About

Christian Lenhart is an Associate Professor in the Department of Bioproducts and Biosystems Engineering at the University of Minnesota. His research focuses on the restoration of streams and wetlands to achieve hydrologic and ecological benefits, including the assessment and design of restoration projects and water quality practices. He contributes to hydrologic and water quality monitoring efforts for The Nature Conservancy in Minnesota, North Dakota, and South Dakota, and has coordinated the professional restoration certification program for the Society of Ecological Restoration International, serving as president of the SER-Midwest-Great Lakes Chapter. Dr. Lenhart has co-authored widely-used management guides such as the Aquatic Organism Passage Handbook for MnDOT and the Agricultural BMP Handbook for Minnesota. His work includes investigating peatland restoration for reducing carbon emissions to address climate change, as well as implementing and assessing stream and wetland restoration projects and water quality practices with various organizations. He is involved in the assessment of agricultural best management practices and has a strong background in ecological engineering, water resources management, and aquatic ecology.

Research topics

• Geology
• Environmental science
• Ecology
• Geography
• Chemistry
• Soil science
• Mathematics
• Remote sensing
• Biology
• Cartography
• Environmental engineering

Selected publications

• Treatment Wetland Plant Harvests as a Tool for Soil Phosphorus Reduction in North Central US Agricultural Watersheds

  Water · 2024-02-22 · 3 citations

  articleOpen accessSenior author

  Agricultural watersheds in the North Central United States have been intensively farmed for decades with widespread application of fertilizer and extensive tilling practices. Soil phosphorus built up in sediments over time as a result of these practices may be released under anaerobic conditions, such as flood events. These floods are increasing in frequency and intensity due to climate change, leading to downstream water-quality concerns. Edge-of-field best management practices, including constructed treatment wetlands, provide a natural buffer for excess phosphorus runoff, but may only be a temporary solution if soil becomes oversaturated with phosphorus over extended periods of time. Preventing wetlands from becoming sources of phosphorus to water bodies may be essential for management in future years when considering impacts from climate change. This research assesses how wetland plant harvesting can reduce soil phosphorus accumulation (measured as Olsen phosphorus) in edge-of-field treatment wetlands, thereby preventing these systems from becoming phosphorus sources and ensuring the longevity of water-quality benefits from these systems. Using several 380 L controlled wetland mesocosm experiments in 2018–2019, we assessed above-ground plant material (S. tabernaemontani and B. fluviatilis) and soil Olsen P through the growing season and after harvest. We observed a reduction in soil phosphorus from wetland plant harvesting between 1–50% over one year, with a mean reduction of 7.9 mg/kg. B. fluviatilis initially contained higher P concentration early in the season (0.82% P content) compared to S. tabernaemontani (0.76% P), but S. tabernaemontani retained higher P later in the season (0.3% P content) compared to B. fluviatilis (0.25%). Time of season may significantly impact plant P removal potential, including accessibility of treatment wetland sites. While controlled mesocosm experiments may not always be applicable to real landscape-level management, this study highlights the potential for reductions in soil phosphorus and corresponding downstream phosphorus fluxes in edge-of-field treatment wetlands through plant harvest during the growing season. Plant harvesting can be used by land managers in edge-of-field treatment wetlands as an adaptation mechanism for shifting environmental conditions, such as increased heavy rainfall occurrences and flood events, that are exacerbated by climate change in this region.

  PublisherOA PDFDOI

• The Stream Guide: A case study of how to teach complex environmental topics to agency personnel and land managers

  Rangelands · 2024-01-25

  articleOpen accessSenior author

  Multipartner publications are often not used due to insufficient dissemination. Incorporating partners into existing Extension programs provides scaffolding to communicate complex scientific concepts to a lay audience, such as land managers or agency personnel. Participation, experiential learning, and creating a community of like-minded individuals is valuable in teaching new concepts to an audience, thereby resulting in a change in knowledge.

  PublisherDOI

• Contributions From a Southern Minnesota Saturated Buffer Field Site: <i>Agricultural Best Management Practices and Dissolved Phosphorus Loss</i>

  Case Studies in the Environment · 2024-01-01 · 2 citations

  articleSenior author

  Phosphorus is a growing water quality concern in agricultural landscapes. Sources of agricultural phosphorus include synthetic fertilizers and manure application that support crop growth. These sources lead to excess phosphorus in adjacent waterways causing harm to aquatic communities and to human health. Phosphorus is transported downstream contributing to larger pollution issues including eutrophication of freshwater bodies. Conservation practices called Best Management Practices (BMPs) have been developed to manage agricultural phosphorus pollution. One common BMP is a riparian, or streamside, buffer. This BMP allows for the reestablishment of vegetation between an agricultural field and adjacent waterway. Riparian buffers act as a filter strip and are effective for nitrogen, sedimentation, and erosion control. The efficacy of these practices to manage phosphorus, however, is less clear, notably regarding dissolved phosphorus. Dissolved phosphorus is highly bioavailable and ready for plant uptake, contributing to pollution from rapid algae growth. A saturated buffer is a specific type of riparian buffer known to be effective for nitrogen and particulate phosphorus removal, but in some cases has been shown to contribute to dissolved reactive phosphorus (DRP) pollution. Through field data collection, the aim of this case study was to document DRP contributions from a saturated buffer field research site located in Southern Minnesota. In addition, this study documents the drivers of DRP contributions including soil characteristics, microbial community structure, and flooding. Results from the work demonstrate the need to account for dissolved phosphorus in meeting water quality goals through the implementation of agricultural BMPs.

  PublisherDOI

• Farmer adoption-based prompt networking and modeling for targeting optimal agro-conservation practices

  Environmental Modelling & Software · 2024-04-27 · 4 citations

  article
  PublisherDOI

• Estimating Soil Properties Distribution at a Restored Wetland Using Electromagnetic Imaging and Limited Soil Core Samples

  Wetlands · 2023 · 19 citations

  • Environmental science
  • Soil science
  • Remote sensing
  PublisherDOI

• Carbon dioxide emissions in relation to water table in a restored fen

  Agricultural & Environmental Letters · 2023-07-13 · 3 citations

  articleOpen access

  Abstract Many peatlands have been drained for anthropogenic purposes, and there is high interest in restoring them for their carbon storage ability and critical habitat. Peatlands hold a disproportionate amount of global soil carbon, making peatland restoration a promising approach for mitigating carbon emissions. In this study, site factors were investigated that affect peat carbon dioxide flux at Cold Spring fen in Minnesota, which is undergoing restoration. Peat carbon dioxide flux and water table depth were monitored throughout the growing season at two locations previously disturbed to different degrees by row‐crop agriculture. Flux ranged from 0.55 to 12.71 µmol m −2 s −1 and was highest during peak growing season. Lower flux corresponded to elevated water table conditions. The more disturbed location often had lower flux, indicating success in hydrological restoration. The water table is an important factor in peatland restoration, and water table management should be considered to maximize carbon sequestration.

  PublisherOA PDFDOI

• Intermittent Prairie Streams in the Northern Great Plains: <i>A Case of an Undervalued Ecosystem</i>

  Case Studies in the Environment · 2023-01-01 · 3 citations

  article1st authorCorresponding

  Small (&amp;lt;15 m wide), intermittent prairie streams in western South Dakota, a semiarid part of the northern United States, are undervalued ecosystems because they do not exemplify the values of classic, flowing streams. However, they are valuable as wildlife corridors, aquatic habitat for drought-adapted species, and support of local grazing economies. We surveyed 90 streams in 2018–2019, collecting data on geomorphic, water chemistry, and biological properties, focusing on vegetation and grazing impacts. We developed an approach for categorizing streams by landscape position and flow regime to facilitate appropriate land management and stream restoration actions. The result was a published landowner guide to provide information on low-tech riparian management and restoration options of the four stream types we categorized. The headwaters streams and woody draws with drainage areas &amp;lt;26 km2 are the most abundant types and exemplify the issues described above. Large rivers, despite drainage areas exceeding 260 km2 can go dry. Management issues include invasive plant species, lack of woody riparian establishment, poor water quality, overgrazing, channel incision, and water stress from climate change. The most cost-effective management practices involve rotational grazing and practices that reduce cattle impacts. More recently, beaver dam analogs have been installed and beaver reintroduction is being considered along with reestablishment of native bison herds in place of cattle. Intermittent prairie streams present an excellent case study of an undervalued ecosystem, illustrating the challenges and opportunities of such systems. Engagement of grazing landowners can improve stewardship of these systems.

  PublisherDOI

• Hydrologic Alteration Drives Channel Widening and Alters Sandbar Vegetation Dynamics on a Large, Alluvial River in Minnesota, USA

  2022-10-18

  book-chapter1st authorCorresponding

  The Minnesota River carries the largest load of sediment to the Mississippi River in MM, most of which comes from channel sources of sediment. This study investigates bank retreat in the lower Minnesota River from 1938 to 2009. Specifically, we asked, How have changes to hydrology affected river form, sediment transport, and deposition in the lower Minnesota River and how did that affect ecohydrological processes? It was hypothesized that channel straightening, reduction in floodplain access, and streamflow increases contributed to increased channel-derived sediment load and decreased point bar deposition. Secondly, it was hypothesized that hydrologic changes have reduced woody riparian vegetation on sandbars, further promoting channel width increased by reducing the narrowing process that occurs on sandbars by plant growth. To quantify channel sediment and phosphorus loading rates in the lower Minnesota Rive: historic aerial photos were used to measure channel change; long-term erosion and deposition rates within the river corridor were assessed and calculations of channel sediment transport rates were made. Results from this study showed that the Minnesota River has widened by 52% between Mankato and St. Paul from 1938 to 2009, on average contributing 280,000 Mg/year with 153 tons of total phosphorus. Additionally, the river has shortened by 7% from 1938 to 2009, increasing bankfull shear stress and stream power. Sediment deposition rates in certain parts of the floodplain have increased since European settlement (circa 1840–1850) by an order of magnitude, approximately tracking the increased loads of sediment that occurred in that time. Ecohydrological studies showed that establishment of woody riparian plants has been inhibited on sandbars by prolonged summer flow duration and scour at high flow. This favored plant species that spread by clonal growth such as sandbar willow (Salix interior). Additional research done since the completion of the original study, published in 2013, was summarized, adding new insight to channel adjustment and ecohydrological processes, particularly on sandbars. Findings from this study provide an example of the geomorphic and ecohydrological consequences of flow increases from climate and land-use changes and inform management of large floodplain river systems.

  PublisherDOI

• Estimating soil properties distribution at a restored wetland using electromagnetic imaging and limited soil core samples

  Research Square · 2022-11-29 · 2 citations

  preprintOpen access

  Abstract Electromagnetic imaging (EMI) provides an efficient approach for characterizing variations in soil physicochemical properties at a high spatial resolution. While EMI has been widely used to estimate variations in soil properties in agricultural, geotechnical, and contaminated sites, limited applications have been reported for wetlands. This study assesses the use of EMI for estimating soil property distributions at a restored wetland in northwestern Ohio, USA. We acquired spatial distribution of soil apparent electrical conductivity (ECa) and apparent magnetic susceptibility (MSa) via EMI over a 162,000 m 2 restored wetland using an EM-38-MK2 instrument towed behind a utility terrain vehicle equipped with a differential ground positioning system. We collected twenty-two undisturbed soil samples and analyzed them in the laboratory for soil moisture (SMC), organic matter (SOM), porosity, bulk density, and texture. A least squares linear regression model was used to compare the correlation between each soil property with measured ECa and MSa while ECa was used to predict the distribution of SMC and SOM using the statistical model validated using the leave-one-out technique. We observed strong correlations between soil texture, SMC, and SOM, and ECa with SOM showing a slightly dominant control. This study shows that ECa can predict the distribution of SMC and SOM in wetland soils to an accuracy of ~ 67–70% for these datasets. The spatial ECa patterns matched the USDA soil map for the site. This study validates the potential of extending EMI for characterizing wetland soil properties, improving sampling plans, and extrapolating soil property estimates to unsampled regions.

  PublisherOA PDFDOI

• Air-Photo-Based Change in Channel Width Sedimentation in the Minnesota River Basin

  2022-10-18

  book-chapter

  The Minnesota River and major tributaries have experienced large increases in discharge over the past century. Aerial photograph-based measurements of channel width were made for the 1938–2015 period at 16 multibend subreaches by digitizing the area between vegetation lines and dividing by centerline length. Results show considerable increases in width for the mainstem (0.62 ± 0.10%/year) and major tributaries (0.31 ± 0.08%/year) but are inconclusive for smaller channels (width &lt; 25 m). Width changes for a 146.5 km reach of the lower Minnesota River between 1938 and 2008 are similar to that from the subreach-scale analysis. Widening was associated with lateral centerline movement and temporal change in at-a-station hydraulic geometry for water surface width, indicating that widening is associated with cross-sectional change and not simply upward movement of the vegetation line. Digital elevation model analysis and regional hydraulic geometry show that the mainstem and larger tributaries account for the vast majority (~85%) of bankfull channel volume. High-order channels are thus disproportionately responsible for sediment production through cross-section enlargement, although floodplains or off-channel water bodies adjacent to these channels likely represent important sediment sinks. Because channel enlargement can play an important role in sediment production, it should be considered in sediment reduction strategies and carefully evaluated in watersheds undergoing long-term increases in discharge.

  PublisherDOI

Frequent coauthors

• John L. Nieber

  University of Minnesota

  13 shared

• Brad A. Gordon

  8 shared

• Joe Magner

  8 shared

• B. Suppes

  6 shared

• Kenneth N. Brooks

  6 shared

• Kristen Blann

  The Nature Conservancy

  5 shared

• Kate Brooks

  5 shared

• Patrick Belmont

  4 shared

Awards & honors

• 2021, Article, “Nutrient Retention in Ecologically Functiona…
• 2020, Selected as a University of Minnesota, Institute on th…
• 2019. AOP guide for Minnesota nominated for MnDOT Research A…
• 2013. American Council of Engineering Companies (ACEC) Honor…
• 2012. Certificate of Excellence for publication with the Cou…