Department of Biological Sciences, The University of Alabama, Tuscaloosa, Alabama, USA.
The Jones Center at Ichauway, Newton, Georgia, USA.
Ecol Appl. 2023 Jun;33(4):e2842. doi: 10.1002/eap.2842. Epub 2023 Apr 5.
The interaction of climate change and increasing anthropogenic water withdrawals is anticipated to alter surface water availability and the transport of carbon (C), nitrogen (N), and phosphorus (P) in river networks. But how changes to river flow will alter the balance, or stoichiometry, of these fluxes is unknown. The Lower Flint River Basin (LFRB) is part of an interstate watershed relied upon by several million people for diverse ecosystem services, including seasonal crop irrigation, municipal drinking water access, and public recreation. Recently, increased water demand compounded with intensified droughts have caused historically perennial streams in the LFRB to cease flowing, increasing ecosystem vulnerability. Our objectives were to quantify how riverine dissolved C:N:P varies spatially and seasonally and determine how monthly stoichiometric fluxes varied with overall water availability in a major tributary of LFRB. We used a long-term record (21-29 years) of solute water chemistry (dissolved organic carbon, nitrate/nitrite, ammonia, and soluble reactive phosphorus) paired with long-term stream discharge data across six sites within a single LFRB watershed. We found spatial and seasonal differences in soluble nutrient concentrations and stoichiometry attributable to groundwater connections, the presence of a major floodplain wetland, and flow conditions. Further, we showed that water availability, as indicated by the Palmer Drought Severity Index (PDSI), strongly predicted stoichiometry with generally lower C:N and C:P and higher N:P fluxes during periods of low water availability (PDSI < -4). These patterns suggest there may be long-term and significant changes to stream ecosystem function as water availability is being dramatically altered by human demand with consequential impacts on solute transport, in-stream processing, and stoichiometric ratios.
预计气候变化和人为增加取水量的相互作用将改变地表水的可利用性以及河流网络中碳（C）、氮（N）和磷（P）的输送。但是，河流流量的变化将如何改变这些通量的平衡或化学计量，目前尚不清楚。下弗林特河流域（LFRB）是一个州际流域的一部分，为数百万依赖于多种生态系统服务的人提供服务，包括季节性作物灌溉、城市饮用水供应和公共娱乐。最近，用水量的增加加上干旱的加剧，导致 LFRB 中的历史上常年溪流停止流动，增加了生态系统的脆弱性。我们的目标是量化河流溶解 C：N：P 如何在空间和季节上变化，并确定在 LFRB 的一条主要支流中，每月化学计量通量如何随总水量变化而变化。我们使用了长期记录（21-29 年）的溶质水化学（溶解有机碳、硝酸盐/亚硝酸盐、氨和可溶解反应性磷）以及 LFRB 流域内六个地点的长期流量数据。我们发现，由于地下水连接、主要洪泛区湿地的存在和流量条件，可溶性养分浓度和化学计量存在空间和季节性差异。此外，我们表明，水的可用性，如帕尔默干旱严重程度指数（PDSI）所表示的那样，强烈预测了化学计量，通常在低水可用性期间（PDSI < -4），C：N 和 C：P 较低，N：P 通量较高。这些模式表明，随着人类需求极大地改变了水的可用性，对溶质输送、溪流中的处理和化学计量比产生了重大影响，溪流生态系统功能可能会发生长期而重大的变化。
