USGS Science⌕ Search
Home/Archive/USGS

USGS · 70022561

Statistical evaluation of effects of riparian buffers on nitrate and ground water quality

T.B. Spruill
View original source ↗Export metadata ↓

Abstract

A study was conducted to statistically evaluate the effectiveness of riparian buffers for decreasing nitrate concentrations in ground water and for affecting other chemical constituents. Values for pH, specific conductance, alkalinity, dissolved organic carbon (DOC), silica, ammonium, phosphorus, iron, and manganese at 28 sites in the Contentnea Creek Basin were significantly higher (p < 0.10) in old (>20 yr) discharging ground water draining areas with riparian buffers compared with areas without riparian buffers. No differences in chloride, nitrate nitrogen, calcium, sodium, and dissolved oxygen concentrations in old ground water between buffer and nonbuffer areas were detected. Comparison of samples of young (<20 yr) discharging ground water samples from buffer and nonbuffer areas indicated significantly higher specific conductance, calcium, chloride, and nitrate nitrogen in nonbuffer areas. Riparian buffers along streams can affect the composition of the hyporheic zone by providing a source of organic carbon to the streambed, which creates reducing geochemical conditions that consequently can affect the chemical quality of old ground water discharging through it. Buffer zones between agricultural fields and streams facilitate dilution of conservative chemical constituents in young ground water that originate from fertilizer applications and also allow denitrification in ground water by providing an adequate source of organic carbon generated by vegetation in the buffer zone. Based on the median chloride and nitrate values for young ground water in the Contentnea Creek Basin, nitrate was 95% lower in buffer areas compared with nonbuffer areas, with a 30 to 35% reduction estimated to be due to dilution and 65 to 70% due to reduction and/or denitrification.

Explore related subjects

Journal of Environmental QualityArticle

Keep this discovery

Explore connections, maps & timelines

BibTeXRIS

T.B. Spruill. 2000. Statistical evaluation of effects of riparian buffers on nitrate and ground water quality. https://doi.org/10.2134/jeq2000.00472425002900050020x

Cite the original work for its findings. Save a collection to share your selection of sources.

KEEP EXPLORING

Related USGS reports

USGS2026

Quantitative microbial risk assessment with microbial source tracking for enteric pathogens in southwest Wisconsin private wells

Private wells supply drinking water for many households, and their contamination by fecal microbes presents a risk of acute gastrointestinal illness (AGI). Risk is thought to vary by contaminating fecal source, but specific associations with fecal source are unknown for most private wells in the United States. This study characterizes AGI risk in Grant, Iowa, and Lafayette counties in southwestern Wisconsin. AGI risk was assessed for 10 viral, bacterial, and protozoan pathogens detected in private wells using quantitative microbial risk assessment. Exposure assessment was based on sampling 138 private wells in the study area, and risk was associated with fecal source by microbial source tracking (MST). Median Monte Carlo estimates indicated 4450 AGI cases/year in the study area associated with drinking water from contaminated private wells (95% confidence interval: 90–37,990). Most annual cases were associated with detection of human MST markers, including median estimates of 2550 associated with only human markers and 880 with human and livestock MST markers detected together. Note that 50 AGI cases/year were associated with detection of only livestock markers, and nearly 1000 cases were estimated to occur in the absence of detectable MST markers. This study characterizes AGI risk for households served by private wells in southwestern Wisconsin. It illustrates that human fecal sources can predominate risk associated with drinking water from private wells, even in a rural region characterized by substantial agricultural activity. MST can characterize the relationship between risk and fecal source; contributions of fecal sources to risk cannot be assumed from land use.

Wisconsin↗
USGS2025

Changing dynamic phosphorus forms from field to stream during surface runoff events

The risk of water quality impairment from agricultural runoff depends on nutrient source, transport, and bioavailability. Phosphorus (P) spirals between dissolved and particulate forms as it is transported with suspended sediment (SS) from agricultural fields, through the stream network, to receiving water bodies. This dynamic sorption-desorption influences bioavailability. We quantified P form and abundance in samples collected during surface-runoff events from a farm field in the East River Basin, Wisconsin and compared them to those in stream water collected from the East River. We sampled five events between late March 2022 and June 2023. During most events, P in surface runoff was mainly in dissolved form, with particulate P sorbed to fine clay, the most abundant particle fraction transported from the field, whereas P in stream water was mainly in particulate form and sorbed to silt, even though fine clay was the most abundant particle fraction in the stream during events. Overall capacity for P sorption to SS in the stream varied among events. Total P and SS concentrations were lower during summer baseflow conditions and smaller surface runoff events; however, what SS was present was more P enriched. This shift in P form from field to stream indicates a potential for sorbing dissolved P to SS during transport through the stream network, which changes the bioavailability of P exported downstream with less bioavailable P as dissolved P binds to SS.

Wisconsin↗
USGS2025

Assessing the topographic distribution of legacy soil phosphorus in agricultural fields of the Delmarva Peninsula, Mid-Atlantic Coastal Plain, USA

Phosphorus (P) management remains a challenge in agricultural watersheds. The Choptank River Conservation Effects Assessment Project watershed, located in Maryland and Delaware and draining to the Chesapeake Bay, contains legacy soil P from historical dairy and poultry manure applications. These practices elevated soil P beyond crop needs, contributing to persistent P export to aquatic ecosystems. We assessed spatial P distribution and analyzed GIS (Geographic Information Systems)-derived landscape features driving legacy P movement on a farm (47 ha). We hypothesized that P accumulates in drained lowlands and depressional areas due to gravity-driven processes that accelerate P-enriched water to receiving waters via overland flow. In collaboration with the US Department of Agriculture Legacy P project, we collected 105 soil samples (0- to 5-cm and 5- to 15-cm depths) and 14 ditch sediment samples across five topographic openness classes from a farm with >100 years of dairy manure application. Average Mehlich-III P concentrations were 218 and 179 mg kg −1 at 0- to 5-cm and 5- to 15-cm depths, respectively, with legacy areas defined by P content > 100 mg kg −1 . Soil P and clay particle size were positively correlated ( r = 0.42, p < 0.05), increased as landscape openness decreased, and were negatively correlated with topographic openness (ranging from −0.2 to −0.4, p < 0.05), indicating accumulation of P and clay in low-lying areas. These patterns suggest that historical field-level managements have primarily shaped P distribution, while hydrologic and landscape properties further influence its redistribution via transport pathways and drainage. These findings support the development of landscape models to map critical source areas in low-relief watersheds and guide targeted mitigation in high-risk P export zones.

Maryland↗