Spartina alterniflora has widely invaded the saltmarshes of the Yangtze River Estuary and brought negative effects to the ecosystem. Remote sensing technique has recently been used to monitor its distribution, but the similar morphology and canopy structure among S. alterniflora and its neighbor species make it difficult even with high-resolution images. Nevertheless, these species have divergence on phenological stages throughout the year, which cause distinguishing spectral characteristics among them and provide opportunities for discrimination. The field spectra of the S. alterniflora community as well as its major victims, native Phragmites australis and Scirpus mariqueter, were measured in 2009 and 2010 at multi-phenological stages in the Yangtze River Estuary, aiming to find the most appropriate periods for mapping S. alterniflora. Collected spectral data were analyzed separately for every stage firstly by re-sampling reflectance curves into continued 5-nm-wide hyper-spectral bands and then by re-sampling into broad multi-spectral bands – the same as the band ranges of the TM sensor, as well as calculating commonly used vegetation indices. The results showed that differences among saltmarsh communities’ spectral characteristics were affected by their phenological stages. The germination and early vegetative growth stage and the flowering stage were probably the best timings to identify S. alterniflora. Vegetation indices like NDVI, ANVI, VNVI, and RVI are likely to enhance spectral separability and also make it possible to discriminate S. alterniflora at its withering stage.

Tidal activity is a major factor determining the distribution of plant species and ecosystem functions, including carbon fluxes. To explore the spatial variations of net ecosystem CO2 exchange (NEE) and related regulatory mechanisms along the tidal inundation gradient (i.e., middle or low tidal flat), an NEE estimation model using piecewise regression analysis was developed by coupling the Moderate Resolution Imaging Spectroradiometer (MODIS)‐ and tower‐based measurements. The results showed that our model achieved an adequate NEE estimation (slope = 0.70, R2 = 0.78). Then the model was applied to estimate NEE variation along a transect with a tidal inundation gradient. The average NEE was −1.75 g C m−2 d−1, varying from −2.02 g C m−2 d−1 to −1.42 g C m−2 d−1 from island‐ to oceanside. Generally, our empirical model captured the spatiotemporal patterns of NEE and the variation of the regulatory factors along the gradient. The sensitivity analysis of various regulatory variables showed that the variations of NEE near the islandside were primarily caused by seasonal shift and annual cycle of vegetation, whereas at the oceanside, NEE was more influenced by tidal activity with no clear phenological influence. In the middle area, NEE seemed to be subjected to both phenological changes of vegetation and tidal activity. In conclusion, this study illustrates that the estimates derived from MODIS‐ and tower‐based flux data are reliable for quantifying the spatiotemporal variations of NEE and reflecting the effect of tidal activity on NEE.

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Contamination of heavy metals would threaten the water and soil resources; phytoremediation can be potentially used to remediate metal contaminated sites. We constructed the Phragmites australis artificial floating wetlands outside the Qingcaosha Reservoir in the Yangtze Estuary. Water characteristic variables were measured in situ by using YSI Professional Pro Meter. Four heavy metals (copper, zinc, lead, and chromium) in both water and plant tissues were determined. Four heavy metals in estuary water were as follows: 0.03 mg/Kg, 0.016 mg/Kg, 0.0015 mg/Kg, and 0.004 mg/Kg. These heavy metals were largely retained in the belowground tissues of P. australis. The bioaccumulation (BAF) and translation factor (TF) value of four heavy metals were affected by the salinity, temperature, and dissolved oxygen. The highest BAF of each metal calculated was as follows: Cr (0.091 in winter) > Cu (0.054 in autumn) > Pb (0.016 in summer) > Zn (0.011 in summer). Highest root-rhizome TF values were recorded for four metals: 6.450 for Cu in autumn, 2.895 for Zn in summer, 7.031 for Pb in autumn, and 2.012 for Cr in autumn. This indicates that the P. australis AFW has potential to be used to protect the water of Qingcaosha Reservoir from heavy metal contamination.