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Rubin, Jessica Ann

Plant and Soil Science

2022

M.S.

When land degradation imperils freshwater quality, land managers can restore ecosystem functions. The premise of three published/accepted thesis chapters is that mycorrhizae can enhance water quality function of riparian buffers and pollinator habitat through diverse, native polyculture associations. Where water quality is threatened through excess phosphorus (P) loads from agriculture, riparian buffers are considered Best Management Practices (BMPs). They intercept agricultural nutrients before reaching waterways. However, their seasonal cycles, saturation capacity, and often degraded conditions limit their ability to protect water quality. In particular, riparian buffers can transition from sinks to sources of P when agricultural practices chronically contribute P, plant cover is sparse, and vegetation senesces. A comprehensive literature review was performed that compiled studies from agriculture, riparian forests and mesocosms which demonstrate that mycorrhizal fungi can decrease P leaching and increase plant P uptake. I conducted further mesocosm and field experiments to obtain data and greater understanding of mechanisms involved in the ecological restoration of critical source areas. A random block mesocosm study investigated the effect of plant species Cornus sericea (red osier dogwood) and Salix niger (black willow), mycorrhizae (added or not), and soil P concentrations (high vs low) on plant P uptake and leaching. The high and low P soils were obtained from the same soil series (Winooski). Contrary to expectations, mycorrhizae were found in both high and low P soils. Dogwood mesocosms had greater P uptake by plants, but also greater leaching of P from the soil than was shown in mesocosms with willow. There were no significant effects of mycorrhizae on plant uptake nor leaching. Mycorrhizal hyphae were present to the same level in soils with high and low P concentrations. More soluble reactive phosphorus (SRP) leached from high P than low P soil. In a field study at Shelburne Farms on unceded Abenaki territory I researched the effects of mycorrhizae on P mitigation and pollinator habitat establishment. The riparian buffer was on poorly drained Covington soil. Plant P uptake, soluble reactive phosphorus (SRP) in soil water, and pollinator habitat establishment (plant richness) were compared in three treatments: a control plot of invasive Rhamnus cathartica (buckthorn), and two plots restored by manual removal of invasive buckthorn, one with and one without mycorrhizae. Thirty-two native plants, likely present when Abenaki ancestors practiced agroforestry cropping, were planted in the restored plots. The plant palette, was designed to establish multi-functional, multi-synusiae pollinator habitat, flowering February to November. Since restoration from May 2020 to November 2021, 1.7 times more plant species, corresponding to 24 more species, appeared in the restored plots than were planted. Restoration increased pollinator plant species fourfold compared to the control. Our data indicated an inverse linear relationship between mycorrhizal hyphal density (measured as hyphal length per gram), and soil SRP and TP concentrations. Coppicing was performed twice; in late summer prior to senescence yielding 3 times more P in plant tissue than coppicing in winter, the time when coppicing is recommended. This field and lab research is conducted on unceded Abenaki territory in the watershed of Lake Pitawbagw (colonially known as Lake Champlain). In addition to addressing environmental degradation of a riparian buffer, this research also aims to reconcile corresponding social injustices that occurred here. The root of the ecological degradation stems from a historical trajectory of events associated with colonization: displacement of the Original Peoples, the Abenaki, from their homeland, and replacing the Abenaki's reciprocal land practices with land clearing, tilling, grazing, fragmenting, and fertilizing which contributed to the soil's current legacy phosphorus concentrations. In addition to meeting the design criteria of the palette, eighty-eight percent of the plant palette is culturally relevant to the Abenaki by providing food, medicine, crafts and utilitarian materials. Over time the restoration can provide harvest ways for the Abenaki peoples and offer a small step towards rematriation. I recommend that restoration projects be evaluated with respect to pollution mitigation and reciprocal collaboration with Original Peoples in addition to current site restoration evaluation criteria. Two years is not enough time to remediate legacy P that has accumulated over 4oo years of colonial and conventional agriculture. Late summer cyclical coppicing of willow and dogwood maximizes phosphorus removal. Harvesting elderberry can remove additional P from the landscape. Current BMPs can be innovated to include manual, non-chemical nonnative species removal, diverse multi-species and multi-layered installations, pollinator habitat establishment, and cultural reparations.