During this 6th Great Extinction, freshwater quality is imperiled by upland terrestrial practices. Phosphorus, a macronutrient critical for life, can be a concerning contaminant when excessively present in waterways due to its stimulation of algal and cyanobacterial blooms, with consequences for ecosystem functioning, water use, and human and animal health. Landscape patterns from residential, industrial and agricultural practices release phosphorus at alarming rates and concentrations threaten watershed communities. In an effort to reconcile the anthropogenic effects of phosphorus pollution, several strategies are available to land managers. These include source reduction, contamination event prevention and interception. A total of 80% of terrestrial plants host mycorrhizae which facilitate increased phosphorus uptake and thus removal from soil and water. This symbiotic relationship between fungi and plants facilitates a several-fold increase in phosphorus uptake. It is surprising how little this relationship has been encouraged to mitigate phosphorus for water quality improvement. This paper explores how facilitating this symbiosis in different landscape and land-use contexts can help reduce the application of fertility amendments, prevent non-point source leaching and erosion, and intercept remineralized phosphorus before it enters surface water ecosystems. This literature survey offers promising insights into how mycorrhizae can aid ecological restoration to reconcile humans’ damage to Earth’s freshwater. We also identify areas where research is needed.

Agricultural pollution, especially phosphorus (P) can cause eutrophication of freshwater quality. Riparian buffers are best management practices (BMPs) which intercept agricultural pollution. However, they are frequently degraded by reduced biodiversity. P mitigation in riparian buffers can be enhanced through mycorrhizal inoculation and cyclical coppicing. We report on a myco‐phytoremediation project that investigates mycorrhizae's effect on vegetation's ability to lower legacy soil P, soil water P, and increase woody biomass P uptake. It also aimed to restore pollinator habitat through planting a diverse, native plant palette (32 species), blooming from February to November. Planting and offering culturally relevant plant materials to the Abenaki contributes to their land rematriation process. The study was located on unceded Abenaki territory at Shelburne Farms, within 300 m of Lake Pitawbagw (Lake Champlain) which is impacted increasingly by P pollution from colonial and conventional agricultural practices. Along a drainage way three treatment plots were installed: buckthorn vegetation (OIV) left in place as the control, and two restored diverse multi‐synusium plant communities, consisting of either uninoculated (RV) or inoculated with 19 mycorrhizal species (RVM). After 2 years, soil water soluble reactive P extracted from lysimeter samples was not affected by treatment but varied over time. However, water extractable SRP (WEP‐SRP) and TP (WEP‐TP) followed this trend RV > OIV > RVM which was inversely and linearly related to mycorrhizal density. Plants are best harvested in late summer when P concentrations are highest. Restoration science can flourish through reciprocally partnering with Original Peoples who hold expertise in ecological reconciliation.

Societal Impact Statement Worldwide, farmers struggle to find the most efficacious practices which balance crop fertility needs and water quality protection. Through a greenhouse experiment, we investigated how soil status (high vs. low phosphorus [P] concentration), mycorrhizae (inoculated vs. not), and plant species (dogwood vs. willow) affected P plant uptake and leaching. We found mycorrhizae did not affect uptake or leaching, more P was leached from high than low P soil, dogwood uptook yet leached more P, and above ground biomass at the end of summer contained more P than roots. This study provides insights to be considered by researchers and practitioners who implement best management practices for water quality. Summary This research examined the effects of mycorrhizal inoculation in high and low phosphorus saturation soils on phosphorus uptake by Cornus sericea and Salix niger. The aim was to identify practices that improved water quality functions of riparian buffers to protect surface waters impacted by eutrophication. A mesocosm experiment arranged as a random block design was conducted with mycorrhizal presence, soil phosphorus saturation status, and plant species as factors. Leachate, plant uptake, and soil phosphorus were measured to assess the effects. Greater leachate and uptake of phosphorus were detected for C. sericea than for S. niger. Mycorrhizae had no effects on leaching nor on uptake of phosphorus in this experiment. High phosphorus saturated soils had greater leaching and uptake than the low phosphorus soils. Above ground biomass contained more phosphorus than below ground biomass in both species at time of harvest. Estimations of phosphorus removal through coppicing suggest a very slow removal rate in biodiverse multi‐functional riparian buffers. Our results suggest that cyclical coppicing can be an improvement to Best Management Practices. Diverse riparian buffers are limited in the amount of phosphorus that they can store and mitigate, even with coppicing. The emphasis therefore should be on agricultural best management practices that reduce phosphorus export from upland fields. Further studies in phosphorus accumulating plant species with appropriate mycorrhizal symbionts are needed.