Improving the design of saturated riparian buffers for removing nitrate from subsurface drainage

In the U.S. Midwest, agricultural subsurface drainage, or tile, is commonly used to improve crop production; however, because nitrate is easily leached, tile drainage typically has high nitrate loads. Nitrate exported via tile drainage impairs water quality and can be reduced by implementing conservation practices, such as saturated riparian buffers (SRBs). SRBs function by redistributing the nitrate-rich tile drainage through the soil of a vegetated buffer zone via a perforated distribution pipe, facilitating denitrification and plant uptake. Because this practice is relatively new, there has been limited research into how SRBs function and how to effectively design them. In the first study, an equation for the optimal SRB width was derived by applying a mass balance to maximize the nitrate removal effectiveness. The optimal width is smaller than the current width at each of the six study sites, and two sites have optimal widths that are smaller than the minimum width specified in the current NRCS design standards. In the second study, a three-dimensional, finite-difference groundwater flow model was developed to better understand how groundwater flows in SRBs. Because flow is one-dimensional in most of the SRB, assuming one-dimensional groundwater flow in an SRB is reasonable. The median error associated with computing the travel time using a one-dimensional approximation is 11.6%. The flow path of the tile drainage toward the stream depends on where it exits the distribution pipe; the flow that exits through the top perforations at the end of the distribution pipe has the greatest potential for nitrate removal. Better understanding how groundwater flows in an SRB is an important step toward improving design to more effectively improve water quality

First episode psychosis and psychological development in young adulthood

Despite the consistent emergence of a psychotic illness during late adolescence and young adulthood, attempts to understand first episode psychosis and psychological disturbances and needs have historically neglected this rich developmental context. When present, disturbances in a young adults\u27 psychological functioning are likely to interfere with the successful negotiation of age-appropriate tasks and complicate the recovery process following a first episode of psychosis. The current study sought to identify developmentally significant and clinically meaningful disturbances in the psychological functioning of young adults recovering from a first episode of psychosis. To accomplish this goal, 27 young adults who were recovering from a first episode of psychosis were compared to 27 young adults whose upward developmental growth trajectory had not been disrupted by psychosis on measures investigating sense of interpersonal relatedness and self-definition, parent representations, and depressive symptoms. Associations between illness characteristics and the various measures of psychological functioning were also examined. Results suggest that the young adults recovering from a first episode of psychosis are more likely to expect and fear rejection in interpersonal encounters, experience difficulties in peer relationships, lack balance in a sense of self and other, feel engulfed and controlled by parents, internalise parent representations characterised by less warmth and slightly more overprotection, and endorse depressive symptoms. Depressive symptoms appear to significantly contribute to expectations of rejection and callousness, and parent representations characterised by less warmth and care. Age of illness onset appears to demonstrate stronger relationships with several disturbances in psychological functioning than does duration of untreated psychosis. Findings of this study are considered in terms of implications for future research, developmental theory, and clinical practice. Early psychosis programs are urged to incorporate psychological interventions that foster positive self-development, the establishment of healthy peer relationships, individuation from parents, and mature identity formation

Improving the design of saturated riparian buffers for removing nitrate from subsurface drainage

In the U.S. Midwest, agricultural subsurface drainage, or tile, is commonly used to improve crop production; however, because nitrate is easily leached, tile drainage typically has high nitrate loads. Nitrate exported via tile drainage impairs water quality and can be reduced by implementing conservation practices, such as saturated riparian buffers (SRBs). SRBs function by redistributing the nitrate-rich tile drainage through the soil of a vegetated buffer zone via a perforated distribution pipe, facilitating denitrification and plant uptake. Because this practice is relatively new, there has been limited research into how SRBs function and how to effectively design them. In the first study, an equation for the optimal SRB width was derived by applying a mass balance to maximize the nitrate removal effectiveness. The optimal width is smaller than the current width at each of the six study sites, and two sites have optimal widths that are smaller than the minimum width specified in the current NRCS design standards. In the second study, a three-dimensional, finite-difference groundwater flow model was developed to better understand how groundwater flows in SRBs. Because flow is one-dimensional in most of the SRB, assuming one-dimensional groundwater flow in an SRB is reasonable. The median error associated with computing the travel time using a one-dimensional approximation is 11.6%. The flow path of the tile drainage toward the stream depends on where it exits the distribution pipe; the flow that exits through the top perforations at the end of the distribution pipe has the greatest potential for nitrate removal. Better understanding how groundwater flows in an SRB is an important step toward improving design to more effectively improve water quality.</p

Improving the Effectiveness of Saturated Riparian Buffers for Removing Nitrate from Subsurface Drainage

A saturated riparian buffer (SRB) is an edge‐of‐field conservation practice that reduces nitrate export from agricultural lands by redistributing tile drainage as shallow groundwater and allowing for denitrification and plant uptake. We propose an approach to improve the design of SRBs by analyzing a tradeoff in choosing the SRB width, and we apply the approach to six sites with SRBs in central Iowa. A larger width allows for more residence time, which increases the opportunity for removing nitrate that enters the buffer. However, because the SRBs considered here treat only a portion of the tile flow when it is large, for the same difference in hydraulic head, a smaller width allows more of the total tile flow to enter the buffer and therefore treats more of the drainage. By maximizing the effectiveness of nitrate removal—defined as the ratio of total nitrate removed by the SRB to total nitrate leaving the field in tile drainage, an equation for the optimal width was derived in terms of soil properties, denitrification rates, and head difference. All six sites with existing SRBs considered here have optimal widths smaller than the current width, and two are below the minimum width listed in current design standards. In terms of uncertainty, the main challenges in computing the optimal width for a site are estimating the removal coefficient for nitrate and determining the saturated hydraulic conductivity. Nevertheless, including a width that accounts for site conditions in the design standards would improve water quality, locally and regionally.This is the peer reviewed version of the following article: McEachran, AR, Dickey, LC, Rehmann, CR, et al. Improving the effectiveness of saturated riparian buffers for removing nitrate from subsurface drainage. J. Environ. Qual. 2020; 49: 1624–1632, which has been published in final form at doi: 10.1002/jeq2.20160. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Use of Self-Archived Versions.</p

Groundwater flow in saturated riparian buffers and implications for nitrate removal

A saturated riparian buffer (SRB) is an edge-of-field conservation practice that intercepts tile drainage and reduces nitrate flux to nearby streams by redistributing the flow as shallow groundwater. In this study, a three-dimensional, finite-difference groundwater model representative of SRBs in central Iowa was developed to assess the flow of groundwater and implications for nitrate removal during spring conditions, when flow to the SRB is highest. The model reproduces field observations of water level with Nash–Sutcliffe efficiency of 0.68, which is deemed acceptable for hydrologic models. The modeling shows that groundwater flow is three-dimensional near the distribution pipe and the stream and primarily one-dimensional in the rest of the buffer. The path the water takes in flowing toward the stream depends on where it exits the distribution pipe. When nitrate is not limiting, the potential for nitrate removal depends on the length of the path—and thus travel time—and depth because denitrification potential varies with depth. Travel time Tt can be estimated well with slight modifications to a one-dimensional approximation: Tt = 1.11Lx/vx, where Lx is the buffer width and vx is a one-dimensional approximation of the average linear velocity of groundwater. Refining knowledge of SRB function is an important step toward enhancing design for improving water quality.This article is published as McEachran, Andrea R., Loulou C. Dickey, Chris R. Rehmann, Thomas M. Isenhart, Tyler A. Groh, Michael A. Perez, and Cassandra J. Rutherford. "Groundwater flow in saturated riparian buffers and implications for nitrate removal." Journal of Environmental Quality 52, no. 1 (2023): 64-73. DOI: 10.1002/jeq2.20428. Copyright 2022 The Authors. Attribution-NonCommercial-NoDerivatives 4.0 International (CC BY-NC-ND 4.0). Posted with permission

Improving the Effectiveness of Saturated Riparian Buffers for Removing Nitrate from Subsurface Drainage

A saturated riparian buffer (SRB) is an edge‐of‐field conservation practice that reduces nitrate export from agricultural lands by redistributing tile drainage as shallow groundwater and allowing for denitrification and plant uptake. We propose an approach to improve the design of SRBs by analyzing a tradeoff in choosing the SRB width, and we apply the approach to six sites with SRBs in central Iowa. A larger width allows for more residence time, which increases the opportunity for removing nitrate that enters the buffer. However, because the SRBs considered here treat only a portion of the tile flow when it is large, for the same difference in hydraulic head, a smaller width allows more of the total tile flow to enter the buffer and therefore treats more of the drainage. By maximizing the effectiveness of nitrate removal—defined as the ratio of total nitrate removed by the SRB to total nitrate leaving the field in tile drainage, an equation for the optimal width was derived in terms of soil properties, denitrification rates, and head difference. All six sites with existing SRBs considered here have optimal widths smaller than the current width, and two are below the minimum width listed in current design standards. In terms of uncertainty, the main challenges in computing the optimal width for a site are estimating the removal coefficient for nitrate and determining the saturated hydraulic conductivity. Nevertheless, including a width that accounts for site conditions in the design standards would improve water quality, locally and regionally

Slope stability of streambanks at saturated riparian buffer sites

Saturated riparian buffers (SRBs) reduce nitrate export from agricultural tile drainage by infusing drainage water into carbon-rich riparian soils where denitrification and plant uptake occur. The water quality benefits from SRBs are well documented, but uncertainties about their effect on streambank stability have led to design standards that limit the maximum bank height and minimum buffer width, thus reducing the number of suitable candidate sites. In this study, the relationship between SRB design and streambank stability was examined through numerical slope stability modeling and validated using field sites. At the study sites, the addition of SRB flow increased the probability of failure by less than 3% for both simulated dry and rainfall scenarios. Furthermore, the simulations provide no evidence to support excluding potential sites based on bank height alone. Multivariate analysis of dimensionless parameters developed for SRB flow conditions was used to predict the factor of safety as a function of the SRB site and design conditions. The equation presented allows designers to assess the stability of a potential site where bank failure poses a heightened risk. The results of this study alleviate the need for extensive geotechnical evaluations at future SRB sites and could increase SRB implementation by expanding the range of eligible sites.This artice is published as Dickey, L. C., McEachran, A. R., Rutherford, C. J., Rehmann, C. R., Perez, M. A., Groh, T. A., & Isenhart, T. M. (2021). Slope stability of streambanks at saturated riparian buffer sites. J Environ Qual. 50:1430–1439. doi:10.1002/jeq2.20281. Posted with permission. This is an open access article under the terms of the Creative Commons Attribution-NonCommercial-NoDerivs License, which permits use and distribution in any medium, provided the original work is properly cited, the use is non-commercial and no modifications or adaptations are made