Browsing by Subject "nutrient cycling"
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Item Agroecological approaches to warm-season cover cropping in northern climate vegetable systems and building collaborations with farmers(2020-07) Wauters, VivianSummer cover crops are a management tool that vegetable farmers can use to counteract the negative effects of soil degradation by physically protecting soil, contributing biomass to soil organic matter (SOM), suppressing weed growth, and enhancing nutrient cycling, but their use may be limited in the short growing season of northern climates. Evaluating the effects of cover crops on soil nutrient cycling and SOM in northern climates is an opportunity to collaborate with farmers, which is important because such collaboration improves the quality of knowledge gained from research by recognizing the incompleteness of any single perspective. Collaborative and participatory research is also a means to address the unequal power dynamics in agriculture that have systemically disadvantaged immigrant and minority farmers through interlocking challenges accessing capital, land, and information. In this dissertation, summer cover crops were evaluated in collaborative on-farm trials in northern climates for their ability to accumulate biomass, suppress weeds, affect soil C and N pools, and contribute to fall cash crop yield. Additionally, this dissertation includes a qualitative analysis of existing collaborative relationships between members of a local immigrant farmer cooperative and representatives from Extension, the Department of Agriculture, and a local agricultural non-profit. The summer cover crop trial consisted of four cover crop species treatments, grown for 30 (SD) or 50 days (LD) alongside bare fertilized and unfertilized control treatments: buckwheat (Fagopyrum esculentum) and sunn hemp (Crotalaria juncea) monocultures, and biculture of chickling vetch (Lathyrus sativus) or cowpea (Vigna unguiculata) with sorghum-sudangrass (sudax) (Sorghum bicolor x S. bicolor var. Sudanese). To quantify cover crop quantity, quality, and weed growth and seed set suppression capability, we measured cover crop and weed biomass and biomass C:N. To quantify effects on cash crops, we measured fall broccoli yield and biomass. Soil N and C cycling were quantified at cover crop peak growth (directly before termination) and one week after cover crop termination for mineral N, PMN, organic N, POX-C, extractable organic C, as well as fluorescein diacetate hydrolysis (FDA) as a proxy for microbial activity to contextualize the other measurements. Cover crops produced biomass consistent with that of more southern climates but legumes did not grow well and did not overcome weed pressure. All cover crops contribute to nutrient retention but not fertility benefits and negatively impacted fall cash crop yield. Collaborative relationships with farmers were dependent on external institutional support, and food systems professionals differed in whether they adopted an equity or equality lens.Item Biogeographic bases for a shift in crop C : N : P stoichiometries during domestication(Wiley, 2016) Delgado‐Baquerizo, Manuel; Reich, Peter B; García‐Palacios, Pablo; Milla, RubénWe lack both a theoretical framework and solid empirical data to understand domestication impacts on plant chemistry. We hypothesised that domestication increased leaf N and P to support high plant production rates, but biogeographic and climate patterns further influenced the magnitude and direction of changes in specific aspects of chemistry and stoichiometry. To test these hypotheses, we used a data set of leaf C, N and P from 21 herbaceous crops and their wild progenitors. Domestication increased leaf N and/or P for 57% of the crops. Moreover, the latitude of the domestication sites (negatively related to temperature) modulated the domestication effects on P (+), C (−), N : P (−) and C : P (−) ratios. Further results from a litter decomposition assay showed that domestication effects on litter chemistry affected the availability of soil N and P. Our findings draw attention to evolutionary effects of domestication legacies on plant and soil stoichiometry and related ecosystem services (e.g. plant yield and soil fertility).Item A brown-world cascade in the dung decomposer food web of an alpine meadow: effects of predator interactions and warming(2011) Wu, Xinwei; Duffy, J. Emmett; Reich, Peter B; Sun, ShucunTop-down control has been extensively documented in food webs based on living plants, where predator limitation of herbivores can cascade to facilitate plant growth (the green-world hypothesis), particularly in grasslands and aquatic systems. Yet the ecosystem role of predators in detrital food webs is less explored, as is the potential effect of climate warming on detritus-based communities. We here show that predators have a “brown-world” role in decomposer communities via a cascading top-down control on plant growth, based on the results of an experiment that factorially manipulated presence and size of two predator species as well as temperature (warmed vs. unwarmed). The inclusion of predatory beetles significantly decreased abundance of coprophagous beetles and thus the rate of dung decomposition and productivity of plants growing surrounding the dung. Moreover, the magnitude of these decreases differed between predator species and, for dung loss, was temperature dependent. At ambient temperature, the larger predators tended to more strongly influence the dung loss rate than did the smaller predators; when both predators were present, the dung loss rate was higher relative to the treatments with the smaller predators but comparable to those with the larger ones, suggesting an antagonistic effect of predator interaction. However, warming substantially reduced dung decomposition rates and eliminated the effects of predation on dung decomposition. Although warming substantially decreased dung loss rates, warming only modestly reduced primary productivity. Consistent with these results, a second experiment exploring the influence of the two predator species and warming on dung loss over time revealed that predatory beetles significantly decreased the abundance of coprophagous beetles, which was positively correlated with dung loss rates. Moreover, experimental warming decreased the water content of dung and hence the survival of coprophagous beetles. These results confirm that the “brown-world” effect of predator beetles was due to cascading top-down control through coprophagous beetles to nutrient cycling and primary productivity. Our results also highlight potentially counterintuitive effects of climate warming. For example, global warming might significantly decrease animal-mediated decomposition of organic matter and recycling of nutrients in a future warmed world.Item Exploring The Impact Of Stream Restoration On Ecosystem Function Through Changes In Nutrient Spiraling(2023) Baldus, DavidMillions of dollars have been spent on stream restoration and habitat improvement projects in the Lake Superior watershed. The impact of these projects on ecological function of a stream reach are not well measured or understood. This knowledge gap is echoed within restoration work worldwide. Here we provide a test case of one method for closing this knowledge gap. We use physical habitat characteristics to explain the differences seen in stream function between a restored treatment reach and an unrestored control reach on Sargent Creek (Duluth, MN) using ammonia/ammonium nutrient spiraling dynamics as a process-based measure of stream health and function. Nutrient spiraling dynamics describe the level of benthic microbial activity and hyporheic processes within the stream as well as the ability of the stream to increase uptake rates in response to increased nutrient loading. The stream’s “resilience”, the ability to adapt uptake rates, governs nutrient export within a reach, which impacts catchment-scale water quality concerns such as basin eutrophication. Thus, changes in spiraling dynamics have implications for both stream health in situ as well as for the catchment at large. Pairing process-based measures of stream function with physical habitat characteristics allows us to go beyond identifying differences in stream function and start to explain what is causing those differences. By identifying what specific elements of habitat structure drive the processes tied to stream function we can target restoration efforts to produce higher functional lift in our streams. Nutrient dynamics were characterized at each reach through Tracer Additions for Spiraling Curve Characterization analysis (TASCC). Habitat characterization surveys were conducted at each reach using standardized methods from the National Rivers and Streams Assessment and the Minnesota Stream Quantification Tool to enable comparison with existing datasets. Nutrient dynamics were compared between matched control and treatment reaches to evaluate the effect of full-channel realignment on nutrient dynamics. In this case study we find that the restored reach of Sargent Creek has stronger nutrient uptake and retention, higher biological demand for NH4, and is further from biological saturation than the unrestored reach. We were able to explain these differences in uptake behavior through the interaction of habitat characteristics altered by restoration activities (such as reach slope, pool-riffle spacing, grain size distribution, canopy cover, and riparian vegetation assemblage). This provides a strong argument for the use of paired physical habitat surveys with process-based measures of stream function in restoration monitoring and assessment.Item Healthy forests to resist invasion: The role of resources, plant traits, and propagule pressure(2015-04) Lodge, AlexandraInvasive species are a global problem, dominating habitats, negatively impacting biodiversity, and changing ecosystem processes. There is no consensus regarding which nonnative species are likely to become invasive if introduced, nor which habitats are most susceptible to invasion. To investigate these questions, we studied the native and nonnative plants in 68 oak forest stands in Minnesota, USA. Nonnative plants possessed functional traits similar to those of some native species, suggesting that they exhibit similar growth strategies. These traits allow nonnatives and some natives to grow quickly in high resource environments. Among these same sites, we also examined whether there are characteristics of forests that make them more susceptible or resistant to a particularly pernicious invasive shrub, common buckthorn (Rhamnus cathartica L.). We found that buckthorn presence was best predicted by high propagule availability and site light levels, while buckthorn was more abundant in sites with higher soil fertility, lower resident plant diversity, and less leaf litter. Timber harvesting also affected buckthorn abundance, with more buckthorn in sites that were clearcut or unharvested than in those that were selection harvested. Management practices that minimize increases in light levels and soil disturbance or maintain or increase resident plant diversity (e.g., reduce deer populations) may help uninvaded forests resist buckthorn invasion, especially if local propagule pressure is also reduced. Finally, we also investigated the below-ground effects of buckthorn by examining nutrient cycling across a natural gradient of buckthorn abundance along an invasion front. Buckthorn appears to increase soil nitrogen, organic carbon, calcium, and pH through deposition of nutrient-rich leaf litter. Increases in soil fertility may lead to increased forest productivity and potentially facilitate further spread of buckthorn or other invasive species that may be better able than natives to take advantage of abundant resources. Overall, both the traits of invasive plants and the characteristics of receiving systems can play key roles in determining the success of nonnative species and the potential impacts they may have on native ecosystems.Item Nutrient transport, transformation, and retention in urban landscapes(2014-08) Nidzgorski, DanielUrban nutrient sustainability faces challenges of both too much and too little: Excess nutrient loading to the environment can degrade ecosystem functions and impact human health, while at the same time depleting nonrenewable nutrient sources and moving nutrients into unrecoverable pools. Most studies and efforts to date have focused on source reduction, identifying and reducing the largest drivers of carbon (C), nitrogen (N), and phosphorus (P) consumption. However, this addresses only one aspect of urban nutrient cycling; processes that transport, transform, or retain nutrients also determine their eventual fate as pollution, inert storage, or recycling. The first chapter examined C, N, and P output fluxes from ~2,700 households in the Twin Cities metropolitan area (Minneapolis-Saint Paul, Minnesota, USA), and tracked these fluxes through various transformations in the waste streams to their eventual fates. We found few opportunities to redirect pollutant fluxes to either inert storage or recycling; reducing household nutrient pollution must rely primarily on reducing consumption. High pollution fluxes were driven not only by household nutrient outputs, but also by waste-management practices (e.g. septic vs. sewer) and spatial considerations. In contrast, we found substantial opportunities to increase household N and P recycling by ten-fold, which could potentially exceed household inputs of N and P in food. To complement this study of opportunities for improving nutrient waste management, the second and third chapters examined opportunities to manage the biophysical environment - specifically, the urban forest - to reduce nutrient pollution. We focused on the role of urban trees driving N and P movement from land to water, both leaching to groundwater and loading to stormwater. In the second chapter, we compared nutrient leaching under 33 trees of 14 species, as well as open turfgrass areas, and explored correlations with soil nutrient pools and plant functional traits. Trees had similar or lower N leaching than turfgrass in 2012 but higher N leaching in 2013; trees reduced P leaching compared with turfgrass in both 2012 and 2013, deciduous trees more than evergreens. Scaling up our measurements to the Capitol Region Watershed (~17,400 ha), we estimated that trees reduced P leaching to groundwater by 533 kg in 2012 and 1201 kg in 2013. Removing the same amounts of P with stormwater infrastructure would cost $2.2 million and $5.0 million per year, respectively. In the third chapter, we measured tree litter nutrient inputs to street gutters, which can ultimately contribute to stormwater loading, under four species of boulevard trees. Differences among tree species in the total amount of nutrients in the street gutters were driven primarily by interspecific differences in the mass of litter dropped, which were much greater than differences in litter chemistry. In developing management recommendations, we found that tree phenology is a more important consideration than litter chemistry. Cleaning up spring and autumn pulses of tree litter shortly after they fall has substantial potential to reduce nutrient inputs to stormwater; for autumn litterfall, we estimated that doing so could remove 219.0-274.4 kg N km-2 and 14.2-20.6 kg P km-2. Because of the wide variation in species' litterfall timing, achieving this goal is likely to require adjusting both boulevard tree selection and litter cleanup strategies.Item Sargent Creek Nutrient Injection Breakthrough Curve(2022-09-15) Baldus, David, B; Gran, Karen, B; baldu024@d.umn.edu; Baldus, David, BBreakthrough curve data from nutrient injection tracer tests conducted at Sargent Creek on 2021-09-15 and 2021-09-22. The tests were conducted in two stream reaches, the treatment reach which was restored with a full channel realignment in 2019 and the control reach which was not restored. These tracer tests were conducted as part of an effort to assess the effects that restoration practices have on a stream ecosystems. A solution of nutrients (Potassium Nitrate (KNO3), Ammonium dihydrogen phosphate ((NH4)H2PO4)) and a conservative tracer (Sodium Chloride (NaCl)) dissolved in stream water was injected into the stream at the top of the reach as an instantaneous release. Water samples were collected in the thalweg at downstream end of the reach to describe reach-scale nutrient spiraling. Additionally water samples were collected at two sites located mid-reach at the upstream and downstream end of a representative riffle type habitat unit to describe the nutrient cycling within these individual habitat units. Timing of sampling was determined by a conductivity meter in order to capture rising, peak, and falling concentrations and generate a breakthrough curve (BTC).Item Sediment mixing and dissolved oxygen and nutrient dynamics in a six week microcosm experiment containing Great Lakes macroinvertebrates(2024-05-06) Huff, Audrey H; Rigdon, Matt; Zalusky, John; Katsev, Sergei; Ozersky, Ted; huff0114@umn.edu; Huff, Audrey E; University of Minnesota Duluth Large Lakes ObservatoryPhysical and geochemical dynamics at the sediment-water interface in a six-week microcosm experiment including Great Lakes macroinvertebrates (dreissenids, Diporeia, and oligochaete worms) with varying functional biology. Microcosms included single and multi-taxon treatments and data includes sediment mixing rate (as luminophore profiles), weekly NO2,3 and NH3 fluxes between the sediment and overlying water, weekly sediment dissolved oxygen microprofiles, and pore water NO2,3, NH3, and P profiles.