Ghosts of landuse past: legacy effects of milldams for riparian nitrogen (N) processing and water quality functions
Open Access
- 8 January 2021
- journal article
- research article
- Published by IOP Publishing in Environmental Research Letters
- Vol. 16 (3), 035016
- https://doi.org/10.1088/1748-9326/abd9f5
Abstract
Milldams and their legacies have significantly influenced fluvial processes and geomorphology. However, less is known about their effects on riparian zone hydrology, biogeochemistry, and water quality. Here, we discuss the potential effects of existing and breached milldams on riparian nitrogen (N) processing through multiple competing hypotheses and observations from complementary studies. Competing hypotheses characterize riparian zone processes that remove (sink) or release (source) N. Elevated groundwater levels and reducing soil conditions upstream of milldams suggest that riparian zones above dams could be hotspots for N removal via denitrification and plant N uptake. On the other hand, dam removals and subsequent drops in stream and riparian groundwater levels result in drained, oxic soils which could increase soil nitrification and decrease riparian plant uptake due to groundwater bypassing the root zone. Whether dam removals would result in a net increase or decrease of N in riparian groundwaters is unknown and needs to be investigated. While nitrification, denitrification, and plant N uptake have typically received the most attention in riparian studies, other N cycle processes such as dissimilatory nitrate reduction to ammonium (DNRA) need to be considered. We also propose a novel concept of riparian discontinuum, which highlights the hydrologic and biogeochemical discontinuities introduced in riparian zones by anthropogenic structures such as milldams. Understanding and quantifying how milldams and similar structures influence the net source or sink behavior of riparian zones is urgently needed for guiding watershed management practices and for informed decision making with regard to dam removals.Funding Information
- National Science Foundation (1929747)
This publication has 108 references indexed in Scilit:
- Hydrologic history influences microbial community composition and nitrogen cycling under experimental drying/wetting treatmentsSoil Biology and Biochemistry, 2013
- Subfossil Leaves Reveal a New Upland Hardwood Component of the Pre-European Piedmont Landscape, Lancaster County, PennsylvaniaPLOS ONE, 2013
- The AnthropoceneAnnual Review of Earth and Planetary Sciences, 2013
- Microbial Community Structure and Denitrification in a Wetland Mitigation BankApplied and Environmental Microbiology, 2010
- The Role of Riparian Vegetation in Protecting and Improving Chemical Water Quality in Streams1Jawra Journal of the American Water Resources Association, 2010
- Impact of dam operations on hyporheic exchange in the riparian zone of a regulated riverHydrological Processes, 2009
- Beaver dams along an agricultural stream in southern Ontario, Canada: their impact on riparian zone hydrology and nitrogen chemistryHydrological Processes, 2009
- Homogenization of regional river dynamics by dams and global biodiversity implicationsProceedings of the National Academy of Sciences of the United States of America, 2007
- Effects of small dam removal on stream chemistry in southeastern PennsylvaniaJournal of the North American Benthological Society, 2006
- Linking the hydrologic and biogeochemical controls of nitrogen transport in near-stream zones of temperate-forested catchments: a reviewJournal of Hydrology, 1997