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Abstract Hydrologic alterations associated with urbanization can weaken connections between riparian zones, streams, and uplands, leading to negative effects on the ability of riparian zones to intercept pollutants carried by surface water runoff and groundwater flow such as nitrate (NO3−) and phosphate (PO43−). We analyzed the monthly water table as an indicator of riparian connectivity, along with groundwater NO3−and PO43−concentrations, at four riparian sites within and near the Gwynns Falls Watershed in Baltimore, MD, from 1998 to 2018. The sites included one forested reference site (Oregon Ridge), two suburban riparian sites (Glyndon and Gwynnbrook), and one urban riparian site (Cahill) with at least two locations and four monitoring wells, located 5 m from the center of the stream, at each site. Results show an increase in connectivity as indicated by shallower water tables at two of the four sites studied: Glyndon and Cahill. This change in connectivity was associated with decreases in NO3−at Glyndon and increases in PO43−at Glyndon, Gwynnbrook, and Cahill. These changes are consistent with previous studies showing that shallower water table depths increase anaerobic conditions, which increase NO3−consumption by denitrification and decrease PO43−retention. The absence of change in the forested reference site, where climate would be expected to be the key driver, suggests that other drivers, including best management practices and stream restoration projects, could be affecting riparian water tables at the two suburban sites and the one urban site. Further research into the mechanisms behind these changes and site‐specific dynamics is needed.
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Assessing transport and retention of nitrate and other materials through the riparian zone and stream channel with simulated precipitation
Abstract Riparian zones, the interfaces between land and stream, perform vital ecosystem functions including transformation and retention of nutrients and sediment moving across the landscape. Although many studies assess transport through and transformation of materials in riparian zones, less is known about the direct influence of precipitation falling on these zones on material retention and transport. Additionally, few experiments can compare riparian retention to stream‐channel retention.We present a novel experimental approach to assess retention of nitrate entering as precipitation in riparian zones and compare riparian retention and movement of nitrate, other ions, sediments to and within the adjacent stream channel. We simulated an intense precipitation event with15N‐labelled nitrate as a bioactive solute and bromide as an inert tracer. This method extends tracer release approaches applied to streams worldwide and links it to processes at the aquatic/ terrestrial interface. It further allows determination of movement of materials into streams from bankside precipitation.The riparian zone removed or retained a greater proportion of nitrate than the stream relative to bromide; over half the added bromide reached the stream through a few metres of riparian zone, compared to only 0.2% of the added nitrate. Of the 0.2% that reached the stream, 30% of that nitrate was removed or retained by instream processes after travelling 60 downstream. Roughly 10% of the total15N addition ended up sequestered in the above‐ground portions of the riparian grasses by the end of the growing season, and very little of it was recovered from the soil. We saw little evidence of bulk transport of other ions or sediment from this riparian soil to the stream.Our data are consistent with the concept of high nitrate retention in vegetated riparian zones, even for nitrate falling directly upon them in the form of atmospheric deposition in precipitation.
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- PAR ID:
- 10447007
- Publisher / Repository:
- Wiley-Blackwell
- Date Published:
- Journal Name:
- Methods in Ecology and Evolution
- Volume:
- 13
- Issue:
- 3
- ISSN:
- 2041-210X
- Page Range / eLocation ID:
- p. 757-766
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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