Trentman Matt T, Tank Jennifer L, Shepherd Heather A M, Marrs Allyson J, Welsh Jonathan R, Goodson Holly V
Department of Biological Sciences, University of Notre Dame, Notre Dame, IN 46556 USA.
Present Address: University of Montana-Flathead Lake Biological Station, Polson, MT 59860 USA.
Biogeochemistry. 2021;154(3):509-524. doi: 10.1007/s10533-021-00803-w. Epub 2021 May 6.
In freshwater ecosystems, phosphorus (P) is often considered a growth-limiting nutrient. The use of fertilizers on agricultural fields has led to runoff-driven increases in P availability in streams, and the subsequent eutrophication of downstream ecosystems. Isolated storms and periodic streambed dredging are examples of two common disturbances that contribute dissolved and particulate P to agricultural streams, which can be quantified as soluble reactive P (SRP) using the molybdate-blue method on filtered water samples, or total P (TP) measured using digestions on unfiltered water reflecting all forms of P. While SRP is often considered an approximation of bioavailable P (BAP), research has shown that this is not always the case. Current methods used to estimate BAP do not account for the role of biology (e.g., NaOH extractions) or require specialized platforms (e.g., algal bioassays). Here, in addition to routine analysis of SRP and TP, we used a novel yeast-based bioassay with unfiltered sample water to estimate BAP concentrations during two storms (top 80% and > 95% flow quantiles), and downstream of a reach where management-associated dredging disturbed the streambed. We found that the BAP concentrations were often greater than SRP, suggesting that SRP is not fully representative of P bioavailability. The SRP concentrations were similarly elevated during the two storms, but remained consistently low during streambed disturbance. In contrast, turbidity and TP were elevated during all events. The BAP concentrations were significantly related to turbidity during all disturbance events, but with TP only during storms. The novel yeast assay suggests that BAP export can exceed SRP, particularly when streams are not in equilibrium, such as the rising limb of storms or during active dredging.
在淡水生态系统中，磷（P）通常被认为是一种限制生长的营养物质。农田施肥导致径流驱动溪流中磷的可用性增加，进而导致下游生态系统富营养化。孤立的暴雨和定期的河床疏浚是两种常见的干扰因素，它们会将溶解态和颗粒态磷输入农业溪流，对于过滤后的水样，可以使用钼酸蓝法将其量化为可溶性活性磷（SRP），对于未过滤的水样进行消解后测量总磷（TP），以反映所有形式的磷。虽然SRP通常被认为是生物可利用磷（BAP）的近似值，但研究表明情况并非总是如此。目前用于估计BAP的方法没有考虑生物学作用（例如氢氧化钠提取法），或者需要专门的平台（例如藻类生物测定法）。在这里，除了对SRP和TP进行常规分析外，我们使用一种基于新型酵母的生物测定法，对未过滤的水样进行分析，以估计两次暴雨期间（流量分位数前80%和>95%）以及一段河床因管理相关疏浚而受到干扰的河段下游的BAP浓度。我们发现，BAP浓度通常高于SRP，这表明SRP不能完全代表磷的生物有效性。两次暴雨期间SRP浓度同样升高，但在河床扰动期间一直保持在低水平。相比之下，所有事件期间浊度和TP均升高。在所有干扰事件中，BAP浓度与浊度显著相关，但仅在暴雨期间与TP显著相关。这种新型酵母测定法表明，BAP的输出量可能超过SRP，特别是当溪流处于非平衡状态时，例如暴雨上升阶段或积极疏浚期间。
