Department of Aquatic Sciences and Assessment, Swedish University of Agricultural Sciences, PO-Box 7050, 750 07, Uppsala, Sweden; Department of Soil and Environment, Swedish University of Agricultural Sciences, Uppsala, Sweden.
Department of Aquatic Sciences and Assessment, Swedish University of Agricultural Sciences, PO-Box 7050, 750 07, Uppsala, Sweden.
J Environ Manage. 2024 Jan 1;349:119500. doi: 10.1016/j.jenvman.2023.119500. Epub 2023 Nov 10.
Globally, significant societal resources are devoted to mitigating negative effects of eutrophication from excessive phosphorus (P) and nitrogen (N) loading. Potential effectiveness of mitigation measures and possible confounding factors are often assessed using studies conducted in headwater catchments. However, success is often evaluated based on trends in river mouth water chemistry. It is not clear how transferrable insights from headwater catchments are to larger rivers. Here, relationships between P and suspended solids (SS) identified in small agricultural headwater catchments were applied to 30 larger, mixed land use catchments draining into Mälaren, a Swedish great lake. Relationships identified in headwater streams between SS concentration, catchment agricultural land percentage and arable land clay content were corroborated for the larger catchments (R = 0.59, p-value<0.001. The same was true for connections between SS and particulate P (R = 0.74, p-value<0.001). This study highlights the importance of agricultural land, clay content and SS for P transport, on both smaller headwater as well as larger catchment scales, supporting the use of headwater findings on larger, management relevant scales. Consequently, these relationships should be used to target mitigation measures to reduce SS and P losses. To explore the effectiveness of mitigation measures on water quality, we assessed long-term (20 year) trends in tributary water quality and compared these trends to the amount of mitigation measures implemented in the catchment. Overall improving trends were detected using regional Mann Kendall tests, but few decreasing trends in nutrient concentrations were found for individual sites using Generalized Additive Models (GAM). The lack of significant trends and identifiable connections to amount of mitigation measures implemented could be due to several reasons, e.g. insufficient time for recently implemented measures to have an effect, ongoing release of legacy P as well as low areal coverage and poor spatial placement of implemented measures. In addition, trend detection requires large amounts of data and the results should be carefully interpreted and communicated.
全球范围内，大量的社会资源都投入到了减轻因过度磷（P）和氮（N）负荷导致的富营养化的负面影响。通常使用在源头集水区进行的研究来评估缓解措施的潜在有效性和可能存在的混杂因素。然而，成功往往是基于河口水质的趋势来评估的。目前还不清楚从源头集水区获得的经验是否可以应用于更大的河流。在这里，在小的农业源头集水区中确定的 P 和悬浮固体（SS）之间的关系被应用于 30 个更大的、混合土地利用的集水区，这些集水区排入瑞典的一个大湖——梅拉伦湖。在更大的集水区中，证实了源头溪流中 SS 浓度、集水区农业用地比例和耕地粘粒含量之间关系的存在（R = 0.59，p 值<0.001）。SS 与颗粒态 P 之间的关系也是如此（R = 0.74，p 值<0.001）。本研究强调了农业用地、粘粒含量和 SS 对 P 输移的重要性，无论是在较小的源头集水区还是更大的集水区，这都支持了在更大的、与管理相关的尺度上使用源头研究结果。因此，这些关系应该用于确定减少 SS 和 P 流失的缓解措施的目标。为了探索缓解措施对水质的有效性，我们评估了支流水质的长期（20 年）趋势，并将这些趋势与集水区中实施的缓解措施的数量进行了比较。使用区域 Mann Kendall 检验检测到了总体改善趋势，但使用广义加性模型（GAM）对个别站点发现，营养物浓度的下降趋势很少。缺乏显著的趋势和与实施的缓解措施数量的可识别联系可能有几个原因，例如，最近实施的措施需要时间才能产生效果、遗留 P 的持续释放以及实施措施的面积覆盖率低和空间位置不佳。此外，趋势检测需要大量数据，并且结果应仔细解释和传达。
