In-stream Wetland Research Articles

A Late Pleistocene Wetland Setting in the Arid Jurf ed Darawish Region in Central Jordan

Current conditions in the southern Levant are hyperarid, and local communities rely on fossil subsurface water resources. The timing of more favourable wetter periods and also their spatial characteristics are not yet well constrained. To improve our understanding of past climate and environmental conditions in the deserts of the southern Levant, sedimentary sections including artefact-bearing beds from Jurf ed Darawish on the Central Jordanian Plateau were investigated using sedimentological and micropalaeontological analyses and OSL dating. Grain-size analysis and structures of the clayey-silty sediments show that they mainly represent reworked loess deposits. The OSL ages suggest that these fine-grained sediments were accumulated during Marine Isotope Stages (MIS) 5-3. Recorded ostracod valves (mostly Potamocypris, Ilyocypris and Pseudocandona), remains of aquatic and terrestrial gastropod shells, and charophyte gyrogonites and stem encrustations indicate that an in-stream wetland existed at the location of Jurf ed Darawish during MIS 5-4 which was replaced by a vegetated alluvial plain in MIS 3. The prevailing aggradational setting was replaced by an erosional setting sometime after 30 ka. Abundant artefacts, distributed over a vertical range of up to 40 cm in a bed covered by a sedimentary sequence of 12-m thickness, provide evidence for the presence of humans in the region during a relatively long period from ca. 85 to 65 ka. The reconstruction of an in-stream wetland at Jurf ed Darawish, and the presence of humans at the site and in other desert regions of the Jordanian Plateau, the Wadi Arava/Araba, and the Negev and the Nefud deserts, show that the regional climate in the late MIS 5 and MIS 4 was significantly wetter than today and provided favourable conditions for humans in the Southern Levant and the northwestern Arabian Peninsula.

Watershed Scale Nitrate-N Abatement of Instream Wetlands: An Appraisal Using the Soil and Water Assessment Tool

HighlightsSWAT used to address watershed scale nitrate-N abatement of instream wetlands (ISWs).Experimental ISW results were incorporated into the watershed modeling framework.SWAT successfully captured and reproduced ISW impact on nitrate-N at sub-basin level.Scenarios of ISWs implementation were simulated, effects on nitrate-N export were evaluated.Results show ISWs can be used as conservation structures aimed at enhancing water quality.Abstract. In watersheds under high agricultural production, nitrate nitrogen (nitrate-N) pollution often originates from intensive application of fertilizers and animal manure to croplands. Surface runoff and nitrate-N export from farmlands contributes to the pollution of nearby reaches which flow into the watershed stream network. Experimental studies reported significant nitrate removal capacities of constructed instream wetlands (ISWs). However, cases of large-scale implementations of ISWs are uncommon, probably due to a paucity of watershed-scale studies which highlight the influence of ISWs on riverine water quality. To elucidate the ISWs nitrate-N abatement potential at the watershed scale, the Soil and Water Assessment Tool (SWAT) was used to model nitrate-N export in a highly agricultural watershed located in the Coastal Plain of North Carolina. SWAT was first calibrated and validated for streamflow and for nitrate-N export using data collected from the inlet and outlet of an experimental instream wetland. The validated SWAT model was used to simulate a decade of nitrate-N export under two scenarios: 1) watershed with ISWs implemented; and 2) watershed without ISWs. The results of the case study indicated that a watershed-wide implementation of ISWs is likely to curtail annual nitrate-N export by 49%. The study also evaluated cases where ISWs are implemented in selected percentage of sub-basins across the watershed. The outcomes show higher increments of nitrate-N curtailment when ISWs are implemented in the first top agricultural sub-basins. Hence, implementation of ISWs on selected sub-basins can mitigate nitrate-N from non-point sources and enhance water quality in the watershed’s stream network. Keywords: Runoff, Croplands, Instream wetland, Nitrate-N export, Denitrification, SWAT model, Watershed.

Low-cost natural wastewater treatment technologies in rural communities using Instream Wetland, Moringa Oleifera, and Aeration Weirs – A comparative study

Low-cost natural wastewater treatment technologies are very useful in developing communities that lacks investment and technologies. Wetland technologies prove excellent results for wastewater trea...

In-stream wetland deposits, megadroughts, and cultural change in the northern Atacama Desert, Chile

AbstractA key concern regarding current and future climate change is the possibility of sustained droughts that can have profound impacts on societies. As such, multiple paleoclimatic proxies are needed to identify megadroughts, the synoptic climatology responsible for these droughts, and their impacts on past and future societies. In the hyperarid Atacama Desert of northern Chile, many streams are characterized by perennial flow and support dense in-stream wetlands. These streams possess sequences of wetland deposits as fluvial terraces that record past changes in the water table. We mapped and radiocarbon dated a well-preserved sequence of in-stream wetland deposits along a 4.3-km reach of the Río San Salvador in the Calama basin to determine the relationship between regional climate change and the incision of in-stream wetlands. The Río San Salvador supported dense wetlands from 11.1 to 9.8, 6.4 to 3.5, 2.8 to 1.3, and 1.0 to 0.5 ka and incised at the end of each of these intervals. Comparison with other in-stream wetland sequences in the Atacama Desert, and with regional paleoclimatic archives, indicates that in-stream wetlands responded similarly to climatic changes by incising during periods of extended drought at ~9.8, 3.5, 1.3, and 0.5 ka.

Effects of instream restoration measures on the physical habitats and benthic macroinvertebrates in an agricultural headwater stream

The effectiveness of instream restoration measures in improving habitats has been extensively examined; however, the evidence is inadequate to infer that these measures have positive effects on benthic macroinvertebrates. In this study, we compared the effects of the instream wetland (IW), groin (GR), artificial drop (AD) and boulder placement (BP) measures on the physical habitat and benthic macroinvertebrates. On a five-year scale (two to six years after the implementation of the restoration project), the sample sites treated with the four restoration measures and the unrestored upstream control sample site were compared. The results show that the instream restoration measures had significant positive effects on the physical habitat and benthic macroinvertebrates in the agricultural headwater stream, that the physical habitat quality was a key factor affecting the restoration of the benthic macroinvertebrates, and that the restorative effects were affected by the interaction between the restoration measure and time. The five-year observation period showed continuous improvement in the habitat quality as well as a continuous increase in the taxon richness and diversity of the benthic macroinvertebrates at the restored sample sites. The AD and BP measures had the most significant positive effects on the richness and diversity of the benthic macroinvertebrates. The density of the benthic macroinvertebrates in the habitat at the sample site treated with the IW continuously remained at a high level. The benthic macroinvertebrates in the habitat at the sample site treated with the GR exhibited outstanding durability against and resilience to a flood. Schemes involving densely placed instream restoration measures had continuous positive effects on the physical habitat and benthic macroinvertebrates in agricultural headwater streams on a medium time scale (six years).

Effects of wetland restoration on nitrate removal in an irrigated agricultural area: The role of in-stream and off-stream wetlands

Eleven in-stream and five off-stream wetlands were restored in the southern portion of the Flumen River basin, an intensively irrigated agricultural area located in NE Spain, to evaluate their efficiency for nitrate removal and to assess the factors affecting their performance. Samples were taken during different periods of the year during 2011–2014 to evaluate the influence of agricultural activities during the two years following their completion. Nitrate concentration was significantly higher in the in-stream wetlands, showing a clear dilution effect caused by the inputs of the irrigation return flows. The patterns followed by the first-order nitrate removal rate constant were different for in-stream and off-stream wetlands and during irrigation and non-irrigation seasons. During non-irrigation seasons, the nitrate outflowing concentration was found to be negatively correlated (p<0.01) to the first-order nitrate removal rate constant for in-stream wetlands, indicating that high nitrate inputs may restrict the effectiveness of the wetlands. Temperature and dissolved oxygen were also found to significantly influence the performance of off-stream wetlands during non-irrigation seasons, but only dissolved oxygen promoted the nitrate removal during the irrigation period, indicating the influence of the seasonal factor on nitrate and wetlands dynamics. The results of this study showed that although a longer time is required to achieve optimal wetland development, wetlands can be used as buffer zones that effectively remove nitrates. This study emphasizes the influence of the agricultural seasonality of the factors affecting nitrate removal in wetlands, expanding the information provided by similar studies and validating a model that is applicable to a wide range of agricultural, hydrological and seasonal conditions.

Evaluating the influence of wetland vegetation on chemical residence time in Mississippi Delta drainage ditches

The presence of emergent vegetation within channelized aquatic environments has the capacity to provide a number of biological functions as well as alter the hydrology of the system. Vegetation within the channel exerts roughness, drag and friction on flowing water, reducing flow rates, increasing water depths and increasing hydraulic retention time. By increasing the hydraulic retention time, chemical residence time (CRT) is increased, thus improving the potential of pollutant mitigation. The study compared two geomorphologically similar drainage ditches, one vegetated and one non-vegetated to evaluate the effect obligate, in-stream wetland vegetation had on CRT. A fluoride (F −) tracer was amended to both ditches with nutrients and sediments to simulate stormwater runoff event. The measured CRT of the vegetated drainage ditch was at least twice that of the non-vegetated ditch. These results suggest that with the presence of vegetation increasing CRT, chemical removal rates will improve, and as a result increase the possibility of microbial transformation, adsorption, and macrophyte assimilation. By dredging or clear-scraping ditches and removing the vegetative component, farmers and managers alike will increase water flows, decrease CRT and potentially increase pollutant loads into aquatic receiving systems.

Methane flux characteristics in forest soils under an East Asian monsoon climate

Methane (CH 4) uptake by soil can possibly be suppressed more in regions with heavy summer precipitation, such as those under the East Asian monsoon climate, as compared to that in regions with a dry summer. In order to determine how precipitation patterns affect seasonal and spatial variations in CH 4 fluxes in temperate forest soils, such fluxes and selected environmental variables were measured on different parts of a hill slope in a cypress forest in central Japan. On the upper and middle parts of the slope, CH 4 uptake was observed throughout the year, and the uptake rates increased slightly with soil temperature and decreased with soil water content. The CH 4 flux predicted using data for the middle and upper parts of the slope ranged from −1.12 to −0.83 kg-CH 4 ha −1 y −1 (i.e. CH 4 uptake by soil) and from −2.30 to −2.04 kg-CH 4 ha −1 y −1, respectively. In contrast, in the relatively wet lower part of the slope near an in-stream wetland, large CH 4 emissions (>2 mg-CH 4 m −1 d −1) were observed during the rainy summer. In this wetter plot, the soil functioned as a net annual CH 4 source in a rainy year. Hence the variation in CH 4 flux with a change in soil water conditions and soil temperature on the lower part of the slope contrasted to that on the upper and middle parts of the slope. The predicted CH 4 flux for this lower plot ranged from −0.45 kg-CH 4 ha −1 y −1 in a dry year to 1.80 kg-CH 4 ha −1 y −1 in a rainy year. Our results suggest that consideration of the soil water conditions across a watershed is important for estimating the CH 4 budgets for entire forest watershed, particularly in regions subject to a wet summer.

Dissolved Phosphorus Export from an Animal Waste Impacted In‐Stream Wetland

The ability of wetlands to retain P makes them an important landscape feature that buffers P movement. However, their P retention ability can be compromised through hydrologic disturbances caused by hurricanes and tropical storms (TS). This study had three objectives: (i) to determine the effects of hurricanes and TS on dissolved phosphorus (DP) concentrations and loads discharged from a Coastal Plain in-stream wetland (ISW); (ii) to evaluate shifts in P storage pools that would reflect P accretion/removal patterns; and (iii) to determine if relationships exist between storm characteristics with releases of DP and water volume. From January 1996 to October 1999, the ISW's outflow DP concentrations and flow volumes (Q) were measured and they were used to calculate DP mass export loads. In addition, the sediment total phosphorus (TP) concentrations were measured, and both the water column and sediment pore water DP concentrations were examined using passive samplers. In several instances, TS facilitated greater DP releases than a single hurricane event. The largest release of DP occurred in 1999 after Hurricanes Dennis, Floyd, and Irene. The large differences in DP exports among the storms were explained by Q variations. Storm activity also caused changes in sediment pore water DP and sediment TP concentrations. This study revealed that some TS events caused higher DP releases than a single hurricane; however, multiple hurricanes delivering heavy precipitation totals significantly increased DP export.

Phosphorus Sorption by Sediments in a Southeastern Coastal Plain In‐Stream Wetland

A close relationship has been reported between sediment organic C (SedOC) content and its P sorption capacity (P(max)) and total P (TP) concentration. Phosphorus sorbed to organically complexed cations is a proposed explanation for this relationship. The objectives of this study were (i) to determine relationships between in-stream wetland SedOC content and both the sediment's P(max) and TP concentrations, and (ii) to ascertain the role of both organically complexed and oxalate-extractable cations on the sediment P(max) and TP values. The sediment's oxalate-extractable Fe (Fe(ox)) and Al (Al(ox)) contents were determined using acidified ammonium oxalate, while sodium pyrophosphate was used to extract organically complexed cations (Al(pryo), Ca(pyro), Fe(pyro), Mg(pyro), and Mn(pyro)). Both the sediment's P(max) and TP contents were strongly correlated with its SedOC concentration (r(2) > 0.90, P < 0.001). Only the Al(ox) contents were significantly correlated with TP and P(max), suggesting that amorphous Al forms have an important role in P sorption. All five pyrophosphate-extracted cations were significantly correlated with SedOC contents. Regression analyses showed that the Al(pyro) accounted for 88% of the variation in sediment P(max) values, whereas a combination of Al(pyro) and Ca(pyro) accounted for 98% of the variation in sediment TP concentrations. Additionally, Al and Ca chelated by SedOC compounds also have an important role in P binding and indicate that a linkage exists between the wetlands SedOC and P(max) content and its ability to accumulate TP. This study identified that two different mechanisms have significant roles in regulating P sorption by sediments in a southeastern Coastal Plain in-stream wetland.

Solutes and soil in and around an in-stream wetland on the Hubbard Brook Experimental Forest, New Hampshire, USA

We characterized soil and the concentrations of solutes in soil solutions and in stream water in and around a wetland located within a first-order stream in a forested watershed at the Hubbard Brook Experimental Forest (New Hampshire, USA). We hypothesized that the in-stream wetland would retain solutes in stream water, especially Ca2+, H+, and strong acid anions (NO3−, SO42−). Rather, the wetland had subtle impact on stream water chemistry causing slightly greater Na+ concentrations and lesser concentrations of H+ and dissolved inorganic C (DIC). We expected anaerobic microbial denitrification and SO42− reduction in wetland soils to consume the strong acid anions and account for less H+, but Na+ release was responsible. The wetland soil produced dissolved organic C (DOC) but did not export it into stream water. The DOC was saturated with monomeric Al, suggesting a sink rather than source for Al. Soil extracted with 1 M NH4Cl yielded much larger amounts of Ca2+ and Mg2+ than in the surrounding mineral forest soil, whereas NH4+, K+, and Na+ budgets were smaller in the wetland soil than in the forest soil. Characterization of soil surface charge and organic matter fractions revealed distinct differences between wetland soil organic matter (SOM) and forest soil SOM. Our results suggest that the wetland behaves much like gelatin: the organic matrix holds water tightly, such that stream water flows mostly over the matrix rather than entering and forcing much of the old water into runoff. The subtle biogeochemical role of the wetland adds to the complex interactions that control solute mobility in small watersheds.

Dissolved phosphorus retention and release from a coastal plain in-stream wetland.

Dissolved phosphorus (DP) can be released from wetlands as a result of flooding or shifts in water column concentrations. Our objectives were to determine the long-term (1460 d) DP retention and release characteristics of an in-stream wetland, and to evaluate how these characteristics respond to flooding, draining, and changes in DP concentrations. The studied in-stream wetland drains an agriculturally intensive subwatershed in the North Carolina Coastal Plain region. The wetland's DP retention and release characteristics were evaluated by measuring inflow and outflow DP concentrations, DP mass balance, and DP movement across the sediment-water column interface. Phosphorus sorption isotherms were measured to determine the sediment's equilibria P concentration (EPCo), and passive samplers were used to measure sediment pore water DP concentrations. Initially, the in-stream wetland was undersized (0.31 ha) and released 1.5 kg of DP. Increasing the in-stream wetland area to 0.67 ha by flooding resulted in more DP retention (28 kg) and low outflow DP concentrations. Draining the in-stream wetland from 0.67 to 0.33 ha caused the release of stored DP (12.1 kg). Shifts both in sediment pore water DP concentrations and sediment EPCo values corroborate the release of stored DP. Reflooding the wetland from 0.33 to 0.85 ha caused additional release of stored DP into the outflowing stream (10.9 kg). We conclude that for a time period, this in-stream wetland did provide DP retention. During other time periods, DP was released due to changes in wetland area, rainfall, and DP concentrations.

IN–STREAM WETLAND DESIGN FOR NON–POINT SOURCE POLLUTION ABATEMENT

Nonpoint source pollution (NPS) of rivers and streams is a major concern worldwide. Most methods for NPSmitigation focus on source reductions; few have been developed to mitigate NPS once nutrients have entered streams. Onesystem that has been shown to be effective in reducing stream nitrogen is by using instream wetlands (ISW). The objectiveof this research was to determine if design approaches used in constructed wetlands could be applied to predict ISWeffectiveness in treating NPS. The 3.3ha ISW studied was located in a 425ha watershed in eastern North Carolina. Weanalyzed the data from the ISW to calculate the firstorder rate constants (K20 and dimensionless temperature coefficient,..)for the kC* model used in constructed wetland design. We found that our calculated rate constants were in close agreementwith literature estimates with TN K20 = 1920 m/y and .= 1.0 1.03. NO3N rate constants were K20 = 38 54 m/y and .= 1.07 1.13. The design equations used for constructed wetlands can be successfully used to predict the performance of theISW.s prior to their implementation.

WATERSHED–SCALE SIMULATION OF SEDIMENT ANDNUTRIENT LOADS IN GEORGIA COASTAL PLAIN STREAMS USING THE ANNUALIZED AGNPS MODEL

Sediment and nutrient loadings in the Little River Research Watershed in south central Georgia were modeledusing the continuous simulation Annualized Agricultural NonpointSource Pollution (AnnAGNPS) model, part of the AGNPSsuite of modeling components. Specifically, nitrogen, phosphorus, sediment, and runoff were predicted over a sevenyearperiod. Land under cultivation makes up approximately 25% of the 333 km2 watershed. Livestock facilities include swine,poultry, dairy cows, and beef cattle. Results from the simulation were compared to seven years of monitoring data at the outletof five nested subwatersheds and at the outlet of the Little River Research Watershed (LRRW). The average annual predictedrunoff in the upper part of the watershed was onethird to half of observed runoff. In contrast, predicted runoff in the lowerpart of the watershed was close to observed, and was 100% of observed at the outlet of the watershed. Runoff underpredictionwas attributed to the method of landcover discretization. The extent of forest land in the upper watershed (55% to 63%) andthe fragmented landscape that has relatively small fields surrounded by riparian forests and tracts of forest resulted inoverestimation of forested area in the watershed. In addition to runoff, sediment and nutrient loads were also underpredictedin the upper part of the LRRW. Two factors are most likely responsible for underprediction. Runoff is underpredicted at thesesites, which reduces the carrying capacity of sediment loads. In addition, the overestimation of forested areas at these sitescoincides with underestimation of sedimentproducing areas, such as cropland. In contrast to the upper part of the watershed,sediment and nutrient loads were overpredicted in the lower part of the watershed. This may have resulted from inadequatelysimulating nonpointsource pollution attenuation by the extensive riparian forests and forested instream wetland areasfound in these watersheds. Prediction results can be improved through better input into the model, as well as modificationof the processes within the model to account for forest and riparian conditions.

In-stream wetlands and their significance for channel filling and the catchment sediment budget, Jugiong Creek, New South Wales

Evidence is presented here of recent and extensive infilling of the incised channel network of the Jugiong Creek catchment, SE Australia. The present channel network resulted from widespread stream and gully incision in the period between 1880 and 1920. Our survey shows that gully floors have been colonised extensively by emergent macrophyte vegetation since before 1944, forming continuous, dense, in-stream wetlands, which now cover 25% of the channel network in the 2175 km 2 catchment and have so far trapped almost 2,000,000 t of nutrient-enriched, fine sediments. This mass of sediments represents the equivalent of 4.7 years of annual sediment production across the catchment and in some tributaries, more than 20 years of annual yield is stored within in-stream wetlands. Previous work on the late Quaternary stratigraphy of the region has shown that there were repeated phases of channel incision in the past following which the channels quickly stabilised by natural means and then filled with fine-grained sediment to the point of channel extinction, creating unchannelled swampy valley floors. The current formation and spread of in-stream wetlands is interpreted to be the onset of the next infill phase but it is not known whether present conditions will allow complete channel filling and reformation of the pre-existing swampy valley floors. Nevertheless, further spread of in-stream wetlands is likely to increase the sediment trapping capacity and further reduce the discharge of sediments and nutrients into the Murrumbidgee River. The in-stream wetlands may provide a significant capacity to buffer erosion from gullied catchments of considerable size (up to 300 km 2) as an adjunct to current riparian management options. They may also assist the recovery of sediment-impacted channels downstream.

In‐Stream Wetland Mitigation of Nitrogen Contamination in a USA Coastal Plain Stream

AbstractNonpoint source N from riverine origin is a major water quality problem throughout the world. Nitrogen removal from a contaminated (6.6 mg L−1, NO3‐N) stream was evaluated in this study using an instream wetland (ISW). The ISW was established at the exit of a 425‐ha USDA Water Quality Demonstration watershed in the Coastal Plain of North Carolina. It ranged in depth from about 0.2 to 2 m, and it was &lt;1% (3.3 ha) the size of the watershed. The ISW dramatically lowered mean stream NO3‐N from 6.6 to 2.0 mg L−1. Nitrate‐N mass removal was highly correlated to inflow NO3‐N (r = 0.93) in the warmer months when biological processes were more active. Ammonia‐N mass removal was opposite that of NO3‐N. It was highly correlated to inflow NH3‐N (r = 0.81) during the cooler months. Removal of both NO3‐N and total‐N (NO3‐N + TKN) were positively correlated to temperature with r values of 0.77 and 0.62, respectively. Total annual N removal for the ISW was approximately 3 kg ha−1 d−1, which was about 37% of the inflow N. The ISWs appear to be very good landscape features for mitigating excess nonpoint source N in the southeastern Coastal Plain of the USA. As such, they are a good complement to other best management practices for improved water quality.

Functional analysis of a two-year-old created in-stream wetland: Hydrology, phosphorus retention, and vegetation survival and growth

Planted vegetation survival and growth, hydrology, and phosphorus dynamics were monitored for the first two years of wetland development at a 6-ha created riparian wetland, in Franklin County, Ohio, USA. Herbaceous vegetation developed clear zonation and appeared to reduce the invasion ofTypha spp. Of the 17 species introduced, 8 were among the 18 most commonly encountered species approximately 2 years after the wetland was constructed. Planted saplings generally survived except where they were found in standing water;Liquidambar styraciflua andBetula nigra were less successful because the site is close to their northern range. Simulation models were developed to predict hydrology, phosphorus retention, and tree growth. The site has a rapidly pulsing hydroperiod driven by runoff from storm events. Annual simulated phosphorus loading was 17.8 gP m−2 yr−1 and retention was 2.9 gP m−2 yr−1 (16% of inflow). Fifty years of tree growth simulated for each planted tree species indicated that the site will develop into a forested wetland dominated byQuercus palustris andFraxinus pennsylvanica with basal area comparable to riparian forests but with lower stem density unless seedlings germinate from the planted trees. Lower water levels in the wetland would favor the development of the woody vegetation over herbaceous vegetation and would also favor higher retention of phosphorus.

Restoration of our lakes and rivers with wetlands – an important application of ecological engineering

The role of wetlands, both natural and man-made, in improving water quality of streams, rivers, and lakes is illustrated with examples of fringe, instream, and riparian wetlands. Fringe wetlands have been shown to reduce inputs to freshwater lakes, instream wetlands can improve habitat and provide some water quality function to small streams, and riparian wetlands along larger rivers provide important roles in both capturing sediments and nutrients from the river itself and serving as buffer between uplands and the river. Two major experimental riparian wetland sites in Midwestern USA are introduced: The Des Plaines River Wetland Demonstration Project and the Olentangy River Wetland Research Park.

Restoration of our lakes and rivers with wetlands — An important application of ecological engineering

The role of wetlands, both natural and man-made, in improving water quality of streams, rivers, and lakes is illustrated with examples of fringe, instream, and riparian wetlands. Fringe wetlands have been shown to reduce inputs to freshwater lakes, instream wetlands can improve habitat and provide some water quality function to small streams, and riparian wetlands along larger rivers provide important roles in both capturing sediments and nutrients from the river itself and serving as buffer between uplands and the river. Two major experimental riparian wetland sites in Midwestern USA are introduced: The Des Plaines River Wetland Demonstration Project and the Olentangy River Wetland Research Park.

Landscape design and the role of created, restored, and natural riparian wetlands in controlling nonpoint source pollution

General design principles, landscape locations, and case studies of natural and constructed riverine wetlands for the control of nonpoint source (NPS) water pollution are presented. General design principles of wetland construction for NPS pollution control emphasize self-design and minimum maintenance systems, with an emphasis on function over form and biological form over rigid designs. These wetlands can be located as instream wetlands or as floodplain riparian wetlands, can be located as several wetlands in upstream reaches or fewer in downstream reaches of a watershed, and can be designed as terraced wetlands in steep terrain. Case studies of a natural riparian wetland in southern Illinois, an instream wetland in a downstream location in a northern Ohio watershed, and several constructed riparian wetlands in northeastern Illinois demonstrate a wide range of sediment and phosphorus retention, with greater efficiencies generally present in the constructed wetlands (63–96% retention of phosphorus) than in natural wetlands (4–10% retention of phosphorus). By itself, this could be misleading since the natural wetlands have much higher loading rates and actually retain an amount of nutrients comparable to constructed wetlands (1–4 g P m −2 year −1).