https://www.jstor.org/stable/10.1641/0006-3568%282002%29052%5B0905%3AUPADLO%5D2.0.CO%3B2

Understanding Processes and Downstream Linkages of Headwater Systems

Ecologists have described an urban stream syndrome with attributes such as elevated nutrients and contaminants, increased hydrologic flashiness, and altered biotic assemblages. Ecosystem function probably also varies with extent of urbanization, although there are few stream networks in which this prediction has been studied. We examined functional characteristics of 6 tributaries of the Chattahoochee River near Atlanta, Georgia, USA, whose catchments differed in degree of urbanization. We conducted short-term NH4- and PO4-addition experiments to measure nutrient uptake velocity, which is the rate at which a nutrient moves through the water column toward the benthos. Both NH4 and soluble reactive P uptake velocities decreased as indicators of urbanization (i.e., % of catchment covered by high-intensity urban development) increased. The amount of fine benthic organic matter (FBOM) also decreased with increasing urbanization, and uptake velocities were directly related to FBOM. Uptake velocities wer...

https://www.jstor.org/stable/10.1899/04-021.1

Stream ecosystem function in urbanizing landscapes

The role of allochthonous organic matter in lotic ecosystems has been an important research topic among aquatic ecologists since the seminal work by Lindeman was published in 1942. Since 1986, studies on organic matter budgets, ecosystem metabolism, and decomposition published in J-NABS have made significant contributions to the overall understanding of organic matter dynamics in streams. In this review, we summarize the utility of organic matter budgets, cover the major advances in research on ecosystem metabolism, and describe the intrinsic and extrinsic factors influencing organic matter decomposition. We also discuss future directions and current applications of research and highlight the need for additional studies on the role of land use and climate change, as well as continued use of organic matter processing as a functional metric in biomonitoring studies. We emphasize the need for continued data synthesis into comprehensive organic matter budgets. Such comparative studies can elucidate important drivers of organic matter dynamics and can assist in the understanding of large continental/ global changes that might be occurring now and in the near future. In general, continued emphasis on synthesizing information into a larger framework for streams and rivers will improve our overall understanding of the importance of organic matter in lotic ecosystems.

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A review of allochthonous organic matter dynamics and metabolism in streams

Linking species and ecosystems is currently one of the great challenges in ecology. To this end, we assess here the contributions of bacteria, fungi, and detritivorous invertebrates (shredders) to leaf litter breakdown, a key ecosystem-level process. We enclosed alder (Alnus glutinosa) and willow (Salix fragilis) leaves in coarse-mesh bags (5 g dry mass), placed them in a stream during peak leaf fall, and retrieved them periodically to determine leaf mass remaining and the biomass of leaf-associated organisms. Shredder biomass was derived from numbers and length–mass relationships, bacterial numbers and biomass were determined by epifluorescence microscopy, and fungal biomass was measured as ergosterol. In addition, conidial production of aquatic hyphomycetes was determined. Leaves decomposed rapidly with exponential breakdown coefficients k of 0.035 d−1 (alder) and 0.027 d−1 (willow). Leaves were also quickly colonized within the first 4 wk of decomposition, when shredder biomass reached 263 and 141 mg d...

/pdf/contribution-of-stream-detrivores-fungi-and-bacteria-to-leaf-qiiay7uwsf.pdf

Contribution of stream detrivores, fungi, and bacteria to leaf breakdown based on biomass estimates

Assessment of the condition of ecosystems is a critical prerequisite for alleviating effects of the multiple anthropogenic stresses imposed on them. For stream ecosystems, a multitude of approaches has been proposed for this purpose. However, they all rest on the assessment of structural attributes, even though it is generally recognized that adequate characterization of ecosystems requires information on both structure (pattern) and function (process). Therefore, we propose a complementary approach to stream assessment based on evaluating ecosystem level processes. Leaf litter breakdown is a prime candidate to consider in this context. This is because of the pivotal role that allochthonous litter plays in streams, the demonstrated effects of anthropogenic perturbations on litter breakdown, and the relative ease of implementation. Leaf breakdown is governed by a variety of internal and external factors that complicate the partitioning of effects due to anthropogenic stress and natural variability (background noise), thus potentially limiting the sensitivity and robustness of litter breakdown assays. However, internal regulation factors can be controlled by standardizing assessment procedures, while variability due to external factors can be accounted for by stream classification and/or a comparative approach (e.g., downstream-upstream comparisons). Composite parameters such as ratios of break- down rates in fine-mesh and coarse-mesh bags may further increase the power of litter breakdown assays. Analyses may also be extended to include both leaf-associated decomposer assemblages (i.e., structural measures) and processes (i.e., additional functional measures). Significant efforts are required for developing standard assessment schemes as refined as extant procedures based on structural stream attributes (e.g., structure of macroinvertebrate assemblages). These efforts are nevertheless worthwhile in view of the new dimension that is added to current assessment procedures when functional elements are incorporated.

/pdf/a-case-for-using-litter-breakdown-to-assess-functional-2u4a8d8izw.pdf

A case for using litter breakdown to assess functional stream integrity

SUMMARY 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.

/pdf/what-happens-to-allochthonous-material-that-falls-into-3z1vn6pna1.pdf

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

Many studies in the past have shown indirect evidence of the importance of terrestrial detritus in woodland streams, but recently WALLACE et al. (1997b) eliminated leaf and wood inputs to a small stream and direcdy demonstrated die importance of this material to stream food webs. Additionally, this whole-stream experiment has shown that terrestrial detritus is more than just food for invertebrates. TANK & WEBSTER (1998) found accelerated wood biofilm development and wood decomposition in the litter exclusion stream, and MEYER et al. (1998) used die litter exclusion experiment to estimate that leaves contribute approximately 30% of dissolved organic carbon exports. Previous studies have also suggested that leaf litter in streams is important to nutrient retention (MULHOLLAND et al. 1985, ELWOOD et al. 1988). The purpose of the current study was to examine the effects of litter exclusion and wood removal on retention of dissolved nutrients.

/pdf/effects-of-litter-exclusion-and-wood-removal-on-phosphorus-935o8h32x7.pdf

T. P. Ehrman

Papers

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

Effects of litter exclusion and wood removal on phosphorus and nitrogen retention in a forest stream