Raposa Kenneth B, Weber Robin L, Ferguson Wenley, Hollister Jeffrey, Rozsa Ron, Maher Nicole, Gettman Alan
Narragansett Bay National Estuarine Research Reserve, Prudence Island RI USA.
Save The Bay, Providence RI USA.
Estuar Coast Shelf Sci. 2019 Dec 31;231. doi: 10.1016/j.ecss.2019.106435.
Drainage enhancement (e.g., ditch digging, open-marsh water management, runnelling) has long been used to reduce tidal marsh soil waterlogging and surface ponding to promote salt hay production and mosquito control. Now it is also being used as a tool to enhance marsh resilience to sea-level rise despite a lack of studies that evaluate its effectiveness as an intervention approach. We therefore conducted a controlled field experiment to evaluate short-term responses to drainage enhancement of a Rhode Island (USA) salt marsh. Drainage enhancement elicited rapid physical changes in portions of the marsh including declines in water levels and marsh elevation, but the biological components examined (e.g., vegetation and bird community composition) were largely unaffected. In two of the four areas monitored, marsh surface inundation duration declined from > 75% to 3-10% and low water levels dropped by 20 cm. Mean annual marsh surface elevation in monitoring plots increased 5 mm one year after drainage enhancement but dropped to 11 mm below initial conditions after three years. The decline in elevation varied among habitats, with the greatest decline (18 mm) found in areas dominated by and/or bare ground. Vegetation community composition and % cover and heights of dominant species were unchanged, but areas that were initially bare had fully revegetated after three years. Drainage enhancement also had no effects on bird community composition or marsh sparrow ( spp.) density. Our study provides evidence that drainage enhancement can relieve waterlogging and some of its impacts without any apparent adverse effects on the composition and abundance of existing vegetation and bird communities. At the same time, it can induce a loss of marsh platform elevation that has the potential to offset declining water levels and inhibit high marsh enhancement. Finally, unanticipated findings from our study provide evidence that the effects of larger-scale drivers such as sea-level rise may predominate over localized responses to drainage enhancement itself.
长期以来，排水增强措施（如挖沟渠、开放式沼泽水管理、挖掘排水渠道）一直被用于减少潮汐沼泽土壤的涝渍和地表积水，以促进盐沼干草生产和控制蚊虫。尽管缺乏评估其作为一种干预方法有效性的研究，但现在它也被用作增强沼泽对海平面上升适应能力的一种手段。因此，我们进行了一项对照田间试验，以评估美国罗德岛州一个盐沼对排水增强措施的短期反应。排水增强措施使沼泽部分区域迅速发生物理变化，包括水位下降和沼泽海拔降低，但所检测的生物成分（如植被和鸟类群落组成）基本未受影响。在监测的四个区域中的两个区域，沼泽表面淹没持续时间从>75%降至3 - 10%，低水位下降了20厘米。排水增强措施实施一年后，监测地块的年平均沼泽表面海拔升高了5毫米，但三年后降至初始条件以下11毫米。海拔下降在不同栖息地有所不同，在以[此处原文缺失相关内容]和/或裸地为主的区域下降最大（18毫米）。植被群落组成、优势物种的覆盖百分比和高度没有变化，但最初为裸地的区域三年后已完全重新植被化。排水增强措施对鸟类群落组成或沼泽麻雀（[此处原文缺失相关物种学名]）密度也没有影响。我们的研究表明，排水增强措施可以缓解涝渍及其一些影响，而对现有植被和鸟类群落的组成及丰度没有任何明显的不利影响。同时，它可能导致沼泽平台海拔降低，这有可能抵消水位下降并抑制高沼泽的增强。最后，我们研究中的意外发现表明，海平面上升等大规模驱动因素的影响可能超过对排水增强措施本身的局部反应。
