Theses and Dissertations at Montana State University (MSU)
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Item Water quality response to water and nitrogen movement through a semi-arid dryland agroecosystem in Montana, USA(Montana State University - Bozeman, College of Agriculture, 2020) Sigler, William Adam; Chairperson, Graduate Committee: Stephanie A. Ewing; Stephanie A. Ewing, Clain A. Jones, Robert A. Payn, E.N. Jack Brookshire, Jane K. Klassen, Douglas Jackson-Smith and Gary S. Weissmann were co-authors of the article, 'Connections among soil, ground, and surface water chemistries characterize nitrogen loss from an agricultural landscape in the upper Missouri River Basin' in the journal 'Journal of hydrology' which is contained within this dissertation.; Stephanie A. Ewing, Clain A. Jones, Robert A. Payn, Perry Miller and Marco Maneta were co-authors of the article, 'Water and nitrate loss from dryland agricultural soils is controlled by management, soils, and weather' submitted to the journal 'Agricultural ecosystems & environment' which is contained within this dissertation.; Stephanie A. Ewing, Scott D. Wankel, Clain A. Jones, Sam Leuthold, E.N. Jack Brookshire and Robert A. Payn were co-authors of the article, 'Drivers of denitrification across a semiarid agroecosystem revealed by nitrate isotopic patterns' which is contained within this dissertation.Humans have increased reactive nitrogen (N) on the planet by an order of magnitude over the past 150 years. Most of this reactive N is used for fertilizer to feed a growing population, but loss of N from cultivated soils threatens agricultural and environmental sustainability. Nitrate accumulated in soil from fertilization or decomposition of soil organic N (SON) may be lost via leaching, which can reduce soil fertility and compromise water quality. Nitrate concentrations commonly exceed human drinking standards in groundwater resources around the globe. In the Judith River Watershed (JRW) in central Montana, nitrate has been detected above the standard since the 1960s. This dissertation contributes to a more holistic understanding of the fate and transport of N in the JRW. An interdisciplinary team engaged with farmers in a participatory research project, making observations in soils, groundwater, and streams to characterize water and N movement. At the landform scale, 5 to 9 cm yr -1 of the 38 cm yr -1 mean annual precipitation moves through soil to recharge groundwater and leaches 11 to 18 kg ha -1 yr -1 of nitrate-N from soil. These leaching rates are approximately 20-30% of fertilizer rates but likely reflect inmixing of nitrate from SON decomposition. Soil modeling analyses suggested that water and N losses were dominated by intense precipitation periods on wetter soils, such that more than half of simulated deep percolation and leaching occurred in two of 14 model years. Simulations further suggest that thinner soils (<25 cm fine-textured materials) experience water and nitrate loss rates five to 16 times higher than thicker soils (>100 cm). Soil sampling demonstrated that increased soil water during fallow periods facilitates conversion of SON to nitrate. Soils are then primed for water and N loss with subsequent precipitation, resulting in disproportionately high leaching rates during and following fallow periods. Isotopic evidence from fallow periods further suggests that nitrate is lost to the atmosphere via denitrification, a gas phase loss combining with leaching losses to compromise the goal of delivering N to crops. These findings suggest that reduction of fallow increases N use efficiency and reduces nitrate loss to groundwater.Item Armored stanchion cattle water access effects on E. coli, suspended sediment, and nutrient loading to spring creeks(Montana State University - Bozeman, College of Agriculture, 2008) Sigler, William Adam; Chairperson, Graduate Committee: James W. Bauder; Clayton B. Marlow (co-chair)Livestock grazing activities contribute to impairment of 5,200 miles of Montana streams. Implementation of most water quality improvement efforts addressing this issue is voluntary. Thus, it is important to present land owners with simple, cost effective approaches to mitigate water quality impairment. An armored stanchion (AS) water access was designed, implemented, and tested on Thompson and Story Creeks near Belgrade, MT. Riparian fencing was constructed to allow access at a water gap where the AS was constructed. The AS allows animals to access spring creek water to drink but does not allow them to enter the stream. An AS was constructed adjacent to a traditional (TRAD) water access on each stream for comparison. Water quality impairment was quantified downstream of each access with and without animals actively using the accesses. Instantaneous loads of E. coli, suspended sediment concentration (SSC), total Kjeldahl nitrogen (TKN), nitrate (NO3), total phosphorus (TP), and orthophosphate (PO4) were evaluated using Kruskal Wallis procedures. Contaminant loading from the AS access was not significantly greater than loading from the control with or without animals present. The Story Site did not consistently produce significant differences for the TRAD access with animals present versus absent under the different analysis approaches employed. Results at the Thompson Site produced significant differences for E. coli, TKN, and TP for the TRAD access when animals were present versus absent from the access. Estimates were made of percentage of time cattle occupied the Thompson TRAD access. These estimates facilitated calculation of daily loads attributed to animals actively using the access. For E. coli the load was 6.0 E9 CFU per day, 425.9 g per day for TKN, and 53.1 g per day for TP. These results indicate the AS access can reduce water quality impacts from cattle, compared to traditional access methods.