What happens to allochthonous material that falls into streams? A synthesis of new and published information from Coweeta

Abstract

1. ,One of two things can happen to allochthonous material once it enters a stream: it can be broken down or it can be transported downstream. The efficiency with which allochthonous material is used is the result of these two opposing factors: breakdown and transport. 2. ,The present synthesis of new and published studies at Coweeta Hydrologic Laboratory compares biological use versus transport for four categories of particulate organic material: (1) large wood (logs); (2) small wood (sticks); (3) leaves; and (4) fine particulate organic matter (FPOM). 3. ,Over 8_years, logs showed no breakdown or movement. 4. ,The breakdown rate of sticks (≤3_cm diameter) ranged from 0.00017 to 0.00103_day−1, while their rate of transport, although varying considerably with discharge, ranged from 0 to 0.1_m_day−1. 5. ,Based on 40 published measurements, the average rate of leaf breakdown was 0.0098_day−1. The leaf transport rate depended on stream size and discharge. 6. ,The average respiration rate of FPOM was 1.4_mg_O2_g_AFDM−1_day−1 over a temperature range of 6–22_°C, which implies a decomposition rate of 0.00104_day−1. Transport distances of both corn pollen and glass beads, surrogates of natural FPOM, were short (<_10_m) except during high discharge. 7. , Estimates of transport rate were substantially larger than the breakdown rates for sticks, leaves and FPOM. Thus, an organic particle on the stream bottom is more likely to be transported than broken down by biological processes, although estimates of turnover length suggest that sticks and leaves do not travel far. However, once these larger particles are converted to refractory FPOM, either by physical or biological processes, they may be transported long distances before being metabolized.

Comparison of Fungal Activities on Wood and Leaf Litter in Unaltered and Nutrient-Enriched Headwater Streams

“…Our estimates of annual wood breakdown rates based on fungal assimilation alone (0.02 to 0.14 year Ϫ1 depending on wood size class and stream) are of the same order of magnitude as annual breakdown rates of hardwood sticks of similar diameter (0.5 to 3 cm) in stream decomposition experiments calculated from mass loss data (0.06 to 0.28 year Ϫ1 (11,18,40,55), underscoring fungal importance in submerged wood decomposition.…”

Nutrient Uptake and Mineralization during Leaf Decay in Streams – a Model Simulation

“…However, the magnitude of change in actual stream concentrations is probably much lower because leaf fall does not occur as a single pulse of uniform leaves. In deciduous forests of temperate areas of the world, leaf fall may be spread over several months and typically consists of a mixture of leaf species with different rates of conditioning and decay (e.g., CUMMINS et al, 1989;WEBSTER et al, 1999). Consequently, the effect of microbial uptake and mineralization in real streams should be much more subdued than we observed in these simulations.…”

“…Many studies have suggested that breakdown of leaves occurs near where they fall into streams (e.g., WEBSTER et al, 1999). However, leaf breakdown includes fragmentation, leaching, animal consumption, and decay.…”

Toxins in transgenic crop byproducts may affect headwater stream ecosystems

“…In each reach, we deployed traps every 20 m (n ϭ 10), 35 cm above the stream surface to collect pollen; microscope slides with exposed double-sided tape were anchored on each trap and deployed for 24 h. We collected two slides from each trap per day during pollen shed and stored slides in the dark until pollen counts were made by using fluorescence microscopy (ϫ40) (28). We calculated pollen input rates as grams of corn pollen deposited per meter squared streambed per day (Ϸ3.5 ϫ 10 6 corn pollen grains in 1 g).…”