the Delaware River, the major tributary supplying Cannonsville Reservoir: 3 years are from the early 1980s, the other 5 years include 1991–1996. Phosphorus, nitrogen, and sediment loads were measured at the mouth of the West Branch using an approach of intensified sampling during runoff events and routine sampling during baseflow intervals. Total river loads of nutrients and sediment are reported on a water-year basis; selected analytes are reported on a monthly basis. Additionally, phosphorus inputs are partitioned into nonpoint and point source loads. The point source phosphorus load decreased about 75% during the 1990's study period primarily due to upgrades at the largest municipal wastewater treatment plant in the watershed. Annual nonpoint source phosphorus loads were variable over the study period: dissolved phosphorus ranged from 6,600 kg · y⁻¹ to 20,800 kg · y⁻¹, while particulate phosphorus ranged from 7,400 kg · y⁻¹ to 115,000 kg · y⁻¹. Most of the annual loads of nonpoint source phosphorus, sediment and ammonia were delivered during runoff events. The loads determined through event-based sampling are compared to loads calculated using two other load estimation approaches: an export coefficient technique and fixed frequency sampling combined with the loading software FLUX. The natural variation in nonpoint source loads is examined in the context of setting management goals for improving water quality.

Key Words:

• load
• runoff
• event
• sampling
• nonpoint
• phosphorus
• nutrients
• tributary