Thesis (doctoral)--Swedish University of Agricultural Sciences, 2004. / Thesis documentation sheet inserted. Appendix reproduces three papers and manuscripts co-authored with R.K. Johnson and two papers co-authored with R.K. Johnson and L. Sandin. Includes bibliographical references. Also issued electronically via World Wide Web in PDF format; online version lacks appendix.

The excessive deposition of fine inorganic sediment (<2 mm) is a major pathway by which agricultural land uses exert pressure on stream ecosystems. However, less well understood are the underlying mechanisms driving threshold biotic responses and the ecological consequences of community changes to sedimentation. Reviewing the literature, I found that sedimentation can affect algal and detrital pathways, and invertebrate community composition may show abrupt shifts with increased sediment. Moreover, functional changes to communities potentially leads to simpler food webs, with altered interactions and decreased ecosystem function. After identifying these knowledge gaps, I conducted survey and experimental research using agricultural streams on the Canterbury Plains of New Zealand’s South Island. Results from my survey of 30 streams along a sedimentation gradient showed that pollution-sensitive invertebrates (% EPT; Ephemeroptera, Plecoptera, Trichoptera) demonstrated threshold responses to sediment that varied with spatial scale, and change-point analysis indicated marked declines beyond 20% fine sediment covering streambed reaches. Structural equation modeling indicated that decreased habitat availability was a key mechanism contributing to these changes. To better understand the functional consequences of altered community structure, I investigated food webs in 12 streams along the gradient. The results showed a compression of community trophic niche space, suggesting that in particular, primary consumers became trophically more equivalent. The simplification of stream food webs with increasing sediment appeared to be the result of functional changes to invertebrate communities, with fewer specialised consumers, and shifts in the availability of basal resources. Using field and laboratory experiments investigating litter breakdown and invertebrate feeding, I found that the net consequence of functionally less diverse stream communities with increased sediment was impaired ecosystem function, demonstrated by a reduction in litter breakdown rates. The reduction of detrital resource availability through burial by sediment in laboratory mesocosm experiments strongly influenced detrital consumption rates, thus leading to reduced growth and survival of detritivorous caddisflies. The survey and experimental results support my postulate that sediment deposition causes environmental stress by degrading benthic habitat and making associated food resources (e.g., periphyton and leaves) less available. Overall, my results have provided new insights into sediment impacts on stream communities and have furthered our understanding of how these changes affect the structure and functioning of stream ecosystems.

Thesis (Ph. D.)--Oregon State University, 2010. / Printout. Includes bibliographical references (leaves 98-108). Also available on the World Wide Web.

Content removed due to copy right restriction: Dewson, Z.S., Death, R.G. & James, A.B.W. (2003) The effects of water abstractions on invertebrate communities in four small North Island streams. New Zealand natural Sciences 28, 51-65. / Small streams are often used for small-scale water abstractions, but the effects of these water abstractions on the instream environment, invertebrate communities and ecosystem functioning of small permanent streams is poorly understood. This research extends current knowledge by surveying existing water abstractions and completing flow manipulation experiments in the field. Reduced discharge often decreases water velocity, water depth, and wetted channel width and can increase sedimentation, modify the thermal regime and alter water chemistry. In a survey of sites upstream and downstream of existing water abstractions, I found that downstream sites had higher densities of invertebrates, but fewer taxa sensitive to low water quality compared with upstream sites. There were greater differences in physicochemical characteristics such as velocity and conductivity and in invertebrate communities between upstream and downstream sites on streams where a larger proportion of total discharge was abstracted. Using before-after, control-impact (BACI) designed experiments, weirs and diversions were created to experimentally decrease discharge by over 85% in each ot three small streams, ranging from pristine to low water quality. The response of invertebrates to short-term (one-month) discharge reduction was to accumulate in the decreased available area, increasing local invertebrate density. After a year of reduced flow, the density of invertebrates and percentage of mayflies, stoneflies and caddisflies decreased at the pristine site, whereas only taxonomic richness decreased at the mildly polluted stream. Reduced discharge had no affect on the invertebrate community at the stream with the lowest water quality. Reduced discharge had little influence on leaf decomposition rates, but distances travelled by released coarse particulate organic matter (CPOM) increased with increasing discharge. The effects of reduced discharge on primary production were not consistent between streams. Overall, the severity (magnitude/duration) of flow reduction appeared to influence invertebrate responses to water abstraction although the outcomes of water abstraction were dependent on the invertebrate assemblage present in each stream.

Urbanization, often characterized by high impervious surface area, can result in excessive inputs of fine sediments into urban streams. Excessive fine sediments can blanket the stream bed filling the interstitial space in the substratum, which may have adverse effects on stream biota. A field survey was conducted in Oregon urban and non-urban basins to investigate the relationship between fine sediments and stream macroinvertebrates. Physical, chemical, and biological data were collected from 59 stream sites in two urban and two rural streams. The stream sites fulfilled a continuous sediment gradient, which ranged from a low of 2% of fine sediment in the substrate to a high of 64% with an average of 22%. The % fines, in Clear Creek (rural basin) was significantly lower than in the urban basins (Johnson Creek and Tryon Creek) (p=0.005). Johnson Creek (mean=23%) had approximately three times more fine sediment than Clear Creek (mean=7%), while Tryon Creek (mean=32%) had nearly five times as much fine sediment as Clear Creek. EPT taxa richness was significantly higher in both rural streams than in both urban streams (p0.05). For example, regression analysis of EPT taxa richness vs. % fine sediments displayed a coefficient of determination (r2) value of 0.2. Other macro invertebrates metrics displayed similar patterns. The lack of significant correlations may be due to the cumulative effect of basin-wide "historical land use past". Past land use activity may have resulted in long-term reductions of sensitive taxa in the basin taxa pool and efforts to improve local habitats may not be quickly colonized by pollution sensitive taxa. Long-term degradation to the urban streams resulted in a relatively homogenous assemblage of macro invertebrates, which may have confounded the quantitative relationship between sediments and macroinvertebrates. This study suggests there is a clear difference between urban and non-urban streams in terms of macro invertebrates, which may be likely due to sediments, but the quantitative relationship between fine sediments and macro invertebrates is weak.

Physical and chemical influences downstream of surface coal mines, including selenium (Se) release, water quality shifts, and habitat alterations can affect aquatic organisms. To evaluate these influences at the community level of organization, fish and macroinvertebrates were studied in mine-affected and reference streams. Se can be toxic to aquatic organisms and was measured in lotic food chains (water, biofilm, macroinvertebrates and juvenile salmonids). Invertebrate Se was significantly related to Se in juvenile fish muscle (westslope cutthroat, bull, rainbow and brook trout) and Se concentrations exceeded proposed individual-level reproductive effects thresholds in some rainbow and cutthroat trout. Community-level effects were only detected in rainbow trout where species specific biomass was negatively related to muscle Se concentration in stream reaches. Macroinvertebrate assemblages varied along a mineinfluence gradient defined by Se, alkalinity, substrate embeddedness and interstitial material size. Ephemeroptera were the most sensitive to mining effects and potential mechanisms influencing community composition included Se and ion toxicity and habitat degradation. This project highlights the need to study multiple organisms at different levels of ecological organization in order to understand and manage diverse mining impacts. / xi, 108 leaves : col. maps ; 29 cm

Rapid Bioassessment Protocols integrate a suite of community, population, and functional metrics, determined from the collection of benthic macroinvertebrates or fish, into a single assessment. This study was conducted in Dallas County Texas, an area located in the blackland prairie eco-region that is semi-arid and densely populated. The objectives of this research were to identify reference streams and propose a set of metrics that are best able to discriminate between differences in community structure due to natural variability from those caused by changes in water quality due to watershed impacts. Using geographic information systems, a total of nine watersheds, each representing a different mix of land uses, were chosen for evaluation. A total of 30 metrics commonly used in RBP protocols were calculated. Efficacy of these metrics to distinguish change was determined using several statistical techniques. Ten metrics were used to classify study area watersheds according to stream quality. Many trends, such as taxa presence along habitat quality gradients, were observed. These gradients coincided with expected responses of stream communities to landscape and habitat variables.

The Pacific Coastal ecoregion contains large tracts of economically important forest lands that also serve as critical stream habitat for endangered Salmonids. Excessive fine sediment deposition in streams of this region is a major environmental concern in the region but difficult to measure directly. The use of stream invertebrates to monitor fine sediment conditions in streams requires careful consideration of several important factors that complicate their use as bioindicators including high spatial and temporal variability and covariance with other environmental variables. To evaluate the use of stream invertebrates as bioindicators of excessive fine sediment, three hypotheses were tested. The first hypothesis was that invertebrates would be related to broad-scale climate variables (Chapter 2). The second hypothesis was that functional aspects of the invertebrate community would serve as useful indicators of excessive fine sediment condition (Chapter 3). The third hypothesis was that invertebrates in streams with naturally high levels of sediment would be tolerant to fine sediment (<2 mm, Chapter 4). Hypotheses were tested using a temporal data set at two streams in western Oregon, spatial data from 214 sites across the Oregon Coast Range, and in-situ experiment conducted in streams with erosive or resistant geologies. In the temporal study, both invertebrate density and functional traits were positively related to El Nino strength (R2 range = 0.22-0.36, ρ range = 0.008-0.04) and air temperature (R2 range = 0.32-0.49, ρ range = 0.002-0.01). The spatial study identified several environmental and hydrological factors that exhibited strong negative controls on both fine sediment (Mantel r range 0.14-0.25, ρ range = 0.001-0.01) and invertebrate Scrapers (R2 range = 0.11-0.14, ρ range = 0.001-0.04). The result of the experimental study provide evidence that invertebrates in streams with erosive geologies exhibit tolerance to sediment addition when compared to invertebrates in resistant geologies (mean loss=15%, ρ <0.01) and that invertebrate grazing traits were most strongly associated with fine sediment dosing frequency (ρ <0.05). The findings of this research demonstrate the role of geology in shaping invertebrate communities and their functional response to fine sediment addition and identify functional indicators that may be useful in different geologic settings. For environmental managers in the Pacific Coastal ecoregion, these findings are of potential value in assisting with the identification of biologically-relevant changes in stream fine sediment conditions and support efforts to balance economic needs in the region while protecting critical Salmonid habitat.