Recovery of three arctic stream reaches from experimental nutrient enrichment

Abstract

1. Nutrient enrichment and resulting eutrophication is a widespread anthropogenic influence on freshwater ecosystems, but recovery from nutrient enrichment is poorly understood, especially in stream environments. We examined multi-year patterns in community recovery from experimental low-concentration nutrient enrichment (N + P or P only) in three reaches of two Arctic tundra streams (Kuparuk River and Oksrukuyik Creek) on the North Slope of Alaska (U.S.A.). 2. Rates of recovery varied among community components and depended on duration of enrichment (2-13 consecutive growing seasons). Biomass of epilithic algae returned to reference levels rapidly (within 2 years), regardless of nutrients added or enrichment duration. Aquatic bryophyte cover, which increased greatly in the Kuparuk River only after long-term enrichment (8 years), took 8 years of recovery to approach reference levels, after storms had scoured most remnant moss in the recovering reach. 3. Multi-year persistence of bryophytes in the Kuparuk River appeared to prevent recovery of insect populations that had either been positively (e.g. the mayfly Ephemerella, most chironomid midge taxa) or negatively (e.g. the tube-building chironomid Orthocladius rivulorum) affected by this shift in dominant primary producer. These lags in recovery (of >3 years) were probably driven by the persistent effect of bryophytes on physical benthic habitat. 4. Summer growth rates of Arctic grayling (both adults and young-of-year) in Oksrukuyik Creek (fertilised for 6 years with no bryophyte colonisation), which were consistently increased by nutrient addition, returned to reference rates within 1-2 years. 5. Rates of recovery of these virtually pristine Arctic stream ecosystems from low-level nutrient enrichment appeared to be controlled largely by duration of enrichment, mediated through physical habitat shifts caused by eventual bryophyte colonisation, and subsequent physical disturbance that removed bryophytes. Nutrient enrichment of oligotrophic Arctic stream ecosystems caused by climate change or local anthropogenic activity may have dramatic and persistent consequences if it results in the colonisation of long-lived primary producers that alter physical habitat.

Spatial variation in the somatic growth rates of European barbel Barbus barbus: a UK perspective

“…The growth analysis was then completed by determining the mean standardised growth residuals for each river (Jones 2000;Benstead et al 2007;Storm & Angilletta 2007). In all cases, there was more variation in lengths at age within a sample than between sampling years, with no significant differences in lengths at age between years (ANOVA P > 0.05).…”

Influences of environmental and chemical parameters on the spatial growth patterns of four riverine cyprinid fishes

“…all growth increments gained from back-calculated lengths) eliminated by use of only one growth metric per individual fish in subsequent analyses (Beardsley and Britton, 2012). The first growth metric was the determination of the mean standardized growth residuals for each river per species (Jones, 2000;Benstead et al, 2007;Storm and Angillett, 2007). For each species, this required the length at age data for all rivers (restricted upper ages; rationale already described), with the mean length at each age determined using the log-log quadratic function of Vilizzi and Walker (1999) who identified this as the most precise and biologically meaningful growth model of five quadratic functions (Vilizzi et al, 2013).…”

Seasonal and hydrologic drivers of dissolved organic matter and nutrients in the upper Kuparuk River, Alaskan Arctic

“…1). For many years, the Arctic LTER project has been adding phosphate to this section of the Kuparuk to study the effects of fertilization on stream function (Benstead et al 2007;Slavik et al 2004;Peterson et al 1993). Our sampling point was located in the reference reach upstream of the fertilizer addition point.…”