Academic journal article The American Midland Naturalist

Expanding American Lotus and Dissolved Oxygen Concentrations of a Shallow Lake

Academic journal article The American Midland Naturalist

Expanding American Lotus and Dissolved Oxygen Concentrations of a Shallow Lake

Article excerpt

ABSTRACT.

Lakes and reservoirs often experience sudden increases in macrophyte biomass. These changes have the potential to alter the abiotic environment in ways that affect other species. The American lotus (Nelumbo lutea) is expanding its distribution across portions of North America. N. lutea forms a dense canopy over the shallow margins of lakes and may influence the abiotic properties of the littoral zone, but this hypothesis has not been tested. Here we investigate the effects of a growing bed of N. lutea on water quality in Pymatuning Reservoir. In summer 2007 we deployed remote logging sensors to measure dissolved oxygen and temperature inside of a N. lutea bed and in adjacent open water. Dissolved oxygen concentrations were consistently lower in the lotus bed than in open water and oxygen concentrations within the N. lutea bed declined over the course of the summer. In Jul. and Aug. the N. lutea beds experienced hypoxia while oxygen concentrations remained high in open water. Low dissolved oxygen levels in N. lutea beds may affect the distribution of fish and invertebrates and alter biochemical processes in the epibenthos.

INTRODUCTION

Lakes often experience sudden increases in macrophyte biomass due to colonization or rapid expansion of an invasive species (Jeppesen et al, 1997; Scheffer, 1998; Unmuth et al, 2000) . Most studies of aquatic invasive macrophytes focus on how environmental conditions facilitate invasion, but relatively few studies examine how changes in macrophyte abundance affect the abiotic environment (Rai and Munshi, 1979; Carpenter and Lodge, 1986; Caraco and Cole, 2002; Veitch et al., 2007) . Increased macrophyte biomass can dramatically influence aquatic ecosystem function because macrophytes fix carbon, attenuate light, produce oxygen, restrict water movements, cycle nutrients and stabilize sediments (Wetzel, 2001). Especially important are the potential effects of macrophytes on dissolved oxygen concentrations. A few studies suggest that dense beds of submerged macrophytes can cause localized oxygen depletion in lakes and reservoirs by reducing turbulent mixing, blocking light penetration and contributing to ecosystem respiration (Unmuth et al., 2000; Mohseni et ai, 2001; ColonGaud et al., 2004) . Warm-water fish and invertebrates begin to experience acute physiological stress when dissolved oxygen falls below 2.5 mg/1 (e.g., Moss and Scott, 1961; Smale and Rabeni, 1995; Killgore and Hoover, 2001; Landman et al., 2005), so hypoxia associated with high macrophyte density will likely lead to depauperate fish and macroinvertebrate assemblages (Saint-Paul and Soares, 1987; Cardinale et ai, 1997; Miranda and Hodges, 2000; Burlakova and Karatayev, 2007). Oxygen deficits may also alter the nature of biogeochemical reactions and sediment oxidation-reduction potentials (Wetzel, 2001).

Studies of macrophytes and dissolved oxygen depletion have focused on submerged macrophytes, but we expect that floating and emergent macrophytes will have the strongest tendency to reduce dissolved oxygen concentrations (Rose and Crumpton, 1996; Caraco and Cole, 2002) . Floating and emergent foliage contribute little oxygen to the water during photosynthesis but dense growths can block light, thereby limiting in-water photosynthesis by submerged macrophytes, periphyton and phytoplankton (Cataneo et ai, 1998; Frodge et al, 1990; Caraco and Cole, 2002). A number of highly invasive aquatic plant species are characterized by floating or emergent leaves (e.g., water chestnut Trapa nutans, water hyacinth Eichornia crassipes, floating fern Salvinia molesta, water lettuce Pistia stratiotes, narrow leaf cattail Typha angusti/olia) , but there are relatively few studies of how these species affect oxygen concentrations in shallow lakes and wetlands (but see Frodge et ai, 1990; Caraco and Cole, 2002).

Here we evaluate the effect of Nelumbo lutea, the American lotus, on oxygen concentrations in a shallow reservoir. …

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