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Energetic carrying capacity of riverine and connected wetlands of the upper Illinois River for fall-migrating waterfowl.

INTRODUCTION

The Illinois River historically provided extensive, productive habitats for waterfowl, but commercial navigation, sedimentation, pollution, fluctuating water levels, suspended sediments, flocculent substrates, and wetland drainage have contributed to reductions in aquatic vegetation and native foods of waterfowl (Starrett and Fritz, 1965; Talkington, 1991; Havera, 1999; Stafford et al., 2007). Most reaches of the Illinois River began to experience loss of aquatic vegetation after connection to Lake Michigan by the Chicago Area Waterway and Sanitary and Ship Canal around 1900 (Talkington, 1991), but spatial extent of aquatic vegetation declined most dramatically between 1940 and 1960 and has not recovered in most of its historic range throughout the Illinois River Valley (IRV; Bellrose et al., 1983; Talkington, 1991; Stafford et al., 2010). Likewise, status of aquatic vegetation, especially obligate submersed and floating-leaf aquatic vegetation (SAV) used as food by or which produces food for waterfowl, is similar in the middle and upper Mississippi River System. Beds of SAV historically covered much of the IRV and Mississippi River system but are now reduced mainly to Pools 4-13 of the Mississippi River. (Moore et al., 2010).

Aquatic vegetation, such as wild celery (Vallisneria americana), sago pondweed (Stuckenia pectinata), and other macrophytes, are or produce important foods for waterfowl (e.g., seeds and tubers; Bellrose, 1941; Anderson and Low, 1976; Korschgen et al., 1988) and are less abundant in the Mississippi River system and IRV (Bellrose et al., 1983; Moore et al., 2010). Riverine wetlands which still contain aquatic vegetation may have become increasingly important habitats for waterfowl, especially dabbling (Anas sp.) and diving ducks (Aytliya sp.) that feed on seeds and tubers of aquatic plants during fall migration (Havera, 1999).

The Dresden reach of the IRV is different from the rest of the Illinois River because it produces a variety of aquatic macrophytes which produce energy-rich seeds and natural foods important to waterfowl. Extensive beds of aquatic macrophytes occupy shallow side channels, backwaters, and channel margins of the Dresden reach, despite connectivity to the main channel. Recently, wetland restoration efforts throughout the Midwest have targeted deepwater marsh communities with extensive, natural aquatic vegetation to provide habitat for waterbirds (Soulliere et al., 2007; Illinois Department of Natural Resources Wildlife Action Plan, 2005). However, few studies have documented energetic carrying capacity in such deepwater marsh communities and generated parameters useful to conservation planning exercises for restoration of natural aquatic vegetation communities (Straub et al., 2012).

Density of plant foods consumed by waterfowl (kg/ha), their metabolizable energy, duck energy days (DED), and overall waterfowl food characterization have been documented for moist-soil wetlands in the Midwest and elsewhere (e.g., Kaminski et al., 2003; Bowyer et al., 2005; Stafford et al., 2011), but little information exists for the upper Illinois River, especially in obligate aquatic vegetation communities. Estimates of food availability for waterfowl in the upper Illinois River can be used by conservation planners to model energetic carrying capacity (Stafford et al., 2011), predict habitat requirements for waterbirds using the region (Soulliere et al., 2007), and guide future restoration efforts seeking to balance tradeoffs in connecting rivers to backwater wetlands and maximizing waterfowl habitat quality (Hagy et al., 2016; Lemke et al., 2016). The goal of this study is to estimate density of seeds and tubers for foraging waterfowlin the upper Illinois River during fall migration, which can be used in energetic carrying capacity models. We predict connected backwater wetlands which provide abundant aquatic vegetation will have greater seed and tuber density than main channel areas, but that these densities will be less than managed wetlands and floodplain wetlands that are disconnected from the Illinois River. Further, we predict greater seed and tuber density in the Kankakee River than the Des Plaines River due to the absence of commercial navigation channels on the Kankakee River.

STUDY AREA

We evaluated seed and tuber densities of waterfowl foods during fall 2013-2014 in the Illinois, Des Plaines, and Kankakee Rivers and Dresden and Starved Rock reaches (41[degrees]23.36'N, 88[degrees]15.27'W; Fig. 1). The upper Illinois River consists of the upper Peoria, Starved Rock, Marseilles, Dresden, and Brandon Road reaches, although aquatic vegetation, including SAV mainly occurs in lhe Dresden and Starved Rock reaches (river km 334-468; Fig. 1). The upper Illinois drops 30 m over 88.5 km relative to lower Illinois River which drops 6.4 m over 371.8 km (Talkington, 1991; U.S. Army Corps of Engineers, 2012). Additionally, commercial traffic of more than 14,000 barges and 5,000 commercial vessels annually requires extensive dredging of a navigation channel throughout the upper Illinois River (U.S. Army Corps of Engineers, 2015). Average flow for the Brandon Road lock and dam, immediately upstream of the Dresden reach, was [80.4.sup.3] m/s in October 2013 and 2014 (U.S. Army Corps of Engineers). Lotic, riverine systems may affect distribution of freefloating seeds as they may be swept away before settling into the seed bank or lost when sediments are removed or dispersed via dredging (Nilsson el al, 2010).

[FIGURE 1 OMITTED]

The Kankakee and Des Plaines Rivers support many aquatic macrophytes that are generally absent throughout the remainder of Illinois River backwater lakes and wetlands with open or partial hydrologic connections (Stafford et al., 2010). Moreover, extensive submersed and floating-leaf aquatic vegetation is mostly extirpated from connected areas within the Mississippi River watershed south of Pool 13 (Moore et al., 2010). Common plants include American white water lily (Nymphaea odorata), American lotus (Nelumbo lutea), broadleaf arrowhead (Sagittaria latifolia), wild celery, sago pondweed, and longleaf pondweed (Potamogeton nodosum, Bellrose, 1941; Tazik, 1988). According to aerial inventories of waterfowl from 1976-1982 and 1984-1985, the upper Illinois River supported >125,000 dabbling ducks annually during fall migration (Havera, 1999).

METHODS

STUDY DESIGN

In October 2013 during early fall migration of waterfowl, we collected sediment core samples in backwaters (i.e., connected, off-channel backwater wetlands) and randomly throughout Dresden reach. We predicted a priori backwater areas would have greater seed and tuber densities than random areas as the former contained extensive beds of SAV, and waterfowl use of these areas has been reported to be high relative to other areas within the reach. Because we did not detect differences between backwater wetlands and random locations in the Dresden reach in 2013, we collected core samples only from random locations throughout the Dresden and Starved Rock reaches in October 2014, but random samples included locations within backwater wetlands. We sampled two backwater wetlands (n = 10 samples; Kross et al., 2008; Behney et al., 2014; Marty et al., 2015) in the Dresden reach where SAV was common and 30 random sites in each of the Dresden and Starved Rock reaches (Ringelman et al., 2015). Sampling sites were generated in each backwater (2013) and throughout each reach (2013 and 2014) using ArcMap 10.2.2 (ESRI, Redlands, California, U.S.A.) and loaded onto a handheld global positioning system for location in the field.

We used benthic core sampler (28 [cm.sup.2] area; 10 cm depth) to collect three core samples and recorded water depth (averaged per sample point) within a 15-[m.sup.2] area at each sample point, homogenized cores, rinsed homogenate through a 500-[micro]m aperture sieve bucket, and transported consolidated material to a lab where samples were rinsed a second time to remove remaining soil and detritus and air dried to facilitate seed and tuber removal. We homogenized the set of three cores to account for foraging patch size of ducks, which we assumed was larger than the sampled. Dry sediment material was weighed, subsampled by 25% when >10 g to reduce processing time (Hagy et al., 2011; Stafford et al., 2011), and searched ocularly for seeds and tubers. Seeds and tubers were identified by microscopy to genus or species (Martin and Barkley, 1961; Delorit, 1970; Bryson and DeFelice, 2010; Schummer et al., 2011), dried at 80[degrees]C for 24 h, and weighed to the nearest 0.1 mg. Leafy plant tissue was uncommon in core samples and is typically of low energy content for most dabbling ducks relative to seeds and tubers; therefore, we did not include it in analyses (Kaminski et al., 2003; Ballard et al., 2004). We did not enumerate aquatic invertebrates because they are a minor item in diets of fall-migrating waterfowl; previous research has indicated they are insignificant relative to contributions of seeds and tubers to energetic carrying capacity during fall and winter (Havera, 1999; Hagy and Kaminski, 2012b). Number of seeds and biontass were corrected for processing and recovery bias using size-specific correction factors, and only seeds and tubers known to be consumed by waterfowl were included in analyses (Hagy et al., 2011; Hagy and Kaminski, 2012a). Using ArcMap 10.2.2, we created a kernel density map of waterfowl food density distribution (kg/ha) throughout the Dresden reach between 2013 and 2014.

We calculated potential energetic carrying capacity of waterfowl foods using available true metabolizable energy (TME) values (Reinecke et al., 1989; Kaminski et al, 2003), and we assumed an average TME of 2.5 kcal/g for foods without available TME values (Kaminski et al., 2003). We calculated duck energy days (DEDs) by dividing seed and tuber biomass by the daily energetic requirements of a mallard-sized duck (294.5 kcal/day; Gray et al., 2013).

STATISTICAL ANALYSIS

We compared mean seed density (dry kg/ha) of all waterfowl food seeds between random and backwater sites. Food density and energetic carrying capacity was estimated for both dabbling ducks (i.e., foods present at water depths [less than or equal to] 75 cm) and diving ducks (i.e., foods available at any depth). We used 75-cm water depth as maximum foraging depth of dabbling ducks during analysis to account for average river level fluctuation during October in the Dresden reach (typically <30 cm during October 2000-2015). We compared waterfowl food density between random and backwater sites for both dabbing and diving ducks using separate two-tailed t-tests, after reviewing plots of residuals to ensure homogeneity of variances and followed normalized distribution (Littell et al., 2006; Hagy and Kaminski, 2012a). Similarly, we compared food density between river reaches and years using separate two-tailed t-tests.

We tested for differences in food density between years within Dresden reach while controlling for variation in water depth using analysis of covariance (ANCOVA; PROC GLM, v. 9.3, SAS Institute, 2012; [alpha] = 0.05). In a separate analysis, we tested for differences in food density between Dresden reach and Starved Rock reach in 2014 while controlling for water depth using the same statistical method. We used Type I sums of squares when interpreting results and reviewed plots of residuals to ensure homogeneity of variances and followed normalized distribution (Littell et al., 2006; Hag)' and Kaminski, 2012a), although parametric analyses are robust to violations of assumptions of linear models (Johnson, 1995; Laara, 2009).

RESULTS

Mean food density in backwater wetlands was 53.0 [+ or -] 13.7 (SE) kg/ha (n = 20; Table 1), an average of Big Basin (69.5 [+ or -] 20.2 kg/ha, n = 10) and Treat Island (36.4 [+ or -] 18 kg/ha; n = 10; Table 1) food densities. During 2013, food density did not differ between backwater wetlands and Dresden reach and averaged 44.4 [+ or -] 10.7 kg/ha (n = 28; P = 0.624). Although food density appeared greater in 2014 (109.0 [+ or -] 85.7 kg/ha; n = 30) than 2013 in the Dresden reach (Table 1), we detected no statistical difference between years (P = 0.473). Food density also did not differ between the Kankakee (37.7 [+ or -] 14.0 kg/ha, n = 18) and Des Plaines Rivers because of great variability (95.8 [+ or -] 64.2 kg/ha, n = 40; P = 0.381). Samples from Starved Rock reach had a mean seed density that was less than any other sampling location in any year (13.9 [+ or -] 35.8 kg/ha; n = 30; Table 1). Controlling for variation in water depth, food density in the Dresden reach did not differ between 2013 and 2014 (x= 127.7 cm; P = 0.089) nor between Starved Rock reach and Dresden reaches in 2014 (x= 131.2 cm; P = 0.418). Kernel density maps illustrate less variation in seed and tuber density in 2013 than in 2014 (Fig. 2).

Sediment cores collected at dabbling duck foraging depths ([less than or equal to] 75 cm) did not differ in seed densities than those collected at any depth, which would be available to diving ducks. Seed density was greatest at dabbling duck available depths (152.0 [+ or -] 122.0 kg/ha; n = 13) and was similar to diving duck available seed density (109.0 [+ or -] 85.7 kg/ha; n = 30; Table 1) in Dresden reach during 2014. Both were greater than seed density available to dabbling ducks (59.9 [+ or -] 16.8; n = 10) and diving ducks (44.4 [+ or -] 10.7 kg/ha; n = 28; Table 1) in Dresden reach during 2013. Backwater seed density for dabbling ducks (67.0 [+ or -] 20.2 kg/ha; n = 12) was also similar to seed density available to diving ducks (53.0 [+ or -] 13.7 kg/ha; n = 20; Table 1).

Dresden reach backwater and random site energetic carrying capacities were totaled to provide information on vegetation which provided greatest seed density (Table 2). Vallisneria americana yielded the greatest total seed density (2504.9 kg/ha), followed by Polygonum spp. (794.7 kg/ha), Verbena sp. (240.8 kg/ha), Potamogeton spp. (215.4 kg/ha) and Chenopodium spp. (196.8 kg/ha; Table 2). Of the five taxon with the greatest seed density, three species are facultative and typical of moist-soil wetlands, and two are obligate submersed aquatic vegetation.

DISCUSSION

Overall, food densities were highly variable among all sampling areas and between years (CV = > 100%; see Marty et al., 2015), and all locations and years yielded low seed density relative to managed wetlands in the Midwest (see Brasher et al., 2007), especially moist-soil wetlands (e.g., Stafford et al., 2011). Fredrickson and Taylor (1982) suggested a goal for managed moist-soil wetlands of 1629 kg/ha; however, the Upper Mississippi River and Great Lakes Region Joint Venture (hereafter: Joint Venture) assumed a seed density of 514 kg/ha for moist-soil seed density in units managed for waterfowl. The Joint Venture estimate is further reduced under the assumption that only 50% of these seeds are available to be consumed (257 kg/ha; Soulliere et al., 2007; Stafford et al., 2011). Following this assumption, food density estimates from the upper Illinois River should be reduced by 50% to account for accessibility and a forage profitability threshold. Compared to seed density estimates used for Joint Venture conservation planning, we estimated waterfowl food availability to be ~85% and ~97% less in the Dresden and Starved Rock reaches, respectively. Furthermore, food density in the upper Illinois River was 92% below estimates from managed moist-soil wetlands owned by the Illinois Department of Natural Resources (Stafford et al., 2011), 93% less than a moist-soil wetland complex in the lower IRV managed by the U.S. Fish and Wildlife Service (Bowyer et al., 2005), 95% below estimates from a restored wetland complex dominated by obligate aquatic vegetation in the lower IRV (Hine et al, 2015b), and 67% below proposed foraging thresholds in published literature for moist-soil wetlands (Hagy and Kaminski, 2015). Stafford et al. (2007) noted submerged vegetation has progressively decreased throughout Illinois, limiting naturally produced foods available to waterfowl. Moreover, mallards (Anas platyrhynchos) in the Dresden reach area of the Illinois River have been shown to feed on agricultural waste grain (i.e., corn), whereas natural foods contributed individually to less than 5.1% volume of mallard gizzard contents in that area as compared to up to 36% in other areas of the region during the same period (Havera, 1999).

[FIGURE 2 OMITTED]

Food density in vegetated, backwater wetlands did not differ significantly from random locations throughout the Dresden reach. The backwater wetlands sampled were connected directly to the main river channel and are subject to unbuffered hydrologic variation, wave action, and other perturbations as the main river channel. Similar seed densities could indicate high rates of dispersal out of backwater locations due to the steep slope and fast flow of the upper as compared to the lower Illinois River. Seed density available to dabbling ducks was similar to seed density available to diving ducks, indicating that seeds produced in shallow areas may not be retained in shallow areas, but may be dispersed into deeper locations. Additionally, seed predation by granivorous fishes such as the common carp (Cyprinus carpio), may further reduce seeds available to waterfowl. Seeds have been found in 75% of common carp diets sampled from the Dresden reach of the Illinois River in 2013-2014 (VonBank, 2015). In several restored backwater wetlands in the lower IRV that are disconnected from the main channel, seed and tuber density and prevalence of submersed aquatic vegetation is much greater than in the upper IRV suggesting possible deleterious effects of unbuffered river connectivity on energetic carrying capacity even in vegetated reaches.

High variances around mean food density estimates indicate heterogeneous distribution of foods. Irregular distribution (i.e., patchiness) of food resources is common in wetlands (Kross et al., 2008; Stafford et al., 2011), resulting in increased search time, failure by foraging birds to locate high-density patches (Amat, 1990), or suboptimal foraging strategies by waterfowl and other waterbirds (Piersma et al., 1995). Acquisition of food at low densities may be energetically unprofitable if waterfowl expend more energy trying to find patches than the energy they may receive from foraging. Despite the Dresden reach containing abundant natural vegetation communities, forage value to waterfowl is likely restricted compared to hydrologically disconnected and managed wetlands.

The potential for the upper Illinois River to provide abundant seeds and tubers for fall migrating waterfowl is dependent upon several factors. Management of water levels via lock and dam or additional water control structures to facilitate drawdowns beneficial to seed producing macrophytes during critical temporal periods of plant growth would potentially allow increased seed production and in turn more seeds available to waterfowl (Moore et al., 2010). Moist-soil plants typically include early successional and annual species which produce copious seeds and provide abundant energy necessary for waterfowl within the Dresden reach (Table 2). Vallisneria americana is unique to the Dresden reach, and provides crucial food resources (i.e., seeds and winter buds) for waterfowl, especially canvasbacks (Aythya valisneria; Korschgen et al., 1988). V. americana seeds and winter buds provided the greatest density of foods collected in the Dresden reach of any species (Table 2). V. americana has undergone widespread declines, and is not easily restored (Moore et al., 2004; McFarland, 2006). Because of the abundant food resources provided by V. americana in the Dresden reach, management efforts should encourage continued persistence and growth of V. americana.

The Kankakee River and Des Plaines River were similar in food density estimates, despite presence of commercial navigation traffic and a maintained (i.e., dredged) commercial navigation channel on the Des Plaines River. It is likely that commercial navigation alone is not a detriment to seed production, but indirect effects of infrastructure to facilitate commercial navigation (e.g., locks and dams) may preclude water level management to benefit aquatic vegetation (e.g., periodic drawdowns).

In highly modified aquatic systems, successful restoration and management may include maintaining disconnected wetlands from rivers or large lakes due to detrimental effects associated with connectivity (Jackson and Pringle, 2010). Several noteworthy restoration projects in the IRV have demonstrated that floodplain lakes and wetlands disconnected from degraded river systems can sustain aquatic vegetation communities and provide important food resources for waterfowl (Bajer et al., 2009; Hine et al., 2015a). Emiquon Preserve, near Havana, Illinois, is a restored, disconnected floodplain lake owned by The Nature Conservancy that produces similar aquatic vegetation species as the upper Illinois River. Waterfowl food seeds in Emiquon Preserve sediment cores collected in 2014 from aquatic vegetation beds had a mean seed density over 12-fold greater (1339.3 kg/ha) than the 2014 upper Illinois River mean (Hine et al., 2015b). Major differences in the Dresden reach and Emiquon Preserve include control over water levels and time since drawdown to consolidate sediments.

In contrast to the Dresden reach, river-disconnected backwater wetlands and moist-soil management areas in the lower IRV produce seed and tuber densities above JV estimates and are important habitats for waterfowl (Bowyer et al., 2005; Stafford et al., 2011; Hagy et al,, 2015). Conservation planners should consider incorporation of managed waterfowl refuge areas into the upper Illinois River system, which encourage growth of remnant naturally occurring aquatic vegetation and integrate moist-soil management practices and water level manipulation (i.e., drawdowns) to maximize the potential for quality waterfowl foraging habitat within this system. Furthermore, conservation planners can use habitat objectives from bioenergetics models to evaluate performance (e.g., percent energy needs met) using results produced from this study as a baseline for future assessments of bioenergetics for waterfowl in regulated rivers with aquatic vegetation (Soulliere et al., 2014).

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U.S. Army Corps of Encineers, Rock Island District. 2012. Illinois Waterway Locks and Dams.

--. 2015. Illinois Waterway Locks and Dams.

VonBank, J. A. 2015. An assessment of aquatic invasive plants in the Illinois River: water hyacinth surveillance, mapping, persistence, and potential seed dispersal. M.S. Thesis. 119 p.

JAY A. VONBANK, (1) HEATH M. HAGY

Illinois Natural History Survey, Forbes Biological Station, 20003 N County Road 1770E, Havana, 62644

AND

ANDREW F. CASPER

Illinois Natural History Survey, Illinois River Biological Station, 704 North Schroder Avenue, Havana 62644

(1) Corresponding author: e-mail: vonbank@illinois.edu

Submitted 15 January 2016

Accepted 27 June 2016
Table 1.--Energetic carrying capacity (ECC, [bar.x], kg/ha, se) and
duck energy days (DED, [bar.x], se) of seeds and tubers from benthic
core samples from sampling locations by total/diving duck (any water
depth sampled) and dabbling duck available (<75 cm water depth)
samples

                                       Total   Dabbling
Type          Location       Year        n        n       [bar.x]
                                                           kg/ha

Backwater     Big Basin        2013     10        9         69.5
              Treat Island     2013     10        3         36.4
              Combined         2013     20        12        53.0
River Reach   Dresden          2013     28        10        44.4
              Dresden          2014     30        21       109.0
              Starved Rock     2014     30        13        13.7
River         Kankakee       2013-14    18        8         37.7
              Des Plaines    2014-14    40        23        95.8

                             Total/diving
Type          Location            SE        [bar.x]     SE
                                              DEDs

Backwater     Big Basin          20.2        405.2     118.6
              Treat Island       18.0        278.4     150.2
              Combined           13.7        456.9     121.1
River Reach   Dresden            10.7        275.4      67.7
              Dresden            85.7        814.1     650.1
              Starved Rock       35.7        112.3      35.7
River         Kankakee           14.0        302.7      98.7
              Des Plaines        64.2        857.3     500.4

                                       Dabbling
Type          Location       [bar.x]      SE      [bar.x]    SE
                              kg/ha                DEDs

Backwater     Big Basin        63.8      21.7      337.9    109.2
              Treat Island     76.5      57.5      617.1    483.2
              Combined         67.0      20.2      341.8     94.3
River Reach   Dresden          59.9      16.8      430.1    130.9
              Dresden         152.0     122.0     1135.6    926.3
              Starved Rock     20.5       8.5      171.0     69.1
River         Kankakee         44.6      20.8      341.0    162.4
              Des Plaines     149.3     111.1     1394.4    860.0

Table 2.--Total energetic carrying capacity [kg-ha and duck energy
days (DEDs)] of seeds and tubers collected in sediment core samples
(n = 78) produced by six submersed aquatic vegetation taxa and six
highest producing moist-soil vegetation taxa collected from Dresden
reach backwaters and random sites, 2013-2014

Taxon                     n (a)    kg/ha      DEDs     Vegetation type

Vallisneria americana      12     2,504.9   18,637.1      Submersed
Polygonum spp.             44       794.7    3,266.6     Moist-soil
Verbena sp.                27       240.8    1,791.3     Moist-soil
Potamogeton spp.           15       215.4    1,039.0      Submersed
Chenopodium spp.           35       196.8    1,671.2     Moist-soil
Amaranthus spp.            19       190.7    1,924.1     Moist-soil
Scirpus spp.               38       173.3      547.4      Submersed
Cornacea                    1       166.6    1,414.9     Moist-soil
Ambrosia spp.               4       137.7    1,169.6     Moist-soil
Ceratophyllum demersum      1        44.8      188.7      Submersed
Myriophyllum spicatum       6        20.9      177.9      Submersed
Najas spp.                  3         6.9       58.3      Submersed

(a) Number of sediment core samples in which a species appeared
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Article Details
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Author:Vonbank, Jay A.; Hagy, Heath M.; Casper, Andrew F.
Publication:The American Midland Naturalist
Article Type:Report
Geographic Code:1U3IL
Date:Oct 1, 2016
Words:5539
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