[1] Northern peatlands represent a globally important stock of soil carbon and have acted as a net sink of atmospheric CO 2 throughout the Holocene. Disturbance for horticultural peat extraction disrupts ecosystem function and converts these ecosystems to large, persistent sources of carbon dioxide (CO 2 ). This study investigates the effect of ecosystem-scale restoration on growing season CO 2 exchange in a peatland by comparing a restored site to a neighboring nonrestored section for 1 year prerestoration (1999) and 3 years postrestoration (2000)(2001)(2002). Prior to restoration, less than 23% of the site was vegetated, and it was a source of 245 g C m À2 to the atmosphere during the growing season (May to early October). Following restoration, the water table remained deep, and soil moisture was significantly higher than the nonrestored section. By the third year postrestoration, vegetation covered 50% of the restored peatland. Moss covered 90% of this vegetated area. Vegetation productivity at the restored site was also enhanced with gross ecosystem photosynthesis under full light conditions significantly higher at the restored site at both moss and herbaceous plots by 2002. While this increase in vegetation productivity provided fresh substrate and resulted in higher CO 2 production potential for restored site peat, ecosystem respiration was similar to or lower than that at the nonrestored site for both bare peat and vegetated areas because of the generally wetter site conditions resulting from restoration. By upscaling chamber CO 2 exchange measurements to the ecosystem level, on the basis of the relative proportion of each surface cover type, we determined the site was a net sink of $20 ± 5 g C m À2 during the growing season only 2 years postrestoration. Combining our results with previous work on CH 4 emissions and dissolved organic carbon export, we suggest that this degraded peatland ecosystem will likely return to a net carbon sink in 6 to 10 years postrestoration.Citation: Waddington, J. M., M. Strack, and M. J. Greenwood (2010), Toward restoring the net carbon sink function of degraded peatlands: Short-term response in CO 2 exchange to ecosystem-scale restoration,
Landscape-driven processes impact the magnitude and direction of cross-ecosystem resource subsidies, but they may also control consumers' numerical and functional responses by altering habitat availability. We investigated effects of the interaction between habitat availability and subsidy level on populations of a riparian fishing spider, Dolomedes aquaticus, using a flood disturbance gradient in the Waimakariri River catchment, New Zealand. D. aquaticus predominantly eat aquatic prey as they hunt from the water surface. However, D. aquaticus biomass peaked at rivers with intermediate flood disturbance, rather than at less flood-prone rivers where the biomass of aquatic insect prey was markedly higher. Flooding positively influenced spider habitat quality, and an experimental manipulation at stable rivers indicated that unembedded cobbles, preferred D. aquaticus habitat, were a limiting factor, preventing response to the increased prey resource at stable sites. Potential terrestrial prey abundance was low, did not vary across the disturbance gradient, and is likely to have been a much smaller component of the fishing spiders' diet than aquatic insect prey. Thus landscape-driven factors not only controlled the magnitude of resource subsidies, but also influenced the ability of consumers to respond to them by altering the physical nature of the ecosystem boundary.
Robust relationships between biological characteristics and hydrological indices are required to provide a quantitative basis for environmental flows. Data from 1075 river sites distributed across New Zealand were used to investigate relationships between invertebrate communities and flow regimes, whilst also including the influence of additional environmental factors. Variance decomposition analysis was used to investigate the proportion of variance explained by hydrological, geomorphological, land cover, and catchment characteristics for the community matrix and each of three biotic indices representing taxon richness, Macroinvertebrate Community Index, and percentage of species in the Ephemeroptera, Plecoptera, and Trichoptera orders. Results showed that hydrological regime contributes a unique component to the explainable variation in the community, but this contribution is overestimated if other explanatory factors are not considered. A gradient forest model comprised of 93 random forest models, each predicting the probability of occurrence of a taxon, indicated the importance of high flows and also other dimensions of hydrological variation for predicting invertebrate taxa and biotic indices. Although many freshwater invertebrates in New Zealand are well adapted to a range of flow conditions through resistance traits and/or rapid colonization, this study suggests that several aspects of the flow regime influence invertebrate communities. These results suggest that environmental flows may be designed to sustain or even optimize specific ecological attributes or taxa, but changes along several dimensions of hydrological variability are likely to disadvantage other taxa and change invertebrate community composition. Copyright © 2014 John Wiley & Sons, Ltd.
Summary1. Riparian management has been embraced by water and land managers globally to offset the deleterious effects of intensive agricultural land use on aquatic ecosystems. However, the documented responses of stream communities to riparian management have been variable, particularly in highly degraded systems. 2. We used boosted regression trees and structural equation models to assess the effects of riparian condition and stream size on the invertebrate communities of 64 agricultural waterways on the Canterbury Plains, New Zealand. We hypothesized that small streams would be more degraded than larger waterways but would show a greater increase in the abundance of pollution-sensitive aquatic invertebrates in response to riparian management. We also predicted that land-use legacies of poor in-stream habitat would reduce the effectiveness of current riparian management. The two strongest determinants of community structure were primarily in-stream habitat, where sedimentation and low water velocity had negative impacts on stream communities, and stream size, with smaller waterways generally more impacted than large waterways. Not surprisingly, with >150 years of agriculture and patchy riparian management on the plains, current management has not greatly improved in-stream habitat and thus had little effect on the abundance of sensitive aquatic insect (EPT) taxa. 3. Managed streams did, however, have more pollution-sensitive communities in general. This was largely mediated by decreased stream temperature, narrower ⁄ deeper channels and greater organic matter resources in streams with riparian planting and restricted stock access. Thus, if water velocity and sedimentation issues can be mitigated, then riparian management should become more effective. 4. Synthesis and applications. Within the context of a degraded agricultural landscape, we identified factors limiting the effectiveness of riparian management for stream invertebrate communities. Riparian management should primarily target and protect small streams and those without degraded in-stream habitat. Intensive management, such as in-stream habitat or channel morphology modification, may be needed to address historical factors (e.g. low velocity and sedimentation), which otherwise may continue to limit community recovery.
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