Geology topics

Keith N. Eshleman

Publications and source records attributed to Keith N. Eshleman.

3 recordsLinked to original sources

USGS2019

Unprocessed atmospheric nitrate in waters of the Northern Forest Region in the USA and Canada

Little is known about the regional extent and variability of nitrate from atmospheric deposition that is transported to streams without biological processing in forests. We measured water chemistry and isotopic tracers (δ 18 O and δ 15 N) of nitrate sources across the Northern Forest Region of the U.S. and Canada and reanalyzed data from other studies to determine when, where, and how unprocessed atmospheric nitrate was transported in catchments. These inputs were more widespread and numerous than commonly recognized, but with high spatial and temporal variability. Only 6 of 32 streams had high fractions (>20%) of unprocessed atmospheric nitrate during baseflow. Seventeen had high fractions during stormflow or snowmelt, which corresponded to large fractions in near-surface soil waters or groundwaters, but not deep groundwater. The remaining 10 streams occasionally had some (<20%) unprocessed atmospheric nitrate during stormflow or baseflow. Large, sporadic events may continue to be cryptic due to atmospheric deposition variation among storms and a near complete lack of monitoring for these events. A general lack of observance may bias perceptions of occurrence; sustained monitoring of chronic nitrogen pollution effects on forests with nitrate source apportionments may offer insights needed to advance the science as well as assess regulatory and management schemes.

Environmental Science and Technology↗

USGS2018

Using United States Geological Survey stream gages to predict flow and temperature conditions to maintain freshwater mussel habitat

Habitat conditions necessary to support freshwater mussels can be difficult to characterize and predict, particularly for rare or endangered species such as the federally endangered dwarf wedgemussel, Alasmidonta heterodon . In this study, we evaluate flow and temperature conditions in three areas of the mainstem Delaware River known to consistently support A . heterodon , and we develop predictive models using the U.S. Geological Survey (USGS) stream gages and thermal stations in order to identify conditions under which habitat alteration could threaten the species. Flow and temperature prediction models based on nearby existing USGS gage and thermal stations were predictive for all three sites. Both discharge prediction and water depth profile models indicate one location (Site 3) was the most vulnerable to low‐flow conditions as it requires the highest discharge rate (26.3 cms) at the USGS Callicoon gage to maintain both the full wetted perimeter (P full ) and minimal wetted perimeter (P min ) and prevent occlusion of areas that contain A . heterodon . Flow management targets aimed at protecting Site 3 should also protect Sites 1 and 2. Although analyses indicated significant benthic habitat available in all three sites even under low discharge rates, specific mussel locations could be vulnerable to dewatering and thermal stress if only P min values were maintained. Results indicate the magnitude of site temperature deviations from thermal stations varied by site and river temperature. In general, our results suggest that existing temperature and stream gage infrastructure may be used predictively to evaluate the effects of different flow targets on mainstem Delaware River A . heterodon habitat.

Delaware River↗

USGS2016

Watershed-scale changes in terrestrial nitrogen cycling during a period of decreased atmospheric nitrate and sulfur deposition

Recent reports suggest that decreases in atmospheric nitrogen (N) deposition throughout Europe and North America may have resulted in declining nitrate export in surface waters in recent decades, yet it is unknown if and how terrestrial N cycling was affected. During a period of decreased atmospheric N deposition, we assessed changes in forest N cycling by evaluating trends in tree-ring δ 15 N values (between 1980 and 2010; n = 20 trees per watershed), stream nitrate yields (between 2000 and 2011), and retention of atmospherically-deposited N (between 2000 and 2011) in the North and South Tributaries (North and South, respectively) of Buck Creek in the Adirondack Mountains, USA. We hypothesized that tree-ring δ 15 N values would decline following decreases in atmospheric N deposition (after approximately 1995), and that trends in stream nitrate export and retention of atmospherically deposited N would mirror changes in tree-ring δ 15 N values. Three of the six sampled tree species and the majority of individual trees showed declining linear trends in δ 15 N for the period 1980–2010; only two individual trees showed increasing trends in δ 15 N values. From 1980 to 2010, trees in the watersheds of both tributaries displayed long-term declines in tree-ring δ 15 N values at the watershed scale (R = −0.35 and p = 0.001 in the North and R = −0.37 and p <0.001 in the South). The decreasing δ 15 N trend in the North was associated with declining stream nitrate concentrations (−0.009 mg N L −1 yr −1 , p = 0.02), but no change in the retention of atmospherically deposited N was observed. In contrast, nitrate yields in the South did not exhibit a trend, and the watershed became less retentive of atmospherically deposited N (−7.3% yr −1 , p < 0.001). Our δ 15 N results indicate a change in terrestrial N availability in both watersheds prior to decreases in atmospheric N deposition, suggesting that decreased atmospheric N deposition was not the sole driver of tree-ring δ 15 N values at these sites. Other factors, such as decreased sulfur deposition, disturbance, long-term successional trends, and/or increasing atmospheric CO 2 concentrations, may also influence trends in tree-ring δ 15 N values. Furthermore, declines in terrestrial N availability inferred from tree-ring δ 15 N values do not always correspond with decreased stream nitrate export or increased retention of atmospherically deposited N.

Atmospheric Environment↗