Watershed Restoration Research Articles

Influence of soil characteristics on physiological and growth responses of Cytharexyllum myrianthum Cham. (Verbenaceae) to flooding

The success of watershed riparian forest restoration programs can be affected by the selection of plant species tolerant to flooding and soil types that occur along water courses. We evaluated physiological and growth responses of Cytharexyllum myrianthum seedlings to flooding in three different soil types representative of the Almada River Watershed (ARW), southern Bahia, Brazil. The soils selected, based on the relative abundance and importance in the ARW, were: Luvisol, Argisol, and Spodosol. After 35 days of flooding, the Argisol had the lowest and the Spodosol had the highest reduction–oxidation (redox) potential (Eh). After 35 days of flooding, the Luvisol had higher pH and electrical conductivity (Ec) than the other soils. Stomatal conductance (gs) and net photosynthesis (A) significantly declined in all soil types after 7 days of flooding. After that period, morphological changes characteristic of flood-tolerant plants, such as lenticel hypertrophy and adventitious root formation, were observed in all flooded plants. Following the morphological changes, gs and A in flooded plants increased to values close to those of the non-flooded plants. The highest relative growth rates based on mass (RGRm) and net assimilation rates (NAR) for the non-flooded plants were observed in the Argisol. After 35 days of flooding, no significant differences in RGRm or NAR were observed between non-flooded and flooded plants in the Luvisol, but large significant decreases in RGRm and NAR were observed for the flooded plants in the Spodosol. Our results demonstrated that the ability of seedlings of the same species to acclimate to flooded soil conditions differs among soil types. Therefore, the characteristics of soils present in a watershed should be considered when selecting tree species for the reforestation of riparian forests.

Participatory research in Northwest Atlanta's Proctor Creek Watershed: Using photovoice to explore environmental health risks at the water's edge.

In this study we used a participatory research method, photovoice, to explore community perceptions about environmental health risks, community assets, and strengths in and around an urban, degraded watershed in Northwest Atlanta, Georgia. This watershed, formed by Proctor Creek, is a focal point for redevelopment and infrastructure investments for years to come. Using a community-based participatory research approach, 10 Proctor Creek residents (watershed researchers), and a university partner, engaged in data collection; participatory data analysis; internal discussions; translation of research findings into watershed restoration, community revitalization, remedial action, and policy solutions; and dissemination of results to fellow watershed residents, stakeholders, and decision makers. We present a conceptual model linking the watershed researchers' understanding of urban policies and practice in the Proctor Creek Watershed to environmental, neighborhood and housing conditions and their influence on health outcomes and quality of life. Engaging community members in defining their own community environmental health challenges and assets yielded the following primary themes: 1) threats to the natural environment, 2) built environment stressors that influence health, 3) blight and divestment of public resources, and 4) hope for the future. Residents' vision for the future of the watershed - a restored creek, revitalized neighborhoods, and restored people - is fueled by a strong connection to history, memory, and sense of place. We demonstrate the value of local knowledge in identifying previously unaddressed environmental health risks in the Proctor Creek Watershed as well as solutions to reduce or eliminate them.

Beyond sticks and stones: Integrating physical and ecological conditions into watershed restoration assessments using a food web modeling approach

Watershed assessments have become common for prioritizing restoration in river networks. These assessments primarily focus on geomorphic conditions of rivers but less frequently incorporate non-geomorphic abiotic factors such as water chemistry and temperature, and biotic factors such as the structure of food webs. Using a dynamic food web model that integrates physical and ecological environmental conditions of rivers, we simulated how juvenile salmon (Oncorhynchus spp.) biomass responded to restoration at twelve sites distributed across the Methow River (Washington, USA), ranging from headwater tributaries to mainstem reaches. We explored responses to three common river restoration strategies: (1) physical habitat modification, (2) nutrient supplementation, and (3) increased riparian vegetation cover. We also simulated how different food web configurations that exist in salmon-bearing streams, such as the presence of ‘non-target’ fishes and ‘armored’ predation resistant invertebrates, could mediate restoration outcomes. Some locations in the river network experienced relatively large increases in modeled fish biomass with restoration, whereas other locations were almost entirely unresponsive. Spatial variation in restoration outcomes was primarily controlled by non-geomorphic environmental conditions, such as nutrient availability, water temperature, and stream canopy cover. Restoration responses also varied significantly with different food web configurations, suggesting that as the structure of food webs varies across river networks, so too could the outcome of restoration. These findings illustrate that ecological responses to restoration may exhibit substantial spatial variation within river networks, resulting from heterogeneity in environmental conditions that are commonly overlooked—but which can and should be considered—in restoration planning and prioritization.

Identifying key environmental factors for enhancing the pollutant removal potential at a river confluence

The confluence area of river networks is a hot spot for pollutant removal. As an essential part of the river ecosystem, sediment bacterial communities played a crucial role in the removal of pollutants. However, how the potential of sediment bacterial communities can be enhanced toward the removal of pollutants remains unclear. Therefore, this study provides a new approach for the identification of key environmental factors that enhance the pollutant removal potential at a river confluence, integrating the bacteria-based index of biotic integrity (Ba-IBI), path model, support vector regression (SVR) model, and sensitivity analysis. The developed Ba-IBI could quantitatively evaluate the differences of both structure and function of bacterial communities before and after the confluence, with a range from 1.52 to 2.78. The flow regime, which was represented by the Froude number, exerted an indirect effect on Ba-IBI mediated through water nutrients and sediment nutrients according to path model results. Sediment nutrients and water nutrients were considered as the main environmental factors that directly affected sediment bacterial communities. A function that could predict the response of sediment bacterial communities to environmental factors in the best possible way was found through SVR modeling, with R2 = 0.8357. The results of the sensitivity analysis indicated that the total phosphorus in water and ammonia nitrogen in sediments were key environmental factors for enhancing the pollutant removal potential at the river confluence. The established approach aids the improvement of the bioremediation potential of river confluence area, and might provide a theoretical basis for watershed restoration.

Handbook of Florida Water Regulation: Florida Watershed Restoration Act

This handbook is designed to provide an accurate, current, and authoritative summary of the principle Federal and Florida laws that directly or indirectly relate to agriculture. This handbook should provide a basic overview of the many rights and responsibilities that farmers and farmland owners have under both Federal and Florida laws as well as the appropriate contact information to obtain more detailed information. However, the reader should be aware that because the laws, administrative rulings, and court decisions on which this handbook is based are subject to constant revision, portions of this publication could become outdated at anytime. Several details of cited laws are also left out due to space limitations. This document is FE608, one of a series of the Food and Resource Economics Department, UF/IFAS Extension. Published December 2005.
 FE608/FE608: 2021 Handbook of Florida Water Regulation: Florida Watershed Restoration Act (ufl.edu)

Patterns and Trends in Secchi Disk Depth over Three Decades in the Chesapeake Bay Estuarine Complex

Water clarity is an important ecosystem indicator of eutrophication in Chesapeake Bay and other coastal and estuarine systems across the globe. Although a variety of measures are available to quantify light availability in water, Secchi disk depths have been the most consistent and frequent measure employed in water monitoring programs. Because light availability is influenced by multiple variables, such as phytoplankton biomass, non-living suspended particles, and colored dissolved organic matter (CDOM), understanding the factors driving long-term variability and trends in water clarity is critical for targeting watershed management actions related to eutrophication. Thus, we conducted a comprehensive statistical analysis of spatial and temporal variations in Secchi disk depth and the key internal and external variables that influence its variability in Chesapeake Bay and its tidal tributaries over the past 30 years. Our results indicate that although watershed nutrient, sediment, and freshwater inputs did not correlate with Secchi depth on a monthly timescale outside of low-salinity regions near river outflows, water-column variables that represent the consequences of those inputs (CDOM, chlorophyll-a, and total suspended solids [TSS]) were strongly associated with Secchi depth variability. The inconsistency of these two findings may be explained by controls on chlorophyll-a and TSS that are not directly related to watershed input, such as grazing and resuspension, and by lags of several months between watershed inputs and the associated water-column concentrations. While salinity (a proxy for CDOM) was a dominant spatial covariate with Secchi depth bay-wide, TSS concentrations were strongly associated with temporal changes in Secchi depths in low-salinity regions and indicators of phytoplankton biomass were more important in mesohaline and polyhaline regions. These findings related to spatially dependent controls on Secchi depth enhance our understanding of long-term changes in estuarine light availability and suggest a region-specific response of Secchi depth to variables (TSS and chlorophyll-a) targeted by watershed restoration actions designed to limit nutrient and sediment inputs to Chesapeake Bay.

Disturbance Type and Sagebrush Community Type Affect Plant Community Structure After Shrub Reduction

Treatments to reduce shrub cover are commonly implemented with the objective of shifting community structure away from shrub dominance and toward shrub and perennial grass codominance. In sagebrush (Artemisia L.) ecosystems, shrub reduction treatments have had variable effects on target shrubs, herbaceous perennials, and non-native annual plants. The factors mediating this variability are not well understood. We used long-term data from Utah’s Watershed Restoration Initiative project to assess short-term (1−4 yr post-treatment) and long-term (5−12 yr post-treatment) responses of sagebrush plant communities to five shrub reduction treatments at 94 sites that span a range of abiotic conditions and sagebrush community types. Treatments were pipe harrow with one or two passes, aerator, and fire with and without postfire seeding. We analyzed effect sizes (log of response ratio) to assess responses of sagebrush, perennial and annual grasses and forbs, and ground cover to treatments. Most treatments successfully reduced sagebrush cover over the short and long term. All treatments increased long-term perennial grass cover in Wyoming big sagebrush (A. tridentata Nutt. ssp. wyomingensis Beetle & Young) communities, but in mountain big sagebrush (ssp. vaseyana [Rydb.] Beetle) communities, perennial grasses increased only when seeded after fire. In both sagebrush communities, treatments generally resulted in short-term, but not long-term, increases in perennial forb cover. Annual grasses (largely invasive cheatgrass, Bromus tectorum L.) increased in all treatments on sites dominated by mountain big sagebrush but stayed constant or decreased on sites dominated by Wyoming big sagebrush. This result was unexpected because sites dominated by Wyoming big sagebrush are typically thought to be less resilient to disturbance and less resistant to invasion than sites dominated by mountain big sagebrush. Together, these results indicate some of the benefits, risks, and contingent outcomes of sagebrush reduction treatments that should be considered carefully in any future decisions about applying such treatments.

The Devil and the Deep Blue Lake: How Natural Area Acquisition and Stewardship Helps Protect the Major Drinking Reservoir in Northwestern Arkansas

The Arkansas Natural Heritage Commission (ANHC)'s 1225-ha Devil's Eyebrow Natural Area (DENA), located at the northern end of Beaver Lake along Indian Creek, Butler Creek, and their tributaries, is an ecologically significant site in the Ozark Highlands that falls primarily within the Beaver Lake Watershed, deemed the number-one priority watershed by Arkansas's Unified Watershed Assessments and Restoration Priorities Report due to its designation as an extraordinary water resource, the presence of imperiled aquatic species in the watershed, its role as one of the most important supplies of drinking water in the state, and its status as both an impaired water body and an interstate “water of concern.” Beaver Lake supplies drinking water to more than 420,000 people, one in eight Arkansans, and industries including the Walmart Home Office in northwest Arkansas. DENA protects 5 km of Beaver Lake frontage and 7.5 km of critical tributaries in the watershed and is part of a broader interconnected Conservation Corridor that includes Nature Conservancy preserves, Army Corps of Engineers property surrounding Beaver Lake, Hobbs State Park Conservation Area in Arkansas, and the Mark Twain National Forest and Roaring River State Park in Missouri. Water quality protection and improvement has been a critical component driving the funding of DENA, as well as both a direct and indirect focus of much of ANHC's ongoing restoration efforts on the property. Road improvements to decrease sedimentation, reforestation efforts, and feral swine removal have all served to improve water quality in the watershed. A project to improve glade habitat for several species of greatest conservation need through cedar removal has had the added benefit of providing aquatic habitat structure for fish and improving angling opportunities in Beaver Lake. This project serves as a model for conservation partnerships in critical watersheds and also highlights how efforts to directly improve water quality, as well as efforts with indirect benefits to watersheds (conceived primarily to restore terrestrial habitats), can have far-ranging benefits for ecosystems, imperiled species, and stakeholders. Here we present how the ANHC and its conservation partners have successfully used various strategies to build local support, leverage funding, engage the public, and conduct meaningful conservation at a regional scale.

Helping HELP with limited resources: The Luquillo experience

By definition the HELP approach involves the active participation of individuals from a wide range of disciplines and backgrounds, including representatives of industry, academics, natural resource managers, and local officials and community leaders. While there is considerable enthusiasm and support for the integrated HELP approach, a central problem for all HELP basins is how to effectively engage individuals and groups with few, if any financial resources. In the Luquillo HELP project we have managed this issue by focusing our efforts on holding small, public meetings and workshops with technocrats and managers who are engaged in local water resource management. To date several forums have been organised, including : technical meetings with the directors of natural resource agencies; presentations and panel discussions at the meetings of local professional societies, including the societies of Civil Engineers and Architects, the Commonwealth Association of Tourism, the Association of Builders and Developers, and the Puerto Rican Association of Lawyers. During these forums HELP specialists gave presentations and led discussions on how integrated watershed management can help resolve local problems. Because the audience are directly involved with these issues, they are quite responsive to these discussions and have often provided unique solutions to common problems. Technical workshops are co-sponsored by local municipalities - these day-long workshops are hosted by a municipality and include managers from other municipalities, the local water authority, and local community leaders. Additional activities include : technical advice on water infrastructure projects is given; there are educational exchanges between local and international students, scientists, natural resource managers, and community leaders; and synthesis publications relevant to integrated water resource management are produced. Other activities have included compiling oral environmental histories and organising watershed restoration activities. This paper describes these activities and discusses the benefits and costs of each approach.

Detection of the effects of stormwater control measure in streams using a Bayesian BACI power analysis

The unpredictable timing and magnitude of precipitation events and the spatiotemporal variability of constituent concentrations are major complications to effective monitoring of watershed nutrient and sediment loads. Furthermore, detecting small changes in constituent loads in response to implementation of Stormwater control measures (SCMs) against natural variability is a challenge. Nevertheless, regulatory frameworks that direct reductions of pollutants to streams frequently depend on the ability to quantify changes in loads after management interventions. The before-after-control impact (BACI) sampling design is often used to assess the effects of an environmental change made at a known point in time. However, this approach may be complicated to apply to nutrient and sediment loads in streams as the relative impact of SCMs on nutrient concentration conditional on the long term variability of discharges has not been evaluated. Multi-scale monitoring studies that provide estimates of the natural temporal and spatial variability of discharge and concentrations could provide useful information in designing a BACI study. Here we use data from the Baltimore Long Term Ecological Research (LTER) sites and urban restoration sites to develop multiple statistical measures of the effectiveness of a given monitoring scheme in revealing the hypothesized restoration effects in terms of hydrology and nutrient loads. Stratified sampling over baseflow and stormflow and the use of multiple control streams were useful tools to detect long term cumulative reductions in concentrations due to SCMs. Moderate reductions in concentration (20%), however, were not detectable with the design options considered. We emphasize that appropriate pre-planning of monitoring schemes and sampling frequency is essential to determine if the effects on constituent loads resulting from a given watershed restoration activity are measurable.

Valuing attributes of forest restoration in a semi-arid watershed

Approximately 1.5 M residents of the Phoenix metropolitan area rely upon the Salt Verde River watershed in central Arizona, USA, to meet their water demands. However, the health of the semi-arid watershed is at risk. Densely populated forests increase the probability of catastrophic wildfire and threaten the watershed’s integrity. Restoration reduces the risk of catastrophic wildfire and improves the health and productivity of the watershed. While current research indicates public support of watershed restoration, little guidance exists for land managers regarding the relative benefits of restoration projects. We estimate benefits of watershed restoration projects in the Salt-Verde River watershed using a choice experiment. The survey focuses on residents of the Phoenix metropolitan area as beneficiaries of watershed restoration and includes public access, surface water quality, groundwater recharge, critical habitat, and cultural significance as attributes. Willingness to pay estimates are obtained using a Bayesian mixed logit model. Respondents have a positive and statistically significant willingness to pay for all attributes. The highest willingness to pay is a one-time fee of $41.92 for restoration projects that protect critical habitats for endangered and threatened species. Our results also provide one of the first estimates for groundwater recharge as an attribute of watershed restoration. The benefit estimates obtained can directly inform land managers regarding restoration in semi-arid landscapes and assist in clearly delineating difficult to quantify environmental benefits in cost-benefit analyses of proposed future projects.

Community-Based Watershed Restoration in Nepal: Learning from EBA South Project

Community-Based Watershed Restoration in Nepal: Learning from EBA South Project

Using Applied Science for Effective Watershed Restoration and Coho Salmon Recovery in Coastal Oregon Streams

Coos Bay, located on the southern Oregon Coast, is the largest estuary between the Columbia River and San Francisco Bay. Palouse and Larson Creeks in the northern section of Coos Bay are the two most productive streams for coho salmon. Such productivity occurs despite the pressure salmon habitats have experienced through a long history of anthropogenic alterations, and continue to face from the region’s robust industrial economy, including recreational and commercial fisheries, agricultural production, and forestry. Restoration efforts since the 1980s have helped mitigate environmental impacts, but the turn of the century brought a new era of coordinated research, monitoring, and restoration. Forming a multi-stakeholder partnership with the goal of restoring salmon runs, the local nonprofitnon-profit Coos Watershed Association and its partners worked together to learn about the strategies that coho use to survive in these altered landscapes and apply research findings to restore habitats. Specifically, they examined the most appropriate habitat restoration strategies for various life histories of coho salmon, while working within social and political constraints. As a result, these efforts over the past 35 years have led to a better understanding of salmon populations in Palouse and Larson Creeks and an effective restoration program that continues till today.

Natural factors or environmental neglect? Understanding the dilemma of a water crisis in a scenario of water plenty

The objective of this study was to discuss how natural factors associated with poor land use policy and ineffective water resources management triggered a severe water crisis in a region with water plenty. The idea developed throughout the text is the result of a water shortage experience in a Brazilian medium-size city, related to recurrent climatological events, indicating the need for national and international water management agencies to elaborate policies, guidelines and mechanisms that take environmental seasonality into account. The study area (Itabuna city) is located within a rainforest biogeographic context, with high rainfall rates and perennial fluvial regimes. Nevertheless, in a period of climatic oscillation (2015-2016), the region experienced a water shortage because it relied on what it neglects. Through GIS and geoprocessing, we estimate the levels of degradation of two neighboring watersheds to illustrate the problem discussed here. The discourse adopted by the urban managers pointed out that the natural factors caused the water crisis. However, one of the watersheds that supply water to urban areas did not meet demand during the dry season, the other is degraded and with reduced ability to deliver ecosystem services. Due to the water crisis, an old proposal of implementing a dam in the watershed with highest level of degradation was resumed and implanted. The method chosen to solve the issue of water shortage, although valid, isn’t enough, in addition to demanding large engineering interventions in the natural environment, it does not guarantee water security without an effective land use policy for watersheds. Therefore, as a complement to the dam, we suggest watershed restoration and preservation policies that can effectively regulate water production and promote resilient and sustainable water security should be implemented.

A multiobjective simulation-optimization tool for assisting in urban watershed restoration planning

Significant efforts are being made to restore urban watersheds. Stormwater control measures (SCMs) reduce runoff and provide water quality treatment, and are the predominate means of achieving restoration objectives. Determining an effective implementation strategy for these measures often requires a simulation model. The Storm Water Management Model (SWMM) is a hydrologic-hydraulic and water quality model specifically developed for use in urban watersheds. We enhanced an existing external control program for SWMM by adding automated calibration for user-selected events, sensitivity analysis capability, and a multiobjective cost-optimization feature using a well-known evolutionary solver, the Non-dominated sorting genetic algorithm (NSGA-II). The enhanced program, RSWMM-Cost, was then applied to a previously developed SWMM model of the Difficult Run watershed of Fairfax County, Virginia. Calibration and verification were performed using the program. Sensitivity analysis was conducted by varying SCM attributes as a function of performance metrics. Cost-optimization was conducted on a 123.4 ha headwater subcatchment of the watershed using generalized cost relationships and constraints based upon SCM design guidance and water quality requirements. A cost-effectiveness curve was generated, consisting of sets of SCMs that either are optimal or nearly so. Thus, RSWMM-Cost can assist decision makers identify watershed management strategies that meet water quality goals.

Effects of Forest Roads on Runoff Initiation in Low‐Order Ephemeral Streams

AbstractUnderstanding hydrologic connectivity is essential for managing ephemeral headwater streams where upstream land use influences downstream aquatic habitats. This study relies on a field‐based approach to evaluate how precipitation and roads affect runoff generation in low‐order ephemeral streams of the U.S. Virgin Islands. Logistic regression analyses show that runoff delivery from unroaded catchments agrees with a water storage conceptual model typical for subsurface storm and saturation overland flow‐dominated settings. Without roads, runoff occurs only about 4 times per year in response to 10 and 78 mm of storm rainfall, depending on antecedent precipitation. In contrast, maximum 15‐min rainfall intensities are a better predictor of runoff generation on unpaved roads than are total rainfall and antecedent conditions. Intensities surpassing ~10 mm/hr lead to road runoff, and this occurs about 40 times per year. Road‐influenced streams represent an intermediate setting for which runoff generation depends on storm and antecedent rainfall, as well as the road surface area captured by drains and flow path distance. In our focus area, roads can provoke streams to deliver runoff to coral bearing waters 10 to 13 times every year as a response to 9.3‐ to 50‐mm storms, depending on antecedent rainfall and road drain characteristics. These results highlight the sensitivity of road connectivity to specific road drain characteristics and display the potential for connectivity as a guiding watershed restoration principle.

Land Use Change using Geospatial Techniques: The Case of AwojaWatershed in Ngora District in Eastern Uganda

This study used remote sensing and Geo-graphical Information System (GIS) to assess the status of Awoja watersheds in Ngora district of Eastern Uganda. Landsat ETM Images covering the whole of Ngora district and part of Lake Kyoga of two time periods was carried out in the period April to July 2015. This wasacquired using USGS Earth Explorer. The images were processed and enhanced with ERDAS 2014 software to aid information extraction and analysis. Land cover change analysis was performed using ENVI 5.3 software. Supervised classification method with maximum likelihood algorithm was performed to obtain land use/ cover types. Five land use/cover types were identified: open water, wetland, tree cover, agriculture and built up area. The findings indicate a fivefold increase in built up area by 154.27km2 (i.e. 375%) and open water increased by 8.7 km2 (i.e. 55.33%). Wetland, tree cover and agriculture reduced in area by -1.0km2 (i.e. 5.1%), - 48.07 km2 (i.e. 34.46%) and -114.0km2 (i.e. 51.05%), respectively. These changes mainly resulted from deforestation, wetland encroachment, poor attitude and over population. Unless, appropriate watershed restoration strategies are designed through afforestation, law enforcement on culprits, continuous sensitisation of the watershed community on the causes of degradation, the over 1,700,000 individuals whose livelihoods depend on Awojawill continue to suffer the effects of degradation. There is need to advocate for non-consumptive projects as alternative sources of income. Keywords: Remote sensing, GIS, Watersheds.

Using Matching Methods to Estimate Impacts of Wildfire and Postwildfire Flooding on House Prices

AbstractThe increasing frequency and severity of landscape‐scale wildfire poses new challenges for forested watershed management. The Schultz Fire burned 6,100 ha on the steep slopes of San Francisco Mountain near Flagstaff, AZ, USA in 2010. Within a month of the wildfire, summer monsoon rains created flooding and debris flows 1–2 orders of magnitude greater than prewildfire rainfall events. We estimate a hedonic property model to determine the loss in house prices from the wildfire and postwildfire flooding. While several studies examine the effects of wildfires and flooding on housing prices separately, to our knowledge, no study has determined the effects of postwildfire flooding in a fire‐adapted watershed. Most hedonic property models estimating impacts of wildfire or flooding use regression analysis to predict impacts. We also contribute to the hedonic property model literature by using nonparametric matching techniques. We find a negative and statistically significant average treatment effect of wildfire and post‐wildfire flooding. The treatment effect, however, differs relative to distance to wildfire perimeter and distance to flood zones. For example, houses located within 5 km of the Schultz Fire perimeter have an estimated 31% loss, while houses within 20 km have an estimated 6% loss. In addition, prices for houses located within 100 m of the 5‐year flood drop by 10% after the flood, whereas prices for houses within 2 km drop by 5%. Our results indicate that careful consideration of the impacts of both wildfire and postwildfire flooding is essential for understanding the net benefits of forested watershed restoration.

Predicting the ecological impacts of large-dam removals on a river network based on habitat-network structure and flow regimes.

Large dams provide vital protection and services to humans. However, an increasing number of large dams worldwide are old and not operating properly. The removal of large dams has excellent potential to restore habitat connectivity and flow regimes; therefore, projecting the related ecological consequences is an emerging need for water resource and ecosystem management. However, no modeling methods are currently available for such projections at the basin scale. We devised a scheme that integrates changes in flow regimes and habitat network structure into a basin-scale impact assessment of removal of large dams and applied it to the Nagara-Ibi Basin, Japan. We used a graph-theoretical approach and a hydrological model, to quantify changes in habitat availability for 11 freshwater fishes at the basin scale under multiple removal scenarios. We compared these results with the change predicted using a conventional scheme that considered only changes to the habitat network due to dam removal. Our proposed scheme revealed that an increase in flow variability associated with dam removal projected both positive and negative effects on basin-scale habitat availability, depending on the focal species, endangered species had a negative response to dam removal. In contrast, the conventional approach projected only positive effects for all species. This difference in the outcomes indicates that large-dam removal can have negative and positive effects on watershed restoration due to changes in flow regimes. Our results also suggest the effect of removal of large dams may depend on the dams and their locations. Our study is the first step in projecting ecological trade-offs associated with the removal of large dams on riverscapes at the basin scale and provides a foundation for future process-based watershed restoration.

A systematic approach for watershed ecological restoration strategy making: An application in the Taizi River Basin in northern China

Aiming to protect freshwater ecosystems, river ecological restoration has been brought into the research spotlight. However, it is challenging for decision makers to set appropriate objectives and select a combination of rehabilitation acts from numerous possible solutions to meet ecological, economic, and social demands. In this study, we developed a systematic approach to help make an optimal strategy for watershed restoration, which incorporated ecological security assessment and multi-objectives optimization (MOO) into the planning process to enhance restoration efficiency and effectiveness. The river ecological security status was evaluated by using a pressure-state-function-response (PSFR) assessment framework, and MOO was achieved by searching for the Pareto optimal solutions via Non-dominated Sorting Genetic Algorithm II (NSGA-II) to balance tradeoffs between different objectives. Further, we clustered the searched solutions into three types in terms of different optimized objective function values in order to provide insightful information for decision makers. The proposed method was applied in an example rehabilitation project in the Taizi River Basin in northern China. The MOO result in the Taizi River presented a set of Pareto optimal solutions that were classified into three types: I - high ecological improvement, high cost and high benefits solution; II - medial ecological improvement, medial cost and medial economic benefits solution; III - low ecological improvement, low cost and low economic benefits solution. The proposed systematic approach in our study can enhance the effectiveness of riverine ecological restoration project and could provide valuable reference for other ecological restoration planning.