Urbanization Affects Stream Ecosystem Function by Altering Hydrology, Chemistry, and Biotic Richness

Abstract

Catchment urbanization can alter physical, chemical, and biological attributes of stream ecosystems. In particular, changes in land use may affect the dynamics of organic matter decomposition, a measure of ecosystem function. We examined leaf-litter decomposition in 18 tributaries of the St. Johns River, Florida, USA. Land use in all 18 catchments ranged from 0% to 93% urban which translated to 0% to 66% total impervious area (TIA). Using a litter-bag technique, we measured mass loss, fungal biomass, and macroinvertebrate biomass for two leaf species (red maple [Acer rubrum] and sweetgum [Liquidambar styraciflua]). Rates of litter mass loss, which ranged from 0.01 to 0.05 per day for red maple and 0.006 to 0.018 per day for sweetgum, increased with impervious catchment area to levels of approximately 30-40% TIA and then decreased as impervious catchment area exceeded 40% TIA. Fungal biomass was also highest in streams draining catchments with intermediate levels of TIA. Macroinvertebrate biomass ranged from 17 to 354 mg/bag for red maple and from 15 to 399 mg/bag for sweetgum. Snail biomass and snail and total invertebrate richness were strongly related to breakdown rates among streams regardless of leaf species. Land-use and physical, chemical, and biological variables were highly intercorrelated. Principal-components analysis was therefore used to reduce the variables into several orthogonal axes. Using stepwise regression, we found that flow regime, snail biomass, snail and total invertebrate richness, and metal and nutrient content (which varied in a nonlinear manner with impervious surface area) were likely factors affecting litter breakdown rates in these streams.

Changes in dominance among species in aquatic hyphomycete assemblages do not affect litter decomposition rates

“…Small forest streams are also highly vulnerable to global warming because most of their biota have relatively low upper thermal tolerance limits (de Koz lowski & Bunting 1981, Eaton & Scheller 1996 and will lack thermal refugia if they are already at their high latitude or highland limit. Also, the hetero trophic nature of these small streams and their strong interaction with the terrestrial surroundings (Vannote et al 1980, Mulholland et al 2001) make them most sensitive to changes in the riparian vegetation, which can result from invasion by exotic species, conversion of diverse deciduous forests into tree monocultures or agricultural fields, vegetation re mo val by forestry practices or urban development (Chadwick et al 2006, Ferreira et al 2006b, Lecerf et al 2007, Castela et al 2008. All these threats have been shown to induce changes in the structure of aquatic communities (Bärlocher & Graça 2002, Pascoal et al 2005, Ferreira et al 2006b, Castela et al 2008, Dang et al 2009), which might have profound consequences for the maintenance of ecosystem processes.…”

Land Use, Stream Habitat and Benthic Invertebrate Assemblages in a Highly Altered Iowa Watershed

“…Additionally, invertebrates have critical functional roles in headwater stream ecosystems as predators, consumers of primary producers, processors of organic detritus and as prey (Chadwick et al, 2006;Weijters et al, 2009). Therefore, assemblage characteristics are indicative of biological production, nutrient and energy flow pathways and efficiency, and other functional qualities of streams that are frequently degraded by human land use (Chadwick et al, 2006;Weijters et al, 2009).…”

“…Therefore, assemblage characteristics are indicative of biological production, nutrient and energy flow pathways and efficiency, and other functional qualities of streams that are frequently degraded by human land use (Chadwick et al, 2006;Weijters et al, 2009).…”

Effects of CO2-altered detritus on growth and chemically mediated decisions in crayfish (Procambarus clarkii)

“…Processing rates of organic matter typically are higher in urban than in forested watersheds because of excess nutrients and stimulated microbial processing (Pascoal et al 2005, Imberger et al 2008) but can decline because of decreases in macroinvertebrate consumers (Chadwick et al 2006). Physical fragmentation associated with higher storm runoff in urban watersheds can increase losses of organic matter to downstream reaches (Paul et al 2006).…”