Key connections in Amazonian stream corridors: Using 15 N to trace N transformations and transport ND-03: Deegan, Neill, Victoria, Krusche, Ballester, Gessner, Haupert, Thomas UPLAND SMALL STREAM RIPARIAN LARGE RIVERS SLOPE

FOREST TO PASTURE CONVERSION dissolved nutrients & nutrient ratios, stream conditions (e.g., oxygen) and biota (e.g., increased algae, loss of invertebrates in pastures) N & P processing affected by changes in:

KEY QUESTIONS How and at what rates is nitrogen transformed in tropical forest streams?How and at what rates is nitrogen transformed in tropical forest streams? How does conversion to pasture alter N cycle?How does conversion to pasture alter N cycle? How far and in what form is nitrogen transported?How far and in what form is nitrogen transported?

FATE AND TRANSFORMATION OF NITROGEN

 15 N NH 4 + UPTAKE Downstream Distance (m) > > > Measure  15 N of 15 NH 4 +, 15 NO 3 - and organic matter (including biota) 15 N Addition Schematic Dripper 1 15N STREAM FLOW 7 9 Add 15 (NH 4 ) 2 SO 4 for 21 days to raise the  15 N of stream NH 4 + Conversion to other components

 15 N of NH 4 + DISTANCE (M) UPTAKE LENGTH - NH m 1000m Temperate Stream ~50m

Day 1 Day 21 DISTANCE (M) NITRIFICATION RATE  15 N RATE: ~5 X m -1 or 2 x ug/m 2 /min ~10% of NH 4 loss converted to NO 3

TemperateTropical Walker Branch, TN Nova Vida, RO NH 4 + uptake length (m) NO 3 - uptake length (m)500 infinite Nitrification rate (1/m) FOREST STREAM COMPARISION

% of 15 N added Temperate Tropical Walker Branch Nova Vida Retained 48 2 Total export3169 FOREST STREAM N MASS BALANCE NO NH Particulate 4 1

Effect of conversion to pasture? Small pasture stream Larger pasture stream  15 N Ammonium uptake length is shorter (~500m) Nitrification rate is near zero For the rest of the story – see the poster Haupert 37.5

NH 4 + uptake length is 10 to 100 times longer than in temperate streams Peterson et al TROPICAL FOREST STREAM At 40 L s -1 Tropical Forest: 2000m Pasture: 500m Temperate Forest: 50 m PASTURE STREAM

New Knowledge Not like temperate forest streams –Little transformation of DIN Low rates of nitrification Little storage; Low rate of N release from stream bottom –Little retention of N occurs Long downstream transport > 1000’s m Primarily as DIN Function as conduits that transport N from upper reaches of watersheds to larger rivers.

New Knowledge Pasture formation radically alters N transformation and transport –Nitrification is near zero in pasture streams –NH 4 + uptake length is shorter (500m) than in tropical forest (2000m) ….. but still 10X longer than temperate forest (50m)

SYNTHESIS & SCALING  Synthesis of stream N, P and C processes across different soil types and regions  Develop a model to integrate land use mosaic with stream chemistry, stream size, riparian area and hydrology to predict the export of materials to larger rivers.