Environmental Science Program, College of Natural Resources, University of Idaho, Moscow, ID, 83844, USA.
United States Forest Service, Emmett, ID, 83617, USA.
J Environ Manage. 2024 Aug;366:121729. doi: 10.1016/j.jenvman.2024.121729. Epub 2024 Jul 7.
Forest water reclamation is a decades-old practice of repurposing municipal reclaimed water using land application on forests to filter nutrients and increase wood production. However, long-term application may lead to nutrient saturation, leaching, and potential impairment of ground and surface water quality. We studied long-term effects of reclaimed water application on nutrient leaching potential in a four-decade time series of forest water reclamation facilities in northern Idaho. Our approach compared reclaimed water treated plots with untreated control plots at each of the forest water reclamation facilities. We measured soil nitrifier abundance and net nitrification rates and used tension lysimeters to sample soil matrix water and drain gauges to sample from a combination of matrix and preferential flow paths. We determined nutrient leaching as the product of soil water nutrient concentrations and model-estimated drainage flux. There was more than 450-fold increase in nitrifier abundance and a 1000-fold increase in net nitrification rates in treated plots compared with control plots at long-established facilities, indicating greater nitrate production with increased cumulative inputs. There were no differences in soil water ammonium, phosphate, and dissolved organic nitrogen concentrations between control and effluent treatments in tension lysimeter samples. However, concurrent with increased nitrifier abundance and net nitrification, nitrate concentration below the rooting zone was 2 to 4-fold higher and nitrate leaching was 4 to 10-fold higher in effluent treated plots, particularly at facilities that have been in operation for over two decades. Thus, net nitrification and nitrifier abundance assays are likely indicators of nitrate leaching potential. Inorganic nutrient concentrations in drain gauge samples were 2 to 11-fold higher than lysimeter samples, suggesting nutrient losses occurred predominantly through preferential flow paths. Nitrate was vulnerable to leaching during the wet season under saturated flow conditions. Although nitrogen saturation is a concern that should be mitigated at long-established facilities, these forest water reclamation facilities were able to maintain average soil water nitrate concentrations to less than 2 mg L, so that nitrogen and phosphorous are effectively filtered to below safe water standards.
森林水再生是一项具有数十年历史的实践，通过在森林中使用土地应用来重新利用城市再生水，以过滤养分并提高木材产量。然而，长期应用可能导致养分饱和、淋失和潜在的地下水和地表水水质受损。我们研究了在北爱达荷州的四个十年森林水再生设施的时间序列中，再生水应用对养分淋失潜力的长期影响。我们的方法是在每个森林水再生设施中，将经过处理的再生水与未经处理的对照进行比较。我们测量了土壤硝化菌丰度和净硝化速率，并使用张力渗透计采集土壤基质水样本，使用排水计采集基质和优先流路径组合的样本。我们通过土壤水分养分浓度与模型估计的排水通量的乘积来确定养分淋失量。在长期建立的设施中，处理过的土壤中的硝化菌丰度增加了 450 多倍，净硝化速率增加了 1000 倍，表明随着累积投入的增加，硝酸盐的产生量更大。张力渗透计样本中，对照和流出物处理之间的土壤水中铵、磷酸盐和溶解有机氮浓度没有差异。然而，随着硝化菌丰度和净硝化的增加，根区以下的硝酸盐浓度增加了 2 到 4 倍，流出物处理的硝酸盐淋失增加了 4 到 10 倍，特别是在运行时间超过二十年的设施中。因此，净硝化和硝化菌丰度测定可能是硝酸盐淋失潜力的指标。排水计样本中的无机养分浓度是渗透计样本的 2 到 11 倍，表明养分损失主要通过优先流路径发生。硝酸盐在饱和流条件下的湿季容易淋失。尽管氮素饱和是长期建立的设施应该缓解的一个问题，但这些森林水再生设施能够将土壤水中硝酸盐浓度维持在 2mg/L 以下，从而有效地将氮和磷过滤到低于安全水标准以下。
