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Background: Agricultural development of former wetlands has resulted in many headwater streams being sourced by subsurface agricultural drainage systems. Subsurface drainage inputs can significantly influence stream environmental conditions, such as temperature, hydrology, and water chemistry, that drive ecological function. However, ecological assessments of subsurface drainage impacts are rare. We assessed the impact of an agricultural drainage system on cellulose decomposition and benthic respiration using a paired stream study in a headwater branch of Nissouri Creek, in Ontario, Canada. Adjacent first order segments sourced by a spring-fed marsh and a cropped field with subsurface drainage, as well as the adjoining trunk segment, were sampled over a year using the cotton strip assay to measure cellulose decomposition and benthic respiration. Results: Assessments of cellulose decomposition revealed a one-third reduction in the drainage-sourced segment compared to marsh-sourced segment. Between segment differences in cellulose decomposition were associated with reduced summer temperatures in the drainage-sourced segment. Impacts of stream cooling from the drainage-sourced segment were transmitted downstream as cellulose decomposition was slower than expected throughout the drainage-sourced segment and for several hundred meters down the adjoining trunk segment. Benthic respiration only differed between the drainage- and marsh-sourced segments in spring, when stream temperatures were similar. Conclusions: Our findings suggest there may be a widespread reduction in cellulose decomposition in streams across similar agricultural regions where subsurface drainage is prevalent. However, cooling of streams receiving significant amounts of water inputs from subsurface drainage systems may impart increased resiliency to future climate warming. [ABSTRACT FROM AUTHOR]

Light, temperature, and discharge control stream metabolism, but the response of gross primary production (GPP) and ecosystem respiration (ER) to seasonal variation in these physical drivers may differ in accordance with the types of human activities present in the catchment. Our study examined three mid-order streams in southern Ontario, Canada that differed in anthropogenic nutrient sources (i.e., sewage treatment plant effluent, sewage lagoon effluent, and agriculture), but had comparable light, temperature, and discharge regimes. For each stream, GPP and ER were estimated daily from June through November. Comparisons of paired daily metabolic rates revealed pairwise differences among all streams, with streams receiving sewage effluent having greater rates and variability of GPP and ER than the stream draining agricultural land. The two sewage influenced streams differed only in ER. Temporal patterns of GPP and ER were correlated for all streams throughout the study period and were most affected by seasonal variation in temperature, whereby effluent receiving streams responded more rapidly to increases in temperature. Our findings suggest that managers may need to balance effects of human activities with regional environmental constraints on stream metabolism to maintain and enhance the ecological condition and services of stream ecosystems. [ABSTRACT FROM AUTHOR]

The aim of this study was to test the effects of agricultural land use on benthic insect population body-mass and community biomass size spectrum. Agricultural land use effects were assessed by conducting a reciprocal transfer experiment between two stream reaches exposed to differing intensities of row crop and livestock agricultural activity representing best attainable and highly developed agricultural land use scenarios. We found that transferred insect communities showed no change in richness, abundance, distribution or biomass, indicating that exposure to increased agricultural intensity did not have selective lethal effects on transferred benthic insect communities. However, populations of Ephemerellidae and Hydropsyche demonstrated an increase and decrease, respectively, in body-mass following the transfer to the best attainable agriculture site. Furthermore, the community biomass size spectrum at the best attainable agriculture site contained large, predatory insects not found at the intensive agriculture site. Our findings suggest that taxon-specific body-mass and biomass size spectra have the potential to detect environmental effects prior to long-term community changes. Further research is needed to explore the mechanisms by which changes in the biomass size spectrum link agricultural intensity to shifts in benthic insect community structure. [ABSTRACT FROM AUTHOR]

Knowledge of benthic macroinvertebrate β-diversity patterns and drivers in an agricultural landscape can inform and improve watershed management decisions. Our study used multi-site and pairwise measures to determine taxonomic and functional β-diversity and associated nestedness and turnover components for benthic macroinvertebrate communities in the agricultural landscape. Total taxonomic β-diversity was mostly due to turnover, whereas total functional β-diversity was composed of turnover and nestedness more equally. Variation partitioning showed that spatial and habitat variables explained the largest proportion of variation in the total and turnover component of both taxonomic and functional β-diversity. Variation in nestedness was associated with local-scale habitat. Agricultural land cover was not a driver of β-diversity; however, extensive agricultural land cover appeared to disrupt the habitat–functional β-diversity relationship. Our findings suggest that distance among benthic macroinvertebrate communities should be considered when making land management or conservation decisions. Moreover, apparent disruption of the habitat–functional β-diversity relationship with extensive agricultural cover suggests managers should strategically target restoration activities to upland or channel areas based on catchment conditions. Finally, differences between taxonomic and functional β-diversity suggest including both measures in monitoring programs may enhance regional biodiversity assessments. [ABSTRACT FROM AUTHOR]

Bioassessment is based upon the premise that biological assemblages have predictable relationships with the surrounding natural and human environments. As the nature of these relationships can vary from region to region, it is important that environment–biota relationships be established prior to the initiation of any bioassessment program. In this study, multivariate analysis was used to establish how fish and benthic macroinvertebrate (BMI) assemblages in southwestern Ontario streams vary across natural and human activity gradients. The use of canonical correspondence analysis allowed us to determine that changes in community composition of both fish and BMI are strongly correlated with variation in the extent of human activity. The primary source of variation in community composition across activity gradients appeared to reflect a shift from intolerant to tolerant taxa as the extent of human activity increased. Habitat and feeding traits, for BMI and fish respectively, accounted for a secondary source of variation primarily attributable to differences in the extent of human activity at the reach scale. However, variation in human activity, especially at the basin scale, covaried with the dominant natural gradient of surface geology, making interpretation of the results difficult. Implications for bioassessment studies are discussed. [ABSTRACT FROM AUTHOR]

Little is known about the importance of landscape and land cover to the implementation and performance of agricultural conservation projects designed to improve stream quality. In our study, we addressed the potential importance of landscape and land cover to conservation projects by measuring variation across 191 μ-basins (100–2400 ha) and integrating the observed variation into a study design aimed at determining the effectiveness of conservation projects. Our findings indicate that there are strong gradients across which landscape and land cover attributes vary. Land cover varied along a gradient of agricultural intensity, basin morphometry across gradients of stream closure and basin size, basin substrate was described by variation in drumlin formation, glacial landform type, and soil drainage, while agricultural conservation projects varied according to the level of project implementation. Correlation of these gradients found several associations between landscape and land cover, indicating that agricultural intensity was being constrained predominantly by drumlin formation and glacial landform type. Landscape and land cover did not appear to be determining factors in the implementation of conservation projects by land owners. Based on these findings we chose 32 μ-basins which represented the variability along each of the defined gradients for further study. We conclude that landscape scale variables demonstrate important variation and covariation that can and should be integrated into study designs for the assessment of streams and human activities affecting streams. [ABSTRACT FROM AUTHOR]