Distribution of soil organic matter in freshwater emergent/open water wetlands in the Portland, Oregon metropolitan area

Abstract

Abstract:We measured soil organic matter (SOM) concentrations in a large sample ~n = 95) of freshwater emergent and open water weltands in the Portland, Oregon, USA, ,area as part of a study of the ecological development of mitigation wetlands. Mean SOM concentrations were higher in naturally occurring wetlands (NOWs) than in mitigation wetlands (MWs) at 0-5 cm (SOM = 9.75 and 5.83%, respectively, p = 0.0001) and at 15-20 cm (SOM = 6.85, 4.68%, p = 0.0551). If temporal accumulation of SOM is occurring, it is slow; we found no significant relationship between SOM and wetland age (p = 0.6003) and no signilicant change in SOM concentration in soils in MWs sampled in 1987 and 1993, Concentrations of SOM were not significantly related to land use but were related to soil series, texture class, and association, and to hydrogcomorphic class. For a subset of wetlands monitorcd for hydrology, we also found a significant negative relationship between SOM and the extent of inundation by standing water. Mitigation may be leading to direct loss of SOM, probably resulting from soil management practices during project construction. We also show that hydrologic regime significantly affects SOM. Because most projects in our study were built in pre-existing wetlands and have extensive areas of open water, our results suggest that low concentrations of SOM are likely to persist. For SOM and probably for SOM-supported wetland functions, fundament~d goals of mitigation and wetland management (in-kind wetland replacement, no-net-loss of structure and function) are not being achieved, at least in the short term. The success of mitigation, in terms of SOM, could be improved by better project design and better management of soils during project construction.

Human Impacts on Macrophyte Diversity, W Ater Quality and Some Soil Properties in the Madikane and Dufuya Wetlands of Lower Gweru, Zimbabwe

“…Agricultural activity in hydric soils does not always result in the depletion of soil organic carbon (Shaffer and Ernst, 1999). In our study, it was shown that the wetness of the soil, which was influenced by the position in the dambo, had an effect on total organic content ( Figure 5) since organic carbon increased with an increase in moisture content.…”

Characteristics of mangrove swamps managed for mosquito control in eastern Florida, USA

“…Because of its importance as an indicator of biogeochemical processing, the status of soil organic matter accumulation has become an important consideration in assessing the success of wetland restoration projects (Craft et al 1988(Craft et al , 1999. It is generally assumed that organic matter levels will increase with time of recovery in restored wetlands (Craft et al 1988(Craft et al , 1999 and that, initially, organic matter levels are lower in restored or created wetlands than in natural (control) wetlands (Bischel-Machung et al 1996, Shaffer & Ernst 1999. In the present study, we found that this simple relationship does not adequately describe soil organic matter content in control versus managed swamps; RIM swamps had more than twice as much soil organic matter than both control and restored (breached-RIM) mangals (Table 3).…”

The United States HGM (Hydrogeomorphic) Approach

“…Data collection and data analysis approaches can be found in previously published regional guidebooks (http://el.erdc.usace.army.mil/wetlands/guidebooks.html) as well as peer-refereed publications that have characterised subclasses in such a way that the natural variability is determined (Magee et al 1999;Rheinhardt et al 1999;Shaffer and Ernst 1999). Techniques for data collection are not unique to the HGM approach, but rather are common ecological sampling methods for forests and grasslands with emphasis on hydrologic indicators.…”