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素。在农田使用化肥导致径流驱动的河流中磷的可用性增加，以及随后的下游生态系统富营养化。孤立的风暴和周期性的河床疏浚是两种常见扰动的例子，它们对农业溪流产生溶解性和颗粒性 P，可以使用过滤水样的钼酸盐蓝法将其量化为可溶性活性 P (SRP)，或总 P (TP)使用反映所有形式 P 的未过滤水的消化来测量。虽然 SRP 通常被认为是生物可利用 P (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的作用（例如，NaOH 提取）或需要专门的平台（例如，藻类生物测定）。在这里，除了 SRP 和 TP 的常规分析外，我们还使用了一种新的基于酵母的生物测定法，使用未经过滤的水样来估计两次风暴（前 80% 和 > 95% 流量分位数）期间以及管理区域下游的 BAP 浓度相关的疏浚扰乱了河床。我们发现 BAP 浓度通常高于 SRP，这表明 SRP 不能完全代表 P 的生物利用度。SRP 浓度在两次风暴期间同样升高，但在河床扰动期间始终保持低水平。相比之下，浊度和 TP 在所有事件中均升高。在所有扰动事件期间，BAP 浓度与浊度显着相关，但仅在风暴期间与 TP 相关。