Progress 06/01/24 to 05/31/25
Outputs
Target Audience:There are several stakeholder groups that are audience to forest water reclamation research. These include: 1) Water treatment facility owners and operators that are obligated to serve the needs of the local community and to meet regulator'srequirements; 2) Communities that bear the cost of wastewater treatment including those that are considering installing and operating new facilities; 3) Indigenous American communities that manage the forest lands and coexist with lands and water resources for sustenance, spirituality, and prosperity; 4) The broader public that enjoy the benefits of clean surface waters; 5) Regulators who are responsible for permitting facilities and overseeing their operation; 6) Wastewater engineers that are designing forest water reclamation facilities as well as alternative treatment approaches; 7) The forest owners and managers that benefit fromenhanced forest growth due to application of water and nutrients. Changes/Problems:Due to delays in design and construction of the Post Falls wastewater reclamation distribution systems we have initiated a small-scale phosphorous application rate study. As with the initial full scale phosphorous rate study in forested plots, the objectives of this small-scale study are to evaluate storage, transformations, and fluxes of P applied to the forests soil surface at various rates in incremental amendments over the growing season. As originally proposed, we are quantifying mineral soil P pools with an extraction series of increasing intensity and assessing risk of environmental loss. Without the full-scale application through the wastewater distribution system, it will not be possible to assess tree phosphorous uptake due to the size of the treatment plots. Instead, we will determine tree P uptake within the regional time-series study that we have running in parallel with this demonstration project. For the time-series study, we have a complete set of overstory, understory and O-horizon samples for assessing the N budget. For these modifications, we will also assess total P content in each of those tissues within the time-series study to assess the P budget, evaluate P uptake and determine critical P loading rates. Quantifying P and N critical loads is important for understanding of the amounts of wastewater constituents that can be applied to forest ecosystems without risk of environmental harm. These delays and modifications require no-cost time extensions for this project. During this reporting period we requested and were granted our first time extension to begin during the next reporting cycle. Considering delays in recruiting graduate students we anticipate requesting one more time extension to fully support their graduate programs and accomplish the revised objectives. What opportunities for training and professional development has the project provided?During this reporting period we were able to start programs for two graduate students; a master's student started in August, and a doctoral student started in April. The master's student prepared a thesis project proposal and initiated the rate trial at Post Falls, reviewed literature on models that describe the soil's capacity to adsorb and retain P and progress with the isotherm experiments. For this student, training and professional development have included design and implementation of both field and lab experiments. The doctoral student is an international student, so on-boarding has taken some time to navigate the student visa process. Nonetheless, during visa processing delays this student successfully completed the Soil Systems manuscript on soil chemical processes described above. That student has been in place less than six weeks at the time of this report and is now developing a dissertation proposal on estimating critical loading rates based on N and P ecosystem budgets. This work will take advantage of 15N enriched wastewater to trace the contribution of applied N to that taken up by the vegetation. Even though this student has only just begun a doctoral program there have already been ample opportunities for training and professional development. How have the results been disseminated to communities of interest?We have been in regular contact with the Post Falls facility manager, managers of other regional facilities including those within the regional time series as well as others interested in establishing new facilities. Dissemination efforts during this reporting period have focused on peer-reviewed publication on hydrology, leaching losses and microbial N transformations, as well as soil chemical responses to wastewater amendments. As student projects mature, they will be asked to present their findings at regional and national meetings on wastewater and ecosystem management. What do you plan to do during the next reporting period to accomplish the goals?During the 2025 growing season, we will complete the modified rate study at the Post Falls FWR facility. Following the completion of the 6 split applications, post treatment soil samples will be collected from each plot. Post treatment soil samples will be subject to the same P extraction series conducted for the pre-treatment samples to determine the fate of applied P treatments within the two 15-cm-deep layers. Post treatment samples will be used to validate models developed with the isotherm studies conducted on pre-treatment samples, which will provide insight on the fate and transport of P within the soil profile. We will also analyze tissue P concentrations to construct the P budgets for the regional time-series plots for the purpose of determining P uptake. Our failure to locate a significant portion of P in soil pools leads us to hypothesize that the applied P has been acquired by the vegetation. Preparing and analyzing samples for the regional time series plots will allow us to construct the P budgets and determine critical P loading rates. This work will be conducted in parallel with constructing N budgets and determining critical N loading rates.
Impacts
What was accomplished under these goals?
Obj 1.Fate and transport of P applied to forest ecosystems We installed a P application rate study at the Post Falls forest water reclamation (FWR) facility to test the fate and transport of P. We designated five 18 m2 experimental blocks and collected pre-treatment soil samples from each block at 0-15 cm and 15-30 cm depth layers to characterize pre-treatment soil chemical conditions. A P extraction series was conducted on pre-treatment samples, including water extractable phosphorus, Bray-extractable phosphorus, oxalate extractable P (plus oxalate extractable Al and Fe), and total extractable P (hydrogen peroxide and aqua regia). We used the oxalate extracted P, Al and Fe to calculate Schoumans' degree of phosphorous saturation (DPS), or the ratio of oxalate extractable P to the sum of oxalate extractable Al and Fe. DPS measures a soil's capacity to adsorb and retain P. Each experimental block contains five 2 m2 treatment plots that receive different levels of P, including 0, 4.5, 15 and 30 kg/ha/yr as sodium phosphate using six monthly split applications to mimic periodic wastewater applications. Soil pore water samples are collected monthly from each plot using suction lysimeters prior to application. The purpose of soil water sampling is to assess transport through the profile. Treatments and sampling continue into the next reporting period. We have also evaluated the FWR regional time-series to identify the fate of the P applied through effluent applications. An average of 13 kg/ha of P has been applied annually at each FWR facility. Each facility has received different total amounts depending on their time-since establishment. During this reporting period we published a paper in Soil Systems that describes, for all sites, total P, Bray extractable P, and P saturation ratio (PSR). PSR is analogous to DPS described above but PSR is based on pragmatic commercial measures of P, Fe and Al rather than consistent oxalate extractable values. Despite the large total amounts of P applied especially at the long-established facilities, we see little to no treatment effects on total P, Bray-extractable P, and PSR. The lack of extractable P response may have been due to the Bray-1 extraction approach, so we conducted oxalate extractions for the long-established Bottle Bay soils and again found no treatment effect (p > 0.10). We also compared two approaches to measuring a soil's capacity to adsorb and retain P: 1) our pragmatic use of typical commercial P, Al and Fe extraction to calculate PSR and 2) the oxalate extracted P, Al and Fe to calculate DPS. Our pragmatic PSR approach yielded equivalent results to that of DPS with a strong correlation. Thus, we concluded that there was no treatment distinction for either measure of phosphorous saturation in Bottle Bay soils, and that PSR is an acceptable approach for experimental comparisons. Furthermore, we did not see treatment differences in litter P concentration or content in Bottle Bay soils, nor differences in leaching loss. In fact, our leaching results (published in the Journal of Environmental Management) indicate that >99% of the applied P is retained by the forest ecosystem. Obj 2.Biophysical interactions of P in forests Our analysis of the long-term impacts of wastewater amendments on forest soil chemical properties was published in Soil Systems. In addition to showing that nitrate was elevated in soils of long-established facilities, we also demonstrate that wastewater amendments increase cations and raise soil pH. However, total P and extractable phosphate were little affected by wastewater treatment except in the 45-75 cm depth layer at long-established facilities, which indicates that the treatment response is associated with transport of phosphate through the soil profile. We document the importance of preferential hydraulic flow through these FWR soils in our Journal of Environmental Management paper, which suggests that enhanced movement of P through these preferential flow paths may allow suspended or dissolved constituent nutrients to percolate downwards through the soil profile and deposit at lower depths. These below-surface effects are consistent with pedogenic P weathering and transport models. We are in the process of assembling P budgets for the regional time-series of FWR facilities including soil, forest tree components (roots, stems, branches and leaves), understory vegetation, and detrital organic matter. Aboveground tissue and soil samples have been prepared for sample digestion and analysis to determine annual P uptake capacity of northern Idaho forest ecosystems. We have nearly completed preparing litterfall samples to learn the magnitude of P return from the vegetation to the soil. We have begun collecting root tissue samples to add a belowground tree component to the P model. The P budget will supply data on tree uptake and allow estimation of critical P loads. If vegetation is the primary fate of applied P, it would mean that managers need only to maintain vigorous annual growth to effectively sequester applied P. Soil P fixation would then provide additional buffer capacity to ecosystem P retention. Obj 3.Risk assessment indicator models for predicting nutrient leaching thresholds. The DPS indicator quantifies how much of the mineral soil P fixation capacity is available to filter applied P. As described above, we calculated DPS for the initial samples at Post Falls and for the surface mineral soil layer for the regional time-series study plots. All the experimental blocks in the initial soil samples at Post Falls averaged less than or equal to 10% saturation. The regional time-series facilities averaged less than 20% saturated, and as mentioned this occurred in both control and treated plots. This collective information suggests that there is a large capacity to store P without risk of leaching loss. The DPS indicator that we are developing for the Post Falls facility and the regional time-series facilities is the type of indicator tool that FWR facilities and regulators can use to assess the risk of P leaching losses from FWR facilities. A phosphorus sorption isotherm experiment was conducted on the pre-treatment soil samples taken from the Post Falls rate trial. Additional isotherm experiments will be conducted on control soils from the regional time series and treated plots will be used to validate parameterized models. For sorption isotherms, soil is allowed to react with a CaCl2 solution, as well as a KH2PO4 or NaH2PO4 to create a soil to solution ratio of 1:25 and allowed to equilibrate before filtration and spectrophotometric analysis. The sorption isotherm allows for the determination of the P sorption maximum (qmax). Maximum P sorption for the samples from the plots ranged from 158 to 200 mg/kg of P.
Publications
- Type:
Peer Reviewed Journal Articles
Status:
Published
Year Published:
2025
Citation:
Wedajo, T.G., E. Joshi, R. Hu, D.G. Strawn and M.D. Coleman. 2025. Soil chemical variation along a four-decade time series of reclaimed water amendments in northern Idaho forests. Soil Systems. 9:32. https://doi.org/10.3390/soilsystems9020032
- Type:
Peer Reviewed Journal Articles
Status:
Published
Year Published:
2024
Citation:
Joshi, E., M.R. Schwarzbach, B. Briggs, E.R. Coats and M.D. Coleman. 2024. Nutrient leaching potential along a time series of forest water reclamation facilities in northern Idaho. Journal of Environmental Management. 366:121729. https://doi.org/10.1016/j.jenvman.2024.121729
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Progress 06/01/23 to 05/31/24
Outputs
Target Audience:There are several stakeholder groups that are audience to forest water reclamation research. These include: 1) Water treatment facility owners and operators that are obligated to serve the needs of the local community and to meet regulators' requirements; 2) Communities that bear the cost of wastewater treatment and those that are considering installing and operating new facilities; 3) Indigenous American communities that manage the forest lands and coexist with lands and water resources for sustenance, spirituality, and prosperity; 4) The broader public that enjoy the benefits of clean surface waters; 5) Regulators who are responsible for permitting facilities and overseeing their operation; 6) Wastewater engineers that are designing forest water reclamation facilities as well as alternative treatment approaches; 7) The forest owners and managers that benefit from enhanced forest growth due to application of water and nutrients. We have been in contact with each of these groups in various public and private settings over the last year. Changes/Problems:Due to delays in design and construction of the Post Falls wastewater reclamation distribution systems we will initiate a small-scale phosphorous application rate study. As with the initial full scale phosphorous rate study, the objectives of this small-scale study are to evaluate storage, transformations, and fluxes of P applied to the forests soil surface at various rates in incremental amendments over a two-year time. As originally proposed, we will quantify mineral soil P pools with an extraction series of increasing intensity, assess risk of environmental loss and evaluate O-horizon P uptake. For the extraction series, we will run composite samples from each plot through a sequential extraction series including, water extractable P, Bray (NH4F-HCl) extractable, oxalate ((NH4)2C2O4) extractable, as well as Incinerated and non-incinerated samples extracted with H2SO4. We will quantify P in all extractions with an inductively coupled plasma (ICP) spectrometer. To assess the risk of environmental P release from mineral soil, we will use oxalate extractable and ICP quantified P, Al and Fe to determine the risk of P loss via the DPS model. To investigate the response of biological activity in O- and mineral soil horizons, we will make quarterly measurements of microbial biomass P and phosphatase activity in O-horizon and mineral soil (10 cm). We will measure acid phosphatase exoenzyme activity using fluorometric microplate assays and assess O-horizon available P with water extraction and determine O-horizon total P with incinerated H2SO4 extraction. Without the full-scale application through the wastewater distribution system (due to the size of the treatment plots), it will not be possible to assess tree phosphorous uptake. Instead, we will determine tree P uptake within the regional time-series study that we have running in parallel with this demonstration project. For the time-series study, we have a complete set of overstory, understory and O-horizon samples for assessing the N budget. For these modifications, we will also assess total P content in each of those tissues within the time-series study to assess the P budget, evaluate P uptake and determine critical P loading rates as we are currently doing for N. These delays and modifications will require a no-cost extension of the project. We will submit a request for the extension following the completion of the annual reporting. What opportunities for training and professional development has the project provided?Thus far, this project has supported training and development for one undergraduate helping to prepare samples for analysis. We have also engaged a postdoc to conduct and report the total P and oxalate extractable nutrients, which reinforced her capacity to run such assays and summarize the results. We had hoped to start two graduate students during the first year, yet student recruitment has been a challenge. We were able to secure an excellent prospect for the second year. Thus, graduate student training opportunities will be a main emphasis in the future. How have the results been disseminated to communities of interest?We have been in regular contact with the Post Falls facility manager, managers of other regional facilities including those within the regional time series as well as those interested in establishing new facilities. We have also reported results of the regional time series at a professional conferences, university seminars, and a regional Natural Resources Council throughout the year and prepared multiple manuscripts on tree growth, hydrology and nutrient leaching, Although, the focus of these talks and papers have been largely on nitrogen cycling, we also consistently describe the importance of P in relation to N and the effectiveness with which FWR facilities filter P from wastewater. We have also been consulting with a couple of wastewater treatment facilities on the potential for land applying effluent to forests: One is a new facility at Bryce Canyon National Park and the second is between the adjacent communities of Fernwood and Santa Idaho. We have made recommendations on loading rates that can maintain long-term nutrient filtering without risk of nutrient saturation. We made forest management recommendations to these facilities managers to assure that vigorous forest growth allows them to meet regulatory requirements. What do you plan to do during the next reporting period to accomplish the goals?We have recruited one graduate student and have targeted a second graduate student to recruit for a second position. The student starting in August will be responsible for conducting the rate study and for conducting the sequential extraction and degree of P saturation analyses based on the modified study plan as described below. Thus, we will commence the modified rate study during the last third of the 2024 growing season and carry that through 2025 and into the 2026 growing seasons. We anticipate that the second student will start in January 2025 and will conduct the O-horizon and mineral soil biological assays and analyze tissue P concentrations to construct the P budgets and determine P uptake.
Impacts
What was accomplished under these goals?
We designated five experimental blocks at the Post Falls forest water reclamation (FWR) facility and collected initial soil samples from three locations in each block from three layers to a depth of 75 cm to characterize pre-treatment soil chemical conditions. Additionally, we are using soil vegetation and detrital samples from a four-decade time-series of regional FWR facilities to evaluate the extent to which wastewater-applied P occurs in these pools. This combination of pre-treatment, early treatment and a decadal time-series of wastewater treatments allow us to achieve three objectives. Obj 1.Fate and transport of P applied to forest ecosystems We have evaluated the FWR regional time-series to identify the fate of 13 kg/ha/yr of P applied annually through effluent applications. We examined oxalate extractable P, Al and Fe in the surface layer to 15 cm depth, as well as total P in three mineral horizons to 75 cm depth and the overlying O-horizon. We then calculated the degree of P saturation (DPS) for the surface soil layer. DPS is the percentage of extractable P to extractable Fe and Al that is available to fix P. Statisical analysis of total P, oxalate-extractable P and DPS indicates that there were no significant differences between effluent treated and control plots, even those that have received annual amendments for over 40 years. The lack of treatment effects on the P pools suggests that there are other P-removal pathways, including leaching losses and uptake by tree root systems. We can eliminate leaching losses because quantification of both matrix and preferential flow pathways indicates that more than 99.8% of the applied P is filtered from the effluent when compared to that leaching below the rooting zone (Joshi et al. 2024, doi.org/10.1016/j.jenvman.2024.121729). This amounts to less than 0.2 kg/ha/yr of P leaching from the site, which is insufficient to account for the amount added with effluent. Consequently, we are focusing our attention on the vegetation as a primary pool for effluent-applied P (Obj 2). Understanding the fate and transport of applied P provides facilities managers and regulators with information on managing forests for maximum effectiveness. The limited magnitude of risks informs other stakeholders about the effectiveness of these facilities. Obj 2.Biophysical interactions of P in forests For the initial Post Falls soil samples, we observed the expected impact of depth on the 23 variables assessed. For example, soil reaction (pH), P concentration (Bray P), N concentration (NO3-), cation exchange capacity (CEC), and degree of P saturation (DPS) are displayed below for the upper and lower depth layers sampled. pH 6.26 ± 0.32 for the 0-15 layer 5.97 ± 0.16 for the 45-75 cm layer Bray P (ppm) 30 ± 15 13 ± 5 NO3- (ppm) 1.96 ± 0.87 1.43 ± 0.19 CEC (meq/100g) 10.2 ± 2.4 7.7 ± 1.4 DPS (%) 9.2 ± 3.4 6.2 ± 1.9 However, there were no statistically significant differences among the experimental blocks. The consistency among experimental blocks demonstrates relatively uniform soil conditions, especially for a forested site, which will provide a sensitive testing platform to examine P amendment effects. We are also assembling P budgets for the regional time-series of FWR facilities including soil, live vegetation, and detrital organic matter. Tissue samples have been prepared for sample digestion and analysis to determine annual P uptake capacity of northern Idaho forest ecosystems. If vegetation is the primary fate of applied P, it would mean that managers need only to maintain vigorous annual growth to effectively sequester applied P. Obj 3.Risk assessment indicator models for predicting nutrient leaching thresholds. The DPS indicator quantifies how much of the mineral soil P fixation capacity is available to filter applied P. As described above, we looked at DPS for the initial samples at Post Falls and for the surface mineral soil layer for the regional time-series study plots. All the experimental blocks in the initial soil samples at Post Falls averaged less than or equal to 10% saturated. The regional time-series facilities averaged less than 20% saturated, and as mentioned this occurred in both control and treated plots. This collective information suggests that there is a large capacity to store P without risk of leaching loss. The DPS indicator we are developing for the Post Falls and the regional time-series facilities is the type of simple indicator tool that FWR facilities and regulators can use to assess the risk of P leaching losses from FWR facilities.
Publications
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