River Restoration From Boundary Layer to Watershed: Integrating Physical and Biological Science Over Space and Time I
Presiding: P Wilcock, Applied Physics Laboratory, Johns Hopkins University; M Power, University of California, Berkeley
NB14G-01 15:45h
Channel Realignment Increases Multi-Scale Sensitivity to Floods in Benthic Snails in a Puerto Rico Stream
The impact of hydromodifications such as channel realignment on diadromous fauna is poorly understood in tropical streams. This study documented the impacts of channel realignment performed at lower Rio Mameyes (NE Puerto Rico) on local and upstream populations of the diadromous Neritina virginea (Gastropoda: Neritidae). The streambed was dredged and leveled during the realignment (Summer 2002) promoting small-substrate patches, and increasing reach-scale heterogeneity. Snail density and size, streambed and channel properties were monthly recorded in a reference reach, and in situ and upstream the realigned reach during the following 18 months. After realignment, the local density was lower compared to previous surveys, and to the reference reach. It was due to individual wash out during flashfloods on gravel patches at the realigned reach. Increased mortality in juvenile snails migrating upstream through the realigned reach was responsible for gradual density decline, and low recovery after a major flood in the upstream population. However, existing data before the realignment showed that this population recovered from storm floods in less than two months. This study evidenced that civil works in flashy streams promote long-lasting negative effects on local populations that may propagate upstream when diadromous species are compromised, and may provide restoration guidelines.
NB14G-02 16:00h
Restoration in Sand-slugged Streams and Drought---the Granite Creeks Project.
European settlement, with accompanying land clearance and heavy grazing, of the Strathbogie Ranges in central Victoria, Australia, resulted in the massive export of sediment to lowland streams. These streams, originally configured as "chains of ponds", were filled with "sand slugs" that generated a raised flat streambed depleted in habitat heterogeneity. The invertebrate fauna of the sand slugs is similar to that of sandbed streams elsewhere, but lacks an abundant hyporheos. The fish fauna was reduced in diversity and abundance. In 2001 habitat restoration in the sand slugs commenced after pre-restoration samples were taken.Timber structures, made from railway sleepers, were installed and subsequently created scour pools. Fish responded positively to restoration measure, but no significant effect was apparent for the invertebrates. In 2001-2004 a very severe drought occurred causing the streams to cease to flow and in the sand-slugged sections faunal abundance declined greatly due to the loss of residential habitat and the lack of refugia. Thus, the large-scale effects of severe drought thwarted the effects of localized habitat restoration, stressing the point that in restoring habitat it is also imperative to generate resilience to the prevailing disturbance regime-a regime that may be exacerbated by human activities.
NB14G-03 16:15h
Control of Vertical Water Exchange in Sand-bed Streams by Instream Wood - Key to Hyporheic Restoration
The vertical water exchange between water column and hyporheic zone is crucial for many aspects of stream ecology. In sand-bed streams this exchange is often low resulting in shallow hyporheic depth and low metabolic activity. Our objective was to assess the effect of wood addition on the vertical connectivity at base-flow. Experiments were conducted in the large dimension Artificial Stream and Pond System (FSA, German Federal Environmental Agency) with and without natural quantity of instream wood (0.53m3 wood / 100 m2 stream bed). The water exchange was assessed from loss of diluted tracer (Uranine) from the water column. The water exchange comprised two superimposed processes, that differed in exchange rate. The presence of wood had no effect on the slower process, but doubled the exchange rate of the faster process. Wood caused re-deposition of 47% of the stream bed. Related to this area the exchange rate was more than threefold the rate at level sand bed. Wood also increased the overall exchange depth. The results underline the potential to restore hyporheic functions in low energy sand-bed streams by management of instream wood and wood recruitment.
NB14G-04 16:30h
Large-scale River Restoration Enhances Geomorphological Diversity and Benthic Biodiversity
An 8-km stretch of the River Isar is being restored within the city limits of Munich; this is one of the largest river restoration projects in Europe. We evaluated effects of the restoration on geomorphological parameters and river invertebrates. Before and after restoration of a channelised 1-km reach, we investigated this reach and two reference reaches (another channelised reach and a natural reach). On four dates before and six dates after restoration, we measured detailed transects of bed topography at each reach to document changes in bed morphology. Sampling periods included 6 (before) and 11 (after) bed-moving floods. On three dates each before and after restoration, we also collected quantitative invertebrate samples. Before restoration, geomorphological diversity (the spatial variability of water depth) was lower at both channelised reaches than at the natural reach. After restoration, diversity at the restored reach became as high as at the natural reach but remained low at the channelised reach. Invertebrate species richness and richness of mayflies, stoneflies and caddis flies also increased at the restored reach relative to both reference reaches, probably as a consequence of enhanced geomorphological diversity, which provided a more distinct spatial patchwork of differing abiotic habitat conditions for invertebrates.
NB14G-05 16:45h
Spatial Heterogeneity of Rana boylii Habitat: Quantification and Ecological Meaningfulness
Analysis of the heterogeneity of stream habitat and how biological communities respond to that complexity are fundamental components of ecosystem analysis that are often inadequately addressed in watershed assessments and restoration practices. Many aquatic species, such as the Foothill Yellow-legged Frog (Rana boylii), known to associate with certain physical habitats at various times throughout their lifecycle may require some degree of habitat complexity at a larger reach scale for a population to persist. Recent research in the field of landscape ecology has expanded the use of spatial heterogeneity indices to other fields of ecology as an objective method to quantify variability in habitat. Provided that indices are used in an appropriate context and are shown to be ecologically meaningful, they provide a potentially useful tool for quantifying the variability in riverine habitat for aquatic species such as R. boylii. This study evaluated whether stream reaches with a high heterogeneity of geomorphic features, as measured by several key spatial heterogeneity indices, correlated with a greater relative abundance of R. boylii. R. boylii habitat associations were quantified throughout a single season to obtain further insight into the local hydraulic and geomorphic conditions preferred by each lifestage. The two best predictors of habitat associations by lifestage were velocity and substrate size, two key characteristics of geomorphic units such as riffles and pools. The heterogeneity of geomorphic units was then quantified and measured at the reach scale using a variety of spatial indices. Indices of spatial composition, such as Shannon's Diversity Index, were found to correlate well with frog abundance, while indices of spatial configuration, such as Contagion, were not significant. These findings indicate R. boylii may select stream reaches with increased geomorphic complexity that potentially provide habitats suitable to each lifestage with multiple functions and a greater variety of refugia as flows fluctuate throughout the season. The findings also show that spatial indices are useful in quantifying aquatic habitat heterogeneity, and when shown to be ecologically meaningful would be useful as an objective means to quantify habitat in river restoration practices.