/pdf/an-introduction-to-the-aquatic-insects-of-north-america-20i7stzjkw.pdf

An Introduction to the Aquatic Insects of North America

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

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.

/pdf/a-review-of-allochthonous-organic-matter-dynamics-and-ew90fcbtp8.pdf

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

The watershed of Big Hurricane Branch, Coweeta Hydrologic Laboratory, North Carolina, USA, was logged in 1976 We measured breakdown rates of experimental leaf packs in this second-order stream prior to logging, during logging, soon after logging, and 3 additional times since then Leaf breakdown was slow just after logging, apparently due to leaf burial by sediments Thereafter, leaf breakdown rates have been consistently faster than before logging and faster than in a reference stream These differences may be related to 3 factors First, the post-logging nitrate concentration has been about 3–10 times higher than pre-logging values in Big Hurricane Branch and 5 times higher than in a reference stream The high nutrient concentration may be stimulating microbial decomposition processes in leaf packs Second, dominance of litterfall by “medium” and “fast” processing leaves from the recovering forest coupled with relatively high sediment loads during storms may hasten breakdown through physical abrasion Third, the interaction of high nutrients and high quality leaves may be attractive to leaf-shredding invertebrates whose feeding activities may also hasten the breakdown rates

Long-term patterns in leaf breakdown in streams in response to watershed logging

We examined red maple (Acer rubrum L.) leaf litter breakdown in streams and riparian zones at two sites in the southern Appalachian Mountains to understand how differences in abiotic and biotic factors influence leaf breakdown rates. Litterbags were placed in three riparian habitats differing in litter layer moisture: stream > bank > upland. Invertebrates colonizing litterbags at one site were also examined to determine how variations in community and functional structure affect breakdown rates. Leaves broke down fastest in streams and slowest in upland habitats, whereas bank habitats were intermediate and characterized by high variability. Faster leaf breakdown rates in streams appeared to be a function of greater moisture availability, a more stable thermal regime, and a higher biomass of leaf-shredding invertebrates, especially the stonefly Tallaperla. In addition, patterns of leaf breakdown and invertebrate community structure provided evidence for a stronger than expected ecological connection between the stream and the bank. Overall, detritus processing within this narrow riparian ecosystem varied considerably depending on the availability of moisture. Results from this study show that stream channel–floodplain interactions in riparian ecosystems of steep forested mountains are analogous to ones in larger downstream or low-gradient systems. Riparian zones throughout a river network display a remarkable heterogeneity in their ability to process organic matter, which is ultimately driven by changes in hydrological conditions.

http://ww2.coastal.edu/jjhutche/Pubs/hutchens%20and%20wallace%202002.pdf

Ecosystem Linkages between Southern Appalachian Headwater Streams and Their Banks: Leaf Litter Breakdown and Invertebrate Assemblages

SUMMARY 1. We characterised aquatic and terrestrial invertebrate drift in six south-western North Carolina streams and their implications for trout production. Streams of this region typically have low standing stock and production of trout because of low benthic productivity. However, little is known about the contribution of terrestrial invertebrates entering drift, the factors that affect these inputs (including season, diel period and riparian cover type), or the energetic contribution of drift to trout. 2. Eight sites were sampled in streams with four riparian cover types. Drift samples were collected at sunrise, midday and sunset; and in spring, early summer, late summer and autumn. The importance of drift for trout production was assessed using literature estimates of annual benthic production in the southern Appalachians, ecotrophic coefficients and food conversion efficiencies. 3. Abundance and biomass of terrestrial invertebrate inputs and drifting aquatic larvae were typically highest in spring and early summer. Aquatic larval abundances were greater than terrestrial invertebrates during these seasons and terrestrial invertebrate biomass was greater than aquatic larval biomass in the autumn. Drift rates of aquatic larval abundance and biomass were greatest at sunset. Inputs of terrestrial invertebrate biomass were greater than aquatic larvae at midday. Terrestrial invertebrate abundances were highest in streams with open canopies and streams adjacent to pasture with limited forest canopy. 4. We estimate the combination of benthic invertebrate production and terrestrial invertebrate inputs can support 3.3–18.2 g (wet weight) m )2 year )1 of trout, which is generally lower than values considered productive [10.0–30.0 g (wet weight) m )2 year )1 ]. 5. Our results indicate terrestrial invertebrates can be an important energy source for trout in these streams, but trout production is still low. Any management activities that attempt to increase trout production should assess trout food resources and ensure their availability.

/pdf/aquatic-and-terrestrial-invertebrate-drift-in-southern-3ysp2pfylr.pdf

Aquatic and terrestrial invertebrate drift in southern Appalachian Mountain streams: implications for trout food resources

Diet and growth of leaf-shredding caddisfly larvae, Pycnopsyche spp.,were examined in streams draining a reference catchment and a 16-year-oldclear-cut (disturbed) catchment at Coweeta Hydrologic Laboratory insouthwestern North Carolina, USA. The objective was to explain why shredderproduction is higher in the disturbed streams despite the larvae having lessfood (i.e., leaves) available. We predicted larvae would grow faster onfast-decaying leaf material representative of the disturbed streams. Larvaeconsumed mostly leaf detritus in three streams draining each catchment overthree seasons (fall, winter, and spring), which showed larvae did notconsume higher quality foods (e.g., algae and animal material) in disturbedstreams. When fed 2-month-old conditioned black birch (Betula lenta L.) (afast-decaying leaf species) and white oak (Quercus alba L.) (a slow-decayingleaf species) leaves in the laboratory, larvae grew significantly faster onthe birch leaves. However, when larvae were fed the same leaf types after3-months conditioning, larvae grew significantly faster on oak leaves. Afield growth experiment conducted for 42 d using mixed-species leaf dietsrepresentative of each catchment and initially conditioned for 2 monthsfound that Pycnopsyche grew significantly better on the diet representativeof the reference catchment. The ’reference diet‘ contained more oak leaveswhich apparently became a more acceptable food as the experiment proceeded.High shredder production in the disturbed streams could not be explained byhigh Pycnopsyche growth rates on fast-decaying leaves. Instead, larvae grewbetter on leaves that were apparently conditioned optimally regardless ofconditioning rate.

/pdf/diet-and-growth-of-a-leaf-shredding-caddisfly-in-southern-2h9c9riz9j.pdf

John J. Hutchens

Papers

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

Long-term patterns in leaf breakdown in streams in response to watershed logging

Ecosystem Linkages between Southern Appalachian Headwater Streams and Their Banks: Leaf Litter Breakdown and Invertebrate Assemblages

Aquatic and terrestrial invertebrate drift in southern Appalachian Mountain streams: implications for trout food resources

Diet and growth of a leaf-shredding caddisfly in southern Appalachian streams of contrasting disturbance history