Global synthesis of the temperature sensitivity of leaf litter breakdown in streams and rivers.

Streams and rivers are important conduits of terrestrially derived carbon (C) to atmospheric and marine reservoirs. Leaf litter breakdown rates are expected to increase as water temperatures rise in response to climate change. The magnitude of increase in breakdown rates is uncertain, given differences in litter quality and microbial and detritivore community responses to temperature, factors that can influence the apparent temperature sensitivity of breakdown and the relative proportion of C lost to the atmosphere vs.

Stream invertebrate productivity linked to forest subsidies: 37 stream-years of reference and experimental data.

Riparian habitats provide detrital subsidies of varying quantities and qualities to recipient ecosystems. We used long-term data from three reference streams (covering 24 stream-years) and 13-year whole-stream organic matter manipulations to investigate the influence of terrestrial detrital quantity and quality on benthic invertebrate community structure, abundance, biomass, and secondary production in rockface (RF) and mixed substrates (MS) of forested headwater streams. Using a mesh canopy covering the entire treatment stream, we examined effects of litter ex'clusion, small- and large-wood removal, and addition of artificial wood (PVC) and leaves of varying quality on organic matter standing crops and invertebrate community structure and function.

Ecosystem function in Appalachian headwater streams during an active invasion by the hemlock woolly adelgid.

Forested ecosystems in the southeastern United States are currently undergoing an invasion by the hemlock woolly adelgid (HWA). Previous studies in this area have shown changes to forest structure, decreases in canopy cover, increases in organic matter, and changes to nutrient cycling on the forest floor and soil. Here, we were interested in how the effects of canopy loss and nutrient leakage from terrestrial areas would translate into functional changes in streams draining affected watersheds.

Stream denitrification across biomes and its response to anthropogenic nitrate loading.

Anthropogenic addition of bioavailable nitrogen to the biosphere is increasing and terrestrial ecosystems are becoming increasingly nitrogen-saturated, causing more bioavailable nitrogen to enter groundwater and surface waters. Large-scale nitrogen budgets show that an average of about 20-25 per cent of the nitrogen added to the biosphere is exported from rivers to the ocean or inland basins, indicating that substantial sinks for nitrogen must exist in the landscape. Streams and rivers may themselves be important sinks for bioavailable nitrogen owing to their hydrological connections with terrestrial systems, high rates of biological activity, and streambed sediment environments that favour microbial denitrification.

Nitrogen saturation in stream ecosystems.

The concept of nitrogen (N) saturation has organized the assessment of N loading in terrestrial ecosystems. Here we extend the concept to lotic ecosystems by coupling Michaelis-Menten kinetics and nutrient spiraling. We propose a series of saturation response types, which may be used to characterize the proximity of streams to N saturation.

Stream detritus dynamics: Regulation by invertebrate consumers.

Insecticide treatment of a small, Appalachian forest stream caused massive downstream insect drift and reduced aquatic insect densities to <10% of an adjacent untreated reference stream. Reduction in breakdown rates of leaf detritus was accompanied by differences in quantity and composition of benthic organic matter between the two streams. Following treatment, transport of particulate organic matter was significantly lower in the treated stream than in the reference stream whereas no significant differences existed prior to treatment.