Can't See the Forest for the Stream? In-stream Processing and Terrestrial Nitrogen Exports

Bernhardt, Emily S.; Likens, Gene E.; Hall, Robert O.; Buso, Donald C.; Fisher, Stuart G.; Burton, Thomas M.; Meyer, Judy L.; McDowell, W. H.; Mayer, Marilyn S.; Bowden, William B.; Findlay, Stuart E. G.; Macneale, Kate H.; Stelzer, Robert S.; Lowe, Winsor H.

doi:10.1641/0006-3568(2005)055[0219:acstff]2.0.co;2

Cited by 191 publications

(162 citation statements)

References 44 publications

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“…Low-order (headwater) streams are important in the downstream transport of diffuse nitrate (Alexander et al 2007). However, rivers are not inert pipelines, on the contrary, they are actually biogeochemical hot spots (Benstead and Leigh 2012;McClain et al 2003;Pinay et al 2015), which also play a major role in the transformation of reactive nitrogen to less ecologically active forms (Bernhardt et al 2005;Bernot and Dodds 2005). Across large catchments, nitrate attenuation is inversely correlated with stream-order, due to the relatively large surface area to volume ratios in smaller streams which aids surface water contact with the hypoxic bed (Alexander et al 2000;Peterson et al 2001).…”

Section: Electronic Supplementary Materialsmentioning

confidence: 99%

Enhanced hyporheic exchange flow around woody debris does not increase nitrate reduction in a sandy streambed

et al. 2017

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Anthropogenic nitrogen pollution is a critical problem in freshwaters. Although riverbeds are known to attenuate nitrate, it is not known if large woody debris (LWD) can increase this ecosystem service through enhanced hyporheic exchange and streambed residence time. Over a year, we monitored the surface water and pore water chemistry at 200 points along a * 50 m reach of a lowland sandy stream with three natural LWD structures. We directly injected 15 N-nitrate at 108 locations within the top 1.5 m of the streambed to quantify in situ denitrification, anammox and dissimilatory nitrate reduction to ammonia, which, on average, contributed 85, 10 and 5% of total nitrate reduction, respectively. Total nitrate reducing activity ranged from 0 to 16 lM h -1 and was highest in the top 30 cm of the stream bed. Depth, ambient nitrate and water residence time explained 44% of the observed variation in nitrate reduction; fastest rates were associated with slow flow and shallow depths. In autumn, when the river was in spate, nitrate reduction (in situ and laboratory measures) was enhanced around the LWD compared with non-woody areas, but this was not seen in the spring and summer. Overall, there was no significant effect of LWD on nitrate reduction rates in surrounding streambed sediments, but higher pore water nitrate concentrations and shorter residence times, close to LWD, indicated enhanced delivery of surface water into the streambed under high flow. When hyporheic exchange is too strong, overall nitrate reduction is inhibited due to short flow-paths and associated high oxygen concentrations.

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Section: Electronic Supplementary Materialsmentioning

confidence: 99%

Enhanced hyporheic exchange flow around woody debris does not increase nitrate reduction in a sandy streambed

et al. 2017

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“…uptake is perhaps negligible (they serve as both source and sink), their importance for other biogeochemical processes, in particular denitrification, may be substantial. In fact, accounting for the effect of debris dams and other organic debris can be essential for elucidating temporal patterns of watershed nitrogen export, as was illustrated by Bernhardt et al (2003Bernhardt et al ( , 2005.…”

Section: How Important Was Ts On Ammonium Uptake?mentioning

confidence: 99%

Longitudinal and seasonal variation of stream N uptake in an urbanizing watershed: effect of organic matter, stream size, transient storage and debris dams

et al. 2009

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? uptake rate patterns had a distinct seasonal reversal; fall had the highest uptake rates in the upper reaches, while summer had the highest uptake rates in the lower reaches. This seasonal reversal was attributed to organic matter and evidenced by DON patterns. Transient storage did not have an expected effect on uptake rates in fall because it was confounded by leaf litter; litter produced higher uptakes, but also may have reduced transient storage. In summer however, uptake rates had a positive correlation with transient storage. Debris dams had no distinct effect on uptake in fall because of their recent formation. In summer however, the debris dam effect was significant; although the debris dams were hydraulically inactive then, the upstream reaches had 2-5 fold higher uptake rates. The seasonal and longitudinal differences in NH 4? uptake reflect interactions between flow conditions and the role of organic matter. Urbanization can alter both of these characteristics, hence affect stream N processing.

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“…In-stream processes influence the transport, retention, and removal of N from the landscape (Peterson et al 2001;Mulholland 2004;Bernhardt et al 2005). Within the context of larger river networks, low-order streams can have a disproportionately large impact on the rate at which N is retained and attenuated within streams (Alexander et al 2000).…”

Section: Introductionmentioning

confidence: 99%

The saturation of N cycling in Central Plains streams: 15N experiments across a broad gradient of nitrate concentrations

et al. 2007

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We conducted 15 NO 3 -stable isotope tracer releases in nine streams with varied intensities and types of human impacts in the upstream watershed to measure nitrate (NO 3 -) cycling dynamics. Mean ambient NO 3 -concentrations of the streams ranged from 0.9 to 21,000 lg l -1 NO 3 --N. Major N-transforming processes, including uptake, nitrification, and denitrification, all increased approximately two to three orders of magnitude along the same gradient. Despite increases in transformation rates, the efficiency with which stream biota utilized available NO 3 --decreased along the gradient of increasing NO 3 -. Observed functional relationships of biological N transformations (uptake and nitrification) with NO 3 -concentration did not support a 1st order model and did not show signs of MichaelisMenten type saturation. The empirical relationship was best described by a Efficiency Loss model, in which log-transformed rates (uptake and nitrification) increase with log-transformed nitrate concentration with a slope less than one. Denitrification increased linearly across the gradient of NO 3 -concentrations, but only accounted for~1% of total NO 3 -uptake. On average, 20% of stream water NO 3 -was lost to denitrification per km, but the percentage removed in most streams was <5% km -1 . Although the rate of cycling was greater in streams with larger NO 3 -concentrations, the relative proportion of NO 3 -retained per unit length of stream decreased as NO 3 -concentration increased. Due to the rapid rate of NO 3 -turnover, these streams have a great potential for short-term retention of N from the landscape, but the ability to remove N through denitrification is highly variable.

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Can't See the Forest for the Stream? In-stream Processing and Terrestrial Nitrogen Exports

Cited by 191 publications

References 44 publications

Enhanced hyporheic exchange flow around woody debris does not increase nitrate reduction in a sandy streambed

Enhanced hyporheic exchange flow around woody debris does not increase nitrate reduction in a sandy streambed

Longitudinal and seasonal variation of stream N uptake in an urbanizing watershed: effect of organic matter, stream size, transient storage and debris dams

The saturation of N cycling in Central Plains streams: 15N experiments across a broad gradient of nitrate concentrations

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