Environmental Science & Technology
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Item Evidence of Phosphate Mining and Agriculture Influence on Concentrations, Forms, and Ratios of Nitrogen and Phosphorus in a Florida River(MDPI, 2021-04-13) Duan, Shuiwang; Banger, Kamaljit; Toor, Gurpal S.Florida has a long history of phosphate-mining, but less is known about how mining affects nutrient exports to coastal waters. Here, we investigated the transport of inorganic and organic forms of nitrogen (N) and phosphorus (P) over 23 sampling events during a wet season (June–September) in primary tributaries and mainstem of Alafia River that drains into the Tampa Bay Estuary. Results showed that a tributary draining the largest phosphate-mining area (South Prong) had less flashy peaks, and nutrients were more evenly exported relative to an adjacent tributary (North Prong), highlighting the effectiveness of the mining reclamation on stream hydrology. Tributaries draining > 10% phosphate-mining area had significantly higher specific conductance (SC), pH, dissolved reactive P (DRP), and total P (TP) than tributaries without phosphate-mining. Further, mean SC, pH, and particulate reactive P were positively correlated with the percent phosphate-mining area. As phosphate-mining occurred in the upper part of the watershed, the SC, pH, DRP, and TP concentrations increased downstream along the mainstem. For example, the upper watershed contributed 91% of TP compared to 59% water discharge to the Alafia River. In contrast to P, the highest concentrations of total N (TN), especially nitrate + nitrite (NOx–N) occurred in agricultural tributaries, where the mean NOx–N was positively correlated with the percent agricultural land. Dissolved organic N was dominant in all streamwaters and showed minor variability across sites. As a result of N depletion and P enrichment, the phosphate-mining tributaries had significantly lower molar ratios of TN:TP and NOx–N:DRP than other tributaries. Bi-weekly monitoring data showed consistent increases in SC and DRP and a decrease in NOx–N at the South Prong tributary (highest phosphate-mining area) throughout the wet season, and different responses of dissolved inorganic nutrients (negative) and particulate nutrients (positive) to water discharge. We conclude that (1) watersheds with active and reclaimed phosphate-mining and agriculture lands are important sources of streamwater P and N, respectively, and (2) elevated P inputs from the phosphate-mining areas altered the N:P ratios in streamwaters of the Alafia River.Item Effects of On-Farm Dairy Manure Composting on Tetracycline Content and Nutrient Composition(MDPI, 2021-04-15) Schueler, Jenna; Naas, Kayla; Hurst, Jerod; Aga, Diana; Lansing, StephanieThis study quantified the potential of farm-scale composting to degrade antibiotics in dairy manure. The compost windrow, consisting of sick cow bedding from a 1000-cow US dairy farm, was managed using the dairy farm’s typical practices and monitored for tetracycline and nutrient composition. Samples were collected over 33 days, which was the time from compost pile formation to land application as fertilizer, and analyzed for solids, antibiotics, and nutrient content. Average tetracycline concentrations at the beginning of the study (452 ng/g DW) were lower than at the end of composting (689 ng/g DW), illustrating that antibiotic degradation was not greater than degradation of the compost solids. Total Kjeldahl nitrogen (TKN) increased from 15.3 to 18.4 g/kg during the composting period due to decreases in solids and likely inhibition of N-mineralization due to the presence of antibiotics. The results indicated that antibiotics were not completely degraded when using the farm’s compost pile management techniques, with antibiotics possibly impacting nitrogen transformation in the compost, which should be considered in nutrient management when using sick cow bedding. Additionally, the results showed that antibiotic degradation during farm-scale composting can vary from reported laboratory-scale due to differences in management, composting duration, and temporal conditions, illustrating the need for more extensive on-farm research including common farm practices and real-world conditions.Item Evaluating Soil Phosphorus Dynamics over Time(2017) Lucas, Emileigh Rosso; Coale, Frank J; Environmental Science and Technology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Agricultural nutrient management became mandatory in Maryland (MD) due to water quality concerns. Phosphorus (P) management is complex due to the stability of P in the soil, nutrient mass imbalance, and “legacy” P. To explore how potential P application bans impact historically manured fields, agronomic and environmental soil tests were conducted on plots treated with five manure-P rates, then no P applications, spanning 15 years. Mehlich-3 extractable P (M3P) declined slowly and then generally did not change during the last six years. Phosphorus saturation declined slowly or not significantly. Excessive P soils had sufficient P for crop growth in solution. Phosphorus saturation and M3P were compared in fifty sites across MD pre- and post- nutrient management planning. Results showed an increase in P concentration of Maryland agricultural fields. This response was logical, as better management would increase below-optimum P concentrations, and the regulations were not designed to draw down P.Item Evaluation of accuracy and sensitivity of the University of Maryland Phosphorus Management Tool and investigation of subsurface phosphorus dynamics in the Maryland Coastal Plains region(2015) Fiorellino, Nicole; McGrath, Joshua M; Environmental Science and Technology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Phosphorus (P) loss from agricultural fields to surface water represents a major environmental challenge in agricultural nutrient management. To reduce P loading, areas where both P source and transport conditions are present must be identified and appropriate management practices implemented to reduce the source or break transport connectivity. The Maryland P Site Index (MD-PSI) was modified from a multiplicative structure to a component structure and renamed University of Maryland Phosphorus Management Tool (UM-PMT). In the UM-PMT, each component is the product of source, transport, and management factors specific to a P loss pathway. Our objectives were to evaluate the UM-PMT for accuracy, investigate soil conditions in ditch-drained agricultural systems, compare different methods for degree of P saturation (DPS) calculation, and compare numerical and categorical final scores of the multiple versions of the Maryland P loss risk indices. Agronomic soil samples were collected from fields across Maryland, and analyzed for P, aluminum (Al), and iron (Fe) concentration using multiple extractions, soil texture was determined, and degree of P saturation (DPS) was calculated using five methods. Deep soil samples were collected and analyzed similarly from three sites on Maryland's eastern shore. A poor relationship was identified between UM-PMT and modeled P loss data (R2=0.09), but the relationship improved with modifications to UM-PMT calculation (R2=0.97), which resulted in UM-PMT Version 2 (UM-PMT v.2). Soil Fe concentration was responsible for a large proportion of DPS at one sample location on the Eastern Shore, demonstrated through poor correlation between two methods for DPS calculation, including and excluding Fe concentration. Numerical differences existed between different methods for DPS calculation and these translated to differences in UM-PMT final score, particularly in the Lower Shore region. The UM-PMT v.2 categorized more fields as HIGH risk than MD-PSI but less than UM-PMT. Neither version of the UM-PMT was very sensitive to management factor input variables. Evaluation of tools like the UM-PMT for accuracy, sensitivity, and magnitude of change is necessary to understand potential economic and environmental impacts of implementing new indices as nutrient management tools.