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Bioretention practices have become a common way to protect natural waterways in urban and suburban landscapes across the United States. However, optimal design, implementation, operation, and maintenance are still in need of study. A field survey of 52 bioretention practices was conducted in Davidson County, Tennessee, to address research questions related to operation and maintenance. A suite of site conditions were documented, such as size, signs of erosion, and dominant surface cover. Samples were collected from the surface of the engineered media layer and analyzed for organic matter content and bulk density. Vegetation was described in terms of dominant species and canopy cover. On average, the organic matter content of media under plant-based mulch cover was significantly greater than that under rock cover (p = 0.002). Bulk density of the surface media is strongly and inversely correlated to organic matter content; bulk density did not generally vary with bioretention area age and was highly variable within treatments. On average, the bulk density of the media under the plant-based mulch cover was significantly less than that under the rock cover. Media under the composite treatments had similar bulk density to both the plant-based mulch (p = 0.233) and the rock covers (p = 0.132). Plant canopy did not surpass 70% in practices with bulk density values above 1.55 g/cm3. These results suggest that consideration should be made regarding the tradeoffs between utilizing rock coverings and potential for plant establishment impacts.
Elevated concentrations of phosphorus (P) and other nutrients common in wastewater treatment plant (WWTP) effluent have been shown to contribute to the proliferation of harmful algal blooms, which may lead to fish kills related to aquatic hypoxia. Increased understanding of the negative effects associated with elevated P concentrations have prompted more strict regulation of WWTP effluent in recent years. The use of low-cost and potentially regenerative adsorptive phosphate filters has the potential to decrease P concentrations in WWTP effluent released to natural waters. This research focuses on assessing the capacities of recycled concrete aggregate (RCA), expanded slate, and expanded clay to remove phosphate from P-amended WWTP effluent. Results from a flow-through column study indicate that RCA consistently removed an average of 97% of phosphate over 20 weeks of continuous flow at an 8-hour hydraulic retention time (HRT). Expanded clay removed an average of 63% of introduced phosphate but decreased in removal capacity from 91 to 42% over the 20-week duration. Sorption data from batch studies were fitted to Langmuir models and RCA was shown to have the highest maximum sorption capacity (6.16 mg P/g), followed by expanded clay (3.65 mg P/g). RCA and expanded clay are promising options for use in passive filters for further reduction of phosphate from WWTP effluent.
Since 1901, heavy rainfall events have increased in the United States in both intensity and frequency, and human population in the United States has increased, resulting in significant land use changes. Both trends contribute to an increase in observed flood magnitude and frequency. To determine if a relationship exists between land use/land cover and changing stream flows in northwest Arkansas, this study analyzed temporal changes in various flow statistics for 14 stream gages and compared the rates of change in flow statistics from gages on streams with watersheds that have varying land uses, i.e., urban, agricultural, and undeveloped. Mann-Kendall analysis was used to determine statistically significant changes in flow statistics, which were then compared to National Land Cover Dataset (NLCD) watershed land uses from 2001 and 2019. All analyzed gages had one or more flow statistics with at least a moderately significant increase, and all analyzed flow statistics showed at least moderately significant streamflow increases at two or more gages (P < 0.100). There were no decreases of any significance in any flow statistic at any gage. In general, urban land development did not happen on native prairies and forests but on previously agricultural land. Significant positive relationships were found between maximum yearly flow and 2019 urban land use, urban land use change from 2001 to 2019, and 2019 Human Development Index (HDI). A similar relationship was found to exist between yearly minimum flow and 2019 HDI. These results highlight the importance of considering the cost of potential stream bank erosion and flooding in future land use planning, permitting, and zoning.
Undergraduate hands-on research can foster innovation and critical thinking among young scholars to delve into real-world challenges. Specifically, exploring the critical nexus between water usage and agricultural yield, can foster academic growth and holds the key to addressing global food security in an era of increasing environmental constraints, where students can unlock insights crucial to enhancing crop yield and sustainability. Investigating the intricate relationship between water management and crop productivity through undergraduate research is exemplified in this article. Undergraduate students acquired hands-on research experience by collecting, processing, and analyzing destructive (crop biomass samples) and non-destructive (plant height, nodes, and leaf chlorophyll content) cropping system data on soybeans under irrigated and dryland production systems, where they worked closely with the farmer. Identifying the current research problem and study site selection, scientific decision-making during the field study, developing critical thinking while ensuring research communication skills, and quality assurance and quality control through technology during data collection and analysis were learning outcomes. The research highlights the observed distinct performance between irrigated and non-irrigated soybeans using non-destructive plant health and growth indicators with plant biomass, following appropriate quality control and assurance steps. Statistically, irrigated soybeans outperformed non-irrigated soybeans in terms of average plant height at maturity (irrigated: 97.0±1.7 cm vs. non-irrigated: 37.4±0.6 cm; p<0.01) and number of nodes on the mainstem (irrigated: 19.5±1.2 vs. non-irrigated: 12.6±0.8; p<0.01). Findings from this study can help ensure quality control and assurance in future cropping system projects. Through the agroecosystem study, we exhibit the importance and role of undergraduate research opportunities in developing the next generation of problem solvers.
Urban water managers and policymakers have adopted demand management strategies to reduce water use and buffer against short-term water supply shortfalls. This article provides a systematic review of publications from 1978-2022 that examine the effectiveness of residential water use restrictions as the primary demand-side management tool. Our results indicate the significant overall effect of restrictions on reducing water consumption, with an average reduction of 12.3% from the 23 studies reviewed in this article. When evaluating effect strength by restriction type (mandatory versus voluntary), voluntary restrictions have a significantly lower effect than mandatory restrictions on water use. We also find an inverse correlation between the number of irrigation days allowed and the estimated effect strength.
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