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- were subjected to external peer-review and accessible through library services;
- were published after January 1, 2016;
- were authored or co-authored by individuals employed with one of the seven principal CRC member institutions or with other major Chesapeake Bay Program partners; and
- have direct relevance to the science and/or management of the Chesapeake Bay or its watershed.
Further details about the the submission process can be found here. Further details about the purpose and "value added" of the RCCP collection (relative to other on-line databases) can be found here.
Comparing reach scale hyporheic exchange and denitrification induced by instream restoration structures and natural streambed morphology
A common water quality issue is an excess of nutrients which can lead to problems such as eutrophication. Stream restoration is one method by which improvements in water quality may be attempted. One strategy is increasing hyporheic zone flow at baseflow by addition of instream structures. The hyporheic zone can be an area of increased biogeochemical activity, with potential enhancement of reactions such as denitrification. However, the comparative effects of various instream restoration techniques, as well as the role of watershed setting and corresponding environmental characteristics in which restoration occurs (e.g., hydraulic conductivity, stream slope), are still poorly understood. In this study we numerically modeled groundwater and surface water interaction in a 200 m second order stream reach in southwestern Virginia using MIKE SHE. We calibrated the model to hydrologic and tracer data available during field tests of restoration techniques. We then simulated different types of instream restoration techniques (e.g., fully and partially channel-spanning weirs and buried structures), and varied hydrologic and biogeochemical controlling factors driven by watershed setting. The measured effects for this sensitivity analysis were direction and magnitude of surface water-groundwater exchange and amount of denitrification. We found that factors related to watershed setting had the greatest effect on surface water-groundwater exchange and on denitrification, including streambed hydraulic conductivity, natural or background stream topography and slope, and groundwater levels. Type and number of instream structures also influenced surface water-groundwater exchange and denitrification, but to a lesser degree, and the effect of structures was in turn controlled by watershed setting. Watershed setting was thus the largest control, both on exchange overall, and the effectiveness of structures. Human effects on watersheds such as agriculture and urbanization therefore likely play a role in whether reach-scale restoration practices succeed in achieving water quality goals. More broadly, restoration efforts at the watershed scale itself, such as reducing fertilizer use or improving stormwater management, may be necessary to achieve ambitious water quality goals. Nevertheless, reach-scale restoration efforts such as in-stream structures may play a useful role in certain watershed settings. Furthermore, other reach-scale restoration techniques that affect streambed topography, such as addition of pool-riffle sequences, may be more effective, and bear investigation.
Get PDFEffectiveness of a bubble-plume mixing system for managing phytoplankton in lakes and reservoirs
Bubble-plume mixing systems are often deployed in eutrophic lakes and reservoirs to manage phytoplankton taxa. Unfortunately, inconsistent outcomes from bubble-plume (induced) mixing are often reported in the literature. The present study investigates the response of phytoplankton to induced mixing using a whole-reservoir field experiment and a three-dimensional hydrodynamic model (Si3D) coupled with the Aquatic EcoDynamics (AED) model through the framework for aquatic biogeochemical modelling (FABM). The coupled Si3D-AED model is validated against a 24-h field mixing experiment and subsequently used for a numerical parametric study to investigate phytoplankton responses to various induced mixing scenarios in which the phytoplankton settling rate, phytoplankton growth rate, reservoir depth, and mixing system diffuser depth were sequentially varied. Field observations during the mixing experiment suggest that the total phytoplankton concentration (measured in across the reservoir was reduced by nearly 10% during the 24-h mixing period. The numerical modeling results show that phytoplankton concentration may be substantially affected by the functional traits of the phytoplankton and the deployment depth of the mixing diffuser. Interestingly, the numerical results indicate that the phytoplankton concentration is controlled by reduced growth rates due to light limitation in deep reservoirs (>20 m), whereas settling loss is a more important factor in shallow reservoirs during the mixing period. In addition, the coupled Si3D-AED model results suggest that deploying the mixing diffuser deeper in the water column to increase mixing depth may generally improve the successful management of cyanobacteria using bubble-plume mixing systems. Thus, the coupled Si3D-AED model introduced in the present study can assist with the design and operation of bubble-plume mixing systems.
Get PDFThree-dimensional effects of epilimnetic mixing in a shallow drinking-water reservoir
Studies that examine the effects of artificial mixing for water-quality mitigation in lakes and reservoirs often view a water column with a one-dimensional (1-D) perspective (e.g., homogenized epilimnetic and hypolimnetic layers). Artificial mixing in natural water bodies, however, is inherently three dimensional (3-D). Using a 3-D approach experimentally and numerically, the present study visualizes thermal structure and analyzes constituent transport under the influence of artificial mixing in a shallow drinking-water reservoir. The purpose is to improve the understanding of artificial mixing, which may help to better design and operate mixing systems. In this reservoir, a side-stream supersaturation (SSS) hypolimnetic oxygenation system and an epilimnetic bubble-plume mixing (EM) system were concurrently deployed in the deep region. The present study found that, while the mixing induced by the SSS system does not have a distinct 3-D effect on the thermal structure, epilimnetic mixing by the EM system causes 3-D heterogeneity. In the experiments, epilimnetic mixing deepened the lower metalimnetic boundary near the diffuser by about 1 m, with 55% reduction of the deepening rate at 120 m upstream of the diffuser. In a tracer study using a 3-D hydrodynamic model, the operational flow rate of the EM system is found to be an important short-term driver of constituent transport in the reservoir, whereas the duration of the EM system operation is the dominant long-term driver. The results suggest that artificial mixing substantially alters both 3-D thermal structure and constituent transport, and thus needs to be taken into account for reservoir management.
Get PDFWhere Did the Agricultural Nonpoint Source Trades Go? Lessons from Virginia Water Quality Trading Programs
Stephenson, Kurt and Leonard Shabman, 2017. Where Did the Agricultural Nonpoint Source Trades Go? Lessons from Virginia Water Quality Trading Programs. Journal of the American Water Resources Association (JAWRA) 53(5):1178–1194. https://doi.org/10.1111/1752-1688.12565
Get PDFEffects of Dairy Slurry Injection on Carbon and Nitrogen Cycling
Bierer, Andrew M., R.,O. Maguire, M.S. Strickland, W.E. Thomason, R.D. Stewart, 2017. Effects of Dairy Slurry Injection on Carbon and Nitrogen Cycling, Soil Science, Vol 182 - Issue 5 - p 181–187. doi: 10.1097/SS.0000000000000209.
Get PDFVerification of phosphorus site assessment tools: Lessons from the U.S.
Sharpley, A., P. Kleinman, C. Baffuat, Z.M. Easton, J. Lory, D. Osmond, and T. Veith. 2017. Verification of phosphorus site assessment tools: Lessons from the U.S. J. Environ. Qual. doi:10.2134/jeq2016.11.0427
Get PDFNutrient Assimilation Services for Water Quality Credit Trading Programs: A Comparative Analysis with Nonpoint Source Credits
Stephenson, K. and L. Shabman. 2017. “Nutrient Assimilation Services for Water Quality Credit Trading Programs: A Comparative Analysis with Nonpoint Source Credits,” Coastal Management. 45(1): 24-43. doi: 10.1080/08920753.2017.1237240
Get PDFDoes it pay to be mature? Assessing the performance of a bioretention cell seven years post-construction.
Willard, L., T. Wynn-Thompson, L.H. Krometis, T. Neher, and B. Badgley. 2017. Does it pay to be mature? Assessing the performance of a bioretention cell seven years post-construction. Journal of Environmental Engineering. 143(9). doi: 10.1061/%28ASCE%29EE.1943-7870.0001232
Get PDFSulfurization of Dissolved Organic Matter Increases Hg-Sulfide-Dissolved Organic Matter Bioavailability to a Hg-Methylating Bacterium
Reactions of dissolved organic matter (DOM) with aqueous sulfide (termed sulfurization) in anoxic environments can substantially increase DOM’s reduced sulfur functional group content. Sulfurization may affect DOM–trace metal interactions, including complexation and metal-containing particle precipitation, aggregation, and dissolution. Using a diverse suite of DOM samples, we found that susceptibility to additional sulfur incorporation via reaction with aqueous sulfide increased with increasing DOM aromatic-, carbonyl-, and carboxyl-C content. The role of DOM sulfurization in enhancing Hg bioavailability for microbial methylation was evaluated under conditions typical of Hg methylation environments (μM sulfide concentrations and low Hg-to-DOM molar ratios). Under the conditions of predicted metacinnabar supersaturation, microbial Hg methylation increased with increasing DOM sulfurization, likely reflecting either effective inhibition of metacinnabar growth and aggregation or the formation of Hg(II)–DOM thiol complexes with high bioavailability. Remarkably, Hg methylation efficiencies with the most sulfurized DOM samples were similar (>85% of total Hg methylated) to that observed in the presence of l-cysteine, a ligand facilitating rapid Hg(II) biouptake and methylation. This suggests that complexes of Hg(II) with DOM thiols have similar bioavailability to Hg(II) complexes with low-molecular-weight thiols. Overall, our results are a demonstration of the importance of DOM sulfurization to trace metal and metalloid (especially mercury) fate in the environment. DOM sulfurization likely represents another link between anthropogenic sulfate enrichment and MeHg production in the environment.
Get PDFSpatial and Temporal Variation in Brackish Wetland Seedbanks: Implications for Wetland Restoration Following Phragmites Control.
Chesapeake Bay tidal wetlands are experiencing a broad-scale, aggressive invasion by the non-native, clonal grass Phragmites australis. The grass is often managed with herbicides in efforts to restore native plant communities and wildlife habitat. Management efforts, however, can act as a disturbance, resulting in increased light availability, potentially fostering reinvasion from soil seedbanks. If native vegetation establishes quickly from seedbanks, the site should have greater resiliency against invasion, while disturbed sites where native plants do not rapidly establish may be rapidly colonized by P. australis. We surveyed the soil seedbank of three vegetation cover types in five Chesapeake Bay subestuaries: areas where P. australis had been removed, where P. australis was left intact, and with native, reference vegetation. We determined the total germination, the proportion of the seedbank that was attributable to invasive species, the richness, the functional diversity, and the overall composition of the seedbanks in each of the cover types (i.e., plots). After 2 years of herbicide treatment in the P. australis removal plots, vegetation cover type impacted the total germination or the proportion of invasive species in the seedbank. In contrast, we also found that seedbank functional composition in tidal brackish wetlands was not influenced by vegetation cover type in most cases. Instead, plots within a subestuary had similar seedbank functional composition across the years and were composed of diverse functional groups. Based on these findings, we conclude that plant community recovery following P. australis removal is not seed-limited, and any lack of native vegetation recruitment is likely the result of yet-to-be-determined abiotic factors. These diverse seedbanks could lead to resilient wetland communities that could resist invasions. However, due to the prevalence of undesirable species in the seedbank, passive revegetation following invasive plant removal may speed up their re-establishment. The need for active revegetation will need to be assessed on a case-by-case basis to ensure restoration goals are achieved.
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