Comparisons of Macrophyte Breakdown, Associated Plant Chemistry, and Macroinvertebrates in a Wastewater Dominated Stream

Abstract

Replacement of native macrophyte species with exotic or invasive ones affects the quality of detritus entering streams and can alter nutrient cycles and community structure in aquatic ecosystems. Decomposition of air-dried native hardstem bulrush (Schoenoplectus acutus), invasive southern cattail (Typha domingensis), and exotic common reed (Phragmites australis) were studied in an urban stream (Las Vegas, Nevada, USA) using litter bags. Samples were analyzed for dry mass, lignin, nutrients, trace elements, and macroinvertebrates. Litter type and sediment deposited on plant material influenced material loss. Trace elements arsenic and selenium increased in plant material to concentrations considered marginal for ecosystem contamination by exposure day 76. Mercury increases were inconsistent across plant species and did not exceed limits. Bulrush decomposed faster, and tended to have higher selenium concentrations, than did invasive southern cattail and exotic common reed. Macroinvertebrate communities colonizing litter bags were similar across plant litter types, but differed from mesh-only bags and samples collected with a kick-net. Macroinvertebrate exclusion resulted in significantly lower loss rates, but functional feeding groups such as shredders were not associated with decomposition differences. The caddisfly, Smicridea, physically modified stem material and aided in processing, but microbes appeared most important in biological material breakdown. IntroductionEmergent macrophytes are often important in wetland environments, with shoots providing structure, primary production, and the basis for detrital food webs after senescence. Important processes may be altered when environments are invaded by invasive plant species associated with increased biomass, increased nitrogen availability, and higher litter decomposition rates relative to native plant species (EHRENFELD, 2003). Replacement of native emergent vegetation by aggressive invasives such as common reed (Phragmites australis (CAV.) TRIN. ex STEUDEL) is considered a threat to affected wetlands (MARKS et al., 1994). Ecosystem changes from reed invasion include increased biomass (FINDLAY et al., 2002) which in theory could impact aquatic organisms via increased biological oxygen demand or habitat alteration. The decomposition of organic matter is often considered an integrative measure of biotic and abiotic attributes of stream ecosystems (e.g., TANK et al., 2010). In urban environments, where non-native plants may be common, some ecological processes, like plant breakdown rates, may be insufficiently known (IMBERGER et al., 2008 Later, increased population growth in the area intensified the discharge of water treatment facilities into the Wash resulting in large amounts of channel erosion. This down-cutting and channelization of the Wash caused the water table to fall, draining the previously inundated floodplain. Wetland areas were largely diminished as a result. The Wash ultimately flows into Lake Mead, on the Colorado River, which is a source...

Effect of spatial scale on macroinvertebrate assemblages along a Mediterranean river

“…For example, investigations at reach scale (Beisel et al, 1998;Peeters et al, 2004), clearly revealed the importance of depth, substrate and hydraulic conditions (Reice, 1980;Schmera & Eros, 2004; Barnes et al, 2013), food availability (Beisel et al, 2000) and biotic factors (Kelly et al, 2003;Nelson, 2011). Conversely, over larger scales, latitudinal gradients and variability in land-use/land-cover and bedrock geology appear to exert stronger influence and thus mask local scale effects (Allan, 2004;Mykrä et al, 2007).…”

Colonization by oligochaetes (Annelida: Clitellata) in decomposing leaves ofEichhornia azurea(SW.) Kunth (Pontederiaceae) in a neotropical lentic system

“…Macrophytes are key components of aquatic systems (Thomaz et al, 2008), since they are the main source of autochthonous detritus in these systems (Pieczn´ska, 1993) and their decomposition is an important source of carbon, nitrogen and phosphorous, principally in small lakes (Nelson, 2011). These plants are often used by invertebrates as refuge for reproduction and protection against predators (Harrison et al, 2005;Ferreiro et al, 2011).…”

“…Therefore, macrophytes serve both as a direct food source (vegetal tissue, principally during decomposition) and indirect food source (substrate for development of periphyton) for invertebrates (Newman, 1991;Nelson, 2011). Invertebrates form an important link between the energy stored in detritus and the higher trophic levels of the aquatic food web (Gessner et al, 1999).…”

Temporal and stoichiometric patterns of algal stimulation of litter‐associated heterotrophic microbial activity

“…Each mesocosm enclosed a known stand of S. acutus or T. angustifolia. These two species were used because they possess different lignin content and decay characteristics (e.g., Nelson, 2011), and were common at the study site. Four mesocosms received eight approximately bi-weekly additions of N and P (~3.5 29 gN/m 2 and ~3 g P/m 2 , as controlled-release isobutylidenediurea fertilizer and K 2 HPO 4 ) during…”