Research

INTRODUCTION

Wetlands cover approximately 5–8% of the world’s land area (Mitsch and Gosselink 2007). Wetland ecosystems are globally important because of the ecological services they provide to the planet’s biota (Millennium Ecosystem Assessment 2005, Ramsar Convention Secretariat 2016). Throughout Earth’s history, the planet’s ecosystems responded to climate changes between greenhouse and icehouse conditions (Behrensmeyer et al. 1992, Zalasiewicz and Williams 2021). Davidson (2014) determined that since the 1700s, the long-term loss of wetlands is approximately 55% and it may have been as high as 87%. Climate change will further contribute to wetland loss and the degradation of their ecosystem services, affecting human well-being (Millennium Ecosystem Assessment 2005).

In the past several decades, attention has increased wordwide toward wetland conservation and management (Reis et al. 2017, Xu et al. 2019, Fois et al. 2021, Kingsford et al. 2021). Wetlands have substantial and significant influences on local and regional hydrology and should be considered important elements in the development and implementation of water management and policy strategies (Bullock and Acreman 2003). The periodicity, timing, and regularity of land-surface inundation by water are important factors that help determine the conditions needed for the survival of wetland biota, as well as humans (Rogers and Ralph 2010, Roberts and Marston 2011). Some species of water birds are reliant on wetlands for breeding (Leigh et al. 2010). In Taiwan, wetlands are crucial because they provide important habitat for birds that follow the east Asian-Australasian flyway during the winter (Crook 2021). The management of environmental variables such as water depth, water-level fluctuation, vegetation type, salinity, topography, food type, and accessibility (Ma et al. 2010) for the benefit of migratory birds is becoming increasingly important.

One common technique used to restore wetlands and control water levels is dredging (Gustavson et al. 2008, Bormans et al. 2016, Chen et al. 2018). For instance, dredging was studied in the coastal reservoir in the Brisbane River estuary. Widening the river and control gates improved water flow, regulated water levels, and assisted in floodwater adaptation (Khalil et al. 2020). Other techniques to control the water levels in coastal wetlands are the use of dikes and water gates. Recently, tidal gate management approaches, together with tidal surge fluctuations, are being used to accomplish water management objectives (Kuo and Wang 2018, Vinten et al. 2019, Khalil et al. 2020, Wang et al. 2020, Gaydon et al. 2021, Guiot et al. 2023). Vinten et al. (2019) assessed the potential for hydraulic structure and dredging to manage water inflow and nutrient input into shallow wetlands in Scotland and to promote an adaptive water management strategy. In France, soft modifications and adaptive water gate management strategies were used to meet local water needs and fish passage. The results showed that the influence of ecology, water level, and salt-water intrusion controls all needed to be considered in the water management plan to obtain a water flow regime appropriate for fish passage (Guiot et al. 2023). In Taiwan, the short-term use of water gates was synchronized with tidal cycles to enhance bird habitat, water flow, flood mitigation, and other ecosystem services in the Budai Saltpan Wetlands (Kuo and Wang 2018, Wang et al. 2020), allowing increasing use by water birds by manipulating water depths while maintaining public safety in the surrounding village communities. Stakeholder experiences also demonstrated the importance of considering communities’ local needs in water management. Using a participatory action research program can be vital for effectively communicating the field activities and science to the community and developing effective wetland management strategies (Wang et al. 2018).

The uncertainty in the sustainable ecological, social, and economic use of natural resources is obvious, especially those provided by wetlands, for both survival and climate change considerations. Virji et al. (2019) pointed out that stakeholders need to understand the importance of complex interactions between environmental change and socioeconomic development and be part of the decision-making process. Addressing these needs will require a robust stakeholder engagement program in which elements of sound science and local knowledge are combined to promote opportunities and adaptation to changing environmental conditions. Participatory action research is a qualitative approach that integrates the methods and techniques of observing, documenting, analyzing, and interpreting characteristics, patterns, attributes, and meanings of the human phenomena under study (Gillis and Jackson 2002, MacDonald 2012). The process has been developed and used by planners and scientists in many fields worldwide to address communication problems and provide a format for moving away from top-down decision-making processes (Hester 1985, Allen 2006, Baum et al. 2006, Kindon et al. 2007, Mcnally 2011). Such practices require willingness to participate and to adapt as new information is gathered and analyzed. The inclusion of local communities in environmental management processes is now considered essential by many experts, especially when community members’ livelihoods are interlinked with the land (Nath et al. 2017). Although studies have acknowledged the need to engage stakeholders in wetland management (Tu 1996, Chen and Chyi 2019), experiences of implementing an inclusive methodology to manage coastal wetlands sustainably in a safe and cost-effective manner are still lacking.

Qigu Saltpan, a wetland of national importance, is located in southwestern Taiwan, where flood risk is high and community safety is a priority. Because of the saltpan’s importance, there are many studies have been done to support wetland management, including a long-term (2004–2017) bird census (Wu and Chen 2019), development of water management scenarios (Liao 2019), and a biodiversity assessment of water birds (Chen et al. 2020). However, engaging stakeholders in the decision-making process on the social, economic, and environmental issues has not been fully considered. Here, we tested water management strategies that were needed to maintain the ecological integrity and functions of the Qigu Saltpan Wetland during the dry season and incorporated stakeholder concerns into the remedy. Since the salt industry ceased operations in 2002, the Qigu Saltpan has suffered water shortages during the dry season because of high evaporation rates, little to no natural water input, and no water management plan. Our objective was to engage with local stakeholders and incorporate their knowledge with sound scientific practices that could bridge gaps in water management strategies, improve waterflow with soft infrastructure modifications such as removing culverts, dikes, and dredging, and adapt the existing rules, policies, and ordinances for gate operation while minimizing the risk of flooding to the surrounding communities.

METHODS

Site description

The Qigu Saltpan complex is located in the coastal zone in Tainan City, southwestern Taiwan, and is bordered by highway 61 to the east and Qigu Lagoon to the west. The complex is mostly surrounded by agricultural land, and Qigu was once home to the largest salt industry in Taiwan. After the salt industry was closed in 2002, the open water habitat was left to natural processes and the return of wetland vegetation, and quickly developed into abundant and diverse wetland habitats. The Qigu Saltpan complex has a slope of 1/800 to 1/1000 and is divided into four saltpans: the Fan-shaped, Chingkunshen, Nanyan, and Taiqu Saltpans, using existing infrastructure such as culverts and dikes (Fig. 1). Of these saltpans, only Taiqu Saltpan is under the management of Taijiang National Park.

Taiqu Saltpan is surrounded by dikes and possesses no natural water connectivity. Water Gates 1, 2, 3, and 18 are used to control the water levels in this saltpan (Fig. 1). The five major communities around the saltpans are Chingkunshen, Dingshan, Xiliao, Zhongliao, and Yancheng, with registered populations of 1970, 870, 450, 700, and 430 inhabitants, respectively. Although Qigu Saltpan is a nationally important wetland, designated since 2007, the Conservation and Utilization Plan for the Qigu Saltpan Wetland is still under examination due to development pressure. As a result, maintenance and management of this wetland complex have been neglected.

The lower part of Taiqu Saltpan, approximately 55 ha, was used to evaluate the water intake performance before and after soft modification of the saltpan’s infrastructure. Permission to conduct a small-scale gate operation experiment to develop a wetland management plan was obtained from the National Park as well as the local government Water Bureau. A site elevation map was created using ArcMap coupled with digital elevation model data field measurements that were obtained using a V100 Global Navigation Satellite System Real-time Kinematic system. A total of 805 points were surveyed and interpolated as a digital elevation model with a resolution of 3 m (Fig. 1).

Taiqu Saltpan’s substrate is composed of uncompressed, strongly permeable, and highly saline gravel that is classified as Quaternary Alluvium (Liao 2019). The precipitation data show that the rainy season in the area starts in May and extends to September, and the dry season starts in October and extends to April (Fig. 2). In October to April, the average monthly precipitation is 0.02 m, and from May to September, it is 0.34 m (Central Weather Bureau 2020). A three-year bird survey from 2018 to 2020 from a National Cheng Kung University (2020) report indicate that each saltpan has different environmental characteristics that are preferred by waterbirds of different families for breeding and foraging. In Fan-shaped Saltpan, most waterbirds were from the Ardeidae (egrets and herons) family; in Chingkunshen Saltpan, most were from the Anatidae (ducks, geese, and swans) family; and in Nanyan and Taiqu saltpans, most were from the Scolopacidae (sandpipers) and Charadriidae (plovers) families (Fig. 2; National Cheng Kung University 2020). The majority of birds were observed in Taiqu Saltpan during October to March, which is the dry season, coincident with the timing of bird migration.

Stakeholder involvement

In the past, the data-collection approaches used and the lack of communication by scientists to stakeholders often created an environment of distrust and disempowerment for stakeholders to participate or become engaged in the decision-making process (Wang et al. 2018). In contrast, we conducted participatory action research (Gillis and Jackson 2002, MacDonald 2012) and followed transdisciplinary research principles and processes (Rigolot 2020) by collaborating with stakeholder groups that had a vested interest in Taiqu Saltpan. This non-authoritarian approach allowed us to gather knowledge, analyze data, and develop solutions together with the stakeholders to better manage the complex issues associated with the saltpan.

From 2017 to 2020, we conducted 14 semi-structured interviews with local stakeholders, including seven former salt workers, two water gate operators, one pump operator, and four village leaders. We used both convenience sampling and snowball sampling methods to select interviewees. The interviews were conducted in public places or in the interviewee’s home. The number of interviewees in an interview ranged from one to three. The interviewees responded to our questions and shared their knowledge and experiences of past flooding in the area, local government responses that were implemented to resolve the flooding problems, and assistance they received during flooding events. They also shared the history of the salt industry in their community, saltpan development, how aquaculture became the main industry in the region after the salt industry ended, and technical information such as water flow directions. They showed us the water level “tipping-point”, which is the community’s knowledge of the elevation that the water must reach before the pumps need to be turned on to decrease flood risk in the community. We asked the following questions during interviews.

• What are the current issues you and your community have? Any issues with the saltpan?
• What is the benefit of the saltpan to you? Is there any value?
• What are the visions you have for the future community and saltpan?
• How was the water flowing into the saltpan during the salt industry era?
• This area is near the shore and surrounded by water gates such as Gates 1, 2, 3, and 18. Which gate do you usually use, and what is the purpose?
• Is it possible to drain the water in or out through Gate 1, 2, 3, or 18?
• Do you have any concerns if we open the water gate during the dry season?
• How high of water in the channel can you tolerate? Under what situation would you start the pump machine?
• Has this place ever been flooded? If yes, when, how deep was the flood, and how long does it need until the water recedes?

We also organized six workshops in May 2017, August 2017, October 2017, March 2018, May 2019, and May 2020 to better understand the problems and concerns held by locals. The topics discussed during the workshops were selected based on the information addressed by the local participants during interviews. The goal of the first workshop was to discuss the stakeholder development and vision, and the environmental issues of Taiqu Saltpan. The second workshop focused on specific environmental issues that were identified during the first workshop. The third workshop focused on the unregistered occupancy of the saltpan for fishery purposes and the saltpan’s potential for solar photovoltaic development. The fourth workshop focused on identifying the existing ecological resources, the farming, commercial, and industrial activities in the saltpan, and the effects of installing solar photovoltaic equipment. Ecosystem services and wetland management planning were the topics discussed in the fifth workshop. In the sixth workshop, the discussion focused on the landscape design and vision for Taiqu Saltpan. The workshop size ranged from 10 to 50 people, with participants including government officials, private companies, nongovernmental organzations (NGOs), residents, academics, and college students. During the process, we created opportunities for stakeholders to explain their positions and concerns and contribute their knowledge and ideas in developing a solution together. We shared our proposed management options with their flood concerns addressed in the workshops using visuals such as maps and drawings, and discussed them with all participating stakeholders.

From the communities’ point of view, the value of Taiqu Saltpan is that of a detention pond and it should be dried completely to provide water capacity during the rainy season rather than used as an ecological resource. They also mentioned that Gate 18 was operated every two to three weeks to flush the sewage and gray water that were being discharged and accumulating in the channel. There was a clear message from the community that they would cooperate only if community safety was improved rather than facing water storage in the salt pan. To better address the issues raised, seven informal consultation meetings were held between workshops to clarify potential conflicts and solutions that could be created by implementing gate operation and wetland management plans. For instance, the option of operating Gate 3 (Fig. 1), which connects to the lagoon, could provide more food for the ecosystem and was proposed based on the monitoring and modeling, but the option was rejected by the community because the size of the gate needed and the amount of water discharged were much larger than Gate 18. In addition, most of the waterbirds that use the saltpan prefer shallow-water habitat, but the local Water Bureau tended to dredge the saltpan deeper to improve flood detention. Deeper water would then affect the bird species that currently use the saltpan because the water depths are shallow. Attendance ranged from 10 to 14 people representing national land, landscape and tourism, wetland conservation, energy development, aquaculture, and flood control, as well as village leaders, residents, and gate operators.

A common goal that emerged from the interviews, workshops, and consultations was recognizing the need to control the water level in the saltpan, and that it could be accomplished by operating the gates during the dry season. The residents shared their past flood experiences in the workshops and consultation meetings and, by discussing the issues associated with shallow vs. deep water habitats and flood risk, they agreed to an elevation that was acceptable and met the goals of both groups. Through water gate management, flooding could be prevented, which satisfied the needs and concerns of the local community and local Water Bureau. Improved water circulation could increase aquatic species and attract bird species into the saltpan to forage and breed, which met the goals of the NGOs and Taijiang National Park. The knowledge provided by both groups played an important role in managing gate operations.

Throughout the process, we opened the lines of communication, increased mutual respect and understanding between groups, and empowered the stakeholders, thus ensuring continued communication and interactions. A gate operation protocol was then discussed with stakeholders, considering the tide height, warning water level, timing, frequency, duration, monitoring, and emergency response of gate operation. A compromise was reached if a water gauge was installed as an early warning system, and in March 2020, Gate 18 was operated for 4 h during a high tide event. Following this pilot study, the stakeholders agreed that Gate 18 could be operated for 6 h in April without increasing or creating risk to the community.

Water gate operation set-up and monitoring

Gate 18 is connected to a water channel and the point where water could enter Taiqu Saltpan in a controlled manner (Fig. 1). The residents provided information about past flooding events, which allowed a water gauge for monitoring water elevation to be installed in the channel as an early warning system (red cross in Fig. 1), thereby minimizing flooding in the community. A critical elevation of 0.15 m above sea level (ASL), what the community called a calm water condition, was based on past flooding events experienced by the community.

A 4-h gate operation was conducted on 15 March 2020 during a high tide event to obtain good water inflow with additional bird surveys before (13 March) and after (16 March) gate operations by our research partner using the same tools and methods as those used in the three-year bird survey (National Cheng Kung University 2020). During gate operation, water velocity and water level were monitored hourly to evaluate if the water volume entering the saltpan was sufficient to maintain habitat and to ensure the critical water level that could cause flooding in the community was not exceeded. A water velocity meter (global water flow probe F111) was used to measure water velocity entering the study area through Gate 18. Water depth and unmanned aerial vehicle surveys were performed alongside gate operations (Fig. 3). Water depths were recorded hourly using water depth rulers at 35 gauge points and the warning gauge (Fig. 1) until gate operations ended. Aerial photos were taken using a DJI Phantom 4 drone before and after gate operations to construct water area maps.

A total of 140 water depths were obtained from 35 locations between 12:00 and 16:00 during gate operations. The purpose of this experiment was to evaluate the integrity of the infrastructure and water connectivity in Taiqu Saltpan. Following this experiment, water connectivity problems were identified because some of the infrastructure was damaged and sediment deposits were affecting water flow in other parts of Taiqu Saltpan. These conditions were expected because the Qigu Saltpan complex had not been maintained since the salt industry was closed, and typhoons and weathering continued contributing to the sedimentation problem. To correct these issues, dredging was performed at nine locations (Fig. 1; A2–A3, A3–A4, A4–A5, B2–B3, B3–B4, B4–B5, B5–ditch, C5–ditch, and D2–D3) to reestablish water connectivity throughout Taiqu Saltpan. Approximately 15 m³ of sediment and bricks was dredged, and the dredged materials were placed aside on nearby dikes.

The results of the March experiment were then discussed with representatives and residents of Yancheng community, which is located near Taiqu Saltpan, and they agreed that a 6-h experiment was warranted. Therefore, a 6-h experiment occurred on 11 April 2020 to determine the extent to which water connectivity in Taiqu Saltpan had been restored, especially in rows 3, 4, and 5 (Fig. 1). Additional bird surveys were performed before (08 April) and after (13 April) gate operations, and water depth and unmanned aerial vehicle surveys were performed in parallel with gate operations (Fig. 3). Water depth data were collected every two hours, and unmanned aerial vehicle data were collected before and after gate operations. A total of 105 water depths were obtained from 35 locations that were taken at 2, 4, and 6-h intervals during gate operations.

We used the hourly water velocity measurements that we recorded to estimate the water volume that passed through Gate 18 by using an open channel flow equation (Q = V × A), where V is hourly water velocity and A is the channel area. We assumed the instantaneous velocity measurement values represented 1 h of flow. To construct the water area maps and calculate the amount of water in each zone of the saltpan, we processed the data sets in ArcMap v.10.4 using aerial images, water depth, and a digital elevation model. We first determined the area of the saltpan that was covered by water using aerial photographs. We then converted the water depth data into the water level for each zone by adding the elevation data to the aerial coverage maps. Next, we used an inverse distance weighted interpolation method to estimate the water depth in each zone. Finally, we clipped the results to create the water area maps and amount of water in each zone.

Physical inundation-drainage modeling

The Physical Inundation Drainage Model is a quasi-2D hydrological model developed by Chen et al. (2007). It uses a continuity equation to calculate water exchange between two adjacent computational cells as follows.

(1)

where A_si is the area of cell i; h_i and h_k are the water stage of cells i and k, respectively; t is the time step; P_ei is the effective rainfall of cell i; N_i is the number of cells encircling cell i; and Q_i,k is the discharge flowing from cell k into cell i, further determined by different formulas according to the flow types. For instance, the free overfall and submerged weir formulas are used to describe the flow rate between two cells divided by a hydraulic structure, whereas Manning’s equation is used for the condition without hydraulic structures existing between two cells. More details can be found in Yang (2000) and Chen et al. (2007).

This model has been used in Taiwan to analyze flood potential and inundation conditions for Yenshui Creek (Chen et al. 2007, Shiau et al. 2012), to predict inundation conditions in the southern Yunlin lowland area (Wang et al. 2013), to optimize simulation scenarios (Chen et al. 2015), to evaluate gate operations in the Budai Saltpan Wetland (Kuo 2015), and to evaluate flood risk under climate change while incorporating land subsidence (Wang et al. 2018). Based on these previous studies, we decided to use this model to simulate water management scenarios for Taiqu Saltpan.

Tidal surges and site elevation were the input for our model baseline. Map analyses were executed in ArcMap v.10.4 using monitoring data from two gate operations. The water depth results from the March experiment were used to calibrate our model, and those from the April experiment were used to verify our model results. We used the root mean square error (RMSE) and R² values to determine the error between observed and predicted data. Higher R² and lower RMSE indicate better agreement between observation and simulation results. A perfect model simulation would give RMSE = 0 and R² = 1. Once the model was calibrated and verified, we simulated various scenarios to consider the best management strategy for Taiqu Saltpan.

Scenario design

To explore gate operation management scenarios and preserve the existing salt pan pattern in Taiqu Saltpan, we considered four scenarios with infrastructure rehabilitation (e.g., removing culverts, dikes) in the lower part of Taiqu Saltpan (Fig. 4). These scenarios were designed to consider different locations and extents of dredging and to evaluate the most suitable management plan that could meet the needs for waterbird habitat, flood detention, and flood mitigation for the community.

In Scenario I, we restored a 400 m long x 4 m wide east-west ditch along the channel from A2A3 to E2E3 by decreasing the ground elevation of the saltpan to −0.4 m ASL. The purpose was to examine whether water supply from the west side channel and row 2 in the saltpan could enhance water flow into row 3 of the saltpan and provide a small deep-water area for aquatic species frequently found, such as milkfish (Chanos chanos), mosquitofish (Gambusia affinis), Taiwan shrimp-goby (Amblyeleotris bleekeri), and various water birds. In Scenario II, we removed dikes along A3B3–A4B4 and C3D3–C4D4 that were 260 m long and 4 m wide, and converted it into a ditch to an elevation of −0.5 m ASL, to test if the water supply from row 2 could distribute water more effectively into rows 3 and 4 of the saltpan. In Scenario III, we created two new ditches in the middle of saltpans B3–B5 and D3–D5 that were 360 m long, 7 m wide, and with a ground surface elevation of −0.5 m ASL to evaluate water connectivity, especially in rows 3 to 5. In Scenario IV, we combined Scenarios I and III with the purpose of obtaining a second water supply from the west-side channel that would better establish connectivity and water distribution in the saltpans while meeting the habitat needs of waterbirds.

The 11 April 2020 water depths in Taiqu Saltpan were used as the initial conditions for the model (Fig. 5). In the four scenarios, we assumed that the culvert connectivity between cells B2B3–C2C3 and D2D3–E2E3 had been restored.

RESULTS

Water depth changes and bird surveys during gate operations

The water level at the warning gauge (Fig. 1) rose from 0.07 to 0.25 m ASL during the 4-h operation in March and from 0 to 0.175 m ASL during the 6-h operation in April. Both experiments had a moment where the water levels surpassed the critical warning level, but they did not cause flooding because the water was flowing, not standing, and under team supervision. The volume of water drawn into the study area was estimated to be approximately 19,237 m³, with approximately 9866 m³ of water entering Taiqu Saltpan. The initial water depths across Taiqu Saltpan ranged from 0.20 to 0.15 m, except for Saltpan H with a water depth of 0.33 m, which is used for water detention by the community, according to the local community leader (Fig. 5). The water areas with a range of 0.10 to 0.15 m and 0.15 to 0.20 m only increased by an average of 5.4%. The gate operations had the greatest effects in rows 1 and 2 of the saltpan. Water connectivity problems had little effect on water depths in rows 3 to 5 of the saltpan (Fig. 5).

Following the March gate study and adjustments that were made to the infrastructure, the volume of water discharged into the study area during the April experiment was estimated to be approximately 27,071 m³, with approximately 14,517 m³ entering Taiqu Saltpan, which was 47.1% higher than in the March experiment. The initial water depths ranged from 0.20 to 0.15 m, except for Saltpan H, which was 0.41 m deep (Fig. 5). The differences between the March and April experiments may be attributed to the topographic adjustments made in Taiqu Saltpan that resulted in establishing better water connectivity, a higher tidal surge, and keeping the gate open longer during the April experiment. Following the April gate operations, water flowed into row 3 of the saltpan, yet still did not reach rows 4 or 5 (Fig. 5). For instance, the water depth in section C3 increased by 0.10 m. These data show that dredging had a positive effect, enhancing water inflow into the saltpans. Each gate operation showed that the water that entered the saltpans remained for 4 to 5 days.

The bird surveys in March and April 2020 were conducted to understand waterbird responses to changing water levels in Taiqu Saltpan. Most of the birds that used the area were members of the Charadriidae and Scolopacidae families, especially in areas with water depths < 0.20 m (Fig. 6). Bird survey results showed that before gate operations, the saltpan was used by four species in March and seven species in April. After gate operations, there were nine bird species in March and eleven in April, and diversity was from two to five families, including Anatidae, Ardeidae, Recurvirostridae (stilts and avocets), Scolopacidae, and Charadriidae, with water depths ranging from 0 to 0.15 m. The Anatidae, Ardeidae, and Recurvirostridae families could only be found at depths of 0.10 to 0.15 m. However, it is not clear whether the changes in the number of birds that were observed correlate directly with changes in water depth. Other factors such as survey times, migration habits, study area size, connectivity, community effects, food resources, and other uncertainties could also be affecting the number of birds using Taiqu Saltpan.

Management scenarios

Model calibration using the March experiment had R² = 0.62 between observed and predicted data and RMSE = 0.096 m. Model verification using the April experiment had R² = 0.37 between observed and predicted data and RMSE = 0.12 m. The R² in March showed a moderate correlation between observation and prediction (i.e., the value was between 0.4 and 0.7), whereas the R² in April showed a low correlation but acceptable RMSE, with water depth in the study area between 0.30 and 0.60 m.

Two of the four water management scenarios outperformed the others with respect to water depth water distribution and saltpan water connectivity (Figs. 5 and 7). Scenario II seems to have the different water depths most equally distributed. To better examine water connectivity, C4 in row 4 and B5 in row 5 were selected to show their hourly variation in water depth. It appears that Scenario II had the best water connectivity because its water depth increased sooner and higher compared to the other scenarios (Fig. 7). For Scenario IV, which had two water sources that would improve water flow, the results also performed well (Figs. 5 and 7), especially in areas with < 0.15 m of water, which are preferred by the bird species that used the area (i.e., the Charadriidae and Scolopacidae families).

DISCUSSION

Lessons learned from gate operation with stakeholder engagement

Dredging has been one general practice to solve sedimentation problems at saltpan sites (Bianchini et al. 2019). Our results were consistent with those obtained by Gustavson et al. (2008) and Stive and Vrijling (2017), who suggested that dredging could restore water connectivity and create a variety of water depths that equate to the creation of biotic habitat. With the appropriate designed operation time to allow better influence of tidal inputs, the water volumes that passed through Gate 18 and entered the saltpan in April were 40.7% and 47.1% higher, respectively, than those measured in the March experiment. The April gate operation showed that small dredging adjustments could restore some water connectivity and enhance water flow into the lower part of the saltpan. The results highlight the effects of tidal fluctuation and site elevation on water depths in Taiqu Saltpan. In addition, we measured habitat variables similar to Ma et al. (2010), which indicated water depth and water level fluctuations were key factors determining the types of waterbirds that forage and breed in the saltpan. However, it is interesting to highlight that the bird survey before and after the March experiment showed a higher increase in the number of bird species, from four species to nine species, compared to the April survey, in which four more species were found in the saltpan after the experiment. In April, the number of bird species ranged from seven to eleven species, which was consistent with the findings of the 2011–2014 seasonal bird survey in Budai Saltpan (Kuo 2015) and Qigu Saltpan (Chen et al. 2020). These surveys indicate that Charadriidae and Scolopacidae were most often identified in these saltpans when water depth was 0 to 0.05 m. The food resources of these families are small fish, shrimp, crabs, snails, shellfish, insects, and polychaeta. Following the March and April gate tests, species of Ardeidae, Recurvirostridae, and Anatidae started to use Taiqu Saltpan. Their food sources were fish, shrimp, and crabs. However, the results of the March and April experiments show that the increased abundance of bird species in the study area requires further investigation. Furthermore, because dredging operations may have negative environmental effects by resuspending contaminants that were deposited and encapsulated in the sediment at a site, which our study did not address, longer field experiments may be required.

Our gate operations would not have been possible if local stakeholders were not engaged. From conversations with local people, the history of the salt industry in their community, saltpan development, the value of the saltpan to the community, and technical information such as water level “tipping points” and water flow directions were all useful information in designing the gate operations. Scenarios for Taiqu Saltpan that all stakeholders agreed with were created by including the local community’s experiences, past practices, and knowledge together with sound scientific approaches, a positive environment, and a win-win adaptive management strategy.

Transparency, shared understanding of the scientific results, and discussions with stakeholders were deemed crucial throughout the study. When stakeholders brought up a concern related to the wetland, it was taken, and scientific analyses were conducted to obtain evidence to engage in further discussion. What was not perceived as feasible, e.g., operating gates for ecological resources given community safety considerations, turned out to be an opportunity. A compromise allowed two gate operation experiments to be conducted and supported management scenarios to be studied. Teodoro et al. (2021) noted that a robust stakeholder engagement program provides opportunities to interact face to face and share points of view among stakeholders. In many cases, stakeholders may know more about a topic than the purported experts. To build trust, respect, and efficient lines of communication, we created dialogues with the people who have a stake in these wetlands, including local community members, Taijiang National Park, and local environmental NGOs. Throughout the dialogues, stakeholders explained their positions and concerns without fear of reprisal or having their concerns dismissed. We were able to gather information on water levels during flood events. Stakeholders participated and contributed to the experimental design, identified issues that we might face, became confident that the final design would not endanger their community, and built trust for future engagement. It became evident that the key to developing management strategies for rewetting Taiqu Saltpan without increasing flood risk to the community required stakeholder input. Our goal to engage people to find a “co-design” and co-produce a solution was met.

Although it may have been easier to follow one stakeholder’s needs, it would have been at the expense of another stakeholder’s needs. While dealing with one set of stakeholder needs may be ideal, it is our responsibility as scientists to consider all stakeholder needs and concerns and find scenarios that provide flood detention, public safety, bird habitat, ecotourism, and food resources. It is also important to remain current and communicate new findings to stakeholders when new challenges arise (Grygoruk and Rannow 2017). Our work has taught us that an effective water management plan must include local community participation because it often requires infrastructure modifications to improve water connectivity. This situation necessitates stakeholder engagement and approval because it essentially means increased costs. Our study framework can be used conceptually as a strategy for developing management plans for engineered habitats that take into account the abundance of bird species and their habitat preferences.

Implications for saltpan wetland management

In human-modified landscapes, constructed saltpan wetlands are important roost, foraging, and conservation habitats for shorebirds migrating along the East Asian-Australasian Flyway (Green et al. 2015). Pandiyan et al. (2014) demonstrated a positive relationship between the density of bird species and benthic organisms in saltpan communities in southern India. Bouzillé et al. (2001) examined the ecological gradients in abandoned saltpans in western France and showed that the composition of the aquatic and palustrine nearshore vegetation could be managed by controlling the duration of flooding and soil salinity. Consequently, to create and maintain saltpan habitat that provides specific ecological services, a saltpan management plan is essential.

This study was conducted to understand better the current physical and biological conditions of Taiqu Saltpan, to explore methods to improve water flow into the saltpan to create ecological habitat that could increase biodiversity, and to propose a water management plan for better managing the resources of this saltpan during the dry season. Four scenario designs were modeled, providing sufficient water for the Charadriidae and Scolopacidae, which are the most common waterbird families in Taiqu Saltpan. Of the four scenarios, those that could provide a variety of water depths and habitats were considered the preferred water management approaches for Taiqu Saltpan. Scenario II had a variety of equally distributed water depths. The outcome of Scenario IV provided the largest area of water with a depth < 0.15 m, which is suitable for waterbirds, and had the best water connectivity throughout Taiqu Saltpan. In addition, Scenario IV could be used to flush Taiqu Saltpan, improving water quality. After implementing the necessary infrastructure modifications, we recommended operating the gate once to twice per week to establish a good water circulation pattern in the saltpan, though food resources may not be available immediately following the implementation of the plan and gate operation. Restoring Taiqu Saltpan to support a diverse array of aquatic species and waterbirds that are able to breed and forage may take time. Our proposed water management plan has been approved by the local Water Bureau, Taijiang National Park, the Taiqu’s village leader, and the gate operator(s).

Through good management practices and mimicking nature, abandoned saltpans in Taiwan have the opportunity to become important wetland habitats and provide important ecosystem services (Kuo and Wang 2018). However, more research will be needed to create a management plan for the rainy season that is safe for the community. In addition, it is not clear whether the changes in the number of birds that were observed correlate directly to changes in water depth. Continued monitoring and research are needed to understand better the effect of the water management plan on salinity and biodiversity in Taiqu Saltpan and its use in other saltpans in Taiwan. In our management strategies, we did not include the effects of soil infiltration, precipitation, evaporation, wind speed, or wind direction, and we assumed that they are minimal. However, these factors may have substantial effects on maintaining the water levels, and we recommend further studies to measure the effects of these variables on water depth and extent. We did not consider soil heterogeneity or the effect of water infiltration into the substrate because our study site was a former salt evaporation pond, where the soil has been compacted by site activities. Moreover, the salt layers that accumulated as a result of previous operations may restrict water infiltration into the substrate, much like a caliche. In addition to the physical features of the site, there is always the possibility for human error related to measurements that could affect the results.

CONCLUSION

Though Taiqu Saltpan is part of the Qigu Saltpan Wetland complex, a designated wetland of national importance in Taiwan, it has been left unmanaged for years. Taijiang National Park has been looking for an environmentally friendly and sustainable approach to manage Taiqu Saltpan and restore it to a healthy coastal wetland ecosystem. The water drainage system of Taiqu Saltpan is connected to the adjacent coastal community that has experienced severe flooding in the past, making its water management even more important and sensitive. We were able to establish dialogues with and between local community members, Taijiang National Park, local environmental NGOs, and researchers. This communication provided vital local data that could be combined with the scientific data needed to conduct the science needed to develop a sound and inclusive water and resource management plan. Measurement and analysis of stakeholder responses was not considered in the scope of this study, as is the case in most academic studies. Stakeholder engagement can be challenging, but it can also be rewarding in creating sound science and achieving the implementation of good and sustainable resource management practices. We also demonstrated that it is possible to include stakeholders as part of the decision-making process and develop solutions to complex problems.

Our modeling experiments indicate that scenarios II and IV are the most suitable for Taiqu Saltpan because they provide a variety of water depths that enhance the ecological connectivity between the saltpans. In our proposed water management plan, we suggest that water intake operations be conducted during the bird migratory season and from October to April if flooding is not an issue at the time. Gate operation will be conducted and monitored by the water gate operators once to twice per week to maintain habitat and water quality, and the water level gauge must not exceed 0.7 m to avoid flooding the wastewater drainage system and community impacts. Our data also indicate that Taiqu Saltpan is an important wetland for waterbirds during the migratory period. Furthermore, our work provides a framework to address the water shortage and approaches to manage stakeholder needs and concerns and water management issues at sites in Taiwan. Salinity is still a problem that needs to be resolved to improve wetland and bird habitat. We also propose generating community risk maps that address the spatial and temporal probabilities of flooding in the study area. The risk maps could provide a reference for cost-benefit analyses that provide stakeholders with the information needed to develop short-, middle-, and long-term strategies in the event of flooding in the study area.

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