Breakdown of tussock grass in streams along a gradient of agricultural development in New Zealand

Abstract

Summary 1. We measured the breakdown rate of tussock grass in 12 New Zealand streams in catchments that provided a gradient of agricultural development. We also examined the microbial and invertebrate communities associated with decomposing tussock litter. 2. Pristine streams in the study had low concentrations of dissolved inorganic nitrogen (<10 μg L−1) and dissolved reactive phosphate (<3 μg L−1), whereas streams in the most developed catchments had high concentrations of nitrate (>2500 μg L−1) and phosphate (35 μg L−1), as well as greater amounts of suspended sediment and fine sediment covering the streambed. 3. Breakdown rate and microbial respiration were significantly related across the sites, and both were positively related to concentrations of nitrate and phosphate. Fungal biomass, measured as ergosterol, was positively related to microbial respiration and was also higher at sites with higher concentrations of nutrients. Total and shredding invertebrates were most abundant at the sites with high nutrient concentrations, but abundance of shredding invertebrates was not significantly related to breakdown rate. Amphipods were the most common shredding invertebrate at most sites, but probably did not contribute greatly to high rates of breakdown in streams in agricultural catchments. 4. With the exception of one site, nutrients from agricultural development appeared to have larger positive effects on litter breakdown than negative effects from sedimentation. Litter breakdown can serve as a functional measure of ecosystem health in streams, but caution should be exercised when a stress, such as land use, can have both positive (nutrients) and negative (sedimentation) effects.

Organic matter breakdown and ecosystem metabolism: functional indicators for assessing river ecosystem health

“…Multiple stressors might operate in concert to increase leaf breakdown rates, as would be the case when temperature and nutrient concentrations are increased simultaneously. On the other hand, positive effects of higher nutrient concentrations have counteracted negative effects of more fine sediment in streams in catchments developed for grazing (Niyogi et al 2003). Similarly, the negative effects of increased heavy metal concentrations have counteracted the positive effects of high nutrient concentrations (Sridhar 606 [Volume 27 R. G. YOUNG .…”

“…One of the problems associated with mass-loss measurements is that some of the measured loss might result from loss of large leaf fragments through physical abrasion rather than biological or chemical decomposition. An alternative measure that could be used on remaining leaf material is a measure of leaf toughness as the force required to drive a blunt metal pin through a leaf (Suberkropp and Klug 1980, Young et al 1994, Huryn et al 2002, Chadwick and Huryn 2003, Niyogi et al 2003. This force can be measured in Newtons with a commercially available penetrometer or as the mass (lead shot or water added to a container directly above the pin) required to force the pin through the leaf.…”

“…See ''Water temperature'' below Gessner et al 1998, Mathuriau and Chauvet 2002, but see Chergui and Pattee 1991 Depends on rate of invertebrate shredding Baldy et al 1995, Jonsson et al 2001, but see Grac¸a et al 2001Fabre and Chauvet 1998, Fleituch 2001 See ''Nutrients'' below Pozo 1993 Invertebrate density or leaf abrasion higher in riffles Meyer 1980, Smith 1986, Casas 1996 Invertebrate densities lower or anaerobic Reice 1974 Higher invertebrate density Rounick and Winterbourn 1983 Crayfish very important, but fish might reduce shredder activity Rosemond et al 1998, Usio 2000, Konishi et al 2001, Schofield et al 2001 Microorganisms most responsive to temperature; if invertebrate density is high in cold season, leaf decay is faster Webster and Benfield 1986, Bunn 1988, Garden and Davies 1988, 1989, McArthur et al 1988, Short and Smith 1989, Lopez et al 2001, Menendez et al 2003 Lower invertebrate density or anaerobic conditions Reice 1974, Triska and Buckley 1978, Herbst 1980, Meyer 1980, Chauvet 1988, Chergui and Pattee 1990, Rader et al 1994, Niyogi et al 2003 Reduced invertebrate or microorganism activity Allard and Moreau 1986, Collier and Winterbourn 1987, Garden and Davies 1989, Griffith and Perry 1994, Rowe et al 1996, Dangles and Gu...…”

The influence of water quality and macroinvertebrate colonization on the breakdown process of native and exotic leaf types in sub-alpine stream

“…Leaf breakdown is generally considered a good indicator of stream integrity, especially because it accounts for a variety of biological, chemical and physical conditions (Niyogi et al 2003;Elosegi et al 2006;Woodward et al 2012). Numerous studies have investigated the relationship between leaf breakdown processes and water quality (Young et al 2008).…”

Biological changes along the continuum of an agricultural stream: influence of a small terrestrial preserve and use of adult caddisflies in biomonitoring

“…Most agricultural streams have minimal riparian shade or coarse allochthonous input, have high levels of primary and secondary production, and contain nutrient concentrations 100s of times higher than those of relatively undisturbed streams (Kemp and Dodds 2001;Vanni et al 2001;Royer et al 2004;Inwood et al 2005). Such streams may not behave in ways predicted by typical disturbance models (Niyogi et al 2003;Spa¨noff and Meyer 2004;Bernot et al 2006;Gulis et al 2006;Paul et al 2006;McTammany et al 2008).…”