Varying Stable Nitrogen Isotope Ratios of Different Coastal Marsh Plants and Their Relationships with Wastewater Nitrogen and Land Use in New England, USA

The stable nitrogen isotope ratios of some biota have been used as indicators of sources of anthropogenic nitrogen. In this study the relationships of the stable nitrogen isotope ratios of marsh plants, Iva frutescens (L.), Phragmites australis (Cav.) Trin ex Steud, Spartina patens (Ait.) Muhl, Spartina alterniflora Loisel, Ulva lactuca (L.), and Enteromorpha intestinalis (L.) with wastewater nitrogen and land development in New England are described. Five of the six plant species (all but U. lactuca) showed significant relationships of increasing δ ¹⁵N values with increasing wastewater nitrogen. There was a significant (P < 0.0001) downward shift in the δ ¹⁵N of S. patens (6.0 ± 0.48‰) which is mycorrhizal compared with S. alterniflora (8.5 ± 0.41‰). The downward shift in δ ¹⁵N may be caused by the assimilation of fixed nitrogen in the roots of S. patens. P. australis within sites had wide ranges of δ ¹⁵N values, evidently influenced by the type of shoreline development or buffer at the upland border. In residential areas, the presence of a vegetated buffer (n = 24 locations) significantly (P < 0.001) reduced the δ ¹⁵N (mean = 7.4 ± 0.43‰) of the P. australis compared to stands where there was no buffer (mean = 10.9 ± 1.0‰; n = 15). Among the plant species, I. frutescens located near the upland border showed the most significant (R ² = 0.64; P = 0.006) inverse relationship with the percent agricultural land in the watershed. The δ ¹⁵N of P. australis and I. frustescens is apparently an indicator of local inputs near the upland border, while the δ ¹⁵N of Spartina relates with the integrated, watershed-sea nitrogen inputs.     

Interaction of leaves and roots of Ruppia maritima in the uptake of phosphate,ammonia and nitrate

Leafy shoots of Ruppia maritima were incubated in two-compartment chambers, with the roots in one compartment and the leaves in the other. Rates of phosphate and ammonia uptake were compared when roots and leaves were supplied with these nutrients separately and simultaneously. Uptake of phosphate and ammonia by leaves was reduced when these nutrients were supplied to the roots, but uptake by roots was not affected by the availability of these nutrients to leaves. This response suggested root-to-shoot translocation predominated. V_max for leaf uptake of phosphate was decreased by 31% when roots were supplied with phosphate simultaneously. Leaf uptake of ammonia was not affected by the availability of ammonia to roots unless the plants were starved for nitrogen. V_max for plants starved for nitrogen was two times greater than for unstarved plants. When roots and leaves of starved plants were exposed simultaneously to ammonia, V_max for ammonia uptake by leaves did not change but K_s increased by 97% to a value similar to that for unstarved plants. Ammonia supplied to leaves or roots inhibited nitrate uptake by leaves by an average of 52%. Ammonia supplied to leaves, however, had no influence on the rate of nitrate uptake by roots.Contribution No. 579 of the Environmental Research Laboratory, US Environmental Protection Agency. Use of product names does not imply endorsement by USEPA     

Leaf-root interaction in the uptake of ammonia by Zostera marina

The effect of ammonia uptake by one organ on the uptake of that nutrient by another organ was determined for the seagrass Zostera marina L. under laboratory conditions. Leafy shoots with roots attached were incubated in two-compartment chambers, with the roots in one compartment and the leaves in the other. Rates of ammonia uptake were compared when roots and leaves were supplied with ammonia separately and simultaneously. Root uptake of ammonia had no influence on the rate of ammonia uptake by leaves. However, leaf uptake of ammonia caused a 77% decrease in the maximum rate of ammonia uptake by roots. The K_s values for ammonia uptake by leaves and roots were 9.2 and 104 M respectively, showing that leaves had a greater affinity for ammonia than roots.     

毒代动力学一毒效动力学(Toxicokinetic-Toxicodynamic, Tk-Td)和种群模型联用评价浓度随时间变化的农药的水生态风险

利用种群模型评价农药暴露时间序列的方法与现有常用的风险评价方法进行了比较。美国环境保护局农药项目办公室(The US Environmental Protection Agency’s Office of Pesticide Programs)在近30年对水生生物农药日暴露值建立了模型，但并未对这些信息进行充分的利用。我们利用糠虾(Americamysis bahia)毒性数据和种群数量统计数据推演了毒代动力学一毒效动力学(Toxicokinetic-Toxicodynamic, Tk-Td)与一系列矩阵种群模型联用的数值。糠虾是一种沿岸浅海底的小型甲壳动物，通常用于常规毒性测试中。我们展示了这种联用方法如何仅用现有的标准常规毒性数据来优化已有的风险评价方法。我们创建了几种暴露场景，每种场景在基于生物的传统方法中有着相同的初始风险表征特征，而种群模型方法中则显示出不同的风险水平。这种TK-TD与种群模型联用的方法可以对不同的急性和慢性毒性数据的场景区分出不同的风险水平，而传统的风险评价方法则做不到。这种联用方法在风险评价方面独具优势，特别是针对污染物的暴露浓度随时间变化的情况。 精选自Glen Thursby, Keith Sappington, Matthew Etterson. Coupling Toxicokinetic-Toxicodynamic (Tk-Td) and Population Models for Assessing Aquatic Ecological Risks to Time-Varying Pesticide Exposures. Environmental Toxicology and Chemistry,2018,37:2633-2644.
详情请见 https://doi.org/10.1002/etc.4224