Submitted to: Journal of Hydrology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/5/2011
Publication Date: 11/12/2011
Citation: Zhu, Q., Schmidt, J.P., Bryant, R.B. 2011. Hot moments and hot spots of nutrient losses from a mixed land use watershed. Journal of Hydrology. 414:393-404. DOI: 10.1016/j.jhydrol.2011.11.011. Interpretive Summary: Agricultural nonpoint source pollution of nitrogen (N) and phosphorus (P) is a major contributing factor to surface water eutrophication, and agriculture has been recognized as the largest source of both N and P entering the Chesapeake Bay. We investigated when and where losses of nitrate-N, dissolved P (DP) and particulate P (PP) occurred in a mixed land use watershed in central Pennsylvania. Generally, PP losses were greatest in storm flow, while nitrate-N export was greatest in base flow. Nitrate-N losses occurred predominantly between October and April, while the predominant PP loss occurred during March to June, and DP losses were greatest between May and November. Although different times and locations within the watershed were considered important to nitrate-N, DP, and PP losses, management practices such as cover crops and no-till should effectively mitigate the hot moments and hot spots for N and P losses from this and similar watersheds in the Chesapeake Bay basin.
Technical Abstract: Non-point nitrogen (N) and phosphorus (P) pollution from agriculture has increasingly received more public attention. However, when, where and how N and P export occurs from a watershed is not completely understood. In this study, nitrate-N, dissolved P and particulate P concentrations and loads were investigated for four sub-basins (labeled 1 to 4 going up the watershed) within a mixed land use watershed (39.5 ha) in the Appalachian Valley and Ridge Physiographic Province. Greater nitrate-N concentration and load were observed in base flow and during the non-growing season than in storm flow and during the growing season. The nitrate-N concentration in base flow was about 1.1-1.7 times of that in the storm flow, while the nitrate-N concentration during the non-growing season was about 1.2-1.9 of that during the growing season. Dissolved P and PP concentrations (about 0.03 mg per L for both) and loads (0-0.3 kg per mo for both) were low and temporally consistent in base flow at all flumes, but high and temporally variable in storm flow. The storm flow DP concentration and load were great from May to Dec. (greater than 0.08 mg per L) and from Sept. to Nov. (generally greater than 0.25 kg per mo), respectively, while the storm flow PP concentration and load were great from Jan. to June (greater than 0.30 mg per L and greater than 0.4 kg per mo). The nitrate-N, DP, and PP loads were compared for all four sub-basins on a loss per length of stream reach basis. The greatest nitrate-N loads were observed in Sub-basins 1 and 4 during the non-growing season base flow period and in Sub-basin 2 during the post-growing season base flow period (greater than 110 g per m per mo). The greatest DP loads were also observed in Sub-basins 1 and 4, but during the growing and post-growing season storm flow period (>1.4 g per m per mo). In contrast, the PP load was the greatest in Sub-basin 3 during the pre-growing and growing season storm flow, as much as 13.4 and 14.1 g per m per mo, respectively. Controlling factors of nutrient export were discussed in this study, including season, hydrology (base flow, storm flow, surface and subsurface runoff) and land use. Although different hot moments and hot spots within the watershed were identified for nitrate-N, DP, and PP losses, the implementation of a couple of management practices (cover crops and no-till) might be sufficient to effectively reduce nutrient losses from this and similar Valley and Ridge watersheds.