Isik Sabahattin, Haas Henrique, Kalin Latif, Hantush Mohamed M, Nietch Christopher
College of Forestry, Wildlife and Environment, Auburn University, 602 Duncan Drive, Auburn, AL 36849, USA.
U.S. EPA Center for Environmental Solutions and Emergency Response, 26 West Martin Luther King Dr., Cincinnati, OH 45268, USA.
Water (Basel). 2023 Jul 25;15(15):1-22. doi: 10.3390/w15152687.
Headwater streams drain over 70% of the land in the United States with headwater wetlands covering 6.59 million hectares. These ecosystems are important landscape features in the southeast United States, with underlying effects on ecosystem health, water yield, nutrient cycling, biodiversity, and water quality. However, little is known about the relationship between headwater wetlands' nutrient function (i.e., nutrient load removal and removal efficiency ) and their physical characteristics. Here, we investigate this relationship for 44 headwater wetlands located within the Upper Fish River watershed (UFRW) in coastal Alabama. To accomplish this objective, we apply the process-based watershed model SWAT (Soil and Water Assessment Tool) to generate flow and nutrient loadings to each study wetland and subsequently quantify the wetland-level nutrient removal efficiencies using the process-based wetland model WetQual. Results show that the calculated removal efficiencies of the headwater wetlands in the UFRW are 75-84% and 27-35% for nitrate and phosphate , respectively. The calculated nutrient load removals are highly correlated with the input loads, and the estimated shows a significant decreasing trend with increased input loadings. The relationship between and wetland physical characteristics such as area, volume, and residence time is statistically insignificant ( > 0.05), while for , the correlation is positive and statistically significant ( < 0.05). On the other hand, flashiness (flow pulsing) and baseflow index (fraction of inflow that is coming from baseflow) have a strong effect on removal but not on removal. Modeling results and statistical analysis point toward denitrification and plant uptake as major removal mechanisms, whereas plant uptake, diffusion, and settling of sediment-bound P were the main mechanisms for removal. Additionally, the computed nutrient is higher during the driest year of the simulated period compared to during the wettest year. Our findings are in line with global-level studies and offer new insights into wetland physical characteristics affecting nutrient removal efficiency and the importance of headwater wetlands in mitigating water quality deterioration in coastal areas. The regression relationships for and load removals in the selected 44 wetlands are then used to extrapolate nutrient load removals to 348 unmodeled non-riverine and non-riparian wetlands in the UFRW (41% of UFRW drains to them). Results show that these wetlands remove 51-61% of the and 5-10% of the loading they receive from their respective drainage areas. Due to geographical proximity and physiographic similarity, these results can be scaled up to the coastal plains of Alabama and Northwest Florida.
源头溪流流经美国70%以上的土地，源头湿地面积达659万公顷。这些生态系统是美国东南部重要的景观特征，对生态系统健康、产水量、养分循环、生物多样性和水质有着潜在影响。然而，关于源头湿地的养分功能（即养分负荷去除和去除效率）与其物理特征之间的关系，人们了解甚少。在此，我们对位于阿拉巴马州沿海的上鱼河流域（UFRW）内的44个源头湿地的这种关系进行了研究。为实现这一目标，我们应用基于过程的流域模型SWAT（土壤和水评估工具）来生成每个研究湿地的流量和养分负荷，随后使用基于过程的湿地模型WetQual来量化湿地水平的养分去除效率。结果表明，UFRW中源头湿地对硝酸盐和磷酸盐的计算去除效率分别为75 - 84%和27 - 35%。计算得出的养分负荷去除量与输入负荷高度相关，并且估计值显示随着输入负荷的增加呈显著下降趋势。去除效率与湿地面积、体积和停留时间等物理特征之间的关系在统计学上不显著（P > 0.05），而对于磷酸盐去除效率，相关性为正且在统计学上显著（P < 0.05）。另一方面，流量变率（流量脉冲）和基流指数（来自基流的入流比例）对硝酸盐去除有强烈影响，但对磷酸盐去除没有影响。模型结果和统计分析表明反硝化作用和植物吸收是硝酸盐去除的主要机制，而植物吸收、扩散以及沉积物结合磷的沉降是磷酸盐去除的主要机制。此外，与模拟期内最湿润年份相比，计算得出的养分去除量在最干旱年份更高。我们的研究结果与全球层面的研究一致，并为影响养分去除效率的湿地物理特征以及源头湿地在减轻沿海地区水质恶化方面的重要性提供了新的见解。然后，利用所选44个湿地中硝酸盐和磷酸盐负荷去除的回归关系，将养分负荷去除量外推至UFRW中348个未建模的非河流和非河岸湿地（UFRW的41%的排水流入这些湿地）。结果表明，这些湿地去除了它们从各自排水区域接收的硝酸盐负荷的51 - 61%和磷酸盐负荷的5 - 10%。由于地理位置接近和地貌相似，这些结果可以扩大到阿拉巴马州沿海平原和佛罗里达州西北部。
