Submitted to: ASA-CSSA-SSSA Annual Meeting Abstracts
Publication Type: Abstract Only
Publication Acceptance Date: 5/12/2010
Publication Date: 11/1/2010
Citation: Zhu, Q., Schmidt, J.P., Buda, A.R. 2010. Nitrogen Loss from a Mixed Land Use Watershed as Influenced by Hydrology and Growing Seasons [abstract]. ASA-CSSA-SSSA Annual Meeting Abstracts. Paper No. 324-8. Interpretive Summary: An interpretive summary is not required.
Technical Abstract: Non-point nitrogen loss from agriculture is an environmental concern among scientists, decision-makers, and the public. This study investigated nitrate-N and total N losses from a mixed land use watershed (39.5 ha) as influenced by hydrology (flow type, runoff volume, storm sizes, and precipitation amount) and seasons (pre-growing, growing, and post-growing seasons) from 2002 to 2006. Stream discharge was monitored every 5-min and water samples for nitrate-N and total N analyses were collected weekly for base flow and for every storm. The majority of nitrate-N (about 75 percent) and total N (about 65 percent) were exported in base flow, which contributed about 64 percent of the total flow in an average year and had greater mean nitrate--N concentration (5.6 mg per L) than storm flow (3.4 mg per L). A substantial proportion of total N was in the form of nitrate-N in base flow and small storms with less than 1-year return period (accounting for 70 percent and 48 percent, respectively), suggesting that base flow and small storm flow were probably dominated by nitrate-N-rich lateral subsurface flow. As storm size (runoff volume, flow rate, and return period) increased, the nitrate-N concentration decreased following a power relationship. In contrast, total N concentrations increased with increasing storm size, which was attributed to surface runoff that flushed ammonium-N and dissolved and particulate organic N into the stream. Nitrate and total N losses from this watershed were greater during the pre-growing (Jan.-Apr.) and post-growing (Oct.-Dec.) seasons, which contributed greater than 73 percent of the overall nitrate-N and total N losses. These two seasons also had greater nitrate-N (4.8 and 5.5 mg per L, respectively) and total N (9.8 and 10.1 mg per L, respectively) concentrations and greater discharge (40 percent and 32 percent of total discharge, respectively) than the growing season. Greater contribution of nitrate-N to total N loss was also observed during the pre-growing and post-growing seasons, which was attributed to lateral subsurface flow with greater nitrate-N concentration. Management practices to reduce N loss from this watershed should target periods of base flow when nitrate--N concentrations are greater (before and after the crop growing season) and target areas along the stream where seeps are present, perhaps including perennial plant species in localized riparian buffers and introducing cover crop during the fallow season.