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Project Contact Information
Project Classification Information
Project Information Project purpose: The purpose of this study is to examine differences among taxa in excretion rate and to determine what percent of nutrient demand is met by invertebrate excretion. Project methodology:
I measured uptake rates of N using short-term, whole-stream additions of
NH4 following standard methods (Stream Solute Workshop 1990, Mulholland et al.
2002). I added low levels of NH4Cl and a conservative tracer dye (Rhodamine WT)
into the stream and monitored the concentration of the dye 600 m downstream every
2 minutes with a submersible fluorometer. When the concentration of Rhodamine
dye reached an equilibrium concentration (~1 hour), I sampled nutrient
concentrations at 50-75 m intervals along the stream section. Per meter
nutrient uptake rate was estimated from the longitudinal decline in nutrient
concentrations along the 600 m reach. I used the per meter nutrient uptake
estimates to calculate areal uptake rates, or ecosystem demand, for N following
the equations in the Stream Solute Workshop (1990). 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: Each row contains the length or width of a section of the East River. Who audited these data? Are the metadata and associated data file of sufficient quality to repeat the study?
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