Algal blooms in Lake Erie have worsened in recent decades and are driven by diffuse export of phosphorus (P) from a large stream network that drains predominately agricultural land. Given the diffuse nature of nonpoint source pollution, best management practices (BMPs) must target areas where P levels are high. This requires long-term watershed-wide monitoring programs that do not currently exist in many jurisdictions. Instead of conventional nutrient analyses that can be costly and time-consuming, we propose the use of periphyton biomass as a bioindicator of trophic status in low-order streams, where agricultural runoff first enters watercourses. We carried out 2-week in-stream bioassays to measure periphytic algal biomass (CHL_peri) in 19 low-order streams in southern Ontario across an agricultural gradient (8 % to 89 %). CHL_peri was significantly related to total P (TP) concentration (r² = 0.46; p = 0.0015) but was not significantly related to soluble reactive P (SRP). A relationship between TP and turbidity (r² = 0.52; p = 0.0007) is consistent with previous observations of increasing SRP uptake in streams draining agriculturally-dominated landscapes. Stream temperature (°C) was correlated with the proportion of agricultural land (R = 0.55; p = 0.019) and may reflect the warming effects of the sun in unshaded agricultural streams. This method involving substrate rods (Peristix) is cost-effective, requires very little training, and yielded data that were significantly related to TP concentrations in agricultural streams. We recommend that environmental agencies and landowners use this bioassay to identify areas for implementing BMPs to reduce P export from the Lake Erie watershed.

近几十年来，伊利湖的藻华现象恶化，这是由于磷（P）从主要排干农业用地的大型河流网络扩散输出所致。鉴于非点源污染的扩散性质，最佳管理实践 (BMP) 必须针对 P 水平高的地区。这需要目前在许多司法管辖区不存在的长期流域范围监测计划。我们建议使用附生生物量作为低级河流中营养状况的生物指标，而不是昂贵且耗时的传统营养分析，在那里农业径流首先进入水道。我们进行了为期 2 周的流式生物测定以测量附生藻类生物量 (CHL _peri) 在安大略省南部的 19 条低阶河流中跨越农业梯度（8% 到 89%）。CHL _peri与总磷 (TP) 浓度显着相关 ( r ²  = 0.46; p  = 0.0015)，但与可溶性活性磷 (SRP) 无显着相关。TP 和浊度之间的关系 ( r ²  = 0.52; p  = 0.0007) 与先前观察到的在以农业为主的景观排水的河流中 SRP 吸收增加的观察结果一致。河流温度 (°C) 与农业用地比例相关 ( R  = 0.55; p = 0.019) 并且可能反映太阳在无阴影的农业溪流中的变暖效应。这种涉及基质棒 (Peristix) 的方法具有成本效益，需要很少的培训，并且产生的数据与农业河流中的 TP 浓度显着相关。我们建议环境机构和土地所有者使用这种生物测定来确定实施 BMP 的区域，以减少伊利湖流域的磷出口。