Australian Rivers Institute, Griffith School of Environment, Griffith University, Kessels Rd, Nathan, Queensland, 4111, Australia.
Australian Rivers Institute, Griffith School of Environment, Griffith University, Kessels Rd, Nathan, Queensland, 4111, Australia.
Sci Total Environ. 2017 Nov 15;598:188-197. doi: 10.1016/j.scitotenv.2017.04.075. Epub 2017 Apr 22.
Agricultural activities in catchments can cause excessive nutrient loads in waterways. Catchment nitrogen (N) and phosphorus (P) flows may be intercepted and assimilated by riparian vegetation. While prior studies suggest that woody vegetation is preferable for reducing P loads, the question remains: is woody vegetation or grass cover more effective at reducing catchment N and P exports to waterways. To address this we investigated the relative importance of vegetation type, hydrologic and soil microbial processes on N and P losses from soil to a stream. The study involved the analysis of data from two soil microcosm experiments, and a field case study. We found P leaching loss from riparian zones depended significantly on vegetation type (woody vs. grass cover), with lower P exported from wooded riparian zones, irrespective of the scale of rainfall. For N leaching losses, the scale of rainfall had an effect. During high rainfall, vegetation type had a major effect on N leaching loss, with lower N exported from grassed verses wooded riparian zones. However, under low rainfall conditions, soil type and soil C and N stores, potential indicators of soil microbial activity, rather than vegetation cover, affected N leaching. It is hypothesized that soil microbes were reducing N removal under these conditions. We reason that nitrifiers may have played an important role in soil N cycling, as increased soil ammonium had a strong positive effect on nitrate leaching loads, mediated through soil nitrate stores. Whereas, N immobilization, via incorporation into microbial biomass, and denitrification processes appeared to be limited by C availability, with increased C associated with reduced N leaching. Overall, this study identified that N leaching losses from riparian zones appeared to be affected by two different processes, vegetative uptake and soil microbial processes, the relative importance of which was driven by hydrological conditions.
农业活动会在集水区中造成过多的营养负荷进入水道。集水区的氮（N）和磷（P）流动可能会被河岸植被拦截和吸收。虽然先前的研究表明木本植被更有利于减少 P 负荷，但问题仍然存在：木本植被还是草覆盖更能有效地减少集水区 N 和 P 向水道的输出。为了解决这个问题，我们调查了植被类型、水文和土壤微生物过程对土壤向溪流中 N 和 P 流失的相对重要性。该研究涉及对两个土壤微宇宙实验和一个野外案例研究的数据进行分析。我们发现，河岸带的 P 淋溶损失显著依赖于植被类型（木本与草覆盖），无论降雨量大小，林地河岸带的 P 输出量都较低。对于 N 的淋溶损失，降雨量的规模有影响。在强降雨期间，植被类型对 N 淋溶损失有主要影响，草地河岸带的 N 输出量低于林地河岸带。然而，在低降雨条件下，土壤类型和土壤 C 和 N 储量，即土壤微生物活性的潜在指标，而不是植被覆盖，影响了 N 的淋溶。据推测，在这些条件下，土壤微生物会减少 N 的去除。我们推断，硝化作用可能在土壤 N 循环中发挥了重要作用，因为土壤铵增加对硝酸盐淋溶负荷有很强的积极影响，这是通过土壤硝酸盐储量介导的。而氮固定，通过微生物生物量的掺入和反硝化过程，似乎受到 C 可用性的限制，随着 C 的增加，N 的淋溶减少。总的来说，本研究表明，河岸带的 N 淋溶损失似乎受到两种不同过程的影响，即植被吸收和土壤微生物过程，而这些过程的相对重要性是由水文条件驱动的。
