## 4 Discussion  
The results showed that our model reflected the flow patterns and water quality in the Sanyang wetland well. In contrast to the traditional field monitoring method, our model showed a much longer time scale as well as more comprehensive spatial scale flow and water quality information, which can help managers better understand the wetland conditions and design better and more economical restoration schemes [24; 25]. The flow velocity was low in the Sanyang wetland, indicating that the residence time in the wetland is long. As previous studies have shown, hydrodynamic characteristics are essential factors in the transport of pollutants, and less water exchange and long residence times increase the risk of eutrophication [26; 27; 28]. The main reason for the low flow and circulation in the wetland is that the river network is densely interconnected by channels  
Figure 10: Distribution of total phosphorus (TP) in the Sanyang wetland during (**a**) the dry period (October 16 to April 15); (**b**) the peak rain season (April 16 to July 15); and (**c**) the flood period (July 16 to October 15) in 2016.  
surrounding the numerous islands. Moreover, the topography is relatively flat, and the wind in this area is not strong [29]. Water quality is an important factor in managing wetlands. Our results indicated that the water quality status in the Sanyang wetland is serious, which corroborates previous findings that the water quality in the study area is extremely poor [30]. This suggests that N and P sources from inlet rivers need to be better controlled. Both NH\({}_{3}\)-N and TP concentrations in the Sanyang wetland were highest in the northwest and lowest in the east, mainly because the predominant water supply comes from the Wernuitang River network to the west [31]. The Wernuitang River causes the wetland water body to become black and emit a strong, foul odor [17]. N and P concentrations gradually decreased in the inner areas of the wetland, possibly because the wetlands are able to remove some pollutants from the flow, which is similar to a pattern documented in China's Taihu Lake [32]. The water quality in the wetland was poorer in the peak rain season, with increased N and P flow in the wetland, thereby increasing the NH\({}_{3}\)-N and TP concentrations. The NH\({}_{3}\)-N and TP levels in the central part of the wetland were lower, which may have resulted partly from dramatic rainfall over a short period of time diluting the NH\({}_{3}\)-N and TP levels. This result was similar to that of [PERSON] et al. [33], who found that copious rainfall played a significant role in improving the water quality of the Wernuitang River by decreasing N and P concentrations. Rainfall can also increase the dissolved oxygen in the water and contribute to reducing pollutant concentrations. Similarly, the NH\({}_{3}\)-N and TP concentrations were lower during the dry season, which might have resulted primarily from lower pollutant levels entering the wetland. The results from our modeling study revealed spatiotemporal variations in the wetland environment. The flow velocity of the wetland was small, and this finding can help managers to select mitigation methods, such as the diversion of water from other rivers or lakes, as has been used in other studies [34; 35; 36; 24; 37]. This approach can increase the water velocity and shorten the water retention time; for example, the studied wetland can be connected with the Ovijang River nearby (Figure 1) to shorten the water retention time [38]. In addition, the spatiotemporal variations in NH\({}_{3}\)-N and TP could indicate where and when some methods should be carried out for improving wetland water quality. We can analyze the hydrodynamic and water quality characteristics of wetlands from the simulation results, and help identify the key causes and factors leading to the pollution. According to the spatiotemporal variation of NH\({}_{3}\)-N and TP, targeted measures can be taken to improve wetland water quality.