The S191 basin contributes significant phosphorous (P) loads to Lake Okeechobee, Florida (the Lake). This basin is located northeast of the Lake, and extensive nonstructural and structural Best Management Practices (BMPs) have been implemented to reduce total P (TP) loads. The Davie Dairy Best Available Technologies (Davie Dairy BAT) and The Taylor Creek Stormwater Treatment Area (Taylor Creek STA) are two of the structural BMP projects. The Taylor Creek STA reduces P loads to the Lake through detention, plant growth and soil sorption. The Davie Dairy BAT project reduces the P loads to the Lake through detention and chemical treatment. The objective of this study was to develop a model tool to simulate the structural BMP projects' daily flow rate and long term treatment volume under different weather scenarios. The MIKE SHE/MIKE 11 coupled model was selected for this study because of its capability to simulate the dynamic exchanges between the overland flow plain, groundwater system, and the river system. This study developed, calibrated and validated a MIKE SHE/MIKE 11 coupled model for this basin. The simulated daily flow rates at structure S191 compared favorably with measured values for a calibration and validation time period. Simulated groundwater levels for calibration were reasonably consistent with the measured groundwater levels. The calibrated and validated model was applied for long term simulation to evaluate the two structural BMP projects' long term treatment performance, annual average TP load reduction, using the observed hydrology and the water quality data.
Core Ideas Matrix flow and macropore flow interact in Vertisols via lateral infiltration. Maximum water infiltration depths are greater in Vertisols with hog manure. Manure does not affect the mobilization of old soil water via macropore flow. Preferential flow has different agronomic and environmental effects in various soils. The objectives of this study were (i) to quantify matrix and preferential flow and (ii) to assess the effect of organic amendments on flow dynamics in agricultural Vertisols. Dye tracing and isotopic analysis were used to infer soil water infiltration and mixing on two plots: one treatment (with liquid hog manure) and one control. Results showed infiltration depths reaching 64 cm for the treatment plot and 45 cm for the control. For both plots, matrix flow was only observed in the top 10 cm, whereas preferential flow extended beyond the tillage depth. Dye traces provided evidence of lateral infiltration across macropore–matrix boundaries, while post‐experiment soil water averaged δ2H = −15.1‰ and δ18O = −118.9‰, hinting at old water mobilization via macropore flow. The potential impacts of these results on chemical transport should be validated across different soils and environmental conditions.
Core Ideas Contrary to established theories, vadose water contributes considerably to Canadian Prairie stormflow. Travel velocities of subsurface flow may exceed surface flow in some cases. Traqnsmissivity feedback and macropore flow promote “old” water deliveryto Prairie streams. Hydrologic literature on the Northern Great Plains, including the Canadian Prairies, has mainly focused on Hortonian overland flow as the dominant runoff generation mechanism. This study focused on subsurface water movement and its contribution to streamflow in high‐latitude, subhumid, prairie landscapes with flat topography. Three “riparian‐to‐stream” sites were monitored in southeastern Manitoba, Canada, and four hydrologic events (snowmelt triggered and rainfall triggered) were selected for analysis. A dual water sourcing strategy, including conservative and non‐conservative tracers, was applied to distinguish the relative importance of event (“new”) and pre‐event (“old”) runoff sources. Surrogate measures of antecedent wetness conditions (AWCs: based on rainfall, snow water equivalent, and soil saturation) data and streamflow and water table fluctuation data were used to identify factors influencing the contributions of different runoff sources. Results showed significant old water contributions during snowmelt‐ and rainfall‐triggered events, especially during the summer season. At an engineered grassland site, decreases in snow cover extent were accompanied by “flashy,” high‐magnitude stream hydrographs. Larger peak discharge was observed coincident to elevated AWCs at all sites. Travel velocities of surface‐applied dye were faster than those of subsurface‐applied dye, except for one rainfall‐triggered event. Rapid delivery of old water to streams was observed and hypothesized to be the result of macropore flow, piston flow, or transmissivity feedback depending on the season and water table position. Further investigations are recommended to increase our understanding of subsurface runoff generation mechanisms that promote the rapid movement of old water from riparian areas to streams in Canadian Prairie landscapes.
The search for life on other planets is an active area of research. Many of the likeliest planetary bodies, such as Europa, Enceladus, and Mars are characterized by cold surface environments and ice-rich terrains. Both Raman and ultraviolet-induced fluorescence (UIF) spectroscopies have been proposed as promising tools for the detection of various kinds of bioindicators in these environments. We examined whether macro-scale Raman and UIF spectroscopy could be applied to the analysis of unprocessed terrestrial frozen peat and clear ground ice samples for detection of bioindicators. It was found that this approach did not provide unambiguous detection of bioindicators, likely for a number of reasons, particularly due to strong broadband induced fluorescence. Other contributing factors may include degradation of organic matter in frozen peat to the point that compound-specific emitted fluorescence or Raman peaks were not resolvable. Our study does not downgrade the utility of either UIF or Raman spectroscopy for astrobiological investigations (which has been demonstrated in previous studies), but does suggest that the choice of instrumentation, operational conditions and sample preparation are important factors in ensuring the success of these techniques.
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