Elsevier

Ecological Engineering

Volume 72, November 2014, Pages 25-34
Ecological Engineering

Sedimentation in created freshwater riverine wetlands: 15 years of succession and contrast of methods

https://doi.org/10.1016/j.ecoleng.2014.09.116Get rights and content

Abstract

This study summarizes five separate sedimentation studies spanning 15 years (years 3–17 following wetland creation in 1994) of two 1 ha experimental flow-through wetlands. Included are methods and analyses of the most recent (2009–2010) comparative study that attempted to quantify both erosion and bioturbation processes. Depending on techniques used, two distinct types of sedimentation rates were estimated—gross and net sedimentation. Gross sedimentation in 2004–2005 (years 11 and 12) using sediment trap bottles was 45 kg m−2 for 4 months during and after spring flood pulsing conditions in 2004 and 39 kg m−2 for the same 4 months during and after steady flow conditions in 2005. Annual sediment accretion using feldspar and other horizon markers was 31.7 ± 4.4 kg m−2 yr−1 (4.2 ± 0.6 cm yr−1) in 1996 (year 3 after wetland creation) and 34.4 ± 4.5 kg m−2 yr−1 (5.5 ± 0.8 cm yr−1) in 2009 (year 16 after wetland creation). Net sedimentation using soil cores to estimate accumulation of sediments over antecedent soil horizon layers was 4.7 ± 0.3 kg m−2 yr−1 (0.9 ± 0.07 cm yr−1) in 2004 (year 11) and 6.0 ± 0.4 kg m−2 yr−1 (0.9 ± 0.06 cm yr−1) in 2009 (year 16). Net sedimentation, using estimates of sedimentation and erosion with the sediment erosion table (SET) method in 2009–2010 (years 16–17) was 3.9 ± 6.1–9.0 kg m−2 yr−1 (1.3 ± 0.8–1.4 cm yr−1). Bioturbation by macrofauna significantly decreased sedimentation rates during the 2009 (year 16) study. Spatial patterns, consistent among horizon marker and net sedimentation studies, showed that deep, open-water areas had higher rates of sedimentation than shallow areas with emergent vegetation, and that sedimentation rates were higher when closer to the inflow than at the outflow of these flow-through wetlands. Net sedimentation of these created riverine wetlands ranged from 1.2 cm/yr to 1.4 cm/yr, suggesting that these wetlands will accumulate about 30 cm of sediments in a little more than two decades.

Introduction

Sedimentation and erosion are important processes in wetlands. Sedimentation improves water quality (Hupp and Morris, 1990, Johnston, 1991, Gilliam, 1994, Mitsch and Gosselink, 2015), increases water clarity for improved submersed plant accessibility to sunlight (Nahlik and Mitsch, 2008), and retains nutrients that otherwise cause eutrophication downstream (Mitsch et al., 2001). Sedimentation is also a fundamental process that leads to carbon sequestration in wetlands (Bernal and Mitsch, 2012, Bernal and Mitsch, 2013). Because water velocity decreases dramatically in wetlands compared to streams and rivers, sedimentation occurs to a greater extent in riparian wetlands than in the adjacent river systems (Brueske and Barrett, 1994). This means that both productivity of the wetlands themselves and pollution control of the watershed can be advanced through sedimentation in wetlands. Sedimentation in freshwater wetlands has been investigated by Brueske and Barrett (1994) and Fennessy et al. (1994) at created wetlands at the Des Plaines River Wetlands in northeastern Illinois; Braskerud et al. (2000) in southeast Norway; Hupp et al. (2008) at the Atchafalaya Basin of Louisiana, USA; Kleiss (1996) in eastern Arkansas, USA; Craft and Casey (2000) in Georgia, USA; Mann and Wetzel (2000) in Alabama, USA; Darke and Megonigal (2003) at coastal marshes of Virginia, USA; and Sánchez-Carillo et al. (2001) at Las Tablas de Daimiel, Spain.

Accurate estimates of erosion patterns are necessary in wetland sedimentation studies to determine the net sedimentation resulting from fluvial and autogenic processes. The study of erosion; however, has only recently become an accurate science and there are few published papers that include erosion measurements in freshwater wetlands. Erosion increases with exposure to strong winds and wave energy (Scarton et al., 1998) while the presence of vegetation and corresponding tensile root strength can help to prevent erosion (Ward et al., 1984, VanEerdt, 1985, Stevenson et al., 1988). Marsh surface elevation changes and/or sediment erosion have been estimated by Rybczyk et al. (1998) in Louisiana, USA; Pasternack (1998) in Chesapeake Bay USA; Morris et al. (2002) in South Carolina, USA; and Perez-Arlucea et al. (2005) in Spain.

Sedimentation has been measured with several methodologies, including: rare-earth stable tracer horizons like Cs-137 and Pb-210 (Craft and Richardson, 1993, Bernal and Mitsch, 2012), horizon markers (Knaus and Van Gent, 1989, Harter and Mitsch, 2003, Hupp et al., 2008), sediment traps and bottles (Mitsch et al., 1979a, Brueske and Barrett, 1994, Fennessy et al., 1994, Braskerud et al., 2000, Braskerud, 2001, Nahlik and Mitsch, 2008), dendrogeomorphic techniques (Hupp and Morris, 1990, Hupp et al., 1993), and sedimentation plates (Mitsch et al., 1979b, Braskerud et al., 2000, Braskerud, 2001). Variable methodologies have led to inconsistent and poorly comparable sedimentation rates. Insight is needed to translate results using one methodology into information comparable with other studies. An accurate method of estimating net sedimentation is needed for wetlands to quantify the net effect of both gross sedimentation measurements and erosion rates.

Erosion has been studied by very few methods, one of which has been stakes and rods (Harbord, 1949, Pestrong, 1965, Reed, 1989). The accuracy of these experiments has yet to be determined. Day and Boumans (1993) developed the SET (sedimentation-erosion table) to measure erosion, specifically in coastal marshes and shallow sub-tidal areas like wetlands. This method is effective, but in many cases is not economical to implement. None of these methods has yet been applied to sedimentation/erosion studies in freshwater wetlands.

Harter and Mitsch (2003), Anderson and Mitsch (2006), Nahlik and Mitsch (2008), and Bernal and Mitsch (2013) all published estimates of sedimentation in the created wetlands at the Olentangy River Wetland Research Park (ORWRP). The goals of this paper are to integrate these previous sedimentation studies with additional field measurements at the 16- to 17-year-old experimental wetlands at the Olentangy River Wetland Research Park to: (1) compare current rates of gross sedimentation in these wetlands with those taken up to 15 years before; (2) to explore spatial and successional patterns of sediment retention in newly created wetlands; and (3) compare sedimentation methodologies in freshwater riverine wetlands. This paper also presents new estimates of net sedimentation in these wetlands determined by estimating erosion and investigates the importance of animal bioturbation using exclosure fences around horizon markers.

Section snippets

Site description

Two identical flow-through wetlands were created in 1994 at the Olentangy River Wetland Research Park on the campus of the Ohio State University in the urban center of Columbus, Ohio, USA (Mitsch et al., 1998, Mitsch et al., 2005, Mitsch et al., 2012). These freshwater, riparian wetlands receive pumped inflow water from the adjacent Olentangy River. Both wetlands have statistically similar hydraulic loads and both have weir-controlled outflows. The Olentangy River carries runoff from

Gross and annual sediment accretion

Of the three studies conducted to estimate gross and annual sediment accretion, an approximate range of annual gross sedimentation of 30–90 kg m−2 yr−1 was observed in these created wetlands by the three separate studies (Table 1) (Harter and Mitsch, 2003, Nahlik and Mitsch, 2008; this study). Annual accretion rates observed using the feldspar horizon marker method resulted in 31.7 ± 4.4 kg m−2 yr−1 (4.2 ± 0.6 cm yr−1) in 1996 and 34.4 ± 4.5 kg m−2 yr−1 (5.5 ± 0.8 cm yr−1) in 2009, with a range of 13.6–63.8 kg m−2 yr−1

Conclusions

  • 1.

    Erosion in temperate freshwater wetlands is higher in the late rather than the early growing season due to higher sediment loads from hydrologic conditions in the spring and high kinetically charged water flow in the summer.

  • 2.

    Erosion is ubiquitous in created, freshwater wetlands, occurring frequently within varied spatial and temporal dimensions and despite positive annual rates of net sedimentation.

  • 3.

    Bioturbation by wetland mammals and waterfowl in freshwater flow-through wetlands appears to

Acknowledgements

Thanks to the many wetlanders who helped the authors in the four separate studies summarized here; you are too numerous to mention but your contributions to wetland science remain important. This research was supported by several sources including Society of Wetland Scientists student support, OARCD graduate research enhancement, Payne, and SEEDS grants, USDA NRI CSREES Grant no. 2002-35102-13518, USEPA AgreementsEM83329801-0 from Cincinnati OH and MX95413108-0 from Gulf of Mexico Program, the

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