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  • Assessing Urban Wetland Soils for Reed Canary Grass Management (Minnesota)
  • William M. Bartodziej (bio), Simba Blood (bio), and Jake Lindeman (bio)

Reed canary grass (Phalaris arundinacea) thrives in urban watersheds where stormwater increases nutrient concentrations, water level fluctuation, and sediment inputs (Wilcox et al. 2007, Stiles et al. 2008). Although managers have attempted to control reed canary grass using a variety of methods, results have been generally negative (Adams and Galatowitsch 2006). Limited public funds and personnel further inhibit effective reed canary grass management, warranting the development of cost effective strategies for prioritizing the restoration of reed canary grass impacted wetlands.

As a case study, the Ramsey-Washington Metro Watershed District (RWMWD) actively manages native plant communities in 30 urban wetlands and stormwater ponds. All of these systems have populations of reed canary grass and receive stormwater inputs. Generally, our management (i.e., herbicide application, mowing, and burning) has resulted in relatively low populations, less than 10% cover site wide, of reed canary grass in created ponds and wetlands with mineral soils. Conversely, we have had very limited success controlling reed canary grass in wetlands with organic soils. From 2000 to 2010, our wetland restoration maintenance records indicate significantly higher labor hours (p<0.05, Wilcoxon rank-sum test) associated with controlling reed canary grass in wetlands with organic soils (x = 31 hr/ha/yr) versus created wetlands and ponds with mineral soils (x = 5 hr/ha/yr). To investigate differences in invasion potential between organic and mineral soil wetlands, we compared reed canary grass abundance, soil organic matter (OM), and soil nitrogen (N) in wetlands throughout our watershed. Nitrogen has been identified as a primary catalyst of reed canary grass expansion in wetland systems (Green and Galatowitsch 2002). Because of these findings and our long-term field observations, we focused on soil N and OM in our assessment. To keep the approach cost effective, we used inexpensive agricultural soil tests. Our working hypothesis was that higher soil N and OM would be detected in systems dominated by reed canary grass. If supported, this guideline could be a first step in assessing wetland soils in relation to reed canary grass management. A practical assessment approach may be useful in gauging management requirements and ranking urban wetlands for restoration priority.


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Figure 1.

Mean Nitrate-N, INST-N, total phosphorus, total nitrogen, and organic matter concentrations (± 1 SD) for wetlands with low (<10% cover) and high (>90% cover) reed canary grass (RCG) abundance in the Ramsey-Washington Metro Watershed District (Minnesota). For each sampling date, different letters indicate significant (p>0.05)differences.

We sampled 16 urban wetlands and stormwater pond transitional zones (henceforth called wetlands) within the [End Page 329] boundaries of the RWMWD, which encompasses a portion of St. Paul (Minnesota) and several first ring suburbs (www.rwmwd.org). Over 95% of the watershed is in urban-residential land use, and all the study wetlands receive stormwater. On a watershed scale, land use and stormwater inputs were consistent across all wetlands. Visual estimates of reed canary grass cover in transitional zones (defined as an area with a predominance of wetland species and soils that are saturated during normal hydrologic conditions) indicated that 8 created wetlands had low reed canary grass abundance (< 10% cover), and 8 wetlands (4 natural and 4 created) had high reed canary grass abundance (> 90% cover). The created wetlands selected for this study were between 6-10 yr old. These systems were excavated, seeded, and/or planted with a variety of herbaceous wetland species and receive periodic (usually 3 visits/yr) invasive plant control.


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Figure 2.

Regression plot of ISNT-N and percent organic matter for both low (<10% cover) and high (>90% cover) reed canary grass (RCG) abundance wetlands (y = 51.2 + 49.7x).

We conducted soil sampling in November 2010. At each wetland, we identified a random 10-m2 patch of vegetation in the transitional zone. Using a hand auger, we collected 3 soil cores (30 cm depth) at 3-m intervals in each patch and combined the cores to produce a composite soil sample for each wetland. We air...

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Additional Information

ISSN
1543-4079
Print ISSN
1543-4060
Pages
pp. 329-331
Launched on MUSE
2011-11-05
Open Access
No
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