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Project Contact Information
Project Classification Information
Project Information Project purpose: The purpose of this study is to examine the differences among taxa in excretion rate and to determine what percent of nutrient demand is met by invertebrate excretion. Project methodology:
(adapted from Koch 2005) I measured the excretion rate of NH4+-N for all
readily identifiable invertebrate taxa in a section of the East River located adjacent
to the dining hall and Snowmass cabin. Invertebrates were collected with a
kick-net and placed into individual 500 mL Whirl-Pak ® bags containing 120 mL filtered
stream water for 50-80 minutes. Each bag contained 1-20 individuals of similar
size and of the same invertebrate taxa (identified to species or at least genera).
The exact number of individuals per bag and the incubation time was dependent
on the particular species of invertebrate. Excretion estimates were replicated 8-10
times (or bags) per species.
The concentration of N as NH4 in the water before incubation (ambient
stream water concentration) was subtracted from the concentration after
incubation to calculate the concentration excreted by the invertebrate. The per
individual rate of excretion was calculated
by dividing total N excreted by both incubation time and total individuals per
bag; the mass-specific excretion rate was calculated similarly except that
total N excreted was also divided by the individual or mean biomass of the
invertebrates in each bag. I measured the concentration of NH4-N
using a flourometric method (Holmes et al. 1999, Taylor et al. 2007). Project abstract:
Nutrient supply into an ecosystem is an important factor that can
influence its productivity. While some nutrients enter the ecosystem from
external sources, cycling of nutrients internally can also be an important
process in determining nutrient supply. In this study I examined the role of benthic
stream macroinvertebrates in supplying nutrients back into the water column. I
measured excretion rates of NH4-N for all readily identifiable taxa
in the upper East River in Gothic, CO and examined how these rates varied by
body size and across taxa. I also measured nutrient uptake rates in order to
determine what percent of ecosystem demand is met by the macroinvertebrate
community. I found that invertebrate N
excretion rates were correlated with individual body mass. Additionally both
mean N excretion rate per individual and per unit of biomass varied by nearly
three orders of magnitude across invertebrate taxa. The invertebrate community
supplied about 13% of nutrient demand. Nutrient supply rate by
macroinvertebrates was dominated by the mayfly Baetis bicaudatus, Chironimidae, and the caddisfly Arctopsyche grandis. I also found that
taxa with high mass-specific excretion rates tend to be most tolerant to
organic pollution. This result could indicate the presence of a positive
feedback chain where an initial disturbance leads to continued change in the
invertebrate community. I determined that macroinvertebrates do play an
important role in nutrient cycling in this Rocky Mountain stream and that changes
in the macroinvertebrate community could have potentially large effects on
stream nutrient cycling. Data variables arrangement: columns Data variables description: A row contains information related to one measurement of invertebrate excretion rate or one measurement of a control. Who audited these data? Are the metadata and associated data file of sufficient quality to repeat the study?
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