Variations in Base‐Flow Nitrate Flux in a First‐Order Stream and Riparian Zone¹

Abstract

Nonpoint source pollution, which contributes to contamination of surface waters, is difficult to control. Some pollutants, particularly nitrate (NO À 3 ), are predominantly transmitted through ground water. Riparian buffer zones have the potential to remove contaminants from ground water and reduce the amount of NO À 3 that enters surface water. This is a justification for setting aside vegetated buffer strips along waterways. Many riparian zone hydrologic models assume uniform ground-water flow through organic-rich soil under reducing conditions, leading to effective removal of ground-water NO À 3 prior to discharge into a stream. However, in a small first-order stream in the mid-Atlantic coastal plain, base-flow generation was highly variable (spatially and temporally). Average base-flow NO À 3 loads were greater in winter than summer, and higher during a wetter year than in dryer years. Specific sections of the stream consistently received greater amounts of high NO À 3 ground water than others. Areas within the riparian zone responsible for most of the NO À 3 exported from the watershed are termed ''critical areas.'' Over this 5-year study, most of the NO À 3 exported during base flow originated from a critical area comprising less than 10% of the total riparian zone land area. Allocation of resources to address and improve mitigation function in critical areas should be a priority for continued riparian zone research.(KEY TERMS: surface water ⁄ ground-water interactions; nonpoint source pollution; nutrients; transport and fate; ground-water hydrology; wetlands.)

The Role of Headwater Wetlands in Altering Streamflow and Chemistry in a Maine, USA Catchment1

“…We did not observe an increase in stream water nitrate concentration such as those found in groundwater discharge areas in nearstream environments (i.e., Angier and McCarty, 2008) as we believe the longitudinal length from seep outflow to the stream (over 100 m) at the study site likely consumes the relatively high nitrate levels at seep outflows such that it does not affect stream-water chemistry (Simon et al, 2010).…”

“…In areas with shallow till over bedrock with low permeability, as found in the northern United States and in our study area, most groundwater flow is comprised of local flow regimes (Toth, 1962;Roulet, 1990;Hill and Devito, 1997). Within catchments, small areas of high groundwater discharge, such as seeps, can exert a strong influence on stream flow and patterns of element retention within wetlands in relation to associated streams (Hill and Devito, 1997;Angier and McCarty, 2008). We investigated the role of headwater wetlands in a region likely dominated by local flow regimes to assess the hydrological and chemical contributions of wetlands to headwater streams.…”

“…These studies have identified important influencing factors such as catchment geology and geomorphology (Devito et al, 1996;Stein et al, 2004), soil conditions that alter water movement (Harr, 1977), groundwater residence time within subsurface layers (Hill and Devito, 1997;Winter, 2007), and catchment land use (Whigham and Jordan, 2003). Commonly, SGW -SW interaction studies are associated with near-stream riparian environments (Hill, 2000;Angier and McCarty, 2008). Headwater F o r P e e r R e v i e w wetlands, and in particular groundwater slope wetlands (which include 'seeps'), have received less attention, especially those indirectly connected to surface-water bodies.…”

The quality of our Nation's waters: water quality in the Northern Atlantic Coastal Plain surficial aquifer system, Delaware, Maryland, New Jersey, New York, North Carolina, and Virginia, 1988-2009

“…Concentrations of nitrate in streams usually are highest during base-flow conditions when most of the water is from groundwater, especially in winter, when consumption of nitrogen by aquatic organisms is minimal. (11,53,54) Although the median concentration of nitrate in streams of the Northern Atlantic Coastal Plain during base flow is less than 1 mg/L as N, concentrations greater than 10 mg/L as N have been measured in some streams. (11,51) During high flow, concentrations of nitrate typically are lower because contributions from precipitation and overland runoff, which have low concentrations of nitrate, dilute the contributions from nitraterich groundwater ( fig.…”

N2O Production and Removal in Streambed Sediments: Understanding Physicochemical Influences on N2O Fluxes From Agricultural Streams on the Eastern Shore of Virginia

“…The deep groundwater samples collected in the fall had a much higher Cl -to NO 3 -ratio than all the other seasons, an observation which is highly indicative of significant riparian influence. Groundwater flow paths can change seasonally as a result of changes in precipitation and evapotranspiration ultimately altering the chemical makeup of the groundwater at a sample point (Mulholland & Hill, 1997;Angier & McCarty, 2008). The present study only had one sampling period for each season, a fact which severely limits any ability to discern smaller changes that might reveal a stronger seasonal signal in NO 3 -concentrations.…”