Transport of N and P in U.S. streams and rivers differs with land use and between dissolved and particulate forms.
Transport of N and P in U.S. streams and rivers differs with land use and between dissolved and particulate forms.
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DOI：
10.1002/eap.2130
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发表时间：
2020-09
期刊：
影响因子：
--
通讯作者：
Kominoski JS
中科院分区：
文献类型：
--
作者：
Manning DWP;Rosemond AD;Benstead JP;Bumpers PM;Kominoski JS
我们使用最近发表的美国溪流氮（N）和磷（P）浓度的开放获取数据集来测试流域土地利用是否对N和P浓度产生差异性影响，包括溶解和颗粒营养成分的相对可用性。我们检验了以下假设：美国溪流和河流中的N和P浓度和摩尔比反映了三种主要土地利用类型（农业、城市和森林）的不同养分输入。我们还测试了溶解无机营养盐和悬浮颗粒营养成分之间的差异，以推断空间和时间尺度上的来源和潜在的处理机制。观察到的总N和P浓度往往超过报告的阈值，底栖藻类（58，57%的报告值，分别），大型无脊椎动物（39%的TN和TP），鱼类（41，37%，分别）的结构变化。溶解的N和P的浓度超过阈值浓度已知刺激底栖藻类生长（85，87%，分别），和有机质分解率（94，58%，分别）。N和P的浓度，总的和溶解的N：P的比例，更高的农业和城市比林地覆盖的溪流和河流。与农业和城市土地利用的营养盐浓度升高的模式是弱颗粒组分。颗粒物中N含量随农业和城市化程度的提高而略有下降，而颗粒物中P含量与土地利用无关。微粒N：P相对恒定（四分位数间距= 2-7），与DIN：DIP的变化无关（四分位数间距= 22-152）。溶解的，但不是颗粒，N：P比是随时间变化的。恒定的颗粒N：P跨越陡峭的DIN：DIP梯度在空间和时间表明，在美国流域的颗粒物的化学计量最有可能是由外部或物理化学instruments因素，而不是由生物处理流。我们的研究结果表明，大多数美国溪流和河流的N和P的浓度超过那些被认为是保护生态完整性，保留溶解N的效率低于P，这是保留比例更多的颗粒，从而运输和出口高N：P溪流下游生态系统在大陆规模。
We used a recently published, open‐access data set of U.S. streamwater nitrogen (N) and phosphorus (P) concentrations to test whether watershed land use differentially influences N and P concentrations, including the relative availability of dissolved and particulate nutrient fractions. We tested the hypothesis that N and P concentrations and molar ratios in streams and rivers of the United States reflect differing nutrient inputs from three dominant land‐use types (agricultural, urban and forested). We also tested for differences between dissolved inorganic nutrients and suspended particulate nutrient fractions to infer sources and potential processing mechanisms across spatial and temporal scales. Observed total N and P concentrations often exceeded reported thresholds for structural changes to benthic algae (58, 57% of reported values, respectively), macroinvertebrates (39% for TN and TP), and fish (41, 37%, respectively). The majority of dissolved N and P concentrations exceeded threshold concentrations known to stimulate benthic algal growth (85, 87%, respectively), and organic matter breakdown rates (94, 58%, respectively). Concentrations of both N and P, and total and dissolved N:P ratios, were higher in streams and rivers with more agricultural and urban than forested land cover. The pattern of elevated nutrient concentrations with agricultural and urban land use was weaker for particulate fractions. The % N contained in particles decreased slightly with higher agriculture and urbanization, whereas % P in particles was unrelated to land use. Particulate N:P was relatively constant (interquartile range = 2–7) and independent of variation in DIN:DIP (interquartile range = 22–152). Dissolved, but not particulate, N:P ratios were temporally variable. Constant particulate N:P across steep DIN:DIP gradients in both space and time suggests that the stoichiometry of particulates across U.S. watersheds is most likely controlled either by external or by physicochemical instream factors, rather than by biological processing within streams. Our findings suggest that most U.S. streams and rivers have concentrations of N and P exceeding those considered protective of ecological integrity, retain dissolved N less efficiently than P, which is retained proportionally more in particles, and thus transport and export high N:P streamwater to downstream ecosystems on a continental scale.
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