That major flows of energy occur along detrital pathways in all ecosystems is a recent recognition. In freshwater ecosystems, detritus or dead organic matter (217) has two possible sources: autochthonous detritus generated within the ecosystem and allochthonous detritus generated externally. This review is concerned with the breakdown of vascular plant detritus whether autochthonous, from aquatic vascular plants, or allochthonous, derived from riparian trees and herbs. The importance to the energetics of streams of vascular plant material from riparian vegetation was recognized in early studies by Nelson & Scott (184), Egglishaw (85), and Minshall (175). Organic matter budgets for various streams have provided quantitative data to support these early observations (96, 132, 182, 254). However, many low-order streams that lack canopies of riparian vegetation may be dominated by autochthonous primary production of nonvascular plant origin. (72, 176). Theoretical models (256) predict increasing importance of autochthonous production by periphyton and aquatic vascular plants for middle-order streams but less importance of these sources in very large streams, mainly due to light limitation. The relative dominance of allochthonous vs autochthonous sources has been shown to vary between stream systems and with local conditions within streams (72, 178). While vascular plant leaves have received most attention in stream research, there is growing recognition that wood is also important. The direct contribution of wood to stream energy budgets is minimal because wood is resistant to breakdown (e.g. 8, 251). However, woody debris is indirectly important because it creates habitat for aquatic organisms (5), promotes

Vascular plant breakdown in freshwater ecosystems

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

An Introduction to the Aquatic Insects of North America

▪ Abstract Aquatic insects and other benthic invertebrates are the most widely used organisms in freshwater biomonitoring of human impact. Because of the high monetary investment in freshwater management, decisions are often based on biomonitoring results, and a critical and comparative review of different approaches is required. We used 12 criteria that should be fulfilled by an “ideal” biomonitoring tool, addressing the rationale, implementation, and performance of a method. After illustrating how the century-old but still widely used Saprobian system does not meet these criteria, we apply them to nine recent approaches that range from the suborganismal to the ecosystem level. Although significant progress has been made in the field, no recent approach meets all 12 criteria. Given that the use of biomonitoring information has important financial consequences, we suggest that societies and governments prioritize how these criteria should be ranked.

DEVELOPMENTS IN AQUATIC INSECT BIOMONITORING: A Comparative Analysis of Recent Approaches

▪ Abstract We review the major conceptual developments that have occurred over the last 50 years concerning the factors that influence insect biodiversity in streams and examine how well empirical descriptions and theory match. Stream insects appear to respond to both spatial and temporal variation in physical heterogeneity. At all spatial scales, the data largely support the idea that physical complexity promotes biological richness, although exceptions to this relationship were found. These exceptions may be related to how we measure habitat complexity at finer spatial scales and to factors that influence regional richness, such as biogeographic history, at broader spatial scales. However, the degree to which local stream insect assemblages are influenced by regional processes is largely unknown.

Biodiversity of stream insects: variation at local, basin, and regional scales.

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

A survey of methods used by US state agencies for collecting and processing benthic macroinvertebrate samples from streams was conducted by questionnaire; 90 responses were received and used to describe trends in methods. The responses represented an estimated 13,000–15,000 samples collected and processed per year. Kicknet devices were used in 64.5% of the methods; other sampling devices included fixed-area samplers (Surber and Hess), artificial substrates (Hester–Dendy and rock baskets), grabs, and dipnets. Regional differences existed, e.g., the 1-m kicknet was used more often in the eastern US than in the western US. Mesh sizes varied among programs but 80.2% of the methods used a mesh size between 500 and 600 μm. Mesh size variations within US Environmental Protection Agency regions were large, with size differences ranging from 100 to 700 μm. Most samples collected were composites; the mean area sampled was 1.7 m2. Samples rarely were collected using a random method (4.7%); most samples (70.6...

/pdf/after-site-selection-and-before-data-analysis-sampling-3cpj9eohxo.pdf

After site selection and before data analysis: sampling, sorting, and laboratory procedures used in stream benthic macroinvertebrate monitoring programs by USA state agencies

Trace element bioaccumulation was studied in immature benthic insects from two contaminated river systems to develop these animals as bioindicators. In one river, Cu, Cd, Pb, and Zn were analysed i...

Aquatic insects as bioindicators of trace element contamination in cobble-bottom rivers and streams

Macroinvertebrates are used more often than any other groups of organisms when assessing the environmental quality of lotic systems. In this chapter we describe the many ways macroinvertebrates are used as indicators of environmental quality—from the molecular-through the community-level of biological organization. We highlight more recent advances in the use of DNA bar coding and species traits and then describe in detail the most commonly used macroinvertebrate-based methods for assessing the quality of streams and rivers. Two exercises are provided. The first can be completed as a full day project by students or volunteers and includes a laboratory-only option. The second provides the basic background and information for a college-level senior thesis, graduate study or governmental monitoring organization.

Macroinvertebrates as Biotic Indicators of Environmental Quality

1. The relationships between three habitat scales and lotic invertebrate species composition were investigated for the 15 540 km2 Yakima River basin in south-central Washington, U.S.A.



2. The three spatial scales were sample (the sampled riffle), reach (a length of ten–twenty stream widths) and segment (a length of stream of nearly uniform slope and valley form having no change in stream order).



3. Physical variables were highly correlated between scales and expressed a relationship between altitude, basin form and small-scale physical structure.



4. Multiple discriminant function analyses indicated that segment- and reach-scale variables discriminated among species-defined groups better than sample-scale variables.



5. Species composition varied along a complex altitudinal gradient of changing basin form and resultant land use.



6. There was no clear relationship between species richness and altitude on a site basis. However, when viewed at the basin scale, maximum richness was observed at the transition between montane and valley sites.

The relationships among three habitat scales and stream benthic invertebrate community structure

SUMMARY 1 Changes in species composition of the periphyton of an oligotrophic Sierra Nevada stream continuously dosed for 1 year at three concentrations of copper (25, 5 and 10 μg 1−1 CuT; approximately 12, 25 and 50 ng 1−1 Cu2+) were determined



2 The numerically most abundant taxa were Bacillariophyceae (Achnanthes minutissima, Cocconeis placentula, Cymbella microcephala, C sinuata, Fragilaria conslruens, F crotonensis Navicula spp, Synedra acus and S rumpens), and the Cyanophyta Lyngbya spp, a co-dominant during spring and summer



3 Population densities of Lyngbya spp were markedly reduced at all test concentrations of copper Population densities of the principal Chlorophyta (Spirogyra spp and Cladophora spp) and the diatom Amphipleura pellucida were reduced at 5 μg 1−1 CUT Of the twenty-two most abundant taxa, sixteen were reduced in abundance by continuous exposure to 10 μg 1−1 CuT



4 There was no commensurate reduction in standing crop (total number of individuals of all taxa) Achnanthes minutissima, a co-dominant in the control, was the primary replacement species Other taxa that were more abundant at 5 μg1−1 CuT than in the control were Ceratoneis arcus, Cocconeis placentula, Navicula spp and Synedra rumpens Only A minutissima and Calothrix spp were more abundant at 10 μg 1−1 than in the control



5 Three resemblance measures (Canberra metric, Bray-Curtis and Dice) and diversity (Brillouin's) were evaluated for detecting differences in species composition among experimental stream sections The Canberra metric, an index sensitive to proportional rather than absolute differences, was the most informative of these indices

James L. Carter

Papers

After site selection and before data analysis: sampling, sorting, and laboratory procedures used in stream benthic macroinvertebrate monitoring programs by USA state agencies

Aquatic insects as bioindicators of trace element contamination in cobble-bottom rivers and streams

Macroinvertebrates as Biotic Indicators of Environmental Quality

The relationships among three habitat scales and stream benthic invertebrate community structure

Effects of copper on species composition of periphyton in a Sierra Nevada, California, stream