School of GeoSciences, The University of Edinburgh, Crew Building, Edinburgh, UK.
Sci Total Environ. 2010 Feb 15;408(6):1235-44. doi: 10.1016/j.scitotenv.2009.12.016. Epub 2010 Jan 13.
Due to its potential adverse effects on freshwater acidification, risk assessments of the impacts of forest expansion on surface waters are required. The critical load methodology is the standard way of assessing these risks and the two most widely used models are the Steady-State Water Chemistry (SSWC) and First-order Acidity Balance (FAB) models. In the UK the recommended risk assessment procedure for assessing the impact of forest expansion on freshwater acidification uses the SSWC model, whilst the FAB model is used for guiding emission policy. This study compared the two models for assessing the sensitivity of streamwater to acidification in 14 catchments with different proportions of broadleaf woodland cover in acid-sensitive areas in the UK. Both models predicted the exceedance of streamwater critical loads in the same catchments, but the magnitudes of exceedance varied due to the different treatment of nitrogen processes. The FAB model failed to account for high nitrogen leaching to streamwater, attributed to nitrogen deposition and/or fixation of nitrogen by alder trees in some study catchments, while both models underestimated the influence of high seasalt deposition. Critical load exceedance in most catchments was not sensitive to the use of different acid neutralising capacity thresholds or runoff estimates, probably due to the large difference between critical load values and acidic deposition loadings. However, the assessments were more sensitive to differences in calculation procedure in catchments where nitrogen deposition was similar to the availability of base cations from weathering and/or where critical load exceedance values were <1keqH(+)ha(-1)yr(-1). Critical load exceedance values from both models agreed with assessments of acid-sensitivity based on indicator macroinvertebrates sampled from the study catchments. Thus the methodology currently used in the UK appears to be robust for assessing the risk of broadleaf woodland expansion on surface water acidification and ecological status.
由于森林扩张可能对淡水酸化产生不利影响，因此需要对其对地表水的影响进行风险评估。临界负荷方法是评估这些风险的标准方法，最广泛使用的两种模型是稳态水化学（SSWC）和一级酸度平衡（FAB）模型。在英国，用于评估森林扩张对淡水酸化影响的推荐风险评估程序使用 SSWC 模型，而 FAB 模型用于指导排放政策。本研究比较了这两种模型，以评估英国敏感地区不同阔叶林地覆盖比例的 14 个集水区中溪流对酸化的敏感性。两种模型都预测了同一集水区的溪流临界负荷超标，但由于氮过程的不同处理，超标幅度有所不同。FAB 模型未能解释溪流中高氮淋溶的情况，这归因于一些研究集水区中氮的沉积和/或桤木对氮的固定，而两种模型都低估了高海盐沉积的影响。大多数集水区的临界负荷超标对使用不同的酸中和能力阈值或径流量估计值并不敏感，这可能是由于临界负荷值与酸性沉积负荷之间存在较大差异。然而，在氮沉积与风化产生的基础阳离子供应相似或临界负荷超标值<1keqH(+)ha(-1)yr(-1)的集水区中，评估结果对计算程序的差异更为敏感。两种模型的临界负荷超标值与基于从研究集水区中采样的指示性大型无脊椎动物评估的酸化敏感性一致。因此，英国目前使用的方法似乎能够可靠地评估阔叶林地扩张对地表水酸化和生态状况的风险。
