Towards improving an Area of Concern: Main-channel habitat rehabilitation priorities for the Maumee River
Introduction
Most large riverine ecosystems are impaired due to habitat modifications, pollution, and invasive species, particularly those running through urban and agricultural landscapes (Allan, 2004, Walsh et al., 2005, Dudgeon et al., 2006). These ecological stressors have led to global losses of river biodiversity and ecosystem services (Jenkins, 2003, Dudgeon et al., 2006, Nilsson et al., 2007). The culturally and economically important Maumee River, the largest watershed of all Laurentian Great Lakes tributaries, drains into western Lake Erie (Maumee Remedial Action Plan Committee, 2006) and is one such highly degraded ecosystem. In 1987, under the revised Great Lakes Water Quality Agreement, the lower 35 km of the Maumee River (Ohio, USA) and many smaller upstream and adjacent watersheds across a 2000 km2 landscape were designated the Maumee Area of Concern (AOC). Of the Maumee River’s 21,538 km2 watershed, over 72.3% is agricultural cropland and over 11.3% is urban development concentrated mostly in the lower 35 km in the Toledo metropolitan region (2001 National Land Cover Dataset (NLCD); Cousino et al., 2015). The abundant agricultural land use in particular has caused excessive nutrient and sediment loading and triggered substantial changes in the hydrology of the Maumee River (Maumee Remedial Action Plan Committee, 2006). Additionally, channelization of streams during landscape drainage construction and maintenance has contributed to the loss of historically abundant vegetated wetland habitat (Mapes et al., 2014). These changes resulted in a significant decline of the diversity of macroinvertebrate communities, and 17 fish species that historically spawned in the Maumee River have been extirpated over the past century (Karr et al., 1985, Ohio Environmental Protection Agency, 2014). Subsequently, under the Maumee AOC program, the lower Maumee River was designated impaired with regard to fish populations, river benthos, and fish habitat (Maumee Remedial Action Plan Committee, 2006).
Despite its watershed degradation, the Maumee River remains a vital migratory corridor for a variety of fish species including walleye (Stizostedion vitreum or Sander vitreus; Trautman, 1981, Pritt et al., 2013, DuFour et al., 2015), a species that supports an economically and culturally important fishery (Roseman et al., 2008). There are some indications that fish communities have marginally improved over the past two decades, with more pollution-sensitive taxa being collected compared to the mid-1990s (Ohio Environmental Protection Agency, 2014). Despite these recent gains in some sensitive fish taxa, the fish and invertebrate communities of the main-channel Maumee River remain impaired compared to less disturbed Great Lakes tributaries and with respect to rehabilitation targets under the Maumee AOC program. Therefore, to promote rehabilitation and facilitate recovery of the beneficial uses of the river ecosystem under the Maumee AOC program, it is necessary to identify and protect existing areas with functional habitat as well as areas that can feasibly be enhanced to increase biodiversity.
The goal of our study was to identify main-channel areas in the lower Maumee River that currently support healthy aquatic communities or areas that could be enhanced to improve fish and invertebrate diversity and abundance. To accomplish this, we sampled fish and macroinvertebrates in a section of the Maumee River that provided habitat rehabilitation opportunities that were ecologically promising and would not disturb navigation routes in the federal shipping channel. The selected study reach contains several large and small island complexes (Fig. 1). Island habitats have been shown to exhibit habitat heterogeneity (Johnson and Jennings, 1998) and are associated with increased density and diversity of benthic invertebrates and fish species in rivers (Thorp, 1992, Chipps et al., 1997, Hintz et al., 2015). Our specific objectives were to identify: 1) areas that exhibit the highest biodiversity, 2) habitat characteristics associated with high biodiversity areas, 3) areas in need of protection from further degradation, and 4) areas that could feasibly be rehabilitated to increase biodiversity.
Section snippets
Study reach
We collected fish, macroinvertebrates, and abiotic data from June – September 2019 in a 13 km reach of the lower Maumee River (Fig. 1). This reach included three large island complexes (between 0.16 and 0.77 km2 each), and several smaller (~0.02 km2) islands interspersed in the main channel. The reach also falls at the upper end of the 24 km lacustrine section of the Maumee River, i.e., the portion of the river that is influenced by Lake Erie. Both the macroinvertebrate and fish communities in
Results
In total, 1937 fish were caught via electrofishing and 5229 fish were caught via trawling during summer 2019 sampling in the Maumee River. Over the two electrofishing periods, we caught 35 fish species, with the five most dominant species being gizzard shad (Dorosoma cepedianum) (40%), yellow perch (Perca flavescens) (7.1%), emerald shiner (Notropis atherinoides) (6.5%), common carp (Cyprinus carpio) (6.2%), and white bass (Morone chrysops) (6.2%). We captured 26 fish species via trawling, with
Discussion
In our study reach, large island complexes and shallow-water habitat were associated with greater species richness and abundance of fish and macroinvertebrates. These data may suggest that drifting invertebrate deposition or production occurs in these shallow areas around islands and might serve as food resources for fishes. However, our data cannot distinguish if fish are responding to the increased invertebrate production in these areas or instead to unmeasured habitat features. Nevertheless,
Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgements
This study was funded by the United States Geological Survey Cooperative Agreement G19AC00077 through the Cooperative Ecosystem Studies Unit program. We thank all technicians, students and volunteers who helped with data collection and sample processing. We would like to especially acknowledge the efforts of Alaina Carson, Ashlynn Benedict, Madison Myers, Christopher M. Kemp, Katrice Williams, and Michael J. Miller. We would also like to thank Jon Bossenbroek and Tim Fischer for providing us
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