Data Package Metadata   View Summary

The following methods have been adapted from Bacmeister et al. (Submitted).

Locations:

Collected at three nested locations in the White Clay Creek (WCC) Watershed, in Pennsylvania.

1. Stroud - Upper part of east branch WCC. 2nd-order stream with a 7-km2 drainage area.

Mostly pasture and crops.

2. Strickersville - Below junction of east and west branches WCC, middle of watershed

area. 154-km2 drainage area. More diverse land use cover than Stroud site.

3. Newark - Most downstream site, lower watershed area. 4th-order stream with a 178-

km2 drainage area.

Field collection:  

Used a combination of passive samplers and grab sampling during storm events. Passive

samplers filled automatically during rising limb of the storm. The were collected within 24-

hours of storm. Grab samples were collected during recovery of passive samples. These were

collected using a 1L bottle attached to a Nasco Extandable Swing Sampler. Used during falling

limb of storm.

Sample Analysis:

Samples of unfiltered water were collected for total N and total P analysis. Filtered subsamples

of water were collected via vacuum filtration using 0.70-µm glass fiber filters for N-NO 3 − , N-NH 4 + ,

and P-PO 4 3 , and 0.22-μm syringe filters for DOC. All nutrient analyses were conducted via EPA

standard methods and discrete colorimetric analysis using an AQ300 discrete analyzer (SEAL

Analytical, Wisconsin, US), and DOC concentrations were determined using UV-catalyzed

persulfate oxidation with conductimetric detection (Sievers 900 TOC Analyzer, Sievers®).

Filtrate was collected and analyzed using EPA standard methods for total organic matter

content, organic C, organic N, and isotopic 15 N signature using a PDZ Europa ANCA-GSL

elemental analyzer interfaced to a PDZ Europa 20–20 isotope ratio mass spectrometer (Sercon,

Cheshire, United Kingdom). Additional filtrate was collected for analysis of chlorophyll-a

concentration using EPA standard methods and a AU-10 portable fluorometer (Turner Designs).

Subsamples of unfiltered water were collected and centrifuged to obtain solids, which were

then analyzed using qPCR and methods described in Henry et al. (2006) to quantify abundance

of nosZ (denitrifying) genes.

Sample Incubations:

Biological oxygen demand (BOD) of storm samples was determined using a 5-day BOD

experiment as described by Delzer & McKenzie (2003) . Unfiltered subsamples were collected

and oxygen concentration was recorded on day 0 and day 5, following a 5-day dark incubation.

Denitrification and assimilatory N uptake rates were determined by conducting a 24h dark

incubation. Unfiltered subsamples were collected, placed in individual chambers, and spiked

with a known concentration of Na 15 NO 3 − . Samples were consistently agitated on a magnetic stir

plate throughout the incubation period, and gas samples from the headspace of each chamber

was collected at 4 and 24h after the start of incubation. Gas samples were analyzed for δ 15 N-N 2

and δ 15 N-N 2 O signatures via continuous flow isotope ratio mass spectrometry (IRMS).

Nitrogen uptake calculations:

Rates of assimilatory uptake by total suspended sediment in each microcosm were calculated

following Mulholland et al. (2000) , where Umicro is the microcosm-specific rate of assimilatory

uptake (µg N d -1 ); 15 N susp-OM is the background-corrected 15 N mass associated with suspended OM;

and Time is the incubation time.

Denitrification rates by total suspended sediment in each microcosm were calculated from the

production rate of 29 N 2 (r 29 ) and 30 N 2 (r 30 ) following calculations for total denitrification rate

associated with sediments described by Nielsen (1992) , where where DNmicro is the microcosm-

specific denitrification rate (µg N d -1 ).

Bibliography

Bacmeister, E., Peck, E., Bernasconi, S., Inamdar, S., Kan, J., Peipoch, M. (Submitted). JGR:

Biogeosciences. Water column nitrogen uptake during storms in a low-order watershed.

Delzer, G. C., & McKenzie, S. W. (2003). Five-Day Biochemical Oxygen Demand. In USGS

Techniques of Water-Resources Investigations (3rd ed., Vol. A7). United States

Geological Survey.

Henry, S., Bru, D., Stres, B., Hallet, S., & Philippot, L. (2006). Quantitative Detection of the nosZ

Gene, Encoding Nitrous Oxide Reductase, and Comparison of the Abundances of 16S

rRNA, narG, nirK , and nosZ Genes in Soils. Applied and Environmental Microbiology,

72(8), 5181–5189. https://doi.org/10.1128/AEM.00231-06

Mulholland, P. J., Tank, J. L., Sanzone, D. M., Wollheim, W. M., Peterson, B. J., Webster, J. R., &

Meyer, J. L. (2000). Nitrogen Cycling in a Forest Stream Determined by a 15N Tracer

Addition. Ecological Monographs, 70(3), 471–493. https://doi.org/10.1890/0012-

9615(2000)070[0471:NCIAFS]2.0.CO;2

Nielsen, L. P. (1992). Denitrification in sediment determined from nitrogen isotope pairing.

FEMS Microbiology Letters, 86(4), 357–362. https://doi.org/10.1111/j.1574-

6968.1992.tb04828.x