Dynamics of Nutrient Runoff Following Wetland Restoration Along the Illinois River Clint Martin, Ashlyn Borges, and Sherri Morris Bradley University, Peoria, IL Land-Use Change Over 95% of the original wetland in Illinois, Indiana, and Iowa has been lost; most of this land has been contained behind levee systems, drained, and converted to farmland (Zedler, 2003). Extensive tiling, tillage, and fertilization has increased the flow of sediments and nutrients into aquatic ecosystems from these lands (Hey, 2002). Importance/Functionality of Wetlands Ecosystem services provided by wetlands include water retention, nutrient sink capacity, and biodiversity support (ESA, 2000). The availability of these ecosystem services depends entirely on proper ecosystem function (long water retention time, sheet flow of water, appropriate vegetation, etc.) (Jordan et al., 2003). The increased runoff due to modern agricultural practices (tillage, fertilization, etc.) has increased the importance of these ecosystem services; excessive additions of nutrients and sediments causes extensive detrimental effects on both freshwater and coastal aquatic ecosystems. Soil uptake and storage can decrease these impacts. Wetland Restoration A growing percentage of land worldwide is undergoing wetland restoration. One such project has been initiated by Ducks Unlimited at Wightman Lake, a 370 acre parcel near Sparland, Illinois; the restoration is part of a larger program to restore/protect a 15-mile stretch of the Illinois River directly north of Peoria, Illinois. The wetland system is fed by the Gimlet Creek watershed, which primarily drains farmland. Restoration plans include enhancing wetland habitat, improving the bottomland forest stand, and replanting former farmland with trees (Figure 1). Project goals include increasing bird habitat, improving water quality, and establishing a demonstration site for conservation practices. Evaluating the degree to which ecosystem services are restored requires assessment of ecosystem function through the monitoring of ecosystem dynamics. Background The objective of this study was to follow changes in ecosystem dynamics as restoration progresses at Wightman Lake by monitoring N and P flow across the site, soil C, and soil nutrient turnover (N and P) pre and post restoration. Objective Figure 1. Map and restoration plans for Wightman Lake (provided courtesy of Ducks Unlimited). Water 04/09/07 05/30/07 06/20/07 d b c a ab e * Nitrogen Phosphorus Soils Water Samples were collected from 6 locations (in the Gimlet Creek watershed and at wetland inflow/outflow locations) over 5 time points from April to June 2007. Samples were filtered to remove suspended sediments and frozen for analysis. N and P content were determined with LACHAT Autoanalyzer using standard procedures. Soils Soil cores were taken from 22 locations across the project area at 3 depths (0-10 cm, 10-25 cm, and 25-50 cm) prior to restoration. Selection of sampling locations attempts to accurately represent different functional areas at the site (wetland, bottomland forest, replanted agricultural land). Soil analysis included C and N mineralization, C/N ratio, and resistant C/N ratio. Analysis All data were analyzed using ANOVA (Proc. Mixed; SAS 1999). Methods Figure 2. Carbon evolution (µg CO2-C/g soil/day) for agriculture and forest soils to 10 cm at Wightman Lake. Incubation data will ultimately be used to evaluate soil C pool sizes a b Ag Forest Figure 3. Mg C/ha, Mg N/ha and C:N ratio to a depth of 50 cm corrected for equivalent soil weight in forest and agricultural soils at Wightman lake. Water Nitrogen Ammonium content of Gimlet Creek was very low across the dates measured. Stream nitrate concentration differed across the season (Figure 4). Water from early season dates (April 9, 23, 30) had relatively low nitrate concentrations and did not differ significantly. Water from late season dates (May 30, June 20) had significantly greater nitrate than early dates. Nitrate was greatest on the slope and decreased as Gimlet Creek approached the wetland. Wetland nitrate output was lower than concentrations in Gimlet Creek. Phosphorus There were significant differences in stream orthophosphate at most sample locations across the season (Figure 5). The pattern detected was less consistent than that for nitrate. Outflow to the Illinois River from the wetland is currently higher than input to the system. Soils There are significant differences in the rate of C evolution between the agricultural soils and forest soils (Figure 2). There is significantly greater soil C and N in the forest soils compared to the agricultural soils (Figure 3). The soils did not differ in C:N ratio. Thirty day nitrogen incubations had significantly greater immobilization in the agricultural soils compared to the forest soils (data not shown). Results Figure 4. Mean nitrate-nitrogen concentration in mg NO32--N/L for six sampling locations across three time points. Each histogram bar represents the mean ± standard error. Histogram bars labeled with the same lower-case letter were not significantly different at P < 0.05. *An asterisk represents a point where no sample was taken due to low water levels. Figure 5. Mean orthophosphate concentration in mg P/L for six sampling locations across three time points. Each histogram bar represents the mean ± standard error. Histogram bars labeled with the same lower-case letter were not significantly different at P < 0.05. *An asterisk represents a point where no sample was taken due to low water levels. Discussion Water Nitrate patterns in this system are likely related to patters of N fertilizer use for agriculture; the Wightman Lake wetland restoration should serve to reduce movement of nitrate into the Illinois River. Contributions of orthophosphate from this system to the Illinois River do not appear to be exceedingly high but appear to be consistent with current regional trends. More research is necessary to understand patterns and the role that wetland restoration will play in managing movement of orthophosphate into the Illinois River. Soils Agricultural soils have a wide C:N ratio with high rates of N immobilization; these soils have great potential to hold the nitrogen that is added as it settles out of diverted agricultural run off. The added N and likely P will increase soil and plant productivity across the restored Wightman Lake property; this should result in increased soil C sequestration. Nitrate and orthophosphate movement in the Illinois River play a significant role in the degrading quality of downstream aquatic ecosystems. Restoration of wetland nutrient dynamics at Wightman lake should decrease nutrient flow to the Illinois River. We will follow changed in ecosystem function as the restoration project is completed and plant establishment becomes permanent. Monitoring will allow us to evaluate the degree to which the restoration project meets stated goals. Restoring functioning wetlands along the Illinois River will improve river quality and protect downstream communities. More studies are needed that follow changes in ecosystem dynamics following restoration to evaluate the degree to which different restoration plans achieve desired goals. Conclusions References Ecological Society of America (ESA). (2000). Nutrient pollution of coastal rivers, bays, and seas. Issues in Ecology, 7. Hey, D.L. (2002). Nitrogen farming: harvesting a different crop. Restoration Ecology, 10(1):1-10. Jordan, T.E., Whigham, D.F., Hofmockel, K.H., Pittek, M.A. (2003) Nutrient and sediment removal by a restored wetland receiving agricultural runoff. J. Environ. Qual., 32:1534-1537. SAS Institute Inc. (1999). SAS OnlineDoc®, Version 8, Cary, NC: SAS Institute Inc. Zedler, J.B. (2003). Wetlands at your service: reducing impacts of agriculture at the watershed scale. Front. Ecol. Environ., 1(2):65-72 . This research was supported by the National Great Rivers Research and Education Center (NGRREC). Thanks to Ducks Unlimited, particularly Eric Schenck, for maps, guidance, and an informative tour of Wightman Lake. Thanks also to students in McConnaughay and Morris labs for their help in collecting and processing samples. Acknowledgements