Responses of a beaded Arctic stream to short‐term N and P fertilisation

Abstract

1. Oligotrophic Arctic streams are likely to be sensitive to changes in hydrology and nutrient inputs predicted to occur as a consequence of future climate and land use change.To investigate the potential consequences of nutrient enrichment for low-order Arctic streams, we added ammonium-N and phosphorous to a second-order beaded, tundra stream on Alaska's north slope. We measured responses in nutrient chemistry, chlorophyll a standing crop, and in the breakdown and macroinvertebrate colonisation of leaf litter over a 38-day summer period. 2. During the addition, nutrient concentrations immediately downstream of the dripper averaged 6.4 lM M ammonium-N and 0.45 lM M soluble reactive P. Concentrations upstream of the dripper averaged 0.54 lM M ammonium-N and 0.03 lM M soluble reactive P. Uptake of both nutrients was rapid. Concentrations were reduced on average to 28% (ammonium-N) and 15% (inorganic P) of maximum values within 1500 m. Standing crops of chlorophyll a on standardised samplers were significantly higher by the end of the experiment. Breakdown rates of senescent willow (Salix sp.) and sedge (Carex sp.) litter and associated fungal biomass were also significantly increased by nutrient addition. 3. Fertilisation resulted in four-to sevenfold higher macroinvertebrate abundance and twoto fourfold higher macroinvertebrate biomass in litter bags, as well as an increase in latesummer body mass of larval Nemoura stoneflies. 4. Our results are consistent with those of similar studies of larger streams in the highArctic region. Based on our short-term experiment, increased inputs of nutrients into these ecosystems, whether caused by climate change or more local disturbance, are likely to have profound ecological consequences. Longer-term effects of enrichment, and their interaction with other components of future change in climate or land use, are more difficult to assess.

Environment shapes invertebrate assemblage structure differences between volcanic spring-fed and runoff rivers in northern California

“…We found that nutrient levels were significantly enhanced in spring-fed rivers and probably contributed to increased invertebrate density at these sites. Benstead et al (2005) found that invertebrate abundance was 4 to 7× greater in an oligotrophic stream ecosystem after the addition of N and P and suggested that these changes were a result of enhanced food resources. Perrin and Richardson (1997) found that N and P additions to mesocosms increased mean invertebrate density by 70% over a period of 33 d and attributed their results to an increase in epilithic algal production.…”

“…Similar correlations between spring-fed invertebrate assemblages and elevated food resources have been reported from both Spain and New Zealand Death 2004, 2006). Nutrient availability and productivity have also been shown to positively affect invertebrate population growth rates and carrying capacity in other stream ecosystems (Slavik et al 2004, Benstead et al 2005.…”

Variation in summer nitrogen and phosphorus uptake among Siberian headwater streams

“…These observed increases in biological activity have been linked to changes in uptake rates of N and P in headwater streams that may influence the mass and form of nutrient exports. Few published studies, however, report direct measurements of nutrient uptake rates for Arctic streams, and these have been geographically limited to streams in Alaska (Wollheim et al 2001;Slavik et al 2004;Benstead et al 2005;Greenwald et al 2008). Comparable studies of streams in the Siberian Arctic are notably absent.…”

Leaf-litter stoichiometry is affected by streamwater phosphorus concentrations and litter type

“…Changes in leaf-litter decomposition rates often are attributed to enhanced heterotrophic activity in response to nutrient enrichment. Increases in N and P availability can stimulate microbial biomass (Rosemond et al 2002, Benstead et al 2005, Suberkropp et al 2010) and respiration rates (Elwood et al 1981, Stelzer et al 2003, Suberkropp et al 2010) associated with leaf litter. However, relatively few investigators have demonstrated how increased nutrient availability might affect leaf-litter quality (defined by nutrient content and stoichiometric ratios).…”