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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