Elevated Nitrate Preference Over Ammonium in Aquatic Plants by Nitrogen Loadings in a City River

Abstract

Nitrogen (N) discharged from domestic sewage has long deteriorated the water quality of urban rivers and caused the eutrophication of downstream aquatic ecosystems (Hobbie et al., 2017). This is particularly severe in many developing cities and countries because of their low rates of wastewater treatment (Cloern et al., 2002). Anthropogenic nitrogen (N) pollutants discharged into urban rivers would significantly change concentrations and proportions of ammonium (NH 4 + ) and nitrate (NO 3 − ), which are important nitrogen (N) sources for aquatic biota (Anisfeld et al., 2007;Mayer et al., 2002). In river ecosystems, the assimilation of ammonium (NH 4 + ) and nitrate (NO 3 − ) by aquatic plants plays a vital role in retaining or removing anthropogenic N pollutants and regulating river primary productivity and ecological functions (Howarth et al., 2011;Miyajima et al., 2009;Peipoch et al., 2014). Within the framework of river N biogeochemistry, relatively more studies have been conducted on river N chemistry and microbial processes with less on plant N-use processes.Aquatic plants are diverse in species and rely on ammonium (NH 4 + ) and nitrate (NO 3 − ) as dominant N sources (Adamec, 2010;Schmidt et al., 2018). Physiological indices (e.g., nutrient concentrations, enzyme activities, and isotopic compositions) of aquatic plants have been measured to indicate river N pollution (Dailer et al., 2010;Schmidt et al., 2018). Total N (TN) contents in aquatic plants have been reported to indicate the elevated N availability or N loadings in river water (Baker et al., 2010;Benson et al., 2008). However, how plant Total N (TN) contents respond to river N loadings remains uncertain for two major reasons. First, plants often differ in N-uptake abilities, while the variability of Total N (TN) contents among different river plants and their sensitivity

The Possible Use of Stable Carbon and Nitrogen Isotope Signal and Spectral Analysis to Identify Habitat Condition of Aquatic Plants

“…Similarly, significantly higher δ 15 N ORG values were obtained in rivers compared to those in lakes for submerged aquatic macrophytes such as Potamogeton crispus L., Potamogeton perfoliatus L., and Stuckenia pectinata (L.) Börner [43]. The δ 15 N ORG values of E. canadensis and three other aquatic plant species in rivers align with the findings of Guo et al [47], who conducted research on the heavily nitrogen-burdened Nanming River in China, originating from anthropogenic sources. Moreover, the lower values of δ 15 N ORG values for E. canadensis are in line with those reported in the literature, following a similar range (i.e., 1.3 to 4.8‰) [19,22,42], which are more characteristic of not highly disturbed, closed lakes ecosystems.…”