Nutrient limitation of benthic primary production and respiration in great plains lotic ecosystems

We tested differences in nutrient limitation of benthic primary production and respiration in 16 Great Plains streams from Western Plains (WP), Western Cornbelt Plains (WCP), and Flint Hills (FH) ecoregions.  Respiration was measured on cellulose sponges and primary producer biomass (chlorophyll a) was measured on glass fritted filters that were placed in situ.  Both substrates were amended with nitrogen (N), phosphorus (P), N and P, or neither (controls) for 10 or 21 days, respectively.  Mean (+1SE) stream water total N, total P, and turbidity did not vary significantly across FH (TN=968+321 mg/L; TP=175+46 mg/L; Turbidity=38+9 NTU), WCP (TN=968+321 mg/L; TP=175+46 mg/L; Turbidity=38+9 NTU), and WP (TN=968+321 mg/L; TP=175+46 mg/L; Turbidity=38+9 NTU) ecoregions (p>0.05).  Primary production was nutrient limited at 7 sites, with N more likely to limit in WP and FH streams and N and P limitation occurring in WCP streams.  Respiration was nutrient limited at 8 sites, with N and P limitation occurring primarily in FH streams and N-limitation occurring primarily in WCP streams.  Nutrient amended sponges in WP streams often had significantly lower respiration rates than control sponges.  Co-limitation suggests that water quality management strategies should strive to reduce N and P in Great Plains streams.