Integrating objectives and scales for planning and implementing wetland restoration and creation in agricultural landscapes

River Basin Simulations Reveal Wide-Ranging Wetland-Mediated Nitrate Reductions

River basin-scale wetland restoration and creation is a primary management option for mitigating nitrogen-based water quality challenges. However, the magnitude of nitrogen reduction that will result from adding wetlands across large river basins is uncertain, partly because the areal extent, location, and physical and functional characteristics of the wetlands are unknown. We simulated over 3600 wetland restoration scenarios across the ∼450,000 km2 Upper Mississippi River Basin (UMRB) depicting varied assumptions for wetland areal extent, physical and functional characteristics, and placement strategy. These simulations indicated that restoring wetlands will reduce local nitrate yields and nitrate loads at the UMRB outlet. However, the projected magnitude of nitrate reduction varied widely across disparate scenario assumptions─e.g., restoring 4500 km2 of wetlands (i.e., 1% of UMRB area) decreased mean annual nitrate loads at the UMRB outlet between 3 and 42%. Higher magnitude nitrate reductions correlated with best-case assumptions, particularly for characteristics controlling nitrate loading rates to the wetlands. These results show that simplified claims about basin-scale wetland-mediated water quality improvements discount the breadth of possible wetland impacts across disparate wetland physical and functional conditions and highlight a need for greater clarity regarding the likelihood of these conditions at river basin scales.

Constructed Wetlands as a Landscape Management Practice for Nutrient Removal from Agricultural Runoff—A Local Practice Case on the East Coast of Taiwan

Runoff with excessive nutrients from rice paddy fields that releases into the Pacific Ocean has been a possible cause of water body pollution and harm to marine life. Constructed wetlands had developed for decades but were rarely implemented in treating agricultural pollution in Taiwan. Moreover, the environmental policies haven’t provided enough instructions, support, or compensation for the establishment of this practice. The rice paddy field that was chosen in this study is located in Xinshe, Taiwan. It is close to the Pacific Ocean where coral reefs are nearby and fishery resource is abundant. In this study, the northern half of the whole organic field was chosen, and the contributing area is approximately 1 × 105 m2. Four plots of constructed wetlands (approximately 17.5 m wide, 16.7 m long, and 0.2 m deep each, covering 1164.74 m2 of the total area) and employing surface flow were established as CW treatment. Water spinach (Ipomoea aquatica) was used for treating the nutrient runoff from organic rice paddy fields. Water samples of input and output of constructed wetlands were collected during 51 days of the experimental period (from the first day of rice transplantation to 10-days before harvest). Ammonia, nitrate, nitrite, phosphate, and total phosphorus concentrations were analyzed to calculate the nutrient load. The runoff of rice paddy fields without constructed wetlands was also sampled as a reference (RPF treatment). In average, about 54.3% ammonia and 42.7% nitrate was removed from the runoff that went through the CW treatment, while 4.2% ammonia and 51.3% nitrate increase were found at the output of the RPF treatment. Meanwhile, 35.6% of total phosphorus and 29.5% of phosphate were removed from the runoff of constructed wetlands. Only 16.4% total phosphorus and 6.4% phosphate were removed from the RPF treatment. Results indicate that constructed wetlands are promising treatment for agricultural runoff and the result can be used as a reference for the future environmental policies enactment in Taiwan.

Biogeochemistry of Mediterranean Wetlands: A Review about the Effects of Water-Level Fluctuations on Phosphorus Cycling and Greenhouse Gas Emissions

Although Mediterranean wetlands are characterized by extreme natural water level fluctuations in response to irregular precipitation patterns, global climate change is expected to amplify this pattern by shortening precipitation seasons and increasing the incidence of summer droughts in this area. As a consequence, a part of the lake sediment will be exposed to air-drying in dry years when the water table becomes low. This periodic sediment exposure to dry/wet cycles will likely affect biogeochemical processes. Unexpectedly, to date, few studies are focused on assessing the effects of water level fluctuations on the biogeochemistry of these ecosystems. In this review, we investigate the potential impacts of water level fluctuations on phosphorus dynamics and on greenhouse gases emissions in Mediterranean wetlands. Major drivers of global change, and specially water level fluctuations, will lead to the degradation of water quality in Mediterranean wetlands by increasing the availability of phosphorus concentration in the water column upon rewetting of dry sediment. CO2 fluxes are likely to be enhanced during desiccation, while inundation is likely to decrease cumulative CO2 emissions, as well as N2O emissions, although increasing CH4 emissions. However, there exists a complete gap of knowledge about the net effect of water level fluctuations induced by global change on greenhouse gases emission. Accordingly, further research is needed to assess whether the periodic exposure to dry–wet cycles, considering the extent and frequency of the cycles, will amplify the role of these especial ecosystems as a source of these gases and thereby act as a feedback mechanism for global warming. To conclude, it is pertinent to consider that a better understanding about the effect of water level fluctuations on the biogeochemistry of Mediterranean wetlands will help to predict how other freshwater ecosystems will respond.

Can Constructed Wetlands be Wildlife Refuges? A Review of Their Potential Biodiversity Conservation Value

The degradation of wetland ecosystems is currently recognized as one of the main threats to global biodiversity. As a means of compensation, constructed wetlands (CWs), which are built to treat agricultural runoff and municipal wastewater, have become important for maintaining biodiversity. Here, we review studies on the relationships between CWs and their associated biodiversity published over the past three decades. In doing so, we provide an overview of how wildlife utilizes CWs, and the effects of biodiversity on pollutant transformation and removal. Beyond their primary aim (to purify various kinds of wastewater), CWs provide sub-optimal habitat for many species and, in turn, their purification function can be strongly influenced by the biodiversity that they support. However, there are some difficulties when using CWs to conserve biodiversity because some key characteristics of these engineered ecosystems vary from natural wetlands, including some fundamental ecological processes. Without proper management intervention, these features of CWs can promote biological invasion, as well as form an ‘ecological trap’ for native species. Management options, such as basin-wide integrative management and building in more natural wetland components, can partially offset these adverse impacts. Overall, the awareness of managers and the public regarding the potential value of CWs in biodiversity conservation remains superficial. More in-depth research, especially on how to balance different stakeholder values between wastewater managers and conservationists, is now required.

Identifying restoration priorities for wetlands based on historical distributions of biodiversity features and restoration suitability

Wetland restoration is a major objective of environmental management worldwide. We present a frameworkat the regional level that prioritizes historical biodiversity and restoration suitability. The goal of the framework is to maximize biodiversity gains from restoration while minimizing the cost. We used C-Plan, a prioritization tool for systematic conservation planning (SCP), to balance the biodiversity gains withthe costs of restoration, or restoration suitability. We overlaid historical spatial data from 1995 to estimate historical distributions of 91 biodiversity features. These features were used to conduct an irreplaceability analysis to assess the restoration value of historical biodiversity. We then modelled restoration suitability based on environmental data of six criteria. Finally, we applied a complementarity analysis to achieve the quantitative targets of all biodiversity features while minimizing the cost of restoration. We tested this framework in the highly degraded wetlands ofSanjiang Plain, China. By applying our framework to Sanjiang Plain, we successfully identified areas with both high restoration value and high restoration suitability. The area of this cost-effective plan was an extension of 4620 km², covering 80% of the disappearing wetlands and 4% of the total Sanjiang Plain. Compared to the restoration value-only plan, which had an extension of 4486 km², the cost-effective plan covered a little more area to achievethe targets forall biodiversity features but with lower implementation costs where the proportion of high restoration suitability increases from 43% to 50%.Our prioritization framework can be used to analyse regional restoration efforts in other regions and ecosystems, and inform planners on how to maximize biodiversity gains while minimizing costs.

Using a multi-criteria analysis to identify rivers with hydromorphological restoration priority: Braided rivers in the south-eastern Subcarpathians (Romania)

In order to systematically plan river restoration actions at a regional scale, this paper develops a multi-criteria analysis that classifies rivers, based on their priority for hydromorphological restoration. This priority is defined by severe human pressures within the erodible corridor of the river, drastic alteration of the stream channel, and low intensity of river pattern functioning. Based on relevant indicators for three groups of features (human pressures, channel changes, and river functionality), a Hydromorphological Restoration Priority Index (HRPI) was designed. The high values (>66%) of HRPI reflect an urgent need for hydromorphological restoration while low values (<33%) reveal a less immediate necessity for restoration. The proposed methodology was applied on braided sectors of rivers crossing the south-eastern (Curvature) Subcarpathians (Romania). The values of the total HRPI ranged between 21% (Zăbrăuţ River) and almost 44% (Prahova River). According to our results, most of the analyzed sectors have a low need for hydromorphological restoration of the braided pattern, while some have a moderate necessity for restoration. Whereas the Prahova River has the highest HRPI, it should be given priority for restoration at a regional scale, which corresponds to the objectives of River Basin Management Plans for the interval beyond 2021.

Building a potential wetland restoration indicator for the contiguous United States

Wetlands provide key functions in the landscape from improving water quality, to regulating flows, to providing wildlife habitat. Over half of the wetlands in the contiguous United States (CONUS) have been converted to agricultural and urban land uses. However, over the last several decades, research has shown the benefits of wetlands to hydrologic, chemical, biological processes, spurring the creation of government programs and private initiatives to restore wetlands. Initiatives tend to focus on individual wetland creation, yet the greatest benefits are achieved when strategic restoration planning occurs across a watershed or multiple watersheds. For watershed-level wetland restoration planning to occur, informative data layers on potential wetland areas are needed. We created an indicator of potential wetland areas (PWA), using nationally available datasets to identify characteristics that could support wetland ecosystems, including: poorly drained soils and low-relief landscape positions as indicated by a derived topographic data layer. We compared our PWA with the National Wetlands Inventory (NWI) from 11 states throughout the CONUS to evaluate their alignment. The state-level percentage of NWI-designated wetlands directly overlapping the PWA ranged from 39 to 95%. When we included NWI that was immediately adjacent to the overlapping NWI, our range of correspondence to NWI ranged from 60 to 99%. Wetland restoration is more likely on certain landscapes (e.g., agriculture) than others due to the lack of substantive infrastructure and the potential for the restoration of hydrology; therefore, we combined the National Land Cover Dataset (NLCD) with the PWA to identify potentially restorable wetlands on agricultural land (PRW-Ag). The PRW-Ag identified a total of over 46 million ha with the potential to support wetlands. The largest concentrations of PRW-Ag occurred in the glaciated corn belt of the upper Mississippi River from Ohio to the Dakotas and in the Mississippi Alluvial Valley. The PRW-Ag layer could assist land managers in identifying sites that may qualify for enrollment in conservation programs, where planners can coordinate restoration efforts, or where decision makers can target resources to optimize the services provided across a watershed or multiple watersheds.

Natural wetlands are efficient at providing long-term metal remediation of freshwater systems polluted by acid mine drainage

This study describes the first long-term (14-year) evaluation of the efficacy of an established (>100 years) natural wetland to remediate highly acidic mine drainage (AMD). Although natural wetlands are highly valued for their biodiversity, this study demonstrates that they also provide important ecosystem service functions through their ability to consistently and reliably improve water quality by mitigating AMD. The Afon Goch river flows from Parys Mountain copper mine via a natural wetland, and was the major source of Zn and Cu contamination to the Irish Sea. Prior to 2003 the wetland received severe acidic metal contamination and retained a large proportion of the contamination (55, 64, and 37% in dissolved Fe, Zn, and Cu) leading to a greatly reduced metal flow to the Irish Sea. Reduced wetland loadings midway through the sampling period led to a reduction of metals by 83-94% and a pH increase from 2.7 to 5.5, resulting in long-term improvements in the downstream benthic invertebrate community. High root metal accumulation by the dominant wetland plant species and the association of acidophilic bacteria in the wetland rhizosphere indicate that multiple interacting processes provide an efficient and self-sustaining system to remediate AMD.

Wetland management reduces sediment and nutrient loading to the upper Mississippi river

Restored riparian wetlands in the Upper Mississippi River basin have potential to remove sediment and nutrients from tributaries before they flow into the Mississippi River. For 3 yr we calculated retention efficiencies of a marsh complex, which consisted of a restored marsh and an adjacent natural marsh that were connected to Halfway Creek, a small tributary of the Mississippi. We measured sediment, N, and P removal through a mass balance budget approach, N removal through denitrification, and N and P removal through mechanical soil excavation. The marsh complex had average retention rates of approximately 30 Mg sediment ha yr, 26 kg total N ha yr, and 20 kg total P ha yr. Water flowed into the restored marsh only during high-discharge events. Although the majority of retention occurred in the natural marsh, portions of the natural marsh were hydrologically disconnected at low discharge due to historical over-bank sedimentation. The natural marsh removed >60% of sediment, >10% of P, and >5% of N loads (except the first year, when it was a N source). The marsh complex was a source of NH and soluble reactive P. The average denitrification rate for the marsh complex was 2.88 mg N m h. Soil excavation removed 3600 Mg of sediment, 5.6 Mg of N, and 2.7 Mg of P from the restored marsh. The marsh complex was effective in removing sediment and nutrients from storm flows; however, retention could be increased if more water was diverted into both restored and natural marshes before entering the river.

Landowners' incentives for constructing wetlands in an agricultural area in south Sweden

Eutrophication of the Baltic Sea has in Sweden led to the initiation of government schemes aiming to increase wetland areas in agricultural regions and thereby reduce nutrient transport to the sea. Landowners play a significant role as providers of this ecosystem service and are currently offered subsidies to cover their costs for constructing and maintaining wetlands. We undertook a grounded theory study, in which landowners were interviewed, aiming at identifying landowners' incentives for constructing wetlands on their land. The study showed that adequate subsidies, additional services that the wetland could provide to the landowner, local environmental benefits, sufficient knowledge, and peers' good experiences could encourage landowners to construct wetlands. Perceived hindrances were burdensome management, deficient knowledge, time-consuming application procedures and unclear effectiveness of nutrient reduction. The main reason for not creating a wetland, however, was that the land was classified as productive by the landowner, i.e., suitable for food production. Current schemes are directed toward landowners as individuals and based on subsidies to cover costs. We propose that landowners instead are approached as ecosystem service entrepreneurs and contracted after a tendering process based on nutrient reduction effects. This would lead to new definitions of production and may stimulate improved design and placement of wetlands.